package lfs

import (
	"strings"
	"sync"
)

// ScanIndex returns a slice of WrappedPointer objects for all Git LFS pointers
// it finds in the index.
//
// Ref is the ref at which to scan, which may be "HEAD" if there is at least one
// commit.
func scanIndex(cb GitScannerFoundPointer, ref string) error {
	indexMap := &indexFileMap{
		nameMap:      make(map[string][]*indexFile),
		nameShaPairs: make(map[string]bool),
		mutex:        &sync.Mutex{},
	}

	revs, err := revListIndex(ref, false, indexMap)
	if err != nil {
		return err
	}

	cachedRevs, err := revListIndex(ref, true, indexMap)
	if err != nil {
		return err
	}

	allRevsErr := make(chan error, 5) // can be multiple errors below
	allRevsChan := make(chan string, 1)
	allRevs := NewStringChannelWrapper(allRevsChan, allRevsErr)
	go func() {
		seenRevs := make(map[string]bool, 0)

		for rev := range revs.Results {
			if !seenRevs[rev] {
				allRevsChan <- rev
				seenRevs[rev] = true
			}
		}
		err := revs.Wait()
		if err != nil {
			allRevsErr <- err
		}

		for rev := range cachedRevs.Results {
			if !seenRevs[rev] {
				allRevsChan <- rev
				seenRevs[rev] = true
			}
		}
		err = cachedRevs.Wait()
		if err != nil {
			allRevsErr <- err
		}
		close(allRevsChan)
		close(allRevsErr)
	}()

	smallShas, _, err := catFileBatchCheck(allRevs, nil)
	if err != nil {
		return err
	}

	ch := make(chan gitscannerResult, chanBufSize)

	barePointerCh, _, err := catFileBatch(smallShas, nil)
	if err != nil {
		return err
	}

	go func() {
		for p := range barePointerCh.Results {
			for _, file := range indexMap.FilesFor(p.Sha1) {
				// Append a new *WrappedPointer that combines the data
				// from the index file, and the pointer "p".
				ch <- gitscannerResult{
					Pointer: &WrappedPointer{
						Sha1:    p.Sha1,
						Name:    file.Name,
						SrcName: file.SrcName,
						Status:  file.Status,
						Pointer: p.Pointer,
					},
				}
			}
		}

		if err := barePointerCh.Wait(); err != nil {
			ch <- gitscannerResult{Err: err}
		}

		close(ch)
	}()

	for result := range ch {
		cb(result.Pointer, result.Err)
	}

	return nil
}

// revListIndex uses git diff-index to return the list of object sha1s
// for in the indexf. It returns a channel from which sha1 strings can be read.
// The namMap will be filled indexFile pointers mapping sha1s to indexFiles.
func revListIndex(atRef string, cache bool, indexMap *indexFileMap) (*StringChannelWrapper, error) {
	scanner, err := NewDiffIndexScanner(atRef, cache)
	if err != nil {
		return nil, err
	}

	revs := make(chan string, chanBufSize)
	errs := make(chan error, 1)

	go func() {
		for scanner.Scan() {
			var name string = scanner.Entry().DstName
			if len(name) == 0 {
				name = scanner.Entry().SrcName
			}

			var sha string = scanner.Entry().DstSha
			if scanner.Entry().Status == StatusModification {
				sha = scanner.Entry().SrcSha
			}

			indexMap.Add(sha, &indexFile{
				Name:    name,
				SrcName: scanner.Entry().SrcName,
				Status:  string(scanner.Entry().Status),
			})

			revs <- sha
		}

		if err := scanner.Err(); err != nil {
			errs <- err
		}

		close(revs)
		close(errs)
	}()

	return NewStringChannelWrapper(revs, errs), nil
}

// indexFile is used when scanning the index. It stores the name of
// the file, the status of the file in the index, and, in the case of
// a moved or copied file, the original name of the file.
type indexFile struct {
	Name    string
	SrcName string
	Status  string
}

type indexFileMap struct {
	// mutex guards nameMap and nameShaPairs
	mutex *sync.Mutex
	// nameMap maps SHA1s to a slice of `*indexFile`s
	nameMap map[string][]*indexFile
	// nameShaPairs maps "sha1:name" -> bool
	nameShaPairs map[string]bool
}

// FilesFor returns all `*indexFile`s that match the given `sha`.
func (m *indexFileMap) FilesFor(sha string) []*indexFile {
	m.mutex.Lock()
	defer m.mutex.Unlock()

	return m.nameMap[sha]
}

// Add appends unique index files to the given SHA, "sha". A file is considered
// unique if its combination of SHA and current filename have not yet been seen
// by this instance "m" of *indexFileMap.
func (m *indexFileMap) Add(sha string, index *indexFile) {
	m.mutex.Lock()
	defer m.mutex.Unlock()

	pairKey := strings.Join([]string{sha, index.Name}, ":")
	if m.nameShaPairs[pairKey] {
		return
	}

	m.nameMap[sha] = append(m.nameMap[sha], index)
	m.nameShaPairs[pairKey] = true
}