from PyQt5 import QtWidgets, QtGui, QtCore
from PyQt5.QtCore import Qt


class _Bar(QtWidgets.QWidget):
    clickedValue = QtCore.pyqtSignal(int)

    def __init__(self, steps, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.setSizePolicy(QtWidgets.QSizePolicy.MinimumExpanding,
                           QtWidgets.QSizePolicy.MinimumExpanding)

        if isinstance(steps, list):
            # list of colors
            self.n_steps = len(steps)
            self.steps = steps
        elif isinstance(steps, int):
            self.n_steps = steps
            self.steps = ['red'] * steps
        else:
            raise TypeError('step must be a list or int')

        self._bar_solid_parent = 0.8
        self._background_color = QtGui.QColor('black')
        self._padding = 4.0

    def sizeHint(self):
        return QtCore.QSize(40, 120)

    def paintEvent(self, e):
        painter = QtGui.QPainter(self)
        brush = QtGui.QBrush()
        brush.setColor(self._background_color)
        brush.setStyle(Qt.SolidPattern)
        rect = QtCore.QRect(0, 0,
                            painter.device().width(),
                            painter.device().height())
        painter.fillRect(rect, brush)

        # Get current state.
        dial = self.parent()._dial
        vmin, vmax = dial.minimum(), dial.maximum()
        value = dial.value()

        pc = (value - vmin) / (vmax - vmin)
        n_steps_to_draw = int(pc * self.n_steps)

        # Define our canvas
        padding = 5
        d_height = painter.device().height() - (padding * 2)
        d_width = painter.device().width() - (padding * 2)

        # Draw the bars
        step_size = d_height / self.n_steps
        bar_height = int(step_size * self._bar_solid_parent)
        bar_spacer = int(step_size * self._bar_solid_parent / 2)

        for n in range(n_steps_to_draw):
            brush.setColor(QtGui.QColor(self.steps[n]))
            rect = QtCore.QRect(
                padding,
                int(padding + d_height - ((n + 1) * step_size) + bar_spacer),
                d_width, bar_height)
            painter.fillRect(rect, brush)

    def _trigger_refresh(self):
        self.update()

    def _calculate_clicked_value(self, e):
        parent = self.parent()
        vmin, vmax = parent.minimum(), parent.maximum()
        d_height = self.size().height() - (self._padding * 2)
        step_size = d_height / self.n_steps
        click_y = e.y() - self._padding - step_size / 2

        pc = (d_height - click_y) / d_height
        value = vmin + pc * (vmax - vmin)
        self.clickedValue.emit(value)

    def mouseMoveEvent(self, e: QtGui.QMouseEvent):
        self._calculate_clicked_value(e)

    def mouseReleaseEvent(self, e: QtGui.QMouseEvent):
        self._calculate_clicked_value(e)


class PowerBar(QtWidgets.QWidget):
    """
    Custom Qt Widget to show a power bar and dial.
    Demonstrating compound and custom-drawn widget.

    Left-clicking the button shows the color-chooser, while
    right-clicking resets the color tho None (no color).
    """

    colorChanged = QtCore.pyqtSignal()

    def __init__(self, steps=5, *args, **kwargs):
        super(PowerBar, self).__init__(*args, **kwargs)

        layout = QtWidgets.QVBoxLayout()
        self._bar = _Bar(steps)
        layout.addWidget(self._bar)

        # Create the QDial widget and set up defaults.
        self._dial = QtWidgets.QDial()
        self._dial.setNotchesVisible(True)
        self._dial.setWrapping(False)
        self._dial.valueChanged.connect(self._bar._trigger_refresh)

        self._bar.clickedValue.connect(self._dial.setValue)

        layout.addWidget(self._dial)
        self.setLayout(layout)

    def __getattr__(self, name):
        if name in self.__dict__:
            return self[name]
        return getattr(self._dial, name)

    def setColor(self, color):
        self._bar.steps = [color] * self._bar.n_steps
        self._bar.update()

    def setColors(self, colors):
        self._bar.n_steps = len(colors)
        self._bar.steps = colors
        self._bar.update()

    def setBarPadding(self, i):
        self._bar._padding = int(i)
        self._bar.update()

    def setBarSolidPercent(self, f):
        self._bar._bar_solid_percent = float(f)
        self._bar.update()

    def setBackgroundColor(self, color):
        self._bar._background_color = QtGui.QColor(color)
        self._bar.update()


if __name__ == '__main__':
    app = QtWidgets.QApplication([])
    volume = PowerBar()
    volume.show()
    app.exec_()