onyx-prebootstrap/internal/git/rerere.go

package git

import (
	"crypto/sha1"
	"encoding/hex"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	"github.com/go-git/go-git/v5"
)

// RerereManager manages git rerere (reuse recorded resolution) functionality
type RerereManager struct {
	repo       *git.Repository
	cachePath  string
	enabled    bool
	repoPath   string
	conflictResolver *ConflictResolver
}

// NewRerereManager creates a new RerereManager instance
func NewRerereManager(repo *git.Repository, onyxPath, repoPath string) *RerereManager {
	cachePath := filepath.Join(onyxPath, "rerere_cache")

	return &RerereManager{
		repo:             repo,
		cachePath:        cachePath,
		enabled:          true,
		repoPath:         repoPath,
		conflictResolver: NewConflictResolver(repo, repoPath),
	}
}

// Enable enables rerere functionality
func (rm *RerereManager) Enable() {
	rm.enabled = true
}

// Disable disables rerere functionality
func (rm *RerereManager) Disable() {
	rm.enabled = false
}

// IsEnabled returns whether rerere is enabled
func (rm *RerereManager) IsEnabled() bool {
	return rm.enabled
}

// RecordConflicts records current conflicts for future resolution
func (rm *RerereManager) RecordConflicts() error {
	if !rm.enabled {
		return nil
	}

	conflicts, err := rm.conflictResolver.DetectConflicts()
	if err != nil {
		return fmt.Errorf("failed to detect conflicts: %w", err)
	}

	if len(conflicts) == 0 {
		return nil
	}

	// For each conflict, create a cache entry
	for _, conflict := range conflicts {
		if err := rm.recordConflict(conflict); err != nil {
			// Log error but continue with other conflicts
			fmt.Fprintf(os.Stderr, "Warning: failed to record conflict for %s: %v\n", conflict.FilePath, err)
		}
	}

	return nil
}

// recordConflict records a single conflict
func (rm *RerereManager) recordConflict(conflict ConflictInfo) error {
	// Read the conflicted file
	fullPath := filepath.Join(rm.repoPath, conflict.FilePath)
	content, err := os.ReadFile(fullPath)
	if err != nil {
		return fmt.Errorf("failed to read conflicted file: %w", err)
	}

	// Generate a unique ID for this conflict pattern
	conflictID := rm.generateConflictID(content)

	// Create cache directory for this conflict
	conflictDir := filepath.Join(rm.cachePath, conflictID)
	if err := os.MkdirAll(conflictDir, 0755); err != nil {
		return fmt.Errorf("failed to create conflict cache directory: %w", err)
	}

	// Save the preimage (conflict state)
	preimagePath := filepath.Join(conflictDir, "preimage")
	if err := os.WriteFile(preimagePath, content, 0644); err != nil {
		return fmt.Errorf("failed to write preimage: %w", err)
	}

	// Save metadata
	metadataPath := filepath.Join(conflictDir, "metadata")
	metadata := fmt.Sprintf("file=%s\nbase=%s\nours=%s\ntheirs=%s\n",
		conflict.FilePath, conflict.BaseHash, conflict.OursHash, conflict.TheirsHash)
	if err := os.WriteFile(metadataPath, []byte(metadata), 0644); err != nil {
		return fmt.Errorf("failed to write metadata: %w", err)
	}

	return nil
}

// RecordResolution records the resolution for previously recorded conflicts
func (rm *RerereManager) RecordResolution() error {
	if !rm.enabled {
		return nil
	}

	// Find all recorded conflicts
	entries, err := os.ReadDir(rm.cachePath)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return fmt.Errorf("failed to read rerere cache: %w", err)
	}

	for _, entry := range entries {
		if !entry.IsDir() {
			continue
		}

		conflictID := entry.Name()
		if err := rm.recordResolutionForConflict(conflictID); err != nil {
			// Log error but continue
			fmt.Fprintf(os.Stderr, "Warning: failed to record resolution for %s: %v\n", conflictID, err)
		}
	}

	return nil
}

// recordResolutionForConflict records the resolution for a specific conflict
func (rm *RerereManager) recordResolutionForConflict(conflictID string) error {
	conflictDir := filepath.Join(rm.cachePath, conflictID)

