#!/usr/bin/env bash
# make-icon-pack.sh: one logo in, the whole favicon / app-icon / OG pack out.
#
#   bash make-icon-pack.sh <logo.(png|svg|jpg)> <out-dir> <plate-hex> [og-hex]
#
#   <logo>       square-ish, 1024px or more on the long edge, transparent ground preferred
#   <plate-hex>  the OPAQUE brand colour placed behind apple-touch-icon, the maskable
#                icons and the OG image. Those three may not carry alpha.
#   [og-hex]     optional separate ground for the 1200x630 share image.
#
# Requires ImageMagick 7. Nothing else. No node, no npm, no online generator.
#
# Written by J.A. Watte for the Agent Site Standards Kit: https://jwatte.com/downloads/
# Free to copy, adapt and ship. Every trap in the comments below cost real time to find.
#
# ---------------------------------------------------------------------------
# TRAP 1: on Windows, `convert` is C:\Windows\system32\convert.exe, the
#         FAT-to-NTFS volume converter. Every command here starts with `magick`.
# TRAP 2: `magick identify -format` emits NO trailing newline, so `read` returns
#         1 and `set -e` kills the script on the first line. Always append \n.
# TRAP 3: on Windows that \n comes out as CRLF, so the last field carries \r and
#         every string comparison fails silently. Always pipe through tr -d '\r'.
# TRAP 4: -format honours \n only. It has no \t and no printf width specifiers
#         ('%-26f' prints the literal "26f"). Use a separator and column -t.
# ---------------------------------------------------------------------------
set -euo pipefail

SRC="${1:?usage: make-icon-pack.sh <logo> <out-dir> <plate-hex> [og-hex]}"
OUT="${2:?output directory required}"
BG="${3:-#ffffff}"
OGBG="${4:-$BG}"
FUZZ="${FUZZ:-12%}"          # tolerance when trimming a flat plate off the mark

mkdir -p "$OUT"
M="$OUT/_master.png"
K="$OUT/_mark.png"

# --------------------------------------------------------------- 0. GUARD
# Refuse silently-wrong sources: a JPEG named .png, or anything under 512px.
# A 357x200 JPEG shipped as an app icon is the single most common version of
# this mistake, and nothing downstream complains about it.
read -r SW SH SFMT < <(magick identify -format '%w %h %m\n' "$SRC" | tr -d '\r')
echo "source: $SRC  ${SW}x${SH}  $SFMT"
[ "$SFMT" = "JPEG" ] && echo "!! WARNING: source is JPEG-encoded: no alpha, ringing at 16px." >&2
if [ "$SW" -lt 512 ] || [ "$SH" -lt 512 ]; then
  echo "!! WARNING: source under 512px: every icon below is an upscale." >&2
fi

# -------------------------------------------------------------- 1. MASTER
# Rasterise ONCE at 1024, square-padded, 8-bit sRGB. Everything else resizes
# from this, so any source-format weirdness is dealt with exactly once.
# -density matters only for SVG input; librsvg is built into ImageMagick 7.
# An SVG's viewBox drives its raster size, so without -density a 100x100
# viewBox rasterises to 100x100 and every icon is a blurry upscale.
magick -background none -density 384 "$SRC" \
  -colorspace sRGB -alpha on \
  -resize 1024x1024 -gravity center -extent 1024x1024 \
  -depth 8 -strip "PNG32:$M"

# The MARK is the artwork's true bounding box, used only by the maskable step.
# A transparent source trims on alpha. A source with a flat opaque plate needs
# -fuzz, or -trim returns the whole canvas and the maskable icon ends up being
# a shrunken screenshot of the plate instead of the mark.
magick -background none "$SRC" -fuzz "$FUZZ" -trim +repage \
  -colorspace sRGB -depth 8 "PNG32:$K"
read -r KW KH < <(magick identify -format '%w %h\n' "$K" | tr -d '\r')
echo "mark bbox: ${KW}x${KH}"

# ---------------------------------------------------------- 2. favicon.svg
# If the source IS an SVG, ship it byte for byte. Never retrace a raster.
# If it is not, you have no SVG favicon, and that is fine: the .ico covers it.
case "${SRC,,}" in *.svg) cp "$SRC" "$OUT/favicon.svg" ;; esac

# --------------------------------------------------------- 3. PNG favicons
magick "$M" -resize 16x16 -depth 8 -strip "PNG32:$OUT/favicon-16.png"
magick "$M" -resize 32x32 -depth 8 -strip "PNG32:$OUT/favicon-32.png"

# ------------------------------------------------------ 4. multi-frame ICO
# One command, three frames. 48/32/16 lands at about 15 KB regardless of the
# artwork, because ICO frames are uncompressed BMP. Adding a 256 frame costs
# roughly 270 KB on its own: never include one.
magick "$M" -background none -define icon:auto-resize=48,32,16 "$OUT/favicon.ico"

# ------------------------------------------------ 5. apple-touch-icon, 180
# MUST be opaque: iOS composites alpha onto black. iOS also applies its own
# rounded mask and gloss, so ship a square with no corner radius of your own.
# Art at 80% leaves the breathing room the mask expects.
magick "$M" -resize 144x144 \
  -background "$BG" -gravity center -extent 180x180 \
  -alpha remove -alpha off -depth 8 -strip "PNG24:$OUT/apple-touch-icon.png"

# ---------------------------------------------------- 6. PWA purpose: any
# Full bleed, alpha kept. These are the two Chrome checks installability on.
magick "$M" -resize 192x192 -depth 8 -strip "PNG32:$OUT/icon-192.png"
magick "$M" -resize 512x512 -depth 8 -strip "PNG32:$OUT/icon-512.png"

