#!/bin/bash

# Check if ffmpeg is installed
if ! command -v ffmpeg &> /dev/null; then
    echo "Error: ffmpeg is not installed. Install ffmpeg to use this script."
    exit 1
fi

# Check if directory argument is provided
if [ -z "$1" ]; then
    echo "Usage: $0 <directory> [--dry-run]"
    exit 1
fi

dir="$1"
dry_run=false

# Check for --dry-run option
if [[ "$2" == "--dry-run" ]]; then
    dry_run=true
fi

# Find all .mkv files recursively
find "$dir" -type f -name "*.mkv" | while read -r file; do
    echo "Processing: $file"
    
    # Get subtitle stream indices with language "jpn"
    mapfile -t subtitle_streams < <(ffprobe -loglevel error -select_streams s -show_entries stream=index:stream_tags=language -of csv=p=0 "$file" | awk -F, '$2 == "jpn" {print NR-1, $1}')
    
    if [[ ${#subtitle_streams[@]} -eq 0 ]]; then
        echo "No Japanese subtitle tracks found in $file. Skipping..."
        continue
    fi
    
    # Temporary output file
    output_file="${file%.mkv}_modified.mkv"
    
    # Build ffmpeg metadata arguments
    ffmpeg_args=()
    for stream_info in "${subtitle_streams[@]}"; do
        read -r stream_index track_id <<< "$stream_info"
        echo "Changing subtitle track ID $track_id (subtitle index $stream_index) to English in $file"
        ffmpeg_args+=("-metadata:s:s:$stream_index" "language=eng")
    done
    
    # Print the command if dry-run is enabled
    echo "ffmpeg -i \"$file\" -map 0 -c copy \"${ffmpeg_args[@]}\" \"$output_file\""
    
    if [ "$dry_run" = false ]; then
        ffmpeg -i "$file" -map 0 -c copy "${ffmpeg_args[@]}" "$output_file" && mv "$output_file" "$file"
    fi
    
    echo "Finished processing: $file"

done

echo "All done!"