package provider

import (
	"bytes"
	"crypto/md5"
	"io/ioutil"
	"os"
	"time"

	"github.com/Dreamacro/clash/log"
)

var (
	fileMode os.FileMode = 0666
)

type parser = func([]byte) (interface{}, error)

type fetcher struct {
	name      string
	vehicle   Vehicle
	updatedAt *time.Time
	ticker    *time.Ticker
	hash      [16]byte
	parser    parser
	onUpdate  func(interface{})
}

func (f *fetcher) Name() string {
	return f.name
}

func (f *fetcher) VehicleType() VehicleType {
	return f.vehicle.Type()
}

func (f *fetcher) Initial() (interface{}, error) {
	var buf []byte
	var err error
	var isLocal bool
	if stat, err := os.Stat(f.vehicle.Path()); err == nil {
		buf, err = ioutil.ReadFile(f.vehicle.Path())
		modTime := stat.ModTime()
		f.updatedAt = &modTime
		isLocal = true
	} else {
		buf, err = f.vehicle.Read()
	}

	if err != nil {
		return nil, err
	}

	proxies, err := f.parser(buf)
	if err != nil {
		if !isLocal {
			return nil, err
		}

		// parse local file error, fallback to remote
		buf, err = f.vehicle.Read()
		if err != nil {
			return nil, err
		}

		proxies, err = f.parser(buf)
		if err != nil {
			return nil, err
		}
	}

	if err := ioutil.WriteFile(f.vehicle.Path(), buf, fileMode); err != nil {
		return nil, err
	}

	f.hash = md5.Sum(buf)

	// pull proxies automatically
	if f.ticker != nil {
		go f.pullLoop()
	}

	return proxies, nil
}

func (f *fetcher) Update() (interface{}, bool, error) {
	buf, err := f.vehicle.Read()
	if err != nil {
		return nil, false, err
	}

	now := time.Now()
	hash := md5.Sum(buf)
	if bytes.Equal(f.hash[:], hash[:]) {
		f.updatedAt = &now
		return nil, true, nil
	}

	proxies, err := f.parser(buf)
	if err != nil {
		return nil, false, err
	}

	if err := ioutil.WriteFile(f.vehicle.Path(), buf, fileMode); err != nil {
		return nil, false, err
	}

	f.updatedAt = &now
	f.hash = hash

	return proxies, false, nil
}

func (f *fetcher) Destroy() error {
	if f.ticker != nil {
		f.ticker.Stop()
	}
	return nil
}

func (f *fetcher) pullLoop() {
	for range f.ticker.C {
		elm, same, err := f.Update()
		if err != nil {
			log.Warnln("[Provider] %s pull error: %s", f.Name(), err.Error())
			continue
		}

		if same {
			log.Debugln("[Provider] %s's proxies doesn't change", f.Name())
			continue
		}

		log.Infoln("[Provider] %s's proxies update", f.Name())
		if f.onUpdate != nil {
			f.onUpdate(elm)
		}
	}
}

func newFetcher(name string, interval time.Duration, vehicle Vehicle, parser parser, onUpdate func(interface{})) *fetcher {
	var ticker *time.Ticker
	if interval != 0 {
		ticker = time.NewTicker(interval)
	}

	return &fetcher{
		name:     name,
		ticker:   ticker,
		vehicle:  vehicle,
		parser:   parser,
		onUpdate: onUpdate,
	}
}