#!/usr/bin/env bash

set -euo pipefail

INPUT_DIR=""
OUTPUT_DIR="./video_chunks"
CHUNK_DURATION=60
MIN_SOURCE_DURATION=1
MIN_CHUNK_DURATION=2

usage() {
  cat <<'EOF'
Usage: ./split_video.sh -i INPUT_DIR [-o OUTPUT_DIR] [-d CHUNK_DURATION]

Split videos into fixed-duration chunks for XVBench-style video evidence.

Options:
  -i INPUT_DIR        Directory containing source videos.
  -o OUTPUT_DIR       Directory for output clips. Default: ./video_chunks
  -d CHUNK_DURATION   Clip duration in seconds. Default: 60
  -h                  Show this help message.
EOF
}

check_dependencies() {
  command -v ffmpeg >/dev/null 2>&1 || { echo "ffmpeg is required." >&2; exit 1; }
  command -v ffprobe >/dev/null 2>&1 || { echo "ffprobe is required." >&2; exit 1; }
}

duration_seconds() {
  ffprobe -v error -show_entries format=duration \
    -of default=noprint_wrappers=1:nokey=1 "$1" 2>/dev/null || echo "0"
}

float_lt() {
  awk -v a="$1" -v b="$2" 'BEGIN { exit !(a < b) }'
}

float_add() {
  awk -v a="$1" -v b="$2" 'BEGIN { printf "%.3f", a + b }'
}

parse_args() {
  while getopts ":i:o:d:h" opt; do
    case "$opt" in
      i) INPUT_DIR="$OPTARG" ;;
      o) OUTPUT_DIR="$OPTARG" ;;
      d) CHUNK_DURATION="$OPTARG" ;;
      h) usage; exit 0 ;;
      *) usage; exit 1 ;;
    esac
  done

  if [[ -z "$INPUT_DIR" || ! -d "$INPUT_DIR" ]]; then
    echo "A valid input directory is required. Use -i INPUT_DIR." >&2
    exit 1
  fi

  if ! [[ "$CHUNK_DURATION" =~ ^[0-9]+$ ]] || [[ "$CHUNK_DURATION" -le 0 ]]; then
    echo "CHUNK_DURATION must be a positive integer." >&2
    exit 1
  fi
}

split_one_video() {
  local input_file="$1"
  local filename extension base_name total_duration process_file temp_mp4
  local start_time=0
  local chunk_index=1

  filename=$(basename "$input_file")
  extension="${filename##*.}"
  extension=$(echo "$extension" | tr '[:upper:]' '[:lower:]')
  base_name="${filename%.*}"
  temp_mp4=""

  total_duration=$(duration_seconds "$input_file")
  if [[ -z "$total_duration" || "$total_duration" == "0" ]] || float_lt "$total_duration" "$MIN_SOURCE_DURATION"; then
    echo "Skip invalid or too-short video: $filename" >&2
    return 1
  fi

  if [[ "$extension" != "mp4" ]]; then
    temp_mp4="${OUTPUT_DIR}/.tmp_${base_name}_$$.mp4"
    if ! ffmpeg -i "$input_file" -c:v libx264 -c:a aac -strict experimental \
      "$temp_mp4" -y -loglevel error; then
      rm -f "$temp_mp4"
      echo "Failed to convert video: $filename" >&2
      return 1
    fi
    process_file="$temp_mp4"
  else
    process_file="$input_file"
  fi

  while float_lt "$start_time" "$total_duration"; do
    local output_file chunk_duration
    output_file="${OUTPUT_DIR}/${base_name}_____${chunk_index}.mp4"

    if ffmpeg -i "$process_file" -ss "$start_time" -t "$CHUNK_DURATION" \
      -c copy "$output_file" -y -loglevel error; then
      chunk_duration=$(duration_seconds "$output_file")
      if [[ -z "$chunk_duration" ]] || float_lt "$chunk_duration" "$MIN_CHUNK_DURATION"; then
        rm -f "$output_file"
      fi
    else
      rm -f "$output_file"
      echo "Failed to create chunk: $output_file" >&2
    fi

    start_time=$(float_add "$start_time" "$CHUNK_DURATION")
    chunk_index=$((chunk_index + 1))
  done

  [[ -n "$temp_mp4" && -f "$temp_mp4" ]] && rm -f "$temp_mp4"
}

main() {
  parse_args "$@"
  check_dependencies
  mkdir -p "$OUTPUT_DIR"

  while IFS= read -r -d '' input_file; do
    local filename
    filename=$(basename "$input_file")
    if [[ "$filename" =~ _____[0-9]+\.mp4$ ]]; then
      continue
    fi
    split_one_video "$input_file" || true
  done < <(find "$INPUT_DIR" -maxdepth 1 -type f \( \
    -iname "*.mp4" -o -iname "*.avi" -o -iname "*.mkv" -o \
    -iname "*.mov" -o -iname "*.wmv" -o -iname "*.flv" -o \
    -iname "*.webm" \) -print0)
}

main "$@"