package renderer

import "core:slice"
import "core:sort"
import "core:math/linalg"
import "core:fmt"
import "core:log"

RENDER_BACKEND_OPENGL       :: #config(RENDER_BACKEND_OPENGL,       false)
RENDER_BACKEND_VULKAN       :: #config(RENDER_BACKEND_VULKAN,       false)
RENDER_BACKEND_DIRECTX11    :: #config(RENDER_BACKEND_DIRECTX11,    false)
RENDER_BACKEND_METAL        :: #config(RENDER_BACKEND_METAL,        false)

Renderer :: struct {
    viewport: Viewport,
    surface_ptr: rawptr,
    backend: rawptr,

    pipeline: Pipeline,

    active_camera: ^Camera, // NOTE: SS - Hardcoded to 1 active camera. Split-screen is likely not possible due to this. Fix(?).

    fullscreen_vertex_shader, fullscreen_fragment_shader: Shader,
    fullscreen_shader_program: Shader_Program,
    fullscreen_mesh: Mesh,
}

Viewport :: struct {
    x, y, width, height: u16,
}

get_aspect_ratio :: proc(renderer: ^Renderer) -> f32 {
    assert(renderer != nil)

    viewport := &renderer.viewport
    return f32(viewport.width) / f32(viewport.height)
}

Color :: union {
    RGB_Color,
    RGBA_Color,
}

RGB_Color  :: [3]u8
RGBA_Color :: [4]u8

create :: proc(surface_ptr: rawptr) -> (^Renderer, bool) {
    renderer := new(Renderer)
    renderer.surface_ptr = surface_ptr

    when RENDER_BACKEND_OPENGL {
        if !opengl_init(renderer) {
            fmt.printfln("Failed to initialize OpenGL.")
            destroy(renderer)
            return nil, false
        }
    }
    else {
        destroy(renderer)
        
        fmt.printfln("Unhandled backend or no backend selected.")
        return nil, false
    }

    { // Create the fullscreen shaders, material and mesh.
        fs_vertex_shader, fs_vertex_shader_ok := create_shader(renderer, .Vertex, "fs_vertex.glsl")
        assert(fs_vertex_shader_ok)
        
        fs_frag_shader, fs_frag_shader_ok := create_shader(renderer, .Fragment, "fs_frag.glsl")
        assert(fs_frag_shader_ok)
    
        fs_program, fs_program_ok := create_shader_program(renderer, &fs_vertex_shader, &fs_frag_shader)
        assert(fs_program_ok)

        fs_quad_mesh, fs_quad_mesh_created := create_mesh(
            renderer = renderer,
            layout = {
                { "position", 2, size_of(f32), },
            },
            vertices = []f32 {
                -1, -1,
                 1, -1,
                 1,  1,
                -1,  1,
            },
            indices = []u32 {
                0, 1, 2,
                0, 2, 3,
            }
        )
        assert(fs_quad_mesh_created)
        
        renderer.fullscreen_vertex_shader = fs_vertex_shader
        renderer.fullscreen_fragment_shader = fs_frag_shader
        renderer.fullscreen_shader_program = fs_program
        renderer.fullscreen_mesh = fs_quad_mesh
    }
    
    return renderer, true
}

set_viewport :: proc(renderer: ^Renderer, x, y, width, height: u16) {
    log.infof("Setting viewport to %v:%v, %vx%v.", x, y, width, height)

    renderer.viewport = {
        x = x,
        y = y,
        width = width,
        height = height,
    }

    when RENDER_BACKEND_OPENGL {
        opengl_viewport_changed(renderer)
    }
}

@(private="file") set_clear_color :: proc(renderer: ^Renderer, color: Color) {
    when RENDER_BACKEND_OPENGL {
        opengl_set_clear_color(renderer, color)
    }
}

@(private="file") clear_screen :: proc(renderer: ^Renderer, clear_color: bool, clear_depth: bool) {
    when RENDER_BACKEND_OPENGL {
        opengl_clear_screen(renderer, clear_color, clear_depth)
    }
}

render_frame :: proc(renderer: ^Renderer, texture_to_present: ^Texture, clear_color: Color) {
    if renderer.active_camera == nil {
        fmt.printfln("No active camera!")
        return
    }

    view_matrix, _       := get_camera_view_matrix(renderer.active_camera)
    projection_matrix, _ := get_camera_projection_matrix(renderer, renderer.active_camera)

    for i in 0 ..< renderer.pipeline.amount_of_passes {
        execute_pass(renderer, renderer.pipeline.passes[i], view_matrix, projection_matrix)
    }
    
    if texture_to_present != nil { // Present.
        // Bind to the screen.
        bind_render_target(renderer, nil)

