#!/usr/bin/env bash
# NextNVR — remux-faststart.sh
#
# Moves the MP4 index atom (moov) to the front of existing recordings so they
# start immediately in browsers, especially Safari/iOS. New recordings already
# use -movflags +faststart; this script fixes the archive recorded before that
# change.
#
# Usage:
#   scripts/remux-faststart.sh [--apply] [recordings-path]
#
# Defaults to a dry run against /mnt/recordings. Writes are atomic (temp file
# in the same directory + rename) and the original mtime is preserved so the
# retention cleaner still sees the true recording age.
#
# Requirements: ffmpeg. python3 is optional — when present, files that already
# have moov before mdat are skipped.

set -euo pipefail

APPLY=0
ROOT="/mnt/recordings"

usage() {
    cat <<'EOF'
Usage: remux-faststart.sh [--apply] [recordings-path]

  --apply    Actually rewrite files (default: dry run, report only)
  -h,--help  Show this help

Rewrites completed rec_*.mp4 files so their MP4 index (moov) is at the front.
In-progress *.part.mp4 files are never touched.
EOF
}

for arg in "$@"; do
    case "$arg" in
        --apply) APPLY=1 ;;
        -h|--help) usage; exit 0 ;;
        --*) echo "error: unknown option: $arg" >&2; usage >&2; exit 2 ;;
        *) ROOT="$arg" ;;
    esac
done

command -v ffmpeg >/dev/null 2>&1 || { echo "error: ffmpeg not found" >&2; exit 1; }
[ -d "$ROOT" ] || { echo "error: not a directory: $ROOT" >&2; exit 1; }

# Returns 0 when moov already precedes mdat (faststart), 1 when it does not,
# 2 when the file cannot be parsed.
moov_is_first() {
    python3 - "$1" <<'PY'
import os
import struct
import sys

path = sys.argv[1]
size = os.path.getsize(path)
off = 0
order = []

try:
    with open(path, "rb") as f:
        while off < size:
            f.seek(off)
            hdr = f.read(8)
            if len(hdr) < 8:
                break
            atom_size = struct.unpack(">I", hdr[:4])[0]
            atom_type = hdr[4:8].decode("latin1")
            if atom_size == 1:
                ext = f.read(8)
                if len(ext) < 8:
                    break
                atom_size = struct.unpack(">Q", ext)[0]
            order.append(atom_type)
            if atom_size == 0:
                break
            off += atom_size
except Exception:
    sys.exit(2)

if "moov" not in order or "mdat" not in order:
    sys.exit(2)
sys.exit(0 if order.index("moov") < order.index("mdat") else 1)
PY
}

HAVE_PYTHON=0
command -v python3 >/dev/null 2>&1 && HAVE_PYTHON=1

total=0
converted=0
skipped=0
failed=0

echo "remux-faststart: root=$ROOT apply=$APPLY"

while IFS= read -r -d '' file; do
    total=$((total + 1))

    if [ "$HAVE_PYTHON" -eq 1 ] && moov_is_first "$file"; then
        skipped=$((skipped + 1))
        continue
    fi

    if [ "$APPLY" -eq 0 ]; then
        echo "would remux: $file"
        converted=$((converted + 1))
        continue
    fi

    tmp="${file%.mp4}.faststart.tmp.mp4"
    if ffmpeg -nostdin -v error -y -i "$file" -c copy -movflags +faststart "$tmp" \
        && touch -r "$file" "$tmp" \
        && mv -f "$tmp" "$file"; then
        converted=$((converted + 1))
        echo "remuxed: $file"
    else
        failed=$((failed + 1))
        rm -f "$tmp"
        echo "FAILED: $file" >&2
    fi

    if [ $((converted % 100)) -eq 0 ] && [ "$converted" -gt 0 ]; then
        echo "--- progress: $converted processed ---"
    fi
done < <(find "$ROOT" -type f -name 'rec_*.mp4' ! -name '*.part.mp4' -print0)

echo
echo "remux-faststart: scanned=$total remuxed=$converted skipped=$skipped failed=$failed"
if [ "$APPLY" -eq 0 ] && [ "$converted" -gt 0 ]; then
    echo "dry run — re-run with --apply to rewrite the files above"
fi