scroll/src/common/editor.ts

import Ansi, { KeyCommand } from './ansi.ts';
import Buffer from './buffer.ts';
import Document from './document.ts';
import { IPoint, ITerminalSize, logToFile, VERSION } from './mod.ts';
import { ctrlKey } from './utils.ts';

export class Editor {
	/**
	 * The output buffer for the terminal
	 * @private
	 */
	#buffer: Buffer;
	/**
	 * The size of the screen in rows/columns
	 * @private
	 */
	#screen: ITerminalSize;
	/**
	 * The current location of the mouse cursor
	 * @private
	 */
	#cursor: IPoint;
	/**
	 * The current scrolling offset
	 */
	#offset: IPoint;
	/**
	 * The document being edited
	 * @private
	 */
	#document: Document;
	constructor(terminalSize: ITerminalSize) {
		this.#buffer = new Buffer();
		this.#screen = terminalSize;
		this.#cursor = {
			x: 0,
			y: 0,
		};
		this.#offset = {
			x: 0,
			y: 0,
		};

		this.#document = Document.empty();
	}

	public async open(filename: string): Promise<Editor> {
		await this.#document.open(filename);

		return this;
	}

	// --------------------------------------------------------------------------
	// Command/input mapping
	// --------------------------------------------------------------------------

	/**
	 * Determine what to do based on input
	 * @param input - the decoded chunk of stdin
	 */
	public processKeyPress(input: string): boolean {
		switch (input) {
			case ctrlKey('q'):
				this.clearScreen().then(() => {});
				return false;

			case KeyCommand.Home:
				this.#cursor.x = 0;
				break;

			case KeyCommand.End:
				this.#cursor.x = this.#screen.cols - 1;
				break;

			case KeyCommand.PageUp:
			case KeyCommand.PageDown:
				{
					let times = this.#screen.rows;
					while (times--) {
						this.moveCursor(
							input === KeyCommand.PageUp
								? KeyCommand.ArrowUp
								: KeyCommand.ArrowDown,
						);
					}
				}
				break;

			case KeyCommand.ArrowUp:
			case KeyCommand.ArrowDown:
			case KeyCommand.ArrowRight:
			case KeyCommand.ArrowLeft:
				this.moveCursor(input);
				break;
		}

		return true;
	}

	private moveCursor(char: string): void {
		switch (char) {
			case KeyCommand.ArrowLeft:
				if (this.#cursor.x > 0) {
					this.#cursor.x--;
				}
				break;
			case KeyCommand.ArrowRight:
				if (this.#cursor.x < this.#screen.cols) {
					this.#cursor.x++;
				}
				break;
			case KeyCommand.ArrowUp:
				if (this.#cursor.y > 0) {
					this.#cursor.y--;
				}
				break;
			case KeyCommand.ArrowDown:
				if (this.#cursor.y < this.#screen.rows) {
					this.#cursor.y++;
				}
				break;
		}
	}

	private scroll(): void {
		if (this.#cursor.y < this.#offset.y) {
			this.#offset.y = this.#cursor.y;
		}
		if (this.#cursor.y >= this.#offset.y + this.#screen.rows) {
			this.#offset.y = this.#cursor.y - this.#screen.rows + 1;
		}
	}

	// --------------------------------------------------------------------------
	// Terminal Output / Drawing
	// --------------------------------------------------------------------------

	/**
	 * Clear the screen and write out the buffer
	 */
	public async refreshScreen(): Promise<void> {
		this.scroll();
		this.#buffer.append(Ansi.HideCursor);
		this.#buffer.append(Ansi.ResetCursor);
		this.drawRows();
		this.#buffer.append(
			Ansi.moveCursor(this.#cursor.y, this.#cursor.x),
		);
		this.#buffer.append(Ansi.ShowCursor);

		await this.#buffer.flush();
	}

	private async clearScreen(): Promise<void> {
		this.#buffer.append(Ansi.ClearScreen);
		this.#buffer.append(Ansi.ResetCursor);

		await this.#buffer.flush();
	}

	private drawRows(): void {
		for (let y = 0; y < this.#screen.rows; y++) {
			let filerow = y + this.#offset.y;
			if (filerow >= this.#document.numRows) {
				this.drawPlaceholderRow(y);
			} else {
				this.drawFileRow(y);
			}
		}
	}

	private drawFileRow(y: number): void {
		const row = this.#document.row(y);
		if (row === null) {
			logToFile(`Warning: trying to draw non-existent row '${y}'`);
			return this.drawPlaceholderRow(y);
		}

		let len = row.chars.length ?? 0;
		if (len > this.#screen.cols) {
			len = this.#screen.cols;
		}

		this.#buffer.append(row.toString(), len);
		this.#buffer.appendLine(Ansi.ClearLine);
	}

	private drawPlaceholderRow(y: number): void {
		if (y === Math.trunc(this.#screen.rows / 2) && this.#document.isEmpty()) {
			const message = `Kilo editor -- version ${VERSION}`;
			const messageLen = (message.length > this.#screen.cols)
				? this.#screen.cols
				: message.length;
			let padding = Math.trunc((this.#screen.cols - messageLen) / 2);
			if (padding > 0) {
				this.#buffer.append('~');
				padding -= 1;

				this.#buffer.append(' '.repeat(padding));
			}

			this.#buffer.append(message, messageLen);
		} else {
			this.#buffer.append('~');
		}

		this.#buffer.append(Ansi.ClearLine);
		if (y < this.#screen.rows - 1) {
			this.#buffer.appendLine();
		}
	}
}