package runner

import (
	"context"
	"errors"
	"sync"
	"sync/atomic"

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

// Common errors
var (
	ErrRunnerClosed = errors.New("lua runner is closed")
	ErrInitFailed   = errors.New("initialization failed")
)

// StateInitFunc is a function that initializes a Lua state
type StateInitFunc func(*luajit.State) error

// LuaRunner runs Lua scripts using a single Lua state
type LuaRunner struct {
	state        *luajit.State     // The Lua state
	jobQueue     chan job          // Channel for incoming jobs
	isRunning    atomic.Bool       // Flag indicating if the runner is active
	mu           sync.RWMutex      // Mutex for thread safety
	wg           sync.WaitGroup    // WaitGroup for clean shutdown
	initFunc     StateInitFunc     // Optional function to initialize Lua state
	bufferSize   int               // Size of the job queue buffer
	requireCache *RequireCache     // Cache for required modules
	requireCfg   *RequireConfig    // Configuration for require paths
	moduleLoader luajit.GoFunction // Keep reference to prevent GC
	sandbox      *Sandbox          // The sandbox environment
}

// NewRunner creates a new LuaRunner
func NewRunner(options ...RunnerOption) (*LuaRunner, error) {
	// Default configuration
	runner := &LuaRunner{
		bufferSize:   10, // Default buffer size
		requireCache: NewRequireCache(),
		requireCfg: &RequireConfig{
			LibDirs: []string{},
		},
		sandbox: NewSandbox(),
	}

	// Apply options
	for _, opt := range options {
		opt(runner)
	}

	// Initialize Lua state
	state := luajit.New()
	if state == nil {
		return nil, errors.New("failed to create Lua state")
	}
	runner.state = state

	// Create job queue
	runner.jobQueue = make(chan job, runner.bufferSize)
	runner.isRunning.Store(true)

	// Create a shared config pointer that will be updated per request
	runner.requireCfg = &RequireConfig{
		ScriptDir: runner.scriptDir(),
		LibDirs:   runner.libDirs(),
	}

	// Set up require functionality
	moduleLoader := func(s *luajit.State) int {
		// Get module name
		modName := s.ToString(1)
		if modName == "" {
			s.PushString("module name required")
			return -1
		}

		// Find and compile module
		bytecode, err := findAndCompileModule(s, runner.requireCache, *runner.requireCfg, modName)
		if err != nil {
			if err == ErrModuleNotFound {
				s.PushString("module '" + modName + "' not found")
			} else {
				s.PushString("error loading module: " + err.Error())
			}
			return -1 // Return error
		}

		// Load the bytecode
		if err := s.LoadBytecode(bytecode, modName); err != nil {
			s.PushString("error loading bytecode: " + err.Error())
			return -1 // Return error
		}

		// Return the loaded function
		return 1
	}

	// Store reference to prevent garbage collection
	runner.moduleLoader = moduleLoader

	// Register with Lua state
	if err := state.RegisterGoFunction("__go_load_module", moduleLoader); err != nil {
		state.Close()
		return nil, ErrInitFailed
	}

	// Set up the require mechanism
	if err := setupRequireFunction(state); err != nil {
		state.Close()
		return nil, ErrInitFailed
	}

	// Set up sandbox
	if err := runner.sandbox.Setup(state); err != nil {
		state.Close()
		return nil, ErrInitFailed
	}

	// Run init function if provided
	if runner.initFunc != nil {
		if err := runner.initFunc(state); err != nil {
			state.Close()
			return nil, ErrInitFailed
		}
	}

	// Start the event loop
	runner.wg.Add(1)
	go runner.processJobs()

	return runner, nil
}

// setupRequireFunction adds the secure require implementation
func setupRequireFunction(state *luajit.State) error {
	return state.DoString(`
		function __setup_secure_require(env)
			-- Replace env.require with our secure version
			env.require = function(modname)
				-- Check if already loaded in package.loaded
				if package.loaded[modname] then
					return package.loaded[modname]
				end

				-- Try to load the module using our Go loader
				local loader = __go_load_module

				-- Load the module
				local f, err = loader(modname)
				if not f then
					error(err or "failed to load module: " .. modname)
				end

				-- Set the environment for the module
				setfenv(f, env)

				-- Execute the module
				local result = f()

				-- If module didn't return a value, use true
				if result == nil then
					result = true
				end

