#include "private/rendering.h"
#include "context.h"
#include "textures.h"

#include <SDL2/SDL.h>
#include <stb_ds.h>

#include <stdlib.h>
#include <tgmath.h>


void render_queue_clear(void) {
    /* since i don't intend to free the queues, */
    /* it's faster and simpler to just "start over" */
    /* and start overwriting the existing data */
    arrsetlen(ctx.render_queue_sprites, 0);
    arrsetlen(ctx.render_queue_rectangles, 0);
    arrsetlen(ctx.render_queue_circles, 0);
}


/*
 * an implementation note:
 * try to avoid doing expensive work in the push functions,
 * because they will be called multiple times in the main loop
 * before anything is really rendered
 */

/* sprite */
void push_sprite(char *path, t_frect rect) {
    textures_load(&ctx.texture_cache, path);

    struct sprite_primitive sprite = {
        .rect = rect,
        .color = (t_color) { 255, 255, 255, 255 },
        .path = path,
        .rotation = 0.0,
        .blend_mode = SDL_BLENDMODE_BLEND,
        .atlas_index =
            textures_get_atlas_index(&ctx.texture_cache, path),
        .layer = 0,
        .flip_x = false,
        .flip_y = false,
    };

    arrput(ctx.render_queue_sprites, sprite);
}


void push_sprite_ex(t_frect rect, t_push_sprite_args args) {
    textures_load(&ctx.texture_cache, args.path);

    struct sprite_primitive sprite = {
        .rect = rect,
        .color = args.color,
        .path = args.path,
        .rotation = args.rotation,
        .blend_mode = args.blend_mode,
        .atlas_index = 
            textures_get_atlas_index(&ctx.texture_cache, args.path),
        .layer = args.layer,
        .flip_x = args.flip_x,
        .flip_y = args.flip_y,
    };

    arrput(ctx.render_queue_sprites, sprite);
}


/* rectangle */
void push_rectangle(t_frect rect, t_color color) {
    struct rect_primitive rectangle = {
        .rect = rect,
        .color = color,
    };

    arrput(ctx.render_queue_rectangles, rectangle);
}


/* circle */
void push_circle(t_fvec2 position, float radius, t_color color) {
    struct circle_primitive circle = {
        .radius = radius,
        .color = color,
        .position = position,
    };

    arrput(ctx.render_queue_circles, circle);
}


/* rendering */
static void render_background(void) {
    SDL_SetRenderDrawColor(ctx.renderer, 230, 230, 230, 255);
    SDL_Rect rect = {
        0,
        0,
        ctx.window_w,
        ctx.window_h
    };
    SDL_RenderFillRect(ctx.renderer, &rect);

    SDL_SetRenderDrawColor(ctx.renderer, 255, 255, 255, 255);
}


/* compare functions for the sort in render_sprites */
static int cmp_atlases(const void *a, const void *b) {
    int index_a = ((const struct sprite_primitive *)a)->atlas_index;
    int index_b = ((const struct sprite_primitive *)b)->atlas_index;

    return (index_a > index_b) - (index_a < index_b);
}


static int cmp_blend_modes(const void *a, const void *b) {
    SDL_BlendMode mode_a = ((const struct sprite_primitive *)a)->blend_mode;
    SDL_BlendMode mode_b = ((const struct sprite_primitive *)b)->blend_mode;

    return (mode_a > mode_b) - (mode_a < mode_b);
}


static int cmp_colors(const void *a, const void *b) {
    t_color color_a = ((const struct sprite_primitive *)a)->color;
    t_color color_b = ((const struct sprite_primitive *)b)->color;

    /* check reds */
    if (color_a.r < color_b.r)
        return -1;
    else if (color_a.r > color_b.r)
        return 1;

    /* reds were equal, check greens */
    else if (color_a.g < color_b.g)
        return -1;
    else if (color_a.g > color_b.g)
        return 1;

    /* greens were equal, check blues */
    else if (color_a.b < color_b.b)
        return -1;
    else if (color_a.b > color_b.b)
        return 1;

    /* blues were equal, check alphas */
    else if (color_a.a < color_b.a)
        return -1;
    else if (color_a.a > color_b.a)
        return 1;

    /* entirely equal */
    else
        return 0;
}


static int cmp_layers(const void *a, const void *b) {
    int layer_a = ((const struct sprite_primitive *)a)->layer;
    int layer_b = ((const struct sprite_primitive *)b)->layer;

    return (layer_a > layer_b) - (layer_a < layer_b);
}


/* necessary to allow the renderer to draw in batches in the best case */
static void sort_sprites(struct sprite_primitive *sprites) {
    size_t sprites_len = arrlenu(sprites);
    qsort(sprites, sprites_len, sizeof *sprites, cmp_atlases);
    qsort(sprites, sprites_len, sizeof *sprites, cmp_blend_modes);
    qsort(sprites, sprites_len, sizeof *sprites, cmp_colors);
    qsort(sprites, sprites_len, sizeof *sprites, cmp_layers);
}


static void render_sprite(struct sprite_primitive *sprite) {
    SDL_Rect srcrect_value = { 0 };
    SDL_Rect *srcrect = &srcrect_value;
    SDL_Texture *texture = NULL;

    /* loner */
    if (sprite->atlas_index == -1) {
        srcrect = NULL;
        texture = textures_get_loner(&ctx.texture_cache, sprite->path);
    } else {
        *srcrect = textures_get_srcrect(&ctx.texture_cache, sprite->path);
        texture = textures_get_atlas(&ctx.texture_cache, sprite->atlas_index);
    }

