package karl2d

import "base:runtime"
import "core:mem"
import "core:log"
import "core:math"
import "core:math/linalg"
import "core:slice"

import "core:image"
import "core:image/bmp"
import "core:image/png"
import "core:image/tga"

import hm "handle_map"

_ :: bmp
_ :: png
_ :: tga

Handle :: hm.Handle
Texture_Handle :: distinct Handle

// Opens a window and initializes some internal state. The internal state will use `allocator` for
// all dynamically allocated memory. The return value can be ignored unless you need to later call
// `set_state`.
init :: proc(window_width: int, window_height: int, window_title: string,
             allocator := context.allocator, loc := #caller_location) -> ^State {
	s = new(State, allocator, loc)
	s.allocator = allocator
	s.custom_context = context

	s.width = window_width
	s.height = window_height

	s.win = WINDOW_INTERFACE_WIN32
	win = s.win

	window_state_alloc_error: runtime.Allocator_Error
	s.window_state, window_state_alloc_error = mem.alloc(win.state_size())
	log.assertf(window_state_alloc_error == nil, "Failed allocating memory for window state: %v", window_state_alloc_error)

	win.init(s.window_state, window_width, window_height, window_title, allocator)
	s.window = win.window_handle()

	s.rb = BACKEND_D3D11
	rb = s.rb
	rb_alloc_error: runtime.Allocator_Error
	s.rb_state, rb_alloc_error = mem.alloc(rb.state_size())
	log.assertf(rb_alloc_error == nil, "Failed allocating memory for rendering backend: %v", rb_alloc_error)
	s.proj_matrix = make_default_projection(window_width, window_height)
	s.view_matrix = 1
	rb.init(s.rb_state, s.window, window_width, window_height, allocator)
	s.vertex_buffer_cpu = make([]u8, VERTEX_BUFFER_MAX, allocator, loc)
	white_rect: [16*16*4]u8
	slice.fill(white_rect[:], 255)
	s.shape_drawing_texture = rb.load_texture(white_rect[:], 16, 16)

	s.default_shader = rb.load_shader(string(DEFAULT_SHADER_SOURCE))

	return s
}

DEFAULT_SHADER_SOURCE :: #load("shader.hlsl")

// Closes the window and cleans up the internal state.
shutdown :: proc() {
	rb.destroy_texture(s.shape_drawing_texture)
	destroy_shader(s.default_shader)
	rb.shutdown()
	delete(s.vertex_buffer_cpu, s.allocator)

	win.shutdown()

	a := s.allocator
	free(s.window_state, a)
	free(s.rb_state, a)
	free(s, a)
	s = nil
}

// Clear the backbuffer with supplied color.
clear :: proc(color: Color) {
	rb.clear(color)
}

// Present the backbuffer. Call at end of frame to make everything you've drawn appear on the screen.
present :: proc() {
	draw_current_batch()
	rb.present()
}

// Call at start or end of frame to process all events that have arrived to the window.
//
// WARNING: Not calling this will make your program impossible to interact with.
process_events :: proc() {
	s.keys_went_up = {}
	s.keys_went_down = {}
	s.mouse_delta = {}
	s.mouse_wheel_delta = 0

	win.process_events()

	events := win.get_events()

	for &event in events {
		switch &e in event {
		case Window_Event_Close_Wanted:
			s.shutdown_wanted = true

		case Window_Event_Key_Went_Down:
			s.keys_went_down[e.key] = true
			s.keys_is_held[e.key] = true

		case Window_Event_Key_Went_Up:
			s.keys_is_held[e.key] = false
			s.keys_went_up[e.key] = true

		case Window_Event_Mouse_Move:
			prev_pos := s.mouse_position
			s.mouse_position = e.position
			s.mouse_delta = prev_pos - s.mouse_position

		case Window_Event_Mouse_Wheel:
			s.mouse_wheel_delta = e.delta
		}
	}

	win.clear_events()
}

/* Flushes the current batch. This sends off everything to the GPU that has been queued in the
current batch. Normally, you do not need to do this manually. It is done automatically when these
procedures run:
	present
	set_camera
	set_shader

