{-# LANGUAGE BangPatterns   #-}
{-# LANGUAGE GADTs          #-}
{-# LANGUAGE NamedFieldPuns #-}

-- | Simple etags formatter. See <https://en.wikipedia.org/wiki/Ctags#Etags>
--
module GhcTags.ETag.Formatter
  ( withByteOffset
  , formatETagsFile 
  , formatTagsFile
  , formatTag
  , BuilderWithSize (..)
  ) where

import qualified Data.ByteString as BS
import           Data.ByteString.Builder (Builder)
import qualified Data.ByteString.Builder as BB
import           Data.List (groupBy)
import           Data.Function (on)
import           Data.Foldable (foldl')
import qualified Data.Text          as Text
import qualified Data.Text.Encoding as Text

import           GhcTags.Tag


-- | A product of two monoids: 'Builder' and 'Sum'.
--
data BuilderWithSize = BuilderWithSize {
    builder     :: Builder,
    builderSize :: !Int
  }

instance Semigroup BuilderWithSize where
    BuilderWithSize b0 s0 <> BuilderWithSize b1 s1 =
      BuilderWithSize (b0 <> b1) (s0 + s1)

instance Monoid BuilderWithSize where
    mempty = BuilderWithSize mempty 0

computeByteOffset
    :: [Int]
    -- ^ lengths of lines
    -> ETagAddress
    -> ETagAddress
computeByteOffset ll (TagLineCol line col) = TagLineCol line byteOffset
  where
    byteOffset =
        foldl' (+) 0 (take (pred line) ll)
      + col

withByteOffset :: [Int] -> ETag -> ETag
withByteOffset ll tag@Tag { tagAddr } = tag { tagAddr = computeByteOffset ll tagAddr }

formatTag :: ETag -> BuilderWithSize
formatTag Tag {tagName, tagAddr = TagLineCol lineNr byteOffset, tagDefinition} =
           flip BuilderWithSize tagSize $
        -- TODO: get access to the original line or pretty print original
        -- declaration
           case tagDefinition of
              NoTagDefinition   -> BB.byteString tagNameBS
              TagDefinition def -> BB.byteString (Text.encodeUtf8 def)
        <> BB.charUtf8 '\DEL' -- or '\x7f'
        <> case tagDefinition of
             NoTagDefinition -> mempty
             TagDefinition _ ->
                   BB.byteString tagNameBS
                <> BB.charUtf8 '\SOH' -- or '\x01'
        <> BB.intDec lineNr
        <> BB.charUtf8 ','
        <> BB.intDec byteOffset
        <> BB.stringUtf8 endOfLine
  where
    tagNameBS = Text.encodeUtf8 . getTagName $ tagName
    tagNameSize = BS.length tagNameBS

    tagDefinitionBS = case tagDefinition of
      NoTagDefinition   -> tagNameBS
      TagDefinition def -> Text.encodeUtf8 def
    tagDefinitionSize = BS.length tagDefinitionBS

    tagSize =
        3 -- delimiters: '\DEL', '\SOH', ','
      + tagNameSize
      + tagDefinitionSize
      + (length $ show lineNr)
      + (length $ show byteOffset)
      + (length $ endOfLine)


-- | The precondition is that all the tags come frome the same file.
--
formatTagsFile :: [ETag] -> Builder
formatTagsFile [] = mempty
formatTagsFile ts@(Tag {tagFilePath} : _) =
    case foldMap formatTag ts of
      BuilderWithSize {builder, builderSize} ->
        if builderSize > 0
          then BB.charUtf8 '\x0c'
            <> BB.stringUtf8 endOfLine
            <> (BB.byteString . Text.encodeUtf8 . Text.pack $ tagFilePath)
            <> BB.charUtf8 ','
            <> BB.intDec builderSize
            <> BB.stringUtf8 endOfLine
            <> builder
          else mempty


-- | Format a list of tags as etags file.  Tags from the same file must be
-- groupped together.
--
formatETagsFile :: [ETag] -> Builder
formatETagsFile =
      foldMap formatTagsFile 
    . groupBy (on (==) tagFilePath)


endOfLine :: String
endOfLine = "\n"