// DragonX Wallet - ImGui Edition
// Copyright 2024-2026 The Hush Developers
// Released under the GPLv3
//
// Pure maths of ApplyScrollEdgeMask (draw_helpers.h), split out so it is unit-testable without ImGui.
#pragma once

#include <algorithm>

namespace dragonx {
namespace ui {
namespace material {

struct ScrollEdgeFade {
    bool top = false;      // content scrolled off the top edge
    bool bottom = false;   // more content below the bottom edge
    bool any() const { return top || bottom; }
};

inline ScrollEdgeFade ComputeScrollEdgeFade(float scrollY, float scrollMaxY)
{
    ScrollEdgeFade f;
    f.top = scrollY > 1.0f;                                    // only when scrolled down
    f.bottom = scrollMaxY > 0 && scrollY < scrollMaxY - 1.0f;  // only when not at the scroll bottom
    return f;
}

// Alpha multiplier (0..1) for a vertex at screen-y `posY`. Same maths as the former inline loop.
inline float ScrollEdgeAlpha(const ScrollEdgeFade& f, float posY, float topEdge, float bottomEdge, float fadeZone)
{
    float alpha = 1.0f;
    if (f.top) {
        float d = posY - topEdge;
        if (d < fadeZone)
            alpha = std::min(alpha, std::max(0.0f, d / fadeZone));
    }
    if (f.bottom) {
        float d = bottomEdge - posY;
        if (d < fadeZone)
            alpha = std::min(alpha, std::max(0.0f, d / fadeZone));
    }
    return alpha;
}

} // namespace material
} // namespace ui
} // namespace dragonx