{-# LANGUAGE OverloadedStrings #-}
-- | Evaluates conditional CSS @rules.
-- Parse a CSS stylesheet to `ConditionalStyles` to evaluate @document & @supports rules.
-- Call `loadImports` to resolve any @import rules to @media rules.
-- And call `resolve` to convert into another `StyleSheet` instance whilst resolving @media rules.
module Data.CSS.Preprocessor.Conditions(
        ConditionalStyles(..), conditionalStyles, ConditionalRule(..),
        extractImports, resolveImports, loadImports, resolve, testIsStyled,
        Datum(..)
    ) where

import qualified Data.CSS.Preprocessor.Conditions.Expr as Query
import Data.CSS.Preprocessor.Conditions.Expr (Datum(..))

import Data.CSS.Syntax.StyleSheet
import Data.CSS.Syntax.Selector
import Data.CSS.Syntax.Tokens(Token(..))
import Data.CSS.Style (PropertyParser(..))

import Data.Text.Internal (Text(..))
import Data.Text (unpack)
import Network.URI (URI(..), URIAuth(..), parseURI)
import Control.Concurrent.Async (forConcurrently)

import Data.List

-- | Collects and evaluates conditional at-rules.
data ConditionalStyles p = ConditionalStyles {
    -- | The URL to the webpage being styled, for `@document` rules.
    hostURL :: URI,
    -- | The type of document, `@document domain(...)` rules.
    mediaDocument :: String,
    -- | Whether the page provided any of it's own styling (valid or not)
    isUnstyled :: Bool,
    -- | Queued style rules, to be evaluated later.
    rules :: [ConditionalRule p],
    -- | PropertyParser to test against for `@supports` rules.
    propertyParser :: p
}

-- | Constructs an empty `ConditionalStyles`.
conditionalStyles :: PropertyParser p => URI -> String -> ConditionalStyles p
conditionalStyles uri mediaDocument' = ConditionalStyles uri mediaDocument' False [] temp

-- | Style rules that can be queued in a `ConditionalStyles`.
data ConditionalRule p = Priority Int | StyleRule' StyleRule | AtRule Text [Token] |
    External Query.Expr URI | Internal Query.Expr (ConditionalStyles p)

addRule' :: ConditionalStyles p -> ConditionalRule p -> ConditionalStyles p
addRule' self rule = self {rules = rule : rules self}

hostUrlS :: ConditionalStyles p -> String
hostUrlS = show . hostURL

parseAtBlock :: StyleSheet t => t -> [Token] -> (t, [Token])
parseAtBlock self (LeftCurlyBracket:toks) =
    let (block, toks') = scanBlock toks in (parse' self block, toks')
parseAtBlock self (_:toks) = parseAtBlock self toks
parseAtBlock self [] = (self, [])

instance PropertyParser p => StyleSheet (ConditionalStyles p) where
    setPriority x self = addRule' self $ Priority x
    addRule self rule = addRule' self $ StyleRule' rule

    addAtRule self "document" (Whitespace:toks) = addAtRule self "document" toks
    addAtRule self "document" (Comma:toks) = addAtRule self "document" toks
    addAtRule self "document" (Url match:toks)
        | unpack match == hostUrlS self = parseAtBlock self toks
        | otherwise = addAtRule self "document" toks
    addAtRule self "document" (Function "url-prefix":String match:RightParen:toks)
        | unpack match `isPrefixOf` hostUrlS self = parseAtBlock self toks
        | otherwise = addAtRule self "document" toks
    addAtRule self "document" (Function "domain":String match:RightParen:toks)
        | unpack match == domain || ('.':unpack match) `isSuffixOf` domain =
            parseAtBlock self toks
        | otherwise = addAtRule self "document" toks
        where
            domain | Just auth <- uriAuthority $ hostURL self = uriRegName auth
                | otherwise = ""
    addAtRule self "document" (Function "media-document":String match:RightParen:toks)
        | unpack match == mediaDocument self = parseAtBlock self toks
        | otherwise = addAtRule self "document" toks
    -- Rhapsode-specific: matches if the document didn't provide any of it's own stylings.
    addAtRule self "document" (Ident "unstyled":toks)
        | isUnstyled self = parseAtBlock self toks
        | otherwise = addAtRule self "document" toks
    -- TODO Support regexp() conditions, requires new dependency
    addAtRule self "document" tokens = (self, skipAtRule tokens)

    addAtRule self "media" toks
        | (cond, LeftCurlyBracket:block) <- Query.parse LeftCurlyBracket toks =
            let (block', toks') = scanBlock block in
                (addRule' self $ Internal cond $ parse' self {rules = []} block', toks')
    addAtRule self "media" tokens = (self, skipAtRule tokens)

    addAtRule self "import" (Whitespace:toks) = addAtRule self "import" toks
    addAtRule self "import" (Url src:toks) = parseAtImport self src toks
    addAtRule self "import" (String src:toks) = parseAtImport self src toks
    addAtRule self "import" tokens = (self, skipAtRule tokens)

    addAtRule self "supports" toks =
            let (cond, toks') = break (== LeftCurlyBracket) toks in
            if evalSupports (propertyParser self) cond
                then parseAtBlock self toks' else (self, skipAtRule toks')

    addAtRule self rule tokens = let (block, rest) = scanAtRule tokens in
        (addRule' self $ AtRule rule block, rest)