	// Read metadata to get file path
	metadataPath := filepath.Join(conflictDir, "metadata")
	metadataContent, err := os.ReadFile(metadataPath)
	if err != nil {
		return fmt.Errorf("failed to read metadata: %w", err)
	}

	// Parse file path from metadata
	filePath := ""
	for _, line := range strings.Split(string(metadataContent), "\n") {
		if strings.HasPrefix(line, "file=") {
			filePath = strings.TrimPrefix(line, "file=")
			break
		}
	}

	if filePath == "" {
		return fmt.Errorf("file path not found in metadata")
	}

	// Check if file still has conflicts
	fullPath := filepath.Join(rm.repoPath, filePath)
	if _, err := os.Stat(fullPath); os.IsNotExist(err) {
		// File was deleted or doesn't exist, skip
		return nil
	}

	hasConflicts, err := rm.conflictResolver.IsFileConflicted(filePath)
	if err != nil {
		return fmt.Errorf("failed to check if file is conflicted: %w", err)
	}

	if hasConflicts {
		// Still has conflicts, not resolved yet
		return nil
	}

	// Read the resolved content
	resolvedContent, err := os.ReadFile(fullPath)
	if err != nil {
		return fmt.Errorf("failed to read resolved file: %w", err)
	}

	// Save the postimage (resolved state)
	postimagePath := filepath.Join(conflictDir, "postimage")
	if err := os.WriteFile(postimagePath, resolvedContent, 0644); err != nil {
		return fmt.Errorf("failed to write postimage: %w", err)
	}

	return nil
}

// ApplyResolutions applies previously recorded resolutions to current conflicts
func (rm *RerereManager) ApplyResolutions() (int, error) {
	if !rm.enabled {
		return 0, nil
	}

	conflicts, err := rm.conflictResolver.DetectConflicts()
	if err != nil {
		return 0, fmt.Errorf("failed to detect conflicts: %w", err)
	}

	appliedCount := 0

	for _, conflict := range conflicts {
		// Read the conflicted file
		fullPath := filepath.Join(rm.repoPath, conflict.FilePath)
		content, err := os.ReadFile(fullPath)
		if err != nil {
			continue
		}

		// Generate conflict ID
		conflictID := rm.generateConflictID(content)

		// Check if we have a resolution for this conflict
		postimagePath := filepath.Join(rm.cachePath, conflictID, "postimage")
		if _, err := os.Stat(postimagePath); os.IsNotExist(err) {
			continue
		}

		// Apply the resolution
		resolvedContent, err := os.ReadFile(postimagePath)
		if err != nil {
			continue
		}

		if err := os.WriteFile(fullPath, resolvedContent, 0644); err != nil {
			continue
		}

		appliedCount++
	}

	return appliedCount, nil
}

// generateConflictID generates a unique ID for a conflict pattern
func (rm *RerereManager) generateConflictID(content []byte) string {
	// Normalize conflict content by removing variable parts
	normalized := rm.normalizeConflict(content)

	// Generate SHA1 hash
	hash := sha1.New()
	io.WriteString(hash, normalized)
	return hex.EncodeToString(hash.Sum(nil))
}

// normalizeConflict normalizes conflict content for matching
func (rm *RerereManager) normalizeConflict(content []byte) string {
	// Convert to string
	str := string(content)

	// Remove commit hashes from conflict markers (they vary)
	lines := strings.Split(str, "\n")
	var normalized []string

	for _, line := range lines {
		if strings.HasPrefix(line, "<<<<<<<") {
			normalized = append(normalized, "<<<<<<<")
		} else if strings.HasPrefix(line, ">>>>>>>") {
			normalized = append(normalized, ">>>>>>>")
		} else {
			normalized = append(normalized, line)
		}
	}

	return strings.Join(normalized, "\n")
}

// ClearCache clears the rerere cache
func (rm *RerereManager) ClearCache() error {
	return os.RemoveAll(rm.cachePath)
}

// GetCachePath returns the path to the rerere cache
func (rm *RerereManager) GetCachePath() string {
	return rm.cachePath
}