bytebeat-composer/src/code-editor/textarea.ts

export function initTextarea(editCallback: () => void, textarea: HTMLTextAreaElement) {
	textarea.addEventListener("input", () => editCallback());
	let keyTrap = true;
	textarea.addEventListener("keydown", e => {
		if (!e.altKey && !e.ctrlKey) {
			if (e.key === "Escape") {
				if (keyTrap) {
					e.preventDefault();
					keyTrap = false;
				}
			} else if (e.key === "Tab" && keyTrap) {
				e.preventDefault();
				const { selectionStart, selectionEnd } = textarea;
				if (e.shiftKey) {
					// remove indentation on all selected lines
					const lines = textarea.value.split("\n");

					function getLine(char: number) {
						let line = 0;
						for (let c = 0; ; line++) {
							c += lines[line].length;
							if (c > char) { 
								break;
							}
						}
						return line;
					};
					const startLine = getLine(selectionStart);
					const endLine = getLine(selectionEnd);
					let newSelectionStart = selectionStart;
					let newSelectionEnd = selectionEnd;
					for (let i = startLine; i <= endLine; i++) {
						if (lines[i][0] === "\t") {
							lines[i] = lines[i].slice(1);
							if (i === startLine) {
								newSelectionStart--;
							}
							newSelectionEnd--;
						}
					}

					textarea.value = lines.join("\n");
					textarea.setSelectionRange(newSelectionStart, newSelectionEnd);
				} else {
					// add tab character
					textarea.value = `${textarea.value.slice(0, selectionStart)}\t${textarea.value.slice(
						selectionEnd,
					)}`;
					textarea.setSelectionRange(selectionStart + 1, selectionStart + 1);
				}
				editCallback();
			} else {
				keyTrap = false;
			}
		}
	});
}