#!/bin/bash
set -euo pipefail
shopt -s nullglob

# SJP 2026-06-09
# Fetch BOM radar layers via anonymous FTP, alpha-composite them,
# publish the last FRAME_COUNT frames as an APNG loop.
# Parameterised on product code; default IDR713 (Sydney 128 km).
# Deployed to /opt/radar/radarFetch.sh on cremonde for radar.pestrel.com.

RADAR_ID="${1:-IDR713}"
FRAME_COUNT="${FRAME_COUNT:-6}"
FRAME_DELAY="${FRAME_DELAY:-50}"           # centiseconds per frame
END_PAUSE="${END_PAUSE:-150}"              # centiseconds, pause on last frame
TRANSPARENCY_TTL_HOURS="${TRANSPARENCY_TTL_HOURS:-24}"

DATA_ROOT="/var/lib/radar/${RADAR_ID,,}"
TRANS_DIR="${DATA_ROOT}/transparencies"
FRAMES_DIR="${DATA_ROOT}/frames"
PLATES_DIR="${DATA_ROOT}/plates"
OUT_DIR="${DATA_ROOT}/out"
PUBLISH_DIR="/srv/www/radar"
PUBLISH_PATH="${PUBLISH_DIR}/${RADAR_ID,,}-loop.apng"

FTP_DYNAMIC="ftp://ftp.bom.gov.au/anon/gen/radar/"
FTP_STATIC="ftp://ftp.bom.gov.au/anon/gen/radar_transparencies/"

require_cmd() {
    command -v "$1" >/dev/null 2>&1 || { echo "Required command not found: $1" >&2; exit 127; }
}
require_cmd curl
require_cmd magick
require_cmd ffmpeg

mkdir -p "$TRANS_DIR" "$FRAMES_DIR" "$PLATES_DIR" "$OUT_DIR"

fetch_validated() {
    # $1 url  $2 dest
    local url="$1" dest="$2" tmp="${2}.tmp"
    curl -q -fs -o "$tmp" "$url" || { rm -f "$tmp"; return 1; }
    if magick identify "$tmp" >/dev/null 2>&1; then
        mv "$tmp" "$dest"
    else
        rm -f "$tmp"
        return 1
    fi
}

# --- 1. Refresh transparencies if stale ----------------------------------
TRANS_MARKER="${TRANS_DIR}/.last_refreshed"
needs_refresh=1
if [ -f "$TRANS_MARKER" ]; then
    age_h=$(( ( $(date +%s) - $(stat -c %Y "$TRANS_MARKER") ) / 3600 ))
    [ "$age_h" -lt "$TRANSPARENCY_TTL_HOURS" ] && needs_refresh=0
fi

if [ "$needs_refresh" -eq 1 ]; then
    echo "Refreshing transparencies for ${RADAR_ID}..."
    if listing=$(curl -q -fs "$FTP_STATIC"); then
        # ls -l style listing; filename is the last whitespace-delimited field
        while read -r fname; do
            [ -n "$fname" ] || continue
            fetch_validated "${FTP_STATIC}${fname}" "${TRANS_DIR}/${fname}" \
                || echo "  failed: ${fname}" >&2
        done < <(echo "$listing" | awk '{print $NF}' | grep "^${RADAR_ID}\." || true)
        touch "$TRANS_MARKER"
        # invalidate precomposited plates
        rm -f "${PLATES_DIR}/lower.png" "${PLATES_DIR}/upper.png"
    else
        echo "Transparency listing failed; keeping cached copies." >&2
    fi
fi

# --- 2. Build precomposited plates ---------------------------------------
BACKGROUND="${TRANS_DIR}/${RADAR_ID}.background.png"
if [ ! -f "$BACKGROUND" ]; then
    echo "No background transparency cached; cannot composite." >&2
    exit 1
fi

existing_layers() {
    # echo paths that exist, in given order
    local base p
    for base in "$@"; do
        p="${TRANS_DIR}/${RADAR_ID}.${base}.png"
        [ -f "$p" ] && echo "$p"
    done
}

if [ ! -f "${PLATES_DIR}/lower.png" ]; then
    # background (opaque) + topography + optional feature overlays under the echo
    readarray -t lower_layers < <(existing_layers \
        background topography catchments waterways wthrDistricts roads rail)
    magick "${lower_layers[@]}" -background none -layers flatten "${PLATES_DIR}/lower.png"
fi

if [ ! -f "${PLATES_DIR}/upper.png" ]; then
    # range rings + place labels go over the echo so they stay legible
    readarray -t upper_layers < <(existing_layers range locations)
    if [ "${#upper_layers[@]}" -gt 0 ]; then
        magick "${upper_layers[@]}" -background none -layers flatten "${PLATES_DIR}/upper.png"
    fi
fi

