#!/bin/sh
set -eu

prog="${0##*/}"

usage() {
  cat <<EOF
${prog} - cut and concat video files with ffmpeg

Usage:
  ${prog} [-j | concat] [-o <output>] <file>
  ${prog}  -c | cut    [-o <output>] <file> <start> [<end|duration>]
  ${prog} -h | --help

Concat (default mode):
  Combines all files matching '<base>*.<ext>' into '<base>_combine.<ext>'.
  Examples:
    ${prog} clip_cut.mp4
    ${prog} -j clip_cut.mp4 -o joined.mp4

Cut:
  <start> uses HH:MM:SS (e.g. 00:01:30).
  Third argument is auto-detected:
    contains ':'  -> end position (ffmpeg -to)
    pure number   -> duration in seconds (ffmpeg -t)
    omitted       -> cut to end of video
  Default output: '<base>_cut.<ext>', auto-incremented if it exists.
  Examples:
    ${prog} -c movie.mp4 00:12:30              # 12:30 -> end
    ${prog} -c movie.mp4 00:12:30 00:15:00     # 12:30 -> 15:00
    ${prog} -c movie.mp4 00:12:30 90 -o trim.mp4

Output (-o):
  May appear before or after the file argument.
  If <output> has no extension, the input's extension is appended.
  If the resolved output exists, you'll be asked whether to overwrite;
  declining (default) auto-increments to '<name>_NN.<ext>'. Non-interactive
  runs always auto-increment.
EOF
}

die() {
  printf '%s: %s\n' "$prog" "$1" >&2
  exit 1
}

require_ffmpeg() {
  command -v ffmpeg >/dev/null 2>&1 || die "ffmpeg not found in PATH"
}

# Globals set by resolve_output (avoids subshell variable loss):
#   RESOLVED_OUTPUT - final output path
#   FF_OVERWRITE    - '-y' if user chose overwrite, '' otherwise
RESOLVED_OUTPUT=""
FF_OVERWRITE=""

increment_name() {
  _base="${1%.*}"
  _ext="${1##*.}"
  _n=1
  while [ -e "${_base}_$(printf '%02d' "$_n").${_ext}" ]; do
    _n=$((_n + 1))
  done
  printf '%s_%02d.%s' "$_base" "$_n" "$_ext"
}

# resolve_output <user-output> <default-extension>
# Sets globals RESOLVED_OUTPUT and FF_OVERWRITE. Must run in current shell
# (NOT inside $(...)) to propagate FF_OVERWRITE to the caller.
resolve_output() {
  _out="$1"
  _default_ext="$2"
  FF_OVERWRITE=""

  [ -n "$_out" ] || die "-o requires a non-empty argument"
  case "$_out" in
    */) die "output cannot be a directory: $_out" ;;
    *.*) ;;
    *)   _out="${_out}.${_default_ext}" ;;
  esac

  if [ -e "$_out" ]; then
    if [ -t 0 ] && [ -t 2 ]; then
      printf '%s: %s exists. Overwrite? [y/N] ' "$prog" "$_out" >&2
      _ans=""
      read _ans || _ans=""
      case "$_ans" in
        [yY]|[yY][eE][sS]) FF_OVERWRITE="-y" ;;
        *) _out=$(increment_name "$_out") ;;
      esac
    else
      _out=$(increment_name "$_out")
    fi
  fi
  RESOLVED_OUTPUT="$_out"
}

cmd_concat() {
  require_ffmpeg
  input_file="$1"
  user_output="$2"

  pattern="${input_file%.*}"
  extension="${input_file##*.}"
  [ "$pattern" != "$input_file" ] || die "input file must have an extension: $input_file"

  set +e
  set -- "${pattern}"*."${extension}"
  set -e
  # Unmatched glob remains literal in POSIX sh; check via -e on the first entry.
  if [ ! -e "$1" ]; then
    die "no files match '${pattern}*.${extension}'"
  fi
  if [ $# -eq 1 ]; then
    printf '%s: warning: only one file matches (%s); nothing to concat\n' \
      "$prog" "$1" >&2
    exit 1
  fi

  if [ -n "$user_output" ]; then
    resolve_output "$user_output" "$extension"
    output_file="$RESOLVED_OUTPUT"
  else
    output_file="${pattern}_combine.${extension}"
    FF_OVERWRITE=""
  fi

