// Health / readiness helpers for the vendored Hasna storage kit.
//
// `checkHealth` proves the database is reachable (a cheap `SELECT 1`).
// `checkReady` additionally proves the schema is migrated up to date, so a
// service can gate its `/ready` probe on pending migrations. These map to the
// contract's health/ready/version response shapes.
//
// PURE REMOTE (Amendment A1): health checks the cloud Postgres directly.

import type { TypedQueryClient } from "./query.js";
import { MigrationLedger, type Migration, type MigrationRunnerOptions } from "./migrations.js";

export interface HealthResult {
  ok: boolean;
  /** Round-trip latency of the probe query, in milliseconds. */
  latencyMs: number;
  error?: string;
}

/** Cheap reachability probe: `SELECT 1`. Never throws — reports `ok: false`. */
export async function checkHealth(client: TypedQueryClient): Promise<HealthResult> {
  const start = Date.now();
  try {
    await client.get<{ ok: number }>("SELECT 1 AS ok");
    return { ok: true, latencyMs: Date.now() - start };
  } catch (error) {
    return {
      ok: false,
      latencyMs: Date.now() - start,
      error: error instanceof Error ? error.message : String(error),
    };
  }
}

export interface ReadyResult extends HealthResult {
  /** Migration ids that are defined but not yet applied. */
  pendingMigrations: string[];
}

/**
 * Readiness probe: reachable AND fully migrated. Reports `ok: false` with the
 * list of pending migration ids when the schema is behind.
 */
export async function checkReady(
  client: TypedQueryClient,
  migrations: readonly Migration[],
  options: MigrationRunnerOptions = {},
): Promise<ReadyResult> {
  const start = Date.now();
  try {
    const ledger = new MigrationLedger(client, migrations, options);
    const result = await ledger.migrate({ dryRun: true });
    const pending = result.plan.filter((item) => item.state === "pending").map((item) => item.migration.id);
    return { ok: pending.length === 0, latencyMs: Date.now() - start, pendingMigrations: pending };
  } catch (error) {
    return {
      ok: false,
      latencyMs: Date.now() - start,
      pendingMigrations: [],
      error: error instanceof Error ? error.message : String(error),
    };
  }
}