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#  This program is free software; you can redistribute it and/or
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#  as published by the Free Software Foundation; either version 2
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#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
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# <pep8 compliant>


def _is_persp_matrix(persmat, eps=0.00001):
    """
    crummy way to check if its a perspective matrix
    """
    return not (
            abs(persmat[0][3]) < eps and \
            abs(persmat[1][3]) < eps and \
            abs(persmat[2][3]) < eps and \
            abs(persmat[3][3] - 1.0) < eps)


def region_2d_to_vector_3d(region, rv3d, coord):
    """
    Return a direction vector from the viewport at the spesific 2d region
    coordinate.

    :arg region: region of the 3D viewport, typically bpy.context.region.
    :type region: :class:`Region`
    :arg rv3d: 3D region data, typically bpy.context.space_data.region_3d.
    :type rv3d: :class:`RegionView3D`
    :arg coord: 2d coordinates relative to the region;
       (event.mouse_region_x, event.mouse_region_y) for example.
    :type coord: 2d vector
    :return: normalized 3d vector.
    :rtype: :class:`Vector`
    """
    from mathutils import Vector

    persmat = rv3d.perspective_matrix.copy()
    viewvec = rv3d.view_matrix.inverted()[2].xyz.normalized()

    if _is_persp_matrix(persmat):
        dx = (2.0 * coord[0] / region.width) - 1.0
        dy = (2.0 * coord[1] / region.height) - 1.0
        
        perspinv_x, perspinv_y = persmat.inverted().to_3x3()[0:2]
        return ((perspinv_x * dx + perspinv_y * dy) - viewvec).normalized()
    else:
        return viewvec


def region_2d_to_location_3d(region, rv3d, coord, depth_location):
    """
    Return a 3d location from the region relative 2d coords, aligned with
    *depth_location*.

    :arg region: region of the 3D viewport, typically bpy.context.region.
    :type region: :class:`Region`
    :arg rv3d: 3D region data, typically bpy.context.space_data.region_3d.
    :type rv3d: :class:`RegionView3D`
    :arg coord: 2d coordinates relative to the region;
       (event.mouse_region_x, event.mouse_region_y) for example.
    :type coord: 2d vector
    :arg depth_location: the returned vectors depth is aligned with this since
       there is no defined depth with a 2d region input.
    :type depth_location: 3d vector
    :return: normalized 3d vector.
    :rtype: :class:`Vector`
    """
    from mathutils.geometry import intersect_point_line

    persmat = rv3d.perspective_matrix.copy()

    if _is_persp_matrix(persmat):
        origin_start = rv3d.view_matrix.inverted()[3].to_3d()
    else:
        dx = (2.0 * coord[0] / region.width) - 1.0
        dy = (2.0 * coord[1] / region.height) - 1.0
        persinv = persmat.inverted()
        viewinv = rv3d.view_matrix.inverted()
        origin_start = (persinv[0].xyz * dx) + (persinv[1].xyz * dy) + viewinv[3].xyz

    origin_end = origin_start + region_2d_to_vector_3d(region, rv3d, coord)
    
    return intersect_point_line(depth_location, origin_start, origin_end)[0]


def location_3d_to_region_2d(region, rv3d, coord):
    """
    Return the *region* relative 2d location of a 3d position.

    :arg region: region of the 3D viewport, typically bpy.context.region.
    :type region: :class:`Region`
    :arg rv3d: 3D region data, typically bpy.context.space_data.region_3d.
    :type rv3d: :class:`RegionView3D`
    :arg coord: 3d worldspace location.
    :type coord: 3d vector
    :return: 2d location
    :rtype: :class:`Vector`
    """
    prj = Vector((coord[0], coord[1], coord[2], 1.0)) * rv3d.perspective_matrix
    if prj.w > 0.0:
        width_half = region.width / 2.0
        height_half = region.height / 2.0

        return Vector((width_half + width_half * (prj.x / prj.w),
                       height_half + height_half * (prj.y / prj.w),
                       ))
    else:
        return None