"""
=========
Link Item
=========

"""
import math
from xml.sax.saxutils import escape

from AnyQt.QtWidgets import (
    QGraphicsItem, QGraphicsEllipseItem, QGraphicsPathItem, QGraphicsObject,
    QGraphicsTextItem, QGraphicsDropShadowEffect
)
from AnyQt.QtGui import QPen, QBrush, QColor, QPainterPath, QTransform
from AnyQt.QtCore import Qt, QPointF, QRectF, QLineF, QEvent

from .nodeitem import SHADOW_COLOR
from .utils import stroke_path

from ...scheme import SchemeLink


class LinkCurveItem(QGraphicsPathItem):
    """
    Link curve item. The main component of a :class:`LinkItem`.
    """
    def __init__(self, parent):
        super().__init__(parent)
        self.setAcceptedMouseButtons(Qt.NoButton)
        self.setAcceptHoverEvents(True)

        self.shadow = QGraphicsDropShadowEffect(
            blurRadius=10, color=QColor(SHADOW_COLOR),
            offset=QPointF(0, 0)
        )

        self.setGraphicsEffect(self.shadow)
        self.shadow.setEnabled(False)

        self.__hover = False
        self.__enabled = True
        self.__shape = None
        self.__curvepath = QPainterPath()
        self.__curvepath_disabled = None
        self.__pen = self.pen()
        self.setPen(QPen(QBrush(QColor("#9CACB4")), 2.0))

    def setCurvePath(self, path):
        if path != self.__curvepath:
            self.prepareGeometryChange()
            self.__curvepath = QPainterPath(path)
            self.__curvepath_disabled = None
            self.__shape = None
            self.__update()

    def curvePath(self):
        return QPainterPath(self.__curvepath)

    def setHoverState(self, state):
        self.prepareGeometryChange()
        self.__hover = state
        self.__update()

    def setLinkEnabled(self, state):
        self.prepareGeometryChange()
        self.__enabled = state
        self.__update()

    def isLinkEnabled(self):
        return self.__enabled

    def setPen(self, pen):
        if self.__pen != pen:
            self.prepareGeometryChange()
            self.__pen = QPen(pen)
            self.__shape = None
            super().setPen(self.__pen)

    def shape(self):
        if self.__shape is None:
            path = self.curvePath()
            pen = QPen(QBrush(Qt.black),
                       max(self.pen().widthF(), 20),
                       Qt.SolidLine)
            self.__shape = stroke_path(path, pen)
        return self.__shape

    def setPath(self, path):
        self.__shape = None
        super().setPath(path)

    def __update(self):
        shadow_enabled = self.__hover
        if self.shadow.isEnabled() != shadow_enabled:
            self.shadow.setEnabled(shadow_enabled)
        basecurve = self.__curvepath
        link_enabled = self.__enabled
        if link_enabled:
            path = basecurve
        else:
            if self.__curvepath_disabled is None:
                self.__curvepath_disabled = path_link_disabled(basecurve)
            path = self.__curvepath_disabled

        self.setPath(path)


def bezier_subdivide(cp, t):
    """
    Subdivide a cubic bezier curve defined by the control points `cp`.

    Parameters
    ----------
    cp : List[QPointF]
        The control points for a cubic bezier curve.
    t : float
        The cut point; a value between 0 and 1.

    Returns
    -------
    cp : Tuple[List[QPointF], List[QPointF]]
        Two lists of new control points for the new left and right part
        respectively.
    """
    # http://www.cs.mtu.edu/~shene/COURSES/cs3621/NOTES/spline/Bezier/bezier-sub.html
    c00, c01, c02, c03 = cp

    c10 = c00 * (1 - t) + c01 * t
    c11 = c01 * (1 - t) + c02 * t
    c12 = c02 * (1 - t) + c03 * t

    c20 = c10 * (1 - t) + c11 * t
    c21 = c11 * (1 - t) + c12 * t

    c30 = c20 * (1 - t) + c21 * t

    first = [c00, c10, c20, c30]
    second = [c30, c21, c12, c03]
    return first, second


def qpainterpath_simple_split(path, t):
    """
    Split a QPainterPath defined simple curve.

    The path must be either empty or composed of a single LineToElement or
    CurveToElement.

