// DPI -> UI scale math for the host overlay, factored out of ImGui/window code so it's unit-testable
// without a live window. The host is per-monitor-DPI-aware (see wWinMain), so GetSystemMetrics and
// GetDpiForWindow report true pixels; we scale ImGui's font and style by this factor ourselves to keep
// the overlay the same physical size -- and crisp -- across display scalings instead of letting Windows
// bitmap-stretch a virtualized-resolution window.
#pragma once

#include <algorithm>

#include <windows.h> // USER_DEFAULT_SCREEN_DPI (== 96, the 100%-scale baseline)

namespace coop {

// ImGui's built-in default font (ProggyClean) rasterizes at this pixel size at 100% scale. Named once
// here so the DPI math scales from a single owned constant instead of a bare 13 sprinkled around.
inline constexpr float kBaseFontPx = 13.0f;

// Bound the derived scale: never shrink the overlay below 100% (a readability floor), and cap absurd
// values so a bogus DPI report can't blow the font atlas up to an enormous texture.
inline constexpr float kMinUiScale = 1.0f;
inline constexpr float kMaxUiScale = 8.0f;

// UI scale factor for a monitor DPI (dots per inch, as GetDpiForWindow / WM_DPICHANGED report it).
// 96 DPI == 100% == 1.0; 144 DPI (150%) == 1.5. A zero/unknown DPI falls back to the 96 baseline so
// callers never derive a zero-size font.
inline float dpi_scale_from(unsigned dpi)
{
	if (dpi == 0) {
		dpi = USER_DEFAULT_SCREEN_DPI;
	}
	const float scale = static_cast<float>(dpi) / static_cast<float>(USER_DEFAULT_SCREEN_DPI);
	return std::clamp(scale, kMinUiScale, kMaxUiScale);
}

// Default-font pixel size for a monitor DPI: the base size scaled so glyphs rasterize crisp at the
// target size. Pair with ImGui::GetStyle().ScaleAllSizes(dpi_scale_from(dpi)) for spacing/padding.
inline float scaled_font_px(unsigned dpi)
{
	return kBaseFontPx * dpi_scale_from(dpi);
}

} // namespace coop