#include "parser.h"
#include "lexer.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct {
    const Token* tokens;
    size_t       count;
    size_t       pos;
    const char*  filename;
    Arena*       arena;
} Parser;

// === 递归深度限制 ===
static int parse_depth = 0;
#define MAX_PARSE_DEPTH 1000

// === 向前看 ===
static const Token* peek(const Parser* p) { return &p->tokens[p->pos]; }
static const Token* advance(Parser* p) { return &p->tokens[p->pos++]; }
static bool match(Parser* p, TokenKind k) {
    if (peek(p)->kind == k) { p->pos++; return true; }
    return false;
}
static const Token* expect(Parser* p, TokenKind k, ErrorInfo* e, const char* msg) {
    if (peek(p)->kind == k) return advance(p);
    e->message = msg; e->filename = p->filename;
    e->line = peek(p)->line; e->col = peek(p)->col;
    return NULL;
}

// === 运算符优先级定义 ===
typedef enum {
    PREC_NONE = 0,
    PREC_PIPE = 10,
    PREC_OR = 20,
    PREC_AND = 30,
    PREC_COMPARE = 40,
    PREC_TERM = 50,
    PREC_FACTOR = 60,
    PREC_UNARY = 70,
    PREC_POSTFIX = 80,  // .field, call()
} Precedence;

static Precedence tok_to_prec(TokenKind kind) {
    switch (kind) {
        case TOK_PIPE_PIPE: return PREC_OR;
        case TOK_AND_AND:   return PREC_AND;
        case TOK_EQ_EQ: case TOK_BANG_EQ:
        case TOK_LT: case TOK_GT: case TOK_LT_EQ: case TOK_GT_EQ: return PREC_COMPARE;
        case TOK_PLUS: case TOK_MINUS: return PREC_TERM;
        case TOK_STAR: case TOK_SLASH: case TOK_PERCENT: return PREC_FACTOR;
        default: return PREC_NONE;
    }
}

static BinaryOp tok_to_binop(TokenKind kind) {
    switch (kind) {
        case TOK_PLUS: return OP_ADD; case TOK_MINUS: return OP_SUB;
        case TOK_STAR: return OP_MUL; case TOK_SLASH: return OP_DIV;
        case TOK_PERCENT: return OP_MOD;
        case TOK_EQ_EQ: return OP_EQ; case TOK_BANG_EQ: return OP_NE;
        case TOK_LT: return OP_LT; case TOK_GT: return OP_GT;
        case TOK_LT_EQ: return OP_LE; case TOK_GT_EQ: return OP_GE;
        case TOK_AND_AND: return OP_AND; case TOK_PIPE_PIPE: return OP_OR;
        default: return OP_ADD;
    }
}

// 向前声明
static AstNode* parse_expr(Parser* p, ErrorInfo* error);
static AstNode* parse_expr_prec(Parser* p, Precedence prec, ErrorInfo* error);
static AstNode* parse_block(Parser* p, ErrorInfo* error);
static AstNode* parse_statement(Parser* p, ErrorInfo* error);
static AstNode* parse_function(Parser* p, bool is_pub, ErrorInfo* error);

// === 前缀解析 ===
static AstNode* parse_unary(Parser* p, ErrorInfo* error) {
    const Token* op = advance(p);
    AstNode* operand = parse_expr_prec(p, PREC_UNARY, error);
    if (!operand) return NULL;
    BinaryOp uop = (op->kind == TOK_MINUS) ? OP_NEG : OP_NOT;
    return ast_make_unary(p->arena, uop, operand, tok_loc(op));
}

static AstNode* parse_group(Parser* p, ErrorInfo* error) {
    advance(p);  // 跳过 (
    AstNode* expr = parse_expr(p, error);
    if (!expr) return NULL;
    if (!expect(p, TOK_RPAREN, error, "缺少 ')'")) return NULL;
    return expr;
}

static AstNode* parse_literal(Parser* p, ErrorInfo* error) {
    const Token* t = advance(p);
    switch (t->kind) {
        case TOK_INT_LIT:   return ast_make_literal_i64(p->arena, tok_int_value(t), tok_loc(t));
        case TOK_FLOAT_LIT: return ast_make_literal_f64(p->arena, tok_float_value(t), tok_loc(t));
        case TOK_CHAR_LIT: {
            int64_t val = 0;
            if (t->length >= 2 && t->start[0] == '\\') {
                switch (t->start[1]) {
                    case 'n': val = '\n'; break;
                    case 't': val = '\t'; break;
                    case '\\': val = '\\'; break;
                    case '\'': val = '\''; break;
                    default: val = t->start[1]; break;
                }
            } else {
                val = (unsigned char)t->start[0];
            }
            return ast_make_literal_char(p->arena, (int)val, tok_loc(t));
        }
        case TOK_TRUE:      return ast_make_literal_bool(p->arena, true, tok_loc(t));
        case TOK_FALSE:     return ast_make_literal_bool(p->arena, false, tok_loc(t));
        case TOK_STR_LIT: {
            char* str = arena_alloc_impl(p->arena, t->length + 1);
            memcpy(str, t->start, t->length);
            str[t->length] = '\0';
            // 字符串插值: "Hello, \(name)!" → "Hello, " + name + "!"
            char* interp = strstr(str, "\\(");
            if (interp) {
                *interp = '\0';  // 截断前半部分
                char* pre = str;
                char* expr_start = interp + 2;  // 跳过 \(
                char* close = strchr(expr_start, ')');
                if (!close) {
                    error->message = "字符串插值缺少 ')'"; error->filename = p->filename;
                    error->line = t->line; error->col = t->col; return NULL;
                }
                *close = '\0';
                char* post = close + 1;
                // 生成: pre + expr + post
                AstNode* result = ast_make_literal_str(p->arena,
                    arena_strdup_impl(p->arena, pre, strlen(pre)), tok_loc(t));
                // 将插值表达式按标识符解析
                AstNode* expr = ast_make_ident(p->arena,
                    arena_strdup_impl(p->arena, expr_start, strlen(expr_start)), tok_loc(t));
                result = ast_make_binary(p->arena, OP_ADD, result, expr, tok_loc(t));
                if (post[0] != '\0') {
                    AstNode* post_str = ast_make_literal_str(p->arena,
                        arena_strdup_impl(p->arena, post, strlen(post)), tok_loc(t));
                    result = ast_make_binary(p->arena, OP_ADD, result, post_str, tok_loc(t));
                }
                return result;
            }
            return ast_make_literal_str(p->arena, str, tok_loc(t));
        }
        default: return NULL;
    }
}