    Parameters
    ----------
    path : QPainterPath

    t : float
        Point where to split specified as a percentage along the path

    Returns
    -------
    splitpath: Tuple[QPainterPath, QPainterPath]
        A pair of QPainterPaths
    """
    assert path.elementCount() > 0
    el0 = path.elementAt(0)
    assert el0.type == QPainterPath.MoveToElement
    if path.elementCount() == 1:
        p1 = QPainterPath()
        p1.moveTo(el0.x, el0.y)
        return p1, QPainterPath(p1)

    el1 = path.elementAt(1)
    if el1.type == QPainterPath.LineToElement:
        pointat = path.pointAtPercent(t)
        l1 = QLineF(el0.x, el0.y, pointat.x(), pointat.y())
        l2 = QLineF(pointat.x(), pointat.y(), el1.x, el1.y)
        p1 = QPainterPath()
        p2 = QPainterPath()
        p1.addLine(l1)
        p2.addLine(l2)
        return p1, p2
    elif el1.type == QPainterPath.CurveToElement:
        c0, c1, c2, c3 = el0, el1, path.elementAt(2), path.elementAt(3)
        assert all(el.type == QPainterPath.CurveToDataElement
                   for el in [c2, c3])
        cp = [QPointF(el.x, el.y) for el in [c0, c1, c2, c3]]
        first, second = bezier_subdivide(cp, t)
        p1, p2 = QPainterPath(), QPainterPath()
        p1.moveTo(first[0])
        p1.cubicTo(*first[1:])
        p2.moveTo(second[0])
        p2.cubicTo(*second[1:])
        return p1, p2
    else:
        assert False


def path_link_disabled(basepath):
    """
    Return a QPainterPath 'styled' to indicate a 'disabled' link.

    A disabled link is displayed with a single disconnection symbol in the
    middle (--||--)

    Parameters
    ----------
    basepath : QPainterPath
        The base path (a simple curve spine).

    Returns
    -------
    path : QPainterPath
        A 'styled' link path
    """
    segmentlen = basepath.length()
    px = 5

    if segmentlen < 10:
        return QPainterPath(basepath)

    t = (px / 2) / segmentlen
    p1, _ = qpainterpath_simple_split(basepath, 0.50 - t)
    _, p2 = qpainterpath_simple_split(basepath, 0.50 + t)

    angle = -basepath.angleAtPercent(0.5) + 90
    angler = math.radians(angle)
    normal = QPointF(math.cos(angler), math.sin(angler))

    end1 = p1.currentPosition()
    start2 = QPointF(p2.elementAt(0).x, p2.elementAt(0).y)
    p1.moveTo(start2.x(), start2.y())
    p1.addPath(p2)

    def QPainterPath_addLine(path, line):
        path.moveTo(line.p1())
        path.lineTo(line.p2())

    QPainterPath_addLine(p1, QLineF(end1 - normal * 3, end1 + normal * 3))
    QPainterPath_addLine(p1, QLineF(start2 - normal * 3, start2 + normal * 3))
    return p1


class LinkAnchorIndicator(QGraphicsEllipseItem):
    """
    A visual indicator of the link anchor point at both ends
    of the :class:`LinkItem`.

    """
    def __init__(self, *args):
        QGraphicsEllipseItem.__init__(self, *args)
        self.setRect(-3.5, -3.5, 7., 7.)
        self.setPen(QPen(Qt.NoPen))
        self.setBrush(QBrush(QColor("#9CACB4")))
        self.__hover = False

    def setHoverState(self, state):
        """
        The hover state is set by the LinkItem.
        """
        if self.__hover != state:
            self.__hover = state
            self.update()

    def paint(self, painter, option, widget=None):
        brush = self.brush()

        if self.__hover:
            brush = QBrush(brush.color().darker(110))

        painter.setBrush(brush)
        painter.setPen(self.pen())
        painter.drawEllipse(self.rect())


class LinkItem(QGraphicsObject):
    """
    A Link item in the canvas that connects two :class:`.NodeItem`\s in the
    canvas.

    The link curve connects two `Anchor` items (see :func:`setSourceItem`
    and :func:`setSinkItem`). Once the anchors are set the curve
    automatically adjusts its end points whenever the anchors move.

