#ifndef RENDER_MESH_H
#define RENDER_MESH_H

/*
 * GPU mesh plus a CPU-side builder.
 * Vertex layout: position (loc 0), normal (loc 1), color (loc 2).
 */

#include <stdbool.h>
#include <stddef.h>

#include "core/gl.h"
#include "math/linalg.h"

typedef struct {
    Vec3 position;
    Vec3 normal;
    Vec3 color;
} Vertex;

typedef struct {
    GLuint  vao;
    GLuint  vbo;
    GLuint  ebo;
    GLsizei index_count;
    Vec3    center;      /* bounding sphere (model space): what isn't in view isn't drawn */
    float   radius;
} Mesh;

typedef struct {
    Vertex   *vertices;
    size_t    vertex_count, vertex_capacity;
    GLuint   *indices;
    size_t    index_count, index_capacity;
    bool      out_of_memory;
} MeshBuilder;

void   MeshBuilder_init(MeshBuilder *b);
void   MeshBuilder_free(MeshBuilder *b);

/* Appends a vertex and returns its index. */
GLuint MeshBuilder_vertex(MeshBuilder *b, Vec3 position, Vec3 normal, Vec3 color);

/*
 * Triangles are always stored counter-clockwise as seen from the side their
 * vertex normals point to, so the given index order does not matter.
 */
void   MeshBuilder_triangle(MeshBuilder *b, GLuint i0, GLuint i1, GLuint i2);
/* Two triangles: (i0, i1, i2) and (i2, i3, i0). */
void   MeshBuilder_quad(MeshBuilder *b, GLuint i0, GLuint i1, GLuint i2, GLuint i3);

/*
 * Flat quad (corners in order around the edge) or triangle, subdivided into
 * cells of at most cell_size so the surface can bend in the vertex shader.
 */
void   MeshBuilder_gridQuad(MeshBuilder *b, Vec3 p0, Vec3 p1, Vec3 p2, Vec3 p3,
                            Vec3 normal, Vec3 color, float cell_size);
void   MeshBuilder_gridTriangle(MeshBuilder *b, Vec3 p0, Vec3 p1, Vec3 p2,
                                Vec3 normal, Vec3 color, float cell_size);

/* Number of segments needed to split a length into cells of cell_size. */
int    MeshBuilder_segments(float length, float cell_size);

/* Uploads the builder to the GPU and frees it. Returns an empty mesh on error. */
Mesh   Mesh_fromBuilder(MeshBuilder *b);
void   Mesh_draw(const Mesh *mesh);
void   Mesh_destroy(Mesh *mesh);

#endif /* RENDER_MESH_H */