// though this panel is called the merge panel, it's really going to use the main panel. This may change in the future

package main

import (
	"bufio"
	"bytes"
	"io/ioutil"
	"math"
	"os"
	"strings"

	"github.com/fatih/color"
	"github.com/jesseduffield/gocui"
)

func findConflicts(content string) ([]conflict, error) {
	conflicts := make([]conflict, 0)
	var newConflict conflict
	for i, line := range splitLines(content) {
		if line == "<<<<<<< HEAD" || line == "<<<<<<< MERGE_HEAD" || line == "<<<<<<< Updated upstream" {
			newConflict = conflict{start: i}
		} else if line == "=======" {
			newConflict.middle = i
		} else if strings.HasPrefix(line, ">>>>>>> ") {
			newConflict.end = i
			conflicts = append(conflicts, newConflict)
		}
	}
	return conflicts, nil
}

func shiftConflict(conflicts []conflict) (conflict, []conflict) {
	return conflicts[0], conflicts[1:]
}

func shouldHighlightLine(index int, conflict conflict, top bool) bool {
	return (index >= conflict.start && index <= conflict.middle && top) || (index >= conflict.middle && index <= conflict.end && !top)
}

func coloredConflictFile(content string, conflicts []conflict, conflictIndex int, conflictTop, hasFocus bool) (string, error) {
	if len(conflicts) == 0 {
		return content, nil
	}
	conflict, remainingConflicts := shiftConflict(conflicts)
	var outputBuffer bytes.Buffer
	for i, line := range splitLines(content) {
		colourAttr := color.FgWhite
		if i == conflict.start || i == conflict.middle || i == conflict.end {
			colourAttr = color.FgRed
		}
		colour := color.New(colourAttr)
		if hasFocus && conflictIndex < len(conflicts) && conflicts[conflictIndex] == conflict && shouldHighlightLine(i, conflict, conflictTop) {
			colour.Add(color.Bold)
		}
		if i == conflict.end && len(remainingConflicts) > 0 {
			conflict, remainingConflicts = shiftConflict(remainingConflicts)
		}
		outputBuffer.WriteString(coloredString(line, colour) + "\n")
	}
	return outputBuffer.String(), nil
}

func handleSelectTop(g *gocui.Gui, v *gocui.View) error {
	state.ConflictTop = true
	return refreshMergePanel(g)
}

func handleSelectBottom(g *gocui.Gui, v *gocui.View) error {
	state.ConflictTop = false
	return refreshMergePanel(g)
}

func handleSelectNextConflict(g *gocui.Gui, v *gocui.View) error {
	if state.ConflictIndex >= len(state.Conflicts)-1 {
		return nil
	}
	state.ConflictIndex++
	return refreshMergePanel(g)
}

func handleSelectPrevConflict(g *gocui.Gui, v *gocui.View) error {
	if state.ConflictIndex <= 0 {
		return nil
	}
	state.ConflictIndex--
	return refreshMergePanel(g)
}

func isIndexToDelete(i int, conflict conflict, pick string) bool {
	return i == conflict.middle ||
		i == conflict.start ||
		i == conflict.end ||
		pick != "both" &&
			(pick == "bottom" && i > conflict.start && i < conflict.middle) ||
		(pick == "top" && i > conflict.middle && i < conflict.end)
}

func resolveConflict(g *gocui.Gui, conflict conflict, pick string) error {
	gitFile, err := getSelectedFile(g)
	if err != nil {
		return err
	}
	file, err := os.Open(gitFile.Name)
	if err != nil {
		return err
	}
	defer file.Close()

	reader := bufio.NewReader(file)
	output := ""
	for i := 0; true; i++ {
		line, err := reader.ReadString('\n')
		if err != nil {
			break
		}
		if !isIndexToDelete(i, conflict, pick) {
			output += line
		}
	}
	devLog(output)
	return ioutil.WriteFile(gitFile.Name, []byte(output), 0644)
}

