#include "twn_draw_c.h"
#include "twn_util.h"
#include "twn_util_c.h"
#include "twn_engine_context_c.h"
#include "twn_text_c.h"
#include "twn_types.h"

#include <glad/glad.h>
#include <stb_ds.h>


/* TODO: try using the fact we utilize edge coloring and step virtual color attributes to bogus points */
/*       this is only doable is we take out color attribute to separate array or a portion of it */
/* interleaved vertex array data */
typedef struct ElementIndexedQuad {
    /* upper-left */
    Vec2 v0;
    Vec2 uv0;
    Color c0;
    /* bottom-left */
    Vec2 v1;
    Vec2 uv1;
    Color c1;
    /* bottom-right */
    Vec2 v2;
    Vec2 uv2;
    Color c2;
    /* upper-right */
    Vec2 v3;
    Vec2 uv3;
    Color c3;
} ElementIndexedQuad;


typedef struct ElementIndexedQuadWithoutColor {
    /* upper-left */
    Vec2 v0;
    Vec2 uv0;
    /* bottom-left */
    Vec2 v1;
    Vec2 uv1;
    /* bottom-right */
    Vec2 v2;
    Vec2 uv2;
    /* upper-right */
    Vec2 v3;
    Vec2 uv3;
} ElementIndexedQuadWithoutColor;


typedef struct ElementIndexedQuadWithoutTexture {
    /* upper-left */
    Vec2 v0;
    Color c0;
    /* bottom-left */
    Vec2 v1;
    Color c1;
    /* bottom-right */
    Vec2 v2;
    Color c2;
    /* upper-right */
    Vec2 v3;
    Color c3;
} ElementIndexedQuadWithoutTexture;


typedef struct ElementIndexedQuadWithoutColorWithoutTexture {
    /* upper-left */
    Vec2 v0;
    /* bottom-left */
    Vec2 v1;
    /* bottom-right */
    Vec2 v2;
    /* upper-right */
    Vec2 v3;
} ElementIndexedQuadWithoutColorWithoutTexture;


typedef struct {
    size_t offset;
    GLenum type;
    GLsizei stride;
    GLuint buffer;
    uint8_t arity; /* leave at 0 to signal pointer as unused */
} AttributeArrayPointer;


/* allows us to have generic way to issue draws as well as */
/* deferring new draw calls while previous frame is still being drawn */
typedef struct {
    AttributeArrayPointer vertices;
    AttributeArrayPointer texcoords;

    bool constant_colored;
    union {
        AttributeArrayPointer colors;        
        Color color;
    };

    bool textured, texture_repeat, uses_gpu_key;
    TextureKey texture_key;
    GPUTexture gpu_texture;

    GLuint element_buffer;
    GLsizei element_count;
    GLsizei range_start, range_end;

    /* could be either `element_count` with supplied `element_buffer`, or this, but not both */
    GLsizei primitive_count;

    double depth_range_low, depth_range_high;
} DeferredCommandDraw;


typedef struct {
    char *paths;
} DeferredCommandDrawSkybox;


typedef struct {
    Color color;
    bool clear_color;
    bool clear_depth;
    bool clear_stencil;
} DeferredCommandClear;


typedef enum {
    PIPELINE_NO,
    PIPELINE_SPACE,
    PIPELINE_2D,
} Pipeline;


typedef struct {
    Pipeline pipeline;
} DeferredCommandUsePipeline;


typedef struct {
    TextureMode mode;
} DeferredCommandUseTextureMode;


typedef struct {
    double low, high;
} DeferredCommandDepthRange;


typedef struct {
    float start, end, density;
    Color color;
} DeferredCommandApplyFog;


typedef struct {
    enum DeferredCommandType {
        DEFERRED_COMMAND_TYPE_DRAW,
        DEFERRED_COMMAND_TYPE_DRAW_SKYBOX,
        DEFERRED_COMMAND_TYPE_CLEAR,
        DEFERRED_COMMAND_TYPE_USE_PIPIELINE,
        DEFERRED_COMMAND_TYPE_USE_TEXTURE_MODE,
        DEFERRED_COMMAND_TYPE_DEPTH_RANGE,
        DEFERRED_COMMAND_TYPE_APPLY_FOG,
        DEFERRED_COMMAND_TYPE_POP_FOG,
    } type;

    union {
        DeferredCommandDraw draw;
        DeferredCommandDrawSkybox draw_skybox;
        DeferredCommandClear clear;
        DeferredCommandUsePipeline use_pipeline;
        DeferredCommandUseTextureMode use_texture_mode;
        DeferredCommandDepthRange depth_range;
        DeferredCommandApplyFog apply_fog;
    };
} DeferredCommand;


static TextureMode texture_mode_last_used = TEXTURE_MODE_UNKNOWN;
static Pipeline pipeline_last_used = PIPELINE_NO;