TODO: complete this list and motivate why it needs to happen on those procs (or do that in the
docs for those procs).
*/   
draw_current_batch :: proc() {
	shader := s.batch_shader.? or_else s.default_shader
	rb.draw(shader, s.batch_texture, s.proj_matrix * s.view_matrix, s.vertex_buffer_cpu[:s.vertex_buffer_cpu_used])
	s.vertex_buffer_cpu_used = 0
}

// Can be used to restore the internal state using the pointer returned by `init`. Useful after
// reloading the library (for example, when doing code hot reload).
set_internal_state :: proc(state: ^State) {
	s = state
	rb = s.rb
	win = s.win
	rb.set_internal_state(s.rb_state)
	win.set_internal_state(s.window_state)
}

get_screen_width :: proc() -> int {
	return rb.get_swapchain_width()
}

get_screen_height :: proc() -> int  {
	return rb.get_swapchain_height()
}

key_went_down :: proc(key: Keyboard_Key) -> bool {
	return s.keys_went_down[key]
}

key_went_up :: proc(key: Keyboard_Key) -> bool {
	return s.keys_went_up[key]
}

key_is_held :: proc(key: Keyboard_Key) -> bool {
	return s.keys_is_held[key]
}

shutdown_wanted :: proc() -> bool {
	return s.shutdown_wanted
}

set_window_position :: proc(x: int, y: int) {
	win.set_position(x, y)
}

set_window_size :: proc(width: int, height: int) {
	panic("Not implemented")
}

set_camera :: proc(camera: Maybe(Camera)) {
	if camera == s.batch_camera {
		return
	}

	draw_current_batch()
	s.batch_camera = camera
	s.proj_matrix = make_default_projection(s.width, s.height)

	if c, c_ok := camera.?; c_ok {
		origin_trans := linalg.matrix4_translate(vec3_from_vec2(-c.origin))
		translate := linalg.matrix4_translate(vec3_from_vec2(c.target))
		scale := linalg.matrix4_scale(Vec3{1/c.zoom, 1/c.zoom, 1})
		rot := linalg.matrix4_rotate_f32(c.rotation * math.RAD_PER_DEG, {0, 0, 1})
		camera_matrix := translate * scale * rot * origin_trans
		s.view_matrix = linalg.inverse(camera_matrix)
	} else {
		s.view_matrix = 1
	}
}

load_texture_from_file :: proc(filename: string) -> Texture {
	img, img_err := image.load_from_file(filename, options = {.alpha_add_if_missing}, allocator = context.temp_allocator)

	if img_err != nil {
		log.errorf("Error loading texture %v: %v", filename, img_err)
		return {}
	}

	backend_tex := rb.load_texture(img.pixels.buf[:], img.width, img.height)

	return {
		handle = backend_tex,
		width = img.width,
		height = img.height,
	}
}

destroy_texture :: proc(tex: Texture) {
	rb.destroy_texture(tex.handle)
}

draw_rect :: proc(r: Rect, c: Color) {
	if s.batch_texture != TEXTURE_NONE && s.batch_texture != s.shape_drawing_texture {
		draw_current_batch()
	}

	s.batch_texture = s.shape_drawing_texture

	_batch_vertex({r.x, r.y}, {0, 0}, c)
	_batch_vertex({r.x + r.w, r.y}, {1, 0}, c)
	_batch_vertex({r.x + r.w, r.y + r.h}, {1, 1}, c)
	_batch_vertex({r.x, r.y}, {0, 0}, c)
	_batch_vertex({r.x + r.w, r.y + r.h}, {1, 1}, c)
	_batch_vertex({r.x, r.y + r.h}, {0, 1}, c)
}

draw_rect_ex :: proc(r: Rect, origin: Vec2, rot: f32, c: Color) {
	if s.batch_texture != TEXTURE_NONE && s.batch_texture != s.shape_drawing_texture {
		draw_current_batch()
	}

	s.batch_texture = s.shape_drawing_texture
	tl, tr, bl, br: Vec2

	// Rotation adapted from Raylib's "DrawTexturePro"
	if rot == 0 {
		x := r.x - origin.x
		y := r.y - origin.y
		tl = { x,         y }
		tr = { x + r.w, y }
		bl = { x,         y + r.h }
		br = { x + r.w, y + r.h }
	} else {
		sin_rot := math.sin(rot * math.RAD_PER_DEG)
		cos_rot := math.cos(rot * math.RAD_PER_DEG)
		x := r.x
		y := r.y
		dx := -origin.x
		dy := -origin.y

