package backblaze

import (
	"context"
	"errors"
	"fmt"
	"io/fs"
	"path"
	"path/filepath"
	"sync"
	"sync/atomic"
	"time"

	"github.com/kurin/blazer/b2"
)

type File struct {
	Path       string
	Size       int // file size in bytes
	ModTime    time.Time
	IsUploaded *bool
}

// localFiles lists the local files in the given backup directory and sends them to a channel.
// It closes the channel after all files are listed.
func (b *BackBlaze) localFiles(backupDir string, fileChan chan<- File) error {
	defer close(fileChan)
	// Walk the directory and send files to the channel
	err := filepath.WalkDir(backupDir, func(path string, d fs.DirEntry, err error) error {
		if err != nil {
			return err
		}
		if !d.IsDir() {
			i, err := d.Info()
			if err != nil {
				return fmt.Errorf("d.Info: %w", err)
			}
			fileChan <- File{Path: filepath.Base(path), Size: int(i.Size()), ModTime: i.ModTime()}
		}
		return nil
	})
	if err != nil {
		return fmt.Errorf("error walking the directory: %w", err)
	}

	return nil
}

// b2BucketFiles lists the files in the given B2 bucket and sends them to a channel.
// It closes the channel after all files are listed.
func (b *BackBlaze) b2BucketFiles(ctx context.Context, bucketName string, fileChan chan<- File) error {
	bucket, err := b.b2Client.Bucket(ctx, bucketName)
	defer close(fileChan)
	if err != nil {
		return fmt.Errorf("b2Client.Bucket %w", err)
	}

	bucketIter := bucket.List(ctx, b2.ListHidden())
	if bucketIter == nil {
		return errors.New("bucket list cannot be nil")
	}

	for {
		if !bucketIter.Next() {
			if bucketIter.Err() != nil {
				return fmt.Errorf("bucketIter err %w", bucketIter.Err())
			}
			break
		}
		if bucketIter.Object() == nil {
			return errors.New("bucketIter Object is nil")
		}

		fileName := path.Base(bucketIter.Object().Name())
		attrs, err := bucketIter.Object().Attrs(ctx)
		if err != nil {
			return fmt.Errorf("bucketIter.Object().Attrs %s err %w", fileName, bucketIter.Err())
		}
		isUploaded := attrs.Status != b2.Uploaded
		fileChan <- File{Path: path.Base(fileName), Size: int(attrs.Size), IsUploaded: &isUploaded, ModTime: attrs.UploadTimestamp}
	}

	return nil
}

var ErrLocalNotInCloud error = errors.New("exists locally but not in the cloud")
var ErrCloudNotInLocal error = errors.New("exists on B2 but not locally")

type B2Local struct {
	File File
	Err  error
}

// CompareConcurrent concurrently fetches the list of local files and cloud files,
// then compares them to ensure all local files exist in the cloud.
// Errors are sent to a provided error channel. The function will panic if an error occurs while listing files.
func (b *BackBlaze) CompareConcurrent(
	ctx context.Context,
	backupDir, bucketName string,
	localChan, b2Chan chan<- B2Local,
	doneChan chan<- int,
) {
	var wg sync.WaitGroup
	localFiles := make(map[string]File)
	cloudFiles := make(map[string]File)
	localFileChan := make(chan File)
	b2FileChan := make(chan File)

	// Local listing
	wg.Add(1)
	go func() {
		defer wg.Done()
		wg.Add(1)
		go func() {
			defer wg.Done()
			for f := range localFileChan {
				if _, ok := localFiles[f.Path]; ok {
					panic(fmt.Errorf("local file already exists in map: %s", f.Path))
				}
				b.logger.Debugf("local file %+v\n", f)
				localFiles[f.Path] = f
			}
		}()

		if err := b.localFiles(backupDir, localFileChan); err != nil {
			panic(fmt.Errorf("b.LocalFilesWithB2: %w", err))
		}
	}()

	// Cloud listing
	wg.Add(1)
	go func() {
		defer wg.Done()
		wg.Add(1)
		go func() {
			defer wg.Done()
			for f := range b2FileChan {
				if _, ok := cloudFiles[f.Path]; ok {
					panic(fmt.Errorf(`cloud file already exists in map: %s\n you should run 'backblazebackup cleanup --bucket "%s"'`, f.Path, b.bucketName))
				}
				b.logger.Debugf("B2 file %+v\n", f)
				cloudFiles[f.Path] = f
			}
		}()
		if err := b.b2BucketFiles(ctx, bucketName, b2FileChan); err != nil {
			panic(fmt.Errorf("b.LocalFilesWithB2: %w", err))
		}
	}()

	// Wait for both to complete
	wg.Wait()

	// Now check local files that are not present in cloud
	var count atomic.Int64
	wg.Add(2)
	go func() {
		defer wg.Done()
		for path, localFile := range localFiles {
			if _, exists := cloudFiles[path]; !exists {
				localChan <- B2Local{File: localFile, Err: ErrLocalNotInCloud}
				continue
			}
			b.logger.Debugf("localFile %+v\n", localFile)
			localChan <- B2Local{File: localFile, Err: nil}
			count.Add(1)
		}
	}()

	// Now check cloud files that are not in local
	go func() {
		defer wg.Done()
		for path, cloudFile := range cloudFiles {
			if _, exists := localFiles[path]; !exists {
				b2Chan <- B2Local{File: cloudFile, Err: ErrCloudNotInLocal}
				continue
			}
			b2Chan <- B2Local{File: cloudFile, Err: nil}
		}
	}()
	wg.Wait()
	close(localChan)
	close(b2Chan)
	doneChan <- int(count.Load())
}