import bpy, mathutils, bmesh
import typing, enum, collections
from . import UTIL_virtools_types, UTIL_functions

#region Param Struct

class FlattenMethod(enum.IntEnum):
    # The legacy flatten uv mode. Only just do space convertion for each individual faces.
    Raw = enum.auto()
    # The floor specific flatten uv.
    # This method will make sure the continuity in V axis in uv when flatten uv.
    # Only support rectangle faces.
    Floor = enum.auto()
    # The wood specific flatten uv.
    # Similar floor, but it will force all horizontal uv edge parallel with U axis.
    # Not only V axis, but also U axis' continuity will been make sure.
    Wood = enum.auto()

class FlattenParam():
    mReferenceEdge: int
    mUseRefPoint: bool
    mFlattenMethod: FlattenMethod

    mScaleSize: float

    mReferencePoint: int
    mReferenceUV: float

    def __init__(self, use_ref_point: bool, reference_edge: int, flatten_method: FlattenMethod) -> None:
        self.mReferenceEdge = reference_edge
        self.mUseRefPoint = use_ref_point
        self.mFlattenMethod = flatten_method

    def is_valid(self) -> bool:
        """Check whether flatten params is valid"""
        if self.mUseRefPoint:
            # ref point should be great than 1.
            # because 0 and 1 is located at the same line with reference edge.
            return self.mReferencePoint > 1
        else:
            # zero scale size make no sense.
            return round(self.mScaleSize, 7) != 0.0

    @classmethod
    def create_by_scale_size(cls, reference_edge: int, flatten_method: FlattenMethod, scale_num: float):
        val = cls(False, reference_edge, flatten_method)
        val.mScaleSize = scale_num
        return val

    @classmethod
    def create_by_ref_point(cls, reference_edge: int, flatten_method: FlattenMethod, ref_point: int, ref_point_uv: float):
        val = cls(True, reference_edge, flatten_method)
        val.mReferencePoint = ref_point
        val.mReferenceUV = ref_point_uv
        return val

#endregion

class BBP_OT_flatten_uv(bpy.types.Operator):
    """Flatten selected face UV. Only works for convex face"""
    bl_idname = "bbp.flatten_uv"
    bl_label = "Flatten UV"
    bl_options = {'REGISTER', 'UNDO'}

    reference_edge: bpy.props.IntProperty(
        name = "Reference Edge",
        description = "The references edge of UV.\nIt will be placed in V axis.",
        min = 0,
        soft_min = 0, soft_max = 3,
        default = 0,
    ) # type: ignore

    flatten_method: bpy.props.EnumProperty(
        name = "Flatten Method",
        items = [
            ('RAW', "Raw", "Legacy flatten UV."),
            ('FLOOR', "Floor", "Floor specific flatten UV."),
            ('WOOD', "Wood", "Wood specific flatten UV."),
        ],
        default = 'RAW'
    ) # type: ignore

    scale_mode: bpy.props.EnumProperty(
        name = "Scale Mode",
        items = [
            ('NUM', "Scale Size", "Scale UV with specific number."),
            ('REF', "Ref. Point", "Scale UV with Reference Point feature."),
        ],
        default = 'NUM'
    ) # type: ignore

    scale_number: bpy.props.FloatProperty(
        name = "Scale Size",
        description = "The size which will be applied for scale.",
        min = 0,
        soft_min = 0, soft_max = 5,
        default = 5.0,
        step = 10,
        precision = 1,
    ) # type: ignore

    reference_point: bpy.props.IntProperty(
        name = "Reference Point",
        description = "The references point of UV.\nIt's U component will be set to the number specified by Reference Point UV.\nThis point index is related to the start point of reference edge.",
        min = 2,  # 0 and 1 is invalid. we can not order the reference edge to be set on the outside of uv axis
        soft_min = 2, soft_max = 3,
        default = 2,
    ) # type: ignore

    reference_uv: bpy.props.FloatProperty(
        name = "Reference Point UV",
        description = "The U component which should be applied to references point in UV.",
        soft_min = 0, soft_max = 1,
        default = 0.5,
        step = 10,
        precision = 2,
    ) # type: ignore

