//! Module resolver for multi-file imports

//!

//! This module provides functionality to resolve file imports in Ruchy programs

//! by pre-processing the AST to inline external modules before transpilation.

//!

//! # Architecture

//! 

//! The module resolver works as a pre-processing step before transpilation:

//! 1. Parse the main file into an AST

//! 2. Scan for file imports (`use module_name;` where `module_name` has no `::`)

//! 3. Load and parse external module files 

//! 4. Replace Import nodes with inline Module nodes

//! 5. Pass the resolved AST to the transpiler

//!

//! # Usage

//!

//! ```rust

//! use ruchy::{ModuleResolver, Parser, Transpiler};

//! 

//! let mut resolver = ModuleResolver::new();

//! resolver.add_search_path("./src");

//! 

//! let mut parser = Parser::new("use math; math::add(1, 2)");

//! let ast = parser.parse()?;

//! 

//! let resolved_ast = resolver.resolve_imports(ast)?;

//! 

//! let transpiler = Transpiler::new();

//! let rust_code = transpiler.transpile(&resolved_ast)?;

//! ```

use crate::frontend::ast::{Expr, ExprKind, ImportItem, Span};

use crate::backend::module_loader::ModuleLoader;

use anyhow::{Result, Context};

/// Module resolver for processing file imports

/// 

/// Resolves file imports by loading external modules and inlining them

/// as Module declarations in the AST before transpilation.

pub struct ModuleResolver {

    /// Module loader for file system operations

    pub(crate) module_loader: ModuleLoader,

}

impl ModuleResolver {

    /// Create a new module resolver with default search paths

    /// 

    /// Default search paths:

    /// - `.` (current directory)

    /// - `./src` (source directory)

    /// - `./modules` (modules directory)

    #[must_use]

    pub fn new() -> Self {

        Self {

            module_loader: ModuleLoader::new(),

        }

    }

    /// Add a directory to the module search path

    /// 

    /// # Arguments

    /// 

    /// * `path` - Directory to search for modules

    pub fn add_search_path<P: AsRef<std::path::Path>>(&mut self, path: P) {

        self.module_loader.add_search_path(path);

    }

    /// Resolve all file imports in an AST

    /// 

    /// Recursively processes the AST to find file imports, loads the corresponding

    /// modules, and replaces Import nodes with inline Module nodes.

    /// 

    /// # Arguments

    /// 

    /// * `ast` - The AST to process

    /// 

    /// # Returns

    /// 

    /// A new AST with all file imports resolved to inline modules

    /// 

    /// # Errors

    /// 

    /// Returns an error if:

    /// - Module files cannot be found or loaded

    /// - Module files contain invalid syntax  

    /// - Circular dependencies are detected

    pub fn resolve_imports(&mut self, ast: Expr) -> Result<Expr> {

        self.resolve_expr(ast)

    }

    /// Recursively resolve imports in an expression

    fn resolve_expr(&mut self, expr: Expr) -> Result<Expr> {

        match expr.kind {

            ExprKind::Import { ref path, ref items } => {

                // Check if this is a file import (no :: and not std:: or http)

                if self.is_file_import(path) {

                    // Load the module file

                    let parsed_module = self.module_loader.load_module(path)

                        .with_context(|| format!("Failed to resolve import '{path}'"))?;

                    // Recursively resolve imports in the loaded module

                    let resolved_module_ast = self.resolve_expr(parsed_module.ast)?;

                    // Create an inline module declaration

                    let module_expr = Expr::new(

                        ExprKind::Module {

                            name: path.clone(),

                            body: Box::new(resolved_module_ast),

                        },

                        expr.span,

                    );

                    // Create a use statement to import from the module

                    let use_statement = if items.iter().any(|item| matches!(item, ImportItem::Wildcard)) || items.is_empty() {

                        // Wildcard import: use module::*;

                        Expr::new(

                            ExprKind::Import {

                                path: path.clone(),

                                items: vec![ImportItem::Wildcard],

                            },

                            Span { start: 0, end: 0 },

                        )

                    } else {

                        // Specific imports: use module::{item1, item2};

                        self.create_use_statements(path, items)

                    };

                    // Return a block with the module declaration and use statement

                    Ok(Expr::new(

                        ExprKind::Block(vec![module_expr, use_statement]),

                        expr.span,

                    ))

                } else {

                    // Not a file import, keep as-is

                    Ok(expr)

                }

            }

            ExprKind::Block(exprs) => {

                // Resolve imports in all block expressions

                let resolved_exprs: Result<Vec<_>> = exprs

                    .into_iter()

                    .map(|e| self.resolve_expr(e))

                    .collect();

                Ok(Expr::new(ExprKind::Block(resolved_exprs?), expr.span))

