import Foundation
import Observation
import RastrilloApple
import RastrilloNative

struct DocsOfflineMetadata: Codable {
    var detail: DocumentDetail
    var pendingTitle: String?
    var draftToken: String?
}

/// All windows for an account share the same outbox and send reservation.
@MainActor @Observable final class DocsOfflineAccount {
    private static var accounts: [String: DocsOfflineAccount] = [:]
    let store: BlobStore
    let outbox: Outbox
    let connectivity: NativeConnectivity
    let replicaCache: DocsReplicaCache
    private var supplier: @MainActor () -> NativeTransport?
    private(set) var drainer: OutboxDrainer!
    static func account(_ id: String, origin: URL, fallback: NativeTransport, transport: (@MainActor () -> NativeTransport?)?) -> DocsOfflineAccount {
        if let existing = accounts[id] { if let transport { existing.supplier = transport; existing.drainer.sessionRestored() }; return existing }
        let root = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask)[0]
            .appendingPathComponent(Bundle.main.bundleIdentifier ?? "works.oficina.docs")
            .appendingPathComponent("accounts").appendingPathComponent(id)
        let store = NativeSealedStore(root: root, accountID: id, keys: KeychainKeyProvider(accountID: id, origin: origin))
        let account = DocsOfflineAccount(store: store, accountID: id, connectivity: .shared, transport: transport ?? { fallback })
        accounts[id] = account; return account
    }
    init(store: BlobStore, accountID: String, connectivity: NativeConnectivity, transport: @escaping @MainActor () -> NativeTransport?) {
        self.store = store; outbox = Outbox(store: store, account: accountID)
        replicaCache = DocsReplicaCache(store: store)
        self.connectivity = connectivity; supplier = transport
        drainer = OutboxDrainer(outbox: outbox, transport: { [weak self] in self?.supplier() }, connectivity: connectivity, maxBatchBytes: 512 * 1024) { [weak self] lane, entries, transport in
            guard let self else { throw CancellationError() }
            return try await self.send(lane, entries: entries, transport: transport)
        }
    }
    func metadata(_ key: String) throws -> DocsOfflineMetadata? {
        guard let bytes = try store.read("cache/docs/\(key)/meta") else { return nil }
        return try JSONDecoder().decode(DocsOfflineMetadata.self, from: bytes)
    }
    private func index() throws -> [String: String] {
        try store.read("cache/docs/index").map { try JSONDecoder().decode([String: String].self, from: $0) } ?? [:]
    }
    func saveMetadata(_ metadata: DocsOfflineMetadata, key: String) throws {
        // Register the immutable key first. A crash may leave an empty slot,
        // never undiscoverable metadata or a rename that Home cannot replay.
        var index = try index()
        if index[key] == nil {
            index[key] = key
            try store.write(JSONEncoder().encode(index), to: "cache/docs/index")
        }
        try store.write(JSONEncoder().encode(metadata), to: "cache/docs/\(key)/meta")
        if metadata.draftToken == nil, index[metadata.detail.sqid] != key {
            index[metadata.detail.sqid] = key
            try store.write(JSONEncoder().encode(index), to: "cache/docs/index")
        }
    }
    func key(for sqid: String) throws -> String {
        let index = try index()
        if let key = index[sqid] { return key }
        // The alias is derived state. Attachment metadata is committed first,
        // so scanning registered keys heals a kill before the alias write.
        for key in Set(index.values).sorted() {
            if let metadata = try metadata(key), metadata.detail.sqid == sqid {
                try saveMetadata(metadata, key: key)
                return key
            }
        }
        return sqid
    }
    func ensureMetadataEntry(_ key: String) async throws {
        let generation = replicaCache.generation(key)
        guard let metadata = try metadata(key), metadata.pendingTitle != nil || metadata.draftToken != nil else { return }
        let entries = await outbox.entries(lane: "doc:" + key, excludingInFlight: true)
        guard replicaCache.generation(key) == generation, !entries.contains(where: { $0.kind == "metadata" }) else { return }
        try await outbox.enqueue(lane: "doc:" + key, kind: "metadata", payload: Data())
    }
    func activate() async throws {
        try await outbox.load()
        // Older K3 records can also be discovered from their durable lane.
        let lanes = await outbox.summary.lanes.keys
        let keys = Set(try index().values).union(lanes.filter { $0.hasPrefix("doc:") }.map { String($0.dropFirst(4)) })
        for key in keys.sorted() { try await ensureMetadataEntry(key) }
        drainer.start(); drainer.kick()
    }
    private static func form(_ values: [String: String]) -> Data {
        var form = URLComponents(); form.queryItems = values.map { URLQueryItem(name: $0.key, value: $0.value) }