    @classmethod
    def poll(cls, context):
        obj = bpy.context.active_object
        if obj is None:
            return False
        if obj.type != 'MESH':
            return False
        if obj.mode != 'EDIT':
            return False
        return True

    def execute(self, context):
        # construct scale data
        flatten_method_: FlattenMethod
        match(self.flatten_method):
            case 'RAW': flatten_method_ = FlattenMethod.Raw
            case 'FLOOR': flatten_method_ = FlattenMethod.Floor
            case 'WOOD': flatten_method_ = FlattenMethod.Wood
            case _: return {'CANCELLED'}

        flatten_param_: FlattenParam
        if self.scale_mode == 'NUM':
            flatten_param_ = FlattenParam.create_by_scale_size(self.reference_edge, flatten_method_, self.scale_number)
        else:
            flatten_param_ = FlattenParam.create_by_ref_point(self.reference_edge, flatten_method_, self.reference_point, self.reference_uv)
        if not flatten_param_.is_valid():
            return {'CANCELLED'}

        # do flatten uv and report
        failed: int = _flatten_uv_wrapper(bpy.context.active_object.data, flatten_param_)
        if failed != 0:
            print(f'[Flatten UV] {failed} faces are not be processed correctly because process failed.')
        return {'FINISHED'}

    def draw(self, context):
        layout = self.layout
        layout.emboss = 'NORMAL'
        layout.label(text = "Flatten Method")
        sublayout = layout.row()
        sublayout.prop(self, "flatten_method", expand = True)
        layout.prop(self, "reference_edge")

        layout.separator()
        layout.label(text = "Scale Mode")
        sublayout = layout.row()
        sublayout.prop(self, "scale_mode", expand = True)

        layout.separator()
        layout.label(text = "Scale Config")
        if self.scale_mode == 'NUM':
            layout.prop(self, "scale_number")
        else:
            layout.prop(self, "reference_point")
            layout.prop(self, "reference_uv")

#region BMesh Visitor Helper

def _set_face_vertex_uv(face: bmesh.types.BMFace, uv_layer: bmesh.types.BMLayerItem, idx: int, uv: UTIL_virtools_types.ConstVxVector2) -> None:
    """
    Help function to set UV data for face.

    @param face[in] The face to be set.
    @param uv_layer[in] The corresponding uv layer. Hint: it was gotten from BMesh.loops.layers.uv.verify()
    @param idx[in] The index of trying setting vertex.
    @param uv[in] The set UV data
    """
    face.loops[idx][uv_layer].uv = uv

def _get_face_vertex_uv(face: bmesh.types.BMFace, uv_layer: bmesh.types.BMLayerItem, idx: int) -> UTIL_virtools_types.ConstVxVector2:
    """
    Help function to get UV data for face.

    @param face[in] The face to be set.
    @param uv_layer[in] The corresponding uv layer. Hint: it was gotten from BMesh.loops.layers.uv.verify()
    @param idx[in] The index of trying setting vertex.
    @return The UV data
    """
    v: mathutils.Vector = face.loops[idx][uv_layer].uv
    return (v[0], v[1])

def _get_face_vertex_pos(face: bmesh.types.BMFace, idx: int) -> UTIL_virtools_types.ConstVxVector3:
    """
    Help function to get vertex position from face by provided index.
    No index overflow checker. Caller must make sure the provided index is not overflow.

    @param face[in] Bmesh face struct.
    @param idx[in] The index of trying getting vertex.
    @return The gotten vertex position.
    """
    v: mathutils.Vector = face.loops[idx].vert.co
    return (v[0], v[1], v[2])

def _circular_clamp_index(v: int, vmax: int) -> int:
    """
    Circular clamp face vertex index.
    Used by _real_flatten_uv.

