import getAccessorByteStride from './getAccessorByteStride.js'
import getComponentReader from './getComponentReader.js'
import numberOfComponentsForType from './numberOfComponentsForType.js'
import arrayFill from '../../Core/arrayFill.js'
import ComponentDatatype from '../../Core/ComponentDatatype.js'
import defined from '../../Core/defined.js'

    /**
     * Finds the min and max values of the accessor.
     *
     * @param {Object} gltf A javascript object containing a glTF asset.
     * @param {Object} accessor The accessor object from the glTF asset to read.
     * @returns {{min: Array, max: Array}} min holding the array of minimum values and max holding the array of maximum values.
     *
     * @private
     */
    function findAccessorMinMax(gltf, accessor) {
        var bufferViews = gltf.bufferViews;
        var buffers = gltf.buffers;
        var bufferViewId = accessor.bufferView;
        var numberOfComponents = numberOfComponentsForType(accessor.type);

        // According to the spec, when bufferView is not defined, accessor must be initialized with zeros
        if (!defined(accessor.bufferView)) {
            return {
                min: arrayFill(new Array(numberOfComponents), 0.0),
                max: arrayFill(new Array(numberOfComponents), 0.0)
            };
        }

        var min = arrayFill(new Array(numberOfComponents), Number.POSITIVE_INFINITY);
        var max = arrayFill(new Array(numberOfComponents), Number.NEGATIVE_INFINITY);

        var bufferView = bufferViews[bufferViewId];
        var bufferId = bufferView.buffer;
        var buffer = buffers[bufferId];
        var source = buffer.extras._pipeline.source;

        var count = accessor.count;
        var byteStride = getAccessorByteStride(gltf, accessor);
        var byteOffset = accessor.byteOffset + bufferView.byteOffset + source.byteOffset;
        var componentType = accessor.componentType;
        var componentTypeByteLength = ComponentDatatype.getSizeInBytes(componentType);
        var dataView = new DataView(source.buffer);
        var components = new Array(numberOfComponents);
        var componentReader = getComponentReader(componentType);

        for (var i = 0; i < count; i++) {
            componentReader(dataView, byteOffset, numberOfComponents, componentTypeByteLength, components);
            for (var j = 0; j < numberOfComponents; j++) {
                var value = components[j];
                min[j] = Math.min(min[j], value);
                max[j] = Math.max(max[j], value);
            }
            byteOffset += byteStride;
        }

        return {
            min: min,
            max: max
        };
    }

    export default findAccessorMinMax;