// The reconcile harness every provider shares. The loop below is identical for postgres, redis,
// minio and umami: read the grants the control plane has written, bring each requested resource to
// existence through the provider's adapter, seal and hand back the credential, and remove what is
// no longer requested. A module writes ONLY the adapter — the per-service half — which is why this
// lives in the sdk and the adapter lives in the module (novox/hq ADR 0044).

import { readdir, readFile, writeFile, rm } from "node:fs/promises";
import { join } from "node:path";
import type { Grant, Credential } from "../contracts/index.js";
import { seal } from "../primitives/index.js";

/** What a provider implements — the only per-service code. It is handed a Grant and creates (or
 *  removes) the resource in its own software, returning the credential a consumer receives. */
export interface Adapter {
  create(grant: Grant): Promise<Credential>;
  remove(grant: Grant): Promise<void>;
}

export interface ProvisionerOptions {
  /** Directory the control plane writes grant requests into and the harness writes credentials to.
   *  Defaults to $GRANTS. */
  grants?: string;
  /** Passphrase a credential is sealed to before it is written. Defaults to $MESH_SEAL_KEY. */
  sealKey?: string;
  /** Reconcile interval in ms. Defaults to 5000. */
  everyMs?: number;
}

export type { Grant, Credential };

/**
 * Run the reconcile loop for one provided resource. Returns a stop function. Never throws for a
 * single bad grant — it logs and keeps converging, because one consumer's failure must not stop
 * the others' provisioning.
 */
export function runProvisioner(resource: string, adapter: Adapter, opts: ProvisionerOptions = {}): () => void {
  const dir = opts.grants ?? envOrThrow("GRANTS");
  const sealKey = opts.sealKey ?? envOrThrow("MESH_SEAL_KEY");
  const everyMs = opts.everyMs ?? 5000;

  const applied = new Map<string, string>(); // consumer -> hash of the grant last applied
  let stopped = false;

  async function reconcile(): Promise<void> {
    const requested = await readGrants(dir, resource);
    const wantById = new Map(requested.map((g) => [g.consumer, g]));

    // Create or update anything requested whose grant has changed.
    for (const grant of requested) {
      const h = hash(grant);
      if (applied.get(grant.consumer) === h) continue;
      try {
        const cred = await adapter.create(grant);
        await writeSealedCredential(dir, grant, cred, sealKey);
        applied.set(grant.consumer, h);
      } catch (err) {
        console.error(`[provisioner:${resource}] ${grant.consumer}: create failed, will retry: ${err}`);
      }
    }

    // Remove anything applied that is no longer requested. Only the harness's own outputs are
    // touched — the credential file it wrote — never anything it did not create.
    for (const consumer of [...applied.keys()]) {
      if (wantById.has(consumer)) continue;
      const grant = lastGrant(dir, resource, consumer);
      try {
        await adapter.remove(grant);
        await rm(credentialPath(dir, resource, consumer), { force: true });
        applied.delete(consumer);
      } catch (err) {
        console.error(`[provisioner:${resource}] ${consumer}: remove failed, will retry: ${err}`);
      }
    }
  }

  const tick = async (): Promise<void> => {
    if (stopped) return;
    try {
      await reconcile();
    } catch (err) {
      console.error(`[provisioner:${resource}] reconcile error: ${err}`);
    }
    if (!stopped) setTimeout(() => void tick(), everyMs);
  };
  void tick();

  return () => {
    stopped = true;
  };
}

// --- grant/credential files ---

async function readGrants(dir: string, resource: string): Promise<Grant[]> {
  let names: string[];
  try {
    names = await readdir(dir);
  } catch {
    return [];
  }
  const out: Grant[] = [];
  for (const name of names) {
    if (!name.endsWith(".grant.json")) continue;
    try {
      const raw = await readFile(join(dir, name), "utf8");
      const g = JSON.parse(raw) as Grant;
      if (g.resource === resource) out.push(g);
    } catch (err) {
      console.error(`[provisioner:${resource}] unreadable grant ${name}: ${err}`);
    }
  }
  return out;
}

function credentialPath(dir: string, resource: string, consumer: string): string {
  return join(dir, `${consumer}.${resource}.credential`);
}

async function writeSealedCredential(dir: string, grant: Grant, cred: Credential, key: string): Promise<void> {
  const body = JSON.stringify({ resource: grant.resource, consumer: grant.consumer, fields: cred.fields });
  await writeFile(credentialPath(dir, grant.resource, grant.consumer), seal(body, key), { mode: 0o600 });
}

function lastGrant(dir: string, resource: string, consumer: string): Grant {
  // For removal the harness needs a Grant to hand the adapter; the identity is enough to act on.
  return { resource, consumer, node: "", values: {} };
}

// --- helpers ---

function hash(g: Grant): string {
  return JSON.stringify([g.resource, g.consumer, g.node, g.values]);
}

function envOrThrow(name: string): string {
  const v = process.env[name];
  if (!v) throw new Error(`${name} is not set — the provisioner cannot run without it`);
  return v;
}