GLOBAL struct {
    G_Resource *solid_white_texture;
} G = ZI, DEBUG_ALIAS(G, G_draw);

/* ========================== *
 * Startup
 * ========================== */

D_StartupReceipt draw_startup(F_StartupReceipt *font_sr)
{
    __prof;
    (UNUSED)font_sr;
    u32 pixel_white = 0xFFFFFFFF;
    G.solid_white_texture = gp_texture_alloc(GP_TEXTURE_FORMAT_R8G8B8A8_UNORM, 0, V2i32FromXY(1, 1), &pixel_white);
    return (D_StartupReceipt) { 0 };
}

/* ========================== *
 * Material
 * ========================== */

void draw_material(G_RenderSig *sig, D_MaterialParams params)
{
    G_RenderCmdDesc cmd = ZI;
    cmd.kind = GP_RENDER_CMD_KIND_DRAW_MATERIAL;
    cmd.material.xf = params.xf;
    cmd.material.texture = params.texture;
    cmd.material.clip = params.clip;
    cmd.material.tint = params.tint;
    cmd.material.is_light = params.is_light;
    cmd.material.light_emittance = params.light_emittance;
    gp_push_render_cmd(sig, &cmd);
}

/* ========================== *
 * Fill shapes
 * ========================== */

void draw_poly_ex(G_RenderSig *sig, V2Array vertices, G_Indices indices, u32 color)
{
    G_RenderCmdDesc cmd = ZI;
    cmd.kind = GP_RENDER_CMD_KIND_DRAW_UI_SHAPE;
    cmd.ui_shape.vertices = vertices;
    cmd.ui_shape.indices = indices;
    cmd.ui_shape.color = color;
    gp_push_render_cmd(sig, &cmd);
}

/* Draws a filled polygon using triangles in a fan pattern */
void draw_poly(G_RenderSig *sig, V2Array vertices, u32 color)
{
    if (vertices.count >= 3) {
        TempArena scratch = BeginScratchNoConflict();

        u32 num_tris = vertices.count - 2;
        u32 num_indices = num_tris * 3;

        /* Generate indices in a fan pattern */
        G_Indices indices = {
            .count = num_indices,
            .indices = PushArrayNoZero(scratch.arena, u32, num_indices)
        };
        for (u32 i = 0; i < num_tris; ++i) {
            u32 tri_offset = i * 3;
            indices.indices[tri_offset + 0] = 0;
            indices.indices[tri_offset + 1] = (i + 1);
            indices.indices[tri_offset + 2] = (i + 2);
        }

        draw_poly_ex(sig, vertices, indices, color);

        EndScratch(scratch);
    }
}

void draw_circle(G_RenderSig *sig, V2 pos, f32 radius, u32 color, u32 detail)
{
    TempArena scratch = BeginScratchNoConflict();

    V2 *points = PushArrayNoZero(scratch.arena, V2, detail);
    for (u32 i = 0; i < detail; ++i) {
        f32 angle = ((f32)i / (f32)detail) * TAU;
        V2 p = V2FromXY(
            radius * math_cos(angle),
            radius * math_sin(angle)
        );
        points[i] = v2_add(pos, p);
    }

    V2Array vertices = {
        .points = points,
        .count = detail
    };
    draw_poly(sig, vertices, color);

    EndScratch(scratch);
}

void draw_quad(G_RenderSig *sig, Quad quad, u32 color)
{
    LOCAL_PERSIST u32 indices_array[6] = {
        0, 1, 2,
        0, 2, 3
    };
    V2Array vertices = { .count = 4, .points = quad.e };
    G_Indices indices = { .count = 6, .indices = indices_array };
    draw_poly_ex(sig, vertices, indices, color);
}

