#!/bin/bash

# Exit immediately if a command exits with a non-zero status.
set -e

# Function to display informational messages in blue
echo_info() {
    echo -e "\033[1;34m[INFO]\033[0m $1"
}

# Function to display error messages in red
echo_error() {
    echo -e "\033[1;31m[ERROR]\033[0m $1"
}

# Function to display usage instructions
usage() {
    echo "Usage: $0 <segments_directory>"
    echo "Example: $0 606-short_segments"
    exit 1
}

# Check if exactly one argument is provided
if [ "$#" -ne 1 ]; then
    echo_error "Incorrect number of arguments."
    usage
fi

# Assign the first argument to SEGMENTS_DIR
SEGMENTS_DIR="$1"

# Resolve the absolute path of SEGMENTS_DIR
SEGMENTS_DIR=$(realpath "$SEGMENTS_DIR")

# Check if the provided argument is a directory
if [ ! -d "$SEGMENTS_DIR" ]; then
    echo_error "The provided path '$SEGMENTS_DIR' is not a directory or does not exist."
    exit 1
fi

echo_info "Segments directory set to: $SEGMENTS_DIR"


# Check if ffmpeg is installed
if ! command -v ffmpeg &> /dev/null; then
    echo_error "ffmpeg could not be found. Please install ffmpeg and ensure it's in your PATH."
    exit 1
fi

# Create a temporary file to store the list of videos to concatenate
concat_list=$(mktemp)

# Ensure the temporary file is deleted on script exit
trap "rm -f $concat_list" EXIT

# Iterate over each segment directory within SEGMENTS_DIR in sorted order
# Assuming segments are named as segment_1, segment_2, etc.
for segment_dir in "$SEGMENTS_DIR"/segment_*; do
    if [ -d "$segment_dir" ]; then
        segment_name=$(basename "$segment_dir")
        echo_info "Processing segment: $segment_name"

        # Define the path to output-matted.mp4
        output_matted="$segment_dir/output-matted.mp4"

        # Check if output-matted.mp4 exists
        if [ ! -f "$output_matted" ]; then
            echo_error "  '$output_matted' does not exist. Skipping this segment."
            continue
        fi

        # Append the file path to the concat list in the required format
        echo "file '$output_matted'" >> "$concat_list"
        echo_info "  Added '$output_matted' to the concatenation list."


    else
        echo_error "'$segment_dir' is not a directory. Skipping."
    fi
done


# Check if the concat list has at least one file
if [ ! -s "$concat_list" ]; then
    echo_error "No 'output-matted.mp4' files found in the provided segments directory."
    exit 1

fi


echo_info "Starting concatenation of videos..."

# Define the output file path
output_full="full_output_matted.mp4"

# Execute ffmpeg to concatenate videos using the concat demuxer
ffmpeg -f concat -safe 0 -i "$concat_list" -c copy "$output_full" \
    && echo_info "Successfully created '$output_full' in $(pwd)"

echo_info "Concatenation process completed."