package zephr

import "core:fmt"
import "core:os"
import "core:mem"

import gl "vendor:OpenGL"

UiIdHash :: u32

Alignment :: enum {
  TOP_LEFT,
  TOP_CENTER,
  TOP_RIGHT,
  LEFT_CENTER,
  CENTER,
  RIGHT_CENTER,
  BOTTOM_LEFT,
  BOTTOM_CENTER,
  BOTTOM_RIGHT,
}

UiConstraint :: enum {
  FIXED,
  RELATIVE,
  RELATIVE_PIXELS,
  ASPECT_RATIO,
}

ButtonState :: enum {
  ACTIVE,
  INACTIVE,
  DISABLED,
}

UiConstraints :: struct {
  x: f32,
  y: f32,
  width: f32,
  height: f32,
  rotation: f32,
  scale: Vec2,
  parent: ^UiConstraints,
}

Rect :: struct {
  pos: Vec2,
  size: Vec2,
}

UiStyle :: struct {
  bg_color: Color,
  fg_color: Color,
  border_radius: f32,
  align: Alignment,
}

Ui :: struct {
  active_element: UiIdHash,
  popup_open: bool,
  popup_parent_hash: UiIdHash,
  popup_rect: Rect,
  popup_parent_constraints: UiConstraints,
  popup_revert_color: ^Color,
}

@private
ui_shader: Shader
@private
color_chooser_shader: Shader
@private
ui_vao: u32
@private
ui_vbo: u32

DEFAULT_UI_CONSTRAINTS :: UiConstraints{
  x = 0,
  y = 0,
  width = 0,
  height = 0,
  rotation = 0,
  scale = Vec2{1, 1},
  parent = nil,
}

@private
ui_init :: proc(font_path: cstring) {
  res := init_fonts(font_path);
  if (res == -1) {
    fmt.printf("[ERROR]: could not initialize freetype library\n");
    os.exit(1)
  } else if (res == -2) {
    fmt.printf("[ERROR]: could not load font file: \"%s\"\n", font_path);
    os.exit(1)
  } else if (res != 0) {
    os.exit(1)
  }

  l_ui_shader, success1 := create_shader("shaders/ui.vert", "shaders/ui.frag")
  l_color_chooser_shader, success2 := create_shader("shaders/ui.vert", "shaders/color_chooser.frag")

  ui_shader = l_ui_shader
  color_chooser_shader = l_color_chooser_shader

  if !success1 || !success2 {
    fmt.printf("[ERROR]: could not load ui shaders\n");
    os.exit(1)
  }

  gl.GenVertexArrays(1, &ui_vao);
  gl.GenBuffers(1, &ui_vbo);

  gl.BindVertexArray(ui_vao);
  gl.BindBuffer(gl.ARRAY_BUFFER, ui_vbo);
  gl.BufferData(gl.ARRAY_BUFFER, size_of(f32) * 6 * 4, nil, gl.DYNAMIC_DRAW);
  gl.EnableVertexAttribArray(0);
  gl.VertexAttribPointer(0, 4, gl.FLOAT, gl.FALSE, 4 * size_of(f32), 0);

  gl.BindBuffer(gl.ARRAY_BUFFER, 0);
  gl.BindVertexArray(0);
}

set_parent_constraint :: proc(constraints: ^UiConstraints, parent_constraints: ^UiConstraints) {
  constraints.parent = parent_constraints;
}

set_x_constraint :: proc(constraints: ^UiConstraints, value: f32, type: UiConstraint) {
  switch (type) {
    case .ASPECT_RATIO: // no-op. fall back to FIXED
    fallthrough
    case .FIXED:
      constraints.x = value;
    case .RELATIVE:
      if (constraints.parent != nil) {
        constraints.x = (value * constraints.parent.width);
      } else {
        constraints.x = (value * zephr_ctx.window.size.x);
      }
    case .RELATIVE_PIXELS:
      constraints.x = zephr_ctx.window.size.x / zephr_ctx.screen_size.x * value;
  }

  if (constraints.parent != nil) {
    constraints.x += constraints.parent.x;
  }
}

set_y_constraint :: proc(constraints: ^UiConstraints, value: f32, type: UiConstraint) {
  switch (type) {
    case .ASPECT_RATIO: // no-op. fall back to FIXED
    fallthrough
    case .FIXED:
      constraints.y = value;
    case .RELATIVE:
      if (constraints.parent != nil) {
        constraints.y = (value * constraints.parent.height);
      } else {
        constraints.y = (value * zephr_ctx.window.size.y);
      }
    case .RELATIVE_PIXELS:
      constraints.y = zephr_ctx.window.size.y / zephr_ctx.screen_size.y * value;
  }