		tl = {
			x + dx * cos_rot - dy * sin_rot,
			y + dx * sin_rot + dy * cos_rot,
		}

		tr = {
			x + (dx + r.w) * cos_rot - dy * sin_rot,
			y + (dx + r.w) * sin_rot + dy * cos_rot,
		}

		bl = {
			x + dx * cos_rot - (dy + r.h) * sin_rot,
			y + dx * sin_rot + (dy + r.h) * cos_rot,
		}

		br = {
			x + (dx + r.w) * cos_rot - (dy + r.h) * sin_rot,
			y + (dx + r.w) * sin_rot + (dy + r.h) * cos_rot,
		}
	}
	
	_batch_vertex(tl, {0, 0}, c)
	_batch_vertex(tr, {1, 0}, c)
	_batch_vertex(br, {1, 1}, c)
	_batch_vertex(tl, {0, 0}, c)
	_batch_vertex(br, {1, 1}, c)
	_batch_vertex(bl, {0, 1}, c)
}

draw_rect_outline :: proc(r: Rect, thickness: f32, color: Color) {
	t := thickness
	
	// Based on DrawRectangleLinesEx from Raylib

	top := Rect {
		r.x,
		r.y,
		r.w,
		t,
	}

	bottom := Rect {
		r.x,
		r.y + r.h - t,
		r.w,
		t,
	}

	left := Rect {
		r.x,
		r.y + t,
		t,
		r.h - t * 2,
	}

	right := Rect {
		r.x + r.w - t,
		r.y + t,
		t,
		r.h - t * 2,
	}

	draw_rect(top, color)
	draw_rect(bottom, color)
	draw_rect(left, color)
	draw_rect(right, color)
}

draw_circle :: proc(center: Vec2, radius: f32, color: Color, segments := 16) {
	if s.batch_texture != TEXTURE_NONE && s.batch_texture != s.shape_drawing_texture {
		draw_current_batch()
	}

	s.batch_texture = s.shape_drawing_texture

	prev := center + {radius, 0}
	for s in 1..=segments {
		sr := (f32(s)/f32(segments)) * 2*math.PI
		rot := linalg.matrix2_rotate(sr)
		p := center + rot * Vec2{radius, 0}
			

		_batch_vertex(prev, {0, 0}, color)
		_batch_vertex(p, {1, 0}, color)
		_batch_vertex(center, {1, 1}, color)

		prev = p
	}
}

draw_line :: proc(start: Vec2, end: Vec2, thickness: f32, color: Color) {
	p := Vec2{start.x, start.y + thickness*0.5}
	s := Vec2{linalg.length(end - start), thickness}

	origin := Vec2 {0, thickness*0.5}
	r := Rect {p.x, p.y, s.x, s.y}

	rot := math.atan2(end.y - start.y, end.x - start.x)

	draw_rect_ex(r, origin, rot * math.DEG_PER_RAD, color)
}

draw_texture :: proc(tex: Texture, pos: Vec2, tint := WHITE) {
	draw_texture_ex(
		tex,
		{0, 0, f32(tex.width), f32(tex.height)},
		{pos.x, pos.y, f32(tex.width), f32(tex.height)},
		{},
		0,
		tint,
	)
}

draw_texture_rect :: proc(tex: Texture, rect: Rect, pos: Vec2, tint := WHITE) {
	draw_texture_ex(
		tex,
		rect,
		{pos.x, pos.y, rect.w, rect.h},
		{},
		0,
		tint,
	)
}

draw_texture_ex :: proc(tex: Texture, src: Rect, dst: Rect, origin: Vec2, rotation: f32, tint := WHITE) {
	if tex.width == 0 || tex.height == 0 {
		return
	}

	if s.batch_texture != TEXTURE_NONE && s.batch_texture != tex.handle {
		draw_current_batch()
	}