# ----------------------------------------------- 7. PWA purpose: maskable
# The W3C safe zone is a CIRCLE whose radius is 2/5 of the icon size: 409.6px
# across at 512. So the mark's DIAGONAL, not its width, is what has to fit:
#   scale = (0.8 * S) / hypot(w, h)
# An "80% square box" is a different, wrong calculation that clips wide marks.
# A maskable icon is a DIFFERENT FILE from the purpose:any icon. Declaring
# "purpose": "maskable" on the full-bleed file is the most common PWA icon bug
# and it is invisible until somebody installs the app on a circular-mask launcher.
for S in 512 192; do
  NW=$(magick identify -format "%[fx:int(w*($S*0.8)/hypot(w,h))]" "$K" | tr -d '\r')
  NH=$(magick identify -format "%[fx:int(h*($S*0.8)/hypot(w,h))]" "$K" | tr -d '\r')
  magick "$K" -resize "${NW}x${NH}" \
    -background "$BG" -gravity center -extent "${S}x${S}" \
    -alpha remove -alpha off -depth 8 -strip "PNG24:$OUT/icon-maskable-$S.png"
  echo "maskable $S: mark fitted to ${NW}x${NH} inside a safe circle of $(awk -v s=$S 'BEGIN{print s*0.8}')px"
done

# ------------------------------------------------------- 8. OG share image
# Exactly 1200x630, which is 1.90476:1. Opaque, because Slack, LinkedIn and X
# flatten alpha to black. Never declare og:image:width/height your file does
# not actually have: the platform crops to the ratio it was promised.
# Composite the MARK, not the square master: dropping a square that carries its
# own ground onto a flat canvas leaves a visible seam wherever the two darks
# disagree by a shade, and you will not see it until somebody shares the link.
magick -size 1200x630 "canvas:$OGBG" \
  \( "$K" -resize 720x360 \) -gravity center -composite \
  -alpha remove -alpha off -depth 8 -strip "PNG24:$OUT/og-image.png"
magick "$OUT/og-image.png" -quality 82 -define webp:method=6 "$OUT/og-image.webp"

rm -f "$M" "$K"

# --------------------------------------------------------------- 9. GATES
# Three assertions. If any of them is not what it says below, do not ship.
echo; echo "=== INVENTORY ==="
magick identify -format '%f|%wx%h|%m|alpha=%A|depth=%z|%B bytes\n' \
  "$OUT"/*.png "$OUT"/*.webp 2>/dev/null | column -t -s '|'
echo "--- favicon.ico frames (expect 48, 32, 16) ---"
magick identify "$OUT/favicon.ico"

echo "--- GATE 1: opacity. apple-touch, both maskables and og MUST read 1 ---"
FAIL=0
for f in apple-touch-icon.png icon-maskable-512.png icon-maskable-192.png og-image.png; do
  A=$(magick "$OUT/$f" -alpha extract -format '%[fx:mean]' info: | tr -d '\r')
  printf '%s mean-alpha=%s\n' "$f" "$A"
  [ "$A" = "1" ] || { echo "   ^^ FAIL: carries transparency"; FAIL=1; }
done

echo "--- GATE 2: maskable safe circle. Expect 0 px outside ---"
magick -size 512x512 xc:black -fill white -draw "circle 256,256 256,51.2" \
  -alpha off -colorspace Gray "$OUT/_c.png"
magick "$OUT/_c.png" -negate -alpha off "$OUT/_o.png"
magick "$OUT/icon-maskable-512.png" -fill white -opaque "$BG" -negate \
  -threshold 1% -alpha off -colorspace Gray "$OUT/_m.png"
magick "$OUT/_m.png" "$OUT/_o.png" -compose multiply -composite \
  -alpha off -colorspace Gray "$OUT/_x.png"
OUTSIDE=$(magick identify -format '%[fx:int(mean*w*h)]' "$OUT/_x.png" | tr -d '\r')
echo "mark px outside safe circle: $OUTSIDE"
[ "$OUTSIDE" = "0" ] || { echo "   ^^ FAIL: the launcher mask will cut the mark"; FAIL=1; }
rm -f "$OUT"/_c.png "$OUT"/_o.png "$OUT"/_m.png "$OUT"/_x.png

echo "--- GATE 3: og-image is exactly 1200x630 ---"
OGDIM=$(magick identify -format '%wx%h\n' "$OUT/og-image.png" | tr -d '\r')
echo "og-image.png $OGDIM"
[ "$OGDIM" = "1200x630" ] || { echo "   ^^ FAIL"; FAIL=1; }

echo
if [ "$FAIL" -eq 0 ]; then
  echo "ALL GATES PASSED."
else
  echo "GATES FAILED: do not ship this pack."; exit 1
fi

cat <<'HEAD'

Head block to paste (adjust paths to where you put the files):

  <meta name="theme-color" content="#f1f0eb" media="(prefers-color-scheme: light)">
  <meta name="theme-color" content="#141420" media="(prefers-color-scheme: dark)">
  <link rel="icon" href="/favicon.ico" sizes="any">
  <link rel="icon" href="/favicon.svg" type="image/svg+xml">
  <link rel="icon" href="/favicon-32.png" type="image/png" sizes="32x32">
  <link rel="icon" href="/favicon-16.png" type="image/png" sizes="16x16">
  <link rel="apple-touch-icon" href="/apple-touch-icon.png">
  <link rel="manifest" href="/site.webmanifest">

Do NOT emit rel="shortcut icon" (non-conforming) or rel="mask-icon" (obsolete
since Safari 12 uses the regular favicon for pinned tabs). Do NOT list the
512px raster as a <link rel="icon">: no browser picks a 512 for a 16px tab.
HEAD