  if (constraints.parent != nil) {
    constraints.y += constraints.parent.y;
  }
}

set_width_constraint :: proc(constraints: ^UiConstraints, value: f32, type: UiConstraint) {
  switch (type) {
    case .FIXED:
      constraints.width = value;
    case .RELATIVE:
      if (constraints.parent != nil) {
        constraints.width = (value * constraints.parent.width);
      } else {
        constraints.width = (value * zephr_ctx.window.size.x);
      }
    case .RELATIVE_PIXELS:
      constraints.width = zephr_ctx.window.size.x / zephr_ctx.screen_size.x * value;
    case .ASPECT_RATIO:
      constraints.width = constraints.height * value;
  }
}

set_height_constraint :: proc(constraints: ^UiConstraints, value: f32, type: UiConstraint) {
  switch (type) {
    case .FIXED:
      constraints.height = value;
    case .RELATIVE:
      if (constraints.parent != nil) {
        constraints.height = (value * constraints.parent.height);
      } else {
        constraints.height = (value * zephr_ctx.window.size.y);
      }
    case .RELATIVE_PIXELS:
      constraints.height = zephr_ctx.window.size.y / zephr_ctx.screen_size.y * value;
    case .ASPECT_RATIO:
      constraints.height = constraints.width * value;
  }
}

set_rotation_constraint :: proc(constraints: ^UiConstraints, angle_d: f32) {
  constraints.rotation = angle_d;
}

@private
apply_constraints :: proc(constraints: ^UiConstraints, pos: ^Vec2, size: ^Vec2) {
  pos^ = Vec2{constraints.x, constraints.y};
  size^ = Vec2{constraints.width, constraints.height};
}

@private
apply_alignment :: proc(align: Alignment, constraints: ^UiConstraints, size: Vec2, pos: ^Vec2) {
  // if we don't have a parent then we're a top level element and we should align against the window
  parent_size := Vec2{zephr_ctx.window.size.x, zephr_ctx.window.size.y};
  if (constraints.parent != nil) {
    parent_size = Vec2{constraints.parent.width, constraints.parent.height};
  }

  switch (align) {
    case .TOP_LEFT:
      pos.x = pos.x;
      pos.y = pos.y;
    case .TOP_CENTER:
      pos.x += parent_size.x / 2 - size.x / 2;
      pos.y = pos.y;
    case .TOP_RIGHT:
      pos.x += parent_size.x - size.x;
      pos.y = pos.y;
    case .BOTTOM_LEFT:
      pos.x = pos.x;
      pos.y += parent_size.y - size.y;
    case .BOTTOM_CENTER:
      pos.x += parent_size.x / 2 - size.x / 2;
      pos.y += parent_size.y - size.y;
    case .BOTTOM_RIGHT:
      pos.x += parent_size.x - size.x;
      pos.y += parent_size.y - size.y;
    case .LEFT_CENTER:
      pos.x = pos.x;
      pos.y += parent_size.y / 2 - size.y / 2;
    case .RIGHT_CENTER:
      pos.x += parent_size.x - size.x;
      pos.y += parent_size.y / 2 - size.y / 2;
    case .CENTER:
      pos.x += parent_size.x / 2 - size.x / 2;
      pos.y += parent_size.y / 2 - size.y / 2;
  }
}

@private
// TODO: make this handle rotated and scaled rects too
inside_rect :: proc(rect: Rect, point: Vec2) -> bool {
  return point.x >= rect.pos.x && point.x <= rect.pos.x + rect.size.x &&
         point.y >= rect.pos.y && point.y <= rect.pos.y + rect.size.y;
}

draw_quad :: proc(constraints: ^UiConstraints, style: UiStyle) {
  use_shader(ui_shader)

  set_vec4f(ui_shader, "aColor", cast(f32)style.bg_color.r / 255, cast(f32)style.bg_color.g / 255, cast(f32)style.bg_color.b / 255, cast(f32)style.bg_color.a / 255)
  set_float(ui_shader, "uiWidth", constraints.width)
  set_float(ui_shader, "uiHeight", constraints.height)
  set_float(ui_shader, "borderRadius", style.border_radius)
  set_mat4f(ui_shader, "projection", zephr_ctx.projection)

  rect: Rect = ---

  apply_constraints(constraints, &rect.pos, &rect.size)
  apply_alignment(style.align, constraints, rect.size, &rect.pos)

