cli: implement db create/drop for sqlite3 (#351)

When running `amber db create` for an sqlite3 database, amber displays
the error:

  could not determine database name

This can be confusing to the user who doesn't know that `amber db
create` does not need to be run for sqlite3 databases. Display a
friendlier message.

Also implement `amber db drop` to delete the database.

spec/amber/cli/commands/generator_spec.cr

@@ -6,6 +6,34 @@ include CLIHelper
 include CLIFixtures
 
 module Amber::CLI
+  context "sqlite" do
+    cleanup
+    MainCommand.run ["new", TESTING_APP, "-d", "sqlite"]
+
+    describe "database" do
+      db_filename = db_yml["sqlite"]["database"].to_s.sub("sqlite3:", "")
+
+      Dir.cd(TESTING_APP)
+
+      it "does not create the database when `db create`" do
+        MainCommand.run ["db", "create"]
+        File.exists?(db_filename).should be_false
+      end
+
+      it "does create the database when `db migrate`" do
+        MainCommand.run ["generate", "model", "Post"]
+        MainCommand.run ["db", "migrate"]
+        File.exists?(db_filename).should be_true
+        File.stat(db_filename).size.should_not eq 0
+      end
+
+      it "deletes the database when `db drop`" do
+        MainCommand.run ["db", "drop"]
+        File.exists?(db_filename).should be_false
+      end
+    end
+  end
+
   describe "amber generate" do
     ENV["AMBER_ENV"] = "test"
     camel_case = "PostComment"

src/amber/cli/commands/database.cr

@@ -58,23 +58,34 @@ module Amber::CLI
       end
 
       def drop_database
-        name = set_database_to_schema
-        Micrate::DB.connect do |db|
-          db.exec "DROP DATABASE #{name};"
+        url = Micrate::DB.connection_url.to_s
+        if url.starts_with? "sqlite3:"
+          path = url.gsub("sqlite3:", "")
+          File.delete(path)
+          puts "Deleted file #{path}"
+        else
+          name = set_database_to_schema url
+          Micrate::DB.connect do |db|
+            db.exec "DROP DATABASE #{name};"
+          end
+          puts "Dropped database #{name}"
         end
-        puts "Dropped database #{name}"
       end
 
       def create_database
-        name = set_database_to_schema
-        Micrate::DB.connect do |db|
-          db.exec "CREATE DATABASE #{name};"
+        url = Micrate::DB.connection_url.to_s
+        if url.starts_with? "sqlite3:"
+          puts "For sqlite3, the database will be created during the first migration."
+        else
+          name = set_database_to_schema url
+          Micrate::DB.connect do |db|
+            db.exec "CREATE DATABASE #{name};"
+          end
+          puts "Created database #{name}"
         end
-        puts "Created database #{name}"
       end
 
-      def set_database_to_schema
-        url = Micrate::DB.connection_url.to_s
+      def set_database_to_schema(url)
         uri = URI.parse(url)
         if path = uri.path
           Micrate::DB.connection_url = url.gsub(path, "/#{uri.scheme}")