import bpy
import mathutils

obj = bpy.context.active_object
mesh = obj.data


def get_layers():
    """
    return: tuple of 20 booleans. True if layer is active layer,False if not
    Allows the mesh to be created on the active layer. There is only 1 active layer
    """
    active_layer = bpy.context.scene.active_layer
    layers = [False] * 20
    layers[active_layer] = True
    return tuple(layers)


def get_global_poly_pos(polygon):
    """
    polygon: bpy_types.MeshPolygon. A edit mode polygon from the bpy module
    return: Vector. A 3d point. The center of the polygon
    Finds the center of a polygon in world space
    """
    location = mathutils.Vector((
        polygon.center[0],
        polygon.center[1],
        polygon.center[2]
        ))
    location = obj.matrix_world * location
    return location


def get_normal(polygon):
    """
    polygon: bpy_types.MeshPolygon. A edit mode polygon from the bpy module
    return: Vector. A 3d point that crosses the normal.
    Finds a 3d point that intersect with the normal
    """
    normal_vector = polygon.normal
    vec_x = normal_vector[0]  # not used atm
    vec_y = normal_vector[1]  # not used atm
    vec_z = normal_vector[2]  # not used atm
    return normal_vector


def create_light_at_face():
    """
    layers: tuple. 20 booleans where exaclty one boolen is True
    return: None
    creates an area light the has the same orientation as the normal at the center of each face
    """
    for poly in mesh.polygons:
        loc = get_global_poly_pos(poly)
        normal = get_normal(poly)  # this is probably needed somehow

        # get the rotation needed for each polygon face, idk how
        # default values in RADIANS, actual values will be computed somehow
        rot_x = 0
        rot_y = 0
        rot_z = 0
        bpy.ops.object.lamp_add(type='AREA', view_align=False, location=(loc[0], loc[1], loc[2]), rotation=(rot_x, rot_y, rot_z), layers=get_layers())
        # scale lamp up a little fo we can see the area
        bpy.context.object.data.size = 3


def create_empty_at_face():
    """
    DEBUG, used for testing
    creates and empty at the center of the face
    Have an object selected in object mode
    """
    # create empty at center of face
    for poly in mesh.polygons:
        loc = get_global_poly_pos(poly)
        bpy.ops.object.empty_add(type='PLAIN_AXES', view_align=False, location=(loc[0], loc[1], loc[2]), rotation=(0.0, 0.0, 0.0), layers=get_layers())

create_light_at_face()