    @param v[in] The index to clamp
    @param vmax[in] The count of used face vertex. At least 3.
    @return The circular clamped value ranging from 0 to vmax.
    """
    return v % vmax

#endregion

#region Real Worker Functions

def _flatten_uv_wrapper(mesh: bpy.types.Mesh, flatten_param: FlattenParam) -> int:
    # create bmesh modifier
    bm: bmesh.types.BMesh = bmesh.from_edit_mesh(mesh)
    # use verify() to make sure there is a uv layer to write data
    # verify() will return existing one or create one if no layer existing.
    uv_layers: bmesh.types.BMLayerCollection = bm.loops.layers.uv
    uv_layer: bmesh.types.BMLayerItem = uv_layers.verify()

    # invoke core
    failed: int
    match(flatten_param.mFlattenMethod):
        case FlattenMethod.Raw:
            failed = _raw_flatten_uv(bm, uv_layer, flatten_param)
        case FlattenMethod.Floor | FlattenMethod.Wood:
            failed = _specific_flatten_uv(bm, uv_layer, flatten_param)

    # show the updates in the viewport
    bmesh.update_edit_mesh(mesh)
    # return process result
    return failed

def _raw_flatten_uv(bm: bmesh.types.BMesh, uv_layer: bmesh.types.BMLayerItem, flatten_param: FlattenParam) -> int:
    # failed counter
    failed: int = 0
    # raw flatten uv always use zero offset
    c_ZeroOffset: mathutils.Vector = mathutils.Vector((0, 0))

    # process each face
    face: bmesh.types.BMFace
    for face in bm.faces:
        # check requirement
        # skip not selected face
        if not face.select: continue
        # skip the face that not fufill reference edge requirement
        edge_count: int = len(face.loops)
        if flatten_param.mReferenceEdge >= edge_count:
            failed += 1
            continue
        # skip ref point overflow when using ref point mode
        if flatten_param.mUseRefPoint and (flatten_param.mReferencePoint >= edge_count):
            failed += 1
            continue

        # process this face
        _flatten_face_uv(face, uv_layer, flatten_param, c_ZeroOffset)

    return failed

def _specific_flatten_uv(bm: bmesh.types.BMesh, uv_layer: bmesh.types.BMLayerItem, flatten_param: FlattenParam) -> int:
    # failed counter
    failed: int = 0

    # reset selected face's tag to False to indicate these face is not processed
    face: bmesh.types.BMFace
    for face in bm.faces:
        if face.select:
            face.tag = False
    
    # prepare a function to check whether face is valid
    def face_validator(f: bmesh.types.BMFace) -> bool:
        # specify use external failed counter
        nonlocal failed
        # a valid face must be
        # selected, not processed, and should be rectangle
        # we check selection first
        if not f.select or f.tag: return False
        # then check tag. if tag == True, it mean this face has been processed.
        if f.tag: return False
        # now this face can be processed, we need check whether it is rectangle
        if len(f.loops) == 4:
            # yes it is rectangle
            return True
        else:
            # no, it is not rectangle
            # we need mark it tag as True to prevent any possible recursive checking
            # because it definately can not be processed in future.
            f.tag = True
            # then we report this face failed
            failed = failed + 1
            # return false
            return False
    # prepare face getter which will be used when stack is empty
    face_getter: typing.Iterator[bmesh.types.BMFace] = filter(
        lambda f: face_validator(f), 
        typing.cast(typing.Iterable[bmesh.types.BMFace], bm.faces)
    )
    # prepare a neighbor getter.
    # this function will help finding the valid neighbor of specified face
    # `loop_idx` is the index of loop getting from given face.
    # `exp_loop_idx` is the expected index of neighbor loop in neighbor face.
    def face_neighbor_getter(f: bmesh.types.BMFace, loop_idx: int, exp_loop_idx: int) -> bmesh.types.BMFace | None:
        # get this face's loop
        this_loop: bmesh.types.BMLoop = f.loops[loop_idx]
        # check requirement for this loop
        # this edge should be shared exactly by 2 faces.
        # 
        # Manifold: For a mesh to be manifold, every edge must have exactly two adjacent faces.
        # Ref: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Manifold-Meshes
        if not this_loop.edge.is_manifold:
            return None

