package com.peachpasswords.sync

import kotlinx.serialization.builtins.serializer
import kotlinx.serialization.json.Json
import org.bouncycastle.crypto.params.Ed25519PrivateKeyParameters

/** 0x03 adds relay routing to each introduced peer edge. */
const val DEVICE_MANIFEST_VERSION = 0x03
private const val DEVICE_MANIFEST_FRESHNESS_MS = 5 * 60_000L
/**
 * Upper bounds on what verifyDeviceManifest will accept. A pathological peer
 * could otherwise craft a manifest that consumes unbounded memory or skips
 * sanity checks (e.g. `issuedAt = Long.MIN_VALUE` bypasses `abs(...) > window`
 * because `abs(Long.MIN_VALUE)` is still negative). These caps match the
 * realistic limits of the pairing protocol: a handful of paired devices, a
 * bounded revocation list, and string fields long enough for any honest use.
 */
private const val MAX_MANIFEST_DEVICES = 256
private const val MAX_MANIFEST_REVOCATIONS = 500
private const val MAX_MANIFEST_STRING = 256
internal const val NO_KEY_SENTINEL = "0000000000000000000000000000000000000000000000000000000000000000"

interface PairedDeviceRegistry {
    fun getAll(): List<PairedDevice>
    fun get(id: String): PairedDevice?
    fun getByPubkey(pubkeyHex: String): PairedDevice? =
        getAll().firstOrNull {
            it.longTermPublicKeyHex?.let { key -> CryptoCompare.hex(key, pubkeyHex) } == true
        }
    fun upsert(device: PairedDevice)
    fun remove(deviceId: String) {}
    fun listRevocations(): List<DeviceRevocation> = emptyList()

    /** Returns the ids that were not already revoked. */
    fun mergeRevocations(incoming: List<DeviceRevocation>): List<String> = emptyList()

    /**
     * True when either the id or the long-term key is under a terminal
     * revocation. `deviceId` is a self-asserted string in a manifest, so
     * keying terminality on it alone is bypassed by re-vouching a revoked
     * device's key under a fresh id. The key is what a revoked device still
     * holds, so it is what terminality has to follow. `0`×64 is the "no key was
     * ever stored" sentinel (see PairedDeviceStore.revoke) and matches nothing.
     */
    fun isRevoked(deviceId: String, longTermPublicKeyHex: String? = null): Boolean {
        val key = longTermPublicKeyHex?.lowercase()?.takeIf { it != NO_KEY_SENTINEL }
        return listRevocations().any {
            it.deviceId == deviceId || (key != null && it.longTermPublicKeyHex.lowercase() == key)
        }
    }

    /** Only a direct, SAS-confirmed re-pair may lift a terminal revocation. */
    fun clearRevocation(deviceId: String) {}
}

fun buildSignedDeviceManifest(
    issuerDeviceId: String,
    devices: List<ManifestDeviceEntry>,
    signingPrivateKey: Ed25519PrivateKeyParameters,
    nowMs: Long = System.currentTimeMillis(),
    revoked: List<DeviceRevocation> = emptyList(),
): SignedDeviceManifest {
    require(issuerDeviceId.isNotBlank()) { "issuerDeviceId is required" }
    val body = DeviceManifestBody(
        manifestVersion = DEVICE_MANIFEST_VERSION,
        issuerDeviceId = issuerDeviceId,
        issuedAt = nowMs,
        // Normalise valid entries but keep invalid ones too — verifyDeviceManifest
        // is the gate that detects malformed input (M-09: silent drop would let
        // a caller believe they sent a valid manifest).
        devices = devices.map { normaliseManifestEntry(it) ?: it },
        revoked = revoked.map(::normaliseRevocation),
    )
    val signature = signEd25519(signingPrivateKey, canonicalDeviceManifestBody(body).toByteArray(Charsets.UTF_8))
    return SignedDeviceManifest(body, pubkeyToHex(signature))
}

fun verifyDeviceManifest(
    manifest: SignedDeviceManifest,
    issuerSigningPublicKey: ByteArray,
    nowMs: Long = System.currentTimeMillis(),
    freshnessMs: Long = DEVICE_MANIFEST_FRESHNESS_MS,
): DeviceManifestBody? {
    val body = manifest.body
    if (body.manifestVersion != DEVICE_MANIFEST_VERSION) return null
    // Two-sided bounds — avoids `abs(...) > window`, which overflows for
    // `Long.MIN_VALUE` and lets a peer-presented timestamp bypass the
    // freshness gate. Reject negative `issuedAt` outright so the bounds
    // arithmetic can't be steered into a wrap-around by the manifest.
    if (body.issuedAt < 0L) return null
    if (body.issuedAt < nowMs - freshnessMs || body.issuedAt > nowMs + freshnessMs) return null
    if (body.issuerDeviceId.isBlank() || body.issuerDeviceId.length > MAX_MANIFEST_STRING) return null
    if (body.devices.size > MAX_MANIFEST_DEVICES) return null
    if (body.revoked.size > MAX_MANIFEST_REVOCATIONS) return null
    if (!isHex(manifest.signatureHex, 128)) return null
    if (!body.devices.all { normaliseManifestEntry(it) != null }) return null
    if (!body.revoked.all { isValidRevocation(it) }) return null
    val signature = runCatching { hexToBytes(manifest.signatureHex) }.getOrNull() ?: return null
    val canonical = canonicalDeviceManifestBody(body).toByteArray(Charsets.UTF_8)
    if (!verifyEd25519(issuerSigningPublicKey, canonical, signature)) return null
    return body
}

