yahoo/pngjs-image

// Copyright 2015 Yahoo! Inc.
// Copyrights licensed under the Mit License. See the accompanying LICENSE file for terms.

/**
 * @class hIST
 * @module PNG
 * @submodule PNGChunks
 */
module.exports = {

    /**
     * Gets the sequence
     *
     * @method getSequence
     * @return {int}
     */
    getSequence: function () {
        return 350;
    },


    /**
     * Gets all frequencies at once
     *
     * @method getFrequencies
     * @return {int[]} List of all frequencies in order of the palette color indexes
     */
    getFrequencies: function () {
        var result = [];

        for(var i = 0, len = this._frequency.length; i < len; i += 2) {
            result.push(this._frequency.readUInt16BE(i));
        }

        return result;
    },

    /**
     * Sets all frequencies at once
     *
     * @method setFrequencies
     * @param {int[]} frequencies List of all frequencies in order of the palette color indexes
     */
    setFrequencies: function (frequencies) {

        this._frequency = new Buffer(frequencies.length * 2);

        for(var i = 0, len = frequencies.length; i < len; i++) {
            this._frequency.writeUInt16BE(frequencies[i], i * 2);
        }
    },


    /**
     * Parsing of chunk data
     *
     * Phase 1
     *
     * @method parse
     * @param {BufferedStream} stream Data stream
     * @param {int} length Length of chunk data
     * @param {boolean} strict Should parsing be strict?
     * @param {object} options Decoding options
     */
    parse: function (stream, length, strict, options) {

        // Validation
        if (strict && (this.getFirstChunk(this.getType(), false) !== null)) {
            throw new Error('Only one ' + this.getType() + ' is allowed in the data.');
        }

        this._frequency = stream.readBuffer(length);
    },

    /**
     * Gathers chunk-data from decoded chunks
     *
     * Phase 5
     *
     * @static
     * @method decodeData
     * @param {object} data Data-object that will be used to export values
     * @param {boolean} strict Should parsing be strict?
     * @param {object} options Decoding options
     */
    decodeData: function (data, strict, options) {

        var chunks = this.getChunksByType(this.getType());

        if (!chunks) {
            return ;
        }

        if (strict && (chunks.length !== 1)) {
            throw new Error('Not more than one chunk allowed for ' + this.getType() + '.');
        }

        data.volatile = data.volatile || {};
        data.volatile.histogram = chunks[0].getFrequencies();
    },


    /**
     * Returns a list of chunks to be added to the data-stream
     *
     * Phase 1
     *
     * @static
     * @method encodeData
     * @param {Buffer} image Image data
     * @param {object} options Encoding options
     * @return {Chunk[]} List of chunks to encode
     */
    encodeData: function (image, options) {

        if (options.histogram) {

            var chunk = this.createChunk(this.getType(), this.getChunks());

            chunk.setFrequencies(options.histogram);

            return [chunk];
        } else {
            return [];
        }
    },

    /**
     * Composing of chunk data
     *
     * Phase 4
     *
     * @method compose
     * @param {BufferedStream} stream Data stream
     * @param {object} options Encoding options
     */
    compose: function (stream, options) {
        if (this._frequency) {
            stream.writeBuffer(this._frequency);
        }
    }
};