#!/bin/bash

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

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

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"