aster/aster-core/src/interpreter/module.rs

//! 模块系统：require() 加载器
//!
//! `require("path/to/module.ast")` 加载并执行指定的 Aster 文件，
//! 返回一个包含模块所有顶层定义的 `Value::Object`。
//! 模块在自己的作用域中执行，只能访问内置函数，无法访问调用者的变量。
//! 第二次 require 同一文件会返回缓存的对象。

use crate::error::RuntimeError;
use crate::lexer::Lexer;
use crate::parser::Parser;
use super::{Interpreter, Env, Value, Signal, Runtime};
use std::cell::RefCell;
use std::collections::HashMap;
use std::path::Path;
use std::rc::Rc;

impl Runtime for Interpreter {
    fn require(&mut self, path: &str) -> Result<Value, RuntimeError> {
        require_impl(self, path)
    }
}

/// require() 的内置函数实现 — 薄包装，委托给 Runtime::require
pub fn require_fn(runtime: &mut dyn Runtime, args: Vec<Value>) -> Result<Value, RuntimeError> {
    let path_str = match args.first() {
        Some(Value::String(s)) => s.clone(),
        Some(other) => return Err(runtime_error(format!(
            "require() expects a string argument, got {}", other))),
        None => return Err(runtime_error(
            "require() expects 1 argument (string path)")),
    };
    runtime.require(&path_str)
}

/// require() 的内部实现 (供 Interpreter::require 使用)
fn require_impl(interp: &mut Interpreter, path_str: &str) -> Result<Value, RuntimeError> {
    // 1. 路径解析
    let resolved = resolve_path(&interp.current_dir, path_str)?;

    // 2. 缓存查找
    if let Some(cached) = interp.module_cache.borrow().get(&resolved) {
        return Ok(cached.clone());
    }

    // 3. 读取文件
    let src = std::fs::read_to_string(&resolved)
        .map_err(|e| runtime_error(format!(
            "Module '{}' not found: {}", path_str, e)))?;

    // 4. 词法分析
    let (tokens, lex_errors) = Lexer::new(&src).tokenize();
    if !lex_errors.is_empty() {
        return Err(runtime_error(format!(
            "Lex error in module '{}': {}", path_str, lex_errors[0])));
    }

    // 5. 语法分析
    let mut parser = Parser::new(tokens);
    let (stmts, parse_errors) = parser.parse();
    if !parse_errors.is_empty() {
        return Err(runtime_error(format!(
            "Parse error in module '{}': {}", path_str, parse_errors[0])));
    }

    // 6. 创建隔离的模块 env（父级 = builtins_env，看不到调用者的变量）
    let module_env = Rc::new(RefCell::new(Env::new(Some(Rc::clone(&interp.builtins_env)))));

    // 7. 在缓存中插入占位符（支持循环 require）
    let exports_map = Rc::new(RefCell::new(HashMap::new()));
    let exports = Value::Object(Rc::clone(&exports_map));
    interp.module_cache.borrow_mut().insert(resolved.clone(), exports.clone());

    // 8. 保存调用者状态
    let previous_env = Rc::clone(&interp.env);
    let previous_dir = interp.current_dir.clone();

    // 9. 切换到模块上下文
    interp.env = module_env.clone();
    interp.current_dir = module_dir(&resolved);

    // 10. 执行模块
    for stmt in &stmts {
        match interp.execute(stmt.clone()) {
            Ok(Signal::Break) | Ok(Signal::Continue) => {
                interp.env = previous_env;
                interp.current_dir = previous_dir;
                interp.module_cache.borrow_mut().remove(&resolved);
                return Err(runtime_error(
                    "break/continue outside of loop in module"));
            }
            Err(e) => {
                interp.env = previous_env;
                interp.current_dir = previous_dir;
                interp.module_cache.borrow_mut().remove(&resolved);
                return Err(e);
            }
            Ok(Signal::None) | Ok(Signal::Return(_)) => {}
        }
    }

    // 11. 恢复调用者状态
    interp.env = previous_env;
    interp.current_dir = previous_dir;

    // 12. 收集 exports（模块 env 中的所有直接绑定）
    for (name, (val, _mutable)) in module_env.borrow().values.clone() {
        exports_map.borrow_mut().insert(name, val);
    }

    Ok(exports)
}

// ============================================================================
// Helpers
// ============================================================================

fn resolve_path(current_dir: &str, path_str: &str) -> Result<String, RuntimeError> {
    let path = Path::new(path_str);
    let resolved = if path.is_absolute() {
        path.to_path_buf()
    } else {
        Path::new(current_dir).join(path)
    };
    std::fs::canonicalize(&resolved)
        .map(|p| p.to_string_lossy().to_string())
        .map_err(|_| runtime_error(format!(
            "Module '{}' not found (resolved to '{}')",
            path_str, resolved.display())))
}

fn module_dir(resolved: &str) -> String {
    Path::new(resolved)
        .parent()
        .map(|p| p.to_string_lossy().to_string())
        .unwrap_or_else(|| ".".to_string())
}

fn runtime_error(msg: impl Into<String>) -> RuntimeError {
    RuntimeError::RuntimeError {
        message: msg.into(),
        token: None,
    }
}