From 5d7cbec34cd5e473d5768b39054d99bc72ddad62 Mon Sep 17 00:00:00 2001
From: jacqueline <me@jacqueline.id.au>
Date: Thu, 27 Apr 2023 12:55:30 +1000
Subject: Move DB interactions to a background thread

---
 src/database/database.cpp | 128 +++++++++++++++++++++++++++++++---------------
 1 file changed, 88 insertions(+), 40 deletions(-)

(limited to 'src/database/database.cpp')

diff --git a/src/database/database.cpp b/src/database/database.cpp
index b677f4ba..8ca72771 100644
--- a/src/database/database.cpp
+++ b/src/database/database.cpp
@@ -4,75 +4,123 @@
 #include "ff.h"
 #include "leveldb/cache.h"
 
+#include "db_task.hpp"
+#include "env_esp.hpp"
 #include "file_gatherer.hpp"
 #include "leveldb/iterator.h"
+#include "leveldb/options.h"
 #include "leveldb/slice.h"
+#include "result.hpp"
 #include "tag_processor.hpp"
-#include "env_esp.hpp"
-#include "leveldb/options.h"
 
 namespace database {
 
 static SingletonEnv<leveldb::EspEnv> sEnv;
-static const char *kTag = "DB";
+static const char* kTag = "DB";
+
+static std::atomic<bool> sIsDbOpen(false);
 
 auto Database::Open() -> cpp::result<Database*, DatabaseError> {
-  leveldb::DB* db;
-  leveldb::Cache* cache = leveldb::NewLRUCache(24 * 1024);
-  leveldb::Options options;
-  options.env = sEnv.env();
-  options.create_if_missing = true;
-  options.write_buffer_size = 48 * 1024;
-  options.max_file_size = 32;
-  options.block_cache = cache;
-  options.block_size = 512;
-
-  auto status = leveldb::DB::Open(options, "/.db", &db);
-  if (!status.ok()) {
-    delete cache;
-    ESP_LOGE(kTag, "failed to open db, status %s", status.ToString().c_str());
-    return cpp::fail(FAILED_TO_OPEN);
+  // TODO(jacqueline): Why isn't compare_and_exchange_* available?
+  if (sIsDbOpen.exchange(true)) {
+    return cpp::fail(DatabaseError::ALREADY_OPEN);
   }
 
-  return new Database(db, cache);
+  if (!StartDbTask()) {
+    return cpp::fail(DatabaseError::ALREADY_OPEN);
+  }
+
+  return RunOnDbTask<cpp::result<Database*, DatabaseError>>(
+             []() -> cpp::result<Database*, DatabaseError> {
+               leveldb::DB* db;
+               leveldb::Cache* cache = leveldb::NewLRUCache(24 * 1024);
+               leveldb::Options options;
+               options.env = sEnv.env();
+               options.create_if_missing = true;
+               options.write_buffer_size = 48 * 1024;
+               options.max_file_size = 32;
+               options.block_cache = cache;
+               options.block_size = 512;
+
+               auto status = leveldb::DB::Open(options, "/.db", &db);
+               if (!status.ok()) {
+                 delete cache;
+                 ESP_LOGE(kTag, "failed to open db, status %s",
+                          status.ToString().c_str());
+                 return cpp::fail(FAILED_TO_OPEN);
+               }
+
+               ESP_LOGI(kTag, "Database opened successfully");
+               return new Database(db, cache);
+             })
+      .get();
 }
 
 Database::Database(leveldb::DB* db, leveldb::Cache* cache)
     : db_(db), cache_(cache) {}
 
-Database::~Database() {}
+Database::~Database() {
+  QuitDbTask();
+  sIsDbOpen.store(false);
+}
 
-auto Database::Initialise() -> void {
-  leveldb::WriteOptions opt;
-  opt.sync = true;
-  FindFiles("", [&](const std::string &path) {
+template <typename Parser>
+auto IterateAndParse(leveldb::Iterator* it, std::size_t limit, Parser p)
+    -> void {
+  for (int i = 0; i < limit; i++) {
+    if (!it->Valid()) {
+      break;
+    }
+    std::invoke(p, it->key(), it->value());
+    it->Next();
+  }
+}
+
+auto Database::Populate() -> std::future<void> {
+  return RunOnDbTask<void>([&]() -> void {
+    leveldb::WriteOptions opt;
+    opt.sync = true;
+    FindFiles("", [&](const std::string& path) {
       ESP_LOGI(kTag, "considering %s", path.c_str());
       FileInfo info;
       if (GetInfo(path, &info)) {
         ESP_LOGI(kTag, "added as '%s'", info.title.c_str());
         db_->Put(opt, "title:" + info.title, path);
       }
+    });
+    db_->Put(opt, "title:coolkeywithoutval", leveldb::Slice());
   });
-  db_->Put(opt, "title:coolkeywithoutval", leveldb::Slice());
 }
 
-auto Database::ByTitle() -> Iterator {
-  leveldb::Iterator *it = db_->NewIterator(leveldb::ReadOptions());
-  it->Seek("title:");
-  while (it->Valid()) {
-    ESP_LOGI(kTag, "%s : %s", it->key().ToString().c_str(), it->value().ToString().c_str());
-    it->Next();
-  }
-  return Iterator(it);
+auto Database::GetSongs(std::size_t page_size) -> std::future<DbResult<Song>> {
+  return RunOnDbTask<DbResult<Song>>([&]() -> DbResult<Song> {
+    std::unique_ptr<leveldb::Iterator> it(
+        db_->NewIterator(leveldb::ReadOptions()));
+    it->Seek("title:");
+    std::vector<Song> results;
+    IterateAndParse(it.get(), page_size,
+                    [&](const leveldb::Slice& key, const leveldb::Slice& val) {
+                      Song s;
+                      s.title = key.ToString();
+                      results.push_back(s);
+                    });
+    return DbResult<Song>(results, std::move(it));
+  });
 }
 
-auto Iterator::Next() -> std::optional<std::string> {
-  if (!it_->Valid()) {
-    return {};
-  }
-  std::string ret = it_->key().ToString();
-  it_->Next();
-  return ret;
+auto Database::GetMoreSongs(std::size_t page_size, DbResult<Song> continuation)
+    -> std::future<DbResult<Song>> {
+  return RunOnDbTask<DbResult<Song>>([&]() -> DbResult<Song> {
+    std::unique_ptr<leveldb::Iterator> it(continuation.it());
+    std::vector<Song> results;
+    IterateAndParse(it.get(), page_size,
+                    [&](const leveldb::Slice& key, const leveldb::Slice& val) {
+                      Song s;
+                      s.title = key.ToString();
+                      results.push_back(s);
+                    });
+    return DbResult<Song>(results, std::move(it));
+  });
 }
 
 }  // namespace database
-- 
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