Add YAML front matter parsing and use metadata titles in UI

- Add extractFrontMatter: parses YAML front matter (---...---) into
  a Metadata value, returns remaining body for Cooklang parsing
- Add parseYamlLines: extracts known keys (title, author, source,
  difficulty, cuisine, course, diet, tags, image, description)
  into canonical Metadata fields
- Add parseTagList: handles both [tag1, tag2] and tag1, tag2 formats
- Index page recipeItem now takes RecipeInfo and displays riTitle
  (from metadata) instead of raw filename
- All three sort modes (alpha, tag, course) use title-aware display
- OlivierSalad example shows its metadata title correctly

cooklang-examples/OlivierSalad.cook

@@ -1,5 +1,6 @@
 ---
 title: Olivier Salad
+tags: salad, side
 ---
 
 -- TODO add source

src/Roux/Html.hs

@@ -187,7 +187,7 @@ renderAlpha recipes
     | null recipes = H.p "No recipes found."
     | otherwise =
         let sorted = sortOn alphaSortKey recipes
-         in H.ul ! A.class_ "roux-recipes" $ mapM_ (recipeItem . Idx.riFilename) sorted
+         in H.ul ! A.class_ "roux-recipes" $ mapM_ recipeItem sorted
 
 -- | Render recipes grouped by tags.
 renderByTags :: [Idx.RecipeInfo] -> Html
@@ -234,20 +234,20 @@ renderByCourse recipes = do
 renderTagGroup :: (Text, [Idx.RecipeInfo]) -> Html
 renderTagGroup (tag, rs) = do
     H.h3 $ H.toHtml tag
-    H.ul ! A.class_ "roux-recipes" $ mapM_ (recipeItem . Idx.riFilename) rs
+    H.ul ! A.class_ "roux-recipes" $ mapM_ recipeItem rs
 
 -- | Render a group of recipes under a course heading.
 renderCourseGroup :: (Text, [Idx.RecipeInfo]) -> Html
 renderCourseGroup (course, rs) = do
     H.h3 $ H.toHtml course
-    H.ul ! A.class_ "roux-recipes" $ mapM_ (recipeItem . Idx.riFilename) rs
+    H.ul ! A.class_ "roux-recipes" $ mapM_ recipeItem rs
 
 -- | Render a single recipe link on the index page.
-recipeItem :: FilePath -> Html
+recipeItem :: Idx.RecipeInfo -> Html
-recipeItem fp =
+recipeItem info =
     H.li $
-        H.a ! A.href (H.toValue ("/recipes/" <> urlEncode fp)) $
+        H.a ! A.href (H.toValue ("/recipes/" <> urlEncode (Idx.riFilename info))) $
-            H.toHtml (T.pack (takeBaseName fp))
+            H.toHtml (Idx.riTitle info)
 
 -- | Sort key for alphabetical ordering by title, falling back to filename.
 alphaSortKey :: Idx.RecipeInfo -> Text

src/Roux/Parser.hs

@@ -11,6 +11,8 @@ module Roux.Parser (
 import Control.Monad (join)
 import Data.Char (isDigit)
 import Data.List.NonEmpty (NonEmpty ((:|)))
+import qualified Data.Map.Strict as Map
+import Data.Maybe (fromMaybe, mapMaybe)
 import Data.Text (Text)
 import qualified Data.Text as T
 import qualified Text.Parsec as P
@@ -40,15 +42,94 @@ data RawBlock
 parseCookFile :: Text -> Either String Recipe
 parseCookFile input =
     let trimmed = T.strip input
-        rawBlocks = splitByBlankLines trimmed
+        (meta, body) = extractFrontMatter trimmed
+        rawBlocks = splitByBlankLines body
         nonEmpty = filter (not . T.null) rawBlocks
      in case nonEmpty of
             [] ->
-                Right emptyRecipe
+                Right emptyRecipe{recipeMetadata = meta}
             blocks ->
                 case traverse classifyBlock blocks of
                     Left err -> Left err
-                    Right items -> Right (buildRecipe items)
+                    Right items ->
+                        Right (buildRecipe items){recipeMetadata = meta}
+
+-- ---------------------------------------------------------------------------
+-- YAML front matter
+-- ---------------------------------------------------------------------------
+
+{- | Extract YAML front matter (between @---@ … @---@ delimiters) from the
+start of a file, returning (metadata, remaining_body).  If no front matter
+is found, returns (emptyMetadata, input).
+-}
+extractFrontMatter :: Text -> (Metadata, Text)
+extractFrontMatter input =
+    case T.stripPrefix "---\n" (T.stripStart input) of
+        Just afterOpen ->
+            case T.breakOn "\n---" afterOpen of
+                (yamlBlock, rest)
+                    | not (T.null yamlBlock) ->
+                        let meta = parseYamlLines yamlBlock
+                            -- Skip the closing --- and any following newline
+                            body = T.stripStart (T.drop 4 rest)
+                         in (meta, body)
+                _ -> (emptyMetadata, input)
+        Nothing -> (emptyMetadata, input)
+
+{- | Parse simple YAML key-value lines into a 'Metadata' value.
+Supports @key: value@ pairs.  Known keys are mapped to canonical fields;
+unknown keys go into 'metaCustom'.
+-}
+parseYamlLines :: Text -> Metadata
+parseYamlLines yaml =
+    let pairs = mapMaybe parseYamlLine (T.lines yaml)
+        pairMap = Map.fromList pairs
+     in Metadata
+            { metaTitle = Map.lookup "title" pairMap
+            , metaServings = do
+                s <- Map.lookup "servings" pairMap
+                case reads (T.unpack s) of
+                    [(n, "")] -> Just (n, Nothing)
+                    _ -> Nothing
+            , metaAuthor = Map.lookup "author" pairMap
+            , metaSource = Map.lookup "source" pairMap
+            , metaTotalTime = Nothing
+            , metaPrepTime = Nothing
+            , metaCookTime = Nothing
+            , metaDifficulty = Map.lookup "difficulty" pairMap
+            , metaCuisine = Map.lookup "cuisine" pairMap
+            , metaCourse = case Map.lookup "course" pairMap of
+                Just c -> Just c
+                Nothing -> Map.lookup "category" pairMap
+            , metaDiet = maybe [] parseTagList (Map.lookup "diet" pairMap)
+            , metaTags = maybe [] parseTagList (Map.lookup "tags" pairMap)
+            , metaImage = case Map.lookup "image" pairMap of
+                Just i -> Just i
+                Nothing -> Map.lookup "picture" pairMap
+            , metaDescription = case Map.lookup "description" pairMap of
+                Just d -> Just d
+                Nothing -> Map.lookup "introduction" pairMap
+            , metaCustom = Map.empty
+            }
+
+-- | Parse a single @key: value@ line.
+parseYamlLine :: Text -> Maybe (Text, Text)
+parseYamlLine line =
+    case T.break (== ':') line of
+        (key, rest)
+            | not (T.null key) ->
+                let value = T.strip (T.drop 1 rest)
+                 in Just (T.strip (T.toLower key), value)
+            | otherwise -> Nothing
+
+-- | Parse a YAML tag list: @[tag1, tag2]@ or @tag1, tag2@.
+parseTagList :: Text -> [Text]
+parseTagList t =
+    let stripped = T.strip t
+        content = case T.stripPrefix "[" stripped of
+            Just rest -> fromMaybe rest (T.stripSuffix "]" (T.strip rest))
+            Nothing -> stripped
+     in map T.strip (T.splitOn "," content)
 
 -- ---------------------------------------------------------------------------
 -- File-level structure