#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 lowest opaque pixel row
// touches the ground; sprites always face the camera around the Y axis.
struct BillboardInstance {
    glm::vec3 pos{0.0f};
    float sway = 0.0f;       // wind / player-push response (0 = rigid)
    glm::vec2 size{1.0f};    // world units of the full texture quad
    float flip = 0.0f;       // 1 = mirror horizontally
    float tint = 1.0f;       // brightness multiplier (breaks up repetition)
};

// Instanced batch of billboards sharing one texture.
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;

    // World size that keeps the texture at `pixelsPerUnit` texel density.
    glm::vec2 sizeForDensity(float pixelsPerUnit) const {
        return glm::vec2(texture.size()) / pixelsPerUnit;
    }

    Texture texture;
    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