// mesh-vault's ledger — vault's own code, living in the module (novox/hq ADR 0039). The provisioner and
// the tools both import it, and nothing outside vault does.
//
// **The vault holds no value.** A `secret` is an ordinary pair credential: the controller mints it,
// seals it to the consumer's node and to this one, and the host unseals this node's copy into the
// file the contribution names (ADR 0048). That file is already on this machine, readable by nothing
// but the vault's runtime, and it is the only copy the vault ever sees. Writing a second copy —
// plain, or sealed to a key the vault keeps — would put back exactly the single place that can open
// everything, which is what sealing to the machine was built to remove (ADR 0085's open question is
// how to recover WITHOUT that; the answer is not "keep one anyway").
//
// So what the vault keeps is what makes a secret *owned* rather than merely delivered: who holds
// one, since when, its fingerprint, and every time it changed. Enough to say "this holder's value is
// the one the mesh last delivered" and "it has been rotated twice, last on Tuesday" — and never
// enough to say what it is. The fingerprint is the only thing a tool may take or return, which is
// the rule the source mesh's secret tools were built on: the secret is never an argument.

import { createHash } from "node:crypto";
import { mkdirSync, readdirSync, readFileSync, renameSync, unlinkSync, writeFileSync } from "node:fs";
import { join } from "node:path";

/** One holder of a secret this vault provides — everything the vault knows, and no value. */
export interface Held {
  /** The login the mesh derived for the consumer — `<node>-<module>`, so it names the holder. */
  readonly as: string;
  /** The consumer's node. */
  readonly consumer: string;
  /** sha256 of the value the mesh last delivered, `sha256:<hex>`. Compared, never inverted. */
  readonly fingerprint: string;
  /** Length of the value, so a holder can tell a truncated file from a wrong one. */
  readonly length: number;
  /** When this holder was first granted a secret. */
  readonly since: string;
  /** When the value last changed — equal to `since` until the first rotation. */
  readonly changed: string;
  /** How many times the value has changed since `since`. */
  readonly rotations: number;
  /** Every earlier fingerprint, oldest first: the audit trail a rotation leaves. */
  readonly history: readonly { readonly fingerprint: string; readonly until: string }[];
}

/** What recording a delivery found: a new holder, a changed value, or nothing new. */
export type Outcome = "granted" | "rotated" | "unchanged";

/** sha256 of a value, as `sha256:<hex>`. The one thing about a secret that may be spoken. */
export function fingerprint(value: string): string {
  return "sha256:" + createHash("sha256").update(value, "utf8").digest("hex");
}

export class Ledger {
  private readonly dir: string;

  constructor(dir: string) {
    this.dir = dir;
    mkdirSync(dir, { recursive: true, mode: 0o700 });
  }

  /** Build from the module's resolved environment: $MESH_VAULT_LEDGER is where holders are kept. */
  static fromEnv(env: NodeJS.ProcessEnv = process.env): Ledger {
    const dir = env.MESH_VAULT_LEDGER;
    if (!dir) {
      throw new Error("MESH_VAULT_LEDGER is not set — the vault has nowhere to keep its ledger");
    }
    return new Ledger(dir);
  }

  /**
   * Record that the mesh delivered `value` for `as`. Idempotent: the same value again changes
   * nothing, a different value is a rotation and is remembered as one. The value is fingerprinted
   * here and goes no further.
   */
  record(as: string, consumer: string, value: string, now = new Date()): { held: Held; outcome: Outcome } {
    const fp = fingerprint(value);
    const at = now.toISOString();
    const before = this.get(as);
    if (!before) {
      const held: Held = {
        as, consumer, fingerprint: fp, length: value.length,
        since: at, changed: at, rotations: 0, history: [],
      };
      this.write(held);
      return { held, outcome: "granted" };
    }
    if (before.fingerprint === fp && before.length === value.length) {
      return { held: before, outcome: "unchanged" };
    }
    const held: Held = {
      ...before, consumer, fingerprint: fp, length: value.length, changed: at,
      rotations: before.rotations + 1,
      history: [...before.history, { fingerprint: before.fingerprint, until: at }],
    };
    this.write(held);
    return { held, outcome: "rotated" };
  }

  /** Forget a holder the mesh withdrew. Returns whether there was one to forget. */
  withdraw(as: string): boolean {
    try {
      unlinkSync(this.pathOf(as));
      return true;
    } catch {
      return false;
    }
  }

  get(as: string): Held | undefined {
    try {
      return JSON.parse(readFileSync(this.pathOf(as), "utf8")) as Held;
    } catch {
      return undefined;
    }
  }

  /** Every holder, by login. */
  list(): Held[] {
    let names: string[];
    try {
      names = readdirSync(this.dir);
    } catch {
      return [];
    }
    return names
      .filter((n) => n.endsWith(".json"))
      .map((n) => this.get(n.slice(0, -".json".length)))
      .filter((h): h is Held => h !== undefined)
      .sort((a, b) => a.as.localeCompare(b.as));
  }

  private pathOf(as: string): string {
    if (!/^[a-z0-9][a-z0-9_.-]*$/.test(as)) {
      throw new Error(`a login is a name, not a path: ${JSON.stringify(as)}`);
    }
    return join(this.dir, `${as}.json`);
  }

  /** Written whole and renamed into place, so a reader never sees half a record. */
  private write(held: Held): void {
    const final = this.pathOf(held.as);
    const tmp = `${final}.${process.pid}.tmp`;
    writeFileSync(tmp, JSON.stringify(held, null, 2) + "\n", { mode: 0o600 });
    renameSync(tmp, final);
  }
}

/** One entry of the mesh's contributions file, as the vault reads it for its tools. */
export interface Contribution {
  readonly from?: string;
  readonly node?: string;
  readonly as: string;
  readonly secret: string;
}

/** The consumers the mesh currently asks this vault to serve — the `receives` file, read plainly. */
export function contributions(receives: string): Contribution[] {
  let doc: { given?: Contribution[] };
  try {
    doc = JSON.parse(readFileSync(receives, "utf8")) as { given?: Contribution[] };
  } catch {
    return [];
  }
  return (doc.given ?? []).filter((g) => g.as && g.secret);
}

/** Fingerprint of the value the host currently holds for one contribution, or why it could not. */
export function deliveredFingerprint(c: Contribution): { fingerprint: string; length: number } | { error: string } {
  try {
    const value = readFileSync(c.secret, "utf8").replace(/\n$/, "");
    return { fingerprint: fingerprint(value), length: value.length };
  } catch (err) {
    return { error: `the delivered secret is not readable: ${err}` };
  }
}