/* potentially double buffered array of vertex array handles */
/* we assume they will be refilled fully each frame */
static size_t scratch_va_front_used, scratch_va_back_used;
static GLuint *front_scratch_vertex_arrays, *back_scratch_vertex_arrays;
static GLuint **current_scratch_vertex_array = &front_scratch_vertex_arrays;

static void restart_scratch_vertex_arrays(void) {
    scratch_va_front_used = 0;
    scratch_va_back_used = 0;

    if (ctx.render_double_buffered) {
        current_scratch_vertex_array = current_scratch_vertex_array == &front_scratch_vertex_arrays ?
                &back_scratch_vertex_arrays : &front_scratch_vertex_arrays;
    }
}


GLuint get_scratch_vertex_array(void) {
    size_t *used = current_scratch_vertex_array == &front_scratch_vertex_arrays ?
            &scratch_va_front_used : &scratch_va_back_used;

    if (arrlenu(*current_scratch_vertex_array) <= *used) {
        GLuint handle;
        glGenBuffers(1, &handle);
        arrpush(*current_scratch_vertex_array, handle);
    }

    (*used)++;
    return (*current_scratch_vertex_array)[*used - 1];
}


static void finally_use_2d_pipeline(void);
static void finally_use_space_pipeline(void);
static void finally_use_texture_mode(TextureMode mode);
static void deferred_render_skybox(char *paths);
static void deferred_apply_fog(float start, float end, float density, Color color);
static void deferred_pop_fog(void);

static DeferredCommand *deferred_commands;

static void issue_deferred_draw_commands(void) {
    for (size_t i = 0; i < arrlenu(deferred_commands); ++i) {
        switch (deferred_commands[i].type) {
            case DEFERRED_COMMAND_TYPE_DEPTH_RANGE: {
                glDepthRange(deferred_commands[i].depth_range.low, deferred_commands[i].depth_range.high);
                break;   
            }
            case DEFERRED_COMMAND_TYPE_CLEAR: {
                glClearColor((1.0f / 255) * deferred_commands[i].clear.color.r,
                             (1.0f / 255) * deferred_commands[i].clear.color.g,
                             (1.0f / 255) * deferred_commands[i].clear.color.b,
                             (1.0f / 255) * deferred_commands[i].clear.color.a);

                /* needed as we might mess with it */
                glDepthRange(0.0, 1.0);
                glDepthMask(GL_TRUE);

                glClear((deferred_commands[i].clear.clear_color   ? GL_COLOR_BUFFER_BIT   : 0) |
                        (deferred_commands[i].clear.clear_depth   ? GL_DEPTH_BUFFER_BIT   : 0) |
                        (deferred_commands[i].clear.clear_stencil ? GL_STENCIL_BUFFER_BIT : 0) );
                break;
            }

            case DEFERRED_COMMAND_TYPE_DRAW: {
                DeferredCommandDraw const command = deferred_commands[i].draw;

                /* TODO: don't assume a single vertex array ? */
                SDL_assert(command.vertices.arity != 0);
                SDL_assert(command.vertices.buffer);
                SDL_assert((command.element_buffer && command.element_count != 0) || command.primitive_count != 0);

                glBindBuffer(GL_ARRAY_BUFFER, command.vertices.buffer);
                glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, command.element_buffer);

                glEnableClientState(GL_VERTEX_ARRAY);
                glVertexPointer(command.vertices.arity,
                                command.vertices.type,
                                command.vertices.stride,
                                (void *)command.vertices.offset);

                if (command.texcoords.arity != 0) {
                    SDL_assert(command.texcoords.buffer == command.vertices.buffer);

                    glEnableClientState(GL_TEXTURE_COORD_ARRAY);
                    glClientActiveTexture(GL_TEXTURE0);
                    glTexCoordPointer(command.texcoords.arity,
                                      command.texcoords.type,
                                      command.texcoords.stride,
                                      (void *)command.texcoords.offset);
                }

                if (command.colors.arity != 0) {
                    SDL_assert(command.colors.buffer == command.vertices.buffer);

                    glEnableClientState(GL_COLOR_ARRAY);
                    glColorPointer(command.colors.arity,
                                   command.colors.type,
                                   command.colors.stride,
                                   (void *)command.colors.offset);
                } else if (command.constant_colored)
                    glColor4ub(command.color.r,
                               command.color.g,
                               command.color.b,
                               command.color.a);