  // set the positions after applying alignment so children can use them
  constraints.x = rect.pos.x;
  constraints.y = rect.pos.y;

  model := identity();
  translate(&model, Vec3{-rect.size.x / 2, -rect.size.y / 2, 0});
  scale(&model, Vec3{constraints.scale.x, constraints.scale.y, 1});
  translate(&model, Vec3{rect.size.x / 2, rect.size.y / 2, 0});

  translate(&model, Vec3{-rect.size.x / 2, -rect.size.y / 2, 0});
  rotate(&model, constraints.rotation, Vec3{0, 0, 1});
  translate(&model, Vec3{rect.size.x / 2, rect.size.y / 2, 0});

  translate(&model, Vec3{rect.pos.x, rect.pos.y, 0});

  set_mat4f(ui_shader, "model", model);

  gl.BindVertexArray(ui_vao)

  vertices: [6][4]f32 = {
    // bottom left tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0,               0,               0.0, 0.0},
    {0 + rect.size.x, 0,               1.0, 0.0},

    // top right tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0 + rect.size.x, 0,               1.0, 0.0},
    {0 + rect.size.x, 0 + rect.size.y, 1.0, 1.0},
  };

  gl.BindBuffer(gl.ARRAY_BUFFER, ui_vbo);
  gl.BufferSubData(gl.ARRAY_BUFFER, 0, size_of(vertices), raw_data(&vertices));
  gl.BindBuffer(gl.ARRAY_BUFFER, 0);

  gl.DrawArrays(gl.TRIANGLES, 0, 6);

  gl.BindVertexArray(0);
}

draw_circle :: proc(constraints: ^UiConstraints, style: UiStyle) {
  radius: f32 = 0;

  if (constraints.width > constraints.height) {
    radius = constraints.height / 2;
  } else {
    radius = constraints.width / 2;
  }

  new_style := style;
  new_style.border_radius = radius;

  draw_quad(constraints, new_style);
}

draw_triangle :: proc(constraints: ^UiConstraints, style: UiStyle) {
  use_shader(ui_shader);

  set_vec4f(ui_shader, "aColor", cast(f32)style.bg_color.r / 255, cast(f32)style.bg_color.g / 255, cast(f32)style.bg_color.b / 255, cast(f32)style.bg_color.a / 255);
  set_float(ui_shader, "borderRadius", 0);
  set_mat4f(ui_shader, "projection", zephr_ctx.projection)

  rect: Rect = ---

  apply_constraints(constraints, &rect.pos, &rect.size);
  apply_alignment(style.align, constraints, rect.size, &rect.pos);

  // set the positions after applying alignment so children can use them
  constraints.x = rect.pos.x;
  constraints.y = rect.pos.y;

  model := identity();
  translate(&model, Vec3{-rect.size.x / 2, -rect.size.y / 2, 0});
  scale(&model, Vec3{constraints.scale.x, constraints.scale.y, 1});
  translate(&model, Vec3{rect.size.x / 2, rect.size.y / 2, 0});

  translate(&model, Vec3{-rect.size.x / 2, -rect.size.y / 2, 0});
  rotate(&model, constraints.rotation, Vec3{0, 0, 1});
  translate(&model, Vec3{rect.size.x / 2, rect.size.y / 2, 0});

  translate(&model, Vec3{rect.pos.x, rect.pos.y, 0});

  set_mat4f(ui_shader, "model", model);

  gl.BindVertexArray(ui_vao);

  vertices := [3][4]f32 {
    {0 + rect.size.x,     0,               0.0, 0.0},
    {0,                   0,               0.0, 0.0},
    {0 + rect.size.x / 2, 0 + rect.size.y, 0.0, 0.0},
  };

  gl.BindBuffer(gl.ARRAY_BUFFER, ui_vbo);
  gl.BufferSubData(gl.ARRAY_BUFFER, 0, size_of(vertices), raw_data(&vertices))
  gl.BindBuffer(gl.ARRAY_BUFFER, 0);

  gl.DrawArrays(gl.TRIANGLES, 0, 3);

  gl.BindVertexArray(0);
}

draw_texture :: proc(constraints: ^UiConstraints, texture_id: TextureId, color: Color, radius: f32, align: Alignment) {
  use_shader(ui_shader);

  set_vec4f(ui_shader, "aColor", cast(f32)color.r / 255, cast(f32)color.g / 255, cast(f32)color.b / 255, cast(f32)color.a / 255);
  set_float(ui_shader, "uiWidth", constraints.width);
  set_float(ui_shader, "uiHeight", constraints.height);
  set_float(ui_shader, "borderRadius", radius);
  set_bool(ui_shader, "hasTexture", true);

  set_mat4f(ui_shader, "projection", zephr_ctx.projection)

  rect: Rect = ---

  apply_constraints(constraints, &rect.pos, &rect.size);
  apply_alignment(align, constraints, rect.size, &rect.pos);