				-- Cache the result
				package.loaded[modname] = result

				return result
			end

			return env
		end
	`)
}

// RunnerOption defines a functional option for configuring the LuaRunner
type RunnerOption func(*LuaRunner)

// WithBufferSize sets the job queue buffer size
func WithBufferSize(size int) RunnerOption {
	return func(r *LuaRunner) {
		if size > 0 {
			r.bufferSize = size
		}
	}
}

// WithInitFunc sets the init function for the Lua state
func WithInitFunc(initFunc StateInitFunc) RunnerOption {
	return func(r *LuaRunner) {
		r.initFunc = initFunc
	}
}

// WithScriptDir sets the base directory for scripts
func WithScriptDir(dir string) RunnerOption {
	return func(r *LuaRunner) {
		r.requireCfg.ScriptDir = dir
	}
}

// WithLibDirs sets additional library directories
func WithLibDirs(dirs ...string) RunnerOption {
	return func(r *LuaRunner) {
		r.requireCfg.LibDirs = dirs
	}
}

// scriptDir returns the current script directory
func (r *LuaRunner) scriptDir() string {
	if r.requireCfg != nil {
		return r.requireCfg.ScriptDir
	}
	return ""
}

// libDirs returns the current library directories
func (r *LuaRunner) libDirs() []string {
	if r.requireCfg != nil {
		return r.requireCfg.LibDirs
	}
	return nil
}

// processJobs handles the job queue
func (r *LuaRunner) processJobs() {
	defer r.wg.Done()
	defer r.state.Close()

	for job := range r.jobQueue {
		// Execute the job and send result
		result := r.executeJob(job)
		select {
		case job.Result <- result:
			// Result sent successfully
		default:
			// Result channel closed or full, discard the result
		}
	}
}

// executeJob runs a script in the sandbox environment
func (r *LuaRunner) executeJob(j job) JobResult {
	// If the job has a script path, update paths without re-registering
	if j.ScriptPath != "" {
		r.mu.Lock()
		UpdateRequirePaths(r.requireCfg, j.ScriptPath)
		r.mu.Unlock()
	}

	// Re-run init function if needed
	if r.initFunc != nil {
		if err := r.initFunc(r.state); err != nil {
			return JobResult{nil, err}
		}
	}

	// Convert context for sandbox
	var ctx map[string]any
	if j.Context != nil {
		ctx = j.Context.Values
	}

	// Execute in sandbox
	value, err := r.sandbox.Execute(r.state, j.Bytecode, ctx)
	return JobResult{value, err}
}

// RunWithContext executes a Lua script with context and timeout
func (r *LuaRunner) RunWithContext(ctx context.Context, bytecode []byte, execCtx *Context, scriptPath string) (any, error) {
	r.mu.RLock()
	if !r.isRunning.Load() {
		r.mu.RUnlock()
		return nil, ErrRunnerClosed
	}
	r.mu.RUnlock()

	resultChan := make(chan JobResult, 1)
	j := job{
		Bytecode:   bytecode,
		Context:    execCtx,
		ScriptPath: scriptPath,
		Result:     resultChan,
	}

	// Submit job with context
	select {
	case r.jobQueue <- j:
		// Job submitted
	case <-ctx.Done():
		return nil, ctx.Err()
	}

	// Wait for result with context
	select {
	case result := <-resultChan:
		return result.Value, result.Error
	case <-ctx.Done():
		return nil, ctx.Err()
	}
}

// Run executes a Lua script
func (r *LuaRunner) Run(bytecode []byte, execCtx *Context, scriptPath string) (any, error) {
	return r.RunWithContext(context.Background(), bytecode, execCtx, scriptPath)
}

// Close gracefully shuts down the LuaRunner
func (r *LuaRunner) Close() error {
	r.mu.Lock()
	defer r.mu.Unlock()

	if !r.isRunning.Load() {
		return ErrRunnerClosed
	}

	r.isRunning.Store(false)
	close(r.jobQueue)

	// Wait for event loop to finish
	r.wg.Wait()

	return nil
}

// ClearRequireCache clears the cache of loaded modules
func (r *LuaRunner) ClearRequireCache() {
	r.requireCache = NewRequireCache()
}

// AddModule adds a module to the sandbox environment
func (r *LuaRunner) AddModule(name string, module any) {
	r.sandbox.AddModule(name, module)
}