package app

import (
	"flag"
	"fmt"
	"strings"
)

func isCLIFlagToken(arg string) bool {
	return strings.HasPrefix(arg, "-") && arg != "-"
}

func pullLeadingSessionID(args []string) (string, []string) {
	if len(args) == 0 || isCLIFlagToken(args[0]) {
		return "", args
	}
	rest := append([]string(nil), args[1:]...)
	return strings.TrimSpace(args[0]), rest
}

func applyPositionalSessionID(command, positional string, sessionID *string) error {
	positional = strings.TrimSpace(positional)
	if positional == "" {
		return nil
	}
	existing := strings.TrimSpace(*sessionID)
	if existing != "" && existing != positional {
		return fmt.Errorf("%s: positional session id %q does not match expected session id %q", command, positional, existing)
	}
	*sessionID = positional
	return nil
}

func applyParsedSessionIDArg(command string, fs *flag.FlagSet, sessionID *string) error {
	switch fs.NArg() {
	case 0:
		return nil
	case 1:
		return applyPositionalSessionID(command, fs.Arg(0), sessionID)
	default:
		return fmt.Errorf("%s: unexpected positional arguments", command)
	}
}

func resolveParsedSessionID(command, positionalSessionID string, fs *flag.FlagSet, sessionID *string) error {
	if strings.TrimSpace(positionalSessionID) == "" {
		return applyParsedSessionIDArg(command, fs, sessionID)
	}
	if fs.NArg() != 0 {
		return fmt.Errorf("%s: unexpected positional arguments", command)
	}
	return applyPositionalSessionID(command, positionalSessionID, sessionID)
}

func parseSessionAwareFlags(command string, fs *flag.FlagSet, args []string, sessionID *string) error {
	positionalSessionID, args := pullLeadingSessionID(args)
	if err := fs.Parse(args); err != nil {
		return fmt.Errorf("%s: invalid flags: %w", command, err)
	}
	return resolveParsedSessionID(command, positionalSessionID, fs, sessionID)
}