  // set the positions after applying alignment so children can use them
  constraints.x = rect.pos.x;
  constraints.y = rect.pos.y;

  model := identity();
  translate(&model, Vec3{-rect.size.x / 2, -rect.size.y / 2, 0});
  scale(&model, Vec3{constraints.scale.x, constraints.scale.y, 1});
  translate(&model, Vec3{rect.size.x / 2, rect.size.y / 2, 0});

  translate(&model, Vec3{-rect.size.x / 2, -rect.size.y / 2, 0});
  rotate(&model, constraints.rotation, Vec3{0, 0, 1});
  translate(&model, Vec3{rect.size.x / 2, rect.size.y / 2, 0});

  translate(&model, Vec3{rect.pos.x, rect.pos.y, 0});

  set_mat4f(ui_shader, "model", model)

  gl.BindVertexArray(ui_vao);

  vertices := [6][4]f32 {
    // bottom left tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0,               0,               0.0, 0.0},
    {0 + rect.size.x, 0,               1.0, 0.0},

    // top right tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0 + rect.size.x, 0,               1.0, 0.0},
    {0 + rect.size.x, 0 + rect.size.y, 1.0, 1.0},
  };

  gl.BindBuffer(gl.ARRAY_BUFFER, ui_vbo);
  gl.BufferSubData(gl.ARRAY_BUFFER, 0, size_of(vertices), raw_data(&vertices))
  gl.BindBuffer(gl.ARRAY_BUFFER, 0);

  gl.ActiveTexture(gl.TEXTURE0);
  gl.BindTexture(gl.TEXTURE_2D, texture_id);

  gl.DrawArrays(gl.TRIANGLES, 0, 6);

  gl.BindVertexArray(0);
  set_bool(ui_shader, "hasTexture", false);
}

draw_button :: proc(constraints: ^UiConstraints, text: string, style: UiStyle, state: ButtonState, caller := #caller_location) -> bool {
  line := caller.line
  line_bytes := mem.byte_slice(&line, size_of(line))
  hash := fnv_hash32(transmute([]byte)caller.file_path, cast(u32)len(caller.file_path), FNV_HASH32_INIT)
  hash = fnv_hash32(line_bytes, size_of(caller.line), hash)

  style := style
  rect: Rect = ---

  apply_constraints(constraints, &rect.pos, &rect.size);
  apply_alignment(style.align, constraints, rect.size, &rect.pos);

  is_hovered := inside_rect(rect, zephr_ctx.mouse.pos);
  is_held := zephr_ctx.ui.active_element == hash
  left_mouse_pressed := zephr_ctx.mouse.pressed && zephr_ctx.mouse.button == .BUTTON_LEFT;
  left_mouse_released := zephr_ctx.mouse.released && zephr_ctx.mouse.button == .BUTTON_LEFT;
  clicked := false;

  if (zephr_ctx.ui.active_element == 0) {
    if (is_hovered && left_mouse_pressed) {
      zephr_ctx.ui.active_element = hash;
    }
  } else if (zephr_ctx.ui.active_element == hash) {
    if (left_mouse_released) {
      zephr_ctx.ui.active_element = 0;

      if (is_hovered) {
        clicked = true;
      }
    }
  }

  if (is_hovered && state == .ACTIVE) {
    set_cursor(Cursor.HAND);

    if (is_held) {
      style.bg_color = mult_color(style.bg_color, 0.8);
      draw_quad(constraints, style);
    } else {
      style.bg_color = mult_color(style.bg_color, 0.9);
      draw_quad(constraints, style);
    }
  } else if (state == .DISABLED) {
    if (is_hovered) {
      set_cursor(Cursor.DISABLED);
    }

    style.bg_color.a = 100;
    style.fg_color.a = 100;
    draw_quad(constraints, style);
  } else {
    draw_quad(constraints, style);
  }

  if (text != "") {
    text_constraints := DEFAULT_UI_CONSTRAINTS

    set_parent_constraint(&text_constraints, constraints);
    set_x_constraint(&text_constraints, 0, .RELATIVE_PIXELS);
    set_y_constraint(&text_constraints, 0, .RELATIVE_PIXELS);
    set_width_constraint(&text_constraints, 1.0, .RELATIVE_PIXELS);

    font_size := ((constraints.width) / (text_constraints.width * 0.1 * 65));