        return Data((form.percentEncodedQuery ?? "").replacingOccurrences(of: "+", with: "%2B").utf8)
    }
    private func send(_ lane: String, entries: [OutboxEntry], transport: NativeTransport) async throws -> [UUID: OutboxDrainer.Disposition] {
        let key = String(lane.dropFirst(4)), generation = replicaCache.generation(String(lane.dropFirst(4)))
        let saved: DocsOfflineMetadata?
        do { saved = try metadata(key) }
        catch BlobStoreError.corrupt { saved = nil }
        catch is DecodingError { saved = nil }
        // A missing/corrupt destination cannot be retried into existence. Keep
        // its lane for resolution, without mistaking a locked store for loss.
        guard lane.hasPrefix("doc:"), var metadata = saved else {
            return Dictionary(uniqueKeysWithValues: entries.map { ($0.id, .hold(Hold(.rejected("metadata")))) })
        }
        if let token = metadata.draftToken {
            let reply = try await transport.responseDetails("/documents", method: "POST", body: Self.form(["title": metadata.detail.title, "creation_token": token]), contentType: "application/x-www-form-urlencoded")
            try reply.requireSuccess()
            let item = try JSONDecoder().decode(DocumentSummary.self, from: reply.data)
            let attached: DocumentDetail = try await transport.request("/d/\(item.sqid)")
            guard replicaCache.generation(key) == generation, let latest = try self.metadata(key) else { throw CancellationError() }
            metadata = latest
            metadata.detail = DocumentDetail(sqid: attached.sqid, title: latest.pendingTitle ?? attached.title, guid: attached.guid, can_write: attached.can_write, can_share: attached.can_share)
            metadata.draftToken = nil
            // Commit identity before publishing it or attempting text sends.
            try saveMetadata(metadata, key: key)
        }
        while let title = metadata.pendingTitle {
            let reply = try await transport.responseDetails("/d/\(metadata.detail.sqid)/title", method: "POST", body: Self.form(["title": title]), contentType: "application/x-www-form-urlencoded")
            try reply.requireSuccess()
            guard replicaCache.generation(key) == generation, var latest = try self.metadata(key) else { throw CancellationError() }
            if latest.pendingTitle == title { latest.pendingTitle = nil; try saveMetadata(latest, key: key) }
            metadata = latest // A rename during this POST must also be sent.
        }
        let updates = entries.filter { $0.kind == "update" }
        var dispositions = Dictionary(uniqueKeysWithValues: entries.filter { $0.kind == "metadata" }.map { ($0.id, OutboxDrainer.Disposition.sent) })
        guard !updates.isEmpty else { return dispositions }
        let merger = CRDTReplica(guid: metadata.detail.guid)
        let update: Data
        var sending = updates
        do {
            _ = try await merger.open(update: Data())
            do { update = try await merger.mergeUpdates(updates.map(\.payload)) }
            catch { sending = Array(updates.prefix(1)); update = sending[0].payload }
            await merger.close()
        } catch { await merger.close(); throw error }
        let reply = try await transport.responseDetails("/d/\(metadata.detail.sqid)/updates", method: "POST", body: update, contentType: "application/octet-stream")
        try reply.requireSuccess()
        var state = update, sequence: Int64 = 0
        if try store.read("cache/docs/\(key)/replica") == nil {
            let initial = try await transport.responseDetails("/d/\(metadata.detail.sqid)/updates", maxBytes: 8 * 1024 * 1024)
            try initial.requireSuccess()
            guard let cursor = Int64(initial.header("Docs-Seq") ?? "") else { throw NativeClientError.invalidResponse }
            state = initial.data; sequence = cursor
        }
        // Keep sent bytes locally before ack can remove their lane files.
        try await replicaCache.commit(PersistedReplica(format: 1, sequence: sequence, guid: metadata.detail.guid, savedAt: Date(), state: state), key: key, generation: generation)
        for entry in sending { dispositions[entry.id] = .sent }
        return dispositions
    }

}

/// Used only by previews and callers that have no NativeAccount (unit tests).
/// The application always supplies its per-account sealed store.
final class EphemeralDocsStore: BlobStore, @unchecked Sendable {
    private let lock = NSLock()
    private var files: [String: Data] = [:]
    func read(_ path: String) throws -> Data? { lock.withLock { files[path] } }
    func write(_ data: Data, to path: String) throws { lock.withLock { files[path] = data } }
    func remove(_ path: String) throws { lock.withLock { files = files.filter { $0.key != path && !$0.key.hasPrefix(path + "/") } } }
    func list(_ directory: String) throws -> [String] { lock.withLock {
        files.keys.filter { $0.hasPrefix(directory + "/") }.map { String($0.dropFirst(directory.count + 1)) }.filter { !$0.contains("/") }.sorted()
    } }
}