#!/bin/sh
set -eu

# Remove dump files with a given prefix while keeping the most recent N days (default 7).

PROG=${0##*/}

usage() {
  cat <<USAGE
Usage: $PROG --prefix=NAME [--dir=DIR] [--days=N]

  --prefix=NAME   Filename prefix to match (required).
  --dir=DIR       Directory to scan (default: current directory).
  --days=N        Retention window in days (default: 7).
  --help          Show this help text.
USAGE
}

error() {
  printf '%s: %s\n' "$PROG" "$1" >&2
}

die_with_usage() {
  error "$1"
  usage >&2
  exit 1
}

PREFIX=""
TARGET_DIR="."
RETENTION_DAYS=3

while [ "$#" -gt 0 ]; do
  case $1 in
    --prefix=*)
      PREFIX="${1#*=}"
      ;;
    --prefix)
      shift
      [ "$#" -gt 0 ] || die_with_usage 'Missing value for --prefix'
      PREFIX="$1"
      ;;
    --dir=*)
      TARGET_DIR="${1#*=}"
      ;;
    --dir)
      shift
      [ "$#" -gt 0 ] || die_with_usage 'Missing value for --dir'
      TARGET_DIR="$1"
      ;;
    --days=*)
      RETENTION_DAYS="${1#*=}"
      ;;
    --days)
      shift
      [ "$#" -gt 0 ] || die_with_usage 'Missing value for --days'
      RETENTION_DAYS="$1"
      ;;
    -h|--help)
      usage
      exit 0
      ;;
    --)
      shift
      break
      ;;
    -*)
      die_with_usage "Unknown option: $1"
      ;;
    *)
      if [ -z "$PREFIX" ]; then
        PREFIX="$1"
      else
        die_with_usage "Unexpected positional argument: $1"
      fi
      ;;
  esac
  shift

done

if [ -z "$PREFIX" ] && [ "$#" -gt 0 ]; then
  PREFIX="$1"
  shift
fi

if [ -z "$PREFIX" ]; then
  die_with_usage 'A prefix is required.'
fi

if [ "$#" -gt 0 ]; then
  die_with_usage "Unexpected positional argument: $1"
fi

case $RETENTION_DAYS in
  ''|*[!0-9]*)
    die_with_usage "Retention days must be a non-negative integer: $RETENTION_DAYS"
    ;;
  *)
    :
    ;;
esac

if [ ! -d "$TARGET_DIR" ]; then
  error "Directory not found: $TARGET_DIR"
  exit 1
fi

# find's +N semantics removes files strictly older than N days, leaving the N day window intact.
find "$TARGET_DIR" \
  -maxdepth 1 \
  -type f \
  -name "${PREFIX}*" \
  -mtime +"$RETENTION_DAYS" \
  -print -delete