fun canonicalDeviceManifestBody(body: DeviceManifestBody): String =
    canonicalise(
        mapOf(
            "devices" to body.devices.map { manifestEntryMap(it) },
            "issuedAt" to body.issuedAt,
            "issuerDeviceId" to body.issuerDeviceId,
            "manifestVersion" to body.manifestVersion,
            "revoked" to body.revoked.map { revocationMap(it) },
        ),
    )

fun PairedDevice.toManifestEntry(): ManifestDeviceEntry? {
    val id = deviceId.takeIf { it.isNotBlank() } ?: return null
    val name = deviceName?.takeIf { it.isNotBlank() } ?: return null
    val type = deviceType?.takeIf { it in setOf("extension", "android", "ios") } ?: return null
    val longTerm = longTermPublicKeyHex?.lowercase()?.takeIf { isHex(it, 64) } ?: return null
    val signing = signingPublicKeyHex?.lowercase()?.takeIf { isHex(it, 64) } ?: return null
    return ManifestDeviceEntry(
        deviceId = id,
        deviceName = name,
        deviceType = type,
        longTermPublicKeyHex = longTerm,
        signingPublicKeyHex = signing,
        wsPort = wsPort,
        relayUrl = relayUrl,
        pairedAt = pairedAt,
    )
}

private fun normaliseManifestEntry(entry: ManifestDeviceEntry): ManifestDeviceEntry? {
    if (entry.deviceId.isBlank() || entry.deviceName.isBlank()) return null
    // Bound string fields — a peer could otherwise send multi-megabyte strings
    // that pass the format checks and bloat the canonical signature input.
    if (entry.deviceId.length > MAX_MANIFEST_STRING || entry.deviceName.length > MAX_MANIFEST_STRING) return null
    if (entry.deviceType !in setOf("extension", "android", "ios")) return null
    if (!isHex(entry.longTermPublicKeyHex, 64) || !isHex(entry.signingPublicKeyHex, 64)) return null
    if (entry.wsPort != null && entry.wsPort !in 1..65_535) return null
    if (entry.pairedAt < 0L) return null
    if (
        entry.relayUrl != null && (
            entry.relayUrl.length > MAX_MANIFEST_STRING ||
            runCatching { Rendezvous.normalizeRelayUrl(entry.relayUrl) }.isFailure
        )
    ) return null
    return entry.copy(
        longTermPublicKeyHex = entry.longTermPublicKeyHex.lowercase(),
        signingPublicKeyHex = entry.signingPublicKeyHex.lowercase(),
    )
}

private fun normaliseRevocation(r: DeviceRevocation): DeviceRevocation =
    r.copy(longTermPublicKeyHex = r.longTermPublicKeyHex.lowercase())

private fun isValidRevocation(r: DeviceRevocation): Boolean =
    r.deviceId.isNotBlank() && r.deviceId.length <= MAX_MANIFEST_STRING &&
        isHex(r.longTermPublicKeyHex.lowercase(), 64) &&
        r.revokedByDeviceId.isNotBlank() && r.revokedByDeviceId.length <= MAX_MANIFEST_STRING &&
        r.revokedAt >= 0L

private fun revocationMap(r: DeviceRevocation): Map<String, Any> = linkedMapOf(
    "deviceId" to r.deviceId,
    "longTermPublicKeyHex" to r.longTermPublicKeyHex.lowercase(),
    "revokedAt" to r.revokedAt,
    "revokedByDeviceId" to r.revokedByDeviceId,
)

private fun manifestEntryMap(entry: ManifestDeviceEntry): Map<String, Any> {
    val normalised = normaliseManifestEntry(entry) ?: entry
    val map = linkedMapOf<String, Any>(
        "deviceId" to normalised.deviceId,
        "deviceName" to normalised.deviceName,
        "deviceType" to normalised.deviceType,
        "longTermPublicKeyHex" to normalised.longTermPublicKeyHex.lowercase(),
        "pairedAt" to normalised.pairedAt,
        "signingPublicKeyHex" to normalised.signingPublicKeyHex.lowercase(),
    )
    normalised.wsPort?.let { map["wsPort"] = it }
    normalised.relayUrl?.let { map["relayUrl"] = it }
    return map
}

private fun canonicalise(value: Any?): String = when (value) {
    null -> "null"
    is Number -> {
        val d = value.toDouble()
        require(d.isFinite()) { "non-finite number" }
        if (d % 1.0 == 0.0) value.toLong().toString() else value.toString()
    }
    is String -> Json.encodeToString(String.serializer(), value)
    is Boolean -> if (value) "true" else "false"
    is List<*> -> value.joinToString(prefix = "[", postfix = "]", separator = ",") { canonicalise(it) }
    is Map<*, *> -> value.entries
        .map { (k, v) -> k.toString() to v }
        .sortedBy { it.first }
        .joinToString(prefix = "{", postfix = "}", separator = ",") { (k, v) ->
            Json.encodeToString(String.serializer(), k) + ":" + canonicalise(v)
        }
    else -> error("cannot canonicalise ${value::class.simpleName}")
}

private fun isHex(value: String, length: Int): Boolean =
    value.length == length && value.all { it in '0'..'9' || it in 'a'..'f' }