// The token the forge's tools and watcher authenticate with — and where it comes from.
//
// Nobody configures it. The forge is raised by the mesh, so there is no operator holding a token to
// paste in, and pasting one into settings would put a secret in the inventory in plaintext. What
// the mesh does deliver is the admin account: a login the manifest names and a password the vault
// minted and the host unsealed into a file (novox/hq ADR 0086). That account is enough to mint a
// token, so the module mints its own (hq issue 100, the forge's tools):
//
//   - at first use, when none is kept: POST /users/{admin}/tokens over basic auth, with the two
//     scopes the tools and the watcher need, and no more;
//   - kept in the module's own state, a 0600 file, and read back on the next start — the forge
//     hands a token's value out exactly once, so a token not kept is a token lost;
//   - re-minted when the forge rejects it (401) or the kept file is gone. The one case that is not
//     a fault: the forge's data was restored from a predecessor and the token the file names never
//     existed there.
//
// An explicitly configured token still wins, and is never minted over: if it is rejected, that is
// reported, not repaired — somebody chose it.
//
// The token is never logged. Lines say that one was minted, reused or renewed, and where it is
// kept; never what it is.

import { chmodSync, mkdirSync, readFileSync, renameSync, writeFileSync } from "node:fs";
import { dirname, join } from "node:path";

/** The name the token carries in the forge's own list — one per mesh runtime, found by name. */
export const TOKEN_NAME = "mesh-tools";

/**
 * The least the fifteen tools and the watcher need (gitea's route groups, 1.20+ scoped tokens):
 *   write:repository — create/delete repositories, pull requests (list/get/open/merge);
 *   write:issue      — issues, comments, labels;
 *   read:user        — GET /user/repos, which the watcher's poll and gitea_list_repos both call.
 *                      It sits under the `user` category despite listing repositories, not `repository`
 *                      — confirmed against the running forge (1.27.3), which answered
 *                      `required=[read:user]` to a token carrying only the other two.
 * Nothing under /admin, /orgs or write:user — the escape-hatch tool reaches only what these three cover.
 */
export const TOKEN_SCOPES: readonly string[] = ["write:repository", "write:issue", "read:user"];

/** Where a client's token comes from, and what to do when the forge says it is wrong. */
export interface TokenSource {
  /** The token to authenticate with now; minted, read or configured. */
  current(): Promise<string>;
  /** The forge answered 401 to `rejected`. A fresh token, or a plain error when there is nothing to renew with. */
  renew(rejected: string): Promise<string>;
}

/** A token somebody set — in settings or the environment. Never minted over. */
export class ConfiguredToken implements TokenSource {
  constructor(private readonly token: string) {}

  async current(): Promise<string> {
    return this.token;
  }

  async renew(): Promise<string> {
    throw new Error(
      "the forge rejected the configured Gitea token (401). It was set explicitly (settings or MESH_GITEA_TOKEN), " +
        "so the module does not mint over it — fix it, or unset it and the module mints its own",
    );
  }
}

/** The forge would not take the admin account: it is missing, or its password is not the one the mesh holds. */
export class AdminRefused extends Error {
  constructor(admin: string, status: number) {
    super(
      `the forge refused the admin account "${admin}" (${status}) — it does not exist there, or its password is not ` +
        `the one the vault delivered. The admin-bootstrap step creates it on a forge the mesh raised; a forge whose data ` +
        `came from a predecessor does not have it. Create "${admin}" on the forge with the delivered password and the ` +
        `token is minted on the next call — the tools stay registered and the watcher keeps trying`,
    );
    this.name = "AdminRefused";
  }
}

export interface MintedTokenOptions {
  /** The forge, e.g. http://127.0.0.1:3000. */
  readonly url: string;
  /** The admin login the manifest names. */
  readonly admin: string;
  /** The file the host unsealed the admin password into (ADR 0086). Read at mint time, so a rotation takes. */
  readonly passwordFile: string;
  /** Where the token is kept: a 0600 file in the module's own state. */
  readonly file: string;
  readonly name?: string;
  readonly scopes?: readonly string[];
  readonly log?: (line: string) => void;
  readonly fetch?: typeof fetch;
}

/** The token the module mints for itself, kept in its state and renewed when the forge rejects it. */
export class MintedToken implements TokenSource {
  private held: string | null = null;
  private readFile = false;
  private inflight: Promise<string> | null = null;
  private readonly name: string;
  private readonly scopes: readonly string[];
  private readonly log: (line: string) => void;
  private readonly fetchImpl: typeof fetch;

  constructor(private readonly opts: MintedTokenOptions) {
    this.name = opts.name ?? TOKEN_NAME;
    this.scopes = opts.scopes ?? TOKEN_SCOPES;
    this.log = opts.log ?? ((line) => console.log(`[gitea] ${line}`));
    this.fetchImpl = opts.fetch ?? fetch;
  }