	flip_x, flip_y: bool
	src := src
	dst := dst

	if src.w < 0 {
		flip_x = true
		src.w = -src.w
	}

	if src.h < 0 {
		flip_y = true
		src.h = -src.h
	}

	if dst.w < 0 {
		dst.w *= -1
	}

	if dst.h < 0 {
		dst.h *= -1
	}

	s.batch_texture = tex.handle
	tl, tr, bl, br: Vec2

	// Rotation adapted from Raylib's "DrawTexturePro"
	if rotation == 0 {
		x := dst.x - origin.x
		y := dst.y - origin.y
		tl = { x,         y }
		tr = { x + dst.w, y }
		bl = { x,         y + dst.h }
		br = { x + dst.w, y + dst.h }
	} else {
		sin_rot := math.sin(rotation * math.RAD_PER_DEG)
		cos_rot := math.cos(rotation * math.RAD_PER_DEG)
		x := dst.x
		y := dst.y
		dx := -origin.x
		dy := -origin.y

		tl = {
			x + dx * cos_rot - dy * sin_rot,
			y + dx * sin_rot + dy * cos_rot,
		}

		tr = {
			x + (dx + dst.w) * cos_rot - dy * sin_rot,
			y + (dx + dst.w) * sin_rot + dy * cos_rot,
		}

		bl = {
			x + dx * cos_rot - (dy + dst.h) * sin_rot,
			y + dx * sin_rot + (dy + dst.h) * cos_rot,
		}

		br = {
			x + (dx + dst.w) * cos_rot - (dy + dst.h) * sin_rot,
			y + (dx + dst.w) * sin_rot + (dy + dst.h) * cos_rot,
		}
	}
	
	ts := Vec2{f32(tex.width), f32(tex.height)}
	up := Vec2{src.x, src.y} / ts
	us := Vec2{src.w, src.h} / ts
	c := tint

	uv0 := up
	uv1 := up + {us.x, 0}
	uv2 := up + us
	uv3 := up
	uv4 := up + us
	uv5 := up + {0, us.y}

	if flip_x {
		uv0.x += us.x
		uv1.x -= us.x
		uv2.x -= us.x
		uv3.x += us.x
		uv4.x -= us.x
		uv5.x += us.x		
	}

	if flip_y {
		uv0.y += us.y
		uv1.y += us.y
		uv2.y -= us.y
		uv3.y += us.y
		uv4.y -= us.y
		uv5.y -= us.y		
	}

	_batch_vertex(tl, uv0, c)
	_batch_vertex(tr, uv1, c)
	_batch_vertex(br, uv2, c)
	_batch_vertex(tl, uv3, c)
	_batch_vertex(br, uv4, c)
	_batch_vertex(bl, uv5, c)
}

load_shader :: proc(shader_source: string, layout_formats: []Shader_Input_Format = {}) -> Shader {
	return rb.load_shader(shader_source, layout_formats)
}

destroy_shader :: proc(shader: Shader) {
	rb.destroy_shader(shader)
}

set_shader :: proc(shader: Maybe(Shader)) {
	if maybe_handle_equal(shader, s.batch_shader) {
		return
	}

	draw_current_batch()
	s.batch_shader = shader
}

maybe_handle_equal :: proc(m1: Maybe($T), m2: Maybe(T)) -> bool {
	if m1 == nil && m2 == nil {
		return true
	}

	m1v, m1v_ok := m1.?
	m2v, m2v_ok := m2.?

	if !m1v_ok || !m2v_ok {
		return false
	}

	return m1v.handle == m2v.handle
}

set_shader_constant :: proc(shd: Shader, loc: Shader_Constant_Location, val: $T) {
	draw_current_batch()

	if int(loc.buffer_idx) >= len(shd.constant_buffers) {
		log.warnf("Constant buffer idx %v is out of bounds", loc.buffer_idx)
		return
	}

	b := &shd.constant_buffers[loc.buffer_idx]

	if int(loc.offset) + size_of(val) > len(b.cpu_data) {
		log.warnf("Constant buffer idx %v is trying to be written out of bounds by at offset %v with %v bytes", loc.buffer_idx, loc.offset, size_of(val))
		return
	}

	dst := (^T)(&b.cpu_data[loc.offset])
	dst^ = val
}

set_shader_constant_mat4 :: proc(shader: Shader, loc: Shader_Constant_Location, val: matrix[4,4]f32) {
	set_shader_constant(shader, loc, val)
}

set_shader_constant_f32 :: proc(shader: Shader, loc: Shader_Constant_Location, val: f32) {
	set_shader_constant(shader, loc, val)
}

