local ui = {}

---@alias UiHandler fun(id: NodeId, x?: integer, y?: integer)

---@class UiSpec
---@field [integer] NodeId Child nodes.
---@field w? number|"fill"|"auto"
---@field h? number|"fill"|"auto"
---@field pad? number
---@field gap? number
---@field align? "start"|"center"|"end"|"stretch"
---@field justify? "start"|"center"|"end"|"between"
---@field row? boolean
---@field at? table
---@field capture? boolean
---@field label? string
---@field font? GuiFont
---@field style? GuiTextStyle
---@field fit? integer Maximum label width.
---@field background? GuiColor
---@field face? GuiColor
---@field pressedFace? GuiColor
---@field pressedColor? GuiColor
---@field focusColor? GuiColor
---@field focusWidth? integer
---@field textStyle? GuiTextStyle
---@field on_enter? UiHandler
---@field on_exit? UiHandler
---@field on_click? UiHandler
---@field paint? fun(id: NodeId, x: integer, y: integer, w: integer, h: integer)

---@class UiConfirmSpec
---@field title string
---@field message? string
---@field ok? string
---@field cancel? string|false
---@field w? number
---@field background? GuiColor
---@field border? GuiColor
---@field on_ok? UiHandler
---@field on_cancel? UiHandler
---@field on_outside? UiHandler

local THEME_PATH = "/.lua/theme"
local THEMES = {
  light = {background = {255, 255, 255}, color = {0, 0, 0}, accent = {0, 120, 255}, radius = 6},
  dark = {background = {18, 18, 20}, color = {235, 235, 235}, accent = {166, 118, 255}, radius = 6},
  mono = {background = {255, 255, 255}, color = {0, 0, 0}, accent = {0, 0, 0}, radius = 0},
}

local enterHandlers, exitHandlers, clickHandlers, painters = {}, {}, {}, {}
local laidOut = false
local themeName
local activeScreen
local applyPalette

local function mix(a, b, amount)
  local out = {}
  for i = 1, 3 do out[i] = math.floor(a[i] + (b[i] - a[i]) * amount + 0.5) end
  return out
end

local function color(rgb)
  return gui.color(rgb[1], rgb[2], rgb[3])
end

local function palette(seed)
  local background, foreground, accent = seed.background, seed.color, seed.accent
  return {
    background = color(background),
    color = color(foreground),
    muted = color(mix(foreground, background, 0.45)),
    accent = color(accent),
    face = color(mix(background, foreground, 0.08)),
    pressedFace = color(accent),
    pressedColor = color(background),
    focusColor = color(accent),
    focusWidth = 2,
    radius = seed.radius,
  }
end

local function loadTheme(name)
  themeName = THEMES[name] and name or "light"
  ui.theme = palette(THEMES[themeName])
end

---@return string
function ui.getTheme()
  return themeName
end

---@return string[]
function ui.themeNames()
  local names = {}
  for name in pairs(THEMES) do names[#names + 1] = name end
  table.sort(names)
  return names
end

---@param name string
---@return true? ok
---@return string? error
function ui.setTheme(name)
  if not THEMES[name] then return nil, "Unknown theme" end
  local ok, err = fs.writeFile(THEME_PATH, name)
  if not ok then return nil, err end
  loadTheme(name)
  if activeScreen then
    applyPalette(activeScreen.root)
    gui.clear(ui.theme.background)
    node.invalidate(activeScreen.root)
  end
  return true
end

local savedTheme = fs.readFile(THEME_PATH, 32)
loadTheme(savedTheme and savedTheme:match("^%s*(.-)%s*$") or "light")

local function clearState()
  enterHandlers, exitHandlers, clickHandlers, painters = {}, {}, {}, {}
end

node.setPainter(function(id, x, y, w, h)
  local painter = painters[id]
  if painter then painter(id, x, y, w, h) end
end)

local STYLE_KEYS = {
  "color", "fill", "border", "face", "pressedFace", "pressedColor",
  "focusColor", "focusWidth", "radius", "font", "textStyle",
}

local function applyStyle(id, spec)
  local style, hasStyle = {}, false
  for _, key in ipairs(STYLE_KEYS) do
    if spec[key] ~= nil then
      style[key], hasStyle = spec[key], true
    end
  end
  if spec.background ~= nil then
    style.background, style.fill, hasStyle = spec.background, spec.background, true
  end
  if hasStyle then node.setStyle(id, style) end
end

