/** @module data */
/** @hidden */ 
const uuid = require('uuid');

// Maps for number <-> hex string conversion
/** @hidden */ 
let byteToHex = [];
for (let i = 0; i < 256; i++) {
    byteToHex[i] = (i + 0x100).toString(16).substr(1);
}

/**
 * Helper class to generate unique object IDs.
 * It supports two types of IDs: long and short.
 * 
 * Long IDs are string GUIDs. They are globally unique and 32-character long.
 * 
 * ShortIDs are just 9-digit random numbers. They are not guaranteed be unique.
 * 
 * ### Example ###
 * 
 *     IdGenerator.nextLong();      // Possible result: "234ab342c56a2b49c2ab42bf23ff991ac"
 *     IdGenerator.nextShort();     // Possible result: "23495247"
 * 
 */
export class IdGenerator {
    
    /**
     * Generates a random 9-digit random ID (code).
     * 
     * Remember: The returned value is not guaranteed to be unique.
     * 
     * @returns a generated random 9-digit code
     */
    public static nextShort(): string {
        return Math.ceil(100000000 + Math.random() * 899999999).toString();
    }

    private static uuidToHex(buffer) {
        return   byteToHex[buffer[0]]  + byteToHex[buffer[1]]
               + byteToHex[buffer[2]]  + byteToHex[buffer[3]] 
               + byteToHex[buffer[4]]  + byteToHex[buffer[5]] 
               + byteToHex[buffer[6]]  + byteToHex[buffer[7]] 
               + byteToHex[buffer[8]]  + byteToHex[buffer[9]] 
               + byteToHex[buffer[10]] + byteToHex[buffer[11]]
               + byteToHex[buffer[12]] + byteToHex[buffer[13]]
               + byteToHex[buffer[14]] + byteToHex[buffer[15]];
    }

    /**
     * Generates a globally unique 32-digit object ID.
     * The value is a string representation of a GUID value.
     * 
     * @returns a generated 32-digit object ID
     */
    public static nextLong(): string {
        var buffer = new Array(16);
        return IdGenerator.uuidToHex(uuid.v4(null, buffer));
    }
        
}