                if (command.textured) {
                    if (command.uses_gpu_key)
                        glBindTexture(GL_TEXTURE_2D, command.gpu_texture);
                    else if (command.texture_repeat)
                        textures_bind_repeating(&ctx.texture_cache, command.texture_key);
                    else
                        textures_bind(&ctx.texture_cache, command.texture_key);
                }

                if (command.element_buffer) {
                    SDL_assert(command.element_count != 0);
                    if (command.range_start == command.range_end)
                        glDrawElements(GL_TRIANGLES, command.element_count, GL_UNSIGNED_SHORT, NULL);
                    else
                        glDrawRangeElements(GL_TRIANGLES,
                                            command.range_start,
                                            command.range_end,
                                            command.element_count,
                                            GL_UNSIGNED_SHORT,
                                            NULL);
                } else {
                    SDL_assert(command.primitive_count != 0);
                    glDrawArrays(GL_TRIANGLES, 0, command.primitive_count);
                }

                /* state clearing */

                if (command.textured)
                    glBindTexture(GL_TEXTURE_2D, 0);

                if (command.colors.arity != 0)
                    glDisableClientState(GL_COLOR_ARRAY);

                if (command.texcoords.arity != 0)
                    glDisableClientState(GL_TEXTURE_COORD_ARRAY);

                glDisableClientState(GL_VERTEX_ARRAY);

                glBindBuffer(GL_ARRAY_BUFFER, 0);
                glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);

                break;
            }

            case DEFERRED_COMMAND_TYPE_DRAW_SKYBOX: {
                deferred_render_skybox(deferred_commands[i].draw_skybox.paths);
                break;
            }

            case DEFERRED_COMMAND_TYPE_USE_PIPIELINE: {
                switch (deferred_commands[i].use_pipeline.pipeline) {
                    case PIPELINE_2D:
                        finally_use_2d_pipeline();
                        break;
                    case PIPELINE_SPACE:
                        finally_use_space_pipeline();
                        break;
                    case PIPELINE_NO:
                    default:
                        SDL_assert(false);
                }

                break;
            }

            case DEFERRED_COMMAND_TYPE_USE_TEXTURE_MODE: {
                finally_use_texture_mode(deferred_commands[i].use_texture_mode.mode);
                break;
            }

            case DEFERRED_COMMAND_TYPE_APPLY_FOG: {
                deferred_apply_fog(deferred_commands[i].apply_fog.start,
                                   deferred_commands[i].apply_fog.end,
                                   deferred_commands[i].apply_fog.density,
                                   deferred_commands[i].apply_fog.color);
                break;
            }

            case DEFERRED_COMMAND_TYPE_POP_FOG: {
                deferred_pop_fog();
                break;
            }

            default:
                SDL_assert(false);
        }
    }
}


void clear_draw_buffer(void) {
    /* TODO: we can optimize a rectangle drawn over whole window to a clear color call*/

    DeferredCommand command = {
        .type = DEFERRED_COMMAND_TYPE_CLEAR,
        .clear = (DeferredCommandClear) {
            .clear_color = true,
            .clear_depth = true,
            .clear_stencil = true,
            .color = (Color) { 230, 230, 230, 1 }
        }
    };

    arrpush(deferred_commands, command);
}


void start_render_frame(void) {
    clear_draw_buffer();
}


void end_render_frame(void) {
    if (!ctx.render_double_buffered || ctx.game.frame_number == 1) {
        issue_deferred_draw_commands();
        SDL_GL_SwapWindow(ctx.window);
        arrsetlen(deferred_commands, 0);
        restart_scratch_vertex_arrays();
    } else {
        /* instead of waiting for frame to finish for the swap, we continue */
        /* while issuing new state for the next call, but deferring any fragment emitting calls for later  */
        /* actual swap will happen when next frame is fully finished, introducing a delay */
        SDL_GL_SwapWindow(ctx.window);
        issue_deferred_draw_commands();
        restart_scratch_vertex_arrays();
        glFlush();
        arrsetlen(deferred_commands, 0);
    }
}


void use_space_pipeline(void) {
    DeferredCommand const command = {
        .type = DEFERRED_COMMAND_TYPE_USE_PIPIELINE,
        .use_pipeline = { PIPELINE_SPACE }
    };

    arrpush(deferred_commands, command);
}


static void finally_use_space_pipeline(void) {
    if (pipeline_last_used == PIPELINE_SPACE)
        return;

    static GLuint list = 0;
    if (!list) {
        list = glGenLists(1);

        glNewList(list, GL_COMPILE); {
            glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
            glShadeModel(GL_SMOOTH);

            if (GLAD_GL_ARB_depth_clamp)
                glDisable(GL_DEPTH_CLAMP);

            glEnable(GL_CULL_FACE);
            glDepthRange(0, 1);
            glEnable(GL_TEXTURE_2D);
            glActiveTexture(GL_TEXTURE0);