// === 结构体初始化解析: Name { field: val, ... } ===
static AstNode* parse_struct_init(Parser* p, const Token* name, ErrorInfo* error) {
    advance(p);  // 跳过 '{'
    const char* fnames[32];
    AstNode* fvals[32];
    int fcount = 0;

    while (peek(p)->kind != TOK_RBRACE && !error->message) {
        if (fcount >= 32) { error->message = "结构体初始化字段过多 (最多32)"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
        const Token* fname = expect(p, TOK_IDENT, error, "字段名");
        if (!fname) return NULL;
        if (!expect(p, TOK_COLON, error, "缺少 ':'")) return NULL;
        AstNode* val = parse_expr(p, error);
        if (!val) return NULL;

        fnames[fcount] = arena_strdup_impl(p->arena, fname->start, fname->length);
        fvals[fcount] = val;
        fcount++;

        if (peek(p)->kind == TOK_COMMA) advance(p);
        else break;
    }
    if (!expect(p, TOK_RBRACE, error, "缺少 '}'")) return NULL;

    const char** n_arr = arena_alloc_impl(p->arena, fcount * sizeof(const char*));
    memcpy(n_arr, fnames, fcount * sizeof(const char*));
    AstNode** v_arr = arena_alloc_impl(p->arena, fcount * sizeof(AstNode*));
    memcpy(v_arr, fvals, fcount * sizeof(AstNode*));

    return ast_make_struct_init(p->arena,
        arena_strdup_impl(p->arena, name->start, name->length),
        n_arr, v_arr, fcount, tok_loc(name));
}

// === 标识符 / 函数调用 / 结构体初始化 ===
static AstNode* parse_ident_or_call(Parser* p, ErrorInfo* error) {
    const Token* name = advance(p);

    // 枚举变体或模块函数: Name::Variant 或 Name::fn
    if (peek(p)->kind == TOK_COLON_COLON) {
        advance(p); // 跳过 ::
        const Token* variant = expect(p, TOK_IDENT, error, "枚举变体名");
        if (!variant) return NULL;
        // Name::fn 或 Name::Variant 或 Name::Variant(payload)
        if (peek(p)->kind == TOK_LPAREN) {
            // 前进探测: 检查括号内是否有多参数或命名参数（→函数调用）还是单表达式（→枚举payload）
            size_t probe = p->pos + 1;
            int paren_depth = 1;
            bool has_comma = false, has_named = false;
            while (paren_depth > 0 && p->tokens[probe].kind != TOK_EOF) {
                if (p->tokens[probe].kind == TOK_LPAREN) paren_depth++;
                else if (p->tokens[probe].kind == TOK_RPAREN) { paren_depth--; if (paren_depth == 0) break; }
                else if (paren_depth == 1 && p->tokens[probe].kind == TOK_COMMA) has_comma = true;
                else if (paren_depth == 1 && p->tokens[probe].kind == TOK_COLON) has_named = true;
                probe++;
            }
            if (has_comma || has_named) {
                // 模块函数调用: Name::fn(a, b) 或 Name::fn(x: 1)
                advance(p);  // 跳过 '('
                AstNode* args[16]; const char* arg_names[16]; int arg_count = 0;
                bool seen_named = false;
                while (peek(p)->kind != TOK_RPAREN && !error->message) {
                    if (arg_count >= 16) { error->message = "参数过多"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
                    if (peek(p)->kind == TOK_IDENT && (p->tokens[p->pos + 1].kind == TOK_COLON)) {
                        const Token* aname = advance(p); advance(p);
                        arg_names[arg_count] = arena_strdup_impl(p->arena, aname->start, aname->length);
                        seen_named = true;
                    } else {
                        if (seen_named) { error->message = "命名参数必须放在位置参数之后"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
                        arg_names[arg_count] = NULL;
                    }
                    args[arg_count] = parse_expr(p, error);
                    if (!args[arg_count]) return NULL;
                    arg_count++;
                    if (peek(p)->kind == TOK_COMMA) advance(p); else break;
                }
                if (!expect(p, TOK_RPAREN, error, "缺少 ')'")) return NULL;
                AstNode** arg_arr = arena_alloc_impl(p->arena, arg_count * sizeof(AstNode*));
                memcpy(arg_arr, args, arg_count * sizeof(AstNode*));
                const char** name_arr = seen_named
                    ? memcpy(arena_alloc_impl(p->arena, arg_count * sizeof(const char*)), arg_names, arg_count * sizeof(const char*))
                    : NULL;
                char* full_name = arena_alloc_impl(p->arena, name->length + variant->length + 4);
                sprintf(full_name, "%.*s::%.*s", name->length, name->start, variant->length, variant->start);
                return ast_make_call(p->arena, full_name, arg_arr, name_arr, arg_count, tok_loc(name));
            }
        }
        // 枚举 payload: Name::Variant 或 Name::Variant(expr)
        AstNode* payload = NULL;
        if (match(p, TOK_LPAREN)) {
            payload = parse_expr(p, error);
            if (!payload) return NULL;
            if (!expect(p, TOK_RPAREN, error, "缺少 ')'")) return NULL;
        }
        return ast_make_enum_variant(p->arena,
            arena_strdup_impl(p->arena, name->start, name->length),
            arena_strdup_impl(p->arena, variant->start, variant->length),
            payload, tok_loc(name));
    }

    // 结构体初始化: Name { field: val, ... }
    // 用提前看来区别 struct init 和 block：
    // struct init → { IDENT COLON ... ；block → { 可能是 let/if/while/...
    if (peek(p)->kind == TOK_LBRACE) {
        const Token* after_brace = &p->tokens[p->pos + 1];
        if (after_brace->kind == TOK_IDENT) {
            const Token* after_fname = &p->tokens[p->pos + 2];
            if (after_fname->kind == TOK_COLON) {
                return parse_struct_init(p, name, error);
            }
        }
    }

    // 函数调用: name(...)
    if (match(p, TOK_LPAREN)) {
        AstNode* args[16]; const char* arg_names[16]; int arg_count = 0;
        bool seen_named = false;
        while (peek(p)->kind != TOK_RPAREN && !error->message) {
            if (arg_count >= 16) {
                error->message = "函数参数过多"; error->filename = p->filename;
                error->line = peek(p)->line; error->col = peek(p)->col; return NULL;
            }
            // 命名参数: name: expr
            if (peek(p)->kind == TOK_IDENT && (p->tokens[p->pos + 1].kind == TOK_COLON)) {
                const Token* aname = advance(p); advance(p);  // 跳过标识符和 ':'
                arg_names[arg_count] = arena_strdup_impl(p->arena, aname->start, aname->length);
                seen_named = true;
            } else {
                if (seen_named) {
                    error->message = "命名参数必须放在位置参数之后"; error->filename = p->filename;
                    error->line = peek(p)->line; error->col = peek(p)->col; return NULL;
                }
                arg_names[arg_count] = NULL;
            }
            args[arg_count] = parse_expr(p, error);
            if (!args[arg_count]) return NULL;
            arg_count++;
            if (peek(p)->kind == TOK_COMMA) advance(p);
            else break;
        }
        if (!expect(p, TOK_RPAREN, error, "缺少 ')'")) return NULL;
        AstNode** arg_arr = arena_alloc_impl(p->arena, arg_count * sizeof(AstNode*));
        memcpy(arg_arr, args, arg_count * sizeof(AstNode*));
        const char** name_arr = seen_named
            ? memcpy(arena_alloc_impl(p->arena, arg_count * sizeof(const char*)), arg_names, arg_count * sizeof(const char*))
            : NULL;
        return ast_make_call(p->arena, arena_strdup_impl(p->arena, name->start, name->length),
                            arg_arr, name_arr, arg_count, tok_loc(name));
    }
    return ast_make_ident(p->arena,
        arena_strdup_impl(p->arena, name->start, name->length),
        tok_loc(name));
}

// === Pratt 主循环 ===
static AstNode* parse_expr_prec(Parser* p, Precedence min_prec, ErrorInfo* error) {
    const Token* tok = peek(p);
    AstNode* left = NULL;

