#+build windows, darwin, linux
#+private file

package karl2d

@(private="package")
RENDER_BACKEND_INTERFACE_GL :: Render_Backend_Interface {
	state_size = gl_state_size,
	init = gl_init,
	shutdown = gl_shutdown,
	clear = gl_clear,
	present = gl_present,
	draw = gl_draw,
	resize_swapchain = gl_resize_swapchain,
	get_swapchain_width = gl_get_swapchain_width,
	get_swapchain_height = gl_get_swapchain_height,
	flip_z = gl_flip_z,
	set_internal_state = gl_set_internal_state,
	create_texture = gl_create_texture,
	load_texture = gl_load_texture,
	update_texture = gl_update_texture,
	destroy_texture = gl_destroy_texture,
	load_shader = gl_load_shader,
	destroy_shader = gl_destroy_shader,

	default_shader_vertex_source = gl_default_shader_vertex_source,
	default_shader_fragment_source = gl_default_shader_fragment_source,
}

import "base:runtime"
import gl "vendor:OpenGL"
import hm "handle_map"
import "core:log"
import "core:strings"
import "core:slice"
import la "core:math/linalg"

_ :: la

GL_State :: struct {
	window_handle: Window_Handle,
	width: int,
	height: int,
	allocator: runtime.Allocator,
	shaders: hm.Handle_Map(GL_Shader, Shader_Handle, 1024*10),
	ctx: GL_Context,
	vertex_buffer_gpu: u32,
}

GL_Shader_Constant_Buffer :: struct {
	buffer: u32,
	size: int,
	block_index: u32,
}

GL_Shader :: struct {
	handle: Shader_Handle,

	// This is like the "input layout"
	vao: u32,

	program: u32,

	constant_buffers: []GL_Shader_Constant_Buffer,
}

s: ^GL_State

gl_state_size :: proc() -> int {
	return size_of(GL_State)
}

gl_init :: proc(state: rawptr, window_handle: Window_Handle, swapchain_width, swapchain_height: int, allocator := context.allocator) {
	s = (^GL_State)(state)
	s.window_handle = window_handle
	s.width = swapchain_width
	s.height = swapchain_height
	s.allocator = allocator

	ctx, ctx_ok := _gl_get_context(window_handle)

	if !ctx_ok {
		log.panic("Could not find a valid pixel format for gl context")
	}

	s.ctx = ctx
	_gl_load_procs()
	gl.Enable(gl.DEPTH_TEST)
	gl.DepthFunc(gl.GREATER)

	gl.GenBuffers(1, &s.vertex_buffer_gpu)
	gl.BindBuffer(gl.ARRAY_BUFFER, s.vertex_buffer_gpu)
	gl.BufferData(gl.ARRAY_BUFFER, VERTEX_BUFFER_MAX, nil, gl.DYNAMIC_DRAW)
}

gl_shutdown :: proc() {
	gl.DeleteBuffers(1, &s.vertex_buffer_gpu)
	_gl_destroy_context(s.ctx)
}

gl_clear :: proc(color: Color) {
	c := f32_color_from_color(color)
	gl.ClearColor(c.r, c.g, c.b, c.a)
	gl.ClearDepth(-1)
	gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
}

gl_present :: proc() {
	_gl_present(s.window_handle)
}

gl_draw :: proc(shd: Shader, texture: Texture_Handle, scissor: Maybe(Rect), vertex_buffer: []u8) {
	shader := hm.get(&s.shaders, shd.handle)

	if shader == nil {
		return
	}

	gl.EnableVertexAttribArray(0)
	gl.EnableVertexAttribArray(1)
	gl.EnableVertexAttribArray(2)

	gl.UseProgram(shader.program)
	assert(len(shd.constant_buffers) == len(shader.constant_buffers))

	for cb_idx in 0..<len(shader.constant_buffers) {
		cpu_data := shd.constant_buffers[cb_idx].cpu_data
		gpu_data := shader.constant_buffers[cb_idx].buffer
		gl.BindBuffer(gl.UNIFORM_BUFFER, gpu_data)
		gl.BufferData(gl.UNIFORM_BUFFER, len(cpu_data), raw_data(cpu_data), gl.DYNAMIC_DRAW)
		gl.BindBufferBase(gl.UNIFORM_BUFFER, u32(cb_idx), gpu_data)
	}
	