            /* solid white, no modulation */
            glColor4ub(255, 255, 255, 255);
        } glEndList();
    }

    glCallList(list);

    glMatrixMode(GL_PROJECTION);
    glLoadMatrixf(&camera_projection_matrix.row[0].x);

    glMatrixMode(GL_MODELVIEW);
    glLoadMatrixf(&camera_look_at_matrix.row[0].x);

    texture_mode_last_used = -1;
    pipeline_last_used = PIPELINE_SPACE;
}


void use_2d_pipeline(void) {
    DeferredCommand const command = {
        .type = DEFERRED_COMMAND_TYPE_USE_PIPIELINE,
        .use_pipeline = { PIPELINE_2D }
    };

    arrpush(deferred_commands, command);
}


static void finally_use_2d_pipeline(void) {
    if (pipeline_last_used == PIPELINE_SPACE) {
        glClear(GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
        glFlush();
    }

    if (pipeline_last_used == PIPELINE_2D)
        return;

    static GLuint list = 0;
    if (!list) {
        list = glGenLists(1);

        glNewList(list, GL_COMPILE); {
            glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_FASTEST);
            glShadeModel(GL_FLAT);

            /* removes near/far plane comparison and discard */
            if (GLAD_GL_ARB_depth_clamp)
                glEnable(GL_DEPTH_CLAMP);

            glEnable(GL_TEXTURE_2D);
            glActiveTexture(GL_TEXTURE0);
            glDisable(GL_CULL_FACE);
            glEnable(GL_DEPTH_TEST);
        } glEndList();
    }

    glCallList(list);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, (double)ctx.base_render_width, (double)ctx.base_render_height, 0, 0, 1);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    texture_mode_last_used = -1;
    pipeline_last_used = PIPELINE_2D;
}


void use_texture_mode(TextureMode mode) {
    DeferredCommand const command = {
        .type = DEFERRED_COMMAND_TYPE_USE_TEXTURE_MODE,
        .use_texture_mode = { mode }
    };

    arrpush(deferred_commands, command);
}


static void finally_use_texture_mode(TextureMode mode) {
    if (texture_mode_last_used == mode)
        return;

    static GLuint lists = 0;
    if (!lists) {
        lists = glGenLists(3);

        /* ghostly */
        glNewList(lists + 0, GL_COMPILE); {
            glEnable(GL_BLEND);
            glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
            glDepthFunc(GL_LESS);
            glDepthMask(GL_FALSE);
            glDisable(GL_ALPHA_TEST);
        } glEndList();

        /* seethrough */
        glNewList(lists + 1, GL_COMPILE); {
            glDisable(GL_BLEND);
            glDepthFunc(GL_LESS);
            glDepthMask(GL_TRUE);
            glEnable(GL_ALPHA_TEST);
            glAlphaFunc(GL_EQUAL, 1.0f);
        } glEndList();

        /* opaque */
        glNewList(lists + 2, GL_COMPILE); {
            glDisable(GL_BLEND);
            glDepthFunc(GL_LESS);
            glDepthMask(GL_TRUE);
            glDisable(GL_ALPHA_TEST);
        } glEndList();
    }

    if (mode == TEXTURE_MODE_GHOSTLY) {
        glCallList(lists + 0);
    } else if (mode == TEXTURE_MODE_SEETHROUGH) {
        glCallList(lists + 1);
    } else {
        glCallList(lists + 2);
    }

    texture_mode_last_used = mode;
}


VertexBufferBuilder build_vertex_buffer(VertexBuffer buffer, size_t bytes) {
    SDL_assert(bytes != 0);
    glBindBuffer(GL_ARRAY_BUFFER, buffer);
    glBufferData(GL_ARRAY_BUFFER, bytes, NULL, GL_STREAM_DRAW);
    void *mapping = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
    if (!mapping)
        CRY("build_vertex_buffer", "Error mapping a vertex array buffer");

    return (VertexBufferBuilder) {
        .mapping = mapping,
        .bytes_left = bytes,
    };
}


bool push_to_vertex_buffer_builder(VertexBufferBuilder *builder,
                                   void const *bytes, size_t size) {
    if (builder->bytes_left == 0)
        return false;

    memcpy(builder->mapping, bytes, size);
    builder->bytes_left -= size;

    /* trigger data send */
    if (builder->bytes_left == 0) {
        glUnmapBuffer(GL_ARRAY_BUFFER);
        return false;
    }

    builder->mapping = (void *)((uintptr_t)builder->mapping + size);

    return true;
}


void finally_render_quads(const Primitive2D primitives[],
                          const struct QuadBatch batch,
                          const VertexBuffer buffer)
{
    DeferredCommandDraw command = {0};

