add function to read a line

src/core/editor.ts

@@ -0,0 +1,110 @@
+import { File } from './file';
+import * as fs from 'fs/promises';
+import * as readline from 'node:readline/promises';
+
+export interface Reader {
+	readLine(pos: number): Promise<string>;
+	close(): Promise<void>;
+}
+
+export interface Writer {
+	close(): Promise<void>;
+}
+
+interface LineInfo {
+	end: number,
+	length: number
+}
+
+export class Editor implements Reader, Writer{
+
+	public readLines: fs.FileHandle['readLines'];
+	protected chunkSize: number = 1024;
+	protected lineInfo: Array<LineInfo>;
+	protected newLineCharacter: number | string = 0x0a;
+	protected currentLine: number = 0;
+	protected EOF: boolean = false;
+	//protected watcher: IterableIterator<fs.FileChangeInfo<string>>;
+
+	constructor(
+		protected ref: File,
+		protected file: fs.FileHandle
+	) {
+		this.readLines = file.readLines;
+		this.lineInfo = [];
+
+		// TODO: watch file for changes
+		//fs.watch(ref.path);
+	}
+
+	get fileHandle() {
+		return this.file;
+	}
+
+	async from(file: File): Promise<Editor> {
+		const handler = await fs.open(file.path);
+		return new Editor(file, handler);
+	}
+
+	async close(): Promise<void> {
+		await this.file.close();
+	}
+
+	protected async addLineInfo(start: number, length: number): void {
+		const end = start + length;
+		this.lineInfo.push({end, length});
+	}
+
+
+
+	protected async analyzeNextLine(): Promise<string> {
+		const start = this.lineInfo.slice(-1)[0].end;
+
+
+		const stream = this.file.createReadStream({start});
+
+		return new Promise((resolve, reject) => {
+			let chunk: Buffer | null = null;
+			const chunks: Buffer[] = [];
+			stream.on('error', reject);
+			stream.on('readable', () => {
+				while(null !== (chunk = stream.read(this.chunkSize))) {
+					const i = chunk.indexOf(this.newLineCharacter);
+					if(i !== -1) {
+						const str = Buffer.concat(chunks).toString() + chunk.toString().slice(0, i);
+						stream.close();
+						this.addLineInfo(start, str.length);
+						return resolve(str);
+					} else {
+						chunks.push(chunk);
+					}
+				}
+
+				const str = Buffer.concat(chunks).toString();
+				this.addLineInfo(start, str.length);
+				this.EOF = true;
+
+				resolve(str);
+
+			});
+		});
+	}
+
+	// TODO: think about to give back a buffer instead of a string
+	async readLine(pos: number = this.currentLine): Promise<string> {
+		let line: string | undefined = undefined;
+		while ( !this.EOF && pos >= this.lineInfo.length ) {
+			line = await this.analyzeNextLine();
+		}
+
+		if(line === undefined) {
+			const {end, length} = this.lineInfo[pos];
+			line = (await this.file.read({position: end - length, length})).buffer.toString();
+		}
+
+
+		return line;
+
+	}
+
+}