	gl.BindBuffer(gl.ARRAY_BUFFER, s.vertex_buffer_gpu)
	vb_data := gl.MapBuffer(gl.ARRAY_BUFFER, gl.WRITE_ONLY)
	{
		gpu_map := slice.from_ptr((^u8)(vb_data), VERTEX_BUFFER_MAX)
		copy(
			gpu_map,
			vertex_buffer,
		)
	}

	gl.UnmapBuffer(gl.ARRAY_BUFFER)
	gl.DrawArrays(gl.TRIANGLES, 0, i32(len(vertex_buffer)/shd.vertex_size))
}

gl_resize_swapchain :: proc(w, h: int) {
}

gl_get_swapchain_width :: proc() -> int {
	return s.width
}

gl_get_swapchain_height :: proc() -> int {
	return s.height
}

gl_flip_z :: proc() -> bool {
	return false
}

gl_set_internal_state :: proc(state: rawptr) {
}

gl_create_texture :: proc(width: int, height: int, format: Pixel_Format) -> Texture_Handle {
	return {}
}

gl_load_texture :: proc(data: []u8, width: int, height: int, format: Pixel_Format) -> Texture_Handle {
	return {}
}

gl_update_texture :: proc(th: Texture_Handle, data: []u8, rect: Rect) -> bool {
	return false
}

gl_destroy_texture :: proc(th: Texture_Handle) {

}

Shader_Compile_Result_OK :: struct {}

Shader_Compile_Result_Error :: string

Shader_Compile_Result :: union #no_nil {
	Shader_Compile_Result_OK,
	Shader_Compile_Result_Error,
}

compile_shader_from_source :: proc(shader_data: string, shader_type: gl.Shader_Type, err_buf: []u8, err_msg: ^string) -> (shader_id: u32, ok: bool) {
	shader_id = gl.CreateShader(u32(shader_type))
	length := i32(len(shader_data))
	shader_cstr := cstring(raw_data(shader_data))
	gl.ShaderSource(shader_id, 1, &shader_cstr, &length)
	gl.CompileShader(shader_id)

	result: i32
	gl.GetShaderiv(shader_id, gl.COMPILE_STATUS, &result)
		
	if result != 1 {
		info_len: i32
		gl.GetShaderInfoLog(shader_id, i32(len(err_buf)), &info_len, raw_data(err_buf))
		err_msg^ = string(err_buf[:info_len])
		gl.DeleteShader(shader_id)
		return 0, false
	}

	return shader_id, true
}

link_shader :: proc(vs_shader: u32, fs_shader: u32, err_buf: []u8, err_msg: ^string) -> (program_id: u32, ok: bool) {
	program_id = gl.CreateProgram()
	gl.AttachShader(program_id, vs_shader)
	gl.AttachShader(program_id, fs_shader)
	gl.LinkProgram(program_id)

	result: i32
	gl.GetProgramiv(program_id, gl.LINK_STATUS, &result)

	if result != 1 {
		info_len: i32
		gl.GetProgramInfoLog(program_id, i32(len(err_buf)), &info_len, raw_data(err_buf))
		err_msg^ = string(err_buf[:info_len])
		gl.DeleteProgram(program_id)
		return 0, false
	}

	return program_id, true
}

gl_load_shader :: proc(vs_source: string, fs_source: string, desc_allocator := frame_allocator, layout_formats: []Pixel_Format = {}) -> (handle: Shader_Handle, desc: Shader_Desc) {
	@static err: [1024]u8
	err_msg: string
	vs_shader, vs_shader_ok := compile_shader_from_source(vs_source, gl.Shader_Type.VERTEX_SHADER, err[:], &err_msg)

	if !vs_shader_ok  {
		log.error(err_msg)
		return {}, {}
	}
	
	fs_shader, fs_shader_ok := compile_shader_from_source(fs_source, gl.Shader_Type.FRAGMENT_SHADER, err[:], &err_msg)

	if !fs_shader_ok {
		log.error(err_msg)
		return {}, {}
	}

	program, program_ok := link_shader(vs_shader, fs_shader, err[:], &err_msg)