    // TODO: need to adjust the font size based on the text height

    draw_text(text, cast(u32)font_size, text_constraints, style.fg_color, .CENTER);
  }

  if (clicked && state == .ACTIVE) {
    return true;
  }

  return false;
}

draw_icon_button :: proc(constraints: ^UiConstraints, icon_tex_id: TextureId, style: UiStyle, state: ButtonState, caller := #caller_location) -> bool {
  assert(icon_tex_id != 0, "draw_icon_button() requires that you provide an icon texture");

  line := caller.line
  line_bytes := mem.byte_slice(&line, size_of(line))
  hash := fnv_hash32(transmute([]byte)caller.file_path, cast(u32)len(caller.file_path), FNV_HASH32_INIT)
  hash = fnv_hash32(line_bytes, size_of(caller.line), hash)

  style := style
  rect: Rect = ---

  apply_constraints(constraints, &rect.pos, &rect.size);
  apply_alignment(style.align, constraints, rect.size, &rect.pos);

  is_held := zephr_ctx.ui.active_element == hash;
  is_hovered := inside_rect(rect, zephr_ctx.mouse.pos);
  left_mouse_pressed := zephr_ctx.mouse.pressed && zephr_ctx.mouse.button == .BUTTON_LEFT;
  left_mouse_released := zephr_ctx.mouse.released && zephr_ctx.mouse.button == .BUTTON_LEFT;
  clicked := false;

  if (zephr_ctx.ui.active_element == 0) {
    if (is_hovered && left_mouse_pressed) {
      zephr_ctx.ui.active_element = hash;
    }
  } else if (zephr_ctx.ui.active_element == hash) {
    if (left_mouse_released) {
      zephr_ctx.ui.active_element = 0;

      if (is_hovered) {
        clicked = true;
      }
    }
  }

  if (is_hovered && state == .ACTIVE) {
    set_cursor(.HAND);

    if (is_held) {
      style.bg_color = mult_color(style.bg_color, 0.8);
      style.fg_color = mult_color(style.fg_color, 0.8);
    } else {
      style.bg_color = mult_color(style.bg_color, 0.9);
      style.fg_color = mult_color(style.fg_color, 0.9);
    }
  } else if (state == .DISABLED) {
    if (is_hovered) {
      set_cursor(.DISABLED);
    }

    style.fg_color.a = 100;
    style.bg_color.a = 100;
  }

  draw_quad(constraints, style);

  icon_constraints := DEFAULT_UI_CONSTRAINTS

  set_parent_constraint(&icon_constraints, constraints);
  set_x_constraint(&icon_constraints, 0, .RELATIVE_PIXELS);
  set_y_constraint(&icon_constraints, 0, .RELATIVE_PIXELS);
  set_width_constraint(&icon_constraints, constraints.width * 0.8, .FIXED);
  set_height_constraint(&icon_constraints, constraints.height * 0.8, .FIXED);
  draw_texture(&icon_constraints, icon_tex_id, style.fg_color, 0, .CENTER);

  if (clicked && state == .ACTIVE) {
    return true;
  }

  return false;
}

@private
draw_color_picker_slider :: proc(constraints: ^UiConstraints, align: Alignment, caller := #caller_location) -> f32 {
  @static
  slider_selection: f32 = 0
  @static
  dragging := false

  line := caller.line
  line_bytes := mem.byte_slice(&line, size_of(line))
  hash := fnv_hash32(transmute([]byte)caller.file_path, cast(u32)len(caller.file_path), FNV_HASH32_INIT);
  hash = fnv_hash32(line_bytes, size_of(caller.line), hash);

  use_shader(color_chooser_shader);

  set_bool(color_chooser_shader, "isSlider", true);
  set_mat4f(color_chooser_shader, "projection", zephr_ctx.projection);

  rect: Rect = ---

  apply_constraints(constraints, &rect.pos, &rect.size);
  apply_alignment(align, constraints, rect.size, &rect.pos);

