package app

import (
	"context"
	"math/rand"
	"sync"
	"time"

	"github.com/dop251/goja"
	"github.com/dop251/goja_nodejs/eventloop"
	"github.com/pkg/errors"
	"gitlab.com/wpetit/goweb/logger"
)

var (
	ErrFuncDoesNotExist = errors.New("function does not exist")
	ErrUnknownError     = errors.New("unknown error")
)

type Server struct {
	loop      *eventloop.EventLoop
	factories []ServerModuleFactory
	modules   []ServerModule
}

func (s *Server) ExecFuncByName(ctx context.Context, funcName string, args ...any) (any, error) {
	ctx = logger.With(ctx, logger.F("function", funcName), logger.F("args", args))

	ret, err := s.Exec(ctx, funcName, args...)
	if err != nil {
		return nil, errors.WithStack(err)
	}

	return ret, nil
}

func (s *Server) Exec(ctx context.Context, callableOrFuncname any, args ...any) (any, error) {
	type result struct {
		value any
		err   error
	}

	done := make(chan result)

	defer func() {
		// Drain done channel
		for range done {
		}
	}()

	s.loop.RunOnLoop(func(rt *goja.Runtime) {
		defer close(done)

		var callable goja.Callable
		switch typ := callableOrFuncname.(type) {
		case goja.Callable:
			callable = typ

		case string:
			call, ok := goja.AssertFunction(rt.Get(typ))
			if !ok {
				done <- result{
					err: errors.WithStack(ErrFuncDoesNotExist),
				}

				return
			}

			callable = call

		default:
			done <- result{
				err: errors.Errorf("callableOrFuncname: expected callable or function name, got '%T'", callableOrFuncname),
			}

			return
		}

		defer func() {
			recovered := recover()
			if recovered == nil {
				return
			}

			recoveredErr, ok := recovered.(error)
			if !ok {
				panic(recovered)
			}

			done <- result{
				err: recoveredErr,
			}
		}()

		jsArgs := make([]goja.Value, 0, len(args))
		for _, a := range args {
			jsArgs = append(jsArgs, rt.ToValue(a))
		}

		logger.Debug(ctx, "executing callable", logger.F("callable", callableOrFuncname))

		start := time.Now()
		value, err := callable(nil, jsArgs...)
		if err != nil {
			done <- result{
				err: errors.WithStack(err),
			}

			return
		}

		done <- result{
			value: value.Export(),
		}

		logger.Debug(ctx, "executed callable", logger.F("callable", callableOrFuncname), logger.F("duration", time.Since(start).String()))
	})

	select {
	case <-ctx.Done():
		if err := ctx.Err(); err != nil {
			return nil, errors.WithStack(err)
		}

		return nil, nil

	case result := <-done:
		if result.err != nil {
			return nil, errors.WithStack(result.err)
		}

		if promise, ok := isPromise(result.value); ok {
			return s.waitForPromise(promise), nil
		}

		return result.value, nil
	}
}

func (s *Server) waitForPromise(promise *goja.Promise) any {
	var (
		wg    sync.WaitGroup
		value any
	)

	wg.Add(1)

	// Wait for promise completion
	go func() {
		for {
			var loopWait sync.WaitGroup
			loopWait.Add(1)

			breakLoop := false

			s.loop.RunOnLoop(func(vm *goja.Runtime) {
				defer loopWait.Done()

				if promise.State() == goja.PromiseStatePending {
					return
				}

				value = promise.Result().Export()

				breakLoop = true
			})

			loopWait.Wait()

			if breakLoop {
				wg.Done()

				return
			}
		}
	}()

	wg.Wait()

	return value
}

func (s *Server) Start(ctx context.Context, name string, src string) error {
	s.loop.Start()

	done := make(chan error)

	s.loop.RunOnLoop(func(rt *goja.Runtime) {
		defer close(done)

		rt.SetFieldNameMapper(goja.TagFieldNameMapper("goja", true))
		rt.SetRandSource(createRandomSource())

		if err := s.loadModules(ctx, rt); err != nil {
			err = errors.WithStack(err)
			done <- err

			return
		}

		if _, err := rt.RunScript(name, src); err != nil {
			done <- errors.Wrap(err, "could not run js script")
			return
		}

		if err := s.initModules(ctx, rt); err != nil {
			err = errors.WithStack(err)
			done <- err

			return
		}

		done <- nil
	})

	if err := <-done; err != nil {
		return errors.WithStack(err)
	}

	return nil
}

func (s *Server) Stop() {
	s.loop.Stop()
}

func (s *Server) loadModules(ctx context.Context, rt *goja.Runtime) error {
	modules := make([]ServerModule, 0, len(s.factories))

	for _, moduleFactory := range s.factories {
		mod := moduleFactory(s)

		export := rt.NewObject()
		mod.Export(export)

		rt.Set(mod.Name(), export)

		modules = append(modules, mod)
	}

	s.modules = modules

	return nil
}

func (s *Server) initModules(ctx context.Context, rt *goja.Runtime) error {
	for _, mod := range s.modules {
		initMod, ok := mod.(InitializableModule)
		if !ok {
			continue
		}

		logger.Debug(ctx, "initializing module", logger.F("module", initMod.Name()))

		if err := initMod.OnInit(ctx, rt); err != nil {
			return errors.WithStack(err)
		}
	}

	return nil
}

func NewServer(factories ...ServerModuleFactory) *Server {
	server := &Server{
		factories: factories,
		loop: eventloop.NewEventLoop(
			eventloop.EnableConsole(false),
		),
	}

	return server
}

func createRandomSource() goja.RandSource {
	rnd := rand.New(&cryptoSource{})

	return rnd.Float64
}