impl: cmd/generate: add inital command interface

Add initial command interface for generator.

cmd/generate/main.go

@@ -0,0 +1,30 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"context"
+	"log"
+	"os"
+
+	"github.com/googleapis/generator/internal/generate"
+)
+
+func main() {
+	ctx := context.Background()
+	if err := generate.Run(ctx, os.Args[1:]...); err != nil {
+		log.Fatal(err)
+	}
+}

internal/generate/errors.go

@@ -0,0 +1,19 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package generate
+
+import "errors"
+
+var errNotImplemented = errors.New("generator: functionality not implemented for language")

internal/generate/flags.go

@@ -0,0 +1,87 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package generate
+
+import (
+	"flag"
+	"fmt"
+)
+
+type config struct {
+	googleapis string
+	language   string
+	output     string
+}
+
+func parseFlags(cfg *config, args []string) (*config, error) {
+	flags := flag.NewFlagSet("", flag.ContinueOnError)
+	flags.StringVar(&cfg.language, "language", "", "specify from cpp, csharp, go, java, node, php, python, ruby, rust")
+	flags.StringVar(&cfg.googleapis, "googleapis", "", "location of googleapis `dir`")
+	flags.StringVar(&cfg.output, "output", "", "location of generated client library output")
+
+	// We don't want to print the whole usage message on each flags
+	// error, so we set to a no-op and do the printing ourselves.
+	flags.Usage = func() {}
+	usage := func() {
+		fmt.Fprint(flags.Output(), `Generator generates client libraries for Google APIs.
+
+Usage:
+
+  generator [command] [flags]
+
+Flags:
+
+`)
+		flags.PrintDefaults()
+		fmt.Fprintf(flags.Output(), "\n\n")
+	}
+
+	if err := flags.Parse(args); err != nil {
+		if err == flag.ErrHelp {
+			usage() // print usage only on help
+		}
+		return nil, err
+	}
+	if err := validateConfig(cfg); err != nil {
+		usage() // print usage only on help
+		return nil, err
+	}
+	return cfg, nil
+}
+
+func validateConfig(cfg *config) error {
+	switch cfg.language {
+	case "cpp":
+		return errNotImplemented
+	case "csharp":
+		return errNotImplemented
+	case "go":
+		return errNotImplemented
+	case "java":
+		return errNotImplemented
+	case "node":
+		return errNotImplemented
+	case "php":
+		return errNotImplemented
+	case "python":
+		return errNotImplemented
+	case "ruby":
+		return errNotImplemented
+	case "rust":
+		return errNotImplemented
+	default:
+		return fmt.Errorf("invalid -language flag specified: %q", cfg.language)
+	}
+}

internal/generate/run.go

@@ -0,0 +1,28 @@
+// Copyright 2024 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//	https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package generate
+
+import (
+	"context"
+)
+
+func Run(ctx context.Context, arg ...string) error {
+	cfg := &config{}
+	_, err := parseFlags(cfg, arg)
+	if err != nil {
+		return err
+	}
+	return nil
+}