build: install pelican with mage

- Add an install mage target for installing pelican.
- Display the app's version information using the version flag.

README.asciidoc

@@ -5,7 +5,7 @@
 
 == Overview
 
-**This project is WIP and is not meant for production use.**
+**This project is in ALPHA state and is not ready for production use yet.**
 
 Pelican is a simple Kanban board for your terminal.
 Data is stored in a https://github.com/etcd-io/bbolt[BoltDB] database.
@@ -29,7 +29,21 @@ You can visit the https://magefile.org[website] for instructions on how to insta
 
 === Install with Mage
 
-_TBC_
+You can install pelican with Mage using the following commands:
+[source,console]
+----
+git clone https://codeflow.dananglin.me.uk/apollo/pelican.git
+cd pelican
+mage install
+----
+
+The default install prefix is set to `/usr/local` so pelican will be installed to `/usr/local/bin/pelican`.
+If you want to change the install prefix you can set the `PELICAN_INSTALL_PREFIX` environment variable
+before installing.
+[source,console]
+----
+PELICAN_INSTALL_PREFIX=~/.local mage install
+----
 
 === Install with Go
 

cmd/pelican/main.go

@@ -1,18 +1,31 @@
 package main
 
 import (
+	"flag"
 	"log"
-	"os"
 
 	"codeflow.dananglin.me.uk/apollo/pelican/internal/ui"
 )
 
 func main() {
-	if len(os.Args) != 2 {
-		log.Fatalf("ERROR: Unexpected number of command-line arguments; want 1; got %d", len(os.Args)-1)
+	var versionFlag bool
+
+	flag.BoolVar(&versionFlag, "version", false, "prints the application's build information")
+	flag.Parse()
+
+	if versionFlag {
+		version()
+
+		return
 	}
 
-	pelican, err := ui.NewUI(os.Args[1])
+	args := flag.Args()
+
+	if len(args) != 1 {
+		log.Fatalf("ERROR: Unexpected number of command-line arguments; want 1; got %d", len(args))
+	}
+
+	pelican, err := ui.NewUI(args[0])
 	if err != nil {
 		log.Fatalf("ERROR: Unable to initialise Pelican; %v", err)
 	}

cmd/pelican/version.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+var (
+	binaryVersion string
+	buildTime     string
+	goVersion     string
+	gitCommit     string
+)
+
+func version() {
+	fmt.Fprintf(
+		os.Stdout,
+		"Pelican\n  Version: %s\n  Git commit: %s\n  Go version: %s\n  Build date: %s\n",
+		binaryVersion,
+		gitCommit,
+		goVersion,
+		buildTime,
+	)
+}

magefiles/mage.go

@@ -3,14 +3,20 @@
 package main
 
 import (
+	"fmt"
 	"os"
+	"path/filepath"
+	"runtime"
 	"strings"
+	"time"
 
+	"github.com/magefile/mage/mg"
 	"github.com/magefile/mage/sh"
 )
 
 const (
-	binary = "pelican"
+	binary               = "pelican"
+	defaultInstallPrefix = "/usr/local"
 )
 
 var Default = Build
@@ -41,8 +47,29 @@ func Lint() error {
 
 // Build build the executable
 func Build() error {
-	main := "./cmd/" + binary + "/main.go"
-	return sh.Run("go", "build", "-o", binary, main)
+	main := "./cmd/" + binary
+	flags := ldflags()
+
+	return sh.Run("go", "build", "-ldflags="+flags, "-a", "-o", binary, main)
+}
+
+func Install() error {
+	mg.Deps(Build)
+
+	installPrefix := os.Getenv("PELICAN_INSTALL_PREFIX")
+	if installPrefix == "" {
+		installPrefix = defaultInstallPrefix
+	}
+
+	dest := filepath.Join(installPrefix, "bin", binary)
+
+	if err := sh.Copy(dest, binary); err != nil {
+		return fmt.Errorf("unable to install %s; %w", dest, err)
+	}
+
+	fmt.Printf("%s successfully installed to %s\n", binary, dest)
+
+	return nil
 }
 
 // Clean clean the workspace
@@ -71,3 +98,31 @@ func Clean() error {
 
 	return nil
 }
+
+// ldflags returns the build flags.
+func ldflags() string {
+	ldflagsfmt := "-s -w -X main.binaryVersion=%s -X main.gitCommit=%s -X main.goVersion=%s -X main.buildTime=%s"
+	buildTime := time.Now().UTC().Format(time.RFC3339)
+
+	return fmt.Sprintf(ldflagsfmt, version(), gitCommit(), runtime.Version(), buildTime)
+}
+
+// version returns the latest git tag using git describe.
+func version() string {
+	version, err := sh.Output("git", "describe", "--tags")
+	if err != nil {
+		version = "N/A"
+	}
+
+	return version
+}
+
+// gitCommit returns the current git commit
+func gitCommit() string {
+	commit, err := sh.Output("git", "rev-parse", "--short", "HEAD")
+	if err != nil {
+		commit = "N/A"
+	}
+
+	return commit
+}