package hercules

import (
	"fmt"
	"os"
	"sort"
	"unicode/utf8"

	"github.com/sergi/go-diff/diffmatchpatch"
	"gopkg.in/src-d/go-git.v4"
	"gopkg.in/src-d/go-git.v4/plumbing"
	"gopkg.in/src-d/go-git.v4/plumbing/object"
	"gopkg.in/src-d/go-git.v4/utils/merkletrie"
)

// RenameAnalysis improves TreeDiff's results by searching for changed blobs under different
// paths which are likely to be the result of a rename with subsequent edits.
// RenameAnalysis is a PipelineItem.
type RenameAnalysis struct {
	// SimilarityThreshold adjusts the heuristic to determine file renames.
	// It has the same units as cgit's -X rename-threshold or -M. Better to
	// set it to the default value of 90 (90%).
	SimilarityThreshold int

	repository *git.Repository
}

const (
	// RenameAnalysisDefaultThreshold specifies the default percentage of common lines in a pair
	// of files to consider them linked. The exact code of the decision is sizesAreClose().
	RenameAnalysisDefaultThreshold = 90

	// ConfigRenameAnalysisSimilarityThreshold is the name of the configuration option
	// (RenameAnalysis.Configure()) which sets the similarity threshold.
	ConfigRenameAnalysisSimilarityThreshold = "RenameAnalysis.SimilarityThreshold"
)

func (ra *RenameAnalysis) Name() string {
	return "RenameAnalysis"
}

func (ra *RenameAnalysis) Provides() []string {
	arr := [...]string{DependencyTreeChanges}
	return arr[:]
}

func (ra *RenameAnalysis) Requires() []string {
	arr := [...]string{DependencyBlobCache, DependencyTreeChanges}
	return arr[:]
}

func (ra *RenameAnalysis) ListConfigurationOptions() []ConfigurationOption {
	options := [...]ConfigurationOption{{
		Name:        ConfigRenameAnalysisSimilarityThreshold,
		Description: "The threshold on the similarity index used to detect renames.",
		Flag:        "M",
		Type:        IntConfigurationOption,
		Default:     RenameAnalysisDefaultThreshold},
	}
	return options[:]
}

func (ra *RenameAnalysis) Configure(facts map[string]interface{}) {
	if val, exists := facts[ConfigRenameAnalysisSimilarityThreshold].(int); exists {
		ra.SimilarityThreshold = val
	}
}

func (ra *RenameAnalysis) Initialize(repository *git.Repository) {
	if ra.SimilarityThreshold < 0 || ra.SimilarityThreshold > 100 {
		fmt.Fprintf(os.Stderr, "Warning: adjusted the similarity threshold to %d\n",
			RenameAnalysisDefaultThreshold)
		ra.SimilarityThreshold = RenameAnalysisDefaultThreshold
	}
	ra.repository = repository
}

func (ra *RenameAnalysis) Consume(deps map[string]interface{}) (map[string]interface{}, error) {
	changes := deps[DependencyTreeChanges].(object.Changes)
	cache := deps[DependencyBlobCache].(map[plumbing.Hash]*object.Blob)

	reducedChanges := make(object.Changes, 0, changes.Len())

	// Stage 1 - find renames by matching the hashes
	// n log(n)
	// We sort additions and deletions by hash and then do the single scan along
	// both slices.
	deleted := make(sortableChanges, 0, changes.Len())
	added := make(sortableChanges, 0, changes.Len())
	for _, change := range changes {
		action, err := change.Action()
		if err != nil {
			return nil, err
		}
		switch action {
		case merkletrie.Insert:
			added = append(added, sortableChange{change, change.To.TreeEntry.Hash})
		case merkletrie.Delete:
			deleted = append(deleted, sortableChange{change, change.From.TreeEntry.Hash})
		case merkletrie.Modify:
			reducedChanges = append(reducedChanges, change)
		}
	}
	sort.Sort(deleted)
	sort.Sort(added)
	a := 0
	d := 0
	stillDeleted := make(object.Changes, 0, deleted.Len())
	stillAdded := make(object.Changes, 0, added.Len())
	for a < added.Len() && d < deleted.Len() {
		if added[a].hash == deleted[d].hash {
			reducedChanges = append(
				reducedChanges,
				&object.Change{From: deleted[d].change.From, To: added[a].change.To})
			a++
			d++
		} else if added[a].Less(&deleted[d]) {
			stillAdded = append(stillAdded, added[a].change)
			a++
		} else {
			stillDeleted = append(stillDeleted, deleted[d].change)
			d++
		}
	}
	for ; a < added.Len(); a++ {
		stillAdded = append(stillAdded, added[a].change)
	}
	for ; d < deleted.Len(); d++ {
		stillDeleted = append(stillDeleted, deleted[d].change)
	}