local function build(spec, kind)
  spec = spec or {}
  if laidOut then ui.reset() end

  local children = {}
  for index, child in ipairs(spec) do
    children[index] = child
    spec[index] = nil
  end

  spec.type = kind
  spec.interactive = spec.on_enter ~= nil or spec.on_exit ~= nil or spec.on_click ~= nil
  local id = node.create(nil, spec)
  for _, child in ipairs(children) do node.attach(id, child) end

  applyStyle(id, spec)
  enterHandlers[id] = spec.on_enter
  exitHandlers[id] = spec.on_exit
  clickHandlers[id] = spec.on_click
  painters[id] = spec.paint
  return id
end

---@param spec UiSpec
---@return NodeId
function ui.box(spec)
  return build(spec, "box")
end

---Side length for a grid of square cards that fits the frame, and the column count that
---produced it. Landscape gets a wider grid, so the same screen reflows on rotation.
---@param count integer Cards to place.
---@param pad integer Padding outside the grid.
---@param gap integer Gap between cards.
---@param reserve? integer Height to leave free below the grid.
---@return integer side
---@return integer columns
function ui.cardSide(count, pad, gap, reserve)
  local columns = gui.getWidth() >= gui.getHeight() and 4 or 3
  local rows = math.ceil(count / columns)
  local byWidth = (gui.getWidth() - 2 * pad - (columns - 1) * gap) // columns
  local byHeight = (gui.getHeight() - 2 * pad - (reserve or 0) - (rows - 1) * gap) // rows
  return math.min(byWidth, byHeight), columns
end

---@param spec UiSpec
---@return NodeId
function ui.spacer(spec)
  spec = spec or {}
  return build({w = spec.w, h = spec.h}, "box")
end

---@param text string
---@param spec? UiSpec
---@return NodeId
function ui.text(text, spec)
  spec = spec or {}
  spec.label = text
  spec.textStyle, spec.style = spec.style, nil
  return build(spec, "text")
end

---@param text string
---@param spec? UiSpec
---@return NodeId
function ui.label(text, spec)
  spec = spec or {}
  local font, style = spec.font or gui.FONT_UI, spec.style or gui.STYLE_NORMAL
  if spec.fit and gui.getTextWidth(font, text, style) > spec.fit then
    while #text > 1 and gui.getTextWidth(font, text .. "~", style) > spec.fit do
      text = text:sub(1, -2)
    end
    text = text .. "~"
  end
  spec.w = gui.getTextWidth(font, text, style)
  spec.h = gui.getFontHeight(font, style)
  spec.font, spec.fit = font, nil
  return ui.text(text, spec)
end

---@param spec UiSpec
---@return NodeId
function ui.button(spec)
  spec = spec or {}
  spec.pad = spec.pad or 8
  spec.align = spec.align or "center"
  local label, font = spec.label, spec.font
  spec.label = nil
  local id = build(spec, "button")
  if label then node.create(id, {type = "text", label = label, font = font or gui.FONT_UI}) end
  return id
end

---@param spec UiSpec
---@return NodeId
function ui.custom(spec)
  return build(spec, "custom")
end

---@param id NodeId
---@param text string
function ui.setText(id, text)
  if node.getLabel(id) == text then return end
  node.setLabel(id, text)
  node.invalidate(id)
end

---@param id NodeId
function ui.invalidate(id)
  node.invalidate(id)
end

---@param spec UiConfirmSpec
---@return NodeId
function ui.confirm(spec)
  local card = {
    w = spec.w or 0.85,
    pad = 16,
    gap = 12,
    background = spec.background or ui.theme.background,
    border = spec.border or ui.theme.muted,
    ui.text(spec.title),
  }
  if spec.message then card[#card + 1] = ui.text(spec.message, {color = ui.theme.muted}) end

  local buttons = {row = true, gap = 8, justify = "end"}
  if spec.cancel ~= false then
    buttons[#buttons + 1] = ui.button{label = spec.cancel or "cancel", on_click = spec.on_cancel}
  end
  buttons[#buttons + 1] = ui.button{label = spec.ok or "ok", on_click = spec.on_ok}
  card[#card + 1] = ui.box(buttons)

  return ui.box{
    at = {x = 0, y = 0}, w = "fill", h = "fill", capture = true,
    align = "center", justify = "center", on_click = spec.on_outside,
    ui.box(card),
  }
end

function ui.reset()
  node.reset()
  clearState()
  laidOut = false
  activeScreen = nil
end