    An optional source/sink text item can be displayed above the curve's
    central point (:func:`setSourceName`, :func:`setSinkName`)

    """

    #: Z value of the item
    Z_VALUE = 0

    #: Runtime link state value
    #: These are pulled from SchemeLink.State for ease of binding to it's
    #: state
    State = SchemeLink.State
    #: The link has no associated state.
    NoState = SchemeLink.NoState
    #: Link is empty; the source node does not have any value on output
    Empty = SchemeLink.Empty
    #: Link is active; the source node has a valid value on output
    Active = SchemeLink.Active
    #: The link is pending; the sink node is scheduled for update
    Pending = SchemeLink.Pending

    def __init__(self, *args):
        self.__boundingRect = None
        QGraphicsObject.__init__(self, *args)
        self.setFlag(QGraphicsItem.ItemHasNoContents, True)
        self.setAcceptedMouseButtons(Qt.RightButton | Qt.LeftButton)
        self.setAcceptHoverEvents(True)

        self.setZValue(self.Z_VALUE)

        self.sourceItem = None
        self.sourceAnchor = None
        self.sinkItem = None
        self.sinkAnchor = None

        self.curveItem = LinkCurveItem(self)

        self.sourceIndicator = LinkAnchorIndicator(self)
        self.sinkIndicator = LinkAnchorIndicator(self)
        self.sourceIndicator.hide()
        self.sinkIndicator.hide()

        self.linkTextItem = QGraphicsTextItem(self)
        self.linkTextItem.setAcceptedMouseButtons(Qt.NoButton)
        self.linkTextItem.setAcceptHoverEvents(False)
        self.__sourceName = ""
        self.__sinkName = ""

        self.__dynamic = False
        self.__dynamicEnabled = False
        self.__state = LinkItem.NoState
        self.hover = False

        self.prepareGeometryChange()
        self.__updatePen()
        self.__boundingRect = None

    def setSourceItem(self, item, anchor=None):
        """
        Set the source `item` (:class:`.NodeItem`). Use `anchor`
        (:class:`.AnchorPoint`) as the curve start point (if ``None`` a new
        output anchor will be created using ``item.newOutputAnchor()``).

        Setting item to ``None`` and a valid anchor is a valid operation
        (for instance while mouse dragging one end of the link).

        """
        if item is not None and anchor is not None:
            if anchor not in item.outputAnchors():
                raise ValueError("Anchor must be belong to the item")

        if self.sourceItem != item:
            if self.sourceAnchor:
                # Remove a previous source item and the corresponding anchor
                self.sourceAnchor.scenePositionChanged.disconnect(
                    self._sourcePosChanged
                )

                if self.sourceItem is not None:
                    self.sourceItem.removeOutputAnchor(self.sourceAnchor)

                self.sourceItem = self.sourceAnchor = None

            self.sourceItem = item

            if item is not None and anchor is None:
                # Create a new output anchor for the item if none is provided.
                anchor = item.newOutputAnchor()

            # Update the visibility of the start point indicator.
            self.sourceIndicator.setVisible(bool(item))

        if anchor != self.sourceAnchor:
            if self.sourceAnchor is not None:
                self.sourceAnchor.scenePositionChanged.disconnect(
                    self._sourcePosChanged
                )

            self.sourceAnchor = anchor

            if self.sourceAnchor is not None:
                self.sourceAnchor.scenePositionChanged.connect(
                    self._sourcePosChanged
                )

        self.__updateCurve()

    def setSinkItem(self, item, anchor=None):
        """
        Set the sink `item` (:class:`.NodeItem`). Use `anchor`
        (:class:`.AnchorPoint`) as the curve end point (if ``None`` a new
        input anchor will be created using ``item.newInputAnchor()``).

        Setting item to ``None`` and a valid anchor is a valid operation
        (for instance while mouse dragging one and of the link).

        """
        if item is not None and anchor is not None:
            if anchor not in item.inputAnchors():
                raise ValueError("Anchor must be belong to the item")

        if self.sinkItem != item:
            if self.sinkAnchor:
                # Remove a previous source item and the corresponding anchor
                self.sinkAnchor.scenePositionChanged.disconnect(
                    self._sinkPosChanged
                )

                if self.sinkItem is not None:
                    self.sinkItem.removeInputAnchor(self.sinkAnchor)

                self.sinkItem = self.sinkAnchor = None

            self.sinkItem = item

            if item is not None and anchor is None:
                # Create a new input anchor for the item if none is provided.
                anchor = item.newInputAnchor()

