Edit.hs

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
-- | This module provides a basic text editor widget. You'll need to
-- embed an 'Editor' in your application state and transform it with
-- 'handleEditorEvent' when relevant events arrive. To get the contents
-- of the editor, just use 'getEditContents'. To modify it, use the
-- 'Z.TextZipper' interface with 'applyEdit'.
--
-- The editor's 'handleEditorEvent' function handles a set of basic
-- input events that should suffice for most purposes; see the source
-- for a complete list.
--
-- Bear in mind that the editor provided by this module is intended to
-- provide basic input support for brick applications but it is not
-- intended to be a replacement for your favorite editor such as Vim or
-- Emacs. It is also not suitable for building sophisticated editors. If
-- you want to build your own editor, I suggest starting from scratch.
module Brick.Widgets.Edit
  ( Editor(editContents, editorName)
  -- * Constructing an editor
  , editor
  , editorText
  -- * Reading editor contents
  , getEditContents
  -- * Handling events
  , handleEditorEvent
  -- * Editing text
  , applyEdit
  -- * Lenses for working with editors
  , editContentsL
  -- * Rendering editors
  , renderEditor
  -- * Attributes
  , editAttr
  , editFocusedAttr
  )
where

import Data.Monoid
import Lens.Micro
import Graphics.Vty (Event(..), Key(..), Modifier(..))

import qualified Data.Text as T
import qualified Data.Text.Zipper as Z hiding ( textZipper )
import qualified Data.Text.Zipper.Generic as Z

import Brick.Types
import Brick.Widgets.Core
import Brick.AttrMap

-- | Editor state.  Editors support the following events by default:
--
-- * Ctrl-a: go to beginning of line
-- * Ctrl-e: go to end of line
-- * Ctrl-d, Del: delete character at cursor position
-- * Backspace: delete character prior to cursor position
-- * Ctrl-k: delete all from cursor to end of line
-- * Ctrl-u: delete all from cursor to beginning of line
-- * Arrow keys: move cursor
-- * Enter: break the current line at the cursor position
data Editor t n =
    Editor { editContents :: Z.TextZipper t
           -- ^ The contents of the editor
           , editorName :: n
           -- ^ The name of the editor
           }

suffixLenses ''Editor

instance (Show t, Show n) => Show (Editor t n) where
    show e =
        concat [ "Editor { "
               , "editContents = " <> show (editContents e)
               , ", editorName = " <> show (editorName e)
               , "}"
               ]

instance Named (Editor t n) n where
    getName = editorName

handleEditorEvent :: (Eq t, Monoid t) => Event -> Editor t n -> EventM n (Editor t n)
handleEditorEvent e ed =
        let f = case e of
                  EvKey (KChar 'a') [MCtrl] -> Z.gotoBOL
                  EvKey (KChar 'e') [MCtrl] -> Z.gotoEOL
                  EvKey (KChar 'd') [MCtrl] -> Z.deleteChar
                  EvKey (KChar 'k') [MCtrl] -> Z.killToEOL
                  EvKey (KChar 'u') [MCtrl] -> Z.killToBOL
                  EvKey KEnter [] -> Z.breakLine
                  EvKey KDel [] -> Z.deleteChar
                  EvKey (KChar c) [] | c /= '\t' -> Z.insertChar c
                  EvKey KUp [] -> Z.moveUp
                  EvKey KDown [] -> Z.moveDown
                  EvKey KLeft [] -> Z.moveLeft
                  EvKey KRight [] -> Z.moveRight
                  EvKey KBS [] -> Z.deletePrevChar
                  _ -> id
        in return $ applyEdit f ed

-- | Construct an editor over 'Text' values
editorText :: n
       -- ^ The editor's name (must be unique)
       -> Maybe Int
       -- ^ The limit on the number of lines in the editor ('Nothing'
       -- means no limit)
       -> T.Text
       -- ^ The initial content
       -> Editor T.Text n
editorText = editor

-- | Construct an editor over 'String' values
editor :: Z.GenericTextZipper a
       => n
       -- ^ The editor's name (must be unique)
       -> Maybe Int
       -- ^ The limit on the number of lines in the editor ('Nothing'
       -- means no limit)
       -> a
       -- ^ The initial content
       -> Editor a n
editor name limit s = Editor (Z.textZipper (Z.lines s) limit) name

-- | Apply an editing operation to the editor's contents. Bear in mind
-- that you should only apply zipper operations that operate on the
-- current line; the editor will only ever render the first line of
-- text.
applyEdit :: (Z.TextZipper t -> Z.TextZipper t)
          -- ^ The 'Data.Text.Zipper' editing transformation to apply
          -> Editor t n
          -> Editor t n
applyEdit f e = e & editContentsL %~ f

-- | The attribute assigned to the editor when it does not have focus.
editAttr :: AttrName
editAttr = "edit"

-- | The attribute assigned to the editor when it has focus. Extends
-- 'editAttr'.
editFocusedAttr :: AttrName
editFocusedAttr = editAttr <> "focused"

-- | Get the contents of the editor.
getEditContents :: Monoid t => Editor t n -> [t]
getEditContents e = Z.getText $ e^.editContentsL

-- | Turn an editor state value into a widget. This uses the editor's
-- name for its scrollable viewport handle and the name is also used to
-- report mouse events.
renderEditor :: (Ord n, Show n, Monoid t, TextWidth t, Z.GenericTextZipper t)
             => ([t] -> Widget n)
             -- ^ The content drawing function
             -> Bool
             -- ^ Whether the editor has focus. It will report a cursor
             -- position if and only if it has focus.
             -> Editor t n
             -- ^ The editor.
             -> Widget n
renderEditor draw foc e =
    let cp = Z.cursorPosition z
        z = e^.editContentsL
        toLeft = Z.take (cp^._2) (Z.currentLine z)
        cursorLoc = Location (textWidth toLeft, cp^._1)
        limit = case e^.editContentsL.to Z.getLineLimit of
            Nothing -> id
            Just lim -> vLimit lim
        atChar = charAtCursor $ e^.editContentsL
        atCharWidth = maybe 1 textWidth atChar
    in withAttr (if foc then editFocusedAttr else editAttr) $
       limit $
       viewport (e^.editorNameL) Both $
       clickable (e^.editorNameL) $
       (if foc then showCursor (e^.editorNameL) cursorLoc else id) $
       visibleRegion cursorLoc (atCharWidth, 1) $
       draw $
       getEditContents e

charAtCursor :: (Z.GenericTextZipper t) => Z.TextZipper t -> Maybe t
charAtCursor z =
    let col = snd $ Z.cursorPosition z
        curLine = Z.currentLine z
        toRight = Z.drop col curLine
    in if Z.length toRight > 0
       then Just $ Z.take 1 toRight
       else Nothing