/**
 * Which browser this harness should drive.
 *
 * Upstream only ever drives a browser on localhost. This fork adds a remote
 * target so pi can drive a shared Chrome on another host (see FORK.md).
 *
 * Resolution is pure — no I/O — so the status command can report the configured
 * intent without touching the network, and the daemon can resolve the same way
 * in its own process.
 */

/** Default remote CDP endpoint: castle's Chrome, exposed on the wire network. */
export const DEFAULT_REMOTE_CDP = "10.88.0.25:9223";

/** Values of BU_CDP_HTTP that mean "ignore the default, use this machine". */
const LOCAL_ALIASES = new Set(["local", "localhost", "off", "none", "0", "no"]);

export type CdpTarget =
  | {
      readonly kind: "remote";
      readonly host: string;
      readonly port: number;
      /** "env" was asked for explicitly; "default" is this fork's built-in. */
      readonly source: "env" | "default";
    }
  | { readonly kind: "local"; readonly source: "env" }
  | { readonly kind: "invalid"; readonly raw: string; readonly reason: string };

/**
 * Precedence:
 *   BU_CDP_HTTP="host:port"  -> that remote, and a failure to reach it is fatal
 *   BU_CDP_HTTP=local|off|…  -> upstream behaviour, this machine's own browser
 *   unset                    -> DEFAULT_REMOTE_CDP, falling back to local when
 *                               it isn't reachable
 *
 * The asymmetry is deliberate. An explicit endpoint is an instruction, so
 * silently driving a different browser instead would be wrong. The built-in
 * default is only a preference, so a laptop away from the wire network still
 * gets the local browser the extension was originally written for.
 */
export const resolveCdpTarget = (env: NodeJS.ProcessEnv = process.env): CdpTarget => {
  const raw = env["BU_CDP_HTTP"]?.trim();

  if (raw === undefined || raw === "") {
    const parsed = parseHostPort(DEFAULT_REMOTE_CDP);
    // Unreachable in practice: the constant above is validated by its own test.
    if (!parsed) return { kind: "local", source: "env" };
    return { kind: "remote", host: parsed.host, port: parsed.port, source: "default" };
  }

  if (LOCAL_ALIASES.has(raw.toLowerCase())) return { kind: "local", source: "env" };

  const parsed = parseHostPort(raw);
  if (!parsed) {
    return {
      kind: "invalid",
      raw,
      reason: `expected "host:port" or one of ${[...LOCAL_ALIASES].join(", ")}`,
    };
  }
  return { kind: "remote", host: parsed.host, port: parsed.port, source: "env" };
};

const parseHostPort = (value: string): { host: string; port: number } | null => {
  const sep = value.lastIndexOf(":");
  if (sep === -1) return null;
  const host = value.slice(0, sep).trim();
  const port = Number(value.slice(sep + 1).trim());
  if (!host) return null;
  if (!Number.isInteger(port) || port <= 0 || port >= 65536) return null;
  return { host, port };
};

/** One-line description for /browser-status and error messages. */
export const describeCdpTarget = (target: CdpTarget): string => {
  switch (target.kind) {
    case "remote":
      return `${target.host}:${target.port}` + (target.source === "default" ? " (built-in default)" : " (BU_CDP_HTTP)");
    case "local":
      return "this machine's own browser (BU_CDP_HTTP=local)";
    case "invalid":
      return `invalid BU_CDP_HTTP "${target.raw}" — ${target.reason}`;
  }
};