            # Update the visibility of the end point indicator.
            self.sinkIndicator.setVisible(bool(item))

        if self.sinkAnchor != anchor:
            if self.sinkAnchor is not None:
                self.sinkAnchor.scenePositionChanged.disconnect(
                    self._sinkPosChanged
                )

            self.sinkAnchor = anchor

            if self.sinkAnchor is not None:
                self.sinkAnchor.scenePositionChanged.connect(
                    self._sinkPosChanged
                )

        self.__updateCurve()

    def setFont(self, font):
        """
        Set the font for the channel names text item.
        """
        if font != self.font():
            self.linkTextItem.setFont(font)
            self.__updateText()

    def font(self):
        """
        Return the font for the channel names text.
        """
        return self.linkTextItem.font()

    def setChannelNamesVisible(self, visible):
        """
        Set the visibility of the channel name text.
        """
        self.linkTextItem.setVisible(visible)

    def setSourceName(self, name):
        """
        Set the name of the source (used in channel name text).
        """
        if self.__sourceName != name:
            self.__sourceName = name
            self.__updateText()

    def sourceName(self):
        """
        Return the source name.
        """
        return self.__sourceName

    def setSinkName(self, name):
        """
        Set the name of the sink (used in channel name text).
        """
        if self.__sinkName != name:
            self.__sinkName = name
            self.__updateText()

    def sinkName(self):
        """
        Return the sink name.
        """
        return self.__sinkName

    def _sinkPosChanged(self, *arg):
        self.__updateCurve()

    def _sourcePosChanged(self, *arg):
        self.__updateCurve()

    def __updateCurve(self):
        self.prepareGeometryChange()
        self.__boundingRect = None
        if self.sourceAnchor and self.sinkAnchor:
            source_pos = self.sourceAnchor.anchorScenePos()
            sink_pos = self.sinkAnchor.anchorScenePos()
            source_pos = self.curveItem.mapFromScene(source_pos)
            sink_pos = self.curveItem.mapFromScene(sink_pos)

            # Adaptive offset for the curve control points to avoid a
            # cusp when the two points have the same y coordinate
            # and are close together
            delta = source_pos - sink_pos
            dist = math.sqrt(delta.x() ** 2 + delta.y() ** 2)
            cp_offset = min(dist / 2.0, 60.0)

            # TODO: make the curve tangent orthogonal to the anchors path.
            path = QPainterPath()
            path.moveTo(source_pos)
            path.cubicTo(source_pos + QPointF(cp_offset, 0),
                         sink_pos - QPointF(cp_offset, 0),
                         sink_pos)

            self.curveItem.setCurvePath(path)
            self.sourceIndicator.setPos(source_pos)
            self.sinkIndicator.setPos(sink_pos)
            self.__updateText()
        else:
            self.setHoverState(False)
            self.curveItem.setPath(QPainterPath())

    def __updateText(self):
        self.prepareGeometryChange()
        self.__boundingRect = None

        if self.__sourceName or self.__sinkName:
            if self.__sourceName != self.__sinkName:
                text = ("<nobr>{0}</nobr> \u2192 <nobr>{1}</nobr>"
                        .format(escape(self.__sourceName),
                                escape(self.__sinkName)))
            else:
                # If the names are the same show only one.
                # Is this right? If the sink has two input channels of the
                # same type having the name on the link help elucidate
                # the scheme.
                text = escape(self.__sourceName)
        else:
            text = ""

        self.linkTextItem.setHtml('<div align="center">{0}</div>'
                                  .format(text))
        path = self.curveItem.curvePath()

        # Constrain the text width if it is too long to fit on a single line
        # between the two ends
        if not path.isEmpty():
            # Use the distance between the start/end points as a measure of
            # available space
            diff = path.pointAtPercent(0.0) - path.pointAtPercent(1.0)
            available_width = math.sqrt(diff.x() ** 2 + diff.y() ** 2)
            # Get the ideal text width if it was unconstrained
            doc = self.linkTextItem.document().clone(self)
            doc.setTextWidth(-1)
            idealwidth = doc.idealWidth()
            doc.deleteLater()

            # Constrain the text width but not below a certain min width
            minwidth = 100
            textwidth = max(minwidth, min(available_width, idealwidth))
            self.linkTextItem.setTextWidth(textwidth)
        else:
            # Reset the fixed width
            self.linkTextItem.setTextWidth(-1)

        if not path.isEmpty():
            center = path.pointAtPercent(0.5)
            angle = path.angleAtPercent(0.5)

            brect = self.linkTextItem.boundingRect()

            transform = QTransform()
            transform.translate(center.x(), center.y())
            transform.rotate(-angle)

