package hercules

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"time"
	"unicode/utf8"

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

type Analyser struct {
	Repository *git.Repository
	Granularity int
	OnProgress func(int)
}

func checkClose(c io.Closer) {
	if err := c.Close(); err != nil {
		panic(err)
	}
}

func loc(file *git.Blob) (int, error) {
	reader, err := file.Reader()
	if err != nil {
		panic(err)
	}
	defer checkClose(reader)
	scanner := bufio.NewScanner(reader)
	counter := 0
	for scanner.Scan() {
		if !utf8.Valid(scanner.Bytes()) {
			return -1, errors.New("binary")
		}
		counter++
	}
	return counter, nil
}

func str(file *git.Blob) (string, error) {
	reader, err := file.Reader()
	if err != nil {
		panic(err)
	}
	defer checkClose(reader)
	buf := new(bytes.Buffer)
	buf.ReadFrom(reader)
	if !utf8.Valid(buf.Bytes()) {
		return "", errors.New("binary")
	}
	return buf.String(), nil
}

func (analyser *Analyser) handleInsertion(
	change *git.Change, day int, status map[int]int64, files map[string]*File) {
	blob, err := analyser.Repository.Blob(change.To.TreeEntry.Hash)
	if err != nil {
		panic(err)
	}
	lines, err := loc(blob)
	if err != nil {
		return
	}
	name := change.To.Name
	file, exists := files[name]
	if exists {
		panic(fmt.Sprintf("file %s already exists", name))
	}
	file = NewFile(day, lines, status)
	files[name] = file
}

func (analyser *Analyser) handleDeletion(
	change *git.Change, day int, status map[int]int64, files map[string]*File) {
	blob, err := analyser.Repository.Blob(change.From.TreeEntry.Hash)
	if err != nil {
		panic(err)
	}
	lines, err := loc(blob)
	if err != nil {
		return
	}
	name := change.From.Name
	file := files[name]
	file.Update(day, 0, 0, lines)
	delete(files, name)
}

func (analyser *Analyser) handleModification(
	change *git.Change, day int, status map[int]int64, files map[string]*File) {
	blob_from, err := analyser.Repository.Blob(change.From.TreeEntry.Hash)
	if err != nil {
		panic(err)
	}
	blob_to, err := analyser.Repository.Blob(change.To.TreeEntry.Hash)
	if err != nil {
		panic(err)
	}
	str_from, err := str(blob_from)
	if err != nil {
		return
	}
	str_to, _ := str(blob_to)
	file, exists := files[change.From.Name]
	if !exists {
		panic(fmt.Sprintf("file %s does not exist", change.From.Name))
	}
	// possible rename
	if change.To.Name != change.From.Name {
		analyser.handleRename(change.From.Name, change.To.Name, files)
	}
	dmp := diffmatchpatch.New()
	src, dst, _ := dmp.DiffLinesToRunes(str_from, str_to)
	diffs := dmp.DiffMainRunes(src, dst, false)
	// we do not call RunesToDiffLines so the number of lines equals
	// to the rune count
	position := 0
	for _, edit := range diffs {
		length := utf8.RuneCountInString(edit.Text)
		switch edit.Type {
		case diffmatchpatch.DiffEqual:
			position += length
		case diffmatchpatch.DiffInsert:
			file.Update(day, position, length, 0)
			position += length
		case diffmatchpatch.DiffDelete:
			file.Update(day, position, 0, length)
			break
		default:
			panic(fmt.Sprintf("diff operation is not supported: %d", edit.Type))
		}
	}
}

func (analyser *Analyser) handleRename(from, to string, files map[string]*File) {
	file, exists := files[from]
	if !exists {
		panic(fmt.Sprintf("file %s does not exist", from))
	}
	files[to] = file
	delete(files, from)
}

func (analyser *Analyser) commits() []*git.Commit {
	result := []*git.Commit{}
	repository := analyser.Repository
	head, err := repository.Head()
	if err != nil {
		panic(err)
	}
	commit, err := repository.Commit(head.Hash())
	if err != nil {
		panic(err)
	}
	result = append(result, commit)
	for ; err != io.EOF; commit, err = commit.Parents().Next() {
		if err != nil {
			panic(err)
		}
		result = append(result, commit)
	}
	// reverse the order
	for i, j := 0, len(result)-1; i < j; i, j = i+1, j-1 {
		result[i], result[j] = result[j], result[i]
	}
	return result
}

func (analyser *Analyser) groupStatus(status map[int]int64, day int) []int64 {
  granularity := analyser.Granularity
  result := make([]int64, day / granularity)
  var group int64
  for i := 0; i < day; i++ {
	  group += status[i]
    if i % granularity == (granularity - 1) {
	    result[i / granularity] = group
	    group = 0
    }
  }
	return result
}

func (analyser *Analyser) Analyse() [][]int64 {
	granularity := analyser.Granularity
	if granularity == 0 {
		granularity = 1
	}
	onProgress := analyser.OnProgress
	if onProgress == nil {
		onProgress = func(int) {}
	}

	// current daily alive number of lines; key is the number of days from the
	// beginning of the history
	status := map[int]int64{}
	// weekly snapshots of status
	statuses := [][]int64{}
	// mapping <file path> -> hercules.File
	files := map[string]*File{}
	// list of commits belonging to the default branch, from oldest to newest
	commits := analyser.commits()

	var day0 time.Time // will be initialized in the first iteration
	var prev_tree *git.Tree = nil
	prev_day := 0

	for index, commit := range commits {
		onProgress(index)
		tree, err := commit.Tree()
		if err != nil {
			panic(err)
		}
		if index == 0 {
			// first iteration - initialize the file objects from the tree
			day0 = commit.Author.When
			func() {
				file_iter := tree.Files()
				defer file_iter.Close()
				for {
					file, err := file_iter.Next()
					if err != nil {
						if err == io.EOF {
							break
						}
						panic(err)
					}
					lines, err := loc(&file.Blob)
					if err == nil {
						files[file.Name] = NewFile(0, lines, status)
					}
				}
			}()
		} else {
			day := int(commit.Author.When.Sub(day0).Hours() / 24)
			delta := (day / granularity) - (prev_day / granularity)
			if delta > 0 {
				prev_day = day
				statuses = append(statuses, analyser.groupStatus(status, day))
			}
			tree_diff, err := git.DiffTree(prev_tree, tree)
			if err != nil {
				panic(err)
			}
			for _, change := range tree_diff {
				switch change.Action {
				case git.Insert:
					analyser.handleInsertion(change, day, status, files)
				case git.Delete:
					analyser.handleDeletion(change, day, status, files)
				case git.Modify:
					analyser.handleModification(change, day, status, files)
				default:
					panic(fmt.Sprintf("unsupported action: %d", change.Action))
				}
			}
		}
		prev_tree = tree
	}
	return statuses
}