Allow querying browser sessions

crates/storage/src/pagination.rs

@@ -0,0 +1,100 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::fmt::Write;
+
+use sqlx::Arguments;
+use ulid::Ulid;
+use uuid::Uuid;
+
+pub fn generate_pagination<'a, A, W>(
+    query: &mut W,
+    id_field: &'static str,
+    arguments: &mut A,
+    before: Option<Ulid>,
+    after: Option<Ulid>,
+    first: Option<usize>,
+    last: Option<usize>,
+) -> Result<(), anyhow::Error>
+where
+    W: Write,
+    A: Arguments<'a>,
+    Uuid: sqlx::Type<A::Database> + sqlx::Encode<'a, A::Database>,
+    i64: sqlx::Type<A::Database> + sqlx::Encode<'a, A::Database>,
+{
+    // ref: https://github.com/graphql/graphql-relay-js/issues/94#issuecomment-232410564
+    // 1. Start from the greedy query: SELECT * FROM table
+
+    // 2. If the after argument is provided, add `id > parsed_cursor` to the `WHERE`
+    // clause
+    if let Some(after) = after {
+        write!(query, " AND {id_field} > ")?;
+        arguments.add(Uuid::from(after));
+        arguments.format_placeholder(query)?;
+    }
+
+    // 3. If the before argument is provided, add `id < parsed_cursor` to the
+    // `WHERE` clause
+    if let Some(before) = before {
+        write!(query, " AND {id_field} < ")?;
+        arguments.add(Uuid::from(before));
+        arguments.format_placeholder(query)?;
+    }
+
+    // 4. If the first argument is provided, add `ORDER BY id ASC LIMIT first+1` to
+    // the query
+    if let Some(count) = first {
+        write!(query, " ORDER BY {id_field} ASC LIMIT ")?;
+        arguments.add((count + 1) as i64);
+        arguments.format_placeholder(query)?;
+    // 5. If the first argument is provided, add `ORDER BY id DESC LIMIT last+1`
+    // to the query
+    } else if let Some(count) = last {
+        write!(query, " ORDER BY ue.user_email_id DESC LIMIT ")?;
+        arguments.add((count + 1) as i64);
+        arguments.format_placeholder(query)?;
+    } else {
+        anyhow::bail!("Either 'first' or 'last' must be specified");
+    }
+
+    Ok(())
+}
+
+pub fn process_page<T>(
+    mut page: Vec<T>,
+    first: Option<usize>,
+    last: Option<usize>,
+) -> Result<(bool, bool, Vec<T>), anyhow::Error> {
+    let limit = match (first, last) {
+        (Some(count), _) | (_, Some(count)) => count,
+        _ => anyhow::bail!("Either 'first' or 'last' must be specified"),
+    };
+
+    let is_full = page.len() == (limit + 1);
+    if is_full {
+        page.pop();
+    }
+
+    let (has_previous_page, has_next_page) = if first.is_some() {
+        (false, is_full)
+    } else if last.is_some() {
+        // 6. If the last argument is provided, I reverse the order of the results
+        page.reverse();
+        (is_full, false)
+    } else {
+        unreachable!()
+    };
+
+    Ok((has_previous_page, has_next_page, page))
+}