#!/bin/sh
# Runs backup_db.sh at each time in BACKUP_TIMES_UTC (comma-separated HH:MM list).
# Defaults: 02:30, 08:30, 14:30, 20:30 UTC — four backups per day.
#
# Back-compat: if BACKUP_TIMES_UTC is unset but legacy BACKUP_HOUR/BACKUP_MINUTE are,
# those are honored as a single slot.

set -eu

if [ -n "${BACKUP_TIMES_UTC:-}" ]; then
  TIMES="$BACKUP_TIMES_UTC"
elif [ -n "${BACKUP_HOUR:-}" ] || [ -n "${BACKUP_MINUTE:-}" ]; then
  TIMES="$(printf '%02d:%02d' "${BACKUP_HOUR:-2}" "${BACKUP_MINUTE:-30}")"
else
  TIMES="02:30,08:30,14:30,20:30"
fi

echo "[$(date -u +%FT%TZ)] backup schedule (UTC): ${TIMES}"

if [ "${BACKUP_RUN_ON_START:-0}" = "1" ]; then
  echo "[$(date -u +%FT%TZ)] BACKUP_RUN_ON_START=1 — running backup immediately"
  /app/backup_db.sh || echo "[$(date -u +%FT%TZ)] initial backup failed (continuing)"
fi

# Compute epoch for "today HH:MM UTC" on both GNU and BSD date.
slot_to_epoch_today() {
  HM="$1"
  date -u -d "today ${HM}:00" +%s 2>/dev/null \
    || date -u -j -f "%H:%M:%S" "${HM}:00" +%s
}

while true; do
  NOW_EPOCH=$(date -u +%s)
  NEXT=""
  # Find the smallest TARGET > NOW across all configured slots (rolling to tomorrow if needed).
  OLDIFS="$IFS"
  IFS=','
  for HM in $TIMES; do
    HM="$(echo "$HM" | tr -d ' ')"
    [ -z "$HM" ] && continue
    T=$(slot_to_epoch_today "$HM")
    if [ "$T" -le "$NOW_EPOCH" ]; then
      T=$((T + 86400))
    fi
    if [ -z "$NEXT" ] || [ "$T" -lt "$NEXT" ]; then
      NEXT="$T"
    fi
  done
  IFS="$OLDIFS"

  if [ -z "$NEXT" ]; then
    echo "[$(date -u +%FT%TZ)] no valid times in BACKUP_TIMES_UTC='${TIMES}'; sleeping 1h"
    sleep 3600
    continue
  fi

  SLEEP=$((NEXT - NOW_EPOCH))
  NEXT_ISO=$(date -u -d "@${NEXT}" +%FT%TZ 2>/dev/null || date -u -r "${NEXT}" +%FT%TZ)
  echo "[$(date -u +%FT%TZ)] next backup in ${SLEEP}s (at ${NEXT_ISO})"
  sleep "$SLEEP"
  /app/backup_db.sh || echo "[$(date -u +%FT%TZ)] backup failed (will retry at next slot)"
done