-- | Flags whether any style rules have been applied yet,
-- for the sake of evaluating "@document unstyled {...}".
testIsStyled :: ConditionalStyles p -> ConditionalStyles p
testIsStyled styles = styles { isUnstyled = null $ rules styles }

--------
---- @import/@media
--------
parseAtImport :: PropertyParser p => ConditionalStyles p -> Text ->
        [Token] -> (ConditionalStyles p, [Token])
parseAtImport self src toks
    | (cond, Semicolon:toks') <- Query.parse Semicolon toks, Just uri <- parseURI $ unpack src =
        (addRule' self $ External cond uri, toks')
parseAtImport self _ toks = (self, skipAtRule toks)

-- | Returns `@import` URLs that need to be imported.
extractImports :: (Text -> Query.Datum) -> (Token -> Query.Datum) -> ConditionalStyles p -> [URI]
extractImports vars evalToken self =
    [uri | External cond uri <- rules self, Query.eval vars evalToken cond]

-- | Substitutes external values in for `@import` rules.
resolveImports :: ConditionalStyles p -> [(URI, ConditionalStyles p)] -> ConditionalStyles p
resolveImports self responses = self {rules = map resolveImport $ rules self}
    where
        resolveImport (External cond uri) | (body:_) <- [body | (uri', body) <- responses, uri' == uri] =
            Internal cond body
        resolveImport x = x

-- | Evaluates a given "loader" to resolve any `@import` rules.
loadImports :: PropertyParser p => (URI -> IO Text) -> (Text -> Query.Datum) -> (Token -> Query.Datum) ->
        ConditionalStyles p -> [URI] -> IO (ConditionalStyles p)
loadImports loader vars evalToken self blocklist = do
        let imports = extractImports vars evalToken self
        let urls = [url | url <- imports, url `notElem` blocklist]
        imported <- forConcurrently urls $ \url -> do
            source <- loader url
            let parsed = parse self {rules = []} source
            styles <- loadImports loader vars evalToken parsed (blocklist ++ urls)
            return (url, styles)
        return $ resolveImports self imported

-- | Evaluates any media queries, returning a new StyleSheet with the queued operations.
resolve :: StyleSheet s => (Text -> Query.Datum) -> (Token -> Query.Datum) ->
        s -> ConditionalStyles p -> s
resolve v t styles self = resolve' v t (reverse $ rules self) styles
resolve' :: StyleSheet s => (Text -> Query.Datum) -> (Token -> Query.Datum) ->
        [ConditionalRule p] -> s -> s
resolve' v t (Priority x:rules') styles = resolve' v t rules' $ setPriority x styles
resolve' v t (StyleRule' rule:rules') styles = resolve' v t rules' $ addRule styles rule
resolve' v t (AtRule name block:rules') styles = resolve' v t rules' $ fst $ addAtRule styles name block
resolve' v t (Internal cond block:rules') styles | Query.eval v t cond =
    resolve' v t rules' $ resolve v t styles block
resolve' v t (_:rules') styles = resolve' v t rules' styles
resolve' _ _ [] styles = styles

--------
---- @supports
--------

evalSupports :: PropertyParser p => p -> [Token] -> Bool
evalSupports self (Whitespace:toks) = evalSupports self toks
evalSupports self (Ident "not":toks) = not $ evalSupports self toks
evalSupports self (LeftParen:toks) = let (block, toks') = scanBlock toks in
    evalSupportsOp toks' self $ supportsProperty block self
evalSupports self (Function "selector":toks) = let (block, toks') = scanBlock toks in
    evalSupportsOp toks' self $ supportsSelector block
evalSupports _ _ = False

evalSupportsOp :: PropertyParser p => [Token] -> p -> Bool -> Bool
evalSupportsOp (Whitespace:toks) self right = evalSupportsOp toks self right
evalSupportsOp (Ident "and":toks) self right = right && evalSupports self toks
evalSupportsOp (Ident "or":toks) self right = right || evalSupports self toks
evalSupportsOp [RightParen] _ ret = ret -- scanBlock captures closing paren
evalSupportsOp [] _ ret = ret
evalSupportsOp _ _ _ = False

supportsProperty :: PropertyParser p => [Token] -> p -> Bool
supportsProperty (Whitespace:toks) self = supportsProperty toks self
supportsProperty toks@(Ident "not":_) self = evalSupports self toks -- Special case fallback
supportsProperty (Ident key:toks) self
    | (Colon:value) <- skipSpace toks = -- "init"'s used to strip trailing RightParen
        shorthand self key (filter (/= Whitespace) $ init value) /= []
    | skipSpace toks `elem` [[RightParen], []] = shorthand self key [Ident "initial"] /= []
    | otherwise = False
supportsProperty toks self = evalSupports self toks -- Fallback to parenthesized expression.

supportsSelector :: [Token] -> Bool
supportsSelector toks = let (sels, toks') = parseSelectors toks in
    sels /= [] && (toks' == [] || toks' == [RightParen])