#pragma once
#include <plot/core/status.hpp>
#include <plot/core/types.hpp>
#include <plot/gl/handle.hpp>

namespace plot::render {

/// Per-instance payload of the line pipeline: one segment in data space. It
/// mirrors the interleaved floats `LineBatch::data()` produces, which is why the
/// attribute offsets in vertex_array.cpp come from `offsetof` rather than from
/// hand-written numbers.
struct LineInstance {
  f32 x0;
  f32 y0;
  f32 x1;
  f32 y1;
};

/// Per-instance payload of the text pipeline: the glyph quad's top-left corner
/// in Rect pixels plus the glyph's atlas texel origin.
struct TextInstance {
  f32 x;
  f32 y;
  f32 u;
  f32 v;
};

static_assert(sizeof(LineInstance) == 4 * sizeof(f32), "line instance must stay 4 floats");
static_assert(sizeof(TextInstance) == 4 * sizeof(f32), "text instance must stay 4 floats");

namespace detail {

/// The growth half of an instance buffer, shared by both pipelines so neither
/// duplicates the GL ownership or the "grow only when the frame needs it" rule.
class InstanceStore {
 public:
  /// Creates the vertex buffer. Reports `ErrorCode::Unsupported` while the GL
  /// entry points are unresolved, `GLFailure` if the driver hands out no name.
  bool create(Status* st = nullptr) noexcept;

  /// Uploads `count` instances of `instance_bytes`. The store only reallocates
  /// when the frame's workload outgrows it, so steady-state frames write into
  /// the existing allocation.
  void upload(const void* data, u32 count, usize instance_bytes) noexcept;

  void bind() const noexcept { buffer_.bind(); }

 private:
  gl::Buffer buffer_;
  u32 capacity_ = 0;  ///< instances the store can hold
};

}  // namespace detail

/// Instance buffer of the line pipeline: one `LineInstance` per segment.
class LineBuffer {
 public:
  bool create(Status* st = nullptr) noexcept { return store_.create(st); }
  void upload(const f32* interleaved, u32 count) noexcept {
    store_.upload(interleaved, count, sizeof(LineInstance));
  }
  void bind() const noexcept { store_.bind(); }

 private:
  detail::InstanceStore store_;
};

/// Instance buffer of the text pipeline: one `TextInstance` per glyph.
class TextBuffer {
 public:
  bool create(Status* st = nullptr) noexcept { return store_.create(st); }
  void upload(const f32* interleaved, u32 count) noexcept {
    store_.upload(interleaved, count, sizeof(TextInstance));
  }
  void bind() const noexcept { store_.bind(); }

 private:
  detail::InstanceStore store_;
};

}  // namespace plot::render