#pragma once
#include "hd2d/GL.h"
#include "hd2d/Texture.h"

#include <glm/glm.hpp>
#include <vector>

namespace hd2d {

// One upright pixel-art sprite. `pos` is where the feet (pivot) row touches
// the ground; sprites face the camera around the Y axis. 64 bytes, read by
// billboard.vert as four vec4 attributes (keep both in sync).
//
// A default-initialised instance draws the whole texture, planted by its
// lowest opaque row. Set `uv` to draw one frame of a sprite sheet / atlas
// cell (see Texture::cellUV, SpriteAtlas::uv) and `anchor` to that frame's
// feet row (Texture::cellAnchor, SpriteAtlas::anchor).
struct BillboardInstance {
    glm::vec3 pos{0.0f};
    float sway = 0.0f;           // wind / player-push response (0 = rigid)
    glm::vec2 size{1.0f};        // world size of the `uv` sub-rect quad
    float flip = 0.0f;           // 1 = mirror horizontally (inside the sub-rect)
    float tint = 1.0f;           // brightness multiplier (breaks up repetition)
    glm::vec4 uv{0, 0, 1, 1};    // texture sub-rect (minU, minV, maxU, maxV), GL orientation (v = 0 is the image bottom)
    float anchor = -1.0f;        // texture-space v of the feet (pivot) row; < 0 = use tex().opaqueBounds().y
    float turn = 0.0f;           // extra yaw (radians) away from camera-facing; color pass only, shadow cards stay sun-facing
    float alpha = 1.0f;          // 0..1 fade, dithered discard in color and shadow passes (no blending)
    float flash = 0.0f;          // 0..1 blend toward bright emissive white (hit / capture flash)
};

// Instanced batch of billboards sharing one texture: its own `texture`, or
// `sharedTexture` (e.g. a SpriteAtlas page shared by many batches) when set.
class BillboardBatch {
public:
    BillboardBatch() = default;
    BillboardBatch(const BillboardBatch&) = delete;
    BillboardBatch& operator=(const BillboardBatch&) = delete;
    ~BillboardBatch();

    bool loadTexture(const std::string& path) { return texture.load(path); }
    void upload();  // call after editing `instances`
    void draw() const;

    // Texture the renderer binds: `sharedTexture` if set, else `texture`.
    const Texture& tex() const { return sharedTexture ? *sharedTexture : texture; }

    // World size that keeps the own `texture` at `pixelsPerUnit` texel density.
    glm::vec2 sizeForDensity(float pixelsPerUnit) const {
        return glm::vec2(texture.size()) / pixelsPerUnit;
    }
    // World size of one `cellPixels` sheet frame / atlas cell at `pixelsPerUnit`.
    static glm::vec2 cellSize(glm::ivec2 cellPixels, float pixelsPerUnit) {
        return glm::vec2(cellPixels) / pixelsPerUnit;
    }

    Texture texture;
    const Texture* sharedTexture = nullptr;  // not owned; must outlive the batch's use
    std::vector<BillboardInstance> instances;
    bool castShadows = true;
    bool inReflections = true;
    float emissive = 0.0f;  // unlit contribution, for glowing sprites

private:
    GLuint vao_ = 0, vbo_ = 0;
    size_t capacity_ = 0;
    GLsizei count_ = 0;
};

}  // namespace hd2d