package mailmux

import (
	"encoding/json"
	"errors"
	"io"
	"time"

	"mailmux.net/aliases"
)

const (
	Tregister = 1 + iota
	Rregister
	Rerror
	Tnew
	Rnew
	Tlist
	Rlist
	Tremove
)

// Mcall represents a message passed between mailmux clients and servers.
// Operations requested by clients are T-messages (such as Tregister).
// Servers respond with the corresponding R-message (such as Rregister).
// Servers may instead respond with Rerror to inform the client, with a diagnostic message,
// that the request was not completed successfully.
// This design is loosely based on the Plan 9 network file protocol 9P.
type Mcall struct {
	Type     uint
	Username string          // Tregister, Rregister
	Password string          // Tregister
	Error    string          // Rerror
	Aliases  aliases.Aliases // Rnew, Rlist, Tremove
	Expiry   time.Time       // Tnew, Rnew
}

// ParseMcall parses and validates a JSON-encoded Mcall from r.
func ParseMcall(r io.Reader) (*Mcall, error) {
	var mc Mcall
	if err := json.NewDecoder(r).Decode(&mc); err != nil {
		return nil, err
	}
	switch mc.Type {
	case Rerror:
		if mc.Error == "" {
			return nil, errors.New("empty error message")
		}
	case Tregister, Tnew, Tlist, Tremove:
		if mc.Username == "" {
			return nil, errors.New("empty username")
		} else if mc.Password == "" {
			return nil, errors.New("empty password")
		}
	}
	return &mc, nil
}