    GLsizei off = 0, voff = 0, uvoff = 0, coff = 0;

    if (!batch.constant_colored && batch.textured) {
        off   = offsetof(ElementIndexedQuad, v1);
        voff  = offsetof(ElementIndexedQuad, v0);
        uvoff = offsetof(ElementIndexedQuad, uv0);
        coff  = offsetof(ElementIndexedQuad, c0);
    } else if (batch.constant_colored && batch.textured) {
        off   = offsetof(ElementIndexedQuadWithoutColor, v1);
        voff  = offsetof(ElementIndexedQuadWithoutColor, v0);
        uvoff = offsetof(ElementIndexedQuadWithoutColor, uv0);
    } else if (!batch.constant_colored && !batch.textured) {
        off   = offsetof(ElementIndexedQuadWithoutTexture, v1);
        voff  = offsetof(ElementIndexedQuadWithoutTexture, v0);
        coff  = offsetof(ElementIndexedQuad, c0);
    } else if (batch.constant_colored && !batch.textured) {
        off   = offsetof(ElementIndexedQuadWithoutColorWithoutTexture, v1);
        voff  = offsetof(ElementIndexedQuadWithoutColorWithoutTexture, v0);
    }

    command.vertices = (AttributeArrayPointer) {
        .arity = 2,
        .type = GL_FLOAT,
        .stride = off,
        .offset = voff,
        .buffer = buffer
    };

    if (batch.textured)
        command.texcoords = (AttributeArrayPointer) {
            .arity = 2,
            .type = GL_FLOAT,
            .stride = off,
            .offset = uvoff,
            .buffer = buffer
        };

    if (!batch.constant_colored) {
        command.colors = (AttributeArrayPointer) {
            .arity = 4,
            .type = GL_UNSIGNED_BYTE,
            .stride = off,
            .offset = coff,
            .buffer = buffer
        };
    } else {
        command.constant_colored = true;
        command.color = primitives[0].sprite.color;
    }

    if (batch.textured) {
        command.textured = true;
        command.texture_key = batch.texture_key;
        command.texture_repeat = batch.repeat;
    }

    command.element_buffer = get_quad_element_buffer();
    command.element_count = 6 * (GLsizei)batch.size;
    command.range_end = 6 * (GLsizei)batch.size;

    use_texture_mode(batch.mode);

    DeferredCommand final_command = {
        .type = DEFERRED_COMMAND_TYPE_DRAW,
        .draw = command
    };

    arrpush(deferred_commands, final_command);
}


size_t get_quad_payload_size(struct QuadBatch batch) {
    if (batch.constant_colored && batch.textured)
        return sizeof (ElementIndexedQuadWithoutColor);
    else if (!batch.constant_colored && batch.textured)
        return sizeof (ElementIndexedQuad);
    else if (batch.constant_colored && !batch.textured)
        return sizeof (ElementIndexedQuadWithoutColorWithoutTexture);
    else if (!batch.constant_colored && !batch.textured)
        return sizeof (ElementIndexedQuadWithoutTexture);

    SDL_assert(false);
    return 0;
}


bool push_quad_payload_to_vertex_buffer_builder(struct QuadBatch batch,
                                                VertexBufferBuilder *builder,
                                                Vec2 v0, Vec2 v1, Vec2 v2, Vec2 v3,
                                                Vec2 uv0, Vec2 uv1, Vec2 uv2, Vec2 uv3,
                                                Color color)
{
    if (!batch.constant_colored && batch.textured) {
        ElementIndexedQuad const buffer_element = {
            .v0 = v0,
            .v1 = v1,
            .v2 = v2,
            .v3 = v3,

            .uv0 = uv0,
            .uv1 = uv1,
            .uv2 = uv2,
            .uv3 = uv3,

            /* equal for all (flat shaded) */
            .c0 = color,
            // .c1 = color,
            .c2 = color,
            // .c3 = color,
        };

        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);

    } else if (batch.constant_colored && batch.textured) {
        ElementIndexedQuadWithoutColor const buffer_element = {
            .v0 = v0,
            .v1 = v1,
            .v2 = v2,
            .v3 = v3,

            .uv0 = uv0,
            .uv1 = uv1,
            .uv2 = uv2,
            .uv3 = uv3,
        };

        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);

    } else if (!batch.constant_colored && !batch.textured) {
        ElementIndexedQuadWithoutTexture const buffer_element = {
            .v0 = v0,
            .v1 = v1,
            .v2 = v2,
            .v3 = v3,

            /* equal for all (flat shaded) */
            .c0 = color,
            // .c1 = color,
            .c2 = color,
            // .c3 = color,
        };

        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);

