-- This file is part of Diohsc
-- Copyright (C) 2020 Martin Bays <mbays@sdf.org>
--
-- This program is free software: you can redistribute it and/or modify
-- it under the terms of version 3 of the GNU General Public License as
-- published by the Free Software Foundation, or any later version.
--
-- You should have received a copy of the GNU General Public License
-- along with this program.  If not, see http://www.gnu.org/licenses/.

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE Safe              #-}

module URI
    ( URI
    , URIRef
    , escapeIRI
    , escapePathString
    , escapeQuery
    , escapeQueryPart
    , nullUri
    , parseAbsoluteUri
    , parseUriAsAbsolute
    , parseUriReference
    , pathSegments
    , relativeFrom
    , relativeTo
    , setQuery
    , stripUri
    , unescapeUriString
    , uriFragment
    , uriPath
    , uriPort
    , uriRegName
    , uriScheme
    , uriQuery
    ) where

import           Control.Monad (mplus, (<=<))
import           Data.Char     (toLower)
import           Data.List     (dropWhileEnd)
import           Data.Maybe    (isNothing)
import           Safe          (readMay)

import qualified Network.URI   as NU

defaultScheme :: String
defaultScheme = "gemini"

defaultPort :: Int
defaultPort = 1965

-- | Represents a normalised absolute URI with scheme and port defaults as above.
-- We use "Uri" rather than "URI" in camelcase,
-- because I prefer to think of it as a word rather than an acronym.
-- Still use "URI" if it's the first/only word of the identifier.
newtype URI = URI {uriUri :: NU.URI}
    deriving (Eq,Ord)
instance Show URI where
    show (URI uri) = show uri

uriPath, uriQuery, uriFragment :: URI -> String
uriPath = NU.uriPath . uriUri
uriQuery = NU.uriQuery . uriUri
uriFragment = NU.uriFragment . uriUri

-- | strips trailing ':'
uriScheme :: URI -> String
uriScheme = init . NU.uriScheme . uriUri

pathSegments :: URI -> [String]
pathSegments (URI uri) = NU.pathSegments uri

nullUri :: URI
nullUri = URI NU.nullURI

-- | URI reference. May be absolute. Not normalised.
newtype URIRef = URIRef NU.URI
    deriving (Eq,Ord)
instance Show URIRef where
    show (URIRef uri) = show uri

normaliseUri :: NU.URI -> URI
normaliseUri uri = URI $ uri
    { NU.uriPath = (\p -> if null p then "/" else p) .
        NU.normalizePathSegments . NU.normalizeEscape $ NU.uriPath uri
    , NU.uriFragment = ""
    , NU.uriScheme = if null $ NU.uriScheme uri
        then defaultScheme else toLower <$> NU.uriScheme uri
    , NU.uriAuthority = (\auth -> auth
        { NU.uriPort =
            if NU.uriPort auth == ':' : show defaultPort
            then "" else NU.uriPort auth
        , NU.uriRegName = toLower <$> NU.uriRegName auth
        , NU.uriUserInfo = ""
        })
        <$> NU.uriAuthority uri
    , NU.uriQuery = NU.normalizeEscape $ NU.uriQuery uri
    }

parseAbsoluteUri :: String -> Maybe URI
parseAbsoluteUri = (normaliseUri <$>) . NU.parseURI

parseUriAsAbsolute :: String -> Maybe URI
parseUriAsAbsolute s = parseAbsoluteUri s `mplus` parseAbsoluteUri (defaultScheme ++ "://" ++ s)

parseUriReference :: String -> Maybe URIRef
parseUriReference = (URIRef <$>) . NU.parseURIReference


setQuery :: String -> URI -> URI
setQuery q (URI uri) = URI $ uri { NU.uriQuery = q }

stripUri :: URI -> URI
stripUri (URI uri) = URI $ uri { NU.uriPath = dropWhileEnd (== '/') $ NU.uriPath uri, NU.uriQuery = "" }

relativeTo :: URIRef -> URI -> URI
relativeTo (URIRef ref) (URI uri) = normaliseUri $ NU.relativeTo ref uri