func pushFileSnapshot(g *gocui.Gui) error {
	gitFile, err := getSelectedFile(g)
	if err != nil {
		return err
	}
	content, err := catFile(gitFile.Name)
	if err != nil {
		return err
	}
	state.EditHistory.Push(content)
	return nil
}

func handlePopFileSnapshot(g *gocui.Gui, v *gocui.View) error {
	if state.EditHistory.Len() == 0 {
		return nil
	}
	prevContent := state.EditHistory.Pop().(string)
	gitFile, err := getSelectedFile(g)
	if err != nil {
		return err
	}
	ioutil.WriteFile(gitFile.Name, []byte(prevContent), 0644)
	return refreshMergePanel(g)
}

func handlePickHunk(g *gocui.Gui, v *gocui.View) error {
	conflict := state.Conflicts[state.ConflictIndex]
	pushFileSnapshot(g)
	pick := "bottom"
	if state.ConflictTop {
		pick = "top"
	}
	err := resolveConflict(g, conflict, pick)
	if err != nil {
		panic(err)
	}
	refreshMergePanel(g)
	return nil
}

func handlePickBothHunks(g *gocui.Gui, v *gocui.View) error {
	conflict := state.Conflicts[state.ConflictIndex]
	pushFileSnapshot(g)
	err := resolveConflict(g, conflict, "both")
	if err != nil {
		panic(err)
	}
	return refreshMergePanel(g)
}

func currentViewName(g *gocui.Gui) string {
	currentView := g.CurrentView()
	return currentView.Name()
}

func refreshMergePanel(g *gocui.Gui) error {
	cat, err := catSelectedFile(g)
	if err != nil {
		return err
	}
	state.Conflicts, err = findConflicts(cat)
	if err != nil {
		return err
	}

	if len(state.Conflicts) == 0 {
		return handleCompleteMerge(g)
	} else if state.ConflictIndex > len(state.Conflicts)-1 {
		state.ConflictIndex = len(state.Conflicts) - 1
	}
	hasFocus := currentViewName(g) == "main"
	if hasFocus {
		renderMergeOptions(g)
	}
	content, err := coloredConflictFile(cat, state.Conflicts, state.ConflictIndex, state.ConflictTop, hasFocus)
	if err != nil {
		return err
	}
	if err := scrollToConflict(g); err != nil {
		return err
	}
	return renderString(g, "main", content)
}

func scrollToConflict(g *gocui.Gui) error {
	mainView, err := g.View("main")
	if err != nil {
		return err
	}
	if len(state.Conflicts) == 0 {
		return nil
	}
	conflict := state.Conflicts[state.ConflictIndex]
	ox, _ := mainView.Origin()
	_, height := mainView.Size()
	conflictMiddle := (conflict.end + conflict.start) / 2
	newOriginY := int(math.Max(0, float64(conflictMiddle-(height/2))))
	return mainView.SetOrigin(ox, newOriginY)
}

func switchToMerging(g *gocui.Gui) error {
	state.ConflictIndex = 0
	state.ConflictTop = true
	_, err := g.SetCurrentView("main")
	if err != nil {
		return err
	}
	return refreshMergePanel(g)
}

func renderMergeOptions(g *gocui.Gui) error {
	return renderOptionsMap(g, map[string]string{
		"↑ ↓":   "select hunk",
		"← →":   "navigate conflicts",
		"space": "pick hunk",
		"b":     "pick both hunks",
		"z":     "undo",
	})
}

func handleEscapeMerge(g *gocui.Gui, v *gocui.View) error {
	filesView, err := g.View("files")
	if err != nil {
		return err
	}
	refreshFiles(g)
	return switchFocus(g, v, filesView)
}

func handleCompleteMerge(g *gocui.Gui) error {
	filesView, err := g.View("files")
	if err != nil {
		return err
	}
	stageSelectedFile(g)
	refreshFiles(g)
	return switchFocus(g, nil, filesView)
}