    {- arch-tag: List utilities main file
    Copyright (C) 2004-2006 John Goerzen <jgoerzen@complete.org>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
    -}

    {- |
       Module     : Data.List.Utils
       Copyright  : Copyright (C) 2004-2006 John Goerzen
       License    : GNU GPL, version 2 or above

       Maintainer : John Goerzen <jgoerzen@complete.org>
       Stability  : provisional
       Portability: portable

    This module provides various helpful utilities for dealing with lists.

    Written by John Goerzen, jgoerzen\@complete.org
    -}

    module Data.List.Utils(-- * Merging
                         merge, mergeBy,
                         -- * Tests
                         startswith, endswith, contains, hasAny,
                         -- * Association List Utilities
                         {- | These functions are designed to augment the
                         association list functions in "Data.List" and
                         provide an interface similar to "Data.FiniteMap" or
                         "Data.Map"
                         for association lists. -}
                         addToAL, delFromAL, flipAL, keysAL, valuesAL,
                         hasKeyAL,
                         -- ** Association List Conversions
                         strFromAL,
                         strToAL,
                         -- * Conversions
                         split, join, replace, genericJoin, takeWhileList,
                         dropWhileList, spanList, breakList,
                         -- ** Advanced Conversions
                         WholeFunc(..), wholeMap, fixedWidth,
                         -- * Fixed-Width and State Monad Utilities
                         grab,
                         -- * Miscellaneous
                         countElem, elemRIndex, alwaysElemRIndex, seqList,
                         subIndex, uniq
                         -- -- * Sub-List Selection
                         -- sub,
                        ) where
    import Data.List(intersperse, concat, isPrefixOf, isSuffixOf, elemIndices,
                    elemIndex, elemIndices, tails, find, findIndex, isInfixOf, nub)
    import Control.Monad.State(State, get, put)
    import Data.Maybe(isJust)

    {- | Merge two sorted lists into a single, sorted whole.

    Example:

    > merge [1,3,5] [1,2,4,6] -> [1,1,2,3,4,5,6]

    QuickCheck test property:

    prop_merge xs ys =
        merge (sort xs) (sort ys) == sort (xs ++ ys)
              where types = xs :: [Int]
    -}
    merge ::  (Ord a) => [a] -> [a] -> [a]
    merge = mergeBy (compare)

    {- | Merge two sorted lists using into a single, sorted whole,
    allowing the programmer to specify the comparison function.

    QuickCheck test property:

    prop_mergeBy xs ys =
        mergeBy cmp (sortBy cmp xs) (sortBy cmp ys) == sortBy cmp (xs ++ ys)
              where types = xs :: [ (Int, Int) ]
                    cmp (x1,_) (x2,_) = compare x1 x2
    -}
    mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a]
    mergeBy cmp [] ys = ys
    mergeBy cmp xs [] = xs
    mergeBy cmp (allx@(x:xs)) (ally@(y:ys))
            -- Ordering derives Eq, Ord, so the comparison below is valid.
            -- Explanation left as an exercise for the reader.
            -- Someone please put this code out of its misery.
        | (x `cmp` y) <= EQ = x : mergeBy cmp xs ally
        | otherwise = y : mergeBy cmp allx ys

    {- | Returns true if the given list starts with the specified elements;
    false otherwise.  (This is an alias for "Data.List.isPrefixOf".)

    Example:

    > startswith "He" "Hello" -> True

    -}

    startswith :: Eq a => [a] -> [a] -> Bool
    startswith = isPrefixOf

    {- | Returns true if the given list ends with the specified elements;
    false otherwise.  (This is an alias for "Data.List.isSuffixOf".)