  // set the positions after applying alignment so children can use them
  constraints.x = rect.pos.x;
  constraints.y = rect.pos.y;

  is_hovered := inside_rect(rect, zephr_ctx.mouse.pos);
  left_mouse_pressed := zephr_ctx.mouse.pressed && zephr_ctx.mouse.button == .BUTTON_LEFT;
  left_mouse_released := zephr_ctx.mouse.released && zephr_ctx.mouse.button == .BUTTON_LEFT;

  if (zephr_ctx.ui.active_element == 0) {
    if (is_hovered && left_mouse_pressed) {
      zephr_ctx.ui.active_element = hash;
      dragging = true;
    }
  } else if (zephr_ctx.ui.active_element == hash) {
    if (left_mouse_released) {
      zephr_ctx.ui.active_element = 0;
      dragging = false;
    }
  }

  if (dragging) {
    slider_selection = clamp((zephr_ctx.mouse.pos.y - constraints.y) / constraints.height, 0, 1);
  }

  model := identity();
  translate(&model, Vec3{rect.pos.x, rect.pos.y, 0})

  set_mat4f(color_chooser_shader, "model", model);

  gl.BindVertexArray(ui_vao);

  vertices := [6][4]f32 {
    // bottom left tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0,               0,               0.0, 0.0},
    {0 + rect.size.x, 0,               1.0, 0.0},

    // top right tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0 + rect.size.x, 0,               1.0, 0.0},
    {0 + rect.size.x, 0 + rect.size.y, 1.0, 1.0},
  };

  gl.BindBuffer(gl.ARRAY_BUFFER, ui_vbo);
  gl.BufferSubData(gl.ARRAY_BUFFER, 0, size_of(vertices), raw_data(&vertices))
  gl.BindBuffer(gl.ARRAY_BUFFER, 0);

  gl.DrawArrays(gl.TRIANGLES, 0, 6);

  gl.BindVertexArray(0);
  set_bool(color_chooser_shader, "isSlider", false);

  // draw the selection
  triangle_con := DEFAULT_UI_CONSTRAINTS
  set_parent_constraint(&triangle_con, constraints);
  set_x_constraint(&triangle_con, -11, .RELATIVE_PIXELS);
  set_y_constraint(&triangle_con, slider_selection, .RELATIVE);
  set_rotation_constraint(&triangle_con, -90);
  set_width_constraint(&triangle_con, 14, .RELATIVE_PIXELS);
  set_height_constraint(&triangle_con, 0.5, .ASPECT_RATIO);
  triangle_con.y += -(triangle_con.height / 2);
  tri_style := UiStyle {
    bg_color = COLOR_BLACK,
    border_radius = 0,
    align = .TOP_LEFT,
  };
  draw_triangle(&triangle_con, tri_style);

  set_x_constraint(&triangle_con, 1, .RELATIVE);
  triangle_con.x -= triangle_con.height / 2;
  set_rotation_constraint(&triangle_con, 90);
  draw_triangle(&triangle_con, tri_style);

  return slider_selection;
}

@private
draw_color_picker_canvas :: proc(constraints: ^UiConstraints, slider_percentage: f32, align: Alignment, caller := #caller_location) -> Color {
  @static
  dragging := false;
  @static
  canvas_pos := Vec2{0, 0};

  line := caller.line
  line_bytes := mem.byte_slice(&line, size_of(line))
  hash := fnv_hash32(transmute([]byte)caller.file_path, cast(u32)len(caller.file_path), FNV_HASH32_INIT);
  hash = fnv_hash32(line_bytes, size_of(caller.line), hash);

  use_shader(color_chooser_shader);

  set_bool(color_chooser_shader, "isSlider", false);
  set_float(color_chooser_shader, "sliderPercentage", slider_percentage);
  set_mat4f(color_chooser_shader, "projection", zephr_ctx.projection);

  rect: Rect = ---

  apply_constraints(constraints, &rect.pos, &rect.size);
  apply_alignment(align, constraints, rect.size, &rect.pos);

  // set the positions after applying alignment so children can use them
  constraints.x = rect.pos.x;
  constraints.y = rect.pos.y;

  is_hovered := inside_rect(rect, zephr_ctx.mouse.pos);
  left_mouse_pressed := zephr_ctx.mouse.pressed && zephr_ctx.mouse.button == .BUTTON_LEFT;
  left_mouse_released := zephr_ctx.mouse.released && zephr_ctx.mouse.button == .BUTTON_LEFT;

  if (zephr_ctx.ui.active_element == 0) {
    if (is_hovered && left_mouse_pressed) {
      zephr_ctx.ui.active_element = hash;
      dragging = true;
    }
  } else if (zephr_ctx.ui.active_element == hash) {
    if (left_mouse_released) {
      zephr_ctx.ui.active_element = 0;
      dragging = false;
    }
  }

  if (dragging) {
    x := (zephr_ctx.mouse.pos.x - constraints.x) / constraints.width;
    y := (zephr_ctx.mouse.pos.y - constraints.y) / constraints.height;

    canvas_pos.x = clamp(x, 0, 1);
    canvas_pos.y = clamp(y, 0, 1);
  }

  model := identity();
  translate(&model, Vec3{rect.pos.x, rect.pos.y, 0});

  set_mat4f(color_chooser_shader, "model", model);

  gl.BindVertexArray(ui_vao);

  vertices := [6][4]f32 {
    // bottom left tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0,               0,                    0.0, 0.0},
    {0 + rect.size.x, 0,                    1.0, 0.0},

