package git

import (
	"bufio"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	gogit "github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/plumbing/format/index"
)

// ConflictInfo represents information about a merge conflict
type ConflictInfo struct {
	FilePath    string
	OursHash    string
	TheirsHash  string
	BaseHash    string
	HasConflict bool
}

// ConflictResolver handles conflict detection and resolution guidance
type ConflictResolver struct {
	repo     *gogit.Repository
	repoPath string
}

// NewConflictResolver creates a new ConflictResolver instance
func NewConflictResolver(repo *gogit.Repository, repoPath string) *ConflictResolver {
	return &ConflictResolver{
		repo:     repo,
		repoPath: repoPath,
	}
}

// DetectConflicts checks for merge conflicts in the working tree
func (cr *ConflictResolver) DetectConflicts() ([]ConflictInfo, error) {
	idx, err := cr.repo.Storer.Index()
	if err != nil {
		return nil, fmt.Errorf("failed to read index: %w", err)
	}

	conflicts := []ConflictInfo{}

	// Check for conflicts in the index
	for _, entry := range idx.Entries {
		// Stage > 0 indicates a conflict
		if entry.Stage != 0 {
			// Find all stages for this file
			conflict := cr.findConflictStages(idx, entry.Name)
			if conflict.HasConflict {
				conflicts = append(conflicts, conflict)
			}
		}
	}

	return conflicts, nil
}

// findConflictStages finds all conflict stages for a file
func (cr *ConflictResolver) findConflictStages(idx *index.Index, path string) ConflictInfo {
	conflict := ConflictInfo{
		FilePath:    path,
		HasConflict: false,
	}

	for _, entry := range idx.Entries {
		if entry.Name == path {
			switch entry.Stage {
			case 1:
				// Base/common ancestor
				conflict.BaseHash = entry.Hash.String()
				conflict.HasConflict = true
			case 2:
				// Ours (current branch)
				conflict.OursHash = entry.Hash.String()
				conflict.HasConflict = true
			case 3:
				// Theirs (incoming branch)
				conflict.TheirsHash = entry.Hash.String()
				conflict.HasConflict = true
			}
		}
	}

	return conflict
}

// HasConflicts checks if there are any conflicts in the working tree
func (cr *ConflictResolver) HasConflicts() (bool, error) {
	conflicts, err := cr.DetectConflicts()
	if err != nil {
		return false, err
	}

	return len(conflicts) > 0, nil
}

// PresentConflicts presents conflicts to the user with clear guidance
func (cr *ConflictResolver) PresentConflicts(conflicts []ConflictInfo) string {
	if len(conflicts) == 0 {
		return "No conflicts detected."
	}

	var sb strings.Builder

	sb.WriteString(fmt.Sprintf("\n%s\n", strings.Repeat("=", 70)))
	sb.WriteString(fmt.Sprintf("  MERGE CONFLICTS DETECTED (%d file(s))\n", len(conflicts)))
	sb.WriteString(fmt.Sprintf("%s\n\n", strings.Repeat("=", 70)))

	for i, conflict := range conflicts {
		sb.WriteString(fmt.Sprintf("%d. %s\n", i+1, conflict.FilePath))
		sb.WriteString(fmt.Sprintf("   Base:   %s\n", conflict.BaseHash[:8]))
		sb.WriteString(fmt.Sprintf("   Ours:   %s\n", conflict.OursHash[:8]))
		sb.WriteString(fmt.Sprintf("   Theirs: %s\n", conflict.TheirsHash[:8]))
		sb.WriteString("\n")
	}

	sb.WriteString("To resolve conflicts:\n")
	sb.WriteString("  1. Edit the conflicting files to resolve conflicts\n")
	sb.WriteString("  2. Look for conflict markers: <<<<<<<, =======, >>>>>>>\n")
	sb.WriteString("  3. Remove the conflict markers after resolving\n")
	sb.WriteString("  4. Stage the resolved files: git add <file>\n")
	sb.WriteString("  5. Continue the rebase: git rebase --continue\n")
	sb.WriteString(fmt.Sprintf("%s\n", strings.Repeat("=", 70)))

	return sb.String()
}

// GetConflictMarkers reads a file and extracts conflict marker sections
func (cr *ConflictResolver) GetConflictMarkers(filePath string) ([]ConflictMarker, error) {
	fullPath := filepath.Join(cr.repoPath, filePath)
	file, err := os.Open(fullPath)
	if err != nil {
		return nil, fmt.Errorf("failed to open file: %w", err)
	}
	defer file.Close()

	markers := []ConflictMarker{}
	scanner := bufio.NewScanner(file)
	lineNum := 0
	var currentMarker *ConflictMarker

	for scanner.Scan() {
		lineNum++
		line := scanner.Text()

		if strings.HasPrefix(line, "<<<<<<<") {
			// Start of conflict
			currentMarker = &ConflictMarker{
				FilePath:  filePath,
				StartLine: lineNum,
			}
		} else if strings.HasPrefix(line, "=======") && currentMarker != nil {
			currentMarker.SeparatorLine = lineNum
		} else if strings.HasPrefix(line, ">>>>>>>") && currentMarker != nil {
			currentMarker.EndLine = lineNum
			markers = append(markers, *currentMarker)
			currentMarker = nil
		}
	}

	if err := scanner.Err(); err != nil {
		return nil, fmt.Errorf("error reading file: %w", err)
	}

	return markers, nil
}

// ConflictMarker represents a conflict marker section in a file
type ConflictMarker struct {
	FilePath      string
	StartLine     int
	SeparatorLine int
	EndLine       int
}

// IsFileConflicted checks if a specific file has conflict markers
func (cr *ConflictResolver) IsFileConflicted(filePath string) (bool, error) {
	markers, err := cr.GetConflictMarkers(filePath)
	if err != nil {
		return false, err
	}

	return len(markers) > 0, nil
}