{-# LANGUAGE RecordWildCards, TemplateHaskell, ViewPatterns #-}
module Yesod.Routes.TH.Simple where

import Prelude hiding (exp)
import Yesod.Routes.TH
import Language.Haskell.TH.Syntax
import Web.PathPieces
import Data.Maybe (catMaybes)
import Control.Monad (forM)
import Data.List (foldl')
import Control.Arrow (second)
import System.Random (randomRIO)

data SDC = SDC
    { clause404 :: Clause
    , extraParams :: [Exp]
    , extraCons :: [Exp]
    , envExp :: Exp
    , reqExp :: Exp
    }

-- | A simpler version of Yesod.Routes.TH.Dispatch.mkDispatchClause, based on
-- view patterns.
--
-- Since 1.2.1
mkSimpleDispatchClause :: MkDispatchSettings -> [ResourceTree a] -> Q Clause
mkSimpleDispatchClause MkDispatchSettings {..} resources = do
    suffix <- qRunIO $ randomRIO (1000, 9999 :: Int)
    envName <- newName $ "env" ++ show suffix
    reqName <- newName $ "req" ++ show suffix
    helperName <- newName $ "helper" ++ show suffix

    let envE = VarE envName
        reqE = VarE reqName
        helperE = VarE helperName

    clause404' <- mkClause404 envE reqE
    getPathInfo <- mdsGetPathInfo
    let pathInfo = getPathInfo `AppE` reqE

    let sdc = SDC
            { clause404 = clause404'
            , extraParams = []
            , extraCons = []
            , envExp = envE
            , reqExp = reqE
            }
    clauses <- mapM (go sdc) resources

    return $ Clause
        [VarP envName, VarP reqName]
        (NormalB $ helperE `AppE` pathInfo)
        [FunD helperName $ clauses ++ [clause404']]
  where
    handlePiece :: Piece a -> Q (Pat, Maybe Exp)
    handlePiece (Static str) = return (LitP $ StringL str, Nothing)
    handlePiece (Dynamic _) = do
        x <- newName "dyn"
        let pat = ViewP (VarE 'fromPathPiece) (ConP 'Just [VarP x])
        return (pat, Just $ VarE x)

    handlePieces :: [Piece a] -> Q ([Pat], [Exp])
    handlePieces = fmap (second catMaybes . unzip) . mapM handlePiece

    mkCon :: String -> [Exp] -> Exp
    mkCon name = foldl' AppE (ConE $ mkName name)

    mkPathPat :: Pat -> [Pat] -> Pat
    mkPathPat final =
        foldr addPat final
      where
        addPat x y = ConP '(:) [x, y]

    go :: SDC -> ResourceTree a -> Q Clause
    go sdc (ResourceParent name _check pieces children) = do
        (pats, dyns) <- handlePieces pieces
        let sdc' = sdc
                { extraParams = extraParams sdc ++ dyns
                , extraCons = extraCons sdc ++ [mkCon name dyns]
                }
        childClauses <- mapM (go sdc') children

        restName <- newName "rest"
        let restE = VarE restName
            restP = VarP restName

        helperName <- newName $ "helper" ++ name
        let helperE = VarE helperName

        return $ Clause
            [mkPathPat restP pats]
            (NormalB $ helperE `AppE` restE)
            [FunD helperName $ childClauses ++ [clause404 sdc]]
    go SDC {..} (ResourceLeaf (Resource name pieces dispatch _ _check)) = do
        (pats, dyns) <- handlePieces pieces

        (chooseMethod, finalPat) <- handleDispatch dispatch dyns

        return $ Clause
            [mkPathPat finalPat pats]
            (NormalB chooseMethod)
            []
      where
        handleDispatch :: Dispatch a -> [Exp] -> Q (Exp, Pat)
        handleDispatch dispatch dyns =
            case dispatch of
                Methods multi methods -> do
                    (finalPat, mfinalE) <-
                        case multi of
                            Nothing -> return (ConP '[] [], Nothing)
                            Just _ -> do
                                multiName <- newName "multi"
                                let pat = ViewP (VarE 'fromPathMultiPiece)
                                                (ConP 'Just [VarP multiName])
                                return (pat, Just $ VarE multiName)

                    let dynsMulti =
                            case mfinalE of
                                Nothing -> dyns
                                Just e -> dyns ++ [e]
                        route' = foldl' AppE (ConE (mkName name)) dynsMulti
                        route = foldr AppE route' extraCons
                        jroute = ConE 'Just `AppE` route
                        allDyns = extraParams ++ dynsMulti
                        mkRunExp mmethod = do
                            runHandlerE <- mdsRunHandler
                            handlerE' <- mdsGetHandler mmethod name
                            let handlerE = foldl' AppE handlerE' allDyns
                            return $ runHandlerE
                                `AppE` handlerE
                                `AppE` envExp
                                `AppE` jroute
                                `AppE` reqExp

                    func <-
                        case methods of
                            [] -> mkRunExp Nothing
                            _ -> do
                                getMethod <- mdsMethod
                                let methodE = getMethod `AppE` reqExp
                                matches <- forM methods $ \method -> do
                                    exp <- mkRunExp (Just method)
                                    return $ Match (LitP $ StringL method) (NormalB exp) []
                                match405 <- do
                                    runHandlerE <- mdsRunHandler
                                    handlerE <- mds405
                                    let exp = runHandlerE
                                            `AppE` handlerE
                                            `AppE` envExp
                                            `AppE` jroute
                                            `AppE` reqExp
                                    return $ Match WildP (NormalB exp) []
                                return $ CaseE methodE $ matches ++ [match405]

                    return (func, finalPat)
                Subsite _ getSub -> do
                    restPath <- newName "restPath"
                    setPathInfoE <- mdsSetPathInfo
                    subDispatcherE <- mdsSubDispatcher
                    runHandlerE <- mdsRunHandler
                    sub <- newName "sub"
                    let sub2 = LamE [VarP sub]
                            (foldl' (\a b -> a `AppE` b) (VarE (mkName getSub) `AppE` VarE sub) dyns)
                    let reqExp' = setPathInfoE `AppE` VarE restPath `AppE` reqExp
                        route' = foldl' AppE (ConE (mkName name)) dyns
                        route = foldr AppE route' extraCons
                        exp = subDispatcherE
                            `AppE` runHandlerE
                            `AppE` sub2
                            `AppE` route
                            `AppE` envExp
                            `AppE` reqExp'
                    return (exp, VarP restPath)

    mkClause404 envE reqE = do
        handler <- mds404
        runHandler <- mdsRunHandler
        let exp = runHandler `AppE` handler `AppE` envE `AppE` ConE 'Nothing `AppE` reqE
        return $ Clause [WildP] (NormalB exp) []