/*************************************************************
 *
 *  Copyright (c) 2018 The MathJax Consortium
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

/**
 * @fileoverview  Implements bit-fields with extendable field names
 *
 * @author dpvc@mathjax.org (Davide Cervone)
 */

export class BitField {

    protected static MAXBIT = 1 << 31;

    /**
     * The next bit to be allocated
     */
    protected static next: number = 1;

    /**
     * The map of names to bit positions
     */
    protected static names: Map<string, number> = new Map();

    /**
     * The bits that are set
     */
    protected bits: number = 0;

    /**
     * @param {string} names    The names of the bit positions to reserve
     */
    public static allocate(...names: string[]) {
        for (const name of names) {
            if (this.has(name)) {
                throw new Error('Bit already allocated for '+name);
            }
            if (this.next === BitField.MAXBIT) {
                throw new Error('Maximum number of bits already allocated');
            }
            this.names.set(name, this.next);
            this.next <<= 1;
        }
    }

    /**
     * @param {string} name   The name of the bit to check for being defined
     * @return {boolean}      True if the named bit is already allocated
     */
    public static has(name: string) {
        return this.names.has(name);
    }

    /**
     * @param {string} name    The name of the bit position to set
     */
    public set(name: string) {
        this.bits |= this.getBit(name);
    }

    /**
     * @param {string} name    The name of the bit position to clear
     */
    public clear(name: string) {
        this.bits &= ~this.getBit(name);
    }

    /**
     * @param {string} name   The name of the bit to check if set
     * @return {boolean}      True if the named bit is set
     */
    public isSet(name: string) {
        return !!(this.bits & this.getBit(name));
    }

    /**
     * Clear all bits
     */
    public reset() {
        this.bits = 0;
    }

    /**
     * @param {string} name   The name whose bit position is needed (error if not defined)
     * @return {number}       The position of the named bit
     */
    protected getBit(name: string) {
        const bit = (this.constructor as typeof BitField).names.get(name);
        if (!bit) {
            throw new Error('Unknown bit-field name: ' + name);
        }
        return bit;
    }

}

/**
 * @param {string[]} names    The name of the positions to allocate initially
 * @return {typeof AbstractBitField}  The bit-field class with names allocated
 */
export function BitFieldClass(...names: string[]): typeof BitField {
    const Bits = class extends BitField {};
    Bits.allocate(...names);
    return Bits;
}