            # Center and move above the curve path.
            transform.translate(-brect.width() / 2, -brect.height())

            self.linkTextItem.setTransform(transform)

    def removeLink(self):
        self.setSinkItem(None)
        self.setSourceItem(None)
        self.__updateCurve()

    def setHoverState(self, state):
        if self.hover != state:
            self.prepareGeometryChange()
            self.__boundingRect = None
            self.hover = state
            self.sinkIndicator.setHoverState(state)
            self.sourceIndicator.setHoverState(state)
            self.curveItem.setHoverState(state)
            self.__updatePen()

    def hoverEnterEvent(self, event):
        # Hover enter event happens when the mouse enters any child object
        # but we only want to show the 'hovered' shadow when the mouse
        # is over the 'curveItem', so we install self as an event filter
        # on the LinkCurveItem and listen to its hover events.
        self.curveItem.installSceneEventFilter(self)
        return QGraphicsObject.hoverEnterEvent(self, event)

    def hoverLeaveEvent(self, event):
        # Remove the event filter to prevent unnecessary work in
        # scene event filter when not needed
        self.curveItem.removeSceneEventFilter(self)
        return QGraphicsObject.hoverLeaveEvent(self, event)

    def sceneEventFilter(self, obj, event):
        if obj is self.curveItem:
            if event.type() == QEvent.GraphicsSceneHoverEnter:
                self.setHoverState(True)
            elif event.type() == QEvent.GraphicsSceneHoverLeave:
                self.setHoverState(False)

        return QGraphicsObject.sceneEventFilter(self, obj, event)

    def boundingRect(self):
        if self.__boundingRect is None:
            self.__boundingRect = self.childrenBoundingRect()
        return self.__boundingRect

    def shape(self):
        return self.curveItem.shape()

    def setEnabled(self, enabled):
        """
        Reimplemented from :class:`QGraphicsObject`

        Set link enabled state. When disabled the link is rendered with a
        dashed line.

        """
        # This getter/setter pair override a property from the base class.
        # They should be renamed to e.g. setLinkEnabled/linkEnabled
        self.curveItem.setLinkEnabled(enabled)

    def isEnabled(self):
        return self.curveItem.isLinkEnabled()

    def setDynamicEnabled(self, enabled):
        """
        Set the link's dynamic enabled state.

        If the link is `dynamic` it will be rendered in red/green color
        respectively depending on the state of the dynamic enabled state.

        """
        if self.__dynamicEnabled != enabled:
            self.__dynamicEnabled = enabled
            if self.__dynamic:
                self.__updatePen()

    def isDynamicEnabled(self):
        """
        Is the link dynamic enabled.
        """
        return self.__dynamicEnabled

    def setDynamic(self, dynamic):
        """
        Mark the link as dynamic (i.e. it responds to
        :func:`setDynamicEnabled`).

        """
        if self.__dynamic != dynamic:
            self.__dynamic = dynamic
            self.__updatePen()

    def isDynamic(self):
        """
        Is the link dynamic.
        """
        return self.__dynamic

    def setRuntimeState(self, state):
        """
        Style the link appropriate to the LinkItem.State

        Parameters
        ----------
        state : LinkItem.State
        """
        if self.__state != state:
            self.__state = state

            if state & LinkItem.Pending:
                self.sinkIndicator.setBrush(QBrush(Qt.yellow))
            else:
                self.sinkIndicator.setBrush(QBrush(QColor("#9CACB4")))
            self.__updatePen()

    def runtimeState(self):
        return self.__state

    def __updatePen(self):
        self.prepareGeometryChange()
        self.__boundingRect = None
        if self.__dynamic:
            if self.__dynamicEnabled:
                color = QColor(0, 150, 0, 150)
            else:
                color = QColor(150, 0, 0, 150)

            normal = QPen(QBrush(color), 2.0)
            hover = QPen(QBrush(color.darker(120)), 2.1)
        else:
            normal = QPen(QBrush(QColor("#9CACB4")), 2.0)
            hover = QPen(QBrush(QColor("#7D7D7D")), 2.1)

        if self.__state & LinkItem.Empty:
            pen_style = Qt.DashLine
        else:
            pen_style = Qt.SolidLine

        normal.setStyle(pen_style)
        hover.setStyle(pen_style)

        if self.hover:
            pen = hover
        else:
            pen = normal

        self.curveItem.setPen(pen)
