import CoreData
import Foundation
import Observation
import SwiftData
import SwiftUI

@MainActor
@Observable
final class Servers {
    static let shared = Servers()

    private(set) var entries: [(origin: String, record: ServerRecord)] = []
    private(set) var connections: [String: Connection] = [:]
    @ObservationIgnored var shown: Set<String> = []
    @ObservationIgnored var windows: [String: WindowSlot] = [:]
    @ObservationIgnored var launched = false
    @ObservationIgnored var openWindow: ((String?) -> Void)?

    private init() {
        load()
        Task {
            for await note in NotificationCenter.default.notifications(named: NSPersistentCloudKitContainer.eventChangedNotification) {
                if let event = note.userInfo?[NSPersistentCloudKitContainer.eventNotificationUserInfoKey] as? NSPersistentCloudKitContainer.Event, event.type == .import, event.endDate != nil {
                    for connection in connections.values {
                        connection.store?.drafts?.reload()
                    }
                    load()
                }
            }
        }
    }

    var origins: [String] {
        entries.map(\.origin)
    }

    func record(_ origin: String) -> ServerRecord? {
        entries.first { $0.origin == origin }?.record
    }

    func color(_ origin: String) -> Color {
        taskPalette[(record(origin)?.color ?? 0) % taskPalette.count]
    }

    private func load() {
        var loaded: [(origin: String, record: ServerRecord)] = []
        for record in fetchRecords(FetchDescriptor<ServerRecord>(sortBy: [SortDescriptor(\.saved)])) {
            if let origin = parseOrigin(record.origin), !loaded.contains(where: { $0.origin == origin.absoluteString }) {
                loaded.append((origin.absoluteString, record))
            }
        }
        entries = loaded
        for (origin, _) in loaded where connections[origin] == nil {
            connections[origin] = Connection(origin: parseOrigin(origin)!)
        }
        for (origin, connection) in connections where !loaded.contains(where: { $0.origin == origin }) {
            connections[origin] = nil
            Task {
                await connection.stop()
            }
        }
    }

    func add(_ origin: URL) {
        if record(origin.absoluteString) == nil {
            let used = Set(entries.map(\.record.color))
            let color = taskPalette.indices.first { !used.contains($0) } ?? entries.count % taskPalette.count
            persistence.insert(ServerRecord(origin: origin.absoluteString, color: color))
            saveRecords()
        }
        load()
    }

    func remove(_ origin: String) {
        for record in fetchRecords(FetchDescriptor<ServerRecord>()) where parseOrigin(record.origin)?.absoluteString == origin {
            persistence.delete(record)
        }
        saveRecords()
        load()
    }

    func setColor(_ origin: String, _ color: Int) {
        for record in fetchRecords(FetchDescriptor<ServerRecord>()) where parseOrigin(record.origin)?.absoluteString == origin {
            record.color = color
        }
        saveRecords()
    }

    func step(from origin: String?, by step: Int) -> String? {
        guard let i = origin.flatMap({ origins.firstIndex(of: $0) }) else {
            return origins.first
        }
        return origins[(i + step + origins.count) % origins.count]
    }

    func arrange(_ group: NSWindowTabGroup?) {
        guard let group else {
            return
        }
        let selected = group.selectedWindow
        let ordered = origins.compactMap { windows[$0]?.window }.filter { group.windows.contains($0) }
        for (i, window) in ordered.enumerated() where group.windows[i] !== window {
            group.insertWindow(window, at: i)
        }
        group.selectedWindow = selected
    }

    func openAll() {
        if origins.isEmpty {
            openWindow?(nil)
        }
        for origin in origins {
            openWindow?(origin)
        }
    }
}

@MainActor
final class WindowSlot {
    weak var window: NSWindow?
}

@MainActor
@Observable
final class Connection {
    enum Phase {
        case starting
        case failed(String)
        case running(Store)
    }

    let origin: URL
    var phase: Phase = .starting
    @ObservationIgnored private var stopped = false

    init(origin: URL) {
        self.origin = origin
        Task {
            await start()
        }
    }

    var store: Store? {
        if case .running(let store) = phase {
            return store
        }
        return nil
    }

    func stop() async {
        stopped = true
        if let store {
            await store.stop()
        }
    }

    private func start() async {
        while !stopped, !(await attempt()) {
            try? await Task.sleep(for: .seconds(2))
        }
    }

    private func attempt() async -> Bool {
        let store = Store(api: API(origin: origin))
        do {
            let status = try await store.api.client.getStatus().ok.body.json
            async let me: Void = store.loadMe()
            async let projects: Void = store.loadProjects()
            async let inbox: Void = store.loadInbox()
            async let lead: Void = store.loadLeadSessions()
            async let reads: Void = store.loadSummaryReads()
            _ = try await (me, projects, inbox, lead, reads)
            store.loadDrafts()
            try await store.loadFocus()
            guard !stopped else {
                await store.stop()
                return true
            }
            Task {
                await store.startLeadStream()
            }
            phase = .running(store)
            store.startGlobalStream(after: status.lastEventSeq)
            store.remote.start()
            Notifier.shared.deliver()
            return true
        } catch {
            await store.stop()
            if !stopped {
                phase = .failed("byre failed to start: \(errorText(error))")
            }
            return false
        }
    }
}

