From 918cc235a4cbc955b25a629c8a2342c97d373752 Mon Sep 17 00:00:00 2001
From: Quentin de Quelen <quentin@dequelen.me>
Date: Mon, 16 Sep 2019 14:49:53 +0200
Subject: [PATCH] feat: expose a common DB tree for the database

---
 meilidb-data/src/cf_tree.rs                   |  7 ++
 .../src/database/index/common_index.rs        | 68 +++++++++++++++++++
 meilidb-data/src/database/index/mod.rs        |  2 +
 meilidb-data/src/database/mod.rs              | 15 +++-
 4 files changed, 89 insertions(+), 3 deletions(-)
 create mode 100644 meilidb-data/src/database/index/common_index.rs

diff --git a/meilidb-data/src/cf_tree.rs b/meilidb-data/src/cf_tree.rs
index 791f0de81..c15bbbcbb 100644
--- a/meilidb-data/src/cf_tree.rs
+++ b/meilidb-data/src/cf_tree.rs
@@ -93,6 +93,13 @@ impl CfTree {
         let mut iter = self.index.db.iterator_cf(cf, IteratorMode::End)?;
         Ok(iter.next().map(|(key, _)| key))
     }
+
+    pub fn prefix_iterator<P>(&self, prefix: P) -> RocksDbResult<rocksdb::DBIterator>
+    where P: AsRef<[u8]>,
+    {
+        let cf = self.index.db.cf_handle(&self.index.name).unwrap();
+        self.index.db.prefix_iterator_cf(cf, prefix)
+    }
 }
 
 pub struct CfIter<'a> {
diff --git a/meilidb-data/src/database/index/common_index.rs b/meilidb-data/src/database/index/common_index.rs
new file mode 100644
index 000000000..d102bb3bb
--- /dev/null
+++ b/meilidb-data/src/database/index/common_index.rs
@@ -0,0 +1,68 @@
+use serde::de::DeserializeOwned;
+use serde::Serialize;
+use super::Error;
+use std::marker::PhantomData;
+
+#[derive(Clone)]
+pub struct CommonIndex(pub crate::CfTree);
+
+impl CommonIndex {
+    pub fn get<T, K>(&self, key: K) -> Result<Option<T>, Error>
+    where T: DeserializeOwned,
+          K: AsRef<[u8]>,
+    {
+        let raw = match self.0.get(key)? {
+            Some(raw) => raw,
+            None => return Ok(None),
+        };
+        let data = bincode::deserialize(&raw)?;
+        Ok(Some(data))
+    }
+
+    pub fn set<T, K>(&self, key: K, data: &T) -> Result<(), Error>
+    where T: Serialize,
+          K: AsRef<[u8]>,
+    {
+        let raw = bincode::serialize(data)?;
+        self.0.insert(key, &raw)?;
+        Ok(())
+    }
+
+    pub fn prefix_iterator<T, P>(&self, prefix: P) -> Result<SerializedIterator<T>, Error>
+    where T: DeserializeOwned,
+          P: AsRef<[u8]>,
+    {
+        let iter = self.0.prefix_iterator(prefix)?;
+        Ok(SerializedIterator { iter, _marker: PhantomData })
+    }
+}
+
+pub struct SerializedIterator<'a, T> {
+    iter: rocksdb::DBIterator<'a>,
+    _marker: PhantomData<T>,
+}
+
+impl<T> Iterator for SerializedIterator<'_, T>
+where T: DeserializeOwned,
+{
+    type Item = (String, T);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let (raw_key, raw_value) = match self.iter.next() {
+            Some((key, value)) => (key, value),
+            None => return None,
+        };
+
+        let value: T = match bincode::deserialize(&raw_value) {
+            Ok(data) => data,
+            Err(_) => return None,
+        };
+
+        let key = match std::str::from_utf8(&raw_key) {
+            Ok(key) => key.to_string(),
+            Err(_) => return None,
+        };
+
+        Some((key, value))
+    }
+}
diff --git a/meilidb-data/src/database/index/mod.rs b/meilidb-data/src/database/index/mod.rs
index 34c71db05..1f04fe934 100644
--- a/meilidb-data/src/database/index/mod.rs
+++ b/meilidb-data/src/database/index/mod.rs
@@ -18,6 +18,7 @@ use crate::ranked_map::RankedMap;
 use crate::serde::{Deserializer, DeserializerError};
 
 pub use self::custom_settings_index::CustomSettingsIndex;
+pub use self::common_index::CommonIndex;
 use self::docs_words_index::DocsWordsIndex;
 use self::documents_index::DocumentsIndex;
 use self::main_index::MainIndex;
@@ -33,6 +34,7 @@ use crate::database::{
     apply_synonyms_addition, apply_synonyms_deletion,
 };
 
+mod common_index;
 mod custom_settings_index;
 mod docs_words_index;
 mod documents_index;
diff --git a/meilidb-data/src/database/mod.rs b/meilidb-data/src/database/mod.rs
index c560bbe94..d5365124f 100644
--- a/meilidb-data/src/database/mod.rs
+++ b/meilidb-data/src/database/mod.rs
@@ -9,8 +9,10 @@ mod error;
 mod index;
 mod update;
 
+use crate::CfTree;
+
 pub use self::error::Error;
-pub use self::index::{Index, CustomSettingsIndex};
+pub use self::index::{Index, CustomSettingsIndex, CommonIndex};
 
 pub use self::update::DocumentsAddition;
 pub use self::update::DocumentsDeletion;
@@ -23,6 +25,7 @@ use self::update::apply_synonyms_addition;
 use self::update::apply_synonyms_deletion;
 
 const INDEXES_KEY: &str = "indexes";
+const COMMON_KEY: &str = "common-index";
 
 fn load_indexes(tree: &rocksdb::DB) -> Result<HashSet<String>, Error> {
     match tree.get(INDEXES_KEY)? {
@@ -34,6 +37,7 @@ fn load_indexes(tree: &rocksdb::DB) -> Result<HashSet<String>, Error> {
 pub struct Database {
     cache: RwLock<HashMap<String, Index>>,
     inner: Arc<rocksdb::DB>,
+    common: Arc<CommonIndex>,
 }
 
 impl Database {
@@ -45,9 +49,10 @@ impl Database {
 
         let cfs = rocksdb::DB::list_cf(&options, &path).unwrap_or_default();
         let inner = Arc::new(rocksdb::DB::open_cf(&options, path, cfs)?);
-
+        let common_tree = CfTree::create(inner.clone(), COMMON_KEY.to_owned())?;
+        let common = Arc::new(CommonIndex(common_tree));
         let indexes = load_indexes(&inner)?;
-        let database = Database { cache, inner };
+        let database = Database { cache, inner, common };
 
         for index in indexes {
             database.open_index(&index)?;
@@ -112,4 +117,8 @@ impl Database {
 
         Ok(index)
     }
+
+    pub fn common_index(&self) -> Arc<CommonIndex> {
+        self.common.clone()
+    }
 }