---@class UiScreen
local Screen = {}
Screen.__index = Screen

applyPalette = function(root)
  node.setStyle(root, {
    color = ui.theme.color,
    background = ui.theme.background,
    border = ui.theme.muted,
    face = ui.theme.face,
    pressedFace = ui.theme.pressedFace,
    pressedColor = ui.theme.pressedColor,
    focusColor = ui.theme.focusColor,
    focusWidth = ui.theme.focusWidth,
    radius = ui.theme.radius,
    font = gui.FONT_UI,
  })
end

---@param root NodeId
---@param style? NodeStyle
---@return UiScreen
function ui.screen(root, style)
  node.setSize(root, "fill", "fill")
  applyPalette(root)
  if style then node.setStyle(root, style) end
  local screen = setmetatable({root = root}, Screen)
  activeScreen = screen
  screen:relayout()
  return screen
end

function Screen:relayout()
  local ok, err = node.layout(self.root, 0, 0, gui.getWidth(), gui.getHeight())
  if not ok then error(err, 2) end
  node.dropScratch()
  laidOut = true
  gui.clear(ui.theme.background)
end

function Screen:draw()
  node.draw(self.root)
end

local function inside(id, x, y)
  local rx, ry, rw, rh = node.getRect(id)
  return x >= rx and x < rx + rw and y >= ry and y < ry + rh
end

local function enter(id, x, y)
  node.setPressed(id, true)
  local handler = enterHandlers[id]
  if handler then handler(id, x, y) end
end

local function exit(id, x, y)
  node.setPressed(id, false)
  local handler = exitHandlers[id]
  if handler then handler(id, x, y) end
end

---@param x integer
---@param y integer
---@return boolean handled
function Screen:down(x, y)
  local focused = node.getFocus()
  if focused then
    node.setFocus(nil)
    local handler = exitHandlers[focused]
    if handler then handler(focused) end
  end

  local target = node.hit(self.root, x, y)
  if not target then return false end
  self.captured, self.inside = target, true
  enter(target, x, y)
  return true
end

---@param x integer
---@param y integer
---@return boolean handled
function Screen:move(x, y)
  local target = self.captured
  if not target then return false end
  local isInside = inside(target, x, y)
  if isInside ~= self.inside then
    self.inside = isInside
    if isInside then enter(target, x, y) else exit(target, x, y) end
  end
  return true
end

---@param x integer
---@param y integer
---@return boolean handled
function Screen:up(x, y)
  local target = self.captured
  if not target then return false end
  local wasActive = self.inside
  local releasedInside = inside(target, x, y)
  local handler = releasedInside and clickHandlers[target] or nil
  self.captured, self.inside = nil, nil
  if wasActive then exit(target, x, y) end
  if handler then handler(target, x, y) end
  return true
end

local DIRECTIONS = {up = true, down = true, left = true, right = true}

local function focusFirst(screen)
  local focused = node.focusFirst(screen.root)
  if focused then
    local handler = enterHandlers[focused]
    if handler then handler(focused) end
  end
  return focused
end

---@param name string Button name; directions and confirm are handled.
---@param pressed boolean
---@return boolean handled
function Screen:button(name, pressed)
  if type(pressed) ~= "boolean" then error("button state must be boolean", 2) end

  if DIRECTIONS[name] then
    if not pressed then return true end
    local previous = node.getFocus()
    if not previous then
      focusFirst(self)
      return true
    end
    local focused = node.moveFocus(self.root, name)
    if focused ~= previous then
      local leave = exitHandlers[previous]
      if leave then leave(previous) end
      local arrive = enterHandlers[focused]
      if arrive then arrive(focused) end
    end
    return true
  end

  if name ~= "confirm" then return false end
  local focused = node.getFocus() or focusFirst(self)
  if not focused then return false end
  if pressed then
    node.setPressed(focused, true)
    self.confirming = focused
  else
    local target = self.confirming
    self.confirming = nil
    if target then
      node.setPressed(target, false)
      local handler = clickHandlers[target]
      if handler then handler(target) end
    end
  end
  return true
end

return ui