set_shader_constant_vec2 :: proc(shader: Shader, loc: Shader_Constant_Location, val: Vec2) {
	set_shader_constant(shader, loc, val)
}

get_default_shader :: proc() -> Shader {
	return s.default_shader
}

set_scissor_rect :: proc(scissor_rect: Maybe(Rect)) {
	panic("not implemented")
}


screen_to_world :: proc(pos: Vec2, camera: Camera) -> Vec2 {
	panic("not implemented")
}

draw_text :: proc(text: string, pos: Vec2, font_size: f32, color: Color) {
	
}

mouse_button_went_down :: proc(button: Mouse_Button) -> bool {
	panic("not implemented")
}

mouse_button_went_up :: proc(button: Mouse_Button) -> bool {
	panic("not implemented")
}

mouse_button_is_held :: proc(button: Mouse_Button) -> bool {
	panic("not implemented")
}

get_mouse_wheel_delta :: proc() -> f32 {
	return s.mouse_wheel_delta
}

get_mouse_position :: proc() -> Vec2 {
	return s.mouse_position
}

_batch_vertex :: proc(v: Vec2, uv: Vec2, color: Color) {
	v := v

	if s.vertex_buffer_cpu_used == len(s.vertex_buffer_cpu) {
		panic("Must dispatch here")
	}

	shd := s.batch_shader.? or_else s.default_shader

	base_offset := s.vertex_buffer_cpu_used
	pos_offset := shd.default_input_offsets[.Position]
	uv_offset := shd.default_input_offsets[.UV]
	color_offset := shd.default_input_offsets[.Color]
	
	mem.set(&s.vertex_buffer_cpu[base_offset], 0, shd.vertex_size)

	if pos_offset != -1 {
		(^Vec2)(&s.vertex_buffer_cpu[base_offset + pos_offset])^ = {v.x, v.y}
	}

	if uv_offset != -1 {
		(^Vec2)(&s.vertex_buffer_cpu[base_offset + uv_offset])^ = uv
	}

	if color_offset != -1 {
		(^Color)(&s.vertex_buffer_cpu[base_offset + color_offset])^ = color
	}

	override_offset: int
	for &o, idx in shd.input_overrides {
		input := &shd.inputs[idx]
		sz := shader_input_format_size(input.format)

		if o.used != 0 {
			mem.copy(&s.vertex_buffer_cpu[base_offset + override_offset], raw_data(&o.val), o.used)
		}

		override_offset += sz
	}
	
	s.vertex_buffer_cpu_used += shd.vertex_size
}


State :: struct {
	allocator: runtime.Allocator,
	custom_context: runtime.Context,
	win: Window_Interface,
	window_state: rawptr,
	rb: Rendering_Backend_Interface,
	rb_state: rawptr,
	
	shutdown_wanted: bool,

	mouse_position: Vec2,
	mouse_delta: Vec2,
	mouse_wheel_delta: f32,

	keys_went_down: #sparse [Keyboard_Key]bool,
	keys_went_up: #sparse [Keyboard_Key]bool,
	keys_is_held: #sparse [Keyboard_Key]bool,

	window: Window_Handle,
	width: int,
	height: int,

	shape_drawing_texture: Texture_Handle,
	batch_camera: Maybe(Camera),
	batch_shader: Maybe(Shader),
	batch_texture: Texture_Handle,

	view_matrix: Mat4,
	proj_matrix: Mat4,

	vertex_buffer_cpu: []u8,
	vertex_buffer_cpu_used: int,
	default_shader: Shader,
}

@(private="file")
s: ^State
win: Window_Interface
rb: Rendering_Backend_Interface

Shader_Input_Format :: enum {
	Unknown,
	RGBA32_Float,
	RGBA8_Norm,
	RGBA8_Norm_SRGB,
	RGB32_Float,
	RG32_Float,
	R32_Float,
}

Color :: [4]u8

Vec2 :: [2]f32
Vec3 :: [3]f32

Mat4 :: matrix[4,4]f32

Vec2i :: [2]int

Rect :: struct {
	x, y: f32,
	w, h: f32,
}

Texture :: struct {
	handle: Texture_Handle,
	width: int,
	height: int,
}

Shader :: struct {
	handle: Shader_Handle,
	constant_buffers: []Shader_Constant_Buffer,
	constant_lookup: map[string]Shader_Constant_Location,
	constant_builtin_locations: [Shader_Builtin_Constant]Maybe(Shader_Constant_Location),

	inputs: []Shader_Input,
	input_overrides: []Shader_Input_Value_Override,
	default_input_offsets: [Shader_Default_Inputs]int,
	vertex_size: int,
}