        // Disable depth
        apply_depth(renderer, false, false)

        // Clear
        set_clear_color(renderer, clear_color)
        clear_screen(renderer, true, true)
        
        // Create a temporary Material.
        mat := Material {
            shader_program = &renderer.fullscreen_shader_program,
            textures = {
                0 = texture_to_present,
            },
            texture_count = 1,
        }

        // Activate.
        activate_fullscreen_material(renderer, &mat)
        defer deactivate_fullscreen_material(renderer)

        // Draw.
        draw_mesh(&renderer.fullscreen_mesh)
    }
    
    when RENDER_BACKEND_OPENGL {
        opengl_swap_buffers(renderer)
    }
}

execute_pass :: proc(renderer: ^Renderer, pass: ^Pass, view_matrix, projection_matrix: linalg.Matrix4x4f32) {
    // fmt.printfln("Executing pass '%v'.", pass.name)
    
    assert(renderer != nil)
    assert(pass != nil)
    
    switch &t in &pass.type {
        case Scene_Pass: {
            assert(t.output_rt != nil)
            bind_render_target(renderer, t.output_rt)

            should_write_depth := t.output_rt.depth_texture != nil
            should_test_depth  := should_write_depth
            should_clear_depth := should_write_depth

            should_clear_color := true
            set_clear_color(renderer, RGBA_Color { 0, 0, 0, 0 })

            clear_screen(renderer, should_clear_color, should_clear_depth)
            apply_depth(renderer, should_test_depth, should_write_depth)
        
            apply_blend_mode(renderer, t.blend_mode)
        
            sort_draw_commands(renderer, &t)
        
            for &dc in &t.draw_commands { // TODO: SS - Don't think we need the address of the draw-commands.
                model_matrix := linalg.identity(linalg.Matrix4x4f32)
        
                // Translate.
                translation := linalg.matrix4_translate(dc.position)
                
                // Rotate.
                rot_x := linalg.matrix4_rotate(linalg.to_radians(dc.rotation.x), [3]f32 { 1, 0, 0 })
                rot_y := linalg.matrix4_rotate(linalg.to_radians(dc.rotation.y), [3]f32 { 0, 1, 0 })
                rot_z := linalg.matrix4_rotate(linalg.to_radians(dc.rotation.z), [3]f32 { 0, 0, 1 })
                rotation := rot_z * rot_y * rot_x
                
                // Scale.
                scale := linalg.matrix4_scale(dc.scale)
        
                model_matrix *= translation * rotation * scale
        
                activate_material(&dc.material, model_matrix, view_matrix, projection_matrix)
        
                draw_mesh(&dc.mesh)
            }

            // Clear the pass' draw-commands.
            clear(&t.draw_commands)

            // TODO: SS - "Deactivate" the pass?
        }
        case Post_Processing_Pass: {
            // Execute the post-processing nodes.
            for &pp in &t.post_processing_nodes {
                execute_post_processing_node(renderer, &pp, view_matrix, projection_matrix)
            }

            // TODO: SS - "Deactivate" the pass?
        }
    }
}

execute_post_processing_node :: proc(renderer: ^Renderer, node: ^Post_Processing_Node, view_matrix, projection_matrix: linalg.Matrix4x4f32) {
    assert(renderer != nil)
    assert(node != nil)
    assert(node.program != nil)
    assert(node.output != nil)

    assert(node.output != nil)
    bind_render_target(renderer, node.output)

    apply_depth(renderer, false, false)
    clear_screen(renderer, true, false)

