package luajit

import (
	"fmt"
	"sync"
)

// LUA_MULTRET is the constant for multiple return values
const LUA_MULTRET = -1

// Sandbox provides a persistent Lua environment for executing scripts
type Sandbox struct {
	state       *State
	mutex       sync.Mutex
	initialized bool
	modules     map[string]any
}

// NewSandbox creates a new sandbox with standard libraries loaded
func NewSandbox() *Sandbox {
	return &Sandbox{
		state:       New(),
		initialized: false,
		modules:     make(map[string]any),
	}
}

// Close releases all resources used by the sandbox
func (s *Sandbox) Close() {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state != nil {
		s.state.Close()
		s.state = nil
	}
}

// RegisterFunction registers a Go function in the sandbox
func (s *Sandbox) RegisterFunction(name string, fn GoFunction) error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	// Make sure sandbox is initialized
	if !s.initialized {
		if err := s.initializeUnlocked(); err != nil {
			return err
		}
	}

	// Register function globally
	if err := s.state.RegisterGoFunction(name, fn); err != nil {
		return err
	}

	// Add to base environment
	return s.state.DoString(`
		-- Add the function to base environment
		__env_system.base_env["` + name + `"] = ` + name + `
	`)
}

// SetGlobal sets a global variable in the sandbox base environment
func (s *Sandbox) SetGlobal(name string, value any) error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	// Make sure sandbox is initialized
	if !s.initialized {
		if err := s.initializeUnlocked(); err != nil {
			return err
		}
	}

	// Push the value onto the stack
	if err := s.state.PushValue(value); err != nil {
		return err
	}

	// Set the global with the pushed value
	s.state.SetGlobal(name)

	// Add to base environment
	return s.state.DoString(`
		-- Add the global to base environment
		__env_system.base_env["` + name + `"] = ` + name + `
	`)
}

// GetGlobal retrieves a global variable from the sandbox base environment
func (s *Sandbox) GetGlobal(name string) (any, error) {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return nil, fmt.Errorf("sandbox is closed")
	}

	// Make sure sandbox is initialized
	if !s.initialized {
		if err := s.initializeUnlocked(); err != nil {
			return nil, err
		}
	}

	// Get the global from the base environment
	code := `return __env_system.base_env["` + name + `"]`
	return s.state.ExecuteWithResult(code)
}

// Run executes Lua code in the sandbox and returns the result
func (s *Sandbox) Run(code string) (any, error) {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return nil, fmt.Errorf("sandbox is closed")
	}

	// Make sure sandbox is initialized
	if !s.initialized {
		if err := s.initializeUnlocked(); err != nil {
			return nil, err
		}
	}

	// Add wrapper for multiple return values
	wrappedCode := `
		local function _execfunc()
			` + code + `
		end

		local function _wrapresults(...)
			local results = {n = select('#', ...)}
			for i = 1, results.n do
				results[i] = select(i, ...)
			end
			return results
		end

		return _wrapresults(_execfunc())
	`

	// Compile the code
	if err := s.state.LoadString(wrappedCode); err != nil {
		return nil, err
	}

	// Get the sandbox executor
	s.state.GetGlobal("__execute_sandbox")

	// Setup call with correct argument order
	s.state.PushCopy(-2) // Copy the function

	// Remove the original function
	s.state.Remove(-3)

	// Execute in sandbox
	if err := s.state.Call(1, 1); err != nil {
		return nil, err
	}

	// Get result
	result, err := s.state.ToValue(-1)
	s.state.Pop(1)

	// Handle multiple return values
	if results, ok := result.([]any); ok && len(results) == 1 {
		return results[0], err
	}

	return result, err
}

// RunFile executes a Lua file in the sandbox
func (s *Sandbox) RunFile(filename string) error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	return s.state.DoFile(filename)
}

// Compile compiles Lua code to bytecode without executing it
func (s *Sandbox) Compile(code string) ([]byte, error) {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return nil, fmt.Errorf("sandbox is closed")
	}

	return s.state.CompileBytecode(code, "sandbox")
}

// RunBytecode executes precompiled Lua bytecode in the sandbox
func (s *Sandbox) RunBytecode(bytecode []byte) (any, error) {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return nil, fmt.Errorf("sandbox is closed")
	}