    // 前缀解析
    if (tok->kind == TOK_IF) {
        const Token* if_tok = advance(p);
        // if let: if let Pattern = expr { then } else { else } → 去糖为 let+if
        if (peek(p)->kind == TOK_LET) {
            advance(p);  // 跳过 let
            // 解析模式: Enum::Variant 或 Enum::Variant(var)
            AstNode* pattern = parse_expr(p, error);  // 解析枚举变体
            if (!pattern) return NULL;
            if (!expect(p, TOK_ASSIGN, error, "if let 缺少 '='")) return NULL;
            AstNode* match_expr = parse_expr(p, error);
            if (!match_expr) return NULL;
            AstNode* then_block = parse_block(p, error);
            if (!then_block) return NULL;
            AstNode* else_block = NULL;
            if (match(p, TOK_ELSE)) {
                if (peek(p)->kind == TOK_IF)
                    else_block = parse_expr_prec(p, min_prec, error);
                else
                    else_block = parse_block(p, error);
                if (!else_block) return NULL;
            }
            // 去糖: { let __match = expr; if __match == pattern { then } else { else } }
            static int iflet_counter = 0;
            char vname_buf[32];
            snprintf(vname_buf, sizeof(vname_buf), "__iflet_%d", iflet_counter++);
            const char* vname = arena_strdup_impl(p->arena, vname_buf, strlen(vname_buf));
            AstNode* let_stmt = ast_make_let(p->arena,
                vname, TYPE_UNKNOWN,
                false, false, match_expr, NULL, 0, NULL, 0, tok_loc(if_tok));
            AstNode* cond = ast_make_binary(p->arena, OP_EQ,
                ast_make_ident(p->arena, vname, tok_loc(if_tok)),
                pattern, tok_loc(if_tok));
            AstNode* if_stmt = ast_make_if(p->arena, cond, then_block, else_block, tok_loc(if_tok));
            AstNode* stmts[2] = { let_stmt, if_stmt };
            AstNode** arr = arena_alloc_impl(p->arena, 2 * sizeof(AstNode*));
            memcpy(arr, stmts, 2 * sizeof(AstNode*));
            left = ast_make_block(p->arena, arr, 2, tok_loc(if_tok));
        } else {
            // if-expr: if cond { then } else { else }
            AstNode* cond = parse_expr(p, error);
            if (!cond) return NULL;
            AstNode* then_block = parse_block(p, error);
            if (!then_block) return NULL;
            AstNode* else_block = NULL;
            if (match(p, TOK_ELSE)) {
                if (peek(p)->kind == TOK_IF)
                    else_block = parse_expr_prec(p, min_prec, error);
                else
                    else_block = parse_block(p, error);
                if (!else_block) return NULL;
            }
            left = ast_make_if(p->arena, cond, then_block, else_block, tok_loc(if_tok));
        }
    } else if (tok->kind == TOK_MINUS || tok->kind == TOK_BANG) {
        left = parse_unary(p, error);
    } else if (tok->kind == TOK_LPAREN) {
        left = parse_group(p, error);
    } else if (tok->kind == TOK_INT_LIT || tok->kind == TOK_FLOAT_LIT ||
               tok->kind == TOK_CHAR_LIT ||
               tok->kind == TOK_TRUE || tok->kind == TOK_FALSE ||
               tok->kind == TOK_STR_LIT) {
        left = parse_literal(p, error);
    } else if (tok->kind == TOK_IDENT) {
        left = parse_ident_or_call(p, error);
    } else {
        error->message = "无法识别的表达式"; error->filename = p->filename;
        error->line = tok->line; error->col = tok->col;
        return NULL;
    }
    if (!left) return NULL;

    // 中缀/后置解析循环
    while (!error->message) {
        TokenKind kind = peek(p)->kind;

        // 管道: expr |> func(args...)  →  func(args..., expr)
        if (kind == TOK_PIPE) {
            Precedence prec = PREC_PIPE;
            if (prec <= min_prec) break;
            const Token* op = advance(p);
            // RHS 必须是函数调用（不带管道时解析）
            AstNode* right = parse_expr_prec(p, prec, error);
            if (!right) return NULL;
            if (right->kind != AST_CALL_EXPR) {
                error->message = "管道右侧必须是函数调用"; error->filename = p->filename;
                error->line = op->line; error->col = op->col;
                return NULL;
            }
            // 将 left 作为第一个参数插入（F#/Elixir 风格）
            if (right->as.call.arg_count >= 16) {
                error->message = "管道参数过多"; error->filename = p->filename;
                error->line = op->line; error->col = op->col; return NULL;
            }
            AstNode** new_args = arena_alloc_impl(p->arena, (right->as.call.arg_count + 1) * sizeof(AstNode*));
            new_args[0] = left;
            memcpy(new_args + 1, right->as.call.args, right->as.call.arg_count * sizeof(AstNode*));
            right->as.call.args = new_args;
            right->as.call.arg_count++;
            left = right;
            continue;
        }

        // 后置字段访问: expr.field 或 expr.method(args)
        if (kind == TOK_DOT) {
            advance(p);  // 跳过 '.'
            const Token* field = expect(p, TOK_IDENT, error, "缺少字段名");
            if (!field) return NULL;
            const char* member_name = arena_strdup_impl(p->arena, field->start, field->length);
            // 方法调用: expr.method(args)
            if (peek(p)->kind == TOK_LPAREN) {
                advance(p);  // 跳过 '('
                AstNode* args[16]; const char* arg_names[16]; int arg_count = 0;
                bool seen_named = false;
                while (peek(p)->kind != TOK_RPAREN && !error->message) {
                    if (arg_count >= 16) { error->message = "参数过多"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
                    if (peek(p)->kind == TOK_IDENT && (p->tokens[p->pos + 1].kind == TOK_COLON)) {
                        const Token* aname = advance(p); advance(p);
                        arg_names[arg_count] = arena_strdup_impl(p->arena, aname->start, aname->length);
                        seen_named = true;
                    } else {
                        if (seen_named) { error->message = "命名参数必须放在位置参数之后"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
                        arg_names[arg_count] = NULL;
                    }
                    args[arg_count] = parse_expr(p, error);
                    if (!args[arg_count]) return NULL;
                    arg_count++;
                    if (peek(p)->kind == TOK_COMMA) advance(p); else break;
                }
                if (!expect(p, TOK_RPAREN, error, "缺少 ')'")) return NULL;
                AstNode** arg_arr = arena_alloc_impl(p->arena, arg_count * sizeof(AstNode*));
                memcpy(arg_arr, args, arg_count * sizeof(AstNode*));
                const char** name_arr = seen_named
                    ? memcpy(arena_alloc_impl(p->arena, arg_count * sizeof(const char*)), arg_names, arg_count * sizeof(const char*))
                    : NULL;
                left = ast_make_method_call(p->arena, left, member_name, arg_arr, name_arr, arg_count, tok_loc(field));
            } else {
                left = ast_make_field_access(p->arena, left, member_name, tok_loc(field));
            }
            continue;
        }

        // 后置索引: expr[expr]
        if (kind == TOK_LBRACKET) {
            const Token* lbrack = advance(p);  // 跳过 '['
            AstNode* index = parse_expr(p, error);
            if (!index) return NULL;
            if (!expect(p, TOK_RBRACKET, error, "缺少 ']'")) return NULL;
            left = ast_make_index_expr(p->arena, left, index, tok_loc(lbrack));
            continue;
        }