            }

            ExprKind::Module { name, body } => {

                // Resolve imports in module body

                let resolved_body = self.resolve_expr(*body)?;

                Ok(Expr::new(

                    ExprKind::Module {

                        name,

                        body: Box::new(resolved_body),

                    },

                    expr.span,

                ))

            }

            ExprKind::Function { 

                name, 

                type_params, 

                params, 

                body, 

                is_async,

                return_type,

                is_pub,

            } => {

                // Resolve imports in function body

                let resolved_body = self.resolve_expr(*body)?;

                Ok(Expr::new(

                    ExprKind::Function {

                        name,

                        type_params,

                        params,

                        body: Box::new(resolved_body),

                        is_async,

                        return_type,

                        is_pub,

                    },

                    expr.span,

                ))

            }

            ExprKind::If { condition, then_branch, else_branch } => {

                let resolved_condition = self.resolve_expr(*condition)?;

                let resolved_then = self.resolve_expr(*then_branch)?;

                let resolved_else = else_branch.map(|e| self.resolve_expr(*e)).transpose()?;

                Ok(Expr::new(

                    ExprKind::If {

                        condition: Box::new(resolved_condition),

                        then_branch: Box::new(resolved_then),

                        else_branch: resolved_else.map(Box::new),

                    },

                    expr.span,

                ))

            }

            // For other expression types, recursively process children as needed

            // For now, just return the expression as-is

            _ => Ok(expr),

        }

    }

    /// Check if an import path represents a file import

    fn is_file_import(&self, path: &str) -> bool {

        !path.contains("::")

            && !path.starts_with("std::")

            && !path.starts_with("http")

            && !path.is_empty()

    }

    /// Create use statements for specific imports

    fn create_use_statements(&self, module_path: &str, items: &[ImportItem]) -> Expr {

        // Create a use statement that imports specific items from the module

        // This will be transpiled to proper Rust use statements

        Expr::new(

            ExprKind::Import {

                path: module_path.to_string(), // Use the module path as-is

                items: items.to_vec(),

            },

            Span { start: 0, end: 0 },

        )

    }

    /// Get module loading statistics

    #[must_use]

    pub fn stats(&self) -> crate::backend::module_loader::ModuleLoaderStats {

        self.module_loader.stats()

    }

    /// Clear the module cache

    /// 

    /// Forces all modules to be reloaded from disk on next access.

    pub fn clear_cache(&mut self) {

        self.module_loader.clear_cache();

    }

}

impl Default for ModuleResolver {

    fn default() -> Self {

        Self::new()

    }

}

#[cfg(test)]

mod tests {

    use super::*;

    use tempfile::TempDir;

    use std::fs;

    use crate::frontend::ast::Literal;

    fn create_test_module(temp_dir: &TempDir, name: &str, content: &str) -> Result<()> {

        let file_path = temp_dir.path().join(format!("{name}.ruchy"));

        fs::write(file_path, content)?;

        Ok(())

    }

    #[test]

    fn test_module_resolver_creation() {

        let resolver = ModuleResolver::new();

        let stats = resolver.stats();

        assert_eq!(stats.cached_modules, 0);

    }

    #[test] 

    fn test_add_search_path() {

        let mut resolver = ModuleResolver::new();

        resolver.add_search_path("/custom/path");

        // Module loader doesn't expose search paths, so we can't directly test this

        // But we can test that it doesn't panic

    }

    #[test]

    fn test_is_file_import() {

        let resolver = ModuleResolver::new();

        // Should be file imports

        assert!(resolver.is_file_import("math"));

        assert!(resolver.is_file_import("utils"));

        assert!(resolver.is_file_import("snake_case_module"));

        // Should NOT be file imports

        assert!(!resolver.is_file_import("std::collections"));

        assert!(!resolver.is_file_import("std::io::Read"));

        assert!(!resolver.is_file_import("https://example.com/module.ruchy"));

        assert!(!resolver.is_file_import("http://localhost/module.ruchy"));

        assert!(!resolver.is_file_import(""));

    }

    #[test]

    fn test_resolve_simple_file_import() -> Result<()> {

        let temp_dir = TempDir::new()?;

        let mut resolver = ModuleResolver::new();

        resolver.add_search_path(temp_dir.path());

        // Create a simple math module

        create_test_module(&temp_dir, "math", r"

            pub fun add(a: i32, b: i32) -> i32 {

                a + b

            }

        ")?;

        // Create an import expression

        let import_expr = Expr::new(

            ExprKind::Import {

                path: "math".to_string(),

                items: vec![ImportItem::Wildcard],

            },

            Span { start: 0, end: 0 },

        );

        // Resolve the import

        let resolved_expr = resolver.resolve_imports(import_expr)?;

