#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

# Configuration - edit or override via environment in the systemd unit
DATA_DIR="${DATA_DIR:-/var/lib/prometheus/data}"    # path to Prometheus TSDB dir (blocks)
PSQL_CONN="${PSQL_CONN:-}"                          # psql connection string, e.g. "postgresql://user:pass@host:5432/db"
CHECK_SQL_TEMPLATE="${CHECK_SQL_TEMPLATE:-}"        # SQL template that must return at least one row when block is present.
                                                    # Use placeholders {min} {max} (epoch ms). Example:
                                                    # "SELECT 1 FROM metrics WHERE time >= to_timestamp({min}/1000.0) AND time <= to_timestamp({max}/1000.0) LIMIT 1;"
MIN_AGE_HOURS="${MIN_AGE_HOURS:-3}"                # minimum block age before being eligible for deletion
GRACE_HOURS="${GRACE_HOURS:-1}"                    # extra grace period before deletion (safety)
DRY_RUN="${DRY_RUN:-false}"                        # set to "true" to test without deleting

log() { echo "$(date -Iseconds) $*"; }

# helper: convert Prometheus block times from meta.json (ms) to integers
get_times_from_meta() {
  local meta="$1"
  # meta.json contains "minTime" and "maxTime" in milliseconds since epoch
  jq -r '.minTime, .maxTime' "$meta"
}

# helper: run SQL check (returns 0 if found)
sql_check_block() {
  local min_ms="$1" max_ms="$2"
  if [[ -z "$PSQL_CONN" || -z "$CHECK_SQL_TEMPLATE" ]]; then
    return 1
  fi

  # fill placeholders
  local sql
  sql="${CHECK_SQL_TEMPLATE//\{min\}/$min_ms}"
  sql="${sql//\{max\}/$max_ms}"

  # run psql quietly - return success if any rows
  if psql "$PSQL_CONN" -t -c "$sql" 2>/dev/null | grep -q '.'; then
    return 0
  fi
  return 1
}

now_s="$(date +%s)"
now_ms="$(( now_s * 1000 ))"

# Iterate blocks. Each block is a directory named <ULID>
shopt -s nullglob
for blockdir in "$DATA_DIR"/*; do
  # find meta.json
  meta="$blockdir/meta.json"
  if [[ ! -f "$meta" ]]; then
    # skip non-blocks (like WAL, lock files)
    continue
  fi

  # ensure it's a directory and readable
  if [[ ! -r "$meta" ]]; then
    log "Skipping unreadable meta: $meta"
    continue
  fi

  read -r min_ms max_ms < <(get_times_from_meta "$meta")
  # if jq didn't return numbers, skip
  if ! [[ "$min_ms" =~ ^[0-9]+$ && "$max_ms" =~ ^[0-9]+$ ]]; then
    log "Skipping malformed meta: $meta"
    continue
  fi

  # compute block age in seconds (use max_ms as block end)
  block_end_s=$(( max_ms / 1000 ))
  age_s=$(( now_s - block_end_s ))
  min_age_s=$(( MIN_AGE_HOURS * 3600 ))
  grace_s=$(( GRACE_HOURS * 3600 ))

  block_name="$(basename "$blockdir")"
  log "Inspecting block $block_name (min=$min_ms max=$max_ms) age=${age_s}s"

  deleted=false

  # First: try SQL verification if configured
  if [[ -n "$PSQL_CONN" && -n "$CHECK_SQL_TEMPLATE" ]]; then
    if sql_check_block "$min_ms" "$max_ms"; then
      log "SQL verification OK for block $block_name → deleting"
      if [[ "$DRY_RUN" == "false" ]]; then
        rm -rf "$blockdir"
      else
        log "DRY_RUN=true, not deleting $blockdir"
      fi
      deleted=true
    else
      log "SQL verification did NOT find block data for $block_name"
    fi
  fi

  # Second: if SQL verification did not run or failed, apply age+grace policy
  if [[ "$deleted" == "false" ]]; then
    if (( age_s >= (min_age_s + grace_s) )); then
      log "Block $block_name is older than MIN_AGE+GRACE → deleting (no SQL verification)"
      if [[ "$DRY_RUN" == "false" ]]; then
        rm -rf "$blockdir"
      else
        log "DRY_RUN=true, not deleting $blockdir"
      fi
      deleted=true
    else
      log "Block $block_name is too new (age ${age_s}s). Skipping."
    fi
  fi

  # finished block
done

log "prune run completed"
exit 0