build.go

package watcher

import (
	"log"
	"os"
	"os/exec"
	"os/signal"
	"syscall"

	"github.com/fatih/color"
)

// Builder composes of both runner and watcher. Whenever watcher gets notified, builder starts a build process, and forces the runner to restart
type Builder struct {
	runner  *Runner
	watcher *Watcher
}

// NewBuilder constructs the Builder instance
func NewBuilder(w *Watcher, r *Runner) *Builder {
	return &Builder{watcher: w, runner: r}
}

// Build listens watch events from Watcher and sends messages to Runner
// when new changes are built.
func (b *Builder) Build(p *Params) {
	go b.registerSignalHandler()
	go func() {
		// used for triggering the first build
		b.watcher.update <- struct{}{}
	}()

	for range b.watcher.Wait() {
		fileName := p.generateBinaryName()

		pkg := p.packagePath()

		log.Println("build started")
		color.Cyan("Building %s...\n", pkg)

		// build package
		cmd, err := runCommand("go", "build", "-i", "-o", fileName, pkg)
		if err != nil {
			log.Fatalf("Could not run 'go build' command: %s", err)
			continue
		}

		if err := cmd.Wait(); err != nil {
			if err := interpretError(err); err != nil {
				color.Red("An error occurred while building: %s", err)
			} else {
				color.Red("A build error occurred. Please update your code...")
			}

			continue
		}
		log.Println("build completed")

		// and start the new process
		b.runner.restart(fileName)
	}
}

func (b *Builder) registerSignalHandler() {
	signals := make(chan os.Signal)
	signal.Notify(signals, syscall.SIGINT, syscall.SIGTERM, syscall.SIGQUIT)
	<-signals
	b.watcher.Close()
	b.runner.Close()
}

// interpretError checks the error, and returns nil if it is
// an exit code 2 error. Otherwise error is returned as it is.
// when a compilation error occurres, it returns with code 2.
func interpretError(err error) error {
	exiterr, ok := err.(*exec.ExitError)
	if !ok {
		return err
	}

	status, ok := exiterr.Sys().(syscall.WaitStatus)
	if !ok {
		return err
	}

	if status.ExitStatus() == 2 {
		return nil
	}

	return err
}