design Command for governor module & decouple web module from task module

pkg/infrastructure/governor/command.go

@@ -0,0 +1,87 @@
+// Copyright 2020
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package governor
+
+import (
+	"github.com/pkg/errors"
+)
+
+// Command is an experimental interface
+// We try to use this to decouple modules
+// All other modules depends on this, and they register the command they support
+// We may change the API in the future, so be careful about this.
+type Command interface {
+	Execute(params ...interface{}) *Result
+}
+
+var CommandNotFound = errors.New("Command not found")
+
+type Result struct {
+	// Status is the same as http.Status
+	Status  int
+	Error   error
+	Content interface{}
+}
+
+func (r *Result) IsSuccess() bool {
+	return r.Status >= 200 && r.Status < 300
+}
+
+// CommandRegistry stores all commands
+// name => command
+type moduleCommands map[string]Command
+
+// Get returns command with the name
+func (m moduleCommands) Get(name string) Command {
+	c, ok := m[name]
+	if ok {
+		return c
+	}
+	return &doNothingCommand{}
+}
+
+// module name => moduleCommand
+type commandRegistry map[string]moduleCommands
+
+// Get returns module's commands
+func (c commandRegistry) Get(moduleName string) moduleCommands {
+	if mcs, ok := c[moduleName]; ok {
+		return mcs
+	}
+	res := make(moduleCommands)
+	c[moduleName] = res
+	return res
+}
+
+var cmdRegistry = make(commandRegistry)
+
+// RegisterCommand is not thread-safe
+// do not use it in concurrent case
+func RegisterCommand(module string, commandName string, command Command) {
+	cmdRegistry.Get(module)[commandName] = command
+}
+
+func GetCommand(module string, cmdName string) Command {
+	return cmdRegistry.Get(module).Get(cmdName)
+}
+
+type doNothingCommand struct{}
+
+func (d *doNothingCommand) Execute(params ...interface{}) *Result {
+	return &Result{
+		Status: 404,
+		Error:  CommandNotFound,
+	}
+}