    // top right tri
    {0,               0 + rect.size.y, 0.0, 1.0},
    {0 + rect.size.x, 0,                    1.0, 0.0},
    {0 + rect.size.x, 0 + rect.size.y, 1.0, 1.0},
  };

  gl.BindBuffer(gl.ARRAY_BUFFER, ui_vbo);
  gl.BufferSubData(gl.ARRAY_BUFFER, 0, size_of(vertices), raw_data(&vertices))
  gl.BindBuffer(gl.ARRAY_BUFFER, 0);

  gl.DrawArrays(gl.TRIANGLES, 0, 6);

  gl.BindVertexArray(0);

  selected_color := hsv2rgb(slider_percentage * 360, canvas_pos.x, 1.0 - canvas_pos.y);

  // draw the selection
  triangle_con := DEFAULT_UI_CONSTRAINTS
  set_parent_constraint(&triangle_con, constraints);
  set_x_constraint(&triangle_con, canvas_pos.x, .RELATIVE);
  set_y_constraint(&triangle_con, canvas_pos.y, .RELATIVE);
  set_width_constraint(&triangle_con, 14, .RELATIVE_PIXELS);
  set_height_constraint(&triangle_con, 0.5, .ASPECT_RATIO);
  triangle_con.x -= triangle_con.height;
  triangle_con.y -= triangle_con.height + triangle_con.height / 2 + triangle_con.width / 2;
  set_rotation_constraint(&triangle_con, 0);
  tri_style := UiStyle {
    bg_color = determine_color_contrast(selected_color),
    border_radius = 0,
    align = .TOP_LEFT,
  };
  draw_triangle(&triangle_con, tri_style);

  triangle_con.x += triangle_con.height * 2;
  triangle_con.y += triangle_con.height * 2;
  set_rotation_constraint(&triangle_con, 90);
  draw_triangle(&triangle_con, tri_style);

  triangle_con.x -= triangle_con.height * 2;
  triangle_con.y += triangle_con.height * 2;
  set_rotation_constraint(&triangle_con, 180);
  draw_triangle(&triangle_con, tri_style);

  triangle_con.x -= triangle_con.height * 2;
  triangle_con.y -= triangle_con.height * 2;
  set_rotation_constraint(&triangle_con, 270);
  draw_triangle(&triangle_con, tri_style);

  return selected_color;
}

// TODO: consume mouse events on the popup
@private
draw_color_picker_popup :: proc(picker_button_con: ^UiConstraints) {
  popup_con := DEFAULT_UI_CONSTRAINTS
  set_parent_constraint(&popup_con, picker_button_con);
  set_x_constraint(&popup_con, 0, .FIXED);
  set_y_constraint(&popup_con, 1.4, .RELATIVE);
  set_width_constraint(&popup_con, 450, .RELATIVE_PIXELS);
  set_height_constraint(&popup_con, 480, .RELATIVE_PIXELS);
  popup_style := UiStyle {
    bg_color = mult_color(COLOR_WHITE, 0.94),
    border_radius = popup_con.width * 0.02,
    align = .TOP_LEFT,
  };
  draw_quad(&popup_con, popup_style);

  color_slider_con := DEFAULT_UI_CONSTRAINTS
  set_parent_constraint(&color_slider_con, &popup_con);
  set_x_constraint(&color_slider_con, -0.04, .RELATIVE);
  set_y_constraint(&color_slider_con, 0.05, .RELATIVE);
  set_height_constraint(&color_slider_con, 400 * 0.9, .RELATIVE_PIXELS);
  set_width_constraint(&color_slider_con, 0.1, .ASPECT_RATIO);
  slider_selection := draw_color_picker_slider(&color_slider_con, .TOP_RIGHT);

  set_x_constraint(&color_slider_con, 0.04, .RELATIVE);
  set_y_constraint(&color_slider_con, 0.05, .RELATIVE);
  set_width_constraint(&color_slider_con, popup_con.width * 0.8, .FIXED);
  selected_color := draw_color_picker_canvas(&color_slider_con, slider_selection, .TOP_LEFT);

