'use strict';

const assert = require('assert'),
    path = require('path'),
    spawn = require('child_process').spawn,
    stream = require('stream'),
    { StringDecoder } = require('string_decoder'),
    TransformStream = stream.Transform;

const LOGTAIL_CMD = path.join(__dirname, 'scripts/logtail.sh');

class LogStream extends TransformStream {
    constructor(options) {
        super();
        this._options = Object.assign({ source: 'unknown', format: 'json' }, options);
        this._decoder = new StringDecoder();
        this._soFar = '';
    }

    _format(line) {
        if (this._options.format !== 'json') return line + '\n';

        const data = line.split(' '); // logs are <ISOtimestamp> <msg>
        let timestamp = (new Date(data[0])).getTime();
        if (isNaN(timestamp)) timestamp = 0;
        const message = line.slice(data[0].length+1);

        // ignore faulty empty logs
        if (!timestamp && !message) return;

        return JSON.stringify({
            realtimeTimestamp: timestamp * 1000,
            message: message,
            source: this._options.source
        }) + '\n';
    }

    _transform(chunk, encoding, callback) {
        const data = this._soFar + this._decoder.write(chunk);
        let start = this._soFar.length, end = -1;
        while ((end = data.indexOf('\n', start)) !== -1) {
            const line = data.slice(start, end); // does not include end
            this.push(this._format(line));
            start = end + 1;
        }
        this._soFar = data.slice(start);
        callback(null);
    }

    _flush(callback) {
        const line = this._soFar + this._decoder.end();
        this.push(this._format(line));
        callback(null);
    }
}

function tail(filePaths, options) {
    assert(Array.isArray(filePaths));
    assert.strictEqual(typeof options, 'object');

    const lines = options.lines === -1 ? '+1' : options.lines,
        follow = options.follow;

    const args = [ '--lines=' + lines ];
    if (follow) args.push('--follow');

    return spawn(LOGTAIL_CMD, args.concat(filePaths));
}

function journalctl(unit, options) {
    assert.strictEqual(typeof unit, 'string');
    assert.strictEqual(typeof options, 'object');

    const args = [];
    args.push('--lines=' + (options.lines === -1 ? 'all' : options.lines));
    args.push(`--unit=${unit}`);
    args.push('--no-pager');
    args.push('--output=short-iso');

    if (options.follow) args.push('--follow');

    return spawn('journalctl', args);
}

exports = module.exports = {
    tail,
    journalctl,
    LogStream
};