        // 中缀运算符
        Precedence prec = tok_to_prec(kind);
        if (prec <= min_prec) break;

        const Token* op = advance(p);
        AstNode* right = parse_expr_prec(p, prec, error);
        if (!right) return NULL;
        left = ast_make_binary(p->arena, tok_to_binop(kind), left, right, tok_loc(op));
    }

    return left;
}

static AstNode* parse_expr(Parser* p, ErrorInfo* error) {
    return parse_expr_prec(p, PREC_NONE, error);
}

// === 类型工具 ===
static TypeKind token_to_type(TokenKind k) {
    switch (k) {
        case TOK_I32:  return TYPE_I32;
        case TOK_I64:  return TYPE_I64;
        case TOK_U64:  return TYPE_U64;
        case TOK_F64:  return TYPE_F64;
        case TOK_BOOL: return TYPE_BOOL;
        case TOK_CHAR: return TYPE_CHAR;
        case TOK_STR:  return TYPE_STR;
        default:       return TYPE_VOID;
    }
}

// === 类型表达式解析（内置类型/结构体名/数组类型）===
// 数组支持后置语法: T[N], T[N][M] 等
static TypeInfo parse_type_expr(Parser* p, ErrorInfo* error) {
    const Token* t = peek(p);
    TypeInfo ti = {0};

    // Self 类型（trait 中引用实现者自身类型）
    if (t->kind == TOK_SELF) {
        advance(p);
        ti.kind = TYPE_STRUCT;
        ti.struct_name = "Self";
        return ti;
    }

    // 解析基础类型
    if (tok_is_type(t->kind)) {
        advance(p);
        ti.kind = token_to_type(t->kind);
    } else if (t->kind == TOK_IDENT) {
        advance(p);
        ti.kind = TYPE_STRUCT;
        ti.struct_name = arena_strdup_impl(p->arena, t->start, t->length);
    } else {
        error->message = "无效的类型"; error->filename = p->filename;
        error->line = t->line; error->col = t->col;
        ti.kind = TYPE_ERROR;
        return ti;
    }

    // 后置数组维度: Type[N] → TYPE_ARRAY
    if (peek(p)->kind == TOK_LBRACKET) {
        advance(p);  // 跳过 '['
        const Token* size_tok = expect(p, TOK_INT_LIT, error, "数组大小必须是整数常量");
        if (!size_tok) { ti.kind = TYPE_ERROR; return ti; }
        int64_t size = tok_int_value(size_tok);
        if (!expect(p, TOK_RBRACKET, error, "缺少 ']'")) {
            ti.kind = TYPE_ERROR; return ti;
        }
        TypeInfo arr_ti = {0};
        arr_ti.kind = TYPE_ARRAY;
        arr_ti.element_type = ti.kind;
        arr_ti.element_struct_name = ti.struct_name;
        arr_ti.array_size = size;
        return arr_ti;
    }

    return ti;
}

// === 结构体声明解析 ===
static AstNode* parse_struct_decl(Parser* p, ErrorInfo* error) {
    const Token* s_tok = advance(p);  // 跳过 'struct'
    const Token* name = expect(p, TOK_IDENT, error, "struct 后应为结构体名");
    if (!name) return NULL;
    if (!expect(p, TOK_LBRACE, error, "缺少 '{'")) return NULL;

    AstNode* fields[32]; int fcount = 0;
    while (peek(p)->kind != TOK_RBRACE && !error->message) {
        if (fcount >= 32) { error->message = "结构体字段过多 (最多32)"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
        const Token* fname = expect(p, TOK_IDENT, error, "字段名");
        if (!fname) return NULL;
        if (!expect(p, TOK_COLON, error, "缺少 ':'")) return NULL;
        TypeInfo fti = parse_type_expr(p, error);
        if (fti.kind == TYPE_ERROR) {
            error->filename = p->filename;
            return NULL;
        }
        fields[fcount++] = ast_make_parameter(p->arena,
            arena_strdup_impl(p->arena, fname->start, fname->length),
            fti.kind, fti.struct_name, tok_loc(fname));
        if (peek(p)->kind == TOK_COMMA) advance(p);
        else break;
    }
    if (!expect(p, TOK_RBRACE, error, "缺少 '}'")) return NULL;

    AstNode** farr = arena_alloc_impl(p->arena, fcount * sizeof(AstNode*));
    memcpy(farr, fields, fcount * sizeof(AstNode*));
    return ast_make_struct_decl(p->arena,
        arena_strdup_impl(p->arena, name->start, name->length),
        farr, fcount, tok_loc(s_tok));
}

// === match 语句解析（脱糖为 let + if-else 链）===
// match <expr> { pat1 => { body1 }, pat2 => { body2 }, _ => { body_default } }
//   → { let __match_val = <expr>; if __match_val == pat1 { body1 } else if __match_val == pat2 { body2 } else { body_default } }
static AstNode* parse_match_stmt(Parser* p, ErrorInfo* error) {
    const Token* match_tok = advance(p);  // 跳过 'match'

    // 解析被匹配的表达式
    AstNode* matched = parse_expr(p, error);
    if (!matched) return NULL;

    if (!expect(p, TOK_LBRACE, error, "match 后缺少 '{'")) return NULL;

    // 分配临时变量名
    const char* varname = arena_strdup_impl(p->arena, "__match_val", 12);

    // 收集所有分支
    enum { MAX_ARMS = 64 };
    bool   arm_is_wildcard[MAX_ARMS];
    AstNode* arm_pattern[MAX_ARMS];
    AstNode* arm_body[MAX_ARMS];
    int arm_count = 0;

    while (peek(p)->kind != TOK_RBRACE && !error->message) {
        if (arm_count >= MAX_ARMS) {
            error->message = "match 分支过多 (最多64)";
            error->filename = p->filename;
            error->line = peek(p)->line; error->col = peek(p)->col;
            return NULL;
        }

        if (peek(p)->kind == TOK_UNDERSCORE) {
            arm_is_wildcard[arm_count] = true;
            arm_pattern[arm_count] = NULL;
            advance(p);  // 跳过 '_'
        } else {
            arm_is_wildcard[arm_count] = false;
            arm_pattern[arm_count] = parse_expr(p, error);
            if (!arm_pattern[arm_count]) return NULL;
        }

        // 解析 '=>'
        if (!expect(p, TOK_MATCH_ARROW, error, "match 分支缺少 '=>'")) return NULL;

        // 解析分支体（必须是一个代码块）
        arm_body[arm_count] = parse_block(p, error);
        if (!arm_body[arm_count]) return NULL;

        arm_count++;

        // 跳过可选逗号
        if (peek(p)->kind == TOK_COMMA) advance(p);
    }

    if (!expect(p, TOK_RBRACE, error, "缺少 '}'")) return NULL;

    if (arm_count == 0) {
        error->message = "match 表达式至少需要一个分支";
        error->filename = p->filename;
        error->line = match_tok->line; error->col = match_tok->col;
        return NULL;
    }

