import net from "node:net";
import tls from "node:tls";
import type { ConnectionOptions } from "node:tls";

export type DatabaseTransportEnvironment = "development" | "production";

/**
 * The two transport modes this release supports, named after the libpq/PostgreSQL vocabulary an
 * operator already knows:
 *
 * - `verify-full` — TLS is required, the server certificate must chain to a trusted CA, **and**
 *   the certificate identity must match the configured database host. This is the production
 *   default, and the only mode a production deployment may use.
 * - `disable` — no TLS at all. Available only for the disposable loopback PostgreSQL used by local
 *   development and this repository's integration harness.
 *
 * There is deliberately no encryption-only mode (`require`/`verify-ca`) and no
 * `rejectUnauthorized: false` escape hatch: both authenticate nothing, and an unauthenticated
 * encrypted channel to an attacker-controlled endpoint is not a security property worth offering.
 */
export type DatabaseTlsMode = "disable" | "verify-full";

export type DatabaseTransportErrorCode =
  | "DATABASE_TLS_CONNECTION_STRING_CONFLICT"
  | "DATABASE_TLS_MODE_INVALID"
  | "DATABASE_TLS_REQUIRED_IN_PRODUCTION"
  | "DATABASE_URL_INVALID";

const errorMessages: Readonly<Record<DatabaseTransportErrorCode, string>> = Object.freeze({
  DATABASE_TLS_CONNECTION_STRING_CONFLICT:
    "The database URL must not carry TLS parameters; configure the database TLS mode explicitly.",
  DATABASE_TLS_MODE_INVALID: 'The database TLS mode must be exactly "verify-full" or "disable".',
  DATABASE_TLS_REQUIRED_IN_PRODUCTION:
    "A production database connection must use certificate-verified TLS.",
  DATABASE_URL_INVALID: "The database URL must be an absolute postgres:// or postgresql:// URL.",
});

/** Never carries the connection string, host, port, database name, credentials, certificate, CA
 * material, or the offending mode value. */
export class DatabaseTransportError extends Error {
  readonly code: DatabaseTransportErrorCode;

  constructor(code: DatabaseTransportErrorCode) {
    super(errorMessages[code]);
    this.name = "DatabaseTransportError";
    this.code = code;
    this.stack = `${this.name}: ${this.message}`;
    Object.freeze(this);
  }
}

export interface DatabaseTransportPolicy {
  readonly mode: DatabaseTlsMode;
  /** PEM trust material for a private PostgreSQL CA. Optional: when omitted, Node's own trusted CA
   * set is used. Never logged, never echoed in an error. */
  readonly certificateAuthority?: string;
}

export interface DatabaseTransportPolicyInput {
  readonly mode?: unknown;
  readonly certificateAuthority?: unknown;
}

export interface CreateDatabaseTransportPolicyOptions {
  /** Defaults to production, so an omitted environment never silently relaxes transport security. */
  readonly environment?: DatabaseTransportEnvironment;
}

/**
 * Every TLS-related parameter `pg-connection-string@2.14.0` recognizes in a PostgreSQL URL. These
 * are rejected outright rather than merged, because the pinned driver resolves them in a way that
 * silently defeats an explicit policy: `pg`'s own `ConnectionParameters` does
 * `Object.assign({}, config, parse(config.connectionString))`
 * (`pg/lib/connection-parameters.js`), so a URL parameter **overwrites** the `ssl` object a caller
 * passed alongside it. Verified directly against a live TLS PostgreSQL instance: a
 * `?sslmode=disable` URL combined with an explicit certificate-verifying `ssl` object connects in
 * plaintext.
 *
 * The pinned release additionally aliases `prefer`/`require`/`verify-ca` to full verification while
 * printing a deprecation warning that they will adopt weaker libpq semantics in `pg@9`, so even
 * a URL that looks safe today is not a durable guarantee. One typed policy is the whole contract.
 */
const CONNECTION_STRING_TLS_PARAMETERS = Object.freeze([
  "ssl",
  "sslcert",
  "sslkey",
  "sslmode",
  "sslnegotiation",
  "sslpassword",
  "sslrootcert",
  "uselibpqcompat",
]);

function parseDatabaseUrl(databaseUrl: string): URL {
  let url: URL;
  try {
    url = new URL(databaseUrl);
  } catch {
    throw new DatabaseTransportError("DATABASE_URL_INVALID");
  }
  if (url.protocol !== "postgres:" && url.protocol !== "postgresql:") {
    throw new DatabaseTransportError("DATABASE_URL_INVALID");
  }
  return url;
}

/** The host a certificate's identity must match — the exact host the driver will connect to. */
export function databaseHostFromUrl(databaseUrl: string): string {
  const url = parseDatabaseUrl(databaseUrl);
  // `URL.hostname` keeps IPv6 literals bracketed; TLS identity checking wants the bare address.
  const hostname = url.hostname;
  return hostname.startsWith("[") && hostname.endsWith("]") ? hostname.slice(1, -1) : hostname;
}

/** Whether the database endpoint is an unambiguous loopback literal. Used only to decide whether
 * the development plaintext mode is even permissible; it is never a production allowance. */
function isLoopbackDatabaseHost(host: string): boolean {
  const normalized = host.toLowerCase();
  if (normalized === "localhost" || normalized.endsWith(".localhost")) {
    return true;
  }
  if (net.isIPv4(normalized)) {
    return normalized.startsWith("127.");
  }
  if (net.isIPv6(normalized)) {
    return normalized === "::1" || normalized === "::ffff:127.0.0.1";
  }
  return false;
}