    SDL_RendererFlip flip = SDL_FLIP_NONE;
    if (sprite->flip_x)
        flip |= SDL_FLIP_HORIZONTAL;
    if (sprite->flip_y)
        flip |= SDL_FLIP_VERTICAL;

    SDL_SetTextureColorMod(texture,
                           sprite->color.r,
                           sprite->color.g,
                           sprite->color.b);
    SDL_SetTextureAlphaMod(texture, sprite->color.a);
    SDL_SetTextureBlendMode(texture, sprite->blend_mode);

    SDL_Rect rect = {
        (int)sprite->rect.x,
        (int)sprite->rect.y,
        (int)sprite->rect.w,
        (int)sprite->rect.h
    };

    SDL_RenderCopyEx(ctx.renderer,
                     texture,
                     srcrect,
                     &rect,
                     sprite->rotation,
                     NULL,
                     flip);
}


static void render_rectangle(struct rect_primitive *rectangle) {
    SDL_SetRenderDrawColor(ctx.renderer,
                           rectangle->color.r,
                           rectangle->color.g,
                           rectangle->color.b,
                           rectangle->color.a);

    SDL_Rect rect = {
        (int)rectangle->rect.x,
        (int)rectangle->rect.y,
        (int)rectangle->rect.w,
        (int)rectangle->rect.h
    };

    SDL_RenderFillRect(ctx.renderer, &rect);
    SDL_SetRenderDrawColor(ctx.renderer, 255, 255, 255, 255);
}


/* vertices_out and indices_out MUST BE FREED */
static void create_circle_geometry(t_fvec2 position,
                                   t_color color,
                                   float radius,
                                   size_t num_vertices,
                                   SDL_Vertex **vertices_out,
                                   int **indices_out)
{
    SDL_Vertex *vertices = cmalloc(sizeof *vertices * (num_vertices + 1));
    int *indices = cmalloc(sizeof *indices * (num_vertices * 3));

    /* the angle (in radians) to rotate by on each iteration */
    float seg_rotation_angle = (360.0f / (float)num_vertices) * ((float)M_PI / 180);
    
    vertices[0].position.x = (float)position.x;
    vertices[0].position.y = (float)position.y;
    vertices[0].color.r = color.r;
    vertices[0].color.g = color.g;
    vertices[0].color.b = color.b;
    vertices[0].color.a = color.a;
    vertices[0].tex_coord = (SDL_FPoint){ 0, 0 };

    /* this point will rotate around the center */
    float start_x = 0.0f - radius;
    float start_y = 0.0f;

    for (size_t i = 1; i < num_vertices + 1; ++i) {
        float final_seg_rotation_angle = (float)i * seg_rotation_angle;

        vertices[i].position.x =
            cos(final_seg_rotation_angle) * start_x -
            sin(final_seg_rotation_angle) * start_y;
        vertices[i].position.y =
            cos(final_seg_rotation_angle) * start_y +
            sin(final_seg_rotation_angle) * start_x;

        vertices[i].position.x += position.x;
        vertices[i].position.y += position.y;

        vertices[i].color.r = color.r;
        vertices[i].color.g = color.g;
        vertices[i].color.b = color.b;
        vertices[i].color.a = color.a;

        vertices[i].tex_coord = (SDL_FPoint){ 0, 0 };


        size_t triangle_offset = 3 * (i - 1);

        /* center point index */
        indices[triangle_offset] = 0;
        /* generated point index */
        indices[triangle_offset + 1] = (int)i;

        size_t index = (i + 1) % num_vertices;
        if (index == 0)
            index = num_vertices;
        indices[triangle_offset + 2] = (int)index;
    }

    *vertices_out = vertices;
    *indices_out = indices;
}


static void render_circle(struct circle_primitive *circle) {
    SDL_Vertex *vertices = NULL;
    int *indices = NULL;
    int num_vertices = (int)circle->radius;

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

    SDL_RenderGeometry(ctx.renderer, NULL,
                       vertices,
                       num_vertices + 1, /* vertices + center vertex */
                       indices,
                       num_vertices * 3);

    free(vertices);
    free(indices);
}


static void render_sprites(void) {
    if (ctx.texture_cache.is_dirty)
        textures_update_current_atlas(&ctx.texture_cache);

    sort_sprites(ctx.render_queue_sprites);

    for (size_t i = 0; i < arrlenu(ctx.render_queue_sprites); ++i) {
        render_sprite(&ctx.render_queue_sprites[i]);
    }
}


static void render_rectangles(void) {
    for (size_t i = 0; i < arrlenu(ctx.render_queue_rectangles); ++i) {
        render_rectangle(&ctx.render_queue_rectangles[i]);
    }
}


static void render_circles(void) {
    for (size_t i = 0; i < arrlenu(ctx.render_queue_circles); ++i) {
        render_circle(&ctx.render_queue_circles[i]);
    }
}


void render(void) {
    SDL_SetRenderDrawBlendMode(ctx.renderer, SDL_BLENDMODE_BLEND);
    SDL_SetRenderDrawColor(ctx.renderer, 0, 0, 0, 255);
    SDL_RenderClear(ctx.renderer);
    SDL_SetRenderDrawColor(ctx.renderer, 255, 255, 255, 255);

    render_background();
    render_sprites();
    render_rectangles();
    render_circles();

    SDL_RenderPresent(ctx.renderer);
}