Start porting to Go: parse flags

Parse help/list/swap command line flags.

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

cmd/kubectx/flags.go

@@ -0,0 +1,46 @@
+package main
+
+import "strings"
+
+type Op interface{}
+
+// HelpOp describes printing help.
+type HelpOp struct{}
+
+// ListOp describes listing contexts.
+type ListOp struct{}
+
+// SwitchOp indicates intention to switch contexts.
+type SwitchOp struct {
+	Target string // '-' for back and forth, or NAME
+}
+
+// UnknownOp indicates an unsupported flag.
+type UnknownOp struct{ Args []string }
+
+// parseArgs looks at flags (excl. executable name, i.e. argv[0])
+// and decides which operation should be taken.
+func parseArgs(argv []string) Op {
+	if len(argv) == 0 {
+		return ListOp{}
+	}
+
+	if len(argv) == 1 {
+		v := argv[0]
+		if v == "--help" || v == "-h" {
+			return HelpOp{}
+		}
+
+		if strings.HasPrefix(v, "-") && v != "-" {
+			return UnknownOp{argv}
+		}
+
+		// TODO handle -d
+		// TODO handle -u/--unset
+		// TODO handle -c/--current
+		return SwitchOp{Target: argv[0]}
+	}
+
+	// TODO handle too many arguments e.g. "kubectx a b c"
+	return UnknownOp{}
+}

cmd/kubectx/flags_test.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func Test_parseArgs_new(t *testing.T) {
+	tests := []struct {
+		name string
+		args []string
+		want Op
+	}{
+		{name: "nil Args",
+			args: nil,
+			want: ListOp{}},
+		{name: "empty Args",
+			args: []string{},
+			want: ListOp{}},
+		{name: "help shorthand",
+			args: []string{"-h"},
+			want: HelpOp{}},
+		{name: "help long form",
+			args: []string{"--help"},
+			want: HelpOp{}},
+		{name: "switch by name",
+			args: []string{"foo"},
+			want: SwitchOp{Target: "foo"}},
+		{name: "switch by swap",
+			args: []string{"-"},
+			want: SwitchOp{Target: "-"}},
+		{name: "unrecognized flag",
+			args: []string{"-x"},
+			want: UnknownOp{Args: []string{"-x"}}},
+		// TODO add more UnknownOp cases
+
+		// TODO consider these cases
+		// - kubectx foo --help
+		// - kubectx -h --help
+		// - kubectx -d foo --h
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := parseArgs(tt.args)
+
+			if diff := cmp.Diff(got, tt.want); diff != "" {
+				t.Errorf("parseArgs(%#v) diff: %s", tt.args, diff)
+			}
+		})
+	}
+}

cmd/kubectx/main.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func main() {
+	// parse command-line flags
+	argv := os.Args[1:]
+	fmt.Printf("%#v\n", argv)
+
+	//var op Op
+	//op _= parseArgs(argv) // -> DeleteOp RenameOp HelpOp UnrecognizedFlags
+}
+

go.mod

@@ -0,0 +1,5 @@
+module github.com/ahmetb/kubectx
+
+go 1.14
+
+require github.com/google/go-cmp v0.4.0

go.sum

@@ -0,0 +1,3 @@
+github.com/google/go-cmp v0.4.0 h1:xsAVV57WRhGj6kEIi8ReJzQlHHqcBYCElAvkovg3B/4=
+github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=