manyfest/source/Manyfest-HashTranslation.js

JSON Object Manifest for Data Description and Parsing

/**
* @author <steven@velozo.com>
*/
let libSimpleLog = require('./Manyfest-LogToConsole.js');

/**
* Hash Translation
*
* This is a very simple translation table for hashes, which allows the same schema to resolve
* differently based on a loaded translation table.
*
* This is to prevent the requirement for mutating schemas over and over again when we want to
* reuse the structure but look up data elements by different addresses.
*
* One side-effect of this is that a translation table can "override" the built-in hashes, since
* this is always used to resolve hashes before any of the functionCallByHash(pHash, ...) perform
* their lookups by hash.
*
* @class ManyfestHashTranslation
*/
class ManyfestHashTranslation
{
    /**
     * @param {function} [pInfoLog] - (optional) A logging function for info messages
     * @param {function} [pErrorLog] - (optional) A logging function for error messages
     */
	constructor(pInfoLog, pErrorLog)
	{
		// Wire in logging
		this.logInfo = (typeof(pInfoLog) === 'function') ? pInfoLog : libSimpleLog;
		this.logError = (typeof(pErrorLog) === 'function') ? pErrorLog : libSimpleLog;

        this.translationTable = {};
	}

    /**
     * @return {number} The number of translations in the table
     */
    translationCount()
    {
        return Object.keys(this.translationTable).length;
    }

    /**
     * @param {object} pTranslation - An object containing source:destination hash pairs to add to the translation table
     */
    addTranslation(pTranslation)
    {
        // This adds a translation in the form of:
        // { "SourceHash": "DestinationHash", "SecondSourceHash":"SecondDestinationHash" }
        if (typeof(pTranslation) != 'object')
        {
            this.logError(`Hash translation addTranslation expected a translation be type object but was passed in ${typeof(pTranslation)}`);
            return false;
        }

        let tmpTranslationSources = Object.keys(pTranslation)

        tmpTranslationSources.forEach(
            (pTranslationSource) =>
            {
                if (typeof(pTranslation[pTranslationSource]) != 'string')
                {
                    this.logError(`Hash translation addTranslation expected a translation destination hash for [${pTranslationSource}] to be a string but the referrant was a ${typeof(pTranslation[pTranslationSource])}`);
                }
                else
                {
                    this.translationTable[pTranslationSource] = pTranslation[pTranslationSource];
                }
            });
    }

    /**
     * @param {string} pTranslationHash - The source hash to remove from the translation table
     */
    removeTranslationHash(pTranslationHash)
    {
        delete this.translationTable[pTranslationHash];
    }

    /**
     * This removes translations.
     * If passed a string, just removes the single one.
     * If passed an object, it does all the source keys.
     *
     * @param {string|object} pTranslation - Either a source hash string to remove, or an object containing source:destination hash pairs to remove
     *
     * @return {boolean} True if the removal was successful, false otherwise
     */
    removeTranslation(pTranslation)
    {
        if (typeof(pTranslation) == 'string')
        {
            this.removeTranslationHash(pTranslation);
            return true;
        }
        else if (typeof(pTranslation) == 'object')
        {
            let tmpTranslationSources = Object.keys(pTranslation)

            tmpTranslationSources.forEach(
                (pTranslationSource) =>
                {
                    this.removeTranslation(pTranslationSource);
                });
            return true;
        }
        else
        {
            this.logError(`Hash translation removeTranslation expected either a string or an object but the passed-in translation was type ${typeof(pTranslation)}`);
            return false;
        }
    }

    clearTranslations()
    {
        this.translationTable = {};
    }

    /**
     * @param {string} pTranslation - The source hash to translate
     *
     * @return {string} The translated hash, or the original if no translation exists
     */
    translate(pTranslation)
    {
        if (pTranslation in this.translationTable)
        {
            return this.translationTable[pTranslation];
        }
        else
        {
            return pTranslation;
        }
    }
}

module.exports = ManyfestHashTranslation;