package object

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"math"
	"strings"

	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/filemode"
	fdiff "github.com/go-git/go-git/v5/plumbing/format/diff"
	"github.com/go-git/go-git/v5/utils/diff"

	dmp "github.com/sergi/go-diff/diffmatchpatch"
)

var (
	ErrCanceled = errors.New("operation canceled")
)

func getPatch(message string, changes ...*Change) (*Patch, error) {
	ctx := context.Background()
	return getPatchContext(ctx, message, changes...)
}

func getPatchContext(ctx context.Context, message string, changes ...*Change) (*Patch, error) {
	var filePatches []fdiff.FilePatch
	for _, c := range changes {
		select {
		case <-ctx.Done():
			return nil, ErrCanceled
		default:
		}

		fp, err := filePatchWithContext(ctx, c)
		if err != nil {
			return nil, err
		}

		filePatches = append(filePatches, fp)
	}

	return &Patch{message, filePatches}, nil
}

func filePatchWithContext(ctx context.Context, c *Change) (fdiff.FilePatch, error) {
	from, to, err := c.Files()
	if err != nil {
		return nil, err
	}
	fromContent, fIsBinary, err := fileContent(from)
	if err != nil {
		return nil, err
	}

	toContent, tIsBinary, err := fileContent(to)
	if err != nil {
		return nil, err
	}

	if fIsBinary || tIsBinary {
		return &textFilePatch{from: c.From, to: c.To}, nil
	}

	diffs := diff.Do(fromContent, toContent)

	var chunks []fdiff.Chunk
	for _, d := range diffs {
		select {
		case <-ctx.Done():
			return nil, ErrCanceled
		default:
		}

		var op fdiff.Operation
		switch d.Type {
		case dmp.DiffEqual:
			op = fdiff.Equal
		case dmp.DiffDelete:
			op = fdiff.Delete
		case dmp.DiffInsert:
			op = fdiff.Add
		}

		chunks = append(chunks, &textChunk{d.Text, op})
	}

	return &textFilePatch{
		chunks: chunks,
		from:   c.From,
		to:     c.To,
	}, nil

}

func fileContent(f *File) (content string, isBinary bool, err error) {
	if f == nil {
		return
	}

	isBinary, err = f.IsBinary()
	if err != nil || isBinary {
		return
	}

	content, err = f.Contents()

	return
}

// Patch is an implementation of fdiff.Patch interface
type Patch struct {
	message     string
	filePatches []fdiff.FilePatch
}

func (p *Patch) FilePatches() []fdiff.FilePatch {
	return p.filePatches
}

func (p *Patch) Message() string {
	return p.message
}

func (p *Patch) Encode(w io.Writer) error {
	ue := fdiff.NewUnifiedEncoder(w, fdiff.DefaultContextLines)

	return ue.Encode(p)
}

func (p *Patch) Stats() FileStats {
	return getFileStatsFromFilePatches(p.FilePatches())
}

func (p *Patch) String() string {
	buf := bytes.NewBuffer(nil)
	err := p.Encode(buf)
	if err != nil {
		return fmt.Sprintf("malformed patch: %s", err.Error())
	}

	return buf.String()
}

// changeEntryWrapper is an implementation of fdiff.File interface
type changeEntryWrapper struct {
	ce ChangeEntry
}

func (f *changeEntryWrapper) Hash() plumbing.Hash {
	if !f.ce.TreeEntry.Mode.IsFile() {
		return plumbing.ZeroHash
	}

	return f.ce.TreeEntry.Hash
}

func (f *changeEntryWrapper) Mode() filemode.FileMode {
	return f.ce.TreeEntry.Mode
}
func (f *changeEntryWrapper) Path() string {
	if !f.ce.TreeEntry.Mode.IsFile() {
		return ""
	}

	return f.ce.Name
}

func (f *changeEntryWrapper) Empty() bool {
	return !f.ce.TreeEntry.Mode.IsFile()
}