	// Stage 2 - apply the similarity threshold
	// n^2 but actually linear
	// We sort the blobs by size and do the single linear scan.
	addedBlobs := make(sortableBlobs, 0, stillAdded.Len())
	deletedBlobs := make(sortableBlobs, 0, stillDeleted.Len())
	for _, change := range stillAdded {
		blob := cache[change.To.TreeEntry.Hash]
		addedBlobs = append(
			addedBlobs, sortableBlob{change: change, size: blob.Size})
	}
	for _, change := range stillDeleted {
		blob := cache[change.From.TreeEntry.Hash]
		deletedBlobs = append(
			deletedBlobs, sortableBlob{change: change, size: blob.Size})
	}
	sort.Sort(addedBlobs)
	sort.Sort(deletedBlobs)
	dStart := 0
	for a = 0; a < addedBlobs.Len(); a++ {
		myBlob := cache[addedBlobs[a].change.To.TreeEntry.Hash]
		mySize := addedBlobs[a].size
		for d = dStart; d < deletedBlobs.Len() && !ra.sizesAreClose(mySize, deletedBlobs[d].size); d++ {
		}
		dStart = d
		foundMatch := false
		for d = dStart; d < deletedBlobs.Len() && ra.sizesAreClose(mySize, deletedBlobs[d].size); d++ {
			blobsAreClose, err := ra.blobsAreClose(
				myBlob, cache[deletedBlobs[d].change.From.TreeEntry.Hash])
			if err != nil {
				return nil, err
			}
			if blobsAreClose {
				foundMatch = true
				reducedChanges = append(
					reducedChanges,
					&object.Change{From: deletedBlobs[d].change.From,
						To: addedBlobs[a].change.To})
				break
			}
		}
		if foundMatch {
			addedBlobs = append(addedBlobs[:a], addedBlobs[a+1:]...)
			a--
			deletedBlobs = append(deletedBlobs[:d], deletedBlobs[d+1:]...)
		}
	}

	// Stage 3 - we give up, everything left are independent additions and deletions
	for _, blob := range addedBlobs {
		reducedChanges = append(reducedChanges, blob.change)
	}
	for _, blob := range deletedBlobs {
		reducedChanges = append(reducedChanges, blob.change)
	}
	return map[string]interface{}{DependencyTreeChanges: reducedChanges}, nil
}

func (ra *RenameAnalysis) sizesAreClose(size1 int64, size2 int64) bool {
	return abs64(size1-size2)*100/max64(1, min64(size1, size2)) <=
		int64(100-ra.SimilarityThreshold)
}

func (ra *RenameAnalysis) blobsAreClose(
	blob1 *object.Blob, blob2 *object.Blob) (bool, error) {
	strFrom, err := BlobToString(blob1)
	if err != nil {
		return false, err
	}
	strTo, err := BlobToString(blob2)
	if err != nil {
		return false, err
	}
	dmp := diffmatchpatch.New()
	src, dst, _ := dmp.DiffLinesToRunes(strFrom, strTo)
	diffs := dmp.DiffMainRunes(src, dst, false)
	common := 0
	for _, edit := range diffs {
		if edit.Type == diffmatchpatch.DiffEqual {
			common += utf8.RuneCountInString(edit.Text)
		}
	}
	return common*100/max(1, min(len(src), len(dst))) >= ra.SimilarityThreshold, nil
}

type sortableChange struct {
	change *object.Change
	hash   plumbing.Hash
}

type sortableChanges []sortableChange

func (change *sortableChange) Less(other *sortableChange) bool {
	for x := 0; x < 20; x++ {
		if change.hash[x] < other.hash[x] {
			return true
		}
	}
	return false
}

func (slice sortableChanges) Len() int {
	return len(slice)
}

func (slice sortableChanges) Less(i, j int) bool {
	return slice[i].Less(&slice[j])
}

func (slice sortableChanges) Swap(i, j int) {
	slice[i], slice[j] = slice[j], slice[i]
}

type sortableBlob struct {
	change *object.Change
	size   int64
}

type sortableBlobs []sortableBlob

func (change *sortableBlob) Less(other *sortableBlob) bool {
	return change.size < other.size
}

func (slice sortableBlobs) Len() int {
	return len(slice)
}

func (slice sortableBlobs) Less(i, j int) bool {
	return slice[i].Less(&slice[j])
}

func (slice sortableBlobs) Swap(i, j int) {
	slice[i], slice[j] = slice[j], slice[i]
}

func init() {
	Registry.Register(&RenameAnalysis{})
}