        # get neighbor loop
        neighbor_loop: bmesh.types.BMLoop = this_loop.link_loop_radial_next
        # get neighbor face and check it
        neighbor_f: bmesh.types.BMFace = neighbor_loop.face
        if not face_validator(neighbor_f):
            return None

        # check expected neighbor index
        if neighbor_loop != neighbor_f.loops[exp_loop_idx]:
            return None

        # all check done, return face
        return neighbor_f
    # prepare face stack.
    # NOTE: all face inserted into this stack should be marked as processed first.
    face_stack: collections.deque[tuple[bmesh.types.BMFace, mathutils.Vector]] = collections.deque()
    # start process faces
    while True:
        # if no item in face stack, pick one from face getter and mark it as processed
        # if face getter failed, it mean that no more face, exit.
        if len(face_stack) == 0:
            try:
                f = next(face_getter)
                f.tag = True
                face_stack.append((f, mathutils.Vector((0, 0))))
            except StopIteration:
                break

        # pick one face from stack and process it
        (face, face_offset) = face_stack.pop()
        _flatten_face_uv(face, uv_layer, flatten_param, face_offset)

        # get 4 point uv because we need use them later
        # NOTE: 4 uv point following this order
        #  +-----------+
        #  |(1)        |(2)
        #  |           |
        #  |(0)        |(3)
        #  +-----------+
        # So the loop index is
        #        (1)
        #  +---------->+
        #  ^           |
        #  |(0)        |(2)
        #  |           v
        #  +<----------+
        #        (3)
        ind0 = _circular_clamp_index(flatten_param.mReferenceEdge, 4)
        ind1 = _circular_clamp_index(flatten_param.mReferenceEdge + 1, 4)
        ind2 = _circular_clamp_index(flatten_param.mReferenceEdge + 2, 4)
        ind3 = _circular_clamp_index(flatten_param.mReferenceEdge + 3, 4)
        uv0 = _get_face_vertex_uv(face, uv_layer, ind0)
        uv1 = _get_face_vertex_uv(face, uv_layer, ind1)
        uv2 = _get_face_vertex_uv(face, uv_layer, ind2)
        uv3 = _get_face_vertex_uv(face, uv_layer, ind3)

        # insert horizontal neighbor if we are wood flatten uv
        if flatten_param.mFlattenMethod == FlattenMethod.Wood:
            # first, make its uv geometry to rectangle from a trapezium.
            # get the average U factor from its right edge.
            # and make top + bottom uv edge be parallel with U axis by using left edge V factor.
            average_u = (uv2[0] + uv3[0]) / 2
            uv2 = (average_u, uv1[1])
            uv3 = (average_u, uv0[1])
            _set_face_vertex_uv(face, uv_layer, ind2, uv2)
            _set_face_vertex_uv(face, uv_layer, ind3, uv3)

            # then, try getting its right neighbor
            r_face: bmesh.types.BMFace | None = face_neighbor_getter(face, ind2, ind0)
            if r_face is not None:
                # mark it as processed
                r_face.tag = True
                # insert face with extra horizontal offset.
                face_stack.append((r_face, mathutils.Vector((uv3[0], uv3[1]))))

        # insert vertical neighbor
        t_face: bmesh.types.BMFace | None = face_neighbor_getter(face, ind1, ind3)
        if t_face is not None:
            # mark it as processed
            t_face.tag = True
            # insert face with extra vertical offset.
            face_stack.append((t_face, mathutils.Vector((uv1[0], uv1[1]))))

    return failed

def _flatten_face_uv(face: bmesh.types.BMFace, uv_layer: bmesh.types.BMLayerItem, flatten_param: FlattenParam, offset: mathutils.Vector) -> None:
    # ========== get correct new corrdinate system ==========
    # yyc mark:
    # we use 3 points located in this face to calc
    # the base of this local uv corredinate system.
    # however if this 3 points are set in a line,
    # this method will cause a error, zero vector error.
    #
    # if z axis is zero vector, we will try using face normal instead
    # to try getting correct data.
    #
    # zero base is not important. because it will not raise any math exception
    # just a weird uv. user will notice this problem.

