package service

import (
	"errors"
	"fmt"
	"math/rand"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"

	"git.server.ky/slackcoder/mirror/internal"
	"git.server.ky/slackcoder/mirror/internal/github"
)

// These commands are required by the service to operate.
var requiredCommands = []string{
	"git",
	"rsync",
}

type Service struct {
	cfg *Config

	mirrorsLock sync.Mutex
	mirrors     []*Mirror
	schedule    []time.Time

	stopCh chan struct{}
}

func NewService(cfg *Config) (*Service, error) {
	// Apply  defaults
	cfg.Append(&DefaultConfig)

	for _, cmd := range requiredCommands {
		if err := internal.RequireCommand(cmd); err != nil {
			return nil, err
		}
	}

	srv := &Service{
		cfg:     cfg,
		mirrors: nil,
		stopCh:  make(chan struct{}),
	}

	for _, m := range cfg.Mirrors {
		err := srv.AddMirror(m)
		if err != nil {
			return nil, err
		}
	}

	return srv, nil
}

func (s *Service) scheduleNextRun(arg *Mirror) {
	// Be polite.
	period := s.cfg.MaxInterval.Duration - s.cfg.MinInterval.Duration
	at := time.Now().Add(s.cfg.MinInterval.Duration + time.Duration(rand.Intn(int(period))))

	for i, m := range s.mirrors {
		if m.Equal(arg) {
			s.schedule[i] = at
		}
	}
}

func (s *Service) AddMirror(arg *Mirror) error {
	defer s.mirrorsLock.Unlock()
	s.mirrorsLock.Lock()

	for _, m := range s.mirrors {
		if m.Equal(arg) {
			return errors.New("must be unique")
		}
	}

	s.schedule = append(s.schedule, time.Time{})
	s.mirrors = append(s.mirrors, arg)
	s.scheduleNextRun(arg)

	return nil
}

func (s *Service) scheduled(yield func(*Mirror) bool) {
	defer s.mirrorsLock.Unlock()
	s.mirrorsLock.Lock()

	now := time.Now()
	for i, m := range s.mirrors {
		if s.schedule[i].After(now) {
			continue
		}

		if !yield(m) {
			break
		}
	}
}

func (s *Service) Mirror(arg *Mirror) error {
	if arg.From.Path == "" || arg.To.Path == "" || arg.Method == "" {
		return fmt.Errorf("badly formatted mirror '%s'", arg.String())
	}

	var err error

	switch arg.Method {
	case "git":
		err = MirrorGit(arg.To, arg.From, arg.Description)
	case "github-assets":
		client := github.NewClient()
		err = client.MirrorAssets(arg.To, arg.From)
	case "rsync":
		err = Rsync(arg.To, arg.From)
	default:
		err = fmt.Errorf("unknown method '%s'", arg.Method)
	}

	if err != nil {
		return fmt.Errorf("could not clone from '%s': %w", arg.From, err)
	}

	return nil
}

func (s *Service) RemoveMirror(arg *Mirror) error {
	defer s.mirrorsLock.Unlock()
	s.mirrorsLock.Lock()

	for i, m := range s.mirrors {
		if m.Equal(arg) {
			s.mirrors[i] = s.mirrors[len(s.mirrors)-1]
			s.mirrors = s.mirrors[:len(s.mirrors)-1]

			s.schedule[i] = s.schedule[len(s.schedule)-1]
			s.schedule = s.schedule[:len(s.schedule)-1]

			return nil
		}
	}

	return errors.New("not found")
}

func (s *Service) Log(str string) {
	escaped := []rune(strconv.Quote(strings.TrimSpace(str)))
	escaped = escaped[1 : len(escaped)-1]

	fmt.Fprintf(os.Stderr, "%s: %s\n", time.Now().Format(time.RFC822Z), string(escaped))
}

func (s *Service) Run() error {
	wakeup := time.NewTicker(time.Second)

mainLoop:
	for {
		select {
		case <-wakeup.C:
		case <-s.stopCh:
			break mainLoop
		}

		s.scheduled(func(m *Mirror) bool {
			err := s.Mirror(m)
			if err != nil {
				s.Log(err.Error())
			}

			s.scheduleNextRun(m)

			return true
		})
	}

	return nil
}

func (s *Service) Stop() {
	select {
	case <-s.stopCh:
	default:
		close(s.stopCh)
	}
}