{-|
Module      : Monomer.Widgets.Containers.ThemeSwitch
Copyright   : (c) 2018 Francisco Vallarino
License     : BSD-3-Clause (see the LICENSE file)
Maintainer  : fjvallarino@gmail.com
Stability   : experimental
Portability : non-portable

Switches to the provided theme for its child nodes.

@
theme = case activeTheme of
  DarkTheme -> darkTheme
  LightTheme -> lightTheme

widgetTree = themeSwitch theme $ vstack [
    hstack [
      label "Select theme:",
      spacer,
      textDropdownS activeTheme [DarkTheme, LightTheme]
    ]
  ]
@

Note: this widget ignores style settings applied to itself. If you need to
display borders or any other kind of style configuration, set it on the child
node or wrap the themeSwitch widget in a "Monomer.Widgets.Containers.Box".
-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE StrictData #-}

module Monomer.Widgets.Containers.ThemeSwitch (
  -- * Configuration
  ThemeSwitchCfg,
  themeClearBg,
  themeClearBg_,
  -- * Constructors
  themeSwitch,
  themeSwitch_
) where

import Control.Applicative ((<|>))
import Control.Monad (when)
import Control.Lens ((&), (^.), (.~), (%~), at)
import Data.Default
import Data.Maybe

import qualified Data.Sequence as Seq

import Monomer.Widgets.Container

import qualified Monomer.Lens as L

{-|
Configuration options for themeSwitch:

- 'themeClearBg': indicates the clear color of the theme should be applied
  before rendering children. Defaults to False.
-}
newtype ThemeSwitchCfg = ThemeSwitchCfg {
  _tmcClearBg :: Maybe Bool
} deriving (Eq, Show)


instance Default ThemeSwitchCfg where
  def = ThemeSwitchCfg {
    _tmcClearBg = Nothing
  }

instance Semigroup ThemeSwitchCfg where
  (<>) s1 s2 = ThemeSwitchCfg {
    _tmcClearBg = _tmcClearBg s2 <|> _tmcClearBg s1
  }

instance Monoid ThemeSwitchCfg where
  mempty = def

-- | Indicates the clear color should be applied before rendering children.
themeClearBg :: ThemeSwitchCfg
themeClearBg = themeClearBg_ True

-- | Sets whether the clear color should be applied before rendering children.
themeClearBg_ :: Bool -> ThemeSwitchCfg
themeClearBg_ clear = def {
  _tmcClearBg = Just clear
}

data ThemeSwitchState = ThemeSwitchState {
  _tssPrevTheme :: Maybe Theme,
  _tssChanged :: Bool
}

-- | Switches to a new theme starting from its child node.
themeSwitch :: Theme -> WidgetNode s e -> WidgetNode s e
themeSwitch theme managed = themeSwitch_ theme def managed

-- | Switches to a new theme starting from its child node. Accepts config.
themeSwitch_ :: Theme -> [ThemeSwitchCfg] -> WidgetNode s e -> WidgetNode s e
themeSwitch_ theme configs managed = makeNode widget managed where
  config = mconcat configs
  state = ThemeSwitchState Nothing False
  widget = makeThemeSwitch theme config state

makeNode :: Widget s e -> WidgetNode s e -> WidgetNode s e
makeNode widget managedWidget = defaultWidgetNode "themeSwitch" widget
  & L.info . L.focusable .~ False
  & L.children .~ Seq.singleton managedWidget

makeThemeSwitch :: Theme -> ThemeSwitchCfg -> ThemeSwitchState -> Widget s e
makeThemeSwitch theme config state = widget where
  widget = createContainer state def {
    containerUpdateCWenv = updateCWenv,
    containerGetCurrentStyle = getCurrentStyle,
    containerInit = init,
    containerMerge = merge
  }

  updateCWenv wenv cidx cnode node = newWenv where
    oldTheme = _tssPrevTheme state
    -- When called during merge, the state has not yet been updated
    themeChanged = _tssChanged state || Just theme /= oldTheme
    parentChanged = wenv ^. L.themeChanged
    newWenv = wenv
      & L.theme .~ theme
      & L.themeChanged .~ (themeChanged || parentChanged)

  getCurrentStyle wenv node = style where
    clearBg = _tmcClearBg config == Just True
    clearColor = theme ^. L.clearColor
    style
      | clearBg = bgColor clearColor
      | otherwise = def

  init wenv node = resultNode newNode where
    newState = ThemeSwitchState (Just theme) False
    newNode = node
      & L.widget .~ makeThemeSwitch theme config newState

  merge wenv node oldNode oldState = resultNode newNode where
    oldTheme = _tssPrevTheme oldState
    newState = ThemeSwitchState (Just theme) (Just theme /= oldTheme)
    newNode = node
      & L.widget .~ makeThemeSwitch theme config newState