	// Make sure sandbox is initialized
	if !s.initialized {
		if err := s.initializeUnlocked(); err != nil {
			return nil, err
		}
	}

	// Load the bytecode
	if err := s.state.LoadBytecode(bytecode, "sandbox"); err != nil {
		return nil, err
	}

	// Add wrapper for multiple return values
	if err := s.state.DoString(`
		__wrap_bytecode = function(f)
			local function _wrapresults(...)
				local results = {n = select('#', ...)}
				for i = 1, results.n do
					results[i] = select(i, ...)
				end
				return results
			end

			return function()
				return _wrapresults(f())
			end
		end
	`); err != nil {
		return nil, err
	}

	// Get wrapper function
	s.state.GetGlobal("__wrap_bytecode")

	// Push bytecode function
	s.state.PushCopy(-2)

	// Call wrapper to create wrapped function
	if err := s.state.Call(1, 1); err != nil {
		return nil, err
	}

	// Remove original bytecode function
	s.state.Remove(-2)

	// Get the sandbox executor
	s.state.GetGlobal("__execute_sandbox")

	// Push wrapped function
	s.state.PushCopy(-2)

	// Remove the wrapped function
	s.state.Remove(-3)

	// Execute in sandbox
	if err := s.state.Call(1, 1); err != nil {
		return nil, err
	}

	// Get result
	result, err := s.state.ToValue(-1)
	s.state.Pop(1)

	// Handle multiple return values
	if results, ok := result.([]any); ok && len(results) == 1 {
		return results[0], err
	}

	return result, err
}

// getResults collects results from the stack (must be called with mutex locked)
func (s *Sandbox) getResults() (any, error) {
	numResults := s.state.GetTop()
	if numResults == 0 {
		return nil, nil
	} else if numResults == 1 {
		// Return single result directly
		value, err := s.state.ToValue(-1)
		s.state.Pop(1)
		return value, err
	}

	// Return multiple results as slice
	results := make([]any, numResults)
	for i := 0; i < numResults; i++ {
		value, err := s.state.ToValue(i - numResults)
		if err != nil {
			s.state.Pop(numResults)
			return nil, err
		}
		results[i] = value
	}
	s.state.Pop(numResults)
	return results, nil
}

// LoadModule loads a Lua module in the sandbox
func (s *Sandbox) LoadModule(name string) error {
	code := fmt.Sprintf("require('%s')", name)
	_, err := s.Run(code)
	return err
}

// SetPackagePath sets the sandbox package.path
func (s *Sandbox) SetPackagePath(path string) error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	return s.state.SetPackagePath(path)
}

// AddPackagePath adds a path to the sandbox package.path
func (s *Sandbox) AddPackagePath(path string) error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	return s.state.AddPackagePath(path)
}

// AddModule adds a module to the sandbox environment
func (s *Sandbox) AddModule(name string, module any) error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	s.modules[name] = module
	return nil
}

// Initialize sets up the environment system
func (s *Sandbox) Initialize() error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	return s.initializeUnlocked()
}

// initializeUnlocked sets up the environment system without locking
// It should only be called when the mutex is already locked
func (s *Sandbox) initializeUnlocked() error {
	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	if s.initialized {
		return nil // Already initialized
	}

	// Register modules
	s.state.GetGlobal("__sandbox_modules")
	if s.state.IsNil(-1) {
		s.state.Pop(1)
		s.state.NewTable()
		s.state.SetGlobal("__sandbox_modules")
		s.state.GetGlobal("__sandbox_modules")
	}

	// Add modules
	for name, module := range s.modules {
		s.state.PushString(name)
		if err := s.state.PushValue(module); err != nil {
			s.state.Pop(2)
			return err
		}
		s.state.SetTable(-3)
	}
	s.state.Pop(1)

	// Create the environment system
	err := s.state.DoString(`
		-- Global shared environment (created once)
		__env_system = __env_system or {
			base_env = nil,       -- Template environment
			initialized = false,   -- Initialization flag
			env_pool = {},        -- Pre-allocated environment pool
			pool_size = 0,        -- Current pool size
			max_pool_size = 8     -- Maximum pool size
		}