    # get point
    all_point: int = len(face.loops)
    pidx_start: int = _circular_clamp_index(flatten_param.mReferenceEdge, all_point)
    p1: mathutils.Vector = mathutils.Vector(_get_face_vertex_pos(face, pidx_start))
    p2: mathutils.Vector = mathutils.Vector(_get_face_vertex_pos(face, _circular_clamp_index(flatten_param.mReferenceEdge + 1, all_point)))
    p3: mathutils.Vector = mathutils.Vector(_get_face_vertex_pos(face, _circular_clamp_index(flatten_param.mReferenceEdge + 2, all_point)))

    # get y axis
    new_y_axis: mathutils.Vector = p2 - p1
    new_y_axis.normalize()
    vec1: mathutils.Vector = p3 - p2
    vec1.normalize()

    # get z axis
    new_z_axis: mathutils.Vector = new_y_axis.cross(vec1)
    new_z_axis.normalize()
    if not any(round(v, 7) for v in new_z_axis):  # if z is a zero vector, use face normal instead
        new_z_axis = typing.cast(mathutils.Vector, face.normal).normalized()

    # get x axis
    new_x_axis: mathutils.Vector = new_y_axis.cross(new_z_axis)
    new_x_axis.normalize()

    # construct rebase matrix
    origin_base: mathutils.Matrix = mathutils.Matrix((
        (1.0, 0, 0), 
        (0, 1.0, 0), 
        (0, 0, 1.0)
    ))
    origin_base.invert_safe()
    new_base: mathutils.Matrix = mathutils.Matrix((
        (new_x_axis.x, new_y_axis.x,  new_z_axis.x), 
        (new_x_axis.y, new_y_axis.y, new_z_axis.y),
        (new_x_axis.z, new_y_axis.z, new_z_axis.z)
    ))
    transition_matrix: mathutils.Matrix = typing.cast(mathutils.Matrix, origin_base @ new_base)
    transition_matrix.invert_safe()

    # ===== rescale correction =====
    rescale: float = 0.0
    if flatten_param.mUseRefPoint:
        # ref point method
        # get reference point from loop
        pidx_refp: int = _circular_clamp_index(pidx_start + flatten_param.mReferencePoint, all_point)
        pref: mathutils.Vector = mathutils.Vector(_get_face_vertex_pos(face, pidx_refp)) - p1

        # calc its U component
        vec_u: float = abs(typing.cast(mathutils.Vector, transition_matrix @ pref).x)
        if round(vec_u, 7) == 0.0:
            rescale = 1.0  # fallback. rescale = 1 will not affect anything
        else:
            rescale = flatten_param.mReferenceUV / vec_u
    else:
        # scale size method
        # apply rescale directly
        rescale = 1.0 / flatten_param.mScaleSize

    # construct matrix
    # we only rescale U component (X component)
    # and constant 5.0 scale for V component (Y component)
    scale_matrix: mathutils.Matrix = mathutils.Matrix((
        (rescale, 0, 0), 
        (0, 1.0 / 5.0, 0), 
        (0, 0, 1.0)
    ))
    # order can not be changed. we order do transition first, then scale it.
    rescale_transition_matrix: mathutils.Matrix = typing.cast(mathutils.Matrix, scale_matrix @ transition_matrix)

    # ========== process each face ==========
    for idx in range(all_point):
        # compute uv
        pp: mathutils.Vector = mathutils.Vector(_get_face_vertex_pos(face, idx)) - p1
        ppuv: mathutils.Vector = typing.cast(mathutils.Vector, rescale_transition_matrix @ pp)
        # u and v component has been calculated properly. no extra process needed.
        # just get abs for the u component
        ppuv.x = abs(ppuv.x)
        # add offset and assign to uv
        _set_face_vertex_uv(face, uv_layer, idx, (ppuv.x + offset.x, ppuv.y + offset.y))

#endregion

def register() -> None:
    bpy.utils.register_class(BBP_OT_flatten_uv)

def unregister() -> None:
    bpy.utils.unregister_class(BBP_OT_flatten_uv)
