package app

import (
	"math/rand"
	"sync"

	"github.com/dop251/goja"
	"github.com/dop251/goja_nodejs/eventloop"
	"github.com/pkg/errors"
)

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

type Backend struct {
	runtime *goja.Runtime
	loop    *eventloop.EventLoop
	modules []BackendModule
}

func (b *Backend) Load(name string, src string) error {
	_, err := b.runtime.RunScript(name, src)
	if err != nil {
		return errors.Wrap(err, "could not run js script")
	}

	return nil
}

func (b *Backend) ExecFuncByName(funcName string, args ...interface{}) (goja.Value, error) {
	callable, ok := goja.AssertFunction(b.runtime.Get(funcName))
	if !ok {
		return nil, errors.WithStack(ErrFuncDoesNotExist)
	}

	return b.Exec(callable, args...)
}

func (b *Backend) Exec(callable goja.Callable, args ...interface{}) (goja.Value, error) {
	var (
		wg    sync.WaitGroup
		value goja.Value
		err   error
	)

	wg.Add(1)

	b.loop.RunOnLoop(func(vm *goja.Runtime) {
		jsArgs := make([]goja.Value, 0, len(args))
		for _, a := range args {
			jsArgs = append(jsArgs, vm.ToValue(a))
		}

		value, err = callable(nil, jsArgs...)
		if err != nil {
			err = errors.WithStack(err)
		}

		wg.Done()
	})

	wg.Wait()

	return value, err
}

func (b *Backend) IsPromise(v goja.Value) (*goja.Promise, bool) {
	promise, ok := v.Export().(*goja.Promise)
	return promise, ok
}

func (b *Backend) WaitForPromise(promise *goja.Promise) goja.Value {
	var (
		wg    sync.WaitGroup
		value goja.Value
	)

	wg.Add(1)

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

			breakLoop := false

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

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

				value = promise.Result()

				breakLoop = true
			})

			loopWait.Wait()

			if breakLoop {
				wg.Done()

				return
			}
		}
	}()

	wg.Wait()

	return value
}

func (b *Backend) NewPromise() *PromiseProxy {
	promise, resolve, reject := b.runtime.NewPromise()

	return NewPromiseProxy(promise, resolve, reject)
}

func (b *Backend) ToValue(v interface{}) goja.Value {
	return b.runtime.ToValue(v)
}

func (b *Backend) Start() error {
	b.loop.Start()

	for _, mod := range b.modules {
		initMod, ok := mod.(InitializableModule)
		if !ok {
			continue
		}

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

	return nil
}

func (b *Backend) Stop() {
	b.loop.Stop()
}

func (b *Backend) initModules(factories ...BackendModuleFactory) {
	runtime := goja.New()

	runtime.SetFieldNameMapper(goja.UncapFieldNameMapper())
	runtime.SetRandSource(createRandomSource())

	modules := make([]BackendModule, 0, len(factories))

	for _, moduleFactory := range factories {
		mod := moduleFactory(b)
		export := runtime.NewObject()
		mod.Export(export)
		runtime.Set(mod.Name(), export)

		modules = append(modules, mod)
	}

	b.runtime = runtime
	b.modules = modules
}

func NewBackend(factories ...BackendModuleFactory) *Backend {
	backend := &Backend{
		loop: eventloop.NewEventLoop(
			eventloop.EnableConsole(false),
		),
	}

	backend.initModules(factories...)

	return backend
}

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

	return rnd.Float64
}