"""Shared marker picking and axis-constrained plot drags (Qt 5/6).

The widget supplies plot/value rectangles, a PlotMath core, viewport/markers,
axis locks and refresh hooks. Geometry and numeric transforms use protocan.plot.
"""
from dataclasses import replace

try:
    from PySide6.QtCore import QPointF, Qt
    from PySide6.QtWidgets import QApplication
except ImportError:
    from PySide2.QtCore import QPointF, Qt
    from PySide2.QtWidgets import QApplication


DRAG_HINT = ('ЛКМ рядом с маркером — двигать маркер; ЛКМ на свободном поле — '
             'перемещение по X; Shift + ЛКМ — перемещение по Y. '
             'Щелчок мимо маркеров — одиночный курсор.')


def vertical_pan_requested(event):
    return bool(event.modifiers() & Qt.ShiftModifier)


def cursor_hit(plot, position, value, event, radius=8):
    """Shift always pans; a cursor can only be grabbed near its visible line."""
    return (not vertical_pan_requested(event) and value is not None
            and plot.core is not None and plot.has_plot_data
            and plot.visible_bounds.left <= value <= plot.visible_bounds.right
            and plot.plot_rect().contains(position)
            and abs(plot.project(value, 0, plot.plot_rect()).x() - position.x()) <= radius)


class PlotDragInteraction:
    """Capture a hit marker or pan one axis, chosen at the start of the drag."""

    def mousePressEvent(self, event):
        if event.button() != Qt.LeftButton or not self.core:
            return super().mousePressEvent(event)
        pos = event.position() if hasattr(event, 'position') else event.localPos()
        rect, values = self.plot_rect(), self.value_rect()
        self._press = self._dragged = None
        if not rect.contains(pos):
            return
        self.setFocus(Qt.MouseFocusReason)
        self._press = QPointF(pos)
        self._press_viewport = self.viewport
        self._press_markers = self.markers
        self._press_bounds = self.visible_bounds
        self._pan_vertical = vertical_pan_requested(event)
        self._pan_moved = False
        if self.marker_mode.isChecked() and not self._pan_vertical and self.has_plot_data:
            # X lines span digital lanes; Y lines only occupy the analog pane.
            markers = self.markers if values.contains(pos) else replace(self.markers, y_enabled=False)
            self._dragged = markers.hit(self.core, pos.x() - rect.left(),
                pos.y() - values.top() if values.contains(pos) else 0,
                rect.width(), values.height(), 12, self._press_bounds)
            if self._dragged is not None:
                self.markers = replace(self.markers, selected=self._dragged)
                self._refresh_controls()
                self.update()
        event.accept()

    def mouseMoveEvent(self, event):
        if not event.buttons() & Qt.LeftButton:
            self._press = self._dragged = None
            return super().mouseMoveEvent(event)
        if self._press is None or not self.core:
            return super().mouseMoveEvent(event)
        pos = event.position() if hasattr(event, 'position') else event.localPos()
        self._update_drag(pos)
        event.accept()

    def _update_drag(self, pos):
        delta = pos - self._press
        self._pan_moved |= delta.manhattanLength() >= QApplication.startDragDistance()
        rect, values = self.plot_rect(), self.value_rect()
        if self._dragged is not None:
            marker = self._dragged
            self.markers = self._press_markers.drag(self.core, marker,
                delta.y() if marker.horizontal else delta.x(),
                values.height() if marker.horizontal else rect.width(), self._press_bounds)
        else:
            self.viewport = self._press_viewport.transform(self.core,
                pan_x=delta.x() / rect.width() if not self._pan_vertical and not self.lock_x else 0,
                pan_y=delta.y() / values.height() if self._pan_vertical and not self.lock_y else 0)
        self._refresh_controls()
        self.update()

    def mouseReleaseEvent(self, event):
        if event.button() != Qt.LeftButton:
            return super().mouseReleaseEvent(event)
        if self._press is not None and self.core:
            # Qt may coalesce moves; always commit the final release position.
            pos = event.position() if hasattr(event, 'position') else event.localPos()
            self._update_drag(pos)
            single_click = (self._dragged is None and not self._pan_vertical
                            and not self._pan_moved and self.plot_rect().contains(pos))
            if single_click:
                # A click with small hand jitter must not pan the time axis.
                self.viewport = self._press_viewport
                self._single_cursor_click(pos)
            self.view_changed.emit()
        self._press = self._dragged = None
        super().mouseReleaseEvent(event)

    def _single_cursor_click(self, pos):
        """Optional widget hook: return from paired markers to a single cursor."""