import bpy
import gpu
# import blf
from gpu_extras.batch import batch_for_shader
from bpy_extras.view3d_utils import location_3d_to_region_2d

from bpy.app.handlers import persistent


def extrapolate_points_by_length(a, b, length):
    '''
    Return a third point C from by continuing in AB direction
    Length define BC distance. both vector2 and vector3
    '''
    # return b + ((b - a).normalized() * length)# one shot
    ab = b - a
    if not ab:
        return None
    return b + (ab.normalized() * length)

def view3d_camera_border_2d(context, cam):
    # based on https://blender.stackexchange.com/questions/6377/coordinates-of-corners-of-camera-view-border
    # cam = context.scene.camera
    frame = cam.data.view_frame(scene=context.scene)
    # to world-space
    frame = [cam.matrix_world @ v for v in frame]
    # to pixelspace
    region, rv3d = context.region, context.space_data.region_3d
    frame_px = [location_3d_to_region_2d(region, rv3d, v) for v in frame]
    return frame_px

def vertices_to_line_loop(v_list, closed=True) -> list:
    '''Take a sequence of vertices
    return a position lists of segments to create a line loop passing in all points
    the result is usable with gpu_shader 'LINES'
    ex: vlist = [a,b,c] -> closed=True return [a,b,b,c,c,a], closed=False return [a,b,b,c]
    '''
    loop = []
    for i in range(len(v_list) - 1):
        loop += [v_list[i], v_list[i + 1]]
    if closed:
        # Add segment between last and first to close loop
        loop += [v_list[-1], v_list[0]]
    return loop

def draw_cam_frame_callback_2d():
    context = bpy.context
    if context.region_data.view_perspective != 'CAMERA':
        return
    if not context.scene.camera or context.scene.camera.name != 'draw_cam':
        return

    main_cam = context.scene.camera.parent
    if not main_cam:
        return

    gpu.state.blend_set('ALPHA')

    frame_point = view3d_camera_border_2d(
        context, context.scene.camera.parent)
    shader_2d = gpu.shader.from_builtin('UNIFORM_COLOR') # POLYLINE_FLAT_COLOR
    # gpu.shader.from_builtin('2D_UNIFORM_COLOR')

    if context.scene.gptoolprops.drawcam_passepartout:
        ### PASSEPARTOUT

        # frame positions
        #
        # lupext   lup   rup   rupext
        #           D-----A
        #           |     |
        #           C-----B
        # ldnext   ldn   rdn   lnext

        a = frame_point[0]
        b = frame_point[1]
        c = frame_point[2]
        d = frame_point[3]

        ext = 10000
        rup = extrapolate_points_by_length(b,a, ext)
        rdn = extrapolate_points_by_length(a,b, ext)
        rupext = rup + ((a-d).normalized() * ext)
        rdnext = rdn + ((a-d).normalized() * ext)
        lup = extrapolate_points_by_length(c,d, ext)
        ldn = extrapolate_points_by_length(d,c, ext)
        lupext = lup + ((c-b).normalized() * ext)
        ldnext = ldn + ((c-b).normalized() * ext)


        # ppp_color = (1.0, 1.0, 0.0, 1)
        ppp_color = (0.0, 0.0, 0.0, context.scene.camera.data.passepartout_alpha)

        rect = [rup, rdn, rupext, rdnext,
                lup, ldn, lupext, ldnext,
                a, b, c, d]
        
        ## convert to 2d
        # region, rv3d = context.region, context.space_data.region_3d
        # rect = [location_3d_to_region_2d(region, rv3d, v) for v in rect]

        # lupext=6  lup=4    rup=0  rupext=2
        #             d=11, a=8
        #             c=10, b=9
        # ldnext=7  ldn=5     rdn=1  dnpext=3
        
        indices =  [(0,1,2), (1,2,3),
                    (4,5,6), (5,6,7),
                    (8,11,4), (8,4,0),
                    (10,9,5), (9,5,1),
                    ]

        # ### passpartout_points

        passepartout = batch_for_shader(
        shader_2d, 'TRIS', {"pos": rect}, indices=indices)
        # shader_2d, 'LINE_LOOP', {"pos": rect})

        shader_2d.bind()
        shader_2d.uniform_float("color", ppp_color)
        passepartout.draw(shader_2d)

    
    ### Camera framing trace over

    gpu.state.line_width_set(1.0)
    # bgl.glEnable(bgl.GL_LINE_SMOOTH) # old smooth
    
    """
    ## need to accurately detect viewport background color (difficult)
    ### COUNTER CURRENT FRAMING
    if False:
        camf = view3d_camera_border_2d(
            context, context.scene.camera)
        ca = (camf[0].x + 1, camf[0].y + 1)
        cb = (camf[1].x + 1, camf[1].y - 1)
        cc = (camf[2].x - 1, camf[2].y - 1)
        cd = (camf[3].x - 1, camf[3].y + 1)
        screen_framing = batch_for_shader(
            shader_2d, 'LINE_LOOP', {"pos": [ca, cb, cc, cd]})
        shader_2d.bind()
        shader_2d.uniform_float("color", (0.25, 0.25, 0.25, 1.0))
        # shader_2d.uniform_float("color", (0.9, 0.9, 0.9, 1.0))
        screen_framing.draw(shader_2d)
    """
    ### FRAMING

    # frame_color = (0.06, 0.4, 0.040, 0.5)
    frame_color = (0.0, 0.0, 0.25, 1.0)

    screen_framing = batch_for_shader(
        shader_2d, 'LINES', {"pos": vertices_to_line_loop(frame_point)})

    shader_2d.bind()
    shader_2d.uniform_float("color", frame_color)
    screen_framing.draw(shader_2d)

    # bgl.glDisable(bgl.GL_LINE_SMOOTH) # old smooth
    gpu.state.blend_set('NONE')


draw_handle = None

def register():
    if bpy.app.background:
        return

    global draw_handle
    draw_handle = bpy.types.SpaceView3D.draw_handler_add(
        draw_cam_frame_callback_2d, (), "WINDOW", "POST_PIXEL")



def unregister():
    if bpy.app.background:
        return

    global draw_handle
    if draw_handle:
        bpy.types.SpaceView3D.draw_handler_remove(draw_handle, 'WINDOW')

if __name__ == "__main__":
    register()