# --- 3. Determine current top-N frames on the FTP ------------------------
echo "Listing dynamic frames..."
if ! listing=$(curl -q -fs "$FTP_DYNAMIC"); then
    echo "Dynamic listing failed; serving last good loop." >&2
    exit 0
fi

mapfile -t remote_frames < <(echo "$listing" \
    | awk '{print $NF}' \
    | grep "^${RADAR_ID}\.T\.[0-9]\{12\}\.png$" \
    | sort \
    | tail -n "$FRAME_COUNT")

if [ "${#remote_frames[@]}" -eq 0 ]; then
    echo "No remote frames for ${RADAR_ID}; serving last good loop." >&2
    exit 0
fi

# --- 4. Fetch missing frames; evict frames outside the rolling buffer ----
for fname in "${remote_frames[@]}"; do
    if [ ! -f "${FRAMES_DIR}/${fname}" ]; then
        echo "  fetching ${fname}"
        fetch_validated "${FTP_DYNAMIC}${fname}" "${FRAMES_DIR}/${fname}" \
            || echo "  failed: ${fname}" >&2
    fi
done

keep_set=" $(printf '%s ' "${remote_frames[@]}")"
for existing in "$FRAMES_DIR"/${RADAR_ID}.T.*.png; do
    bn=$(basename "$existing")
    case "$keep_set" in
        *" $bn "*) ;;
        *) rm -f "$existing" ;;
    esac
done

# --- 5. Composite each held frame ----------------------------------------
LEGEND="${TRANS_DIR}/${RADAR_ID}.legend.0.png"
HAVE_UPPER=0; [ -f "${PLATES_DIR}/upper.png" ] && HAVE_UPPER=1
HAVE_LEGEND=0; [ -f "$LEGEND" ] && HAVE_LEGEND=1

# clear stale composited frames
rm -f "${OUT_DIR}"/frame.*.png

composited=()
seq=0
for fname in "${remote_frames[@]}"; do
    src="${FRAMES_DIR}/${fname}"
    [ -f "$src" ] || continue
    out="${OUT_DIR}/frame.$(printf '%02d' "$seq").png"

    cmd=(magick "${PLATES_DIR}/lower.png" "$src" -composite)
    [ "$HAVE_UPPER" -eq 1 ]  && cmd+=("${PLATES_DIR}/upper.png" -composite)
    [ "$HAVE_LEGEND" -eq 1 ] && cmd+=(-gravity southeast "$LEGEND" -composite +gravity)
    cmd+=("$out")
    "${cmd[@]}"

    composited+=("$out")
    seq=$((seq + 1))
done

if [ "${#composited[@]}" -eq 0 ]; then
    echo "No frames composited; serving last good loop." >&2
    exit 0
fi

# --- 6. Assemble APNG loop via ffmpeg concat demuxer ---------------------
# ImageMagick's PNG writer on Arch lacks APNG support; ffmpeg's apng muxer
# handles it. Per-frame durations: last frame gets END_PAUSE.
mkdir -p "$PUBLISH_DIR"
TMP_APNG="${OUT_DIR}/loop.apng.tmp"
LIST_FILE="${OUT_DIR}/concat.txt"

: > "$LIST_FILE"
last_idx=$(( ${#composited[@]} - 1 ))
for i in "${!composited[@]}"; do
    printf "file '%s'\n" "${composited[$i]}" >> "$LIST_FILE"
    if [ "$i" -eq "$last_idx" ]; then
        printf "duration %s\n" "$(awk "BEGIN{print $END_PAUSE/100}")" >> "$LIST_FILE"
    else
        printf "duration %s\n" "$(awk "BEGIN{print $FRAME_DELAY/100}")" >> "$LIST_FILE"
    fi
done
# ffmpeg concat quirk: last file must be repeated without a duration line
printf "file '%s'\n" "${composited[$last_idx]}" >> "$LIST_FILE"

ffmpeg -y -hide_banner -loglevel error \
    -f concat -safe 0 -i "$LIST_FILE" \
    -plays 0 -vf format=rgba -f apng "$TMP_APNG"

install -m 644 "$TMP_APNG" "$PUBLISH_PATH"
rm -f "$TMP_APNG"

echo "Published ${PUBLISH_PATH} (frames=${#composited[@]}, latest=${remote_frames[-1]})"