-- | lift NU.relativeFrom, but set scheme when the result is absolute,
-- and avoid initial slash where possible, and prefer "." to "" and ".." to "../"
relativeFrom :: URI -> URI -> URIRef
relativeFrom (URI uri1) (URI uri2) =
    URIRef . fixDots . stripSlash . setScheme $ NU.relativeFrom uri1 uri2 where
    setScheme ref | isNothing (NU.uriAuthority ref) = ref
        | otherwise = ref { NU.uriScheme = NU.uriScheme uri1 }
    stripSlash ref | '/':path' <- NU.uriPath ref
            , not $ null path'
            , ref' <- ref { NU.uriPath = path' }
            , NU.relativeTo ref' uri2 == uri1 = ref'
        | otherwise = ref
    fixDots ref = case NU.uriPath ref of
        ""    | ref' <- ref { NU.uriPath = "." }
            , NU.relativeTo ref' uri2 == uri1 -> ref'
        "../" -> ref { NU.uriPath = ".." }
        _     -> ref

uriRegName :: URI -> Maybe String
uriRegName = (NU.uriRegName <$>) . NU.uriAuthority . uriUri

uriPort :: URI -> Maybe Int
uriPort = (readPort . NU.uriPort) <=< (NU.uriAuthority . uriUri)
    where
    readPort (':':n) = readMay n
    readPort _       = Nothing

escapePathString :: String -> String
escapePathString = NU.escapeURIString (\c -> NU.isUnreserved c || c == '/')

unescapeUriString :: String -> String
unescapeUriString = NU.unEscapeString

-- | unreserved / sub-delims / ":" / "@" / "/" / "?"
isUnescapedInQuery :: Char -> Bool
isUnescapedInQuery c = NU.isUnescapedInURI c && c `notElem` ("#[]"::String)

escapeQuery :: String -> String
escapeQuery = NU.escapeURIString isUnescapedInQuery . withEscapes
    where
    withEscapes "" = ""
    withEscapes ('\\':'x':h1:h2:s) | Just c <- readMay $ "'\\x" <> [h1,h2,'\''] = c:withEscapes s
    withEscapes ('\\':'e':s) = '\ESC':withEscapes s
    withEscapes ('\\':'r':s) = '\r':withEscapes s
    withEscapes ('\\':'n':s) = '\n':withEscapes s
    withEscapes ('\\':'t':s) = '\t':withEscapes s
    withEscapes ('\\':c:s) = c:withEscapes s
    withEscapes (c:s) = c:withEscapes s

-- |escape the query part of an unparsed uri string
escapeQueryPart :: String -> String
escapeQueryPart s
    | (s','?':q) <- break (== '?') s = s' ++ '?' : escapeQuery q
    | otherwise = s

-- |conversion of IRI to URI according to Step 2 in Section 3.1 in RFC3987
-- (for now at least, we apply this also to the regname rather than
-- punycoding)
escapeIRI :: String -> String
escapeIRI = NU.escapeURIString (not . escape)
    where
    -- |ucschar or iprivate in RFC3987
    escape :: Char -> Bool
    escape c = let i = fromEnum c in
        i >= 0xA0 && i <= 0xD7FF ||
        i >= 0xE000 && i <= 0xF8FF ||
        i >= 0xF900 && i <= 0xFDCF ||
        i >= 0xFDF0 && i <= 0xFFEF ||
        i >= 0x10000 && i <= 0x1FFFD ||
        i >= 0x20000 && i <= 0x2FFFD ||
        i >= 0x30000 && i <= 0x3FFFD ||
        i >= 0x40000 && i <= 0x4FFFD ||
        i >= 0x50000 && i <= 0x5FFFD ||
        i >= 0x60000 && i <= 0x6FFFD ||
        i >= 0x70000 && i <= 0x7FFFD ||
        i >= 0x80000 && i <= 0x8FFFD ||
        i >= 0x90000 && i <= 0x9FFFD ||
        i >= 0xA0000 && i <= 0xAFFFD ||
        i >= 0xB0000 && i <= 0xBFFFD ||
        i >= 0xC0000 && i <= 0xCFFFD ||
        i >= 0xD0000 && i <= 0xDFFFD ||
        i >= 0xE1000 && i <= 0xEFFFD ||
        i >= 0xF0000 && i <= 0xFFFFD ||
        i >= 0x100000 && i <= 0x10FFFD