/* ========================== *
 * Line shapes
 * ========================== */

void draw_gradient_line(G_RenderSig *sig, V2 start, V2 end, f32 thickness, u32 start_color, u32 end_color)
{
#if 0
    Quad quad = quad_from_line(start, end, thickness);
    draw_material(sig, DRAW_MATERIAL_PARAMS(.texture = G.solid_white_texture, .tint0 = start_color, .tint1 = end_color, .quad = quad));
#else
    /* Placeholder */
    (UNUSED)end_color;
    Quad quad = quad_from_line(start, end, thickness);
    draw_quad(sig, quad, start_color);
#endif
}

void draw_line(G_RenderSig *sig, V2 start, V2 end, f32 thickness, u32 color)
{
    Quad quad = quad_from_line(start, end, thickness);
    draw_quad(sig, quad, color);
}

void draw_ray(G_RenderSig *sig, V2 pos, V2 rel, f32 thickness, u32 color)
{
    Quad quad = quad_from_ray(pos, rel, thickness);
    draw_quad(sig, quad, color);
}

void draw_poly_line(G_RenderSig *sig, V2Array points, b32 loop, f32 thickness, u32 color)
{
    if (points.count >= 2) {
        for (u64 i = 1; i < points.count; ++i) {
            V2 p1 = points.points[i - 1];
            V2 p2 = points.points[i];
            Quad q = quad_from_line(p1, p2, thickness);
            draw_quad(sig, q, color);
        }
        if (loop && points.count > 2) {
            V2 p1 = points.points[points.count - 1];
            V2 p2 = points.points[0];
            Quad q = quad_from_line(p1, p2, thickness);
            draw_quad(sig, q, color);
        }
    }
}

void draw_circle_line(G_RenderSig *sig, V2 pos, f32 radius, f32 thickness, u32 color, u32 detail)
{
    TempArena scratch = BeginScratchNoConflict();

    V2 *points = PushArrayNoZero(scratch.arena, V2, detail);
    for (u32 i = 0; i < detail; ++i) {
        f32 angle = ((f32)i / (f32)detail) * TAU;
        V2 p = V2FromXY(
            radius * math_cos(angle),
            radius * math_sin(angle)
        );
        points[i] = v2_add(pos, p);
    }

    V2Array a = {
        .points = points,
        .count = detail
    };
    draw_poly_line(sig, a, 1, thickness, color);

    EndScratch(scratch);
}

void draw_quad_line(G_RenderSig *sig, Quad quad, f32 thickness, u32 color)
{
    V2 points[] = { quad.p0, quad.p1, quad.p2, quad.p3 };
    V2Array a = { .points = points, .count = countof(points) };
    draw_poly_line(sig, a, 1, thickness, color);
}

void draw_arrow_line(G_RenderSig *sig, V2 start, V2 end, f32 thickness, f32 arrowhead_height, u32 color)
{
    const f32 head_width_ratio = 0.5f;  /* Width of arrowhead relative to its length */

    const f32 max_height_to_line_ratio = 0.9f;  /* Maximum length of arrowhead relative to total line length */
    arrowhead_height = min_f32(arrowhead_height, v2_len(v2_sub(end, start)) * max_height_to_line_ratio);

    V2 head_start_dir = v2_sub(start, end);
    head_start_dir = v2_norm(head_start_dir);
    head_start_dir = v2_mul(head_start_dir, arrowhead_height);

    V2 head_start = v2_add(end, head_start_dir);

    V2 head_p1_dir = v2_perp_mul(head_start_dir, head_width_ratio);
    V2 head_p2_dir = v2_neg(head_p1_dir);

    V2 head_p1 = v2_add(head_start, head_p1_dir);
    V2 head_p2 = v2_add(head_start, head_p2_dir);

    V2 head_points[] = { end, head_p1, head_p2 };
    V2Array head_points_v2_array = {
        .points = head_points,
        .count = countof(head_points)
    };
    draw_poly(sig, head_points_v2_array, color);

    Quad line_quad = quad_from_line(start, head_start, thickness);
    draw_quad(sig, line_quad, color);
}

void draw_arrow_ray(G_RenderSig *sig, V2 pos, V2 rel, f32 thickness, f32 arrowhead_height, u32 color)
{
    V2 end = v2_add(pos, rel);
    draw_arrow_line(sig, pos, end, thickness, arrowhead_height, color);
}

void draw_collider_line(G_RenderSig *sig, CLD_Shape shape, Xform shape_xf, f32 thickness, u32 color, u32 detail)
{
    TempArena scratch = BeginScratchNoConflict();
    V2Array poly = ZI;
    if (shape.radius == 0) {
        poly.count = shape.count;
        poly.points = PushArrayNoZero(scratch.arena, V2, shape.count);
        for (u32 i = 0; i < shape.count; ++i) {
            V2 p = xform_mul_v2(shape_xf, shape.points[i]);
            poly.points[i] = p;
        }
    } else {
        poly.count = detail;
        poly.points = PushArrayNoZero(scratch.arena, V2, detail);
        for (u32 i = 0; i < detail; ++i) {
            f32 angle = ((f32)i / (f32)detail) * TAU;
            V2 dir = V2FromXY(math_cos(angle), math_sin(angle));
            V2 p = collider_get_support_point(&shape, shape_xf, dir).p;
            poly.points[i] = p;
        }
    }
    draw_poly_line(sig, poly, 1, thickness, color);
    EndScratch(scratch);
}

