package scanner

import (
	"context"
	"log"
	"os"
	"path/filepath"
	"strings"
	"time"
)

type ChangeType int

const (
	Unchanged ChangeType = iota
	Created
	Modified
	Deleted
)

type ChangeHandler interface {
	HandleCreate(path string) error
	HandleModify(path string) error
	HandleDelete(path string) error
}

type Change struct {
	Type    ChangeType
	Path    string
	ModTime time.Time
}

type ScannerService struct {
	RootDir    string
	interval   time.Duration
	lastStates map[string]time.Time
	handler    ChangeHandler
}

func NewScanner(path string) *ScannerService {
	return &ScannerService{RootDir: path}
}

func (s *ScannerService) FindAll() ([]string, error) {
	var notePath []string
	err := filepath.Walk(s.RootDir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		// skip the root dir itself
		if s.RootDir == path {
			return nil
		}

		if !isValidNoteFile(path, info) {
			return nil
		}

		notePath = append(notePath, path)
		return nil
	})
	return notePath, err
}

func (s *ScannerService) Scan() ([]Change, error) {
	var changes []Change
	currentStates := make(map[string]time.Time)

	// Walk filesystem
	filepath.Walk(s.RootDir, func(path string, info os.FileInfo, err error) error {

		// skip the root dir itself
		if s.RootDir == path {
			return nil
		}

		if !isValidNoteFile(path, info) {
			return nil
		}

		currentStates[path] = info.ModTime()

		lastMod, existed := s.lastStates[path]
		if !existed {
			changes = append(changes, Change{Type: Created, Path: path, ModTime: lastMod})
		} else if info.ModTime().After(lastMod) {
			changes = append(changes, Change{Type: Modified, Path: path, ModTime: info.ModTime()})
		}

		return nil
	})

	// Check for deletions
	for path := range s.lastStates {
		if _, exists := currentStates[path]; !exists {
			changes = append(changes, Change{Type: Deleted, Path: path})
		}
	}

	s.lastStates = currentStates
	return changes, nil
}

func (s *ScannerService) Monitor(ctx context.Context) error {
	ticker := time.NewTicker(s.interval)
	defer ticker.Stop()

	for {
		select {
		case <-ticker.C:
			changes, err := s.Scan()
			if err != nil {
				log.Printf("scan error: %v", err)
				continue
			}

			for _, change := range changes {
				var err error
				switch change.Type {
				case Created:
					err = s.handler.HandleCreate(change.Path)
				case Modified:
					err = s.handler.HandleModify(change.Path)
				case Deleted:
					err = s.handler.HandleDelete(change.Path)
				}

				if err != nil {
					log.Printf("handler error for %s: %v", change.Path, err)
				}
			}

		case <-ctx.Done():
			return ctx.Err()
		}
	}
}

func isValidNoteFile(path string, info os.FileInfo) bool {
	// ignore temp and backup files
	for _, nono := range []string{".#", "~"} {
		if strings.Contains(path, nono) {
			return false
		}
	}

	// ignore files that are not markdown
	if info.IsDir() || filepath.Ext(path) != ".md" {
		return false
	}

	// ignore empty folder
	if info.IsDir() {
		files, err := os.ReadDir(path)
		if err != nil {
			log.Println(err.Error())
		}
		if len(files) == 0 {
			return false
		}
	}

	return true
}