sub-cli/internal/sync/sync.go

package sync

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

	"sub-cli/internal/format/lrc"
	"sub-cli/internal/format/srt"
	"sub-cli/internal/model"
)

// SyncLyrics synchronizes the timeline of a source lyrics file with a target lyrics file
func SyncLyrics(sourceFile, targetFile string) error {
	sourceFmt := strings.TrimPrefix(filepath.Ext(sourceFile), ".")
	targetFmt := strings.TrimPrefix(filepath.Ext(targetFile), ".")
	
	// Check for supported format combinations
	if sourceFmt == "lrc" && targetFmt == "lrc" {
		return syncLRCFiles(sourceFile, targetFile)
	} else if sourceFmt == "srt" && targetFmt == "srt" {
		return syncSRTFiles(sourceFile, targetFile)
	} else {
		return fmt.Errorf("sync only supports files of the same format (lrc-to-lrc or srt-to-srt)")
	}
}

// syncLRCFiles synchronizes two LRC files
func syncLRCFiles(sourceFile, targetFile string) error {
	source, err := lrc.Parse(sourceFile)
	if err != nil {
		return fmt.Errorf("error parsing source file: %w", err)
	}
	
	target, err := lrc.Parse(targetFile)
	if err != nil {
		return fmt.Errorf("error parsing target file: %w", err)
	}
	
	// Check if line counts match
	if len(source.Timeline) != len(target.Content) {
		fmt.Printf("Warning: Source timeline (%d entries) and target content (%d entries) have different counts. Timeline will be scaled.\n", 
			len(source.Timeline), len(target.Content))
	}
	
	// Apply timeline from source to target
	syncedLyrics := syncLRCTimeline(source, target)
	
	// Write the synced lyrics to the target file
	return lrc.Generate(syncedLyrics, targetFile)
}

// syncSRTFiles synchronizes two SRT files
func syncSRTFiles(sourceFile, targetFile string) error {
	sourceEntries, err := srt.Parse(sourceFile)
	if err != nil {
		return fmt.Errorf("error parsing source SRT file: %w", err)
	}
	
	targetEntries, err := srt.Parse(targetFile)
	if err != nil {
		return fmt.Errorf("error parsing target SRT file: %w", err)
	}
	
	// Check if entry counts match
	if len(sourceEntries) != len(targetEntries) {
		fmt.Printf("Warning: Source (%d entries) and target (%d entries) have different entry counts. Timeline will be adjusted.\n", 
			len(sourceEntries), len(targetEntries))
	}
	
	// Sync the timelines
	syncedEntries := syncSRTTimeline(sourceEntries, targetEntries)
	
	// Write the synced entries to the target file
	return srt.Generate(syncedEntries, targetFile)
}

// syncLRCTimeline applies the timeline from the source lyrics to the target lyrics
func syncLRCTimeline(source, target model.Lyrics) model.Lyrics {
	result := model.Lyrics{
		Metadata: target.Metadata,
		Content:  target.Content,
	}
	
	// Use source timeline if available and lengths match
	if len(source.Timeline) > 0 && len(source.Timeline) == len(target.Content) {
		result.Timeline = source.Timeline
	} else if len(source.Timeline) > 0 {
		// If lengths don't match, scale timeline
		result.Timeline = scaleTimeline(source.Timeline, len(target.Content))
	}
	
	return result
}

// syncSRTTimeline applies the timing from source SRT entries to target SRT entries
func syncSRTTimeline(sourceEntries, targetEntries []model.SRTEntry) []model.SRTEntry {
	result := make([]model.SRTEntry, len(targetEntries))
	
	// Copy target entries
	copy(result, targetEntries)
	