	if !program_ok {
		log.error(err_msg)
		return {}, {}
	}

	stride: int

	{
		num_attribs: i32
		gl.GetProgramiv(program, gl.ACTIVE_ATTRIBUTES, &num_attribs)
		desc.inputs = make([]Shader_Input, num_attribs, desc_allocator)

		attrib_name_buf: [256]u8

		for i in 0..<num_attribs {
			attrib_name_len: i32
			attrib_size: i32
			attrib_type: u32
			gl.GetActiveAttrib(program, u32(i), i32(len(attrib_name_buf)), &attrib_name_len, &attrib_size, &attrib_type, raw_data(attrib_name_buf[:]))

			name_cstr := cstring(raw_data(attrib_name_buf[:attrib_name_len]))
			
			loc := gl.GetAttribLocation(program, name_cstr)

			if loc >= num_attribs {
				continue
			}

			type: Shader_Input_Type

			switch attrib_type {
			case gl.FLOAT: type = .F32
			case gl.FLOAT_VEC2: type = .Vec2
			case gl.FLOAT_VEC3: type = .Vec3
			case gl.FLOAT_VEC4: type = .Vec4
			
			/* Possible (gl.) types:

			   FLOAT, FLOAT_VEC2, FLOAT_VEC3, FLOAT_VEC4, FLOAT_MAT2,
			   FLOAT_MAT3, FLOAT_MAT4, FLOAT_MAT2x3, FLOAT_MAT2x4,
			   FLOAT_MAT3x2, FLOAT_MAT3x4, FLOAT_MAT4x2, FLOAT_MAT4x3,
			   INT, INT_VEC2, INT_VEC3, INT_VEC4, UNSIGNED_INT, 
			   UNSIGNED_INT_VEC2, UNSIGNED_INT_VEC3, UNSIGNED_INT_VEC4,
			   DOUBLE, DOUBLE_VEC2, DOUBLE_VEC3, DOUBLE_VEC4, DOUBLE_MAT2,
			   DOUBLE_MAT3, DOUBLE_MAT4, DOUBLE_MAT2x3, DOUBLE_MAT2x4,
			   DOUBLE_MAT3x2, DOUBLE_MAT3x4, DOUBLE_MAT4x2, or DOUBLE_MAT4x3 */

			case: log.errorf("Unknwon type: %v", attrib_type)
			}

			name := strings.clone(string(attrib_name_buf[:attrib_name_len]), desc_allocator)
			
			format := len(layout_formats) > 0 ? layout_formats[loc] : get_shader_input_format(name, type)
			desc.inputs[loc] = {
				name = name,
				register = int(loc),
				format = format,
				type = type,
			}


			input_format := get_shader_input_format(name, type)
			format_size := pixel_format_size(input_format)

			stride += format_size
		}
	}


	shader := GL_Shader {
		program = program,
	}

	gl.GenVertexArrays(1, &shader.vao)
	gl.BindVertexArray(shader.vao)
	gl.BindBuffer(gl.ARRAY_BUFFER, s.vertex_buffer_gpu)

	offset: int
	for idx in 0..<len(desc.inputs) {
		input := desc.inputs[idx]
		format_size := pixel_format_size(input.format)
		gl.EnableVertexAttribArray(u32(idx))	
		format, num_components, norm := gl_describe_pixel_format(input.format)
		gl.VertexAttribPointer(u32(idx), num_components, format, norm ? gl.TRUE : gl.FALSE, i32(stride), uintptr(offset))
		offset += format_size
	}

	/*{
		num_uniforms: i32
		uniform_name_buf: [256]u8
		gl.GetProgramiv(program, gl.ACTIVE_UNIFORMS, &num_uniforms)
		
		for u_idx in 0..<num_uniforms {
			name_len: i32
			size: i32
			type: u32
			gl.GetActiveUniform(program, u32(u_idx), len(uniform_name_buf), &name_len, &size, &type, raw_data(&uniform_name_buf))

			if type == gl.SAMPLER_2D {

			}
		}
	}*/

	{
		num_uniform_blocks: i32
		gl.GetProgramiv(program, gl.ACTIVE_UNIFORM_BLOCKS, &num_uniform_blocks)
		desc.constant_buffers = make([]Shader_Constant_Buffer_Desc, num_uniform_blocks, desc_allocator)
		shader.constant_buffers = make([]GL_Shader_Constant_Buffer, num_uniform_blocks, s.allocator)