    // 从最后一个分支往前构建 if-else 链（最后一个分支 = 最内层 else）
    AstNode* result = NULL;
    for (int i = arm_count - 1; i >= 0; i--) {
        if (arm_is_wildcard[i]) {
            // 通配符分支：if (true) { body } else { result }
            AstNode* true_cond = ast_make_literal_bool(p->arena, true, tok_loc(match_tok));
            result = ast_make_if(p->arena, true_cond, arm_body[i], result, tok_loc(match_tok));
        } else {
            // if (__match_val == pattern) { body } else { result }
            AstNode* cond = ast_make_binary(p->arena, OP_EQ,
                ast_make_ident(p->arena, varname, tok_loc(match_tok)),
                arm_pattern[i], tok_loc(match_tok));
            result = ast_make_if(p->arena, cond, arm_body[i], result, tok_loc(match_tok));
        }
    }

    // 构建 let __match_val = <matched>;
    AstNode* let_stmt = ast_make_let(p->arena, varname, TYPE_UNKNOWN,
        false, false, matched, NULL, 0, NULL, 0, tok_loc(match_tok));

    // 包装为代码块: { let __match_val = <expr>; <if-else 链> }
    AstNode* stmts_arr[2] = { let_stmt, result };
    AstNode** stmts = arena_alloc_impl(p->arena, 2 * sizeof(AstNode*));
    memcpy(stmts, stmts_arr, 2 * sizeof(AstNode*));
    return ast_make_block(p->arena, stmts, 2, tok_loc(match_tok));
}

// === 语句解析 ===

static AstNode* parse_block(Parser* p, ErrorInfo* error) {
    if (++parse_depth > MAX_PARSE_DEPTH) {
        error->message = "嵌套过深"; error->filename = p->filename;
        error->line = peek(p)->line; error->col = peek(p)->col;
        parse_depth--; return NULL;
    }
    const Token* open = peek(p);
    if (!expect(p, TOK_LBRACE, error, "缺少 '{'")) { parse_depth--; return NULL; }
    AstNode* stmts[256]; int count = 0;
    while (peek(p)->kind != TOK_RBRACE && peek(p)->kind != TOK_EOF && !error->message) {
        if (count >= 256) { error->message = "代码块语句过多 (最多256)"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; parse_depth--; return NULL; }
        AstNode* s = parse_statement(p, error);
        if (!s) { parse_depth--; return NULL; }
        stmts[count++] = s;
    }
    if (!expect(p, TOK_RBRACE, error, "缺少 '}'")) { parse_depth--; return NULL; }
    AstNode** arr = arena_alloc_impl(p->arena, count * sizeof(AstNode*));
    memcpy(arr, stmts, count * sizeof(AstNode*));
    parse_depth--;
    return ast_make_block(p->arena, arr, count, tok_loc(open));
}

static AstNode* parse_statement(Parser* p, ErrorInfo* error) {
    const Token* t = peek(p);

    if (t->kind == TOK_LET || t->kind == TOK_VAR) {
        bool is_mut = (advance(p)->kind == TOK_VAR);
        const Token* name = expect(p, TOK_IDENT, error,
            is_mut ? "var 后应为变量名" : "let 后应为变量名");
        if (!name) return NULL;
        // 可选的类型标注
        TypeKind annot_type = TYPE_UNKNOWN;
        bool has_type_annot = false;
        const char* struct_type_name = NULL;
        TypeKind annot_elem_type = 0;
        const char* annot_elem_struct = NULL;
        int64_t annot_arr_size = 0;
        if (match(p, TOK_COLON)) {
            TypeInfo ti = parse_type_expr(p, error);
            if (ti.kind == TYPE_ERROR) return NULL;
            annot_type = ti.kind;
            struct_type_name = ti.struct_name;
            annot_elem_type = ti.element_type;
            annot_elem_struct = ti.element_struct_name;
            annot_arr_size = ti.array_size;
            has_type_annot = true;
        }
        if (!expect(p, TOK_ASSIGN, error, "缺少 '='")) return NULL;
        AstNode* init = parse_expr(p, error);
        if (!init) return NULL;
        if (!expect(p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
        return ast_make_let(p->arena,
            arena_strdup_impl(p->arena, name->start, name->length),
            annot_type, has_type_annot, is_mut, init, struct_type_name,
            annot_elem_type, annot_elem_struct, annot_arr_size, tok_loc(t));
    }

    if (t->kind == TOK_IF) {
        // 委托给表达式解析器（含 if let 去糖）
        AstNode* if_expr = parse_expr_prec(p, PREC_NONE, error);
        if (!if_expr) return NULL;
        return if_expr;  // AST_IF_STMT 或 AST_BLOCK(if-let去糖)
    }

    if (t->kind == TOK_WHILE) {
        advance(p);
        AstNode* cond = parse_expr(p, error);
        if (!cond) return NULL;
        AstNode* body = parse_block(p, error);
        if (!body) return NULL;
        return ast_make_while(p->arena, cond, body, tok_loc(t));
    }

    if (t->kind == TOK_FOR) {
        advance(p);  // 跳过 'for'

        // 解析循环变量名
        const Token* var_name = expect(p, TOK_IDENT, error, "for 后应为变量名");
        if (!var_name) return NULL;

        // 解析 'in'
        if (!expect(p, TOK_IN, error, "缺少 'in'")) return NULL;

        // 解析起始表达式
        AstNode* start_expr = parse_expr(p, error);
        if (!start_expr) return NULL;

        // 解析 'to'
        if (!expect(p, TOK_TO, error, "缺少 'to'")) return NULL;

        // 解析结束表达式
        AstNode* end_expr = parse_expr(p, error);
        if (!end_expr) return NULL;

        // 解析循环体
        AstNode* body = parse_block(p, error);
        if (!body) return NULL;

        // 脱糖: for i in start to end { body; }
        //   → { var i = start; while i < end { body; i = i + 1; } }

        const char* vname = arena_strdup_impl(p->arena, var_name->start, var_name->length);

        // 构建: var i = start;
        AstNode* let_stmt = ast_make_let(p->arena, vname, TYPE_UNKNOWN, false, true, start_expr, NULL, 0, NULL, 0, tok_loc(var_name));

        // 构建: i < end  (while 条件)
        AstNode* cond = ast_make_binary(p->arena, OP_LT,
            ast_make_ident(p->arena, vname, tok_loc(var_name)),
            end_expr, tok_loc(var_name));

        // 构建: i = i + 1  (循环增量)
        AstNode* incr = ast_make_assign(p->arena, vname,
            ast_make_binary(p->arena, OP_ADD,
                ast_make_ident(p->arena, vname, tok_loc(var_name)),
                ast_make_literal_i64(p->arena, 1, tok_loc(var_name)),
                tok_loc(var_name)),
            tok_loc(var_name));

        // 将增量追加到循环体末尾
        AstNode** new_stmts = arena_alloc_impl(p->arena,
            (body->as.block.stmt_count + 1) * sizeof(AstNode*));
        memcpy(new_stmts, body->as.block.stmts, body->as.block.stmt_count * sizeof(AstNode*));
        new_stmts[body->as.block.stmt_count] = incr;
        AstNode* new_body = ast_make_block(p->arena, new_stmts,
            body->as.block.stmt_count + 1, body->loc);

        // 构建: while i < end { ... body ... ; i = i + 1; }
        AstNode* while_loop = ast_make_while(p->arena, cond, new_body, tok_loc(t));

