package patch

import (
	"sort"
	"strings"

	"github.com/jesseduffield/generics/maps"
	"github.com/samber/lo"
	"github.com/sirupsen/logrus"
)

type PatchStatus int

const (
	// UNSELECTED is for when the commit file has not been added to the patch in any way
	UNSELECTED PatchStatus = iota
	// WHOLE is for when you want to add the whole diff of a file to the patch,
	// including e.g. if it was deleted
	WHOLE
	// PART is for when you're only talking about specific lines that have been modified
	PART
)

type fileInfo struct {
	mode                PatchStatus
	includedLineIndices []int
	diff                string
	// For a renamed file, the path it was renamed from; empty otherwise. We
	// need to keep hold of it so we can re-render the file's patch (which is
	// keyed by the new path) without the caller having to supply it again.
	previousPath string
}

type (
	loadFileDiffFunc func(from string, to string, reverse bool, filename string, previousPath string, plain bool) (string, error)
)

// PatchBuilder manages the building of a patch for a commit to be applied to another commit (or the working tree, or removed from the current commit). We also support building patches from things like stashes, for which there is less flexibility
type PatchBuilder struct {
	// To is the commit hash if we're dealing with files of a commit, or a stash ref for a stash
	To      string
	From    string
	reverse bool

	// CanRebase tells us whether we're allowed to modify our commits. CanRebase should be true for commits of the currently checked out branch and false for everything else
	// TODO: move this out into a proper mode struct in the gui package: it doesn't really belong here
	CanRebase bool

	// fileInfoMap starts empty but you add files to it as you go along
	fileInfoMap map[string]*fileInfo
	Log         *logrus.Entry

	// loadFileDiff loads the diff of a file, for a given to (typically a commit hash)
	loadFileDiff loadFileDiffFunc
}

func NewPatchBuilder(log *logrus.Entry, loadFileDiff loadFileDiffFunc) *PatchBuilder {
	return &PatchBuilder{
		Log:          log,
		loadFileDiff: loadFileDiff,
	}
}

func (p *PatchBuilder) Start(from, to string, reverse bool, canRebase bool) {
	p.To = to
	p.From = from
	p.reverse = reverse
	p.CanRebase = canRebase
	p.fileInfoMap = map[string]*fileInfo{}
}

func (p *PatchBuilder) PatchToApply(reverse bool, turnAddedFilesIntoDiffAgainstEmptyFile bool) string {
	var patch strings.Builder

	for filename, info := range p.fileInfoMap {
		if info.mode == UNSELECTED {
			continue
		}

		patch.WriteString(p.RenderPatchForFile(RenderPatchForFileOpts{
			Filename:                               filename,
			PreviousPath:                           info.previousPath,
			Plain:                                  true,
			Reverse:                                reverse,
			TurnAddedFilesIntoDiffAgainstEmptyFile: turnAddedFilesIntoDiffAgainstEmptyFile,
		}))
	}

	return patch.String()
}

func (p *PatchBuilder) addFileWhole(info *fileInfo) {
	if info.mode != WHOLE {
		info.mode = WHOLE
		lineCount := len(strings.Split(info.diff, "\n"))
		// add every line index
		// TODO: add tests and then use lo.Range to simplify
		info.includedLineIndices = make([]int, lineCount)
		for i := range lineCount {
			info.includedLineIndices[i] = i
		}
	}
}

func (p *PatchBuilder) removeFile(info *fileInfo) {
	info.mode = UNSELECTED
	info.includedLineIndices = nil
}

func (p *PatchBuilder) AddFileWhole(filename string, previousPath string) error {
	info, err := p.getFileInfo(filename, previousPath)
	if err != nil {
		return err
	}

	p.addFileWhole(info)

	return nil
}

func (p *PatchBuilder) RemoveFile(filename string, previousPath string) error {
	info, err := p.getFileInfo(filename, previousPath)
	if err != nil {
		return err
	}

	p.removeFile(info)

	return nil
}

func (p *PatchBuilder) getFileInfo(filename string, previousPath string) (*fileInfo, error) {
	info, ok := p.fileInfoMap[filename]
	if ok {
		return info, nil
	}

	diff, err := p.loadFileDiff(p.From, p.To, p.reverse, filename, previousPath, true)
	if err != nil {
		return nil, err
	}
	info = &fileInfo{
		mode:         UNSELECTED,
		diff:         diff,
		previousPath: previousPath,
	}