    } else if (batch.constant_colored && !batch.textured) {
        ElementIndexedQuadWithoutColorWithoutTexture const buffer_element = {
            .v0 = v0,
            .v1 = v1,
            .v2 = v2,
            .v3 = v3,
        };

        return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
    }

    SDL_assert(false);
    return false;
}


void finally_draw_uncolored_space_traingle_batch(const MeshBatch *batch,
                                                 const TextureKey texture_key,
                                                 const VertexBuffer buffer)
{
    DeferredCommandDraw command = {0};

    command.vertices = (AttributeArrayPointer) {
        .arity = 3,
        .type = GL_FLOAT,
        .stride = offsetof(struct UncoloredSpaceTrianglePayload, v1),
        .offset = offsetof(struct UncoloredSpaceTrianglePayload, v0),
        .buffer = buffer
    };

    command.texcoords = (AttributeArrayPointer) {
        .arity = 2,
        .type = GL_FLOAT,
        .stride = offsetof(struct UncoloredSpaceTrianglePayload, v1),
        .offset = offsetof(struct UncoloredSpaceTrianglePayload, uv0),
        .buffer = buffer
    };

    command.textured = true;
    command.texture_key = texture_key;

    const GLuint primitives_len = arrlenu(batch->primitives);
    command.primitive_count = 3 * primitives_len;

    DeferredCommand final_command = {
        .type = DEFERRED_COMMAND_TYPE_DRAW,
        .draw = command
    };

    arrpush(deferred_commands, final_command);
}


bool push_text_payload_to_vertex_buffer_builder(FontData const *font_data,
                                                VertexBufferBuilder *builder,
                                                stbtt_aligned_quad quad)
{
    (void)font_data;

    ElementIndexedQuadWithoutColor buffer_element = {
        .v0 = (Vec2){ quad.x0, quad.y0 },
        .v1 = (Vec2){ quad.x1, quad.y0 },
        .v2 = (Vec2){ quad.x1, quad.y1 },
        .v3 = (Vec2){ quad.x0, quad.y1 },

        .uv0 = (Vec2){ quad.s0, quad.t0 },
        .uv1 = (Vec2){ quad.s1, quad.t0 },
        .uv2 = (Vec2){ quad.s1, quad.t1 },
        .uv3 = (Vec2){ quad.s0, quad.t1 },
    };

    return push_to_vertex_buffer_builder(builder, &buffer_element, sizeof buffer_element);
}


void finally_draw_text(FontData const *font_data,
                       size_t len,
                       Color color,
                       VertexBuffer buffer)
{
    DeferredCommandDraw command = {0};

    command.vertices = (AttributeArrayPointer) {
        .arity = 2,
        .type = GL_FLOAT,
        .stride = offsetof(ElementIndexedQuadWithoutColor, v1),
        .offset = offsetof(ElementIndexedQuadWithoutColor, v0),
        .buffer = buffer
    };

    command.texcoords = (AttributeArrayPointer) {
        .arity = 2,
        .type = GL_FLOAT,
        .stride = offsetof(ElementIndexedQuadWithoutColor, v1),
        .offset = offsetof(ElementIndexedQuadWithoutColor, uv0),
        .buffer = buffer
    };

    command.constant_colored = true;
    command.color = color;

    command.gpu_texture = font_data->texture;
    command.uses_gpu_key = true;
    command.textured = true;

    command.element_buffer = get_quad_element_buffer();
    command.element_count = 6 * (GLsizei)len;
    command.range_end = 6 * (GLsizei)len;

    use_texture_mode(TEXTURE_MODE_GHOSTLY);

    DeferredCommand final_command = {
        .type = DEFERRED_COMMAND_TYPE_DRAW,
        .draw = command
    };

    arrpush(deferred_commands, final_command);

    /* TODO: why doesn't it get restored if not placed here? */
    // glDepthMask(GL_TRUE);
}


size_t get_text_payload_size(void) {
    return sizeof (ElementIndexedQuadWithoutColor);
}

static void load_cubemap_side(const char *path, GLenum target) {
    SDL_Surface *surface = textures_load_surface(path);
    /* TODO: sanity check whether all of them have same dimensions? */
    glTexImage2D(target,
                 0,
                 GL_RGBA8,
                 surface->w, surface->h,
                 0,
                 surface->format->BytesPerPixel == 4 ? GL_RGBA : GL_RGB,
                 GL_UNSIGNED_BYTE,
                 surface->pixels);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_CUBE_MAP, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

    SDL_free(surface->pixels);
    SDL_FreeSurface(surface);
}


void render_circle(const CirclePrimitive *circle) {
    static Vec2 vertices[CIRCLE_VERTICES_MAX];
    int num_vertices = MIN((int)circle->radius, CIRCLE_VERTICES_MAX);

    create_circle_geometry(circle->position,
                           circle->radius,
                           num_vertices,
                           vertices);