        // 包装: { var i = start; while i < end { ... } }
        AstNode* stmts_arr[2] = { let_stmt, while_loop };
        AstNode** stmts = arena_alloc_impl(p->arena, 2 * sizeof(AstNode*));
        memcpy(stmts, stmts_arr, 2 * sizeof(AstNode*));
        return ast_make_block(p->arena, stmts, 2, tok_loc(t));
    }

    if (t->kind == TOK_MATCH) {
        return parse_match_stmt(p, error);
    }

    if (t->kind == TOK_GUARD) {
        // guard expr else { ... }  →  if !(expr) { ... }
        const Token* guard_tok = advance(p);
        AstNode* cond = parse_expr(p, error);
        if (!cond) return NULL;
        if (!expect(p, TOK_ELSE, error, "guard 缺少 'else'")) return NULL;
        AstNode* body = parse_block(p, error);
        if (!body) return NULL;
        // 去糖: if !cond { body }
        AstNode* not_cond = ast_make_unary(p->arena, OP_NOT, cond, tok_loc(guard_tok));
        return ast_make_if(p->arena, not_cond, body, NULL, tok_loc(guard_tok));
    }

    if (t->kind == TOK_RETURN) {
        advance(p);
        if (match(p, TOK_SEMICOLON)) {
            return ast_make_return(p->arena, NULL, tok_loc(t));
        }
        AstNode* expr = parse_expr(p, error);
        if (!expr) return NULL;
        if (!expect(p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
        return ast_make_return(p->arena, expr, tok_loc(t));
    }

    // 数组元素赋值: ident[expr] = expr ;
    // 需要前瞻: 检查 ']' 后面是否是 '=' (而非 ';' 或其它)
    if (t->kind == TOK_IDENT && (t + 1)->kind == TOK_LBRACKET) {
        // 向前扫描找到对应的 ']'（不支持嵌套 '[' 在索引中）
        int ahead_idx = 2;
        int bracket_depth = 1;
        while (bracket_depth > 0 && (t + ahead_idx)->kind != TOK_EOF) {
            if ((t + ahead_idx)->kind == TOK_LBRACKET) bracket_depth++;
            else if ((t + ahead_idx)->kind == TOK_RBRACKET) bracket_depth--;
            if (bracket_depth > 0) ahead_idx++;
        }
        // 检查 ']' 后是否是 '='
        if ((t + ahead_idx + 1)->kind == TOK_ASSIGN) {
            const Token* name = advance(p);  // 消费标识符
            advance(p);  // 消费 '['
            AstNode* index = parse_expr(p, error);
            if (!index) return NULL;
            if (!expect(p, TOK_RBRACKET, error, "缺少 ']'")) return NULL;
            if (!expect(p, TOK_ASSIGN, error, "缺少 '='")) return NULL;
            AstNode* value = parse_expr(p, error);
            if (!value) return NULL;
            if (!expect(p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
            return ast_make_array_assign(p->arena,
                arena_strdup_impl(p->arena, name->start, name->length),
                index, value, tok_loc(name));
        }
        // 否则: 不是数组赋值, 回退到下方表达式语句处理
    }

    // 赋值语句: ident = expr ;
    if (t->kind == TOK_IDENT && (t + 1)->kind == TOK_ASSIGN) {
        const Token* name = advance(p);  // 消费标识符
        advance(p);  // 消费 '='
        AstNode* value = parse_expr(p, error);
        if (!value) return NULL;
        if (!expect(p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
        return ast_make_assign(p->arena,
            arena_strdup_impl(p->arena, name->start, name->length),
            value, tok_loc(name));
    }

    // 复合赋值: ident += expr  →  ident = ident + expr
    if (t->kind == TOK_IDENT) {
        TokenKind next_kind = (t + 1)->kind;
        if (next_kind >= TOK_PLUS_EQ && next_kind <= TOK_SLASH_EQ) {
            const Token* name = advance(p);  // 消费标识符
            TokenKind comp_op = advance(p)->kind;

            BinaryOp binop;
            switch (comp_op) {
                case TOK_PLUS_EQ:  binop = OP_ADD; break;
                case TOK_MINUS_EQ: binop = OP_SUB; break;
                case TOK_STAR_EQ:  binop = OP_MUL; break;
                case TOK_SLASH_EQ: binop = OP_DIV; break;
                default: break;
            }

            AstNode* rhs = parse_expr(p, error);
            if (!rhs) return NULL;
            if (!expect(p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;

            AstNode* lhs_ident = ast_make_ident(p->arena,
                arena_strdup_impl(p->arena, name->start, name->length),
                tok_loc(name));
            AstNode* bin_expr = ast_make_binary(p->arena, binop, lhs_ident, rhs,
                tok_loc(name));
            return ast_make_assign(p->arena,
                arena_strdup_impl(p->arena, name->start, name->length),
                bin_expr, tok_loc(name));
        }
    }

    // 表达式语句
    AstNode* expr = parse_expr(p, error);
    if (!expr) return NULL;
    if (!expect(p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
    return ast_make_expr_stmt(p->arena, expr, tok_loc(t));
}

// === 函数解析 ===
static AstNode* parse_function(Parser* p, bool is_pub, ErrorInfo* error) {
    const Token* fn_tok = advance(p);  // fn
    const Token* name = expect(p, TOK_IDENT, error, "fn 后应为函数名");
    if (!name) return NULL;
    // 泛型类型参数: <T, U, ...>
    const char* type_params[8]; int tp_count = 0;
    if (peek(p)->kind == TOK_LT) {
        advance(p);  // 跳过 '<'
        while (peek(p)->kind != TOK_GT && !error->message) {
            if (tp_count >= 8) { error->message = "类型参数过多 (最多8)"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
            const Token* tp = expect(p, TOK_IDENT, error, "类型参数名");
            if (!tp) return NULL;
            type_params[tp_count++] = arena_strdup_impl(p->arena, tp->start, tp->length);
            if (peek(p)->kind == TOK_COMMA) advance(p); else break;
        }
        if (!expect(p, TOK_GT, error, "缺少 '>'")) return NULL;
    }
    if (!expect(p, TOK_LPAREN, error, "缺少 '('")) return NULL;

    // 参数列表（泛型参数可标注为类型参数名）
    AstNode* params[64]; int pcount = 0;
    while (peek(p)->kind != TOK_RPAREN && !error->message) {
        if (pcount >= 64) { error->message = "函数参数过多 (最多64)"; error->filename = p->filename; error->line = peek(p)->line; error->col = peek(p)->col; return NULL; }
        const Token* pname = expect(p, TOK_IDENT, error, "参数名");
        if (!pname) return NULL;
        if (!expect(p, TOK_COLON, error, "缺少 ':'")) return NULL;
        TypeInfo pti = parse_type_expr(p, error);
        if (pti.kind == TYPE_ERROR) return NULL;
        params[pcount++] = ast_make_parameter(p->arena,
            arena_strdup_impl(p->arena, pname->start, pname->length),
            pti.kind, pti.struct_name, tok_loc(pname));
        if (match(p, TOK_COMMA)) continue;
        else break;
    }
    if (!expect(p, TOK_RPAREN, error, "缺少 ')'")) return NULL;

    // 返回类型
    TypeKind ret = TYPE_VOID;
    const char* ret_struct_name = NULL;
    if (match(p, TOK_ARROW)) {
        TypeInfo rti = parse_type_expr(p, error);
        if (rti.kind == TYPE_ERROR) return NULL;
        ret = rti.kind;
        ret_struct_name = rti.struct_name;
    }