/**
 * Validates the typed transport policy. Parsing is deliberately separate from environment policy,
 * matching the convention the public-signup gate already established: a malformed mode is reported
 * as malformed in every environment, never relabeled as a production failure.
 */
export function createDatabaseTransportPolicy(
  input: DatabaseTransportPolicyInput = {},
  options: CreateDatabaseTransportPolicyOptions = {},
): DatabaseTransportPolicy {
  const environment = options.environment ?? "production";

  let mode: DatabaseTlsMode;
  if (input.mode === undefined) {
    // Production fails safe to verified TLS; development keeps the plaintext disposable-PostgreSQL
    // workflow this repository's harness relies on.
    mode = environment === "production" ? "verify-full" : "disable";
  } else if (input.mode === "verify-full" || input.mode === "disable") {
    mode = input.mode;
  } else {
    // No coercion of booleans, `1`, `"TRUE"`, `" verify-full "`, or any other loose spelling.
    throw new DatabaseTransportError("DATABASE_TLS_MODE_INVALID");
  }

  if (environment === "production" && mode !== "verify-full") {
    throw new DatabaseTransportError("DATABASE_TLS_REQUIRED_IN_PRODUCTION");
  }

  if (
    input.certificateAuthority !== undefined &&
    (typeof input.certificateAuthority !== "string" ||
      input.certificateAuthority.trim().length === 0)
  ) {
    throw new DatabaseTransportError("DATABASE_TLS_MODE_INVALID");
  }

  return Object.freeze({
    ...(typeof input.certificateAuthority === "string"
      ? { certificateAuthority: input.certificateAuthority }
      : {}),
    mode,
  });
}

/**
 * Rejects any database URL carrying its own TLS parameters. Called before a pool or client is ever
 * constructed, so a URL can never silently downgrade or contradict the validated policy — there is
 * exactly one place transport security is decided.
 */
export function assertNoConnectionStringTlsParameters(databaseUrl: string): void {
  const url = parseDatabaseUrl(databaseUrl);
  for (const [name] of url.searchParams) {
    if (CONNECTION_STRING_TLS_PARAMETERS.includes(name.toLowerCase())) {
      throw new DatabaseTransportError("DATABASE_TLS_CONNECTION_STRING_CONFLICT");
    }
  }
}

/**
 * Translates the validated policy into the exact pinned-`pg` options that achieve it, and asserts
 * the URL cannot override them.
 *
 * `verify-full` is **not** simply `ssl: true` or `{ rejectUnauthorized: true }`. Verified directly
 * against a live TLS PostgreSQL instance: those verify the certificate *chain*, but `pg` only sets
 * `options.servername` for non-IP hosts (`pg/lib/connection.js`) and passes `tls.connect` a bare
 * socket carrying no host, so for an IP endpoint Node has no identity to check and falls back to
 * the fixed name `localhost` — never the address actually dialled. A certificate issued for an
 * entirely different name is therefore accepted when connecting to an IP address. Supplying an
 * explicit `checkServerIdentity` pinned to the configured host closes that gap for DNS and IP hosts
 * alike (proven: a certificate valid only for `localhost` is rejected with
 * `ERR_TLS_CERT_ALTNAME_INVALID` when reached via `127.0.0.1`).
 */
export function databaseTlsConnectionOptions(
  databaseUrl: string,
  policy: DatabaseTransportPolicy,
): false | ConnectionOptions {
  assertNoConnectionStringTlsParameters(databaseUrl);
  if (policy.mode === "disable") {
    return false;
  }
  const host = databaseHostFromUrl(databaseUrl);
  return {
    ...(policy.certificateAuthority === undefined ? {} : { ca: policy.certificateAuthority }),
    // Chain verification. There is no configuration that can set this to `false`.
    rejectUnauthorized: true,
    // Identity verification against the host actually being connected to — never the SNI value pg
    // may or may not have set, and never skipped for an IP endpoint.
    checkServerIdentity: (_servername: string, certificate: tls.PeerCertificate) =>
      tls.checkServerIdentity(host, certificate),
  };
}

/**
 * The one production guard every executable database path shares: a production deployment must use
 * `verify-full`, and its URL must not carry TLS parameters. There is no production plaintext
 * exception — not for loopback, not for an RFC1918 address, not for a Docker service name. A
 * production process that genuinely runs beside its database still gets certificate-verified TLS,
 * which costs nothing and removes an entire class of "it was only internal" misconfiguration.
 */
export function assertProductionDatabaseTransport(
  databaseUrl: string,
  policy: DatabaseTransportPolicy,
  environment: DatabaseTransportEnvironment,
): void {
  assertNoConnectionStringTlsParameters(databaseUrl);
  if (environment !== "production") {
    return;
  }
  if (policy.mode !== "verify-full") {
    throw new DatabaseTransportError("DATABASE_TLS_REQUIRED_IN_PRODUCTION");
  }
}

/** A fixed, generic description of the effective transport for diagnostics. Never includes the
 * URL, host, port, database name, credentials, certificate, or CA path. */
export function describeDatabaseTransport(policy: DatabaseTransportPolicy): string {
  return policy.mode === "verify-full"
    ? `TLS required with certificate and hostname verification${
        policy.certificateAuthority === undefined ? "" : " (explicit private CA supplied)"
      }.`
    : "TLS disabled (development/test plaintext).";
}

export { isLoopbackDatabaseHost };