introduce outbox page

app/Main.hs

@@ -41,8 +41,8 @@ mkFediApp :: IO Twain.Application
 mkFediApp = do
   detailsFile <- lookupEnv "FEDI_DETAILS"
     <&> maybe (error "missing FEDI_DETAILS") id
-  details <- A.decodeFileStrict detailsFile
+  details <- A.eitherDecodeFileStrict detailsFile
-    <&> maybe (error $ "could not read file '" <> detailsFile <> "'.") id
+    <&> either (\err -> error $ "could not read file '" <> detailsFile <> "'.\n" <> err) id
 
   pure $ foldr ($)
     (Twain.notFound $ Twain.send $ Twain.text "Error: not found.")

src/Fedi/Activity.hs

@@ -1,5 +1,6 @@
 module Fedi.Activity where
 
+import Data.Maybe (listToMaybe)
 import Data.Aeson qualified as A
 import Data.Text qualified as T
 import Fedi.Types
@@ -35,11 +36,18 @@ type Following = [Actor]
 
 type Inbox = Collection Ordered Activity
 type Outbox = Collection Unordered Activity
-type OutboxPage = Collection Unordered Activity
+type OutboxPage = OrderedCollectionPage Activity
 
 data Ordered
 data Unordered
 
+data OrderedCollectionPage a
+  = OrderedCollectionPage
+    { id :: Url
+    , partOf :: Url
+    , orderedItems :: [a]
+    }
+
 data Collection order a
   = Collection
     { summary :: String
@@ -87,6 +95,8 @@ instance A.ToJSON a => A.ToJSON (Collection Ordered a) where
       , "summary" A..= collection.summary
       , "totalItems" A..= length collection.items
       , "orderedItems" A..= collection.items
+      , "first" A..= listToMaybe (take 1 collection.items)
+      , "last" A..= listToMaybe (take 1 $ reverse collection.items)
       ]
 
 instance A.ToJSON a => A.ToJSON (Collection Unordered a) where
@@ -99,4 +109,17 @@ instance A.ToJSON a => A.ToJSON (Collection Unordered a) where
       , "summary" A..= collection.summary
       , "totalItems" A..= length collection.items
       , "items" A..= collection.items
+      , "first" A..= listToMaybe (take 1 collection.items)
+      , "last" A..= listToMaybe (take 1 $ reverse collection.items)
+      ]
+
+instance A.ToJSON a => A.ToJSON (OrderedCollectionPage a) where
+  toJSON collection =
+    A.object
+      [ "@context" A..=
+        [ "https://www.w3.org/ns/activitystreams" :: String
+        ]
+      , "type" A..= ("OrderedCollectionPage" :: String)
+      , "partOf" A..= collection.partOf
+      , "orderedItems" A..= collection.orderedItems
       ]

src/Fedi/Routes.hs

@@ -18,7 +18,7 @@ routes details =
     handleUser details
 
   , Twain.get (matchOutbox details) do
-    handleOutbox details
+    handleOutbox details []
 
   , Twain.get matchWebfinger do
     handleWebfinger details
@@ -61,7 +61,36 @@ matchOutbox :: UserDetails -> Twain.PathPattern
 matchOutbox details =
   fromString ("/" <> details.username <> "/outbox")
 
-handleOutbox :: UserDetails -> Twain.ResponderM b
+handleOutbox :: UserDetails -> [Activity] -> Twain.ResponderM b
-handleOutbox details = do
+handleOutbox details items = do
-  let content = Collection { summary = details.username <> "'s notes", items = [] } :: Outbox
+  isPage <- Twain.queryParamMaybe "page"
-  Twain.send $ jsonLD (A.encode content)
+  let
+    outboxUrl =
+      "https://"
+        <> details.domain
+        <> "/"
+        <> details.username
+        <> "/outbox"
+  let
+    response =
+      case isPage of
+        Just True ->
+          let
+            content :: OutboxPage
+            content =
+              OrderedCollectionPage
+                { id = outboxUrl <> "?page=true"
+                , partOf = outboxUrl
+                , orderedItems = items
+                }
+          in A.encode content
+        _ ->
+          let
+            content :: Outbox
+            content =
+              Collection
+                { summary = details.username <> "'s notes"
+                , items = items
+                }
+          in A.encode content
+  Twain.send $ jsonLD response