    Example:

    > endswith "lo" "Hello" -> True

    -}
    endswith :: Eq a => [a] -> [a] -> Bool
    endswith = isSuffixOf

    {- | Returns true if the given list contains any of the elements in the search
    list. -}
    hasAny :: Eq a => [a]           -- ^ List of elements to look for
           -> [a]                   -- ^ List to search
           -> Bool                  -- ^ Result
    hasAny [] _ = False             -- An empty search list: always false
    hasAny _ [] = False             -- An empty list to scan: always false
    hasAny search (x:xs) = if x `elem` search then True else hasAny search xs

    {- | Similar to Data.List.takeWhile, takes elements while the func is true.
    The function is given the remainder of the list to examine. -}
    takeWhileList :: ([a] -> Bool) -> [a] -> [a]
    takeWhileList _ [] = []
    takeWhileList func list@(x:xs) =
        if func list
           then x : takeWhileList func xs
           else []

    {- | Similar to Data.List.dropWhile, drops elements while the func is true.
    The function is given the remainder of the list to examine. -}
    dropWhileList :: ([a] -> Bool) -> [a] -> [a]
    dropWhileList _ [] = []
    dropWhileList func list@(x:xs) =
        if func list
           then dropWhileList func xs
           else list

    {- | Similar to Data.List.span, but performs the test on the entire remaining
    list instead of just one element.

    @spanList p xs@ is the same as @(takeWhileList p xs, dropWhileList p xs)@
    -}
    spanList :: ([a] -> Bool) -> [a] -> ([a], [a])

    spanList _ [] = ([],[])
    spanList func list@(x:xs) =
        if func list
           then (x:ys,zs)
           else ([],list)
        where (ys,zs) = spanList func xs

    {- | Similar to Data.List.break, but performs the test on the entire remaining
    list instead of just one element.
    -}
    breakList :: ([a] -> Bool) -> [a] -> ([a], [a])
    breakList func = spanList (not . func)

    {- | Given a delimiter and a list (or string), split into components.

    Example:

    > split "," "foo,bar,,baz," -> ["foo", "bar", "", "baz", ""]

    > split "ba" ",foo,bar,,baz," -> [",foo,","r,,","z,"]
    -}
    split :: Eq a => [a] -> [a] -> [[a]]
    split _ [] = []
    split delim str =
        let (firstline, remainder) = breakList (startswith delim) str
            in
            firstline : case remainder of
                                       [] -> []
                                       x -> if x == delim
                                            then [] : []
                                            else split delim
                                                     (drop (length delim) x)

    {- | Given a list and a replacement list, replaces each occurance of the search
    list with the replacement list in the operation list.

    Example:

    >replace "," "." "127,0,0,1" -> "127.0.0.1"

    This could logically be thought of as:

    >replace old new l = join new . split old $ l
    -}

    replace :: Eq a => [a] -> [a] -> [a] -> [a]
    replace old new l = join new . split old $ l

    {- | Given a delimiter and a list of items (or strings), join the items
    by using the delimiter.

    Example:

    > join "|" ["foo", "bar", "baz"] -> "foo|bar|baz"
    -}
    join :: [a] -> [[a]] -> [a]
    join delim l = concat (intersperse delim l)

    {- | Like 'join', but works with a list of anything showable, converting
    it to a String.

    Examples:

    > genericJoin ", " [1, 2, 3, 4] -> "1, 2, 3, 4"
    > genericJoin "|" ["foo", "bar", "baz"] -> "\"foo\"|\"bar\"|\"baz\""

    -}
    genericJoin :: Show a => String -> [a] -> String
    genericJoin delim l = join delim (map show l)

    {-# DEPRECATED contains "Use Data.List.isInfixOf, will be removed in MissingH 1.1.0" #-}
    {- | Returns true if the given parameter is a sublist of the given list;
    false otherwise.

    Example:

    > contains "Haskell" "I really like Haskell." -> True
    > contains "Haskell" "OCaml is great." -> False

    This function was submitted to GHC and was applied as
    'Data.List.isInfixOf'.  This function therefore is deprecated and will
    be removed in future versions.
    -}

    contains :: Eq a => [a] -> [a] -> Bool
    contains = isInfixOf

    -- above function submitted to GHC as Data.List.isInfixOf on 8/31/2006

    {- | Adds the specified (key, value) pair to the given list, removing any
    existing pair with the same key already present. -}
    addToAL :: Eq key => [(key, elt)] -> key -> elt -> [(key, elt)]
    addToAL l key value = (key, value) : delFromAL l key

    {- | Removes all (key, value) pairs from the given list where the key
    matches the given one. -}
    delFromAL :: Eq key => [(key, a)] -> key -> [(key, a)]
    delFromAL l key = filter (\a -> (fst a) /= key) l

    {- | Returns the keys that comprise the (key, value) pairs of the given AL.

