#+private
package renderer

import "core:strings"
import "core:fmt"
import gl "vendor:OpenGL"
import win "core:sys/windows"


when RENDER_BACKEND_OPENGL {
    Backend_OpenGL_Windows :: struct {
        hwnd: win.HWND,
        hdc: win.HDC,
        gl_context: win.HGLRC,
    }

    backend: Backend_OpenGL_Windows

    OPENGL_MAJOR :: 3
    OPENGL_MINOR :: 3
    
    opengl_init :: proc(renderer: ^Renderer) -> bool {
        renderer.backend = &backend

        backend.hwnd = win.HWND(renderer.surface_ptr)
        backend.hdc = win.GetDC(backend.hwnd)

        pfd := win.PIXELFORMATDESCRIPTOR {
            nSize = size_of(win.PIXELFORMATDESCRIPTOR),
            nVersion = 1,
            dwFlags = win.PFD_DRAW_TO_WINDOW | win.PFD_SUPPORT_OPENGL | win.PFD_DOUBLEBUFFER,
            iPixelType = win.PFD_TYPE_RGBA,
            cColorBits = 32,
            cDepthBits = 24,
            cStencilBits = 8,
            iLayerType = win.PFD_MAIN_PLANE,
        }

        format_index := win.ChoosePixelFormat(backend.hdc, &pfd)
        assert(format_index != 0, "ChoosePixelFormat failed")

        set_pixel_format_ok := win.SetPixelFormat(backend.hdc, format_index, &pfd)
        assert(set_pixel_format_ok == win.TRUE, "SetPixelFormat failed")

        temp_context := win.wglCreateContext(backend.hdc)
        assert(temp_context != nil, "Failed to create temp OpenGL context")
        win.wglMakeCurrent(backend.hdc, temp_context)

        win.wglCreateContextAttribsARB = transmute(win.CreateContextAttribsARBType)win.wglGetProcAddress("wglCreateContextAttribsARB")
        assert(win.wglCreateContextAttribsARB != nil, "wglCreateContextAttribsARB not available")

        attribs := [?]i32 {
            win.WGL_CONTEXT_MAJOR_VERSION_ARB, OPENGL_MAJOR,
            win.WGL_CONTEXT_MINOR_VERSION_ARB, OPENGL_MINOR,
            win.WGL_CONTEXT_PROFILE_MASK_ARB,
            win.WGL_CONTEXT_CORE_PROFILE_BIT_ARB,
            0
        }

        backend.gl_context = win.wglCreateContextAttribsARB(backend.hdc, nil, raw_data(&attribs))
        assert(backend.gl_context != nil, fmt.tprintf("Failed to create OpenGL %v.%v core context", OPENGL_MAJOR, OPENGL_MINOR))

        win.wglMakeCurrent(nil, nil)
        win.wglDeleteContext(temp_context)

        win.wglMakeCurrent(backend.hdc, backend.gl_context)

        gl.load_up_to(3, 3, proc(p: rawptr, name: cstring) {
            addr := win.wglGetProcAddress(name)
            if addr == nil {
                dll := win.LoadLibraryW(win.utf8_to_wstring("opengl32.dll"))
                addr = win.GetProcAddress(dll, name)
            }
            (^rawptr)(p)^ = addr
        })

        opengl_swap_buffers(renderer)
        return true
    }


    opengl_viewport_changed :: proc(renderer: ^Renderer) {
        opengl_clear_screen(renderer)

        gl.Viewport(
            i32(renderer.viewport.x),
            i32(renderer.viewport.y),
            i32(renderer.viewport.width),
            i32(renderer.viewport.height)
        )
    }

    opengl_set_clear_color :: proc(renderer: ^Renderer, color: RGB_Color) {
        gl.ClearColor(
            f32(color.r) / f32(max(u8)),
            f32(color.g) / f32(max(u8)),
            f32(color.b) / f32(max(u8)),
            1.0
        )
    }
    
    opengl_clear_screen :: proc(renderer: ^Renderer) {
        gl.Clear(gl.COLOR_BUFFER_BIT)
    }

    opengl_swap_buffers :: proc(renderer: ^Renderer) {
        win.SwapBuffers(backend.hdc)
        opengl_clear_screen(renderer)
    }

    opengl_destroy :: proc(renderer: ^Renderer) {
        win.wglMakeCurrent(nil, nil)
        win.wglDeleteContext(backend.gl_context)
        win.ReleaseDC(backend.hwnd, backend.hdc)

        backend = {}
    }

    Mesh_Backend :: Mesh_OpenGL
    Shader_Backend :: Shader_OpenGL
    Shader_Program_Backend :: Shader_Program_OpenGL
    