    // trait 方法签名或普通函数体
    AstNode* body = NULL;
    if (match(p, TOK_SEMICOLON)) {
        body = NULL;  // trait 方法签名，无实现
    } else {
        body = parse_block(p, error);
        if (!body) return NULL;
    }

    AstNode** parr = arena_alloc_impl(p->arena, pcount * sizeof(AstNode*));
    memcpy(parr, params, pcount * sizeof(AstNode*));
    const char** tparr = NULL;
    if (tp_count > 0) {
        tparr = arena_alloc_impl(p->arena, tp_count * sizeof(const char*));
        memcpy(tparr, type_params, tp_count * sizeof(const char*));
    }
    return ast_make_function(p->arena,
        arena_strdup_impl(p->arena, name->start, name->length),
        parr, pcount, ret, ret_struct_name, body, is_pub, tparr, tp_count, tok_loc(fn_tok));
}

// === 模块文件加载辅助 ===
// parse 前向声明（定义在后面）
AstNode* parse(Arena* a, const Token* tokens, size_t count,
              const char* filename, ErrorInfo* error);

static AstNode* load_module(Arena* a, const char* parent_file,
                             const char* mod_name, ErrorInfo* error) {
    // 构造模块文件路径: 同目录下 mod_name.l
    char mod_path[512];
    const char* last_slash = strrchr(parent_file, '/');
    const char* last_bs = strrchr(parent_file, '\\');
    const char* dir_end = parent_file;
    if (last_slash && last_slash > dir_end) dir_end = last_slash;
    if (last_bs && last_bs > dir_end) dir_end = last_bs;
    if (dir_end != parent_file) {
        size_t dir_len = dir_end - parent_file + 1;
        memcpy(mod_path, parent_file, dir_len);
        snprintf(mod_path + dir_len, sizeof(mod_path) - dir_len, "%s.l", mod_name);
    } else {
        snprintf(mod_path, sizeof(mod_path), "%s.l", mod_name);
    }
    // 读取文件
    FILE* f = fopen(mod_path, "rb");
    if (!f) {
        error->message = "无法打开模块文件"; error->filename = mod_path;
        error->line = 0; error->col = 0;
        return NULL;
    }
    fseek(f, 0, SEEK_END);
    size_t sz = ftell(f); fseek(f, 0, SEEK_SET);
    char* src = malloc(sz + 1);
    if (!src) { fclose(f); return NULL; }
    fread(src, 1, sz, f); src[sz] = '\0'; fclose(f);

    size_t tc;
    ErrorInfo lex_err = {0};
    Token* toks = lex(a, src, mod_path, &tc, &lex_err);
    free(src);
    if (!toks) { *error = lex_err; return NULL; }

