package services

import (
	"context"
	"fmt"
	"mailsrv/mail"
	"mailsrv/runtime"
	"os"
	"path"
	"strings"
	"time"

	"github.com/rs/zerolog/log"
)

const (
	TickerInterval time.Duration = 10 * time.Second
	JSONSuffix     string        = ".json"
	ErrorSuffix    string        = ".err"
)

type Watcher interface {
	Watch()
	Done() <-chan struct{}
}

// DirectoryWatch watches a directory every `tick` interval and collect email files.
type DirectoryWatch struct {
	ctx      context.Context
	fnCancel context.CancelFunc

	outboxPath string
	queue      *runtime.Queue
}

func NewDirectoryWatch(ctx context.Context, outboxPath string, queue *runtime.Queue) DirectoryWatch {
	ctxChild, fnCancel := context.WithCancel(ctx)

	return DirectoryWatch{
		ctx:        ctxChild,
		fnCancel:   fnCancel,
		outboxPath: outboxPath,
		queue:      queue,
	}
}

func (dw DirectoryWatch) Done() <-chan struct{} {
	return dw.ctx.Done()
}

// Watch reads the `outbox` directory every `TickInterval` and put JSON format e-mail in the queue.
func (dw DirectoryWatch) Watch() {
	log.Info().Str("outbox", dw.outboxPath).Msg("watching outbox directory...")

	ticker := time.NewTicker(TickerInterval)

	go func() {
		for {
			select {
			case <-dw.Done():
				log.Err(dw.ctx.Err()).Msg("context done")
				return
			case <-ticker.C:
				log.Debug().Str("action", "retrieving json e-mail format...").Str("path", dw.outboxPath)

				files, err := os.ReadDir(dw.outboxPath)
				if err != nil && !os.IsExist(err) {
					log.Err(err).Msg("outbox directory does not exist")
					dw.fnCancel()
					return
				}

				for _, file := range files {
					filename := file.Name()
					if !strings.HasSuffix(filename, JSONSuffix) {
						continue
					}

					emailPath := path.Join(dw.outboxPath, filename)
					email, err := mail.FromJSON(emailPath)

					if err != nil {
						log.Err(err).Str("path", emailPath).Msg("unable to parse JSON email")

						// if JSON parsing failed the `path` is renamed with an error suffix to not watch it again
						newPath := fmt.Sprintf("%s%s", emailPath, ErrorSuffix)
						if err := os.Rename(emailPath, newPath); err != nil {
							log.Err(err).Str("path", emailPath).Str("new path", newPath).Msg("unable to rename bad JSON email path")
						}

						continue
					}

					email.Path = emailPath
					dw.queue.Add(email)
				}
			}
		}
	}()
}