  button_con := DEFAULT_UI_CONSTRAINTS
  set_parent_constraint(&button_con, &popup_con);
  set_x_constraint(&button_con, 0.04, .RELATIVE);
  set_y_constraint(&button_con, -0.05, .RELATIVE);
  set_width_constraint(&button_con, 0.43, .RELATIVE);
  set_height_constraint(&button_con, 0.3, .ASPECT_RATIO);
  button_style := UiStyle {
    bg_color = zephr_ctx.ui.popup_revert_color^,
    fg_color = determine_color_contrast(zephr_ctx.ui.popup_revert_color^),
    border_radius = 4,
    align = .BOTTOM_LEFT,
  }
  if (draw_button(&button_con, "Revert", button_style, .ACTIVE)) {
    zephr_ctx.ui.popup_open = false;
    zephr_ctx.ui.popup_parent_hash = 0;
  }

  button_style.align = .BOTTOM_RIGHT;
  button_style.fg_color = determine_color_contrast(selected_color);
  set_x_constraint(&button_con, -0.04, .RELATIVE);
  set_y_constraint(&button_con, -0.05, .RELATIVE);
  button_style.bg_color = selected_color;
  if (draw_button(&button_con, "Apply", button_style, .ACTIVE)) {
    zephr_ctx.ui.popup_revert_color^ = selected_color;
    zephr_ctx.ui.popup_open = false;
    zephr_ctx.ui.popup_parent_hash = 0;
  }

  rect := Rect {
    {popup_con.x, popup_con.y},
    {popup_con.width, popup_con.height},
  };

  zephr_ctx.ui.popup_rect = rect;
}

draw_color_picker :: proc(constraints: ^UiConstraints, color: ^Color, align: Alignment, state: ButtonState, id: u32 = 0, caller := #caller_location) {
  line := caller.line
  line_bytes := mem.byte_slice(&line, size_of(line))
  id := id
  id_bytes := mem.byte_slice(&id, size_of(id))
  hash := fnv_hash32(id_bytes, size_of(id), FNV_HASH32_INIT);
  hash = fnv_hash32(transmute([]byte)caller.file_path, cast(u32)len(caller.file_path), hash);
  hash = fnv_hash32(line_bytes, size_of(line), hash);

  rect: Rect = ---
  display_color := color^;

  con := constraints^;

  apply_constraints(&con, &rect.pos, &rect.size);
  apply_alignment(align, &con, rect.size, &rect.pos);

  is_held := zephr_ctx.ui.active_element == hash
  is_hovered := inside_rect(rect, zephr_ctx.mouse.pos);
  left_mouse_pressed := zephr_ctx.mouse.pressed && zephr_ctx.mouse.button == .BUTTON_LEFT;
  left_mouse_released := zephr_ctx.mouse.released && zephr_ctx.mouse.button == .BUTTON_LEFT;
  clicked := false;

  if (zephr_ctx.ui.active_element == 0) {
    if (is_hovered && left_mouse_pressed) {
      zephr_ctx.ui.active_element = hash;
    }
  } else if (zephr_ctx.ui.active_element == hash) {
    if (left_mouse_released) {
      zephr_ctx.ui.active_element = 0;

      if (is_hovered) {
        clicked = true;
      }
    }
  }

  if (is_hovered && state == .ACTIVE) {
    set_cursor(.HAND);
    con.scale.y *= 1.08;
    con.scale.x *= 1.08;

    if (is_held) {
      display_color = mult_color(display_color, 0.8);
    } else {
      display_color = mult_color(display_color, 0.9);
    }
  } else if (state == .DISABLED) {
    if (is_hovered) {
      set_cursor(.DISABLED);
    }

    display_color.a = 100;
  }

  style := UiStyle {
    bg_color = display_color,
    border_radius = con.width * 0.08,
    align = align,
  };
  draw_quad(&con, style);

  if (clicked && state == .ACTIVE) {
    zephr_ctx.ui.popup_open = true;
    zephr_ctx.ui.popup_parent_constraints = con;
    zephr_ctx.ui.popup_revert_color = color;
    zephr_ctx.ui.popup_parent_hash = hash;
  }

  if (zephr_ctx.ui.popup_parent_hash == hash) {
    zephr_ctx.ui.popup_open = true;
    zephr_ctx.ui.popup_parent_constraints = con;
  }

  /* if (is_hovered && state == BUTTON_STATE_ACTIVE && zephr_ctx->mouse.released && zephr_ctx->mouse.button == ZEPHR_MOUSE_BUTTON_LEFT) { */
  /*   return true; */
  /* } */

  /* return false; */
}