#!/usr/bin/env bash

MAX_MB=10

usage() {
    cat <<'EOF'
Usage: shrink [-s MB] <input> [output]

Compress a video to a target file size using two-pass x264 encoding.

Options:
  -s MB         Target file size in MB (default: 10)
  -h            Show this help

If output is omitted, saves to <input>-shrunk.mp4.
EOF
    exit 0
}

while getopts ":s:h" opt; do
    case $opt in
        s) MAX_MB=$OPTARG ;;
        h) usage ;;
        :) echo "Option -$OPTARG requires an argument" >&2; exit 1 ;;
        *) usage ;;
    esac
done
shift $((OPTIND - 1))

input=${1:?Usage: shrink [-s MB] <input> [output]}
output=${2:-${input%.mp4}-shrunk.mp4}

[[ -f $input ]] || { echo "File not found: $input" >&2; exit 1; }

file_bytes=$(stat -c%s "$input")
max_bytes=$((MAX_MB * 1048576))
file_mb=$(awk "BEGIN {printf \"%.1f\", $file_bytes / 1048576}")

if [[ $file_bytes -le $max_bytes ]]; then
    echo "Already ${file_mb}MB (under ${MAX_MB}MB), nothing to do"
    exit 0
fi

duration=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$input")
audio_bitrate=128
video_bitrate=$(awk "BEGIN {v = ($MAX_MB * 8192 / $duration) - $audio_bitrate; printf \"%d\", (v > 0 ? v : 1)}")

echo "Compressing ${file_mb}MB → ${MAX_MB}MB target..."
echo "  Pass 1/2 (video: ${video_bitrate}kbps)..."
ffmpeg -y -i "$input" -c:v libx264 -b:v "${video_bitrate}k" -pass 1 -an -f null /dev/null 2>/dev/null
echo "  Pass 2/2..."
ffmpeg -y -i "$input" -c:v libx264 -b:v "${video_bitrate}k" -pass 2 -c:a aac -b:a "${audio_bitrate}k" "$output" 2>/dev/null
rm -f ffmpeg2pass-0.log ffmpeg2pass-0.log.mbtree

final_mb=$(awk "BEGIN {printf \"%.1f\", $(stat -c%s "$output") / 1048576}")
echo "Done: ${file_mb}MB → ${final_mb}MB → $output"