    // fmt.printfln("TODO: SS - Execute post-processing node '%v' (VS: '%v', FS: '%v').", "NAME", node.program.vertex_shader.path, node.program.fragment_shader.path)

    t: [MATERIAL_MAX_TEXTURES]^Texture
    t_count := u8(0)
    for input_texture, i in node.input {
        if i > MATERIAL_MAX_TEXTURES {
            break
        }

        set_shader_value(node.program, input_texture, u8(i))
        t[i] = input_texture
        t_count += 1
    }

    mat := Material {
        shader_program = node.program,
        textures = t,
        texture_count = t_count,
    }

    activate_fullscreen_material(renderer, &mat)
    draw_mesh(&renderer.fullscreen_mesh)
}

set_shader_value :: proc {
    set_shader_value_texture,
}

set_shader_value_texture :: proc(program: ^Shader_Program, value: ^Texture, index: u8) {
    assert(program != nil)
    assert(value != nil)

    when RENDER_BACKEND_OPENGL {
        opengl_set_shader_value_texture(program, value, index)
    }
}

destroy :: proc(renderer: ^Renderer) {
    when RENDER_BACKEND_OPENGL {
        opengl_destroy(renderer)
    }
    
    assert(renderer != nil)
    free(renderer)
}

@(private) activate_material :: proc(material: ^Material, model_matrix, view_matrix, projection_matrix: linalg.Matrix4x4f32) {
    assert(material != nil)

    when RENDER_BACKEND_OPENGL {
        opengl_activate_material(material, model_matrix, view_matrix, projection_matrix)
    }
}

@(private) draw_mesh :: proc(mesh: ^Mesh) {
    assert(mesh != nil)

    when RENDER_BACKEND_OPENGL {
        opengl_draw_mesh(mesh)
    }
}

@(private) apply_depth :: proc(renderer: ^Renderer, test_depth, write_depth: bool) {
    when RENDER_BACKEND_OPENGL {
        opengl_apply_depth(renderer, test_depth, write_depth)
    }
}

@(private) apply_blend_mode :: proc(renderer: ^Renderer, blend_mode: Blend_Mode) {
    table := BLEND_FACTOR_TABLE

    when RENDER_BACKEND_OPENGL {
        opengl_set_blending(renderer, blend_mode != .None, table[blend_mode])
    }
}

@(private) sort_draw_commands :: proc(renderer: ^Renderer, pass: ^Scene_Pass) {
    switch pass.sort_mode {
        case .None: {}
        case .Back_To_Front: {
            slice.sort_by(
                pass.draw_commands[:],
                proc(i, j: Draw_Command) -> bool {
                    assert(i.renderer != nil)
                    assert(j.renderer != nil)
                    assert(i.renderer == j.renderer)

                    active_camera := get_active_camera(i.renderer)
                    if active_camera == nil {
                        return false
                    }

                    i_dist := distance_to_camera(active_camera, i.position)
                    j_dist := distance_to_camera(active_camera, j.position)
                    
                    return i_dist > j_dist
                }
            )
        }
        case .Front_To_Back: {
            slice.sort_by(
                pass.draw_commands[:],
                proc(i, j: Draw_Command) -> bool {
                    assert(i.renderer != nil)
                    assert(j.renderer != nil)
                    assert(i.renderer == j.renderer)
                    
                    active_camera := get_active_camera(i.renderer)
                    if active_camera == nil {
                        return false
                    }

                    i_dist := distance_to_camera(active_camera, i.position)
                    j_dist := distance_to_camera(active_camera, j.position)
                    
                    return i_dist < j_dist
                }
            )
        }
    }
}

distance_to_camera :: proc(camera: ^Camera, position: [3]f32) -> f32 {
    assert(camera != nil)
    return linalg.distance(camera.position, position)
}

@(private) bind_render_target :: proc(renderer: ^Renderer, rt: ^Render_Target) {
    when RENDER_BACKEND_OPENGL {
        opengl_bind_render_target(renderer, rt)
    }
}


@(private) activate_fullscreen_material :: proc(renderer: ^Renderer, material: ^Material) { // TODO: SS - Maybe remove.
    assert(renderer != nil)
    when RENDER_BACKEND_OPENGL {
        opengl_activate_fullscreen_material(material)
    }
}

@(private) deactivate_fullscreen_material :: proc(renderer: ^Renderer) { // TODO: SS - Maybe remove.
    assert(renderer != nil)
    when RENDER_BACKEND_OPENGL {
        opengl_deactivate_fullscreen_material()
    }
}