"""A horizontal QSlider that paints marks at frames where censorship was found.

Used as the navigation scrubber under the image: the file list / `_results`
cache is projected onto the groove as small vertical ticks, so you can see at a
glance where the detected regions are along the whole sequence.
"""

from __future__ import annotations

from collections.abc import Iterable

from PySide6.QtCore import Qt
from PySide6.QtGui import QColor, QPainter
from PySide6.QtWidgets import QSlider, QStyle, QStyleOptionSlider


class MarkerSlider(QSlider):
    def __init__(self, orientation=Qt.Horizontal, parent=None) -> None:
        super().__init__(orientation, parent)
        self._marks: set[int] = set()
        # Bright cyan stands out against both the dark track and the orange fill.
        self._mark_color = QColor(0, 220, 255)

    def set_marks(self, marks: Iterable[int]) -> None:
        marks = set(marks)
        if marks != self._marks:
            self._marks = marks
            self.update()

    def paintEvent(self, event) -> None:
        super().paintEvent(event)
        if not self._marks or self.maximum() <= self.minimum():
            return

        opt = QStyleOptionSlider()
        self.initStyleOption(opt)
        groove = self.style().subControlRect(
            QStyle.CC_Slider, opt, QStyle.SC_SliderGroove, self
        )
        handle = self.style().subControlRect(
            QStyle.CC_Slider, opt, QStyle.SC_SliderHandle, self
        )
        span = groove.width() - handle.width()
        if span <= 0:
            return
        lo, hi = self.minimum(), self.maximum()
        half = handle.width() // 2
        # Span (almost) the full widget height so marks read over the fill/handle.
        top = self.rect().top() + 1
        bottom = self.rect().bottom() - 1

        painter = QPainter(self)
        pen = painter.pen()
        pen.setColor(self._mark_color)
        pen.setWidth(2)
        painter.setPen(pen)
        # Many frames can collapse onto the same pixel column — dedupe to keep
        # repaint cheap on big folders (tens of thousands of frames).
        seen_x: set[int] = set()
        for m in self._marks:
            pos = QStyle.sliderPositionFromValue(lo, hi, m, span, opt.upsideDown)
            x = groove.x() + half + pos
            if x not in seen_x:
                seen_x.add(x)
                painter.drawLine(x, top, x, bottom)
        painter.end()