Add a bunch of positional argument validators

Taskfile.yml

@@ -30,7 +30,7 @@ tasks:
         msg: golines not installed, see https://github.com/segmentio/golines
     cmds:
       - go fmt ./...
-      - golines . --chain-split-dots --ignore-generated --write-output
+      - golines . --ignore-generated --write-output
 
   test:
     desc: Run the test suite

command/args.go

@@ -1,6 +1,9 @@
 package command
 
-import "fmt"
+import (
+	"fmt"
+	"slices"
+)
 
 // AnyArgs is a positional argument validator that allows any arbitrary args,
 // it never returns an error.
@@ -18,3 +21,105 @@ func NoArgs(cmd *Command, args []string) error {
 	}
 	return nil
 }
+
+// MinArgs is a positional argument validator that requires at least n arguments.
+func MinArgs(n int) func(cmd *Command, args []string) error {
+	return func(cmd *Command, args []string) error {
+		if len(args) < n {
+			return fmt.Errorf(
+				"command %s requires at least %d arguments, but got %d: %v",
+				cmd.name,
+				n,
+				len(args),
+				args,
+			)
+		}
+		return nil
+	}
+}
+
+// MaxArgs is a positional argument validator that returns an error if there are more than n arguments.
+func MaxArgs(n int) func(cmd *Command, args []string) error {
+	return func(cmd *Command, args []string) error {
+		if len(args) > n {
+			return fmt.Errorf(
+				"command %s has a limit of %d arguments, but got %d: %v",
+				cmd.name,
+				n,
+				len(args),
+				args,
+			)
+		}
+		return nil
+	}
+}
+
+// ExactArgs is a positional argument validator that allows exactly n args, any more
+// or less will return an error.
+func ExactArgs(n int) func(cmd *Command, args []string) error {
+	return func(cmd *Command, args []string) error {
+		if len(args) != n {
+			return fmt.Errorf(
+				"command %s requires exactly %d arguments, but got %d: %v",
+				cmd.name,
+				n,
+				len(args),
+				args,
+			)
+		}
+		return nil
+	}
+}
+
+// BetweenArgs is a positional argument validator that allows between min and max arguments (inclusive),
+// any outside that range will return an error.
+func BetweenArgs(min, max int) func(cmd *Command, args []string) error {
+	return func(cmd *Command, args []string) error {
+		nArgs := len(args)
+		if nArgs < min || nArgs > max {
+			return fmt.Errorf(
+				"command %s requires between %d and %d arguments, but got %d: %v",
+				cmd.name,
+				min,
+				max,
+				nArgs,
+				args,
+			)
+		}
+		return nil
+	}
+}
+
+// ValidArgs is a positional argument validator that only allows arguments that are contained in
+// the valid slice. If any non-valid arguments are seen, an error will be returned.
+func ValidArgs(valid []string) func(cmd *Command, args []string) error {
+	return func(cmd *Command, args []string) error {
+		for _, arg := range args {
+			if !slices.Contains(valid, arg) {
+				return fmt.Errorf(
+					"command %s got an invalid argument %s, expected one of %v",
+					cmd.name,
+					arg,
+					valid,
+				)
+			}
+		}
+		return nil
+	}
+}
+
+// Combine allows multiple positional argument validators to be composed together.
+//
+// The first validator to fail will be the one that returns the error.
+func Combine(
+	validators ...func(cmd *Command, args []string) error,
+) func(cmd *Command, args []string) error {
+	return func(cmd *Command, args []string) error {
+		for _, validator := range validators {
+			if err := validator(cmd, args); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+}