TailDemo.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
module Main where

#if !(MIN_VERSION_base(4,11,0))
import Data.Monoid ((<>))
#endif
import qualified Data.Text as T
import Control.Monad (void)
import Control.Concurrent
import Lens.Micro.TH
import Lens.Micro.Mtl
import System.Random

import Brick
import Brick.BChan
import Brick.Widgets.Border
import qualified Graphics.Vty as V

data AppState =
    AppState { _textAreaHeight :: Int
             , _textAreaWidth :: Int
             , _textAreaContents :: [T.Text]
             }

makeLenses ''AppState

draw :: AppState -> Widget n
draw st =
    header st <=> box st

header :: AppState -> Widget n
header st =
    padBottom (Pad 1) $
    hBox [ padRight (Pad 7) $
           (str $ "Max width: " <> show (_textAreaWidth st)) <=>
           (str "Left(-)/Right(+)")
         , (str $ "Max height: " <> show (_textAreaHeight st)) <=>
           (str "Down(-)/Up(+)")
         ]

box :: AppState -> Widget n
box st =
    border $
    hLimit (_textAreaWidth st) $
    vLimit (_textAreaHeight st) $
    (renderBottomUp (txtWrap <$> _textAreaContents st))

-- | Given a list of widgets, draw them bottom-up in a vertical
-- arrangement, i.e., the first widget in this list will appear at the
-- bottom of the rendering area. Rendering stops when the rendering area
-- is full, i.e., items that cannot be rendered are never evaluated or
-- drawn.
renderBottomUp :: [Widget n] -> Widget n
renderBottomUp ws =
    Widget Greedy Greedy $ do
        let go _ [] = return V.emptyImage
            go remainingHeight (c:cs) = do
                cResult <- render c
                let img = image cResult
                    newRemainingHeight = remainingHeight - V.imageHeight img
                if newRemainingHeight == 0
                   then return img
                   else if newRemainingHeight < 0
                        then return $ V.cropTop remainingHeight img
                        else do
                            rest <- go newRemainingHeight cs
                            return $ V.vertCat [rest, img]

        ctx <- getContext
        img <- go (availHeight ctx) ws
        render $ fill ' ' <=> raw img

textLines :: [T.Text]
textLines =
    [ "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut"
    , "labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco"
    , "laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit"
    , "in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat"
    , "cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
    ]

handleEvent :: BrickEvent n CustomEvent -> EventM n AppState ()
handleEvent (AppEvent (NewLine l)) =
    textAreaContents %= (l :)
handleEvent (VtyEvent (V.EvKey V.KUp [])) =
    textAreaHeight %= (+ 1)
handleEvent (VtyEvent (V.EvKey V.KDown [])) =
    textAreaHeight %= max 0 . subtract 1
handleEvent (VtyEvent (V.EvKey V.KRight [])) =
    textAreaWidth %= (+ 1)
handleEvent (VtyEvent (V.EvKey V.KLeft [])) =
    textAreaWidth %= max 0 . subtract 1
handleEvent (VtyEvent (V.EvKey V.KEsc [])) =
    halt
handleEvent _ =
    return ()

data CustomEvent =
    NewLine T.Text

app :: App AppState CustomEvent ()
app =
    App { appDraw = (:[]) . draw
        , appChooseCursor = neverShowCursor
        , appHandleEvent = handleEvent
        , appAttrMap = const $ attrMap V.defAttr []
        , appStartEvent = return ()
        }

initialState :: AppState
initialState =
    AppState { _textAreaHeight = 20
             , _textAreaWidth = 40
             , _textAreaContents = []
             }

-- | Run forever, generating new lines of text for the application
-- window, prefixed with a line number. This function simulates the kind
-- of behavior that you'd get from running 'tail -f' on a file.
generateLines :: BChan CustomEvent -> IO ()
generateLines chan = go (1::Integer)
    where
        go lineNum = do
            -- Wait a random amount of time (in milliseconds)
            let delayOptions = [500, 1000, 2000]
            delay <- randomVal delayOptions
            threadDelay $ delay * 1000

            -- Choose a random line of text from our collection
            l <- randomVal textLines

            -- Send it to the application to be added to the UI
            writeBChan chan $ NewLine $ (T.pack $ "Line " <> show lineNum <> " - ") <> l

            go $ lineNum + 1

randomVal :: [a] -> IO a
randomVal as = do
    idx <- randomRIO (0, length as - 1)
    return $ as !! idx

main :: IO ()
main = do
    chan <- newBChan 10

    -- Run thread to simulate incoming data
    void $ forkIO $ generateLines chan

    (_, vty) <- customMainWithDefaultVty (Just chan) app initialState
    V.shutdown vty