// The reconcile harness every provider shares. The loop below is identical for postgres, redis,
// minio and umami: read the contributions the mesh delivered, bring each consumer's resource into
// being through the provider's adapter under the login and password the mesh minted, and withdraw
// what the mesh no longer asks for. 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).
//
// **A provider creates the credential the mesh minted, and seals nothing (novox/hq ADR 0053).** The
// control plane mints one password per consumer and seals it to this node; the host unseals it into
// the file the contribution names. The provider does not generate a password, does not seal one, and
// does not hand one back — the consumer already receives its copy through the mesh's own channel.
// This is why the old $MESH_SEAL_KEY, the symmetric seal, and the *.grant.json / *.credential files
// are gone: they described a second, contradictory credential path the mesh does not have.

import { readFile } from "node:fs/promises";

/** One consumer's resource to bring into being — everything the mesh derived and delivered. */
export interface Provision {
  /** The login the mesh derived and gave the consumer to present. The provider creates exactly
   *  this name — a name the consumer cannot learn is a name it cannot authenticate with. */
  readonly as: string;
  /** The password the mesh minted for this consumer, read from the file the mesh sealed to this
   *  node and the host unsealed. The provider sets it; it never invents one. */
  readonly password: string;
  /** What the consumer contributed, per the interface's spec keys (e.g. `{ name: "umami" }`). */
  readonly values: Readonly<Record<string, unknown>>;
  /** Where the consumer is, for a provider that must reach back to it. Usually unused. */
  readonly at?: string;
  /** The consumer node, for logging and lifecycle events. */
  readonly consumer?: string;
}

/** What a provider implements — the only per-service code. It is handed the login and password the
 *  mesh made and brings the resource into being under them, or withdraws it. It returns nothing:
 *  the credential is the mesh's, already delivered to the consumer. */
export interface Adapter {
  create(p: Provision): Promise<void>;
  remove(p: { readonly as: string }): Promise<void>;
}

export interface ProvisionerOptions {
  /** The contributions file the mesh writes for this resource (the module's `receives` path).
   *  Defaults to $MESH_RECEIVES. */
  receives?: string;
  /** Reconcile interval in ms. Defaults to 5000. */
  everyMs?: number;
}

/** One entry in the mesh's contributions file: a consumer the provider must serve. */
interface Contribution {
  readonly as: string;
  readonly secret: string;
  readonly node?: string;
  readonly at?: string;
  readonly values?: Readonly<Record<string, unknown>>;
}

/**
 * Run the reconcile loop for one provided resource. Returns a stop function. Never throws for a
 * single bad contribution — 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 receives = opts.receives ?? envOrThrow("MESH_RECEIVES");
  const everyMs = opts.everyMs ?? 5000;

  const applied = new Map<string, string>(); // login (`as`) -> hash of what was last applied
  let stopped = false;

  async function reconcile(): Promise<void> {
    const given = await readContributions(receives, resource);
    const wantByAs = new Map(given.map((g) => [g.as, g]));

    // Create or update every consumer whose login, password or values changed.
    for (const g of given) {
      let password: string;
      try {
        // The file the mesh sealed to this node, unsealed by the host into plaintext. Trailing
        // newline trimmed: a sealed value is exactly the secret, and a host writing a file may add
        // one.
        password = (await readFile(g.secret, "utf8")).replace(/\n$/, "");
      } catch (err) {
        // The contribution names a secret the host has not written yet — a normal race on the
        // first pass. Skipped, retried on the next tick, never fatal.
        console.error(`[provisioner:${resource}] ${g.as}: secret not readable yet (${g.secret}): ${err}`);
        continue;
      }
      const h = hash(g.as, password, g.values ?? {});
      if (applied.get(g.as) === h) continue;
      try {
        await adapter.create({ as: g.as, password, values: g.values ?? {}, at: g.at, consumer: g.node });
        applied.set(g.as, h);
      } catch (err) {
        console.error(`[provisioner:${resource}] ${g.as}: create failed, will retry: ${err}`);
      }
    }

    // Withdraw every login the provider made that the mesh no longer asks for. The mesh drops a
    // consumer from the file when it goes away; that is how a login is withdrawn rather than kept
    // working for ever. Only logins this harness created are touched.
    for (const as of [...applied.keys()]) {
      if (wantByAs.has(as)) continue;
      try {
        await adapter.remove({ as });
        applied.delete(as);
      } catch (err) {
        console.error(`[provisioner:${resource}] ${as}: 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;
  };
}

/**
 * Read the mesh's contributions file for one resource. Absent or empty means "no consumer asks for
 * this" — the file is always written, so a provider can tell that from "the mesh never wrote it".
 */
async function readContributions(path: string, resource: string): Promise<Contribution[]> {
  let raw: string;
  try {
    raw = await readFile(path, "utf8");
  } catch {
    return []; // not written yet, or nobody serves anything here — nothing to converge to
  }
  let doc: { requirement?: string; given?: Contribution[] };
  try {
    doc = JSON.parse(raw) as { requirement?: string; given?: Contribution[] };
  } catch (err) {
    console.error(`[provisioner:${resource}] contributions file is not JSON (${path}): ${err}`);
    return [];
  }
  if (doc.requirement && doc.requirement !== resource) {
    console.error(`[provisioner:${resource}] ${path} is for ${doc.requirement}, not ${resource}`);
    return [];
  }
  // A contribution with no `as` is not a credential grant (a module offering something on its own
  // machine) — the provisioner has nothing to create for it.
  return (doc.given ?? []).filter((g) => g.as && g.secret);
}

function hash(as: string, password: string, values: Readonly<Record<string, unknown>>): string {
  return JSON.stringify([as, password, 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;
}