From 5ed4c01cc3c16b06eaf9babbb219f11082cabb15 Mon Sep 17 00:00:00 2001
From: Stefan Pranger <stefan.pranger@student.tugraz.at>
Date: Mon, 28 Jun 2021 16:56:50 +0200
Subject: [PATCH] added Schema and Migration

---
 db/Schema.cpp               | 62 +++++++++++++++++++++++++++++++++++++
 db/Schema.h                 | 21 +++++++++++++
 db/db.h                     |  3 +-
 db/migrations/Migration.cpp | 16 ++++++++++
 db/migrations/Migration.h   | 12 +++++--
 5 files changed, 110 insertions(+), 4 deletions(-)
 create mode 100644 db/Schema.cpp
 create mode 100644 db/Schema.h

diff --git a/db/Schema.cpp b/db/Schema.cpp
new file mode 100644
index 0000000..9b06de0
--- /dev/null
+++ b/db/Schema.cpp
@@ -0,0 +1,62 @@
+#include "Schema.h"
+#include <io/debug.h>
+
+#include "migrations/1624829187_create_events.h"
+
+
+namespace db {
+  namespace db_builder = db::migrations::builder;
+
+  Schema::Schema(sql::Database* db) : m_db(db) {
+  }
+
+  uint32_t Schema::get_user_version() const {
+    try {
+      int user_version = m_db->execAndGet("PRAGMA user_version;");
+      return user_version;
+    } catch (std::exception& e) {
+      std::cout << "Exception: " << e.what() << std::endl;
+      return -1;
+    }
+  }
+
+  void Schema::set_user_version(uint32_t version) {
+    try {
+      m_db->exec("PRAGMA user_version = " + std::to_string(version) + ";");
+    } catch (std::exception& e) {
+      std::cout << "Exception: " << e.what() << std::endl;
+    }
+  }
+
+  void Schema::run_migrations() {
+    assemble_migrations();
+    if(migrations.begin() == migrations.end()) {
+      DEBUG << "No migrations found...";
+      return;
+    }
+    // TODO try and catch block
+    // migration should stop on error and restore old schema
+
+    uint32_t user_version = get_user_version();
+    for(auto const& [epoch, migration] : migrations) {
+      if(epoch <= user_version) {
+        DEBUG << "Skipping: " << migration->get_migration_name();
+        continue;
+      }
+      DEBUG << "migrating: " << migration->get_migration_name();
+      try {
+        m_db->exec(migration->get_statement());
+      } catch (std::exception& e) {
+        std::cout << "Exception: " << e.what() << std::endl;
+      }
+    }
+    DEBUG << migrations.rbegin()->first;
+    set_user_version(migrations.rbegin()->first);
+    user_version = get_user_version();
+    DEBUG << user_version;
+  }
+
+  void Schema::assemble_migrations() {
+    migrations.emplace(1624829187, new db::migrations::m1624829187_create_events());
+  }
+}
diff --git a/db/Schema.h b/db/Schema.h
new file mode 100644
index 0000000..d545fdc
--- /dev/null
+++ b/db/Schema.h
@@ -0,0 +1,21 @@
+#pragma once
+
+#include <db/db.h>
+#include <map>
+#include <db/migrations/Migration.h>
+
+namespace db {
+  class Schema {
+  public:
+    Schema(sql::Database* db);
+    void run_migrations();
+
+  private:
+    uint32_t get_user_version() const;
+    void set_user_version(uint32_t user_version);
+    void assemble_migrations();
+
+    sql::Database* m_db;
+    std::map<uint32_t, db::migrations::Migration*> migrations;
+  };
+}
diff --git a/db/db.h b/db/db.h
index e118d8e..cf1ab3a 100644
--- a/db/db.h
+++ b/db/db.h
@@ -5,8 +5,7 @@
 
 namespace sql = SQLite;
 
-#include <db/create.h>
-#include <db/schema.h>
+#include <db/Schema.h>
 #include <db/migrations/builder/Table.h>
 #include <db/migrations/builder/TableBuilder.h>
 
diff --git a/db/migrations/Migration.cpp b/db/migrations/Migration.cpp
index e69de29..743fdf3 100644
--- a/db/migrations/Migration.cpp
+++ b/db/migrations/Migration.cpp
@@ -0,0 +1,16 @@
+#include "Migration.h"
+
+#include <boost/core/typeinfo.hpp>
+
+namespace db {
+  namespace migrations {
+    namespace db_builder = db::migrations::builder;
+
+    std::string Migration::get_migration_name() const {
+      return std::string(boost::core::demangled_name(BOOST_CORE_TYPEID(*this)));
+    }
+    std::string Migration::get_statement() const {
+      return m_statement;
+    }
+  }
+}
diff --git a/db/migrations/Migration.h b/db/migrations/Migration.h
index 9e02be7..69bdeec 100644
--- a/db/migrations/Migration.h
+++ b/db/migrations/Migration.h
@@ -1,11 +1,19 @@
 #pragma once
 
-#include <db/db.h>
+#include <string>
+#include <db/migrations/builder/Table.h>
+#include <db/migrations/builder/TableBuilder.h>
 
 namespace db {
   namespace migrations {
     class Migration {
+    public:
+      Migration() = default;
 
-    }
+      std::string get_statement() const;
+      virtual std::string get_migration_name() const;
+    protected:
+      std::string m_statement = "";
+    };
   }
 }