/* ========================== *
 * Grid
 * ========================== */

void draw_grid(G_RenderSig *sig, Xform xf, u32 bg0_color, u32 bg1_color, u32 line_color, u32 x_color, u32 y_color, f32 thickness, f32 spacing, V2 offset)
{
    i32 grid_id = 0;
    {
        G_RenderCmdDesc cmd = ZI;
        cmd.kind = GP_RENDER_CMD_KIND_PUSH_GRID;
        cmd.grid.bg0_color = bg0_color;
        cmd.grid.bg1_color = bg1_color;
        cmd.grid.line_color = line_color;
        cmd.grid.x_color = x_color;
        cmd.grid.y_color = y_color;
        cmd.grid.line_thickness = thickness;
        cmd.grid.line_spacing = spacing;
        cmd.grid.offset = offset;
        grid_id = gp_push_render_cmd(sig, &cmd);
    }

    G_RenderCmdDesc cmd = ZI;
    cmd.kind = GP_RENDER_CMD_KIND_DRAW_MATERIAL;
    cmd.material.xf = xf;
    cmd.material.tint = COLOR_WHITE;
    cmd.material.grid_cmd_id = grid_id;
    gp_push_render_cmd(sig, &cmd);
}

/* ========================== *
 * UI
 * ========================== */

void draw_ui_rect(G_RenderSig *sig, D_UiRectParams params)
{
    G_RenderCmdDesc cmd = ZI;
    cmd.kind = GP_RENDER_CMD_KIND_DRAW_UI_RECT;
    cmd.ui_rect.xf = params.xf;
    cmd.ui_rect.texture = params.texture;
    cmd.ui_rect.clip = params.clip;
    cmd.ui_rect.tint = params.tint;
    gp_push_render_cmd(sig, &cmd);
}

/* ========================== *
 * Text
 * ========================== */

 /* Returns the rect of the text area */
Rect draw_text(G_RenderSig *sig, D_TextParams params)
{
    TempArena scratch = BeginScratchNoConflict();

    f32 inv_font_image_width = 1.0 / (f32)params.font->image_width;
    f32 inv_font_image_height = 1.0 / (f32)params.font->image_height;
    f32 line_spacing = params.font->point_size * 1.5f * params.scale;

    /* ========================== *
     * Build line glyphs
     * ========================== */

    struct drawable_glyph {
        f32 off_x;
        f32 off_y;
        f32 width;
        f32 height;
        f32 advance;
        ClipRect clip;
    };

    struct drawable_line {
        f32 line_width;
        u32 num_glyphs;
        struct drawable_glyph *glyphs;
        struct drawable_line *next;
    };

    u64 num_lines = 0;
    f32 widest_line = 0;

    struct drawable_line *first_line = 0;
    struct drawable_line *last_line = 0;
    f32 first_line_top_offset = 0;
    f32 last_line_bottom_offset = 0;

    if (params.str.len > 0) {
        b32 string_done = 0;
        struct string_codepoint_iter iter = string_codepoint_iter_begin(params.str);
        while (!string_done) {
            f32 line_width = 0;
            f32 top_offset = 0;
            f32 bottom_offset = 0;
            u64 num_line_glyphs = 0;
            struct drawable_glyph *line_glyphs = PushDry(scratch.arena, struct drawable_glyph);

