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

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

namespace hd2d {

// Fixed-cell dynamic atlas on one Texture: images of up to `cellPixels` are
// packed into a cols x rows grid at runtime (e.g. sprites generated or
// downloaded while the game runs) so many billboards share a texture. Use
// with `BillboardBatch::sharedTexture = &atlas.texture()` and per-instance
// `uv = atlas.uv(slot)`, `anchor = atlas.anchor(slot)`.
//
// Every cell keeps its own 1-px transparent border (gutter), so sharp
// bilinear sampling and the first mip levels never bleed between cells.
// Images are placed bottom-centered in their cell; images larger than the
// cell are cropped to it (keeping the bottom rows and the horizontal center).
class SpriteAtlas {
public:
    // Allocates a transparent texture of cols x rows cells. Clears all slots.
    bool init(glm::ivec2 cellPixels, int cols, int rows);

    int add(const Image& img);             // first free slot, or -1 when full
    void set(int slot, const Image& img);  // replace (or fill) a slot
    void remove(int slot);                 // clear a slot and free it

    // BillboardInstance::uv of the whole cell (cellPixels, gutter excluded).
    glm::vec4 uv(int slot) const;
    // BillboardInstance::anchor: v of the lowest opaque (alpha >= 128) row of
    // the image in `slot`; the cell bottom if it has no opaque pixels.
    float anchor(int slot) const;
    glm::ivec2 imageSize(int slot) const;  // size placed in the cell (after cropping)
    bool inUse(int slot) const;

    const Texture& texture() const { return texture_; }
    glm::ivec2 cellPixels() const { return cell_; }
    int capacity() const { return cols_ * rows_; }
    int used() const { return used_; }

private:
    struct Slot {
        bool used = false;
        glm::ivec2 size{0};
        int feetRow = 0;  // lowest opaque row, in cell pixels from the cell bottom
    };
    glm::ivec2 origin(int slot) const;  // GL-orientation pixel of the cell's bottom-left (inside the gutter)
    bool valid(int slot) const { return slot >= 0 && slot < capacity(); }

    Texture texture_;
    glm::ivec2 cell_{0};
    int cols_ = 0, rows_ = 0, used_ = 0;
    std::vector<Slot> slots_;
};

}  // namespace hd2d