#!/bin/bash
# Convert animated PNG to animated WebP. Maximum compression no blend.

set -euo pipefail

if [[ $# -lt 2 ]]; then
    echo "Usage: ${0} input.png output.webp" >&2
    exit 1
fi
input="$(realpath "${1}")"
output="$(realpath "${2}")"

mkdir -p apng2webp_work
pushd apng2webp_work

mkdir -p apngdis
pushd apngdis
cp "${input}" "input.png"
apngdis "input.png"
popd

counter=1
for file in apngdis/apngframe*.png; do
    cwebp -lossless -q 100 "${file}" -o "$(printf "%02d" ${counter}).webp"
    counter=$((counter+1))
done

webpmux_options=""
counter=1
for file in apngdis/apngframe*.txt; do
    delay=$(grep -Po '=\d+/' "${file}")
    delay="${delay:1:-1}"
    webpmux_options="${webpmux_options} -frame $(printf "%02d" ${counter}).webp +${delay}+0+0+0-b"
    counter=$((counter+1))
done

# shellcheck disable=2086
webpmux ${webpmux_options} -o "${output}"

popd
rm -r apng2webp_work