    Mesh_OpenGL :: struct {
        vbo, vao, ebo: u32,
    }

    Shader_OpenGL :: struct {
        handle: u32,
    }

    Shader_Program_OpenGL :: struct {
        handle: u32,
    }

    opengl_create_mesh :: proc(renderer: ^Renderer, vertices: []Vertex, indices: []Index) -> (Mesh_OpenGL, bool) {
        fmt.printfln("OPENGL: Creating mesh from vertices: %v.", vertices)
        
        m: Mesh_OpenGL
        
        gl.GenVertexArrays(1, &m.vao)
        gl.GenBuffers(1, &m.vbo)
        gl.GenBuffers(1, &m.ebo)

        gl.BindVertexArray(m.vao)
        {
            gl.BindBuffer(gl.ARRAY_BUFFER, m.vbo)
            gl.BufferData(gl.ARRAY_BUFFER, len(vertices) * size_of(Vertex), raw_data(&vertices[0]), gl.STATIC_DRAW)

            gl.BindBuffer(gl.ELEMENT_ARRAY_BUFFER, m.ebo)
            gl.BufferData(gl.ELEMENT_ARRAY_BUFFER, len(indices) * size_of(Index), raw_data(indices), gl.STATIC_DRAW)

            gl.VertexAttribPointer(0, 3, gl.FLOAT, gl.FALSE, 3 * size_of(f32), 0)
            gl.EnableVertexAttribArray(0)
            
        }
        gl.BindVertexArray(0)
        gl.BindBuffer(gl.ARRAY_BUFFER, 0)

        return m, true
    }

    opengl_create_shader :: proc(renderer: ^Renderer, type: Shader_Type, data: []u8) -> (Shader_OpenGL, bool) {
        handle: u32
        
        switch type {
            case .Vertex: {
                handle = gl.CreateShader(gl.VERTEX_SHADER)
            }
            case .Fragment: {
                handle = gl.CreateShader(gl.FRAGMENT_SHADER)
            }
        }

        assert(handle != 0)
        
        src := strings.clone_to_cstring(transmute(string)data, context.allocator)
        defer delete(src)
        gl.ShaderSource(handle, 1, &src, nil)

        gl.CompileShader(handle)

        success: i32
        info_log: [512]u8
        gl.GetShaderiv(handle, gl.COMPILE_STATUS, &success)
        if success != 1 {
            gl.GetShaderInfoLog(handle, 512, nil, raw_data(&info_log))
            fmt.printfln("OPENGL: Failed to compile shader of type %v. Log: '%v'.", type, info_log)

            return {}, false
        }

        s: Shader_OpenGL
        s.handle = handle
        return s, true
    }

    opengl_delete_shader :: proc(renderer: ^Renderer, shader: ^Shader) {
        gl.DeleteShader(shader.backend.handle)
    }

    opengl_create_shader_program :: proc(renderer: ^Renderer, vertex_shader, fragment_shader: ^Shader) -> (Shader_Program_OpenGL, bool) {
        handle := gl.CreateProgram()
        
        gl.AttachShader(handle, vertex_shader.backend.handle)
        gl.AttachShader(handle, fragment_shader.backend.handle)
        gl.LinkProgram(handle)
        
        success: i32
        info_log: [512]u8
        gl.GetProgramiv(handle, gl.LINK_STATUS, &success)
        if success != 1 {
            gl.GetProgramInfoLog(handle, 512, nil, raw_data(&info_log))
            fmt.printfln("OPENGL: Failed to create shader-program. Log: '%v'.", info_log)
            
            return {}, false
        }
        
        s: Shader_Program_OpenGL
        s.handle = handle
        return s, true
    }

    opengl_delete_shader_program :: proc(renderer: ^Renderer, shader_program: ^Shader_Program) {
        gl.DeleteProgram(shader_program.backend.handle)
    }

    opengl_activate_material :: proc(material: ^Material) {
        gl.UseProgram(material.shader_program.backend.handle)
    }

    opengl_draw_mesh :: proc(mesh: ^Mesh) {
        gl.BindVertexArray(mesh.backend.vao)
        assert(mesh.amount_of_indices < u32(max(i32)))
        gl.DrawElements(gl.TRIANGLES, i32(mesh.amount_of_indices), gl.UNSIGNED_INT, nil)
        gl.BindVertexArray(0)
    }
}