#!/usr/bin/env bash
#
# Create a compressed PostgreSQL backup and remove old backup files.
#
# Required environment variables:
#   PGHOST       PostgreSQL host.
#   PGUSER       PostgreSQL user.
#   PGPASSWORD   PostgreSQL password.
#   PGDATABASE   Database name to back up.
#
# Usage:
#   PGHOST=localhost PGUSER=app PGPASSWORD=secret PGDATABASE=appdb \
#     bash postgres_backup.sh --destination /backups/postgres
#
# Options:
#   --destination DIR   Backup directory. Default: ./backups
#   --retention-days N  Delete backups older than N days. Default: 14.
#   --help              Show this help message.

set -Eeuo pipefail

destination="./backups"
retention_days="14"

usage() {
  sed -n '2,24p' "$0" | sed 's/^# \{0,1\}//'
}

log() {
  printf '[%s] %s\n' "$(date -Is)" "$*"
}

require_env() {
  local name="$1"
  if [[ -z "${!name:-}" ]]; then
    printf 'ERROR: required environment variable is missing: %s\n' "$name" >&2
    exit 1
  fi
}

while [[ "$#" -gt 0 ]]; do
  case "$1" in
    --destination)
      destination="${2:-}"
      [[ -n "$destination" ]] || { printf 'ERROR: --destination requires a directory.\n' >&2; exit 1; }
      shift 2
      ;;
    --retention-days)
      retention_days="${2:-}"
      [[ "$retention_days" =~ ^[0-9]+$ ]] || { printf 'ERROR: retention must be a positive integer.\n' >&2; exit 1; }
      shift 2
      ;;
    --help|-h)
      usage
      exit 0
      ;;
    *)
      printf 'ERROR: unknown option: %s\n' "$1" >&2
      usage >&2
      exit 1
      ;;
  esac
done

command -v pg_dump >/dev/null 2>&1 || { printf 'ERROR: pg_dump command not found.\n' >&2; exit 1; }
command -v gzip >/dev/null 2>&1 || { printf 'ERROR: gzip command not found.\n' >&2; exit 1; }

require_env PGHOST
require_env PGUSER
require_env PGPASSWORD
require_env PGDATABASE

mkdir -p "$destination"

timestamp="$(date +%Y%m%d-%H%M%S)"
backup_file="${destination}/${PGDATABASE}-${timestamp}.sql.gz"

log "Starting PostgreSQL backup for database '${PGDATABASE}'."
pg_dump --format=plain --no-owner --no-privileges "$PGDATABASE" | gzip -9 > "$backup_file"

if [[ ! -s "$backup_file" ]]; then
  printf 'ERROR: backup file was not created or is empty: %s\n' "$backup_file" >&2
  exit 1
fi

log "Backup created: ${backup_file}"
log "Removing backups older than ${retention_days} days from ${destination}."
find "$destination" -type f -name "${PGDATABASE}-*.sql.gz" -mtime "+${retention_days}" -print -delete
log "Backup job completed successfully."