    Same as:

    >map fst
    -}
    keysAL :: [(key, a)] -> [key]
    keysAL = map fst

    {- | Returns the values the comprise the (key, value) pairs of the given
    AL.

    Same as:

    >map snd
    -}
    valuesAL :: [(a, value)] -> [value]
    valuesAL = map snd

    {- | Indicates whether or not the given key is in the AL. -}
    hasKeyAL :: Eq a => a -> [(a, b)] -> Bool
    hasKeyAL key list =
        elem key (keysAL list)

    {- | Flips an association list.  Converts (key1, val), (key2, val) pairs
    to (val, [key1, key2]). -}
    flipAL :: (Eq key, Eq val) => [(key, val)] -> [(val, [key])]
    flipAL oldl =
        let worker :: (Eq key, Eq val) => [(key, val)] -> [(val, [key])] -> [(val, [key])]
            worker [] accum = accum
            worker ((k, v):xs) accum =
                case lookup v accum of
                                    Nothing -> worker xs ((v, [k]) : accum)
                                    Just y -> worker xs (addToAL accum v (k:y))
            in
            worker oldl []

    {- | Converts an association list to a string.  The string will have
    one pair per line, with the key and value both represented as a Haskell string.

    This function is designed to work with [(String, String)] association lists,
    but may work with other types as well. -}

    strFromAL :: (Show a, Show b) => [(a, b)] -> String
    strFromAL inp =
        let worker (key, val) = show key ++ "," ++ show val
            in unlines . map worker $ inp

    {- | The inverse of 'strFromAL', this function reads a string and outputs the
    appropriate association list.

    Like 'strFromAL', this is designed to work with [(String, String)] association
    lists but may also work with other objects with simple representations.
    -}
    strToAL :: (Read a, Read b) => String -> [(a, b)]
    strToAL inp =
        let worker line =
                case reads line of
                   [(key, remainder)] -> case remainder of
                         ',':valstr -> (key, read valstr)
                         _ -> error "Data.List.Utils.strToAL: Parse error on value"
                   _ -> error "Data.List.Utils.strToAL: Parse error on key"
            in map worker (lines inp)

    {- FIXME TODO: sub -}

    {- | Returns a count of the number of times the given element occured in the
    given list. -}
    countElem :: Eq a => a -> [a] -> Int
    countElem i = length . filter (i==)

    {- | Returns the rightmost index of the given element in the
    given list. -}
    elemRIndex :: Eq a => a -> [a] -> Maybe Int
    elemRIndex item l =
        case reverse $ elemIndices item l of
                                       [] -> Nothing
                                       (x:_) -> Just x
    {- | Like elemRIndex, but returns -1 if there is nothing
    found. -}
    alwaysElemRIndex :: Eq a => a -> [a] -> Int
    alwaysElemRIndex item list =
        case elemRIndex item list of
                                  Nothing -> -1
                                  Just x -> x

    {- | Forces the evaluation of the entire list. -}
    seqList :: [a] -> [a]
    seqList [] = []
    seqList list@(x:xs) = seq (seqList xs) list

    --------------------------------------------------
    -- Advanced Conversions
    --------------------------------------------------

    {- | The type used for functions for 'wholeMap'.  See 'wholeMap' for details.
    -}
    newtype WholeFunc a b = WholeFunc ([a] -> (WholeFunc a b, [a], [b]))

    {- | This is an enhanced version of the concatMap or map functions in
    Data.List.

