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

# SJP 2026-06-10
# Build a 30-day morph timelapse of BOM synoptic charts.
# Cache structure: /mnt/enclave/synoptic/pairs/<chartA>__<chartB>/p_NNNN.png
# On each call: identify rolling window, fill any missing pairs, evict
# out-of-window pairs, stitch with linger/dwell, encode mp4.
# Triggered via OnSuccess= on synoptic.service.

ARCHIVE_DIR="${ARCHIVE_DIR:-/var/lib/synoptic/archive}"
WORK_ROOT="${WORK_ROOT:-/mnt/enclave/synoptic}"
PAIRS_DIR="$WORK_ROOT/pairs"
OUT_DIR="$WORK_ROOT/out"
PUBLISH_PATH="${PUBLISH_PATH:-/srv/www/pestrel/morph.mp4}"

WINDOW_DAYS="${WINDOW_DAYS:-30}"
WINDOW_CHARTS=$((WINDOW_DAYS * 4))
MORPH_N="${MORPH_N:-23}"
FPS="${FPS:-12}"
LINGER="${LINGER:-8}"
DWELL="${DWELL:-36}"
FADE_IN="${FADE_IN:-1}"
FADE_OUT="${FADE_OUT:-2}"

require_cmd() {
    command -v "$1" >/dev/null 2>&1 || { echo "Required: $1" >&2; exit 127; }
}
require_cmd magick
require_cmd ffmpeg
require_cmd flock

mkdir -p "$PAIRS_DIR" "$OUT_DIR"

exec 9>"$WORK_ROOT/.lock"
flock -n 9 || { echo "Morph already in progress; skipping."; exit 0; }

# --- 1. Rolling window --------------------------------------------------
mapfile -t window < <(ls -1 "$ARCHIVE_DIR"/[0-9]*.png 2>/dev/null | tail -n "$WINDOW_CHARTS")
if [ "${#window[@]}" -lt 2 ]; then
    echo "Need at least 2 charts in window (have ${#window[@]})." >&2
    exit 1
fi
first=$(basename "${window[0]}" .png)
last=$(basename "${window[-1]}" .png)
echo "Window: ${#window[@]} charts ($first → $last)"

# --- 2. Identify needed pair slugs --------------------------------------
needed=()
for i in $(seq 0 $((${#window[@]} - 2))); do
    a=$(basename "${window[$i]}" .png)
    b=$(basename "${window[$((i+1))]}" .png)
    needed+=("${a}__${b}")
done

# --- 3. Fill any missing pairs ------------------------------------------
SLOT=$((MORPH_N + 1))
new_pairs=0
for slug in "${needed[@]}"; do
    dir="$PAIRS_DIR/$slug"
    sentinel="$dir/p_$(printf '%04d' $SLOT).png"
    if [ ! -f "$sentinel" ]; then
        a="${slug%__*}"; b="${slug##*__}"
        echo "  computing pair $a → $b"
        mkdir -p "$dir"
        magick "$ARCHIVE_DIR/${a}.png" "$ARCHIVE_DIR/${b}.png" \
            -morph "$MORPH_N" "$dir/p_%04d.png"
        new_pairs=$((new_pairs + 1))
    fi
done
echo "Computed $new_pairs new pair(s)"

# --- 4. Evict pairs outside the window ----------------------------------
declare -A needed_set
for slug in "${needed[@]}"; do needed_set[$slug]=1; done
evicted=0
for dir in "$PAIRS_DIR"/*/; do
    slug=$(basename "$dir")
    if [ -z "${needed_set[$slug]:-}" ]; then
        rm -rf "$dir"
        evicted=$((evicted + 1))
    fi
done
echo "Evicted $evicted out-of-window pair(s)"

# --- 5. Assemble sequence with linger/dwell -----------------------------
SEQ_DIR=$(mktemp -d "$WORK_ROOT/seq.XXXXXX")
trap 'rm -rf "$SEQ_DIR"' EXIT

last_pair_idx=$(( ${#needed[@]} - 1 ))
out=0

# Per pair: take frames 0..MORPH_N (24 frames), dropping the joint with next.
# For the very last pair only, also take frame SLOT (the final chartB).
# Insert LINGER after every j==0 (each source chart appears once, as next
# pair's j==0). Insert DWELL after the final j==SLOT (the latest chart).
for i in "${!needed[@]}"; do
    dir="$PAIRS_DIR/${needed[$i]}"
    last_frame=$MORPH_N
    if [ "$i" -eq "$last_pair_idx" ]; then last_frame=$SLOT; fi
    for j in $(seq 0 $last_frame); do
        src="$dir/p_$(printf '%04d' $j).png"
        if [ ! -f "$src" ]; then
            echo "Missing pair frame: $src" >&2
            exit 2
        fi
        ln -sf "$src" "$SEQ_DIR/seq_$(printf '%06d' $out).png"
        out=$((out + 1))
        if [ "$j" -eq 0 ]; then
            for k in $(seq 1 $LINGER); do
                ln -sf "$src" "$SEQ_DIR/seq_$(printf '%06d' $out).png"
                out=$((out + 1))
            done
        elif [ "$i" -eq "$last_pair_idx" ] && [ "$j" -eq "$SLOT" ]; then
            for k in $(seq 1 $DWELL); do
                ln -sf "$src" "$SEQ_DIR/seq_$(printf '%06d' $out).png"
                out=$((out + 1))
            done
        fi
    done
done

dur=$(awk "BEGIN{printf \"%.2f\", $out/$FPS}")
fout=$(awk "BEGIN{printf \"%.3f\", $out/$FPS - $FADE_OUT}")
echo "Sequence: $out frames = ${dur}s at ${FPS} fps; fade-out ${FADE_OUT}s from ${fout}s"

# --- 6. Encode ----------------------------------------------------------
TMP_MP4=$(mktemp "$OUT_DIR/morph.XXXXXX.mp4")
ffmpeg -y -hide_banner -loglevel error -framerate "$FPS" \
    -i "$SEQ_DIR/seq_%06d.png" \
    -vf "fade=t=in:st=0:d=$FADE_IN,fade=t=out:st=$fout:d=$FADE_OUT" \
    -c:v libx264 -pix_fmt yuv420p -movflags +faststart "$TMP_MP4"

mkdir -p "$(dirname "$PUBLISH_PATH")"
install -m 644 "$TMP_MP4" "$PUBLISH_PATH"
rm -f "$TMP_MP4"
echo "Published $PUBLISH_PATH ($(stat -c %s "$PUBLISH_PATH") bytes)"