main.go

// SPDX-License-Identifier: Apache-2.0
// Copyright Authors of Cilium

package main

import (
	"log/slog"
	"os"

	"github.com/spf13/cobra"

	"github.com/cilium/hive"
	"github.com/cilium/hive/cell"
	"github.com/cilium/hive/job"
)

var (
	// Create a hive from a set of cells.
	Hive = hive.New(
		cell.SimpleHealthCell,
		job.Cell,

		cell.Module(
			"example",
			"Example application",

			serverCell,        // An HTTP server, depends on HTTPHandler's
			eventsCell,        // Example event source (ExampleEvents)
			helloHandlerCell,  // Handler for /hello
			eventsHandlerCell, // Handler for /events

			// Constructors are lazy and only invoked if they are a dependency
			// to an "invoke" function or an indirect dependency of a constructor
			// referenced in an invoke. This allows composing "bundles" of modules
			// and then only paying for what's actually used from the bundle.
			//
			// Think of invoke functions as the driver that decides what things
			// should be constructed and how they should integrate with each other.
			//
			// Modules that provide a service to others should usually not have any invoke
			// functions that force object construction whether or not it is needed.
			//
			// In this example we have the server at the top of the dependency tree,
			// so we'll just depend on it here to make sure it gets instantiated.
			cell.Invoke(func(Server) {}),
		),
	)

	// Define a cobra command that runs the hive.
	cmd = &cobra.Command{
		Use: "example",
		RunE: func(_ *cobra.Command, args []string) error {
			// When we get here, cobra has parsed all the command-line flags and hive
			// can be started.
			// This first populates all configurations from Viper (and via pflag)
			// and then constructs all objects, followed by executing the start
			// hooks in dependency order. It will then block waiting for signals
			// after which it will run the stop hooks in reverse order.
			if err := Hive.Run(slog.Default()); err != nil {
				// Run() can fail if:
				// - There are missing types in the object graph
				// - Executing the lifecycle start or stop hooks fails
				// - Shutdowner.Shutdown() is called with an error
				return err
			}
			return nil
		},
	}

	// Define the "repl" command to run the application in an interactive
	// read-eval-print-loop:
	//
	//   $ go run . repl
	//   example> hive start
	//   time=2024-10-08T09:39:00.881+02:00 level=INFO msg=Starting hive
	//   ...
	//   example> events
	//   ...
	//   example> hive stop
	replCmd = &cobra.Command{
		Use: "repl",
		Run: func(_ *cobra.Command, args []string) {
			hive.RunRepl(Hive, os.Stdin, os.Stdout, "example> ")
		},
	}
)

func main() {
	// Register all configuration flags in the hive to the command
	Hive.RegisterFlags(cmd.Flags())

	cmd.AddCommand(
		// Add the "hive" sub-command for inspecting the hive
		Hive.Command(),

		// Add the "repl" command to interactively run the application.
		replCmd,
	)

	// And finally execute the command to parse the command-line flags and
	// run the hive
	cmd.Execute()
}