"""TelemetryOverlay — draws the performance metrics box on the camera view."""

from __future__ import annotations

from PySide6.QtCore import QRect, Qt, Slot
from PySide6.QtGui import QColor, QFont, QPainter, QPen

from app.config import (
    OVERLAY_BG_COLOR,
    OVERLAY_FONT_SIZE,
    OVERLAY_MARGIN,
    OVERLAY_PADDING,
    OVERLAY_TEXT_COLOR,
)
from app.overlay.overlay_layer import IOverlayLayer
from app.telemetry.telemetry_collector import TelemetrySnapshot


class TelemetryOverlay(IOverlayLayer):
    """
    Renders a semi-transparent metrics box in the top-left corner.

    Usage:
        overlay = TelemetryOverlay()
        camera_view.add_overlay_layer(overlay)
        telemetry_collector.metrics_updated.connect(overlay.on_metrics_updated)
    """

    def __init__(self) -> None:
        super().__init__()
        self._snapshot: TelemetrySnapshot | None = None

        self._font = QFont("Monospace")
        self._font.setStyleHint(QFont.StyleHint.TypeWriter)
        self._font.setPointSize(OVERLAY_FONT_SIZE)
        self._font.setBold(False)

    @Slot(object)
    def on_metrics_updated(self, snapshot: TelemetrySnapshot) -> None:
        """Receive a new snapshot from TelemetryCollector."""
        self._snapshot = snapshot

    # ------------------------------------------------------------------
    # IOverlayLayer
    # ------------------------------------------------------------------

    def paint(self, painter: QPainter, video_rect: QRect) -> None:
        if self._snapshot is None:
            return

        lines = self._format_lines(self._snapshot)
        if not lines:
            return

        painter.setFont(self._font)
        fm = painter.fontMetrics()
        line_height = fm.height()
        max_width = max(fm.horizontalAdvance(line) for line in lines)

        box_w = max_width + OVERLAY_PADDING * 2
        box_h = line_height * len(lines) + OVERLAY_PADDING * 2

        # Position relative to the actual video area, not the full widget
        x = video_rect.left() + OVERLAY_MARGIN
        y = video_rect.top() + OVERLAY_MARGIN

        # Background
        painter.setBrush(QColor(*OVERLAY_BG_COLOR))
        painter.setPen(Qt.PenStyle.NoPen)
        painter.drawRoundedRect(QRect(x, y, box_w, box_h), 6, 6)

        # Text
        painter.setPen(QPen(QColor(*OVERLAY_TEXT_COLOR)))
        text_x = x + OVERLAY_PADDING
        text_y = y + OVERLAY_PADDING + fm.ascent()
        for line in lines:
            painter.drawText(text_x, text_y, line)
            text_y += line_height

    # ------------------------------------------------------------------
    # Private
    # ------------------------------------------------------------------

    @staticmethod
    def _format_lines(snap: TelemetrySnapshot) -> list[str]:
        lines = [
            f"FPS    {snap.fps:>6.1f}",
            f"Frame  {snap.frame_time_ms:>6.1f} ms",
            f"Drop   {snap.dropped_frames:>6d}",
            f"CPU    {snap.cpu_percent:>5.1f} %",
        ]
        if snap.memory_mb is not None:
            lines.append(f"Mem    {snap.memory_mb:>5.0f} MB")
        return lines