    VertexBuffer buffer = get_scratch_vertex_array();
    specify_vertex_buffer(buffer, vertices, sizeof (Vec2) * num_vertices);

    DeferredCommandDraw command = {0};

    command.vertices = (AttributeArrayPointer) {
        .arity = 2,
        .type = GL_FLOAT,
        .stride = sizeof (Vec2),
        .offset = 0,
        .buffer = buffer
    };

    command.constant_colored = true;
    command.color = circle->color;

    command.element_buffer = get_circle_element_buffer();
    command.element_count = (num_vertices - 2) * 3;
    command.range_end = (num_vertices - 2) * 3;

    use_texture_mode(circle->color.a == 255 ? TEXTURE_MODE_OPAQUE : TEXTURE_MODE_GHOSTLY);

    DeferredCommand final_command = {
        .type = DEFERRED_COMMAND_TYPE_DRAW,
        .draw = command
    };

    arrpush(deferred_commands, final_command);
}


void finally_render_skybox(char *paths) {
    DeferredCommand command = {
        .type = DEFERRED_COMMAND_TYPE_DRAW_SKYBOX,
        .draw_skybox = (DeferredCommandDrawSkybox){
            .paths = paths
        }
    };

    arrpush(deferred_commands, command);
}


static void deferred_render_skybox(char *paths) {
    static GLuint cubemap = 0;
    static char *paths_cache = NULL;

    bool loading_needed = false;

    /* drop it */
    if (!paths_cache || (SDL_strcmp(paths_cache, paths) != 0)) {
        if (cubemap)
            glDeleteTextures(1, &cubemap);
        glGenTextures(1, &cubemap);
        if (paths_cache)
            SDL_free(paths_cache);
        paths_cache = paths;
        loading_needed = true;
    } else
        SDL_free(paths);

    Matrix4 camera_look_at_matrix_solipsist = camera_look_at_matrix;
    camera_look_at_matrix_solipsist.row[3].x = 0;
    camera_look_at_matrix_solipsist.row[3].y = 0;
    camera_look_at_matrix_solipsist.row[3].z = 0;

    glMatrixMode(GL_MODELVIEW);
    glLoadMatrixf(&camera_look_at_matrix_solipsist.row[0].x);

    glDisable(GL_TEXTURE_2D);
    glEnable(GL_TEXTURE_CUBE_MAP);
    glBindTexture(GL_TEXTURE_CUBE_MAP, cubemap);

    if (loading_needed) {
        /* load all the sides */
        char *expanded = expand_asterisk(paths, "up");
        load_cubemap_side(expanded, GL_TEXTURE_CUBE_MAP_POSITIVE_Y);
        SDL_free(expanded);

        expanded = expand_asterisk(paths, "down");
        load_cubemap_side(expanded, GL_TEXTURE_CUBE_MAP_NEGATIVE_Y);
        SDL_free(expanded);

        expanded = expand_asterisk(paths, "east");
        load_cubemap_side(expanded, GL_TEXTURE_CUBE_MAP_POSITIVE_X);
        SDL_free(expanded);

        expanded = expand_asterisk(paths, "north");
        load_cubemap_side(expanded, GL_TEXTURE_CUBE_MAP_POSITIVE_Z);
        SDL_free(expanded);

        expanded = expand_asterisk(paths, "west");
        load_cubemap_side(expanded, GL_TEXTURE_CUBE_MAP_NEGATIVE_X);
        SDL_free(expanded);

        expanded = expand_asterisk(paths, "south");
        load_cubemap_side(expanded, GL_TEXTURE_CUBE_MAP_NEGATIVE_Z);
        SDL_free(expanded);
    }

    /* TODO: figure out which coordinates to use to not have issues with far z */
    /* TODO: recalculate the list if far z requirement changes */

    static GLuint list = 0;
    if (!list) {
        list = glGenLists(1);

        glNewList(list, GL_COMPILE); {
            /* note: assumes that space pipeline is applied already */
            glDisable(GL_ALPHA_TEST);
            glDepthMask(GL_FALSE);

            /* removes near/far plane comparison and discard */
            if (GLAD_GL_ARB_depth_clamp)
                glEnable(GL_DEPTH_CLAMP);

            glBegin(GL_QUADS); {
                /* up */
                glTexCoord3f(50.f, 50.f, 50.f);
                glVertex3f(50.f, 50.f, 50.f);
                glTexCoord3f(-50.f, 50.f, 50.f);
                glVertex3f(-50.f, 50.f, 50.f);
                glTexCoord3f(-50.f, 50.f, -50.f);
                glVertex3f(-50.f, 50.f, -50.f);
                glTexCoord3f(50.f, 50.f, -50.f);
                glVertex3f(50.f, 50.f, -50.f);

