#!/bin/sh -eu
WIDTH=800

usage() { echo "usage: ${0##*/} <src> [<dst>]" >&2 && exit 1; }
check_first_arg() { if test -z "$1"; then usage; fi; }
dry_run_if_no_dst() { if test -z "$2"; then dry_run "$1" && return 1; fi; }
dry_run() { sed 's,\.[^./]*_$,\.png,;s,^'"$1"/',,' && echo "$HTML"; }
trim_() { sed 's,^'"$1"/',,'; }
stat_() { 
	s_src=$(stat -f'%z' "$SRC/$2")
	s_dst=$(stat -f'%z' "$DST/$3")
	echo 'sh stat   '"${1#"$SRC/"}"' > '"$3"' '"$s_src"' -> '"$s_dst"; 
}

find_() { find "$1" -type f \
	\( -name '*.jpg_' -o -name '*.png_' -o -name '*.gif_' \); }

html_head() { echo '<link rel="stylesheet" href="/style.css" /><p>'; }
html_img() { echo '<img src="'"$1"'"><br>'; }
html_p() { echo '<p>'"$1"; }

magick_cmd() { if command -v magick \
	>/dev/null 2>&1; then echo 'magick'; else echo 'convert'; fi; }

magick_() { "$(magick_cmd)" "$SRC/$1" \
	-resize "${WIDTH}x"\> \
	-ordered-dither 4x4 \
	-colors 8 PNG8:"$DST/$2"; }

write_png() {
	out="${1%.*_}.png"
	mkdir -p "$(dirname "$DST/$out")"
	magick_ "$1" "$out"
	pngquant --strip --force --ext .png "$DST/$out"
	echo "$out"
	stat_ "$0" "$1" "$out" >&2
}

generate() { while read -r f; do write_png "$f"; done; }
size() { while read -r f; do stat -f'%z' "$DST/$f"; done; }
sum() { (echo 0 && sed 's/^/ + /') | tr -d '\n' | bc; }

html_imgs() { echo "$1" | while read -r f; do html_img "$f"; done; }
write_html() { (html_head && html_imgs "$1" &&
	html_p "$2") >"$DST/$HTML" && echo "$HTML"; }

main() {
	check_first_arg "$@"
	SRC="$1"
	HTML='.ssg.imgs.html'
	imgs=$(find_ "$SRC")

	echo "$imgs" | dry_run_if_no_dst "$@" || exit 1
	DST="$2"

	files=$(echo "$imgs" | trim_ "$SRC" | generate)
	echo "$files"

	total_size=$(echo "$files" | size | sum)
	write_html "$files" "$total_size"
}

main "$@"