Internally reformulate all pagination queries as before-queries

This fixes the pagination links so they only show up when relevant

src/resources/changes_resource.rs

@@ -1,4 +1,5 @@
 use futures::{self, Future};
+use futures::future::finished;
 use hyper;
 use hyper::header::ContentType;
 use hyper::server::*;
@@ -11,14 +12,44 @@ use web::{Resource, ResponseFuture};
 
 use super::pagination::Pagination;
 
+const PAGE_SIZE: i32 = 30;
+
 pub struct ChangesResource {
     state: State,
     pagination: Pagination<i32>,
 }
 
 impl ChangesResource {
-    pub fn new(state: State, pagination: Pagination<i32>) -> Self {
-        Self { state, pagination }
+    pub fn new(state: State, pagination: Pagination<i32>) -> Box<Future<Item=ChangesResource, Error=::web::Error>> {
+        match pagination {
+            Pagination::After(x) => Box::new(
+                state.query_article_revision_stubs(move |query| {
+                    use diesel::prelude::*;
+                    use schema::article_revisions::dsl::*;
+
+                    query
+                        .limit(PAGE_SIZE as i64 + 1)
+                        .filter(sequence_number.gt(x))
+                        .order(sequence_number.asc())
+                }).and_then(|mut data| {
+                    let extra_element = if data.len() > PAGE_SIZE as usize {
+                        data.pop()
+                    } else {
+                        None
+                    };
+
+                    Ok(Self {
+                        state,
+                        pagination: match extra_element {
+                            Some(x) => Pagination::Before(x.sequence_number),
+                            None => Pagination::None
+                        }
+                    })
+                })
+            ),
+            Pagination::Before(x) => Box::new(finished(Self { state, pagination })),
+            Pagination::None => Box::new(finished(Self { state, pagination })),
+        }
     }
 }
 
@@ -63,8 +94,6 @@ impl Resource for ChangesResource {
             changes: &'a [Row],
         }
 
-        const PAGE_SIZE: i32 = 30;
-
         let pagination = self.pagination.clone();
         let data = self.state.query_article_revision_stubs(move |query| {
             use diesel::prelude::*;

src/wiki_lookup.rs

@@ -83,12 +83,12 @@ impl WikiLookup {
             ("_assets", Some(asset)) =>
                 Box::new(asset_lookup(asset)),
             ("_changes", None) => {
-                Box::new(done(
-                    pagination::from_str(query.unwrap_or("")).map_err(Into::into)
-                    .and_then(|pagination| Ok(Some(
-                        Box::new(ChangesResource::new(self.state.clone(), pagination)) as BoxResource
-                    )))
-                ))
+                let state = self.state.clone();
+                Box::new(
+                    done(pagination::from_str(query.unwrap_or("")).map_err(Into::into))
+                    .and_then(move |pagination| ChangesResource::new(state, pagination))
+                    .and_then(|changes_resource| Ok(Some(Box::new(changes_resource) as BoxResource)))
+                )
             },
             ("_new", None) =>
                 Box::new(finished(Some(Box::new(NewArticleResource::new(self.state.clone(), None)) as BoxResource))),