dbmedialab/reader-critics

//
// LESERKRITIKK v2 (aka Reader Critics)
// Copyright (C) 2017 DB Medialab/Aller Media AS, Oslo, Norway
// https://github.com/dbmedialab/reader-critics/
//
// This program is free software: you can redistribute it and/or modify it under
// the terms of the GNU General Public License as published by the Free Software
// Foundation, either version 3 of the License, or (at your option) any later
// version.
//
// This program is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
// FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License along with
// this program. If not, see <http://www.gnu.org/licenses/>.
//

import * as callsite from 'callsite';
import * as cluster from 'cluster';
import * as debug from 'debug';

import { isObject } from 'lodash';

/** First component of debug's logger */
export const appName = 'app';  // As short as possible, please

const regexFileSuffix = /\.[a-z]+?$/;
const regexDeleteIndex = /\/index$/;
const regexForwardSlashes = /\//g;
const regexEnvSuffix = /\.(:?live|mock)$/;
const regexEnvFolder = /\/(:?live|mock)\//;

/**
 * Dynamically create a log channel based on the caller location.
 * @return function (...args : any[]) => void
 */
export function createLog(moduleName? : string) : (...args : any[]) => void {
    const processID = getProcessID();
    const name = moduleName !== undefined ? moduleName : logChannelName (callsite());

    return debug(`${appName}${processID}:${name}`);
}

/**
 * Creates a log channel name from a callstack.
 * @return string
 */
const logChannelName = (callstack: callsite.CallSite[]) : string => {
    if (!isCallTrace(callstack)) {
        return appName;
    }

    // Get second item of the call stack, this points back to the place where
    // "createLog" is invoked. Then replace several things in the file path
    // to create a log channel name in "debug" syntax.
    const originName = deleteDuplicates(callstack[1].getFileName()
        // strip file suffix
        .replace(regexFileSuffix, '')
        // strip "index"
        .replace(regexDeleteIndex, '')
        // string environment suffixes from...
        .replace(regexEnvFolder, ':')
        // ...service modules etc.
        .replace(regexEnvSuffix, '')
        // replace slashes with colons
        .replace(regexForwardSlashes, ':'));

    // Replace "app" directory name with the application name
    const pos = originName.lastIndexOf(':app:');
    return originName.substr(pos + 5);
};

/**
 * Deletes duplicate entries at the end of the log channel name
 */
const deleteDuplicates = (s : string) : string => {
    const a = s.split(/:/);

    if (a.length > 1 && (a[a.length - 1] === a[a.length - 2])) {
        a.pop();
    }

    return a.join(':');
};

/**
 * Checks if the callstack is useable.
 * @return boolean
 */
const isCallTrace = (callstack: callsite.CallSite[]) : boolean => (
    typeof callstack.length === 'number'
    && callstack.length > 1
    && callstack[1].getFunctionName() === null
);

/**
 * Checks for cluster environments and returns a number > 1 for worker processes,
 * a 0 for the master node if running multiple processes. Returns an empty string
 * when run as a single process.
 */
function getProcessID() : string {
    const hasWorkers = isObject(cluster.workers) && Object.keys(cluster.workers).length > 0;
    const isM = cluster.isMaster;
    const isW = cluster.isWorker;

    // Multi-process master
    if (isM && !isW && hasWorkers) {
        return ':m';
    }

    // Multi-process worker
    if (!isM && isW && !hasWorkers) {
        return `:${cluster.worker.id}`;
    }

    // Single-process environment
    return '';
}