package main

import "core:math/linalg"
import "core:fmt"
import "core:mem"

UiElementType :: enum {
	Input,
	Button,
	Container,
}

UiElementData :: union {
	UiElementData_Button,
	UiElementData_Input,
	UiElementData_Container,
}

UiElementData_Button :: struct {
	label: cstring,
}

UiElementData_Container :: struct {
	label: cstring,
}

UiElementData_Input :: struct {
	label: cstring,
}

UiElement :: struct {
	area: rect2,
	type: UiElementType,
	data: UiElementData,
}

UiState :: struct {
	origin, position_left, position: v2,
	same_line: bool,
	style: UiStyle,
	elements: [dynamic]UiElement,
	container: ^UiElement,
	group_element_count: int,
}

UiStyle :: struct {
	margin, padding: f32,
}

ui_button :: proc(state: ^UiState, size: v2, data: UiElementData_Button) {
	area := _ui_advance_element(state, size)
	append(&state.elements, UiElement{area = area, type = .Button, data = data})
}

ui_container_begin :: proc(state: ^UiState, data: UiElementData_Container) {
	assert(state.container == nil)
	append(&state.elements, UiElement{area = _ui_advance_container(state), type = .Container, data = data})
	state.container = &state.elements[len(state.elements) - 1]
}

ui_container_end :: proc(state: ^UiState) {
	assert(state.container != nil)
	state.container = nil
}

_ui_advance_element :: proc(state: ^UiState, size: v2) -> rect2 {
	if state.group_element_count > 0 {
		if state.same_line {
			state.position.x += size.x + state.style.padding
			state.same_line = false
		} else {
			state.position_left.y += size.y + state.style.padding
			state.position = state.position_left
		}
	} else {
		state.position += state.style.padding
	}
	area := rect2{**state.position, **size}
	if state.container != nil {
		element_bottom_left := rect_get_br(area)
		container_bottom_left := rect_get_br(state.container.area)
		new_br := linalg.max(element_bottom_left + state.style.padding, container_bottom_left)
		state.container.area.width = new_br.x - state.container.area.x
		state.container.area.height = new_br.y - state.container.area.y
	}
	state.group_element_count += 1
	return area
}

_ui_advance_container :: proc(state: ^UiState) -> rect2 {
	state.position += state.style.margin
	return {**state.position, 0.0, 0.0}
}

ui_input :: proc(state: ^UiState, size: v2, data: UiElementData_Input) {
	area := _ui_advance_element(state, size)
	append(&state.elements, UiElement{area = area, type = .Input, data = data})
}

ui_same_line :: proc(state: ^UiState) {
	state.same_line = true
}

ui_start :: proc(state: ^UiState) {
	clear(&state.elements)
	state.position_left = state.origin
	state.position = state.position_left
}

ui_end :: proc(state: UiState) -> []UiElement {
	return state.elements[:]
}

ui_init :: proc(state: ^UiState, style: UiStyle, origin: v2, allocator: mem.Allocator) {
	state^ = {
		origin = origin,
		position = origin,
		style = style,
		elements = make(type_of(state.elements), 0, 512, allocator)
	}
}