package runner

import (
	"crypto/subtle"

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

// LuaCSRFModule provides CSRF protection functionality to Lua scripts
const LuaCSRFModule = `
-- CSRF protection module
local csrf = {
    -- Session key where the token is stored
    TOKEN_KEY = "_csrf_token",

    -- Default form field name
    DEFAULT_FIELD = "csrf",

    -- Generate a new CSRF token and store it in the session
    generate = function(length)
        -- Default length is 32 characters
        length = length or 32

        if length < 16 then
            -- Enforce minimum security
            length = 16
        end

        -- Check if we have a session module
        if not session then
            error("CSRF protection requires the session module", 2)
        end

        -- Use Go's secure token generation
        local token = go.generate_token(length)

        -- Store in session
        session.set(csrf.TOKEN_KEY, token)

        return token
    end,

    -- Get the current token or generate a new one
    token = function()
        -- Get from session if exists
        local token = session.get(csrf.TOKEN_KEY)

        -- Generate if needed
        if not token then
            token = csrf.generate()
        end

        return token
    end,

    -- Generate a hidden form field with the CSRF token
    field = function(field_name)
        field_name = field_name or csrf.DEFAULT_FIELD
        local token = csrf.token()
        return string.format('<input type="hidden" name="%s" value="%s">', field_name, token)
    end,

    -- Verify a given token against the session token
	verify = function(token, field_name)
		field_name = field_name or csrf.DEFAULT_FIELD

		local env = getfenv(2)

		local form = nil
		if env.ctx and env.ctx.form then
			form = env.ctx.form
		else
			return false
		end

		token = token or form[field_name]
		if not token then
			return false
		end

		local session_token = session.get(csrf.TOKEN_KEY)
		if not session_token then
			return false
		end

		-- Constant-time comparison to prevent timing attacks
		-- This is safe since Lua strings are immutable
		if #token ~= #session_token then
			return false
		end

		local result = true
		for i = 1, #token do
			if token:sub(i, i) ~= session_token:sub(i, i) then
				result = false
				-- Don't break early - continue to prevent timing attacks
			end
		end

		return result
	end
}

-- Install CSRF module
_G.csrf = csrf

-- Make sure the CSRF module is accessible in sandbox
if __env_system and __env_system.base_env then
    __env_system.base_env.csrf = csrf
end
`

// CSRFModuleInitFunc returns an initializer for the CSRF module
func CSRFModuleInitFunc() StateInitFunc {
	return func(state *luajit.State) error {
		return state.DoString(LuaCSRFModule)
	}
}

// ValidateCSRFToken checks if the CSRF token is valid for a request
func ValidateCSRFToken(state *luajit.State, ctx *Context) bool {
	// Only validate for form submissions
	method, ok := ctx.Get("method").(string)
	if !ok || (method != "POST" && method != "PUT" && method != "PATCH" && method != "DELETE") {
		return true
	}

	// Get form data
	formData, ok := ctx.Get("form").(map[string]any)
	if !ok || formData == nil {
		logger.Warning("CSRF validation failed: no form data")
		return false
	}

	// Get token from form
	formToken, ok := formData["csrf"].(string)
	if !ok || formToken == "" {
		logger.Warning("CSRF validation failed: no token in form")
		return false
	}

	// Get session token
	state.GetGlobal("session")
	if state.IsNil(-1) {
		state.Pop(1)
		logger.Warning("CSRF validation failed: session module not available")
		return false
	}

	state.GetField(-1, "get")
	if !state.IsFunction(-1) {
		state.Pop(2)
		logger.Warning("CSRF validation failed: session.get not available")
		return false
	}

	state.PushCopy(-1) // Duplicate function
	state.PushString("_csrf_token")

	if err := state.Call(1, 1); err != nil {
		state.Pop(3) // Pop error, function and session table
		logger.Warning("CSRF validation failed: %v", err)
		return false
	}

	if state.IsNil(-1) {
		state.Pop(3) // Pop nil, function and session table
		logger.Warning("CSRF validation failed: no token in session")
		return false
	}

	sessionToken := state.ToString(-1)
	state.Pop(3) // Pop token, function and session table

	// Constant-time comparison to prevent timing attacks
	return subtle.ConstantTimeCompare([]byte(formToken), []byte(sessionToken)) == 1
}

// WithCSRFProtection creates a runner option to add CSRF protection
func WithCSRFProtection() RunnerOption {
	return func(r *LuaRunner) {
		r.AddInitHook(func(state *luajit.State, ctx *Context) error {
			// Get request method
			method, ok := ctx.Get("method").(string)
			if !ok {
				return nil
			}

			// Only validate for form submissions
			if method != "POST" && method != "PUT" && method != "PATCH" && method != "DELETE" {
				return nil
			}

			// Check for form data
			form, ok := ctx.Get("form").(map[string]any)
			if !ok || form == nil {
				return nil
			}

			// Validate CSRF token
			if !ValidateCSRFToken(state, ctx) {
				return ErrCSRFValidationFailed
			}

			return nil
		})
	}
}

// Error for CSRF validation failure
var ErrCSRFValidationFailed = &CSRFError{message: "CSRF token validation failed"}

// CSRFError represents a CSRF validation error
type CSRFError struct {
	message string
}

// Error implements the error interface
func (e *CSRFError) Error() string {
	return e.message
}