	// If source and target have the same number of entries, directly apply timings
	if len(sourceEntries) == len(targetEntries) {
		for i := range result {
			result[i].StartTime = sourceEntries[i].StartTime
			result[i].EndTime = sourceEntries[i].EndTime
		}
	} else {
		// If entry counts differ, scale the timing
		for i := range result {
			// Calculate scaled index
			sourceIdx := 0
			if len(sourceEntries) > 1 {
				sourceIdx = i * (len(sourceEntries) - 1) / (len(targetEntries) - 1)
			}
			
			// Ensure the index is within bounds
			if sourceIdx >= len(sourceEntries) {
				sourceIdx = len(sourceEntries) - 1
			}
			
			// Apply the scaled timing
			result[i].StartTime = sourceEntries[sourceIdx].StartTime
			
			// Calculate end time: if not the last entry, use duration from source
			if i < len(result)-1 {
				// If next source entry exists, calculate duration
				var duration model.Timestamp
				if sourceIdx+1 < len(sourceEntries) {
					duration = calculateDuration(sourceEntries[sourceIdx].StartTime, sourceEntries[sourceIdx+1].StartTime)
				} else {
					// If no next source entry, use the source's end time (usually a few seconds after start)
					duration = calculateDuration(sourceEntries[sourceIdx].StartTime, sourceEntries[sourceIdx].EndTime)
				}
				
				// Apply duration to next start time
				result[i].EndTime = addDuration(result[i].StartTime, duration)
			} else {
				// For the last entry, add a fixed duration (e.g., 3 seconds)
				result[i].EndTime = sourceEntries[sourceIdx].EndTime
			}
		}
	}
	
	// Ensure proper sequence numbering
	for i := range result {
		result[i].Number = i + 1
	}
	
	return result
}

// scaleTimeline scales a timeline to match a different number of entries
func scaleTimeline(timeline []model.Timestamp, targetCount int) []model.Timestamp {
	if targetCount <= 0 || len(timeline) == 0 {
		return []model.Timestamp{}
	}
	
	result := make([]model.Timestamp, targetCount)
	
	if targetCount == 1 {
		result[0] = timeline[0]
		return result
	}
	
	sourceLength := len(timeline)
	
	for i := 0; i < targetCount; i++ {
		// Scale index to match source timeline
		sourceIndex := i * (sourceLength - 1) / (targetCount - 1)
		result[i] = timeline[sourceIndex]
	}
	
	return result
}

// calculateDuration calculates the time difference between two timestamps
func calculateDuration(start, end model.Timestamp) model.Timestamp {
	startMillis := start.Hours*3600000 + start.Minutes*60000 + start.Seconds*1000 + start.Milliseconds
	endMillis := end.Hours*3600000 + end.Minutes*60000 + end.Seconds*1000 + end.Milliseconds
	
	durationMillis := endMillis - startMillis
	if durationMillis < 0 {
		durationMillis = 3000 // Default 3 seconds if negative
	}
	
	hours := durationMillis / 3600000
	durationMillis %= 3600000
	minutes := durationMillis / 60000
	durationMillis %= 60000
	seconds := durationMillis / 1000
	milliseconds := durationMillis % 1000
	
	return model.Timestamp{
		Hours:        hours,
		Minutes:      minutes,
		Seconds:      seconds,
		Milliseconds: milliseconds,
	}
}

// addDuration adds a duration to a timestamp
func addDuration(start, duration model.Timestamp) model.Timestamp {
	startMillis := start.Hours*3600000 + start.Minutes*60000 + start.Seconds*1000 + start.Milliseconds
	durationMillis := duration.Hours*3600000 + duration.Minutes*60000 + duration.Seconds*1000 + duration.Milliseconds
	
	totalMillis := startMillis + durationMillis
	
	hours := totalMillis / 3600000
	totalMillis %= 3600000
	minutes := totalMillis / 60000
	totalMillis %= 60000
	seconds := totalMillis / 1000
	milliseconds := totalMillis % 1000
	
	return model.Timestamp{
		Hours:        hours,
		Minutes:      minutes,
		Seconds:      seconds,
		Milliseconds: milliseconds,
	}
}