		uniform_block_name_buf: [256]u8
		uniform_name_buf: [256]u8

		for cb_idx in 0..<num_uniform_blocks {
			name_len: i32
			gl.GetActiveUniformBlockName(program, u32(cb_idx), len(uniform_block_name_buf), &name_len, raw_data(&uniform_block_name_buf))
			name_cstr := cstring(raw_data(uniform_block_name_buf[:name_len]))
			idx := gl.GetUniformBlockIndex(program, name_cstr)

			if i32(idx) >= num_uniform_blocks {
				continue
			}

			size: i32

			// TODO investigate if we need std140 layout in the shader or what is fine?
			gl.GetActiveUniformBlockiv(program, idx, gl.UNIFORM_BLOCK_DATA_SIZE, &size)

			if size == 0 {
				log.errorf("Uniform block %v has size 0", name_cstr)
				continue
			}

			buf: u32

			gl.GenBuffers(1, &buf)
			gl.BindBuffer(gl.UNIFORM_BUFFER, buf)
			gl.BufferData(gl.UNIFORM_BUFFER, int(size), nil, gl.DYNAMIC_DRAW)
			gl.BindBufferBase(gl.UNIFORM_BUFFER, idx, buf)

			shader.constant_buffers[cb_idx] = {
				block_index = idx,
				buffer = buf,
				size = int(size),
			}

			desc.constant_buffers[cb_idx] = {
				name = strings.clone_from_cstring(name_cstr, desc_allocator),
				size = int(size),
			}

			num_uniforms: i32
			gl.GetActiveUniformBlockiv(program, idx, gl.UNIFORM_BLOCK_ACTIVE_UNIFORMS, &num_uniforms)

			uniform_indices := make([]i32, num_uniforms, frame_allocator)
			gl.GetActiveUniformBlockiv(program, idx, gl.UNIFORM_BLOCK_ACTIVE_UNIFORM_INDICES, raw_data(uniform_indices))

			variables := make([]Shader_Constant_Buffer_Variable_Desc, num_uniforms, desc_allocator)
			desc.constant_buffers[cb_idx].variables = variables

			for var_idx in 0..<num_uniforms {
				uniform_idx := u32(uniform_indices[var_idx])

				offset: i32
				gl.GetActiveUniformsiv(program, 1, &uniform_idx, gl.UNIFORM_OFFSET, &offset)

				variable_name_len: i32
				gl.GetActiveUniformName(program, uniform_idx, len(uniform_name_buf), &variable_name_len, raw_data(&uniform_name_buf))

				variables[var_idx] = {
					name = strings.clone(string(uniform_name_buf[:variable_name_len]), desc_allocator),
					loc = {
						buffer_idx = u32(cb_idx),
						offset = u32(offset),
					},
				}
			}
		}
	}

	h := hm.add(&s.shaders, shader)

	return h, desc
}

gl_describe_pixel_format :: proc(f: Pixel_Format) -> (format: u32, num_components: i32, normalized: bool) {
	switch f {
	case .RGBA_32_Float: return gl.FLOAT, 4, false
	case .RGB_32_Float: return gl.FLOAT, 3, false
	case .RG_32_Float: return gl.FLOAT, 2, false
	case .R_32_Float: return gl.FLOAT, 1, false

	case .RGBA_8_Norm: return gl.UNSIGNED_BYTE, 4, true
	case .RG_8_Norm: return gl.UNSIGNED_BYTE, 2, true
	case .R_8_Norm: return gl.UNSIGNED_BYTE, 1, true
	case .R_8_UInt: return gl.BYTE, 1, false
	
	case .Unknown: 
	}

	log.error("Unknown format")
	return 0, 0, false
}

gl_destroy_shader :: proc(h: Shader_Handle) {
	
}

gl_default_shader_vertex_source :: proc() -> string {
	return #load("default_shader_vertex.glsl")
}


gl_default_shader_fragment_source :: proc() -> string {
	return #load("default_shader_fragment.glsl")
}