{-# LANGUAGE TupleSections #-}
-- | Parser for .prof files generated by GHC.
module ProfFile
  ( Time(..)
  , Line(..)
  , lIndividualTime
  , lInheritedTime
  , lIndividualAlloc
  , lInheritedAlloc
  , parse
  , processLines
  , findStart
  ) where

import           Control.Arrow (second, left)
import           Data.Char (isSpace)
import           Data.List (isPrefixOf)
import           Text.Read (readEither)
import           Control.Monad (unless)
import           Control.Applicative
import           Prelude -- Quash AMP related warnings in GHC>=7.10

data Time = Time
  { tIndividual :: Double
  , tInherited :: Double
  } deriving (Show, Eq)

data Line = Line
  { lCostCentre :: String
  , lModule :: String
  , lNumber :: Int
  , lEntries :: Int
  , lTime :: Time
  , lAlloc :: Time
  , lTicks :: Int
  , lBytes :: Int
  , lChildren :: [Line]
  } deriving (Show, Eq)

lIndividualTime :: Line -> Double
lIndividualTime = tIndividual . lTime

lInheritedTime :: Line -> Double
lInheritedTime = tInherited . lTime

lIndividualAlloc :: Line -> Double
lIndividualAlloc = tIndividual . lAlloc

lInheritedAlloc :: Line -> Double
lInheritedAlloc = tInherited . lAlloc

data ProfFormat = NoSources | IncludesSources

-- | Returns a function accepting the children and returning a fully
-- formed 'Line'.
parseLine :: ProfFormat -> String -> Either String ([Line] -> Line)
parseLine format s =
  case format of
    NoSources ->
      case words s of
        (costCentre:module_:no:entries:indTime:indAlloc:inhTime:inhAlloc:other) ->
          parse' costCentre module_ no entries indTime indAlloc inhTime inhAlloc other
        _ -> Left $ "Malformed .prof file line:\n" ++ s
    IncludesSources ->
      case words s of
        (costCentre:module_:rest) | (no:entries:indTime:indAlloc:inhTime:inhAlloc:other) <- dropSRC rest ->
          parse' costCentre module_ no entries indTime indAlloc inhTime inhAlloc other
        _ -> Left $ "Malformed .prof file line:\n" ++ s
  where
    -- XXX: The SRC field can contain arbitrary characters (from the
    --      subdirectory name)!
    --
    -- As a heuristic, assume SRC spans until the last word which:
    --
    -- * Ends with '>'
    --   (for special values emitted by GHC like "<no location info>")
    --
    -- or
    --
    -- * Contains a colon eventually followed by another colon or a minus
    --   (to identify the source span, e.g. ":69:55-64" or ":(36,1)-(38,30)",
    --    or maybe for a single character ":30:3")
    --
    -- If there is no such word, assume SRC is just one word.
    --
    -- This heuristic will break if:
    --
    -- * In the future, columns to the right of SRC can match the above
    --   condition (currently, they're all numeric)
    --
    -- or
    --
    -- * GHC doesn't add a source span formatted as assumed above, and the
    --   SRC contains spaces
    --
    -- The implementation is not very efficient, but I suppose this is not
    -- performance-critical.
    dropSRC (_:rest) = reverse . takeWhile (not . isPossibleEndOfSRC) . reverse $ rest
    dropSRC [] = []

    isPossibleEndOfSRC w = last w == '>'
                           || case break (==':') w of
                                (_, _:rest) -> any (`elem` ":-") rest
                                _ -> False

    parse' costCentre module_ no entries indTime indAlloc inhTime inhAlloc other = do
      pNo <- readEither' no
      pEntries <- readEither' entries
      pTime <- Time <$> readEither' indTime <*> readEither' inhTime
      pAlloc <- Time <$> readEither' indAlloc <*> readEither' inhAlloc
      (pTicks, pBytes) <-
        case other of
          (ticks:bytes:_) -> (,) <$> readEither' ticks <*> readEither' bytes
          _ -> pure (0, 0)
      return $ Line costCentre module_ pNo pEntries pTime pAlloc pTicks pBytes

    readEither' str = left (("Could not parse value "++show str++": ")++)
                           (readEither str)

type LineNumber = Int

processLines :: ProfFormat -> [String] -> LineNumber -> Either String [Line]
processLines format lines0 lineNumber0 = do
  ((ss,_), lines') <- go 0 lines0 lineNumber0
  unless (null ss) $
    error "processLines: the impossible happened, not all strings were consumed."
  return lines'
  where
    go :: Int -> [String] -> LineNumber -> Either String (([String], LineNumber), [Line])
    go _depth [] lineNumber = do
      return (([], lineNumber), [])
    go depth0 (line : lines') lineNumber = do
      let (spaces, rest) = break (not . isSpace) line
      let depth = length spaces
      if depth < depth0
        then return ((line : lines', lineNumber), [])
        else do
          parsedLine <- left (("Parse error in line "++show lineNumber++": ")++) $
                             parseLine format rest
          ((lines'', lineNumber''), children) <- go (depth + 1) lines' (lineNumber + 1)
          second (parsedLine children :) <$> go depth lines'' lineNumber''

firstLineNoSources :: [String]
firstLineNoSources = ["COST", "CENTRE", "MODULE", "no.", "entries", "%time", "%alloc", "%time", "%alloc"]

-- Since GHC 8.0.2 the cost centres include the src location
firstLineIncludesSources :: [String]
firstLineIncludesSources = ["COST", "CENTRE", "MODULE", "SRC", "no.", "entries", "%time", "%alloc", "%time", "%alloc"]

findStart :: [String] -> LineNumber -> Either String (ProfFormat, [String], [String], LineNumber)
findStart [] _ = Left "Malformed .prof file: couldn't find start line"
findStart (line : _empty : lines') lineNumber | (firstLineNoSources `isPrefixOf` words line) = return (NoSources, words line, lines', lineNumber + 2)
                                              | (firstLineIncludesSources `isPrefixOf` words line) = return (IncludesSources, words line, lines', lineNumber + 2)
findStart (_line : lines') lineNumber = findStart lines' (lineNumber + 1)

parse :: String -> Either String ([String], [Line])
parse s = do
  (format, names, ss, lineNumber) <- findStart (lines s) 1
  return . (names,) =<< processLines format ss lineNumber