// mautrix-discord - A Matrix-Discord puppeting bridge.
// Copyright (C) 2026 The mautrix-discord contributors
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

package meowcord

import (
	"encoding"
	"fmt"

	"github.com/google/uuid"
)

const uuidv4ByteSize = 16

// A LaunchSignature is a valid version 4 UUID that doubles as a bitfield denoting the presence
// of certain properties on the JavaScript window object.
//
// In the first-party client, launch signatures are generated by libdiscore.
type LaunchSignature uuid.UUID

// A bitmask that, when ANDed with the bytes of a version 4 UUID, produces a launch signature reflecting
// no detected properties.
//
// Note that this incidentally includes the bits that must be zeroed in a valid version 4 UUID.
var vanillaBitmask = [uuidv4ByteSize]byte{0xff, 0x7f, 0xef, 0xef, 0xf7, 0xef, 0x47, 0xff, 0x9f, 0x7e, 0xff, 0xbf, 0xfe, 0xff, 0xf7, 0xff}

// NewVanillaSignature randomly generates a valid launch signature corresponding to a completely unmodified
// client, i.e. a browser environment that does not trip any of the property checks.
func NewVanillaSignature() (LaunchSignature, error) {
	uuid := uuid.New()

	for i := 0; i < uuidv4ByteSize; i++ {
		uuid[i] &= vanillaBitmask[i]
	}

	return LaunchSignature(uuid), nil
}

var _ encoding.TextMarshaler = (*LaunchSignature)(nil)
var _ fmt.Stringer = (*LaunchSignature)(nil)

func (l LaunchSignature) MarshalText() (text []byte, err error) {
	return uuid.UUID(l).MarshalText()
}

func (l LaunchSignature) String() string {
	return uuid.UUID(l).String()
}