#!/usr/bin/env bash
# ash-wallpaper.sh — turn a color photo into Ash-palette wallpapers:
# grayscale body tinted toward the Ash tones, with warm "ember" highlights
# (reds/oranges/golds) selectively preserved. Pleasantville-style.
#
# usage: tools/ash-wallpaper.sh INPUT [OUTBASE]
#
# By default BOTH variants are rendered:
#   OUTBASE-dark.png   (void -> chalk ramp)
#   OUTBASE-light.png  (stone -> paper ramp)
# Set DARK=1 to render only dark, LIGHT=1 to render only light.
# OUTBASE defaults to INPUT-without-extension + "-ash".
#
# tuning via environment (defaults shown):
#   HUE_MAX=13%          warm band: hue <= HUE_MAX
#   HUE_MIN=94%          ... or hue >= HUE_MIN (catches pure reds)
#   SAT_MIN=12%          below this saturation pixels lose the highlight
#   SAT_MAX=45%          at/above this saturation the highlight is full
#   EMBER_BOOST=130      saturation multiplier (%) applied to highlight areas
#   SENSITIVITY=8x45%    sigmoidal contrast of the final mask
#   BASE_LO= BASE_HI=    override the grey ramp endpoints (applies to both
#                        rendered variants unless only one is generated)
set -euo pipefail

IN=${1:?usage: ash-wallpaper.sh INPUT [OUTBASE]}
OUTBASE=${2:-${IN%.*}-ash}
HUE_MAX=${HUE_MAX:-13%}
HUE_MIN=${HUE_MIN:-94%}
SAT_MIN=${SAT_MIN:-12%}
SAT_MAX=${SAT_MAX:-45%}
EMBER_BOOST=${EMBER_BOOST:-130}
SENSITIVITY=${SENSITIVITY:-8x45%}

if command -v magick >/dev/null; then IM=magick; else IM=convert; fi

if [[ ${DARK:-0} == 1 ]]; then VARIANTS=(dark)
elif [[ ${LIGHT:-0} == 1 ]]; then VARIANTS=(light)
else VARIANTS=(dark light); fi

TMP=$(mktemp -d)
trap 'rm -rf "$TMP"' EXIT

# warmth mask: (hue in warm band) x (saturation ramp)
"$IM" "$IN" -colorspace HSL -channel R -separate "$TMP/hue.png"
"$IM" "$IN" -colorspace HSL -channel G -separate "$TMP/sat.png"
"$IM" "$TMP/hue.png" -threshold "$HUE_MAX" -negate "$TMP/low.png"
"$IM" "$TMP/hue.png" -threshold "$HUE_MIN" "$TMP/high.png"
"$IM" "$TMP/low.png" "$TMP/high.png" -compose Lighten -composite "$TMP/band.png"
"$IM" "$TMP/sat.png" -level "$SAT_MIN","$SAT_MAX" "$TMP/satmask.png"
"$IM" "$TMP/band.png" "$TMP/satmask.png" -compose Multiply -composite \
  -gaussian-blur 0x2 -sigmoidal-contrast "$SENSITIVITY" "$TMP/mask.png"

for preset in "${VARIANTS[@]}"; do
  case "$preset" in
    dark)  lo=${BASE_LO:-#100f12}; hi=${BASE_HI:-#f3ede1} ;;
    light) lo=${BASE_LO:-#b7ae98}; hi=${BASE_HI:-#f2ecdf} ;;
  esac
  # ash base + ember-touched highlights, joined by the mask
  "$IM" "$IN" \
    \( -clone 0 -modulate 100,0 +level-colors "$lo","$hi" \) \
    \( -clone 0 -modulate "100,$EMBER_BOOST" \) \
    -delete 0 \
    \( +clone "$TMP/mask.png" -alpha off -compose CopyOpacity -composite \) \
    -delete 1 -compose Over -composite \
    -colorspace sRGB "$OUTBASE-$preset.png"
  echo "wrote $OUTBASE-$preset.png"
done