Camera :: struct {
	target: Vec2,
	origin: Vec2,
	rotation: f32,
	zoom: f32,
}

// Support for up to 255 mouse buttons. Cast an int to type `Mouse_Button` to use things outside the
// options presented here.
Mouse_Button :: enum {
	Left,
	Right,
	Middle,
	Max = 255,
}

// TODO: These are just copied from raylib, we probably want a list of our own "default colors"
WHITE :: Color { 255, 255, 255, 255 }
BLACK :: Color { 0, 0, 0, 255 }
GRAY :: Color{ 130, 130, 130, 255 }
RED :: Color { 230, 41, 55, 255 }
YELLOW :: Color { 253, 249, 0, 255 }
BLUE :: Color { 0, 121, 241, 255 }
MAGENTA :: Color { 255, 0, 255, 255 }
DARKGRAY :: Color{ 80, 80, 80, 255 }
GREEN :: Color{ 0, 228, 48, 255 }

Shader_Handle :: distinct Handle
SHADER_NONE :: Shader_Handle {}

// Based on Raylib / GLFW
Keyboard_Key :: enum {
	None            = 0,

	// Alphanumeric keys
	Apostrophe      = 39,
	Comma           = 44,
	Minus           = 45,
	Period          = 46,
	Slash           = 47,
	Zero            = 48,
	One             = 49,
	Two             = 50,
	Three           = 51,
	Four            = 52,
	Five            = 53,
	Six             = 54,
	Seven           = 55,
	Eight           = 56,
	Nine            = 57,
	Semicolon       = 59,
	Equal           = 61,
	A               = 65,
	B               = 66,
	C               = 67,
	D               = 68,
	E               = 69,
	F               = 70,
	G               = 71,
	H               = 72,
	I               = 73,
	J               = 74,
	K               = 75,
	L               = 76,
	M               = 77,
	N               = 78,
	O               = 79,
	P               = 80,
	Q               = 81,
	R               = 82,
	S               = 83,
	T               = 84,
	U               = 85,
	V               = 86,
	W               = 87,
	X               = 88,
	Y               = 89,
	Z               = 90,
	Left_Bracket    = 91,
	Backslash       = 92,
	Right_Bracket   = 93,
	Grave           = 96,

	// Function keys
	Space           = 32,
	Escape          = 256,
	Enter           = 257,
	Tab             = 258,
	Backspace       = 259,
	Insert          = 260,
	Delete          = 261,
	Right           = 262,
	Left            = 263,
	Down            = 264,
	Up              = 265,
	Page_Up         = 266,
	Page_Down       = 267,
	Home            = 268,
	End             = 269,
	Caps_Lock       = 280,
	Scroll_Lock     = 281,
	Num_Lock        = 282,
	Print_Screen    = 283,
	Pause           = 284,
	F1              = 290,
	F2              = 291,
	F3              = 292,
	F4              = 293,
	F5              = 294,
	F6              = 295,
	F7              = 296,
	F8              = 297,
	F9              = 298,
	F10             = 299,
	F11             = 300,
	F12             = 301,
	Left_Shift      = 340,
	Left_Control    = 341,
	Left_Alt        = 342,
	Left_Super      = 343,
	Right_Shift     = 344,
	Right_Control   = 345,
	Right_Alt       = 346,
	Right_Super     = 347,
	Menu            = 348,

	// Keypad keys
	KP_0            = 320,
	KP_1            = 321,
	KP_2            = 322,
	KP_3            = 323,
	KP_4            = 324,
	KP_5            = 325,
	KP_6            = 326,
	KP_7            = 327,
	KP_8            = 328,
	KP_9            = 329,
	KP_Decimal      = 330,
	KP_Divide       = 331,
	KP_Multiply     = 332,
	KP_Subtract     = 333,
	KP_Add          = 334,
	KP_Enter        = 335,
	KP_Equal        = 336,
}