  file_list=$(mktemp)
  trap 'rm -f "$file_list"' EXIT INT HUP TERM

  for video do
    full_path=$(realpath "$video")
    # concat demuxer: escape single quotes by closing/reopening.
    escaped=$(printf '%s' "$full_path" | sed "s/'/'\\\\''/g")
    printf "file '%s'\n" "$escaped" >>"$file_list"
  done

  count=$#
  set -- ffmpeg -hide_banner
  [ -n "$FF_OVERWRITE" ] && set -- "$@" "$FF_OVERWRITE"
  set -- "$@" -f concat -safe 0 -i "$file_list" -c copy "$output_file"
  "$@"

  printf 'Combined %d files into %s\n' "$count" "$output_file"
}

cmd_cut() {
  require_ffmpeg
  file="$1"
  start="$2"
  end_or_dur="$3"
  user_output="$4"

  [ -f "$file" ] || die "file not found: $file"

  base="${file%.*}"
  ext="${file##*.}"
  [ "$base" != "$file" ] || die "input file must have an extension: $file"

  if [ -n "$user_output" ]; then
    resolve_output "$user_output" "$ext"
    out="$RESOLVED_OUTPUT"
  else
    FF_OVERWRITE=""
    if [ -f "${base}_cut.${ext}" ]; then
      n=1
      while [ -f "${base}_cut_$(printf '%02d' "$n").${ext}" ]; do
        n=$((n + 1))
      done
      out="${base}_cut_$(printf '%02d' "$n").${ext}"
    else
      out="${base}_cut.${ext}"
    fi
  fi

  # -ss / -to / -t go BEFORE -i so they apply as input options against the
  # source's absolute timestamps. Placed after -i, -to/-t use the output's
  # reset timeline and cut for the entire END value instead of START->END.
  set -- ffmpeg -hide_banner
  [ -n "$FF_OVERWRITE" ] && set -- "$@" "$FF_OVERWRITE"
  set -- "$@" -ss "$start"
  if [ -n "$end_or_dur" ]; then
    case "$end_or_dur" in
      *:*)        set -- "$@" -to "$end_or_dur" ;;
      *[!0-9.]*)  die "invalid end/duration: $end_or_dur" ;;
      *)          set -- "$@" -t  "$end_or_dur" ;;
    esac
  fi
  set -- "$@" -i "$file" -c copy "$out"
  "$@"

  printf 'Created %s\n' "$out"
}

# ---- Argument parsing ----

[ $# -eq 0 ] && { usage; exit 0; }

mode_explicit=""
out_override=""

# Rotate args: separate flags from positionals while preserving original order
# of positionals. After the loop, $@ holds positional args only.
i=$#
while [ "$i" -gt 0 ]; do
  arg="$1"
  shift
  i=$((i - 1))
  case "$arg" in
    -h|--help)
      usage; exit 0 ;;
    -j|concat)
      [ -z "$mode_explicit" ] || die "mode specified twice"
      mode_explicit="concat" ;;
    -c|cut)
      [ -z "$mode_explicit" ] || die "mode specified twice"
      mode_explicit="cut" ;;
    -o)
      [ "$i" -gt 0 ] || die "-o requires an argument"
      out_override="$1"
      shift
      i=$((i - 1))
      [ -n "$out_override" ] || die "-o requires a non-empty argument" ;;
    -o=*)
      out_override="${arg#-o=}"
      [ -n "$out_override" ] || die "-o requires a non-empty argument" ;;
    -*)
      die "unknown option: $arg" ;;
    *)
      set -- "$@" "$arg" ;;
  esac
done

if [ -z "$mode_explicit" ]; then
  case $# in
    1)   mode_explicit="concat" ;;
    2|3) mode_explicit="cut" ;;
    *)   usage >&2; exit 1 ;;
  esac
fi

case "$mode_explicit" in
  concat)
    [ $# -eq 1 ] || die "concat takes 1 file argument, got $#"
    cmd_concat "$1" "$out_override"
    ;;
  cut)
    case $# in
      2) cmd_cut "$1" "$2" ""   "$out_override" ;;
      3) cmd_cut "$1" "$2" "$3" "$out_override" ;;
      *) die "cut takes 2 or 3 positional arguments, got $#" ;;
    esac
    ;;
esac