// math.js
export function mat4Identity() {
    return new Float32Array([
        1, 0, 0, 0,
        0, 1, 0, 0,
        0, 0, 1, 0,
        0, 0, 0, 1
    ]);
}

export function mat4Multiply(out, a, b) {
    let a00 = a[0], a01 = a[1], a02 = a[2], a03 = a[3];
    let a10 = a[4], a11 = a[5], a12 = a[6], a13 = a[7];
    let a20 = a[8], a21 = a[9], a22 = a[10], a23 = a[11];
    let a30 = a[12], a31 = a[13], a32 = a[14], a33 = a[15];

    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;
    return out;
}

export function mat4Ortho(out, left, right, bottom, top, near, far) {
    let lr = 1 / (left - right);
    let bt = 1 / (bottom - top);
    let nf = 1 / (near - far);
    out.fill(0);
    out[0] = -2 * lr;
    out[5] = -2 * bt;
    out[10] = 2 * nf;
    out[12] = (left + right) * lr;
    out[13] = (top + bottom) * bt;
    out[14] = (far + near) * nf;
    out[15] = 1;
    return out;
}

export function mat4LookAt(out, eyeX, eyeY, eyeZ, centerX, centerY, centerZ, upX, upY, upZ) {
    let z0 = eyeX - centerX, z1 = eyeY - centerY, z2 = eyeZ - centerZ;
    let len = 1 / Math.hypot(z0, z1, z2);
    z0 *= len;
    z1 *= len;
    z2 *= len;

    let x0 = upY * z2 - upZ * z1, x1 = upZ * z0 - upX * z2, x2 = upX * z1 - upY * z0;
    len = 1 / Math.hypot(x0, x1, x2);
    x0 *= len;
    x1 *= len;
    x2 *= len;

    let y0 = z1 * x2 - z2 * x1, y1 = z2 * x0 - z0 * x2, y2 = z0 * x1 - z1 * x0;

    out[0] = x0;
    out[1] = y0;
    out[2] = z0;
    out[3] = 0;
    out[4] = x1;
    out[5] = y1;
    out[6] = z1;
    out[7] = 0;
    out[8] = x2;
    out[9] = y2;
    out[10] = z2;
    out[11] = 0;
    out[12] = -(x0 * eyeX + x1 * eyeY + x2 * eyeZ);
    out[13] = -(y0 * eyeX + y1 * eyeY + y2 * eyeZ);
    out[14] = -(z0 * eyeX + z1 * eyeY + z2 * eyeZ);
    out[15] = 1;
    return out;
}

export function mat4Translate(out, a, v) {
    let x = v[0], y = v[1], z = v[2];
    if (a === out) {
        out[12] = a[0] * x + a[4] * y + a[8] * z + a[12];
        out[13] = a[1] * x + a[5] * y + a[9] * z + a[13];
        out[14] = a[2] * x + a[6] * y + a[10] * z + a[14];
        out[15] = a[3] * x + a[7] * y + a[11] * z + a[15];
    } else {
        // We only use this in-place for this prototype
    }
    return out;
}

export function mat4RotateY(out, a, rad) {
    let s = Math.sin(rad), c = Math.cos(rad);
    let a00 = a[0], a01 = a[1], a02 = a[2], a03 = a[3];
    let a20 = a[8], a21 = a[9], a22 = a[10], a23 = a[11];

    if (a !== out) {
        out[4] = a[4];
        out[5] = a[5];
        out[6] = a[6];
        out[7] = a[7];
        out[12] = a[12];
        out[13] = a[13];
        out[14] = a[14];
        out[15] = a[15];
    }

    out[0] = a00 * c - a20 * s;
    out[1] = a01 * c - a21 * s;
    out[2] = a02 * c - a22 * s;
    out[3] = a03 * c - a23 * s;
    out[8] = a00 * s + a20 * c;
    out[9] = a01 * s + a21 * c;
    out[10] = a02 * s + a22 * c;
    out[11] = a03 * s + a23 * c;
    return out;
}

export function mat4RotateX(out, a, rad) {
    let s = Math.sin(rad), c = Math.cos(rad);
    let a10 = a[4], a11 = a[5], a12 = a[6], a13 = a[7];
    let a20 = a[8], a21 = a[9], a22 = a[10], a23 = a[11];

    if (a !== out) {
        out[0] = a[0];
        out[1] = a[1];
        out[2] = a[2];
        out[3] = a[3];
        out[12] = a[12];
        out[13] = a[13];
        out[14] = a[14];
        out[15] = a[15];
    }

    out[4] = a10 * c + a20 * s;
    out[5] = a11 * c + a21 * s;
    out[6] = a12 * c + a22 * s;
    out[7] = a13 * c + a23 * s;
    out[8] = a20 * c - a10 * s;
    out[9] = a21 * c - a11 * s;
    out[10] = a22 * c - a12 * s;
    out[11] = a23 * c - a13 * s;
    return out;
}