// textFilePatch is an implementation of fdiff.FilePatch interface
type textFilePatch struct {
	chunks   []fdiff.Chunk
	from, to ChangeEntry
}

func (tf *textFilePatch) Files() (from fdiff.File, to fdiff.File) {
	f := &changeEntryWrapper{tf.from}
	t := &changeEntryWrapper{tf.to}

	if !f.Empty() {
		from = f
	}

	if !t.Empty() {
		to = t
	}

	return
}

func (tf *textFilePatch) IsBinary() bool {
	return len(tf.chunks) == 0
}

func (tf *textFilePatch) Chunks() []fdiff.Chunk {
	return tf.chunks
}

// textChunk is an implementation of fdiff.Chunk interface
type textChunk struct {
	content string
	op      fdiff.Operation
}

func (t *textChunk) Content() string {
	return t.content
}

func (t *textChunk) Type() fdiff.Operation {
	return t.op
}

// FileStat stores the status of changes in content of a file.
type FileStat struct {
	Name     string
	Addition int
	Deletion int
}

func (fs FileStat) String() string {
	return printStat([]FileStat{fs})
}

// FileStats is a collection of FileStat.
type FileStats []FileStat

func (fileStats FileStats) String() string {
	return printStat(fileStats)
}

func printStat(fileStats []FileStat) string {
	padLength := float64(len(" "))
	newlineLength := float64(len("\n"))
	separatorLength := float64(len("|"))
	// Soft line length limit. The text length calculation below excludes
	// length of the change number. Adding that would take it closer to 80,
	// but probably not more than 80, until it's a huge number.
	lineLength := 72.0

	// Get the longest filename and longest total change.
	var longestLength float64
	var longestTotalChange float64
	for _, fs := range fileStats {
		if int(longestLength) < len(fs.Name) {
			longestLength = float64(len(fs.Name))
		}
		totalChange := fs.Addition + fs.Deletion
		if int(longestTotalChange) < totalChange {
			longestTotalChange = float64(totalChange)
		}
	}

	// Parts of the output:
	// <pad><filename><pad>|<pad><changeNumber><pad><+++/---><newline>
	// example: " main.go | 10 +++++++--- "

	// <pad><filename><pad>
	leftTextLength := padLength + longestLength + padLength

	// <pad><number><pad><+++++/-----><newline>
	// Excluding number length here.
	rightTextLength := padLength + padLength + newlineLength

	totalTextArea := leftTextLength + separatorLength + rightTextLength
	heightOfHistogram := lineLength - totalTextArea

	// Scale the histogram.
	var scaleFactor float64
	if longestTotalChange > heightOfHistogram {
		// Scale down to heightOfHistogram.
		scaleFactor = longestTotalChange / heightOfHistogram
	} else {
		scaleFactor = 1.0
	}

	finalOutput := ""
	for _, fs := range fileStats {
		addn := float64(fs.Addition)
		deln := float64(fs.Deletion)
		addc := int(math.Floor(addn/scaleFactor))
		delc := int(math.Floor(deln/scaleFactor))
		if addc < 0 {
			addc = 0
		}
		if delc < 0 {
			delc = 0
		}
		adds := strings.Repeat("+", addc)
		dels := strings.Repeat("-", delc)
		finalOutput += fmt.Sprintf(" %s | %d %s%s\n", fs.Name, (fs.Addition + fs.Deletion), adds, dels)
	}

	return finalOutput
}

func getFileStatsFromFilePatches(filePatches []fdiff.FilePatch) FileStats {
	var fileStats FileStats

	for _, fp := range filePatches {
		// ignore empty patches (binary files, submodule refs updates)
		if len(fp.Chunks()) == 0 {
			continue
		}

		cs := FileStat{}
		from, to := fp.Files()
		if from == nil {
			// New File is created.
			cs.Name = to.Path()
		} else if to == nil {
			// File is deleted.
			cs.Name = from.Path()
		} else if from.Path() != to.Path() {
			// File is renamed.
			cs.Name = fmt.Sprintf("%s => %s", from.Path(), to.Path())
		} else {
			cs.Name = from.Path()
		}

		for _, chunk := range fp.Chunks() {
			s := chunk.Content()
			if len(s) == 0 {
				continue
			}

			switch chunk.Type() {
			case fdiff.Add:
				cs.Addition += strings.Count(s, "\n")
				if s[len(s)-1] != '\n' {
					cs.Addition++
				}
			case fdiff.Delete:
				cs.Deletion += strings.Count(s, "\n")
				if s[len(s)-1] != '\n' {
					cs.Deletion++
				}
			}
		}

		fileStats = append(fileStats, cs)
	}

	return fileStats
}
