//go:build go1.21
// +build go1.21

package pflag

import (
	"errors"
	"flag"
	"io"
	"strings"
	"testing"
)

func TestFuncCompat(t *testing.T) {
	// compare behavior with the stdlib 'flag' package
	type FuncFlagSet interface {
		Func(name string, usage string, fn func(string) error)
		Parse([]string) error
	}

	unitTestErr := errors.New("unit test error")
	runCase := func(f FuncFlagSet, name string, args []string) (values []string, err error) {
		fn := func(s string) error {
			values = append(values, s)
			if s == "err" {
				return unitTestErr
			}
			return nil
		}
		f.Func(name, "Callback function", fn)

		err = f.Parse(args)
		return values, err
	}

	t.Run("regular parsing", func(t *testing.T) {
		flagName := "fnflag"
		args := []string{"--fnflag=xx", "--fnflag", "yy", "--fnflag=zz"}

		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
		stdValues, err := runCase(stdFSet, flagName, args)
		if err != nil {
			t.Fatalf("std flag: expected no error, got %v", err)
		}
		expected := []string{"xx", "yy", "zz"}
		if !cmpLists(expected, stdValues) {
			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
		}

		fset := NewFlagSet("pflag test", ContinueOnError)
		pflagValues, err := runCase(fset, flagName, args)
		if err != nil {
			t.Fatalf("pflag: expected no error, got %v", err)
		}
		if !cmpLists(stdValues, pflagValues) {
			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
		}
	})

	t.Run("error triggered by callback", func(t *testing.T) {
		flagName := "fnflag"
		args := []string{"--fnflag", "before", "--fnflag", "err", "--fnflag", "after"}

		// test behavior of standard flag.Fset with an error triggered by the callback:
		// (note: as can be seen in 'runCase()', if the callback sees "err" as a value
		//  for the flag, it will return an error)
		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
		stdFSet.SetOutput(io.Discard) // suppress output

		// run test case with standard flag.Fset
		stdValues, err := runCase(stdFSet, flagName, args)

		// double check the standard behavior:
		// - .Parse() should return an error, which contains the error message
		if err == nil {
			t.Fatalf("std flag: expected an error triggered by callback, got no error instead")
		}
		if !strings.HasSuffix(err.Error(), unitTestErr.Error()) {
			t.Fatalf("std flag: expected unittest error, got unexpected error value: %T %v", err, err)
		}
		// - the function should have been called twice, with the first two values,
		//   the final "=after" should not be recorded
		expected := []string{"before", "err"}
		if !cmpLists(expected, stdValues) {
			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
		}

		// now run the test case on a pflag FlagSet:
		fset := NewFlagSet("pflag test", ContinueOnError)
		pflagValues, err := runCase(fset, flagName, args)

		// check that there is a similar error (note: pflag will _wrap_ the error, while the stdlib
		// currently keeps the original message but creates a flat errors.Error)
		if !errors.Is(err, unitTestErr) {
			t.Fatalf("pflag: got unexpected error value: %T %v", err, err)
		}
		// the callback should be called the same number of times, with the same values:
		if !cmpLists(stdValues, pflagValues) {
			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
		}
	})
}