                /* down */
                glTexCoord3f(50.f, -50.f, 50.f);
                glVertex3f(50.f, -50.f, 50.f);
                glTexCoord3f(50.f, -50.f, -50.f);
                glVertex3f(50.f, -50.f, -50.f);
                glTexCoord3f(-50.f, -50.f, -50.f);
                glVertex3f(-50.f, -50.f, -50.f);
                glTexCoord3f(-50.f, -50.f, 50.f);
                glVertex3f(-50.f, -50.f, 50.f);

                /* east */
                glTexCoord3f(50.f, -50.f, 50.f);
                glVertex3f(50.f, -50.f, 50.f);
                glTexCoord3f(50.f, 50.f, 50.f);
                glVertex3f(50.f, 50.f, 50.f);
                glTexCoord3f(50.f, 50.f, -50.f);
                glVertex3f(50.f, 50.f, -50.f);
                glTexCoord3f(50.f, -50.f, -50.f);
                glVertex3f(50.f, -50.f, -50.f);

                /* west */
                glTexCoord3f(-50.f, -50.f, 50.f);
                glVertex3f(-50.f, -50.f, 50.f);
                glTexCoord3f(-50.f, -50.f, -50.f);
                glVertex3f(-50.f, -50.f, -50.f);
                glTexCoord3f(-50.f, 50.f, -50.f);
                glVertex3f(-50.f, 50.f, -50.f);
                glTexCoord3f(-50.f, 50.f, 50.f);
                glVertex3f(-50.f, 50.f, 50.f);

                /* north */
                glTexCoord3f(-50.f, -50.f, 50.f);
                glVertex3f(-50.f, -50.f, 50.f);
                glTexCoord3f(-50.f, 50.f, 50.f);
                glVertex3f(-50.f, 50.f, 50.f);
                glTexCoord3f(50.f, 50.f, 50.f);
                glVertex3f(50.f, 50.f, 50.f);
                glTexCoord3f(50.f, -50.f, 50.f);
                glVertex3f(50.f, -50.f, 50.f);

                /* south */
                glTexCoord3f(-50.f, -50.f, -50.f);
                glVertex3f(-50.f, -50.f, -50.f);
                glTexCoord3f(50.f, -50.f, -50.f);
                glVertex3f(50.f, -50.f, -50.f);
                glTexCoord3f(50.f, 50.f, -50.f);
                glVertex3f(50.f, 50.f, -50.f);
                glTexCoord3f(-50.f, 50.f, -50.f);
                glVertex3f(-50.f, 50.f, -50.f);
            } glEnd();

            if (GLAD_GL_ARB_depth_clamp)
                glDisable(GL_DEPTH_CLAMP);

            glDepthMask(GL_TRUE);
            glDisable(GL_TEXTURE_CUBE_MAP);

        } glEndList();
    }

    glCallList(list);
}


void finally_apply_fog(float start, float end, float density, Color color) {
    DeferredCommand command = {
        .type = DEFERRED_COMMAND_TYPE_APPLY_FOG,
        .apply_fog = (DeferredCommandApplyFog){
            .start = start,
            .end = end,
            .density = density,
            .color = color
        }
    };

    arrpush(deferred_commands, command);
}


static void deferred_apply_fog(float start, float end, float density, Color color) {
    if (density < 0.0f || density > 1.0f)
        log_warn("Invalid fog density given, should be in range [0..1]");

    /* TODO: cache it for constant parameters, which is a common case */

    glEnable(GL_FOG);

    glFogf(GL_FOG_DENSITY, density);
    glFogf(GL_FOG_START, start);
    glFogf(GL_FOG_END, end);

    float color_conv[4];
    color_conv[0] = (float)color.r / UINT8_MAX;
    color_conv[1] = (float)color.g / UINT8_MAX;
    color_conv[2] = (float)color.b / UINT8_MAX;
    color_conv[3] = (float)color.a / UINT8_MAX;

    glFogfv(GL_FOG_COLOR, color_conv);
}


void finally_pop_fog(void) {
    DeferredCommand command = {
        .type = DEFERRED_COMMAND_TYPE_POP_FOG,
    };

    arrpush(deferred_commands, command);
}


static void deferred_pop_fog(void) {
    glDisable(GL_FOG);
}


void set_depth_range(double low, double high) {
    DeferredCommand const command = {
        .type = DEFERRED_COMMAND_TYPE_DEPTH_RANGE,
        .depth_range = {
            .low = low,
            .high = high
        }
    };

    arrpush(deferred_commands, command);
}