-- -----------------------------------------------------------------------
--
-- $Source: /repository/uni/htk/components/Index.hs,v $
--
-- HTk - a GUI toolkit for Haskell  -  (c) Universitaet Bremen
--
-- $Revision: 1.5 $ from $Date: 2002/01/07 21:14:12 $  
-- Last modification by $Author: ludi $
--
-- -----------------------------------------------------------------------

---
-- This module exports basic types and classes on index positions, e.g.
-- inside an editor or entry widget.
module Index (

  EndOfText(..),
  HasIndex(..),

  BaseIndex(..),
  Pixels(..),
  First(..),
  Last(..),

) where

import Core
import Geometry
import ExtendedPrelude
import Char


-- -----------------------------------------------------------------------
-- HasIndex
-- -----------------------------------------------------------------------

---
-- Internal.
class HasIndex w i b where
---
-- Internal.
  getBaseIndex :: w -> i -> IO b


-- -----------------------------------------------------------------------
-- Index: End of text
-- -----------------------------------------------------------------------

---
-- The <code>EndOfText</code> datatype - a handle indexing the last
-- position inside the concerned widget.
data EndOfText = EndOfText deriving Eq

---
-- Internal.
instance Show EndOfText where
---
-- Internal.
  showsPrec d _ r = "end" ++ r 

---
-- Internal.
instance Read EndOfText where
---
-- Internal.
  readsPrec p str = 
    case str of ('e':'n':'d':xs) -> [(EndOfText,xs)]
                _ -> []

---
-- Internal.
instance GUIValue EndOfText where
---
-- Internal.
  cdefault = EndOfText


-- -----------------------------------------------------------------------
-- Index: Pixels i.e. @x,y for listbox and text widgets
-- -----------------------------------------------------------------------

---
-- The <code>Pixels</code> datatype - a handle indexing a position inside
-- a widget with its coordinates.
data Pixels = Pixels Distance Distance

---
-- Internal.
instance Show Pixels where
---
-- Internal.
   showsPrec d (Pixels x y) r = "@" ++ show x ++ "," ++ show y ++ r


-- -----------------------------------------------------------------------
-- Index: First, for entry and text widgets
-- -----------------------------------------------------------------------

---
-- The <code>First</code> datatype - a handle indexing the first entry
-- e.g. inside a listbox.
data First = First 

---
-- Internal.
instance Show First where
---
-- Internal.
   showsPrec d _ r = "first" ++ r
        

-- -----------------------------------------------------------------------
-- Index: Last, for entry and text widgets
-- -----------------------------------------------------------------------

---
-- The <code>Last</code> datatype - a handle indexing the last entry
-- e.g. inside a listbox.
data Last = Last 

---
-- Internal.
instance Show Last where
---
-- Internal.
   showsPrec d _ r = "first" ++ r
        

-- -----------------------------------------------------------------------
-- BaseIndex
-- -----------------------------------------------------------------------

---
-- The <code>BaseIndex</code> datatype - an index handle specified by
-- an index number, an index position (line, char) or an index text (see
-- text marks).
data BaseIndex =
          IndexNo Int                   --' entries, listboxes
        | IndexPos Position             --' text widgets
        | IndexText String              --' listboxes, "end" etc.

---
-- Internal.
instance GUIValue BaseIndex where
---
-- Internal.
  cdefault = IndexNo 0

---
-- Internal.
instance Show BaseIndex where
---
-- Internal.
   showsPrec d c r = cshow c ++ r where
        cshow (IndexNo i) = show i
        cshow (IndexPos (x,y)) = show x ++ "." ++ show y
        cshow (IndexText s) = s

---
-- Internal.
instance Read BaseIndex where
---
-- Internal.
    readsPrec p str = [(cread str,[])] where
        cread (s @ (x:l)) | isDigit x =
                case map read (split (== '.') s) of
                        [Distance i] -> IndexNo i
                        [x,y] -> IndexPos (x,y)
                        _ -> error "illegal index specification"
        cread s = IndexText s