    Unlike those functions, this one:

     * Can consume a varying number of elements from the input list during
       each iteration

     * Can arbitrarily decide when to stop processing data

     * Can return a varying number of elements to insert into the output list

     * Can actually switch processing functions mid-stream

     * Is not even restricted to processing the input list intact

    The function used by wholeMap, of type 'WholeFunc', is repeatedly called
    with the input list.  The function returns three things: the function
    to call for the next iteration (if any), what remains of the input list,
    and the list of output elements generated during this iteration.  The return
    value of 'wholeMap' is the concatenation of the output element lists from
    all iterations.

    Processing stops when the remaining input list is empty.  An example
    of a 'WholeFunc' is 'fixedWidth'. -}
    wholeMap :: WholeFunc a b -> [a] -> [b]
    wholeMap _ [] = []              -- Empty input, empty output.
    wholeMap (WholeFunc func) inplist =
        let (nextfunc, nextlist, output) = func inplist
            in
            output ++ wholeMap nextfunc nextlist

    {- | A parser designed to process fixed-width input fields.  Use it with
    'wholeMap'.

    The Int list passed to this function is the list of the field widths desired
    from the input.  The result is a list of those widths, if possible.  If any
    of the input remains after processing this list, it is added on as the final
    element in the result list.  If the input is less than the sum of the requested
    widths, then the result list will be short the appropriate number of elements,
    and its final element may be shorter than requested.

    Examples:

    >wholeMap (fixedWidth [1, 2, 3]) "1234567890"
    > --> ["1","23","456","7890"]
    >wholeMap (fixedWidth (repeat 2)) "123456789"
    > --> ["12","34","56","78","9"]
    >wholeMap (fixedWidth []) "123456789"
    > --> ["123456789"]
    >wholeMap (fixedWidth [5, 3, 6, 1]) "Hello, This is a test."
    > --> ["Hello",", T","his is"," ","a test."]
    -}
    fixedWidth :: [Int] -> WholeFunc a [a]
    fixedWidth len =
        WholeFunc (fixedWidthFunc len)
        where -- Empty input: Empty output, stop
              fixedWidthFunc _ [] = ((fixedWidth []), [], [])
              -- Empty length: Stop here.
              fixedWidthFunc [] x = ((fixedWidth []), [], [x])
              -- Stuff to process: Do it.
              fixedWidthFunc (len:lenxs) input =
                  (fixedWidth lenxs, next, [this])
                  where (this, next) = splitAt len input

    {- | Helps you pick out fixed-width components from a list.

    Example:

    >conv :: String -> (String,String)
    >conv = runState $
    >        do f3 <- grab 3
    >           n2 <- grab 2
    >           return $ f3 ++ "," ++ n2
    >
    >main = print $ conv "TestIng"

    Prints:

    >("Tes,tI","ng")
    -}

    grab :: Int -> State [a] [a]
    grab count =
        do g <- get
           (x, g') <- return $ splitAt count g
           put g'
           return x

    {- | Similar to Data.List.elemIndex.  Instead of looking for one element in a
    list, this function looks for the first occurance of a sublist in the list,
    and returns the index of the first element of that occurance.  If there is no
    such list, returns Nothing.

    If the list to look for is the empty list, will return Just 0 regardless
    of the content of the list to search.

    Examples:

    >subIndex "foo" "asdfoobar" -> Just 3
    >subIndex "foo" [] -> Nothing
    >subIndex "" [] -> Just 0
    >subIndex "" "asdf" -> Just 0
    >subIndex "test" "asdftestbartest" -> Just 4
    >subIndex [(1::Int), 2] [0, 5, 3, 2, 1, 2, 4] -> Just 4
     -}
    subIndex :: Eq a => [a] -> [a] -> Maybe Int
    subIndex substr str = findIndex (isPrefixOf substr) (tails str)

    {- | Given a list, returns a new list with all duplicate elements removed.
    For example:

    >uniq "Mississippi" -> "Misp"

    You should not rely on this function necessarily preserving order, though
    the current implementation happens to.

    This function is not compatible with infinite lists.

    This is presently an alias for Data.List.nub
     -}
    uniq :: Eq a => [a] -> [a]
    uniq = nub

    ----- same as
    --uniq (x:xs) = x : [y | y <- uniq xs, y /= x]