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)
}

func parseSessionIDAndOnePositionalArg(command, argName string, fs *flag.FlagSet, args []string, sessionID *string) (string, error) {
	var positionalSessionID string
	value := ""
	if len(args) >= 2 && !isCLIFlagToken(args[0]) && !isCLIFlagToken(args[1]) {
		positionalSessionID = strings.TrimSpace(args[0])
		value = strings.TrimSpace(args[1])
		args = append([]string(nil), args[2:]...)
	}

	if err := fs.Parse(args); err != nil {
		return "", fmt.Errorf("%s: invalid flags: %w", command, err)
	}
	if value == "" {
		switch fs.NArg() {
		case 2:
			positionalSessionID = strings.TrimSpace(fs.Arg(0))
			value = strings.TrimSpace(fs.Arg(1))
		case 1:
			if strings.TrimSpace(*sessionID) == "" {
				return "", fmt.Errorf("%s: expected session_id and %s", command, argName)
			}
			value = strings.TrimSpace(fs.Arg(0))
		default:
			return "", fmt.Errorf("%s: expected session_id and %s", command, argName)
		}
	} else if fs.NArg() != 0 {
		return "", fmt.Errorf("%s: unexpected positional arguments", command)
	}
	if err := applyPositionalSessionID(command, positionalSessionID, sessionID); err != nil {
		return "", err
	}
	return value, nil
}