#!/bin/sh
# Network-triggered backup daemon
# Monitors for NAS availability and triggers backups with safeguards

set -e

# Config
CONFIG_FILE="/etc/backup.conf"
LOG_DIR="${HOME}/.local/var/log"
LOG_FILE="${LOG_DIR}/backup-monitor.log"
STATE_DIR="${HOME}/.local/var/backup"
LAST_BACKUP_FILE="${STATE_DIR}/last-backup"
LAST_CHECK_FILE="${STATE_DIR}/last-check"
BACKUP_IN_PROGRESS_FILE="${STATE_DIR}/backup-in-progress"

# Ensure directories exist
mkdir -p "$LOG_DIR" "$STATE_DIR"

# Logging
log() {
  echo "[$(date '+%Y-%m-%d %H:%M:%S')] $*" >> "$LOG_FILE"
}

# Load config
if [ ! -f "$CONFIG_FILE" ]; then
  log "ERROR: Configuration file not found: $CONFIG_FILE"
  exit 1
fi

# shellcheck source=/dev/null
. "$CONFIG_FILE"

# Check if backup is already running
is_backup_running() {
  # Check if any backup lock files exist
  if ls /tmp/backup-*.lock >/dev/null 2>&1; then
    return 0  # Backup is running
  fi

  # Check our own in-progress marker
  if [ -f "$BACKUP_IN_PROGRESS_FILE" ]; then
    # Check if marker is stale (older than 6 hours)
    if [ -n "$(find "$BACKUP_IN_PROGRESS_FILE" -mmin +360 2>/dev/null)" ]; then
      log "WARNING: Stale backup-in-progress marker found, removing"
      rm -f "$BACKUP_IN_PROGRESS_FILE"
      return 1  # Not running
    fi
    return 0  # Backup is running
  fi

  return 1  # Not running
}

# Check if cooldown period has passed
check_cooldown() {
  if [ ! -f "$LAST_BACKUP_FILE" ]; then
    return 0  # No previous backup, proceed
  fi

  LAST_BACKUP=$(cat "$LAST_BACKUP_FILE")
  NOW=$(date +%s)
  ELAPSED=$((NOW - LAST_BACKUP))

  if [ "$ELAPSED" -lt "$BACKUP_COOLDOWN" ]; then
    REMAINING=$((BACKUP_COOLDOWN - ELAPSED))
    log "Cooldown active: ${REMAINING}s remaining until next backup allowed"
    return 1  # Still in cooldown
  fi

  return 0  # Cooldown passed
}

# Check if we recently checked (prevent spam checks)
check_rate_limit() {
  CHECK_INTERVAL=300  # 5 minutes between checks

  if [ ! -f "$LAST_CHECK_FILE" ]; then
    date +%s > "$LAST_CHECK_FILE"
    return 0  # First check, proceed
  fi

  LAST_CHECK=$(cat "$LAST_CHECK_FILE")
  NOW=$(date +%s)
  ELAPSED=$((NOW - LAST_CHECK))

  if [ "$ELAPSED" -lt "$CHECK_INTERVAL" ]; then
    return 1  # Too soon since last check
  fi

  date +%s > "$LAST_CHECK_FILE"
  return 0  # Can check now
}

# Check if NAS is available
check_nas_available() {
  # Quick ping check
  if ! ping -c 1 -W 2 "$NAS_HOST" >/dev/null 2>&1; then
    return 1
  fi

  # SSH check
  if ! ssh -p "$NAS_PORT" -o ConnectTimeout=5 -o BatchMode=yes \
       "${NAS_USER}@${NAS_HOST}" "echo test" >/dev/null 2>&1; then
    return 1
  fi

  return 0
}

# Trigger backup
trigger_backup() {
  BACKUP_TYPE="${1:-incremental}"

  log "NAS detected, triggering $BACKUP_TYPE backup..."

  # Mark backup in progress
  touch "$BACKUP_IN_PROGRESS_FILE"

  # Run backup in background
  (
    if /usr/local/bin/backup-"$BACKUP_TYPE" >> "$LOG_FILE" 2>&1; then
      log "Backup completed successfully"
    else
      log "ERROR: Backup failed"
    fi

    # Remove in-progress marker
    rm -f "$BACKUP_IN_PROGRESS_FILE"
  ) &

  # Don't wait for backup to complete
  log "Backup started in background (PID: $!)"
}

# Main monitoring loop
main() {
  log "=========================================="
  log "Backup monitor started"
  log "Monitoring for NAS: ${NAS_HOST}"
  log "Check interval: 5 minutes"
  log "Backup cooldown: ${BACKUP_COOLDOWN}s ($(( BACKUP_COOLDOWN / 3600 ))h)"
  log "=========================================="

  while true; do
    # Rate limit checks (every 5 minutes)
    if ! check_rate_limit; then
      sleep 60
      continue
    fi

    # Skip if backup already running
    if is_backup_running; then
      log "Backup already in progress, skipping check"
      sleep 300  # Sleep 5 minutes
      continue
    fi

    # Check if NAS is available
    if check_nas_available; then
      log "NAS is available at ${NAS_HOST}"

      # Check cooldown before triggering
      if check_cooldown; then
        log "Cooldown passed, backup allowed"
        trigger_backup "incremental"
      else
        log "Cooldown active, skipping backup"
      fi
    else
      log "NAS not available (offline or not connected)"
    fi

    # Sleep before next check (5 minutes)
    sleep 300
  done
}

# Handle signals
trap 'log "Received shutdown signal, exiting..."; exit 0' TERM INT

# Start monitoring
main