scroll/src/common/termios.ts

import { die, importForRuntime } from './mod.ts';

export const STDIN_FILENO = 0;
export const STOUT_FILENO = 1;
export const TCSANOW = 0;
export const TCSAFLUSH = 2;

export const TERMIOS_SIZE = 60;

/**
 * Common interface for setting Termios properties
 */
export interface ITermios {
	/**
	 * Are we currently in raw mode?
	 */
	inRawMode: boolean;

	/**
	 * Toggles on raw mode
	 */
	enableRawMode(): void;

	/**
	 * Restores canonical mode
	 */
	disableRawMode(): void;
}

let termiosSingleton: ITermios | null = null;

export const getTermios = async () => {
	if (termiosSingleton !== null) {
		return termiosSingleton;
	}

	// Get the runtime-specific ffi wrappers
	const { tcgetattr, tcsetattr, cfmakeraw, getPointer } =
		await importForRuntime('ffi');

	/**
	 * Implementation to toggle raw mode
	 */
	class Termios implements ITermios {
		/**
		 * Are we in raw mode?
		 * @private
		 */
		#inRawMode: boolean;

		/**
		 * The saved version of the termios struct for cooked/canonical mode
		 * @private
		 */
		#cookedTermios: Uint8Array;

		/**
		 * The data for the termios struct we are manipulating
		 * @private
		 */
		readonly #termios: Uint8Array;

		/**
		 * The pointer to the termios struct
		 * @private
		 */
		readonly #ptr: any;

		constructor() {
			this.#inRawMode = false;

			// These are the TypedArrays linked to the raw pointer data
			this.#cookedTermios = new Uint8Array(TERMIOS_SIZE);
			this.#termios = new Uint8Array(TERMIOS_SIZE);

			// The current pointer for C
			this.#ptr = getPointer(this.#termios);
		}

		get inRawMode() {
			return this.#inRawMode;
		}

		enableRawMode() {
			if (this.#inRawMode) {
				throw new Error('Can not enable raw mode when in raw mode');
			}

			// Get the current termios settings
			let res = tcgetattr(STDIN_FILENO, this.#ptr);
			if (res === -1) {
				die('Failed to get terminal settings');
			}

			// The #ptr property is pointing to the #termios TypedArray. As the pointer
			// is manipulated, the TypedArray is as well. We will use this to save
			// the original canonical/cooked terminal settings for disabling raw mode later.
			this.#cookedTermios = new Uint8Array(this.#termios, 0, 60);

			// Update termios struct with (most of the) raw settings
			res = cfmakeraw(this.#ptr);
			if (res === -1) {
				die('Failed to call cfmakeraw');
			}

			// @TODO: Tweak a few more terminal settings

			// Actually set the new termios settings
			res = tcsetattr(STDIN_FILENO, TCSANOW, this.#ptr);
			if (res === -1) {
				die('Failed to update terminal settings. Can\'t enter raw mode');
			}

			this.#inRawMode = true;
		}

		disableRawMode() {
			// Don't even bother throwing an error if we try to disable raw mode
			// and aren't in raw mode. It just doesn't really matter.
			if (!this.#inRawMode) {
				return;
			}

			const oldTermiosPtr = getPointer(this.#cookedTermios);
			const res = tcsetattr(STDIN_FILENO, TCSANOW, oldTermiosPtr);
			if (res === -1) {
				die('Failed to restore canonical mode.');
			}

			this.#inRawMode = false;
		}
	}

	termiosSingleton = new Termios();

	return termiosSingleton;
};