            b32 line_done = 0;
            while (!line_done) {
                string_done = !string_codepoint_iter_next(&iter);
                if (string_done) {
                    line_done = 1;
                } else {
                    u32 codepoint = iter.codepoint;
                    if (codepoint == '\n') {
                        line_done = 1;
                    } else {
                        struct drawable_glyph *tg = PushStruct(scratch.arena, struct drawable_glyph);
                        ++num_line_glyphs;
                        F_Glyph *glyph = font_get_glyph(params.font, codepoint);
                        tg->off_x = glyph->off_x * params.scale;
                        tg->off_y = glyph->off_y * params.scale;
                        tg->width = glyph->width * params.scale;
                        tg->height = glyph->height * params.scale;
                        tg->advance = glyph->advance * params.scale;
                        Rect glyph_atlas_rect = glyph->atlas_rect;
                        tg->clip = (ClipRect) {
                            {
                                glyph_atlas_rect.x * inv_font_image_width,
                                glyph_atlas_rect.y * inv_font_image_height
                            },
                            {
                                (glyph_atlas_rect.x + glyph_atlas_rect.width) * inv_font_image_width,
                                (glyph_atlas_rect.y + glyph_atlas_rect.height) * inv_font_image_height
                            }
                        };
                        line_width += tg->advance;
                        top_offset = min_f32(top_offset, tg->off_y);
                        bottom_offset = max_f32(bottom_offset, tg->off_y + tg->height);
                    }
                }
            }

            /* Line ended */
            /* TODO: Only create nodes for non-empty lines. Embed line number in the node. */
            struct drawable_line *node = PushStruct(scratch.arena, struct drawable_line);
            node->line_width = line_width;
            node->num_glyphs = num_line_glyphs;
            node->glyphs = line_glyphs;
            if (last_line) {
                last_line->next = node;
            } else {
                first_line = node;
                first_line_top_offset = top_offset;
            }
            last_line = node;
            last_line_bottom_offset = bottom_offset;
            widest_line = max_f32(widest_line, line_width);
            ++num_lines;
        }
        string_codepoint_iter_end(&iter);
    }

    /* ========================== *
     * Determine text bounds
     * ========================== */

    Rect bounds = ZI;
    bounds.x = params.pos.x;
    bounds.y = params.pos.y;
    bounds.width = widest_line;
    bounds.height = num_lines * line_spacing + first_line_top_offset + last_line_bottom_offset;

    /* Offset bounds X */
    switch (params.offset_x) {
        case DRAW_TEXT_OFFSET_X_LEFT: break;
        case DRAW_TEXT_OFFSET_X_CENTER:
        {
            bounds.x -= bounds.width / 2.f;
        } break;
        case DRAW_TEXT_OFFSET_X_RIGHT:
        {
            bounds.x -= bounds.width;
        } break;
    }

    /* Offset bounds Y */
    switch (params.offset_y) {
        case DRAW_TEXT_OFFSET_Y_TOP: break;
        case DRAW_TEXT_OFFSET_Y_CENTER:
        {
            bounds.y -= bounds.height / 2.f;
        } break;
        case DRAW_TEXT_OFFSET_Y_BOTTOM:
        {
            if (last_line) {
                bounds.y -= bounds.height + last_line_bottom_offset;
            }
        } break;
    }

    /* ========================== *
     * Draw lines
     * ========================== */

    u64 line_number = 0;
    for (struct drawable_line *line = first_line; line; line = line->next) {
        V2 draw_pos = bounds.pos;
        draw_pos.y += line_number * line_spacing - first_line_top_offset;

        /* Alignment */
        switch (params.alignment) {
            case DRAW_TEXT_ALIGNMENT_LEFT: break;
            case DRAW_TEXT_ALIGNMENT_CENTER:
            {
                draw_pos.x += (bounds.width - line->line_width) / 2.f;
            } break;
            case DRAW_TEXT_ALIGNMENT_RIGHT:
            {
                draw_pos.x += bounds.width - line->line_width;
            } break;
        }

        /* Draw glyphs */
        for (u64 i = 0; i < line->num_glyphs; ++i) {
            struct drawable_glyph *tg = &line->glyphs[i];
            V2 pos = V2FromXY(draw_pos.x + tg->off_x, draw_pos.y + tg->off_y);
            V2 size = V2FromXY(tg->width, tg->height);
            Xform xf = xform_from_rect(RECT_FROM_V2(pos, size));
            draw_ui_rect(sig, DRAW_UI_RECT_PARAMS(.xf = xf, .texture = params.font->texture, .tint = params.color, .clip = tg->clip));
            draw_pos.x += tg->advance;

        }
        ++line_number;
    }

    EndScratch(scratch);
    return bounds;
}