feat(cmd): Enable setting flags via env vars

Author: cluttrdev

go.mod

@@ -2,7 +2,4 @@ module github.com/cluttrdev/deepl-go
 
 go 1.21
 
-require (
-	github.com/pkg/errors v0.9.1
-	golang.org/x/text v0.7.0
-)
+require golang.org/x/text v0.7.0

go.sum

@@ -1,4 +1,2 @@
-github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
-github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 golang.org/x/text v0.7.0 h1:4BRB4x83lYWy72KwLD/qYDuTu7q9PjSagHvijDw7cLo=
 golang.org/x/text v0.7.0/go.mod h1:mrYo+phRRbMaCq/xk9113O4dZlRixOauAjOtrjsXDZ8=

internal/cmd/root.go

@@ -115,7 +115,12 @@ func Execute() error {
 		return errors.New("failed to configure root command")
 	}
 
-	if err := rootCmd.Parse(os.Args[1:]); err != nil {
+	args := os.Args[1:]
+	opts := []command.ParseOption{
+		command.WithEnvVarPrefix("DEEPL"),
+	}
+
+	if err := rootCmd.Parse(args, opts...); err != nil {
 		if errors.Is(err, flag.ErrHelp) {
 			return nil
 		} else {

internal/command/command.go

@@ -5,7 +5,6 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"strings"
 )
 
 type Command struct {
@@ -24,42 +23,6 @@ type Command struct {
 	args     []string
 }
 
-func (cmd *Command) Parse(args []string) error {
-	if cmd.Name == "" {
-		return errors.New("name is required")
-	}
-	if cmd.Flags == nil {
-		cmd.Flags = flag.NewFlagSet(cmd.Name, flag.ContinueOnError)
-	}
-
-	cmd.Flags.Usage = func() {
-		fmt.Fprintln(cmd.Flags.Output(), DefaultUsage(cmd))
-	}
-
-	if err := cmd.Flags.Parse(args); err != nil {
-		return fmt.Errorf("%s: %w", cmd.Name, err)
-	}
-
-	cmd.args = cmd.Flags.Args()
-
-	// check for subcommands
-	if len(cmd.args) > 0 {
-		arg0 := cmd.args[0]
-		for _, subcmd := range cmd.Subcommands {
-			if strings.EqualFold(arg0, subcmd.Name) {
-				cmd.selected = subcmd
-				subcmd.parent = cmd
-				return subcmd.Parse(cmd.args[1:])
-			}
-		}
-	}
-
-	// select self if no subcommand was found
-	cmd.selected = cmd
-
-	return nil
-}
-
 func (cmd *Command) Run(ctx context.Context) (err error) {
 	if !cmd.Flags.Parsed() {
 		return errors.New("not parsed")

internal/command/parse.go

@@ -0,0 +1,138 @@
+package command
+
+import (
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"strings"
+)
+
+type ParseOptions struct {
+	envVarEnabled bool
+	envVarPrefix  string
+}
+
+type ParseOption func(*ParseOptions) error
+
+func WithEnvVars() ParseOption {
+	return func(po *ParseOptions) error {
+		po.envVarEnabled = true
+		return nil
+	}
+}
+
+func WithEnvVarPrefix(prefix string) ParseOption {
+	return func(po *ParseOptions) error {
+		po.envVarEnabled = true
+		po.envVarPrefix = prefix
+		return nil
+	}
+}
+
+func (cmd *Command) Parse(args []string, options ...ParseOption) error {
+	if cmd.Name == "" {
+		return errors.New("name is required")
+	}
+	if cmd.Flags == nil {
+		cmd.Flags = flag.NewFlagSet(cmd.Name, flag.ContinueOnError)
+	}
+
+	cmd.Flags.Usage = func() {
+		fmt.Fprintln(cmd.Flags.Output(), DefaultUsage(cmd))
+	}
+
+	if err := parse(cmd.Flags, args, options...); err != nil {
+		return fmt.Errorf("%s: %w", cmd.Name, err)
+	}
+
+	cmd.args = cmd.Flags.Args()
+
+	// check for subcommands
+	if len(cmd.args) > 0 {
+		for _, subcmd := range cmd.Subcommands {
+			if strings.EqualFold(args[0], subcmd.Name) {
+				cmd.selected = subcmd
+				subcmd.parent = cmd
+
+				return subcmd.Parse(cmd.args[1:], options...)
+			}
+		}
+	}
+
+	// select self if no subcommand was found
+	cmd.selected = cmd
+
+	return nil
+}
+
+func parse(fs *flag.FlagSet, args []string, options ...ParseOption) error {
+	var opts ParseOptions
+	for _, option := range options {
+		if err := option(&opts); err != nil {
+			return err
+		}
+	}
+
+	provided := map[string]bool{}
+
+	// command-line flags first
+	{
+		if err := fs.Parse(args); err != nil {
+			return fmt.Errorf("parse args: %w", err)
+		}
+
+		// mark set flags as provided
+		fs.Visit(func(f *flag.Flag) {
+			provided[f.Name] = true
+		})
+	}
+
+	// environment variables next
+	if opts.envVarEnabled {
+		var visitErr error
+		fs.VisitAll(func(f *flag.Flag) {
+			// skip flags already provided
+			if provided[f.Name] {
+				return
+			}
+
+			key := getEnvVarKey(f.Name, opts.envVarPrefix)
+
+			val := os.Getenv(key)
+			if val == "" {
+				return
+			}
+
+			if err := fs.Set(f.Name, val); err != nil {
+				visitErr = err
+			}
+		})
+		if visitErr != nil {
+			return fmt.Errorf("parse env: %w", visitErr)
+		}
+
+		// mark set flags as provided
+		fs.Visit(func(f *flag.Flag) {
+			provided[f.Name] = true
+		})
+	}
+
+	return nil
+}
+
+func getEnvVarKey(name string, prefix string) string {
+	replacer := strings.NewReplacer(
+		"-", "_",
+		".", "_",
+		"/", "_",
+	)
+
+	key := strings.ToUpper(name)
+	key = replacer.Replace(key)
+	if prefix != "" {
+		key = strings.ToUpper(prefix) + "_" + key
+	}
+
+	return key
+}