#!/bin/sh
set -e

BACKUP_DIR="${BACKUP_DIR:-/backups}"
DB_HOST="${POSTGRES_HOST:-db}"
DB_NAME="${POSTGRES_DB:-bollwerk}"
DB_USER="${POSTGRES_USER:-bollwerk}"
MAX_SIZE_BYTES=$((1 * 1024 * 1024 * 1024))   # 1 GB

mkdir -p "$BACKUP_DIR"

TIMESTAMP=$(date -u +"%Y-%m-%d_%H%M")
BACKUP_FILE="${BACKUP_DIR}/${DB_NAME}_${TIMESTAMP}.sql.gz"
CHECKSUM_FILE="${BACKUP_DIR}/.last_checksum"

echo "[$(date -u)] Starting backup of database '${DB_NAME}' on host '${DB_HOST}'..."

# Dump to temp file for checksum comparison
TEMP_DUMP=$(mktemp)
export PGPASSWORD="${POSTGRES_PASSWORD:-}"
pg_dump -h "$DB_HOST" -U "$DB_USER" "$DB_NAME" > "$TEMP_DUMP"

# Compute MD5 of dump content, excluding lines that change every run:
# - pg_dump comment lines (timestamps, version info)
# - PostgreSQL 17 security tokens (\restrict / \unrestrict with random token)
CURRENT_CHECKSUM=$(grep -Ev '^(--|\\restrict|\\unrestrict)' "$TEMP_DUMP" | md5sum | cut -d' ' -f1)
LAST_CHECKSUM=""
if [ -f "$CHECKSUM_FILE" ]; then
    LAST_CHECKSUM=$(cat "$CHECKSUM_FILE")
fi

if [ "$CURRENT_CHECKSUM" = "$LAST_CHECKSUM" ]; then
    echo "[$(date -u)] No changes since last backup. Skipping."
    rm -f "$TEMP_DUMP"
    exit 0
fi

# Compress and save
gzip -c "$TEMP_DUMP" > "$BACKUP_FILE"
rm -f "$TEMP_DUMP"
printf '%s' "$CURRENT_CHECKSUM" > "$CHECKSUM_FILE"
echo "[$(date -u)] Backup saved: ${BACKUP_FILE}"

# Rotate: remove oldest .sql.gz until total backup dir size <= 1 GB
while true; do
    TOTAL=$(du -sb "$BACKUP_DIR" | cut -f1)
    if [ "$TOTAL" -le "$MAX_SIZE_BYTES" ]; then
        break
    fi
    OLDEST=$(ls -tr "${BACKUP_DIR}"/*.sql.gz 2>/dev/null | head -1)
    if [ -z "$OLDEST" ]; then
        echo "[$(date -u)] Warning: Cannot reduce backup dir below 1 GB, no more files to delete."
        break
    fi
    echo "[$(date -u)] Rotation: removing ${OLDEST} (dir total: ${TOTAL} bytes)"
    rm -f "$OLDEST"
done

echo "[$(date -u)] Backup complete."