    AstNode* ast = parse(a, toks, tc, mod_path, error);
    return ast;
}

// === 程序入口 ===
AstNode* parse(Arena* a, const Token* tokens, size_t count,
               const char* filename, ErrorInfo* error) {
    Parser p = {.tokens = tokens, .count = count, .pos = 0,
                .filename = filename, .arena = a};
    AstNode* functions[256]; int fn_count = 0;
    AstNode* structs[64];   int struct_count = 0;
    AstNode* aliases[64];   int alias_count = 0;
    AstNode* enums[64];     int enum_count = 0;
    AstNode* impls[64];     int impl_count = 0;
    AstNode* mods[64];      int mod_count = 0;
    AstNode* uses[64];      int use_count = 0;
    while (peek(&p)->kind != TOK_EOF && !error->message) {
        // pub 前缀
        bool is_pub = false;
        if (peek(&p)->kind == TOK_PUB) {
            is_pub = true; advance(&p);
        }
        if (peek(&p)->kind == TOK_TRAIT) {
            const Token* tt = advance(&p);
            const Token* tname = expect(&p, TOK_IDENT, error, "trait 后应为接口名");
            if (!tname) return NULL;
            if (!expect(&p, TOK_LBRACE, error, "缺少 '{'")) return NULL;
            AstNode* methods[64]; int mcount = 0;
            while (peek(&p)->kind != TOK_RBRACE && !error->message) {
                if (mcount >= 64) { error->message = "trait 方法过多(最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
                if (peek(&p)->kind != TOK_FN) { error->message = "trait 内只允许 fn"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
                // trait 方法只解析签名（body 为空）
                AstNode* m = parse_function(&p, false, error);
                if (!m) return NULL;
                m->as.function.body = NULL;  // trait 方法无实现
                methods[mcount++] = m;
                if (peek(&p)->kind == TOK_COMMA) advance(&p);
            }
            if (!expect(&p, TOK_RBRACE, error, "缺少 '}'")) return NULL;
            AstNode** marr = arena_alloc_impl(p.arena, mcount * sizeof(AstNode*));
            memcpy(marr, methods, mcount * sizeof(AstNode*));
            // 复用 impl_count 存储 trait（共用计数）
            if (impl_count >= 64) { error->message = "trait 过多(最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
            impls[impl_count++] = ast_make_trait_decl(p.arena,
                arena_strdup_impl(p.arena, tname->start, tname->length),
                marr, mcount, tok_loc(tt));
        } else if (peek(&p)->kind == TOK_STRUCT) {
            if (struct_count >= 64) { error->message = "结构体过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
            structs[struct_count++] = parse_struct_decl(&p, error);
        } else if (peek(&p)->kind == TOK_TYPE) {
            if (alias_count >= 64) { error->message = "类型别名过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
            const Token* type_tok = advance(&p);  // 跳过 'type'
            const Token* alias_name = expect(&p, TOK_IDENT, error, "type 后应为别名");
            if (!alias_name) return NULL;
            if (!expect(&p, TOK_ASSIGN, error, "缺少 '='")) return NULL;
            TypeInfo rti = parse_type_expr(&p, error);
            if (rti.kind == TYPE_ERROR) return NULL;
            if (!expect(&p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
            aliases[alias_count++] = ast_make_type_alias(a,
                arena_strdup_impl(a, alias_name->start, alias_name->length),
                rti.kind, rti.struct_name, tok_loc(type_tok));
        } else if (peek(&p)->kind == TOK_ENUM) {
            advance(&p);
            const Token* name = expect(&p, TOK_IDENT, error, "enum 后应为枚举名");
            if (!name) return NULL;
            if (!expect(&p, TOK_LBRACE, error, "缺少 '{'")) return NULL;
            const char* variants[64];
            TypeKind payload_types[64];
            const char* payload_snames[64];
            int vcount = 0;
            while (peek(&p)->kind != TOK_RBRACE && !error->message) {
                if (vcount >= 64) { error->message = "枚举变体过多(最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
                const Token* vname = expect(&p, TOK_IDENT, error, "变体名");
                if (!vname) return NULL;
                variants[vcount] = arena_strdup_impl(p.arena, vname->start, vname->length);
                payload_types[vcount] = TYPE_VOID;
                payload_snames[vcount] = NULL;
                // 可选 payload: Variant(Type)
                if (peek(&p)->kind == TOK_LPAREN) {
                    advance(&p);
                    TypeInfo pti = parse_type_expr(&p, error);
                    if (pti.kind == TYPE_ERROR) return NULL;
                    payload_types[vcount] = pti.kind;
                    payload_snames[vcount] = pti.struct_name;
                    if (!expect(&p, TOK_RPAREN, error, "缺少 ')'")) return NULL;
                }
                vcount++;
                if (peek(&p)->kind == TOK_COMMA) advance(&p); else break;
            }
            if (!expect(&p, TOK_RBRACE, error, "缺少 '}'")) return NULL;
            const char** v_arr = arena_alloc_impl(p.arena, vcount * sizeof(const char*));
            memcpy(v_arr, variants, vcount * sizeof(const char*));
            TypeKind* pt_arr = arena_alloc_impl(p.arena, vcount * sizeof(TypeKind));
            memcpy(pt_arr, payload_types, vcount * sizeof(TypeKind));
            const char** ps_arr = arena_alloc_impl(p.arena, vcount * sizeof(const char*));
            memcpy(ps_arr, payload_snames, vcount * sizeof(const char*));
            AstNode* enum_decl = ast_make_enum_decl(p.arena,
                arena_strdup_impl(p.arena, name->start, name->length),
                v_arr, pt_arr, ps_arr, vcount, tok_loc(name));
            if (enum_count >= 64) { error->message = "枚举过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
            enums[enum_count++] = enum_decl;
        } else if (peek(&p)->kind == TOK_EXTEND) {
            const Token* i_tok = advance(&p);
            const Token* first = expect(&p, TOK_IDENT, error, "extend 后应为结构体名");
            if (!first) return NULL;
            const char* trait_name = NULL;
            const char* struct_name;
            // extend Trait Struct { ... }（trait 实现：两个标识符）
            if (peek(&p)->kind == TOK_IDENT) {
                trait_name = arena_strdup_impl(p.arena, first->start, first->length);
                struct_name = arena_strdup_impl(p.arena, peek(&p)->start, peek(&p)->length);
                advance(&p);
            } else {
                struct_name = arena_strdup_impl(p.arena, first->start, first->length);
            }
            if (!expect(&p, TOK_LBRACE, error, "缺少 '{'")) return NULL;
            AstNode* methods[64]; int mcount = 0;
            while (peek(&p)->kind != TOK_RBRACE && !error->message) {
                if (mcount >= 64) { error->message = "方法过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
                if (peek(&p)->kind != TOK_FN) { error->message = "extend 块内只允许 fn"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
                AstNode* m = parse_function(&p, false, error);
                if (!m) return NULL;
                // trait 实现: 方法名 mangled 为 TraitName$methodName
                if (trait_name) {
                    char* mn = arena_alloc_impl(p.arena, strlen(trait_name) + strlen(m->as.function.name) + 4);
                    sprintf(mn, "%s$%s", trait_name, m->as.function.name);
                    m->as.function.name = mn;
                }
                methods[mcount++] = m;
            }
            if (!expect(&p, TOK_RBRACE, error, "缺少 '}'")) return NULL;
            AstNode** m_arr = arena_alloc_impl(p.arena, mcount * sizeof(AstNode*));
            memcpy(m_arr, methods, mcount * sizeof(AstNode*));
            if (impl_count >= 64) { error->message = "extend 块过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
            impls[impl_count++] = ast_make_impl_block(p.arena, struct_name, m_arr, mcount, tok_loc(i_tok));
        } else if (peek(&p)->kind == TOK_MOD) {
            advance(&p);
            const Token* mn = expect(&p, TOK_IDENT, error, "mod 后应为模块名");
            if (!mn) return NULL;
            if (!expect(&p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
            const char* mod_name = arena_strdup_impl(p.arena, mn->start, mn->length);
            AstNode* sub = load_module(a, filename, mod_name, error);
            if (!sub) return NULL;
            // 合并子模块项到当前文件（以 mod_name:: 为前缀）
            for (size_t i = 0; i < sub->as.program.fn_count; i++) {
                AstNode* fn = sub->as.program.functions[i];
                if (fn->as.function.is_pub) {
                    char* mangled = arena_alloc_impl(p.arena, strlen(mod_name) + strlen(fn->as.function.name) + 4);
                    sprintf(mangled, "%s::%s", mod_name, fn->as.function.name);
                    fn->as.function.name = mangled;
                    if (fn_count >= 256) { error->message = "函数过多"; error->filename = p.filename; return NULL; }
                    functions[fn_count++] = fn;
                }
            }
            for (size_t i = 0; i < sub->as.program.struct_count; i++) {
                if (struct_count >= 64) break;
                structs[struct_count++] = sub->as.program.structs[i];
            }
            for (size_t i = 0; i < sub->as.program.enum_count; i++) {
                if (enum_count >= 64) break;
                enums[enum_count++] = sub->as.program.enums[i];
            }
            if (mod_count < 64) mods[mod_count++] = ast_make_mod_decl(a, mod_name, sub, tok_loc(mn));
        } else if (peek(&p)->kind == TOK_USE) {
            advance(&p);
            const Token* path_tok = expect(&p, TOK_IDENT, error, "use 后应为模块名");
            if (!path_tok) return NULL;
            if (!expect(&p, TOK_COLON_COLON, error, "缺少 '::'")) return NULL;
            const Token* item_tok = expect(&p, TOK_IDENT, error, "use 后应为项目名");
            if (!item_tok) return NULL;
            if (!expect(&p, TOK_SEMICOLON, error, "缺少 ';'")) return NULL;
            if (use_count >= 64) { error->message = "use 过多 (最多64)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
            uses[use_count++] = ast_make_use_decl(a,
                arena_strdup_impl(p.arena, path_tok->start, path_tok->length),
                arena_strdup_impl(p.arena, item_tok->start, item_tok->length),
                tok_loc(path_tok));
        } else if (peek(&p)->kind == TOK_FN) {
            if (fn_count >= 256) { error->message = "函数过多 (最多256)"; error->filename = p.filename; error->line = peek(&p)->line; error->col = peek(&p)->col; return NULL; }
            functions[fn_count++] = parse_function(&p, is_pub, error);
        } else {
            error->message = "顶层只允许 fn、struct、type、enum、extend、mod 或 use";
            error->filename = p.filename;
            error->line = peek(&p)->line;
            error->col = peek(&p)->col;
            return NULL;
        }
    }
    if (error->message) return NULL;
    AstNode** fn_arr = arena_alloc_impl(a, fn_count * sizeof(AstNode*));
    memcpy(fn_arr, functions, fn_count * sizeof(AstNode*));
    AstNode** st_arr = arena_alloc_impl(a, struct_count * sizeof(AstNode*));
    memcpy(st_arr, structs, struct_count * sizeof(AstNode*));
    AstNode** al_arr = arena_alloc_impl(a, alias_count * sizeof(AstNode*));
    memcpy(al_arr, aliases, alias_count * sizeof(AstNode*));
    AstNode** en_arr = arena_alloc_impl(a, enum_count * sizeof(AstNode*));
    memcpy(en_arr, enums, enum_count * sizeof(AstNode*));
    AstNode** im_arr = arena_alloc_impl(a, impl_count * sizeof(AstNode*));
    memcpy(im_arr, impls, impl_count * sizeof(AstNode*));
    return ast_make_program(a, fn_arr, fn_count, st_arr, struct_count,
                            al_arr, alias_count, en_arr, enum_count,
                            im_arr, impl_count, loc_at(0, 0));
}