package com.peachpasswords.sync

import java.util.Base64
import kotlinx.serialization.Serializable
import kotlinx.serialization.encodeToString
import kotlinx.serialization.json.Json

private const val PAIRING_INVITATION_PREFIX = "peach-pair-v1:"
private val PairingTokenPattern = Regex("^[A-Za-z0-9_-]{22}$")

data class PairingInvitation(
    val relayUrl: String,
    val token: String,
)

@Serializable
private data class PairingInvitationWire(
    val relay: String,
    val token: String,
)

/**
 * QR/manual first-pair payload. Only reachability is present before Noise:
 * a credential-free wss relay and a fresh 128-bit token. Never add identity or
 * vault fields here.
 */
fun createPairingInvitation(
    relayUrl: String,
    token: String = Rendezvous.newPairingToken(),
): String {
    require(PairingTokenPattern.matches(token)) {
        "pairing invitation token must be 128-bit base64url"
    }
    val wire = PairingInvitationWire(Rendezvous.normalizeRelayUrl(relayUrl), token)
    val encoded = Base64.getUrlEncoder().withoutPadding()
        .encodeToString(Json.encodeToString(wire).toByteArray(Charsets.UTF_8))
    return PAIRING_INVITATION_PREFIX + encoded
}

fun parsePairingInvitation(input: String): PairingInvitation? {
    val value = input.trim()
    if (!value.startsWith(PAIRING_INVITATION_PREFIX)) return null
    return runCatching {
        val decoded = Base64.getUrlDecoder().decode(
            value.removePrefix(PAIRING_INVITATION_PREFIX),
        )
        val wire = Json.decodeFromString<PairingInvitationWire>(
            String(decoded, Charsets.UTF_8),
        )
        require(PairingTokenPattern.matches(wire.token))
        PairingInvitation(
            relayUrl = Rendezvous.normalizeRelayUrl(wire.relay),
            token = wire.token,
        )
    }.getOrNull()
}

fun PairingInvitation.roomUrl(): String = Rendezvous.buildUrl(relayUrl, token)