	p.fileInfoMap[filename] = info

	return info, nil
}

func (p *PatchBuilder) AddFileLineRange(filename string, previousPath string, lineIndices []int) error {
	info, err := p.getFileInfo(filename, previousPath)
	if err != nil {
		return err
	}
	info.mode = PART
	info.includedLineIndices = lo.Union(info.includedLineIndices, lineIndices)

	return nil
}

func (p *PatchBuilder) RemoveFileLineRange(filename string, previousPath string, lineIndices []int) error {
	info, err := p.getFileInfo(filename, previousPath)
	if err != nil {
		return err
	}
	info.mode = PART
	info.includedLineIndices, _ = lo.Difference(info.includedLineIndices, lineIndices)
	if len(info.includedLineIndices) == 0 {
		p.removeFile(info)
	}

	return nil
}

type RenderPatchForFileOpts struct {
	Filename                               string
	PreviousPath                           string
	Plain                                  bool
	Reverse                                bool
	TurnAddedFilesIntoDiffAgainstEmptyFile bool
}

func (p *PatchBuilder) RenderPatchForFile(opts RenderPatchForFileOpts) string {
	info, err := p.getFileInfo(opts.Filename, opts.PreviousPath)
	if err != nil {
		p.Log.Error(err)
		return ""
	}

	if info.mode == UNSELECTED {
		return ""
	}

	if info.mode == WHOLE && opts.Plain {
		// Use the whole diff (spares us parsing it and then formatting it).
		// TODO: see if this is actually noticeably faster.
		// The reverse flag is only for part patches so we're ignoring it here.
		return info.diff
	}

	patch := Parse(info.diff).
		Transform(TransformOpts{
			Reverse:                                opts.Reverse,
			TurnAddedFilesIntoDiffAgainstEmptyFile: opts.TurnAddedFilesIntoDiffAgainstEmptyFile,
			// For a partial selection of a renamed file we keep only the
			// content change and drop the rename, so that the rename stays in
			// the commit. A whole-file selection keeps the rename (and short-
			// circuits before this for plain output).
			StripRename:         info.mode == PART && info.previousPath != "",
			IncludedLineIndices: info.includedLineIndices,
		})

	if opts.Plain {
		return patch.FormatPlain()
	}
	return patch.FormatView(FormatViewOpts{})
}

func (p *PatchBuilder) renderEachFilePatch(plain bool) []string {
	// sort files by name then iterate through and render each patch
	filenames := maps.Keys(p.fileInfoMap)

	sort.Strings(filenames)
	patches := lo.Map(filenames, func(filename string, _ int) string {
		return p.RenderPatchForFile(RenderPatchForFileOpts{
			Filename:                               filename,
			PreviousPath:                           p.fileInfoMap[filename].previousPath,
			Plain:                                  plain,
			Reverse:                                false,
			TurnAddedFilesIntoDiffAgainstEmptyFile: true,
		})
	})
	output := lo.Filter(patches, func(patch string, _ int) bool {
		return patch != ""
	})

	return output
}

func (p *PatchBuilder) RenderAggregatedPatch(plain bool) string {
	return strings.Join(p.renderEachFilePatch(plain), "")
}

func (p *PatchBuilder) GetFileStatus(filename string, parent string) PatchStatus {
	if parent != p.To {
		return UNSELECTED
	}

	info, ok := p.fileInfoMap[filename]
	if !ok {
		return UNSELECTED
	}

	return info.mode
}

func (p *PatchBuilder) GetFileIncLineIndices(filename string, previousPath string) ([]int, error) {
	info, err := p.getFileInfo(filename, previousPath)
	if err != nil {
		return nil, err
	}
	return info.includedLineIndices, nil
}

// clears the patch
func (p *PatchBuilder) Reset() {
	p.To = ""
	p.fileInfoMap = map[string]*fileInfo{}
}

func (p *PatchBuilder) Active() bool {
	return p.To != ""
}

func (p *PatchBuilder) IsEmpty() bool {
	for _, fileInfo := range p.fileInfoMap {
		if fileInfo.mode == WHOLE || (fileInfo.mode == PART && len(fileInfo.includedLineIndices) > 0) {
			return false
		}
	}

	return true
}

// if any of these things change we'll need to reset and start a new patch
func (p *PatchBuilder) NewPatchRequired(from string, to string, reverse bool) bool {
	return from != p.From || to != p.To || reverse != p.reverse
}

func (p *PatchBuilder) AllFilesInPatch() []string {
	return lo.Keys(p.fileInfoMap)
}
