package runner

import (
	"errors"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	luajit "git.sharkk.net/Sky/LuaJIT-to-Go"
)

// Common errors
var (
	ErrModuleNotFound = errors.New("module not found")
	ErrPathTraversal  = errors.New("path traversal not allowed")
)

// ModuleEntry represents a cached module with timestamp
type ModuleEntry struct {
	Bytecode []byte
	LastUsed time.Time
}

// RequireConfig holds configuration for Lua's require function
type RequireConfig struct {
	ScriptDir string   // Base directory for script being executed
	LibDirs   []string // Additional library directories
}

// RequireCache is a thread-safe cache for loaded Lua modules
type RequireCache struct {
	modules  sync.Map // Maps full file paths to ModuleEntry
	mu       sync.Mutex
	maxItems int // Maximum number of modules to cache
}

// NewRequireCache creates a new, empty require cache
func NewRequireCache() *RequireCache {
	return &RequireCache{
		modules:  sync.Map{},
		maxItems: 100, // Default cache size - can be adjusted based on expected module load
	}
}

// SetCacheSize adjusts the maximum cache size
func (c *RequireCache) SetCacheSize(size int) {
	if size > 0 {
		c.mu.Lock()
		c.maxItems = size
		c.mu.Unlock()
	}
}

// Size returns the approximate number of items in the cache
func (c *RequireCache) Size() int {
	size := 0
	c.modules.Range(func(_, _ interface{}) bool {
		size++
		return true
	})
	return size
}

// Get retrieves a module from the cache, updating its last used time
func (c *RequireCache) Get(path string) ([]byte, bool) {
	value, ok := c.modules.Load(path)
	if !ok {
		return nil, false
	}

	entry, ok := value.(ModuleEntry)
	if !ok {
		// Handle legacy entries (plain bytecode)
		bytecode, ok := value.([]byte)
		if !ok {
			return nil, false
		}

		// Convert to ModuleEntry and update
		entry = ModuleEntry{
			Bytecode: bytecode,
			LastUsed: time.Now(),
		}
		c.modules.Store(path, entry)
		return bytecode, true
	}

	// Update last used time
	entry.LastUsed = time.Now()
	c.modules.Store(path, entry)

	return entry.Bytecode, true
}

// Store adds a module to the cache with LRU eviction
func (c *RequireCache) Store(path string, bytecode []byte) {
	c.mu.Lock()
	defer c.mu.Unlock()

	// Check if we need to evict
	if c.Size() >= c.maxItems {
		c.evictOldest()
	}

	// Store the new entry
	c.modules.Store(path, ModuleEntry{
		Bytecode: bytecode,
		LastUsed: time.Now(),
	})
}

// evictOldest removes the least recently used item from the cache
func (c *RequireCache) evictOldest() {
	var oldestTime time.Time
	var oldestKey string
	first := true

	// Find oldest entry
	c.modules.Range(func(key, value interface{}) bool {
		// Handle different value types
		var lastUsed time.Time

		switch v := value.(type) {
		case ModuleEntry:
			lastUsed = v.LastUsed
		default:
			// For non-ModuleEntry values, treat as oldest
			if first {
				oldestKey = key.(string)
				first = false
				return true
			}
			return true
		}

		if first || lastUsed.Before(oldestTime) {
			oldestTime = lastUsed
			oldestKey = key.(string)
			first = false
		}
		return true
	})

	// Remove oldest entry
	if oldestKey != "" {
		c.modules.Delete(oldestKey)
	}
}

// UpdateRequirePaths updates the require paths in the config without further allocations or re-registering the loader.
func UpdateRequirePaths(config *RequireConfig, scriptPath string) {
	if scriptPath != "" {
		config.ScriptDir = filepath.Dir(scriptPath)
	}
}

// findAndCompileModule finds a module in allowed directories and compiles it to bytecode
func findAndCompileModule(
	state *luajit.State,
	cache *RequireCache,
	config RequireConfig,
	modName string,
) ([]byte, error) {
	// Convert module name to relative path
	modPath := strings.ReplaceAll(modName, ".", string(filepath.Separator))

	// List of paths to check
	paths := []string{}

	// 1. Check adjacent to script directory first
	if config.ScriptDir != "" {
		paths = append(paths, filepath.Join(config.ScriptDir, modPath+".lua"))
	}

	// 2. Check in lib directories
	for _, libDir := range config.LibDirs {
		if libDir != "" {
			paths = append(paths, filepath.Join(libDir, modPath+".lua"))
		}
	}

	// Try each path
	for _, path := range paths {
		// Clean the path to handle .. and such (security)
		cleanPath := filepath.Clean(path)

		// Check for path traversal (extra safety)
		if !isSubPath(config.ScriptDir, cleanPath) {
			isValidLib := false
			for _, libDir := range config.LibDirs {
				if isSubPath(libDir, cleanPath) {
					isValidLib = true
					break
				}
			}

			if !isValidLib {
				continue // Skip paths outside allowed directories
			}
		}

		// Check if already in cache - using our Get method to update LRU info
		if bytecode, ok := cache.Get(cleanPath); ok {
			return bytecode, nil
		}

		// Check if file exists
		_, err := os.Stat(cleanPath)
		if os.IsNotExist(err) {
			continue
		}

		// Read and compile the file
		content, err := os.ReadFile(cleanPath)
		if err != nil {
			return nil, err
		}

		// Compile to bytecode
		bytecode, err := state.CompileBytecode(string(content), cleanPath)
		if err != nil {
			return nil, err
		}

		// Store in cache - using our Store method with LRU eviction
		cache.Store(cleanPath, bytecode)

		return bytecode, nil
	}

	return nil, ErrModuleNotFound
}

// isSubPath checks if path is contained within base directory
func isSubPath(baseDir, path string) bool {
	if baseDir == "" {
		return false
	}

	// Clean and normalize paths
	baseDir = filepath.Clean(baseDir)
	path = filepath.Clean(path)

	// Get relative path
	rel, err := filepath.Rel(baseDir, path)
	if err != nil {
		return false
	}

	// Check if path goes outside baseDir
	return !strings.HasPrefix(rel, ".."+string(filepath.Separator)) && rel != ".."
}