import * as fs from "fs";
import * as readline from "readline";

import { Readable } from "stream";
import { Observer } from "rxjs/Observer";
import { Observable, Subscription } from "rxjs";

import { Line } from "./Line";
import { IExamImportParser } from "../models/IExamImportParser";
import { IParserLine } from "../models/IParserLine";

/**
 * Handles the parsing of file directly
 *
 * @export
 * @class FileParser
 */
export class Parser implements IExamImportParser {
    constructor() { }
    /**
     * Take a stream (Line) and parses
     * @param stream stream to parse
     */
    private parse(stream: Readable): Observable<IParserLine> {
        return Observable.create((observer: any) => {
            let lineNo = 0;
            let eof = false;

            const rl = readline.createInterface({
                input: stream,
                terminal: false
            });

            rl.on("line", line => {
                if (line != null && line.length > 0) {
                    observer.next(new Line(lineNo++, line));
                }
            });
            rl.on("close", () => {
                observer.complete();
            });
        });
    }
    /**
     * Opens a file and starts breaking down the lines
     *
     * @param {string} fileName
     * @returns {(Subscriber<string[]> | null)}
     * @memberof FileParser
     */
    open(fileName: string): Observable<IParserLine> {
        const readStream = fs.createReadStream(fileName);
        return this.parse(readStream);
    }
    fromString(file: string): Observable<IParserLine> {
        let stream = new Readable();
        stream.push(file);
        stream.push(null);
        return this.parse(stream);
    }
}