  /**
   * Build from the runtime's environment: the forge's URL, the admin login and password file the
   * manifest hands the runtime, and the module's state directory (MESH_GITEA_STATE_DIR, a directory
   * the runtime mounts writable). Throws, naming what is missing, rather than hand back a source
   * that cannot mint.
   */
  static fromEnv(url: string, env: NodeJS.ProcessEnv = process.env): MintedToken {
    const opts = MintedToken.optionsFromEnv(url, env);
    // One source per kept file in a process. The watcher and the tools entrypoint both build a
    // client in the same runtime; two sources over one file would each renew on a 401 and drop the
    // other's token by name, forever. Shared, a renewal is one renewal.
    const shared = MintedToken.shared.get(opts.file);
    if (shared) return shared;
    const source = new MintedToken(opts);
    MintedToken.shared.set(opts.file, source);
    return source;
  }

  private static readonly shared = new Map<string, MintedToken>();

  private static optionsFromEnv(url: string, env: NodeJS.ProcessEnv): MintedTokenOptions {
    const admin = env.MESH_GITEA_ADMIN_USER;
    const passwordFile = env.MESH_GITEA_ADMIN_PASSWORD_FILE;
    const stateDir = env.MESH_GITEA_STATE_DIR;
    const missing = [
      admin ? null : "MESH_GITEA_ADMIN_USER",
      passwordFile ? null : "MESH_GITEA_ADMIN_PASSWORD_FILE",
      stateDir ? null : "MESH_GITEA_STATE_DIR",
    ].filter((v): v is string => v !== null);
    if (missing.length) {
      throw new Error(`no Gitea token, and nothing to mint one with — set MESH_GITEA_TOKEN, or ${missing.join(", ")}`);
    }
    return { url, admin: admin!, passwordFile: passwordFile!, file: join(stateDir!, "token") };
  }

  async current(): Promise<string> {
    if (this.held !== null) return this.held;
    if (!this.readFile) {
      this.readFile = true;
      const kept = this.read();
      if (kept !== null) {
        this.held = kept;
        this.log(`reusing the token kept at ${this.opts.file}`);
        return kept;
      }
    }
    return this.mint("no token kept — minting one");
  }

  async renew(rejected: string): Promise<string> {
    // Another caller already renewed while this one was in flight with the old token.
    if (this.held !== null && this.held !== rejected) return this.held;
    // Or another process did, and kept it: use what is kept before minting over it.
    const kept = this.read();
    if (kept !== null && kept !== rejected) {
      this.held = kept;
      this.log(`the forge rejected the token held; the kept one at ${this.opts.file} is newer — reusing it`);
      return kept;
    }
    this.held = null;
    return this.mint("the forge rejected the kept token — minting a fresh one");
  }

  /** One mint at a time: concurrent first calls share it, rather than each minting its own. */
  private mint(why: string): Promise<string> {
    if (this.inflight === null) {
      this.log(why);
      this.inflight = this.doMint().finally(() => {
        this.inflight = null;
      });
    }
    return this.inflight;
  }

  private read(): string | null {
    try {
      const token = readFileSync(this.opts.file, "utf8").replace(/\n$/, "");
      return token.length ? token : null;
    } catch (err) {
      if ((err as NodeJS.ErrnoException).code === "ENOENT") return null;
      throw new Error(`cannot read the kept Gitea token at ${this.opts.file}: ${(err as Error).message}`);
    }
  }

  /** Write the token at 0600, whole or not at all: a temp file beside it, then a rename. */
  private keep(token: string): void {
    mkdirSync(dirname(this.opts.file), { recursive: true, mode: 0o700 });
    const tmp = `${this.opts.file}.tmp`;
    writeFileSync(tmp, token + "\n", { mode: 0o600 });
    chmodSync(tmp, 0o600);
    renameSync(tmp, this.opts.file);
  }

  private async doMint(): Promise<string> {
    let password: string;
    try {
      password = readFileSync(this.opts.passwordFile, "utf8").replace(/\n$/, "");
    } catch (err) {
      throw new Error(`cannot read the admin password at ${this.opts.passwordFile}: ${(err as Error).message}`);
    }
    const authorization = "Basic " + Buffer.from(`${this.opts.admin}:${password}`).toString("base64");
    const tokens = `${this.opts.url.replace(/\/+$/, "")}/api/v1/users/${encodeURIComponent(this.opts.admin)}/tokens`;
    const call = async (method: string, path = "", body?: unknown): Promise<{ status: number; body: any }> => {
      const res = await this.fetchImpl(tokens + path, {
        method,
        headers: { "Content-Type": "application/json", Authorization: authorization },
        ...(body === undefined ? {} : { body: JSON.stringify(body) }),
      });
      const text = await res.text();
      let parsed: any = null;
      if (text) {
        try { parsed = JSON.parse(text); } catch { parsed = text; }
      }
      return { status: res.status, body: parsed };
    };

    let res = await call("POST", "", { name: this.name, scopes: this.scopes });
    if (res.status === 401 || res.status === 403) throw new AdminRefused(this.opts.admin, res.status);
    if (res.status === 400 || res.status === 422) {
      // The forge still holds a token by this name whose value we no longer have — the kept file
      // went while the forge's data stayed. It is ours to replace: drop it by name and mint again.
      this.log(`the forge already holds a token named "${this.name}" — replacing it`);
      const dropped = await call("DELETE", `/${encodeURIComponent(this.name)}`);
      if (dropped.status !== 204 && dropped.status !== 404) {
        throw new Error(`Gitea DELETE /users/${this.opts.admin}/tokens/${this.name}: ${dropped.status} ${detail(dropped.body)}`);
      }
      res = await call("POST", "", { name: this.name, scopes: this.scopes });
    }
    if (res.status !== 201 && res.status !== 200) {
      throw new Error(`Gitea POST /users/${this.opts.admin}/tokens: ${res.status} ${detail(res.body)}`);
    }
    const token = typeof res.body?.sha1 === "string" ? res.body.sha1 : null;
    if (!token) throw new Error(`Gitea POST /users/${this.opts.admin}/tokens: ${res.status} but no token in the reply`);

    this.keep(token);
    this.held = token;
    this.log(`minted a token for "${this.opts.admin}" (${this.scopes.join(", ")}), kept at ${this.opts.file}`);
    return token;
  }
}

function detail(body: unknown): string {
  return typeof body === "string" ? body : JSON.stringify(body);
}