package com.peachpasswords.sync

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

/** 0x05 adds signed per-issuer revocation records to the vouch graph. */
const val DEVICE_MANIFEST_VERSION = 0x05
const val MAX_VOUCH_DEPTH = 3
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
/**
 * Display/storage bound for device names, matching the browser's
 * MAX_DEVICE_NAME_CHARS (shared/sync-limits.ts) and both platforms' local
 * setDeviceName bound. Inbound seams cap rather than reject so old peers
 * with long-but-honest names keep syncing; a device name was never a
 * 256-char string.
 */
internal const val MAX_DEVICE_NAME_CHARS = 64

/** Truncate a peer- or user-supplied device name to the shared bound. */
internal fun capDeviceName(name: String): String =
    if (name.length > MAX_DEVICE_NAME_CHARS) name.take(MAX_DEVICE_NAME_CHARS) else name
internal const val NO_KEY_SENTINEL = "0000000000000000000000000000000000000000000000000000000000000000"

/**
 * Fully staged membership change. Implementations must linearize the whole
 * batch; callers hold the vault session epoch fence while invoking it, so a
 * lock/re-unlock cannot observe or leave behind a half-applied manifest.
 */
data class DeviceManifestRegistryBatch(
    val incomingRevocations: List<DeviceRevocation>,
    val removals: Set<String>,
    val upserts: List<PairedDevice>,
)

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()

    /**
     * Immutable issuer signing-key history. Implementations must append only;
     * the default keeps lightweight test registries source-compatible.
     */
    fun issuerSigningKeys(issuerDeviceId: String): Set<String> = emptySet()
    fun appendIssuerSigningKey(issuerDeviceId: String, signingKeyHex: String): Boolean = true

    /** Commit a complete staged manifest as one logical registry mutation. */
    fun applyManifestBatch(batch: DeviceManifestRegistryBatch): Boolean

    /** 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,
        devices = devices.map { normaliseManifestEntry(it) ?: it },
        revoked = revoked.map { record ->
            // A forwarded revocation is an immutable issuer statement. Preserve
            // its original issuer and signature; only sign locally-created
            // records that have not been signed yet.
            if (record.signatureHex.isNotBlank()) record else signDeviceRevocation(record, signingPrivateKey)
        },
    )
    val signature = signEd25519(signingPrivateKey, canonicalDeviceManifestBody(body).toByteArray(Charsets.UTF_8))
    return SignedDeviceManifest(body, pubkeyToHex(signature))
}

/** Sign the immutable record, excluding its signature field from canonical bytes. */
fun signDeviceRevocation(
    record: DeviceRevocation,
    signingPrivateKey: Ed25519PrivateKeyParameters,
): DeviceRevocation {
    val unsigned = record.copy(signatureHex = "")
    val signature = signEd25519(
        signingPrivateKey,
        canonicalDeviceRevocation(unsigned).toByteArray(Charsets.UTF_8),
    )
    return unsigned.copy(signatureHex = pubkeyToHex(signature))
}

/** The exact bytes an issuer signs; identical in Browser and Android. */
fun canonicalDeviceRevocation(record: DeviceRevocation): String =
    canonicalise(
        mapOf(
            "deviceId" to record.deviceId,
            "longTermPublicKeyHex" to record.longTermPublicKeyHex.lowercase(),
            "recordVersion" to record.recordVersion,
            "revokedAt" to record.revokedAt,
            "revokedByDeviceId" to record.revokedByDeviceId,
        ),
    )

fun verifyDeviceRevocation(record: DeviceRevocation, issuerSigningPublicKey: ByteArray): Boolean {
    if (!isHex(record.signatureHex, 128)) return false
    val signature = runCatching { hexToBytes(record.signatureHex) }.getOrNull() ?: return false
    return verifyEd25519(
        issuerSigningPublicKey,
        canonicalDeviceRevocation(record.copy(signatureHex = "")).toByteArray(Charsets.UTF_8),
        signature,
    )
}

/**
 * A relayed revocation counts only when its signature verifies under a key the
 * receiver already trusts for `revokedByDeviceId` — that device's current
 * signing key or an entry in its immutable known-key history. The record names
 * no key of its own, so a relaying peer cannot authorise anything by supplying
 * one.
 *
 * An unresolvable issuer fails closed: the manifest is rejected rather than the
 * record being skipped, so a dropped history entry can never silently
 * un-revoke a device.
 */
private fun isAuthorisedRevocation(
    record: DeviceRevocation,
    resolveIssuerSigningKeys: (String) -> Set<String>,
): Boolean {
    val signature = runCatching { hexToBytes(record.signatureHex) }.getOrNull() ?: return false
    val payload = canonicalDeviceRevocation(record.copy(signatureHex = "")).toByteArray(Charsets.UTF_8)
    val trusted = resolveIssuerSigningKeys(record.revokedByDeviceId)
    if (trusted.isEmpty()) return false
    return trusted.any { key ->
        val hex = key.lowercase()
        isHex(hex, 64) && verifyEd25519(hexToPubkey(hex), payload, signature)
    }
}

fun verifyDeviceManifest(
    manifest: SignedDeviceManifest,
    issuerSigningPublicKey: ByteArray,
    resolveIssuerSigningKeys: (String) -> Set<String>,
    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
    // Validate every entry before the normalised return mapping below. Without
    // this guard, malformed but correctly signed manifests reached `!!` and
    // crashed the sync path instead of being rejected.
    if (body.devices.any { normaliseManifestEntry(it) == null }) return null
    if (!isHex(manifest.signatureHex, 128)) 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
    // Forwarded tombstones retain the original issuer's immutable signature.
    // The enclosing manifest signature authenticates the forwarder only, so the
    // revocation's own issuer key MUST be one the receiver already knows for
    // `revokedByDeviceId` — never the key carried inside the record. Trusting
    // the record's own claim would let any admitted peer that can issue a
    // manifest eject any third device.
    if (!body.revoked.all { record -> isAuthorisedRevocation(record, resolveIssuerSigningKeys) }) return null
    // Return entries with the display name capped so every consumer (registry
    // upserts, pending-vouch queue, key-rotation alerts) stores the bounded
    // name. The signature above was verified against the raw body.
    return body.copy(devices = body.devices.map { normaliseManifestEntry(it)!! })
}

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() }?.let(::capDeviceName) ?: 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,
        vouchDepth = 0,
    )
}

private fun normaliseManifestEntry(entry: ManifestDeviceEntry): ManifestDeviceEntry? {
    if (entry.deviceId.isBlank() || entry.deviceName.isBlank()) return null
    if (entry.deviceId.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 || entry.vouchDepth !in 0..MAX_VOUCH_DEPTH) return null
    if (
        entry.relayUrl != null && (
            entry.relayUrl.length > MAX_MANIFEST_STRING ||
            runCatching { Rendezvous.normalizeRelayUrl(entry.relayUrl) }.isFailure
        )
    ) return null
    return entry.copy(
        deviceName = capDeviceName(entry.deviceName),
        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.recordVersion == DEVICE_REVOCATION_RECORD_VERSION &&
        r.deviceId.isNotBlank() && r.deviceId.length <= MAX_MANIFEST_STRING &&
        isHex(r.longTermPublicKeyHex.lowercase(), 64) &&
        r.revokedByDeviceId.isNotBlank() && r.revokedByDeviceId.length <= MAX_MANIFEST_STRING &&
        isHex(r.signatureHex, 128) &&
        r.revokedAt >= 0L
 

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

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(),
        "vouchDepth" to normalised.vouchDepth,
    )
    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' }