{-# LANGUAGE CPP #-}

-- | Helper functions for dealing with import declarations.
module HIndent.Pretty.Import
  ( importsExist
  , extractImports
  , extractImportsSorted
  , groupImports
  ) where

import GHC.Types.SrcLoc
import HIndent.GhcLibParserWrapper.GHC.Hs
import HIndent.Pretty.Import.Sort

-- | Returns if the module has import declarations.
importsExist :: HsModule' -> Bool
importsExist = not . null . hsmodImports

-- | Extracts import declarations from the given module. Adjacent import
-- declarations are grouped as a single list.
extractImports :: HsModule' -> [[LImportDecl GhcPs]]
extractImports = groupImports . sortImportsByLocation . hsmodImports

-- | Extracts import declarations from the given module and sorts them by
-- their names. Adjacent import declarations are grouped as a single list.
extractImportsSorted :: HsModule' -> [[LImportDecl GhcPs]]
extractImportsSorted = fmap sortImportsByName . extractImports

-- | Combines adjacent import declarations into a single list.
groupImports :: [LImportDecl GhcPs] -> [[LImportDecl GhcPs]]
groupImports = groupImports' []
  where
    groupImports' ::
         [[LImportDecl GhcPs]] -> [LImportDecl GhcPs] -> [[LImportDecl GhcPs]]
    groupImports' xs [] = xs
    groupImports' [] (x:xs) = groupImports' [[x]] xs
    groupImports' [[]] (x:xs) = groupImports' [[x]] xs
    groupImports' ([]:x:xs) (y:ys) = groupImports' ([y] : x : xs) ys
    groupImports' ((z:zs):xs) (y:ys)
      | z `isAdjacentTo` y = groupImports' ((y : z : zs) : xs) ys
      | otherwise = groupImports' ([y] : (z : zs) : xs) ys
    a `isAdjacentTo` b =
      srcSpanEndLine (sp a) + 1 == srcSpanStartLine (sp b)
        || srcSpanEndLine (sp b) + 1 == srcSpanStartLine (sp a)
    sp x =
      case locA $ getLoc x of
        RealSrcSpan x' _ -> x'
        _ -> error "Src span unavailable."