#!/bin/bash

input="$1"
output="$2"
target_size_raw="$3"

if [[ -z "$input" || -z "$output" || -z "$target_size_raw" ]]; then
    echo "Usage: $0 input output.jpg <target size>"
    exit 1
fi

parse_size() {
    local size="$1"

    size=$(echo "$size" | tr '[:lower:]' '[:upper:]' | tr -d ' ')

    if [[ "$size" =~ ^([0-9]+(\.[0-9]+)?)(B|KB|MB)?$ ]]; then
        value="${BASH_REMATCH[1]}"
        unit="${BASH_REMATCH[3]}"

        case "$unit" in
            ""|"B") multiplier=1 ;;
            "KB") multiplier=1024 ;;
            "MB") multiplier=$((1024 * 1024)) ;;
            *) echo "Invalid size unit: $unit"; exit 1 ;;
        esac

        awk "BEGIN {printf \"%d\", $value * $multiplier}"
    else
        echo "Invalid size format: $size"
        exit 1
    fi
}

target_size=$(parse_size "$target_size_raw")

compress_and_get_size() {
    local q=$1
    magick "$work" -strip -interlace Plane -quality "$q" "$output"
    stat -c%s "$output"
}


work=$(mktemp --suffix=.jpg)
cp "$input" "$work"

magick "$input" \
    -auto-orient \
    -colorspace sRGB \
    -strip \
    -background white -alpha remove -alpha off \
    "$work"

echo "Trying to fit below $target_size bytes"

while true; do

    # Binary search
    low=1
    high=95
    best_q=1

    while (( low <= high )); do
        mid=$(((low + high) / 2))
        size=$(compress_and_get_size "$mid")

        echo "    Quality $mid -> $size bytes"

        best_size=$size

        if (( size <= target_size )); then
            best_q=$mid
            low=$((mid + 1))
        else
            high=$((mid - 1))
        fi
    done

    echo "Best quality this round: $best_q ($best_size bytes)"

    if (( best_size <= target_size )); then
        echo "DONE: $output is $best_size bytes"
        break
    fi

    echo "  Reducing resolution"
    tmp=$(mktemp --suffix=.jpg)

    magick "$work" -resize 75% -quality 85 "$tmp"
    mv "$tmp" "$work"
done

rm -f "$work"