joplin/packages/editor/CodeMirror/utils/overwriteModeExtension.ts

import { keymap, EditorView } from '@codemirror/view';
import { StateField, Facet, StateEffect } from '@codemirror/state';

const overwriteModeFacet = Facet.define({
	combine: values => values[0] ?? false,
	enables: facet => [
		EditorView.inputHandler.of((
			view, _from, _to, text, insert,
		) => {
			if (view.composing || view.compositionStarted || view.state.readOnly) {
				return false;
			}

			if (view.state.facet(facet) && text) {
				const originalTransaction = insert();
				const newState1 = originalTransaction.state;
				const emptySelections1 = newState1.selection.ranges.filter(
					range => range.empty,
				);

				view.dispatch([
					originalTransaction,
					newState1.update({
						changes: emptySelections1.map(range => {
							const line = newState1.doc.lineAt(range.to);
							return {
								from: range.to,
								to: Math.min(line.to, range.to + text.length),
								insert: '',
							};
						}).filter(change => change.from !== change.to || change.insert),
					}),
				]);
				return true;
			}
			return false;
		}),
		EditorView.theme({
			'&.-overwrite .cm-cursor': {
				borderLeftWidth: '0.5em',
			},
		}),
	],
});

export const toggleOverwrite = StateEffect.define<boolean>();
const overwriteModeState = StateField.define({
	create: () => false,
	update: (oldValue, tr) => {
		for (const e of tr.effects) {
			if (e.is(toggleOverwrite)) {
				return e.value;
			}
		}
		return oldValue;
	},
	provide: (field) => [
		overwriteModeFacet.from(field),
		EditorView.editorAttributes.from(field, on => ({
			class: on ? '-overwrite' : '',
		})),
	],
});

const overwriteModeExtension = [
	overwriteModeState,
	keymap.of([{
		key: 'Insert',
		run: (view) => {
			view.dispatch({
				effects: toggleOverwrite.of(!view.state.field(overwriteModeState)),
			});
			return false;
		},
	}]),
];

export default overwriteModeExtension;