#!/usr/bin/env zsh
# Convert animated PNG to animated WebP. Maximum lossless compression no blend.

setopt LOCAL_OPTIONS ERR_RETURN NO_UNSET PIPE_FAIL

zmodload zsh/zutil
local -a o_help=()
local -a o_delay=()
zparseopts -D -K -- h=o_help -help=o_help -delay:=o_delay
if [[ ${#o_help} -ne 0 || ! -v 2 ]]; then
    local ret=$(( ${#o_help} ^ 1 ))
    print -u $(( 1 + ${ret} )) \
          "usage: ${0} [-h|--help] [--delay MILLISECONDS]" \
          "<INPUT FILE> <OUTPUT FILE>"
    return ${ret}
fi
local input="$(realpath "${1}")"
local output="$(realpath "${2}")"

local tmpdir=$(mktemp --directory --suffix='.apng2webp')
pushd ${tmpdir}

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

local -a webpmux_options=()
local -i counter=1
for file in apngdis/apngframe*.txt; do
    local delay=$(grep -Po '=\d+/' "${file}")
    delay=${delay:1:-1}
    [[ ${#o_delay} -eq 2 ]] && delay=${o_delay[2]}

    webpmux_options+=(-frame $(printf "%02d.webp" ${counter}) +${delay}+0+0+0-b)
    counter+=1
done

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

popd
rm -r ${tmpdir}