Establish initial Go application skeleton

internal/cli/root.go

@@ -0,0 +1,45 @@
+package cli
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"io"
+)
+
+const helpText = `weatherreporter prepares weather reports from normalized forecast data.
+
+Usage:
+  weatherreporter --help
+
+Options:
+  -h, --help    Show this help message.
+`
+
+// Run parses the root command and executes the selected behavior.
+func Run(ctx context.Context, args []string, stdout io.Writer, stderr io.Writer) error {
+	_ = ctx
+	_ = stderr
+
+	fs := flag.NewFlagSet("weatherreporter", flag.ContinueOnError)
+	fs.SetOutput(io.Discard)
+
+	help := fs.Bool("help", false, "show help")
+	fs.BoolVar(help, "h", false, "show help")
+
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	if *help {
+		_, err := fmt.Fprint(stdout, helpText)
+		return err
+	}
+
+	if fs.NArg() > 0 {
+		return fmt.Errorf("unknown argument %q", fs.Arg(0))
+	}
+
+	_, err := fmt.Fprint(stdout, helpText)
+	return err
+}

internal/cli/root_test.go

@@ -0,0 +1,50 @@
+package cli
+
+import (
+	"bytes"
+	"context"
+	"strings"
+	"testing"
+)
+
+func TestRunHelpLongFlag(t *testing.T) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+
+	err := Run(context.Background(), []string{"--help"}, &stdout, &stderr)
+	if err != nil {
+		t.Fatalf("Run() error = %v", err)
+	}
+
+	if !strings.Contains(stdout.String(), "Usage:") {
+		t.Fatalf("help output missing usage:\n%s", stdout.String())
+	}
+}
+
+func TestRunHelpShortFlag(t *testing.T) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+
+	err := Run(context.Background(), []string{"-h"}, &stdout, &stderr)
+	if err != nil {
+		t.Fatalf("Run() error = %v", err)
+	}
+
+	if !strings.Contains(stdout.String(), "weatherreporter --help") {
+		t.Fatalf("help output missing root help command:\n%s", stdout.String())
+	}
+}
+
+func TestRunUnknownArgument(t *testing.T) {
+	var stdout bytes.Buffer
+	var stderr bytes.Buffer
+
+	err := Run(context.Background(), []string{"generate"}, &stdout, &stderr)
+	if err == nil {
+		t.Fatal("Run() error = nil, want unknown argument error")
+	}
+
+	if !strings.Contains(err.Error(), `unknown argument "generate"`) {
+		t.Fatalf("Run() error = %q, want unknown argument message", err.Error())
+	}
+}