		-- Initialize base environment once
		if not __env_system.initialized then
			-- Create base environment with all standard libraries
			local base = {}

			-- Safe standard libraries
			base.string = string
			base.table = table
			base.math = math
			base.os = {
				time = os.time,
				date = os.date,
				difftime = os.difftime,
				clock = os.clock
			}

			-- Basic functions
			base.print = print
			base.tonumber = tonumber
			base.tostring = tostring
			base.type = type
			base.pairs = pairs
			base.ipairs = ipairs
			base.next = next
			base.select = select
			base.pcall = pcall
			base.xpcall = xpcall
			base.error = error
			base.assert = assert
			base.collectgarbage = collectgarbage
			base.unpack = unpack or table.unpack

			-- Package system
			base.package = {
				loaded = {},
				path = package.path,
				preload = {}
			}

			base.require = function(modname)
				if base.package.loaded[modname] then
					return base.package.loaded[modname]
				end

				local loader = base.package.preload[modname]
				if type(loader) == "function" then
					local result = loader(modname)
					base.package.loaded[modname] = result or true
					return result
				end

				error("module '" .. modname .. "' not found", 2)
			end

			-- Add registered custom modules
			if __sandbox_modules then
				for name, mod in pairs(__sandbox_modules) do
					base[name] = mod
				end
			end

			-- Store base environment
			__env_system.base_env = base
			__env_system.initialized = true
		end

		-- Global variable for tracking current environment
		__last_env = nil

		-- Get an environment for execution
		function __get_sandbox_env()
			local env

			-- Try to reuse from pool
			if __env_system.pool_size > 0 then
				env = table.remove(__env_system.env_pool)
				__env_system.pool_size = __env_system.pool_size - 1
			else
				-- Create new environment with metatable inheritance
				env = setmetatable({}, {
					__index = _G  -- Use global environment as fallback
				})
			end

			-- Store reference to current environment
			__last_env = env

			return env
		end

		-- Return environment to pool for reuse
		function __recycle_env(env)
			-- Only recycle if pool isn't full
			if __env_system.pool_size < __env_system.max_pool_size then
				-- Clear all fields except metatable
				for k in pairs(env) do
					env[k] = nil
				end

				-- Add to pool
				table.insert(__env_system.env_pool, env)
				__env_system.pool_size = __env_system.pool_size + 1
			end
		end

		-- Execute code in sandbox
		function __execute_sandbox(f)
			-- Get environment
			local env = __get_sandbox_env()

			-- Set environment for function
			setfenv(f, env)

			-- Execute with protected call
			local success, result = pcall(f)

			-- Recycle environment
			__recycle_env(env)

			-- Process result
			if not success then
				error(result, 0)
			end

			-- Handle multiple return values
			if type(result) == "table" and result.n ~= nil then
				local returnValues = {}
				for i=1, result.n do
					returnValues[i] = result[i]
				end
				return returnValues
			end

			return result
		end
	`)

	if err != nil {
		return err
	}

	s.initialized = true
	return nil
}

// AddPermanentLua adds Lua code to the environment permanently
// This code becomes part of the base environment
func (s *Sandbox) AddPermanentLua(code string) error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	// Make sure sandbox is initialized
	if !s.initialized {
		if err := s.initializeUnlocked(); err != nil {
			return err
		}
	}

	// Add code to base environment
	return s.state.DoString(`
		-- First compile the code
		local f, err = loadstring([=[` + code + `]=], "permanent")
		if not f then
			error(err, 0)
		end

		-- Create a temporary environment based on base env
		local temp_env = setmetatable({}, {__index = __env_system.base_env})
		setfenv(f, temp_env)

		-- Run the code in the temporary environment
		local ok, err = pcall(f)
		if not ok then
			error(err, 0)
		end

		-- Copy new values to base environment
		for k, v in pairs(temp_env) do
			__env_system.base_env[k] = v
		end
	`)
}

// ResetEnvironment resets the sandbox to its initial state
func (s *Sandbox) ResetEnvironment() error {
	s.mutex.Lock()
	defer s.mutex.Unlock()

	if s.state == nil {
		return fmt.Errorf("sandbox is closed")
	}

	// Reinitialize the environment system
	s.initialized = false
	return s.Initialize()
}