// mongodb's admin client — mongodb's own code, living in the module (novox/hq ADR 0039). Both this
// module's tools and its provisioner import it, and nothing outside mongodb does.
//
// Commands run through `mongosh`, not a wire-protocol driver: the module may take NO npm dependency
// beyond @novox/mesh-sdk, and hand-rolling the MongoDB wire protocol + SCRAM auth is more surface
// than this should carry — so it shells out to the shell the mongodb image ships, the same way
// postgres drives itself through `psql`, minio through `mc` and mailu through doveadm. One boundary,
// `evalJs()`, and every method is built on it: a snippet of JavaScript is evaluated server-side and
// its result comes back as EJSON on stdout.

import { randomBytes } from "node:crypto";
import { readFileSync } from "node:fs";
import { execFile } from "node:child_process";
import { promisify } from "node:util";

const run = promisify(execFile);

export interface DatabaseInfo {
  readonly name: string;
  readonly sizeBytes: number;
}

export interface MongoConn {
  readonly host: string;
  readonly port: number;
  readonly user: string;
  readonly password: string;
  /** The database the admin user authenticates against — `admin` for the root user. */
  readonly authSource: string;
}

export class MongoClient {
  constructor(private readonly conn: MongoConn) {}

  /**
   * Build from the module's resolved environment. Reads MESH_MONGODB_* first (the documented names),
   * falling back to the MESH_PROVISION_* keys the manifest already sets on the provisioner container.
   * Throws if it cannot find a host and an admin password.
   */
  static fromEnv(env: NodeJS.ProcessEnv = process.env): MongoClient {
    const url = env.MESH_PROVISION_MONGODB ? safeUrl(env.MESH_PROVISION_MONGODB) : undefined;
    const host = env.MESH_MONGODB_HOST ?? url?.hostname;
    const port = Number(env.MESH_MONGODB_PORT ?? url?.port ?? "27017") || 27017;
    const user = env.MESH_MONGODB_USER ?? (url?.username ? decodeURIComponent(url.username) : "root");
    const authSource =
      env.MESH_MONGODB_AUTHSOURCE ?? url?.searchParams.get("authSource") ?? "admin";
    const password = env.MESH_MONGODB_PASSWORD ?? readSecretFile(env.MESH_PROVISION_PASSWORD_FILE);
    if (!host || !password) {
      throw new Error("mongodb host or admin password is not set — mongodb's own code cannot reach the server");
    }
    return new MongoClient({ host, port, user, password, authSource });
  }

  get host(): string {
    return this.conn.host;
  }

  get port(): number {
    return this.conn.port;
  }

  /** The admin connection URI mongosh authenticates with, credentials percent-encoded. */
  private uri(): string {
    const u = encodeURIComponent(this.conn.user);
    const p = encodeURIComponent(this.conn.password);
    const a = encodeURIComponent(this.conn.authSource);
    return `mongodb://${u}:${p}@${this.conn.host}:${this.conn.port}/?authSource=${a}`;
  }

  /**
   * Evaluate a JavaScript snippet server-side through `mongosh` and parse the JSON it prints (see
   * header). The snippet MUST `print()` exactly one JSON document as its only stdout — every method
   * below ends in `print(EJSON.stringify(...))`. `--quiet` suppresses the shell banner so stdout is
   * the JSON alone; a non-zero exit (auth failure, bad command) rejects here rather than returning
   * a partial success.
   */
  async evalJs<T>(js: string): Promise<T> {
    const { stdout } = await run(
      "mongosh",
      [this.uri(), "--quiet", "--eval", js],
      { maxBuffer: 16 << 20 },
    );
    const text = stdout.trim();
    if (text.length === 0) {
      throw new Error("mongosh returned no output — the eval printed nothing");
    }
    return JSON.parse(text) as T;
  }

  /**
   * Create a login user and the database it owns, idempotently. The user is created inside the
   * target database with the `dbOwner` role scoped to that database, so the consumer owns exactly
   * its own and authenticates with the target database as its authSource. Re-running updates the
   * password and roles, so a rotated credential converges.
   */
  async createDatabaseAndUser(database: string, user: string, password: string): Promise<void> {
    const js = `
const target = db.getSiblingDB(${lit(database)});
let existing = null;
try { existing = target.getUser(${lit(user)}); } catch (e) { existing = null; }
const roles = [{ role: "dbOwner", db: ${lit(database)} }];
if (existing) {
  target.updateUser(${lit(user)}, { pwd: ${lit(password)}, roles: roles });
} else {
  target.createUser({ user: ${lit(user)}, pwd: ${lit(password)}, roles: roles });
}
print(EJSON.stringify({ ok: 1 }));
`;
    await this.evalJs<{ ok: number }>(js);
  }

  /** Drop a database and its owning user, idempotently. Dropping the database evicts its data; the
   *  user is removed first so a re-grant of the same login starts clean. */
  async dropDatabaseAndUser(database: string, user: string): Promise<void> {
    const js = `
const target = db.getSiblingDB(${lit(database)});
try { target.dropUser(${lit(user)}); } catch (e) {}
target.dropDatabase();
print(EJSON.stringify({ ok: 1 }));
`;
    await this.evalJs<{ ok: number }>(js);
  }

  /** List the databases on the server, with on-disk size, for the mongodb_list_databases tool. */
  async listDatabases(): Promise<DatabaseInfo[]> {
    const res = await this.evalJs<{ databases: { name: string; sizeOnDisk?: number }[] }>(
      `print(EJSON.stringify(db.adminCommand({ listDatabases: 1 })));`,
    );
    return (res.databases ?? [])
      .map((d) => ({ name: String(d.name), sizeBytes: Number(d.sizeOnDisk ?? 0) }))
      .sort((a, b) => a.name.localeCompare(b.name));
  }

  /**
   * Run a read-only `find` against a collection in a named database, for the mongodb_query tool.
   * `find` mutates nothing; the limit is capped so a tool call cannot stream an unbounded result.
   */
  async find(
    database: string,
    collection: string,
    filter: Readonly<Record<string, unknown>>,
    limit: number,
  ): Promise<Record<string, unknown>[]> {
    const capped = Math.max(1, Math.min(limit, 1000));
    const js =
      `print(EJSON.stringify(` +
      `db.getSiblingDB(${lit(database)}).getCollection(${lit(collection)})` +
      `.find(${JSON.stringify(filter)}).limit(${capped}).toArray()` +
      `));`;
    return this.evalJs<Record<string, unknown>[]>(js);
  }
}

/** Generate a URL-safe password. */
export function generatePassword(): string {
  return randomBytes(24).toString("base64url");
}

/** Embed a value as a JavaScript literal inside a mongosh snippet — JSON.stringify escapes quotes,
 *  backslashes and control characters, so a string cannot break out of the snippet. */
function lit(val: unknown): string {
  return JSON.stringify(val);
}

function readSecretFile(path: string | undefined): string | undefined {
  if (!path) return undefined;
  try {
    return readFileSync(path, "utf8").trim();
  } catch {
    return undefined;
  }
}

function safeUrl(raw: string): URL | undefined {
  try {
    return new URL(raw);
  } catch {
    return undefined;
  }
}