// Copyright (c) 2016- Daniel Oaks <daniel@danieloaks.net>
// released under the MIT license

package irc

import (
	"encoding/base64"
	"strings"
	"time"

	"github.com/DanielOaks/girc-go/ircmsg"
)

var (
	// EnabledSaslMechanisms contains the SASL mechanisms that exist and that we support.
	// This can be moved to some other data structure/place if we need to load/unload mechs later.
	EnabledSaslMechanisms = map[string]func(*Server, *Client, string, []byte) bool{
		"PLAIN":    authPlainHandler,
		"EXTERNAL": authExternalHandler,
	}

	// NoAccount is a placeholder which means that the user is not logged into an account.
	NoAccount = ClientAccount{
		Name: "*", // * is used until actual account name is set
	}
)

// ClientAccount represents a user account.
type ClientAccount struct {
	// Name of the account.
	Name string
	// RegisteredAt represents the time that the account was registered.
	RegisteredAt time.Time
	// Clients that are currently logged into this account (useful for notifications).
	Clients []*Client
}

// authenticateHandler parses the AUTHENTICATE command (for SASL authentication).
func authenticateHandler(server *Server, client *Client, msg ircmsg.IrcMessage) bool {
	// sasl abort
	if len(msg.Params) == 1 && msg.Params[0] == "*" {
		if client.saslInProgress {
			client.Send(nil, server.nameString, ERR_SASLABORTED, client.nickString, "SASL authentication aborted")
		} else {
			client.Send(nil, server.nameString, ERR_SASLFAIL, client.nickString, "SASL authentication failed")
		}
		client.saslInProgress = false
		client.saslMechanism = ""
		client.saslValue = ""
		return false
	}

	// start new sasl session
	if !client.saslInProgress {
		mechanism := strings.ToUpper(msg.Params[0])
		_, mechanismIsEnabled := EnabledSaslMechanisms[mechanism]

		if mechanismIsEnabled {
			client.saslInProgress = true
			client.saslMechanism = mechanism
			client.Send(nil, server.nameString, "AUTHENTICATE", "+")
		} else {
			client.Send(nil, server.nameString, ERR_SASLFAIL, client.nickString, "SASL authentication failed")
		}

		return false
	}

	// continue existing sasl session
	rawData := msg.Params[0]

	if len(rawData) > 400 {
		client.Send(nil, server.nameString, ERR_SASLTOOLONG, client.nickString, "SASL message too long")
		client.saslInProgress = false
		client.saslMechanism = ""
		client.saslValue = ""
		return false
	} else if len(rawData) == 400 {
		client.saslValue += rawData
		// allow 4 'continuation' lines before rejecting for length
		if len(client.saslValue) > 400*4 {
			client.Send(nil, server.nameString, ERR_SASLFAIL, client.nickString, "SASL authentication failed: Passphrase too long")
			client.saslInProgress = false
			client.saslMechanism = ""
			client.saslValue = ""
			return false
		}
		return false
	} else if len(client.saslValue) > 0 {
		client.saslValue += rawData
		return false
	}
	client.saslValue += rawData

	data, err := base64.StdEncoding.DecodeString(client.saslValue)
	if err != nil {
		client.Send(nil, server.nameString, ERR_SASLFAIL, client.nickString, "SASL authentication failed: Invalid b64 encoding")
		client.saslInProgress = false
		client.saslMechanism = ""
		client.saslValue = ""
		return false
	}

	// call actual handler
	handler, handlerExists := EnabledSaslMechanisms[client.saslMechanism]

	// like 100% not required, but it's good to be safe I guess
	if !handlerExists {
		client.Send(nil, server.nameString, ERR_SASLFAIL, client.nickString, "SASL authentication failed")
		client.saslInProgress = false
		client.saslMechanism = ""
		client.saslValue = ""
		return false
	}

	return handler(server, client, client.saslMechanism, data)
}

// authPlainHandler parses the SASL PLAIN mechanism.
func authPlainHandler(server *Server, client *Client, mechanism string, value []byte) bool {
	client.Send(nil, server.nameString, ERR_SASLFAIL, client.nickString, "SASL authentication failed: Mechanism not yet implemented")
	return false
}

// authExternalHandler parses the SASL EXTERNAL mechanism.
func authExternalHandler(server *Server, client *Client, mechanism string, value []byte) bool {
	client.Send(nil, server.nameString, ERR_SASLFAIL, client.nickString, "SASL authentication failed: Mechanism not yet implemented")
	return false
}