        // Should be converted to a Block with Module declaration and use statement

        match resolved_expr.kind {

            ExprKind::Block(exprs) => {

                assert_eq!(exprs.len(), 2);

                // First should be Module declaration

                match &exprs[0].kind {

                    ExprKind::Module { name, .. } => {

                        assert_eq!(name, "math");

                    }

                    _ => unreachable!("Expected first element to be Module, got {:?}", exprs[0].kind),

                }

                // Second should be use statement

                match &exprs[1].kind {

                    ExprKind::Import { path, items } => {

                        assert_eq!(path, "math");

                        assert_eq!(items.len(), 1);

                        assert!(matches!(items[0], ImportItem::Wildcard));

                    }

                    _ => unreachable!("Expected second element to be Import, got {:?}", exprs[1].kind),

                }

            }

            _ => unreachable!("Expected Block expression, got {:?}", resolved_expr.kind),

        }

        Ok(())

    }

    #[test]

    fn test_resolve_non_file_import() -> Result<()> {

        let mut resolver = ModuleResolver::new();

        // Create a standard library import

        let import_expr = Expr::new(

            ExprKind::Import {

                path: "std::collections".to_string(),

                items: vec![ImportItem::Named("HashMap".to_string())],

            },

            Span { start: 0, end: 0 },

        );

        // Resolve the import - should remain unchanged

        let resolved_expr = resolver.resolve_imports(import_expr)?;

        match resolved_expr.kind {

            ExprKind::Import { path, items } => {

                assert_eq!(path, "std::collections");

                assert_eq!(items.len(), 1);

            }

            _ => unreachable!("Expected Import expression to remain unchanged"),

        }

        Ok(())

    }

    #[test]

    fn test_resolve_block_with_imports() -> Result<()> {

        let temp_dir = TempDir::new()?;

        let mut resolver = ModuleResolver::new();

        resolver.add_search_path(temp_dir.path());

        create_test_module(&temp_dir, "math", "42")?;

        // Create a block with mixed imports

        let block_expr = Expr::new(

            ExprKind::Block(vec![

                Expr::new(

                    ExprKind::Import {

                        path: "math".to_string(),

                        items: vec![ImportItem::Wildcard],

                    },

                    Span { start: 0, end: 0 },

                ),

                Expr::new(

                    ExprKind::Import {

                        path: "std::io".to_string(),

                        items: vec![ImportItem::Named("Read".to_string())],

                    },

                    Span { start: 0, end: 0 },

                ),

                Expr::new(

                    ExprKind::Literal(Literal::Integer(42)),

                    Span { start: 0, end: 0 },

                ),

            ]),

            Span { start: 0, end: 0 },

        );

        let resolved_block = resolver.resolve_imports(block_expr)?;

        if let ExprKind::Block(exprs) = resolved_block.kind {

            assert_eq!(exprs.len(), 3);

            // First should be Block containing Module and use statement (from file import)

            match &exprs[0].kind {

                ExprKind::Block(inner_exprs) => {

                    assert_eq!(inner_exprs.len(), 2);

                    assert!(matches!(inner_exprs[0].kind, ExprKind::Module { .. }));

                    assert!(matches!(inner_exprs[1].kind, ExprKind::Import { .. }));

                }

                _ => unreachable!("Expected first element to be Block, got {:?}", exprs[0].kind),

            }

            // Second should remain as Import (std::io - not a file import)

            assert!(matches!(exprs[1].kind, ExprKind::Import { .. }));

            // Third should remain as Literal

            assert!(matches!(exprs[2].kind, ExprKind::Literal(Literal::Integer(42))));

        } else {

            unreachable!("Expected Block expression");

        }

        Ok(())

    }

    #[test]

    fn test_stats_and_cache() -> Result<()> {

        let temp_dir = TempDir::new()?;

        let mut resolver = ModuleResolver::new();

        resolver.module_loader.search_paths.clear(); // Remove default paths

        resolver.add_search_path(temp_dir.path());

        create_test_module(&temp_dir, "test", "42")?;

        let initial_stats = resolver.stats();

        assert_eq!(initial_stats.files_loaded, 0);

        // Load a module

        let import_expr = Expr::new(

            ExprKind::Import {

                path: "test".to_string(),

                items: vec![ImportItem::Wildcard],

            },

            Span { start: 0, end: 0 },

        );

        resolver.resolve_imports(import_expr)?;

        let after_stats = resolver.stats();

        assert_eq!(after_stats.files_loaded, 1);

        assert_eq!(after_stats.cached_modules, 1);

        // Clear cache

        resolver.clear_cache();

        let cleared_stats = resolver.stats();

        assert_eq!(cleared_stats.files_loaded, 0);

        assert_eq!(cleared_stats.cached_modules, 0);

        Ok(())

    }

}