import { assert } from "../../../assert.js";

/**
 * Multiplies two 4x4 matrices.
 * `out = a * b`.
 *
 * @param {number[]|ArrayLike<number>|Float32Array} out the receiving matrix
 * @param {number[]|ArrayLike<number>|Float32Array} a the first operand
 * @param {number[]|ArrayLike<number>|Float32Array} b the second operand
 * @returns {number[]} `out` parameter
 */
export function m4_multiply(out, a, b) {
    assert.isArrayLike(out, 'out');

    assert.isArrayLike(a, 'a');
    assert.greaterThanOrEqual(a.length, 16, 'a.length');

    assert.isArrayLike(b, 'b');
    assert.greaterThanOrEqual(b.length, 16, 'b.length');

    // Adapted from gl-matrix

    const a00 = a[0],
        a01 = a[1],
        a02 = a[2],
        a03 = a[3],
        a10 = a[4],
        a11 = a[5],
        a12 = a[6],
        a13 = a[7],
        a20 = a[8],
        a21 = a[9],
        a22 = a[10],
        a23 = a[11],
        a30 = a[12],
        a31 = a[13],
        a32 = a[14],
        a33 = a[15];

    // Cache only the current line of the second matrix
    let b0 = b[0],
        b1 = b[1],
        b2 = b[2],
        b3 = b[3];

    out[0] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30;
    out[1] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31;
    out[2] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32;
    out[3] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33;

    b0 = b[4];
    b1 = b[5];
    b2 = b[6];
    b3 = b[7];

    out[4] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30;
    out[5] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31;
    out[6] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32;
    out[7] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33;

    b0 = b[8];
    b1 = b[9];
    b2 = b[10];
    b3 = b[11];

    out[8] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30;
    out[9] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31;
    out[10] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32;
    out[11] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33;

    b0 = b[12];
    b1 = b[13];
    b2 = b[14];
    b3 = b[15];

    out[12] = b0 * a00 + b1 * a10 + b2 * a20 + b3 * a30;
    out[13] = b0 * a01 + b1 * a11 + b2 * a21 + b3 * a31;
    out[14] = b0 * a02 + b1 * a12 + b2 * a22 + b3 * a32;
    out[15] = b0 * a03 + b1 * a13 + b2 * a23 + b3 * a33;

    assert.greaterThanOrEqual(out.length, 16, 'out.length'); // check at the end to avoid having to explicitly deal with the `Array` type

    return out;
}
