Move DB interactions to a background thread

5 files changed, 88 insertions, 40 deletions

diff --git a/src/database/include/database.hpp b/src/database/include/database.hpp
index cb1437df..bc102ca8 100644
--- a/src/database/include/database.hpp
+++ b/src/database/include/database.hpp
@@ -1,29 +1,85 @@
 #pragma once
 
-#include <string>
+#include <cstdint>
+#include <future>
 #include <memory>
 #include <optional>
+#include <string>
+#include <utility>
+#include <vector>
 
 #include "leveldb/cache.h"
 #include "leveldb/db.h"
 #include "leveldb/iterator.h"
+#include "leveldb/slice.h"
 #include "result.hpp"
 
 namespace database {
 
-class Iterator;
+struct Artist {
+  std::string name;
+};
+
+struct Album {
+  std::string name;
+};
+
+typedef uint64_t SongId_t;
+
+struct Song {
+  std::string title;
+  uint64_t id;
+};
+
+struct SongMetadata {};
+
+template <typename T>
+class DbResult {
+ public:
+  DbResult(const std::vector<T>& values, std::unique_ptr<leveldb::Iterator> it)
+      : values_(values), it_(std::move(it)) {}
+  auto values() -> std::vector<T> { return values_; }
+  auto it() -> leveldb::Iterator* { return it_.release(); };
+
+ private:
+  std::vector<T> values_;
+  std::unique_ptr<leveldb::Iterator> it_;
+};
 
 class Database {
  public:
   enum DatabaseError {
+    ALREADY_OPEN,
     FAILED_TO_OPEN,
   };
   static auto Open() -> cpp::result<Database*, DatabaseError>;
 
   ~Database();
 
-  auto Initialise() -> void;
-  auto ByTitle() -> Iterator;
+  auto Populate() -> std::future<void>;
+
+  auto GetArtists(std::size_t page_size) -> std::future<DbResult<Artist>>;
+  auto GetMoreArtists(std::size_t page_size, DbResult<Artist> continuation)
+      -> std::future<DbResult<Artist>>;
+
+  auto GetAlbums(std::size_t page_size, std::optional<Artist> artist)
+      -> std::future<DbResult<Album>>;
+  auto GetMoreAlbums(std::size_t page_size, DbResult<Album> continuation)
+      -> std::future<DbResult<Album>>;
+
+  auto GetSongs(std::size_t page_size) -> std::future<DbResult<Song>>;
+  auto GetSongs(std::size_t page_size, std::optional<Artist> artist)
+      -> std::future<DbResult<Song>>;
+  auto GetSongs(std::size_t page_size,
+                std::optional<Artist> artist,
+                std::optional<Album> album) -> std::future<DbResult<Song>>;
+  auto GetMoreSongs(std::size_t page_size, DbResult<Song> continuation)
+      -> std::future<DbResult<Song>>;
+
+  auto GetSongIds(std::optional<Artist> artist, std::optional<Album> album)
+      -> std::future<std::vector<SongId_t>>;
+  auto GetSongFilePath(SongId_t id) -> std::future<std::optional<std::string>>;
+  auto GetSongMetadata(SongId_t id) -> std::future<std::optional<SongMetadata>>;
 
   Database(const Database&) = delete;
   Database& operator=(const Database&) = delete;
@@ -35,17 +91,4 @@ class Database {
   Database(leveldb::DB* db, leveldb::Cache* cache);
 };
 
-class Iterator {
-  public:
-    explicit Iterator(leveldb::Iterator *it) : it_(it) {}
-
-    auto Next() -> std::optional<std::string>;
-
-    Iterator(const Iterator&) = delete;
-    Iterator& operator=(const Iterator&) = delete;
-
-  private:
-    std::unique_ptr<leveldb::Iterator> it_;
-};
-
 }  // namespace database
diff --git a/src/database/include/db_task.hpp b/src/database/include/db_task.hpp
new file mode 100644
index 00000000..39f932b0
--- /dev/null
+++ b/src/database/include/db_task.hpp
@@ -0,0 +1,25 @@
+#pragma once
+
+#include <functional>
+#include <future>
+#include <memory>
+
+namespace database {
+
+auto StartDbTask() -> bool;
+auto QuitDbTask() -> void;
+
+auto SendToDbTask(std::function<void(void)> fn) -> void;
+
+template <typename T>
+auto RunOnDbTask(std::function<T(void)> fn) -> std::future<T> {
+  std::shared_ptr<std::promise<T>> promise =
+      std::make_shared<std::promise<T>>();
+  SendToDbTask([=]() { promise->set_value(std::invoke(fn)); });
+  return promise->get_future();
+}
+
+template <>
+auto RunOnDbTask(std::function<void(void)> fn) -> std::future<void>;
+
+}  // namespace database
diff --git a/src/database/include/env_esp.hpp b/src/database/include/env_esp.hpp
index b8819b05..cf5a20e1 100644
--- a/src/database/include/env_esp.hpp
+++ b/src/database/include/env_esp.hpp
@@ -2,9 +2,8 @@
 
 #include <mutex>
 #include <set>
+#include <string>
 
-#include "freertos/FreeRTOS.h"
-#include "freertos/queue.h"
 #include "leveldb/env.h"
 #include "leveldb/status.h"
 
@@ -89,25 +88,6 @@ class EspEnv : public leveldb::Env {
   void BackgroundThreadMain();
 
  private:
-  // Stores the work item data in a Schedule() call.
-  //
-  // Instances are constructed on the thread calling Schedule() and used on the
-  // background thread.
-  //
-  // This structure is thread-safe beacuse it is immutable.
-  struct BackgroundWorkItem {
-    explicit BackgroundWorkItem(void (*f)(void*), void* a)
-        : function(f), arg(a) {}
-
-    void (*const function)(void*);
-    void* const arg;
-  };
-
-  std::mutex background_work_mutex_;
-  bool started_background_thread_;
-
-  QueueHandle_t background_work_queue_;
-
   InMemoryLockTable locks_;  // Thread-safe.
 };
 
diff --git a/src/database/include/file_gatherer.hpp b/src/database/include/file_gatherer.hpp
index 7cf00b41..5df5a61b 100644
--- a/src/database/include/file_gatherer.hpp
+++ b/src/database/include/file_gatherer.hpp
@@ -45,7 +45,7 @@ auto FindFiles(const std::string& root, Callback cb) -> void {
           to_explore.push_back(full_path.str());
         } else {
           // This is a file! Let the callback know about it.
-          //std::invoke(cb, full_path.str(), info);
+          // std::invoke(cb, full_path.str(), info);
           std::invoke(cb, full_path.str());
         }
       }
diff --git a/src/database/include/tag_processor.hpp b/src/database/include/tag_processor.hpp
index 88c95b61..fb2201db 100644
--- a/src/database/include/tag_processor.hpp
+++ b/src/database/include/tag_processor.hpp
@@ -9,6 +9,6 @@ struct FileInfo {
   std::string title;
 };
 
-auto GetInfo(const std::string &path, FileInfo *out) -> bool;
+auto GetInfo(const std::string& path, FileInfo* out) -> bool;
 
 }  // namespace database