@MainActor
@Observable
final class ConnectForm {
    var serverText = ""
    var problem: String?
    var missing: [Check] = []
    var connecting = false

    func connect() async -> URL? {
        guard let origin = parseOrigin(serverText) else {
            problem = "The server URL must be an https origin with no path, such as https://byre.example.ts.net."
            return nil
        }
        connecting = true
        problem = nil
        do {
            _ = try await API(origin: origin).client.getStatus().ok
        } catch {
            connecting = false
            problem = explain(error, origin)
            return nil
        }
        connecting = false
        Servers.shared.add(origin)
        return origin
    }

    func installHere() async -> URL? {
        connecting = true
        problem = nil
        missing = []
        do {
            let checks = try await Server.checks()
            if !checks.ready {
                missing = checks.checks.filter { !$0.ok }
                connecting = false
                return nil
            }
            let origin = try await Server.turnOn()
            serverText = origin.absoluteString
            try await waitForServer(origin)
        } catch {
            connecting = false
            problem = errorText(error)
            return nil
        }
        return await connect()
    }

    private func waitForServer(_ origin: URL) async throws {
        let api = API(origin: origin)
        try await withThrowingTaskGroup(of: Void.self) { group in
            group.addTask {
                while (try? await api.client.getStatus().ok) == nil {
                    try await Task.sleep(for: .milliseconds(500))
                }
            }
            group.addTask {
                try await Task.sleep(for: .seconds(10))
                throw ProcessFailure(errorDescription: "byre was installed but \(origin.absoluteString) didn't answer within 10 s.")
            }
            defer {
                group.cancelAll()
            }
            try await group.next()
        }
    }
}

private let tlsErrors: Set<URLError.Code> = [
    .serverCertificateUntrusted, .serverCertificateHasBadDate, .serverCertificateNotYetValid, .serverCertificateHasUnknownRoot,
    .secureConnectionFailed, .clientCertificateRejected, .clientCertificateRequired,
]

private let unreachableErrors: Set<URLError.Code> = [
    .cannotFindHost, .cannotConnectToHost, .dnsLookupFailed, .timedOut, .notConnectedToInternet, .networkConnectionLost,
]

func explain(_ error: any Error, _ origin: URL) -> String {
    let host = origin.host() ?? origin.absoluteString
    let e = rootError(error)
    if let api = e as? ApiError {
        switch api.status {
        case 401:
            return "\(host) answered 401, no Tailscale identity: \(api.message). Use byre's ts.net HTTPS address, the one tailscale serve gives it, so the request carries your Tailscale login."
        case 403:
            return "\(host) answered 403, the request didn't come through tailscale serve: \(api.message). Use the HTTPS address tailscale serve gives byre."
        default:
            return api.message
        }
    }
    if let url = e as? URLError {
        if tlsErrors.contains(url.code) {
            return "\(host)'s certificate isn't trusted: \(url.localizedDescription) Use byre's ts.net HTTPS address, whose certificate tailscale serve provides."
        }
        if unreachableErrors.contains(url.code) {
            return "Can't reach \(host): \(url.localizedDescription) Is Tailscale connected?"
        }
        return url.localizedDescription
    }
    return errorText(e)
}

struct ConnectView: View {
    @Bindable var form: ConnectForm
    let connected: (URL) -> Void

    var body: some View {
        GeometryReader { g in
            ScrollView {
                fields
                    .padding(.vertical, 24)
                    .frame(maxWidth: .infinity, minHeight: g.size.height)
            }
        }
    }

    private var fields: some View {
        VStack(alignment: .leading, spacing: 10) {
            Text("Server URL")
            TextField("https://byre.example.ts.net", text: $form.serverText)
                .textFieldStyle(.roundedBorder)
                .onSubmit(connect)
            HStack(spacing: 10) {
                Button("Connect", action: connect)
                Button("Run byre on this Mac", action: installHere)
            }
            .disabled(form.connecting)
            if let problem = form.problem {
                Text(problem)
                    .foregroundStyle(Palette.danger)
                    .textSelection(.enabled)
                    .fixedSize(horizontal: false, vertical: true)
            }
            if !form.missing.isEmpty {
                Text("byre can't run on this Mac yet. Install what's missing, then click Run byre on this Mac again.")
                    .fixedSize(horizontal: false, vertical: true)
                    .padding(.top, 6)
                ChecksView(checks: form.missing)
            }
        }
        .frame(width: 460)
    }

    private func connect() {
        Task {
            if let origin = await form.connect() {
                connected(origin)
            }
        }
    }

    private func installHere() {
        Task {
            if let origin = await form.installHere() {
                connected(origin)
            }
        }
    }
}

struct FatalView: View {
    let message: String

    var body: some View {
        Text(message)
            .foregroundStyle(Palette.danger)
            .textSelection(.enabled)
            .padding(24)
            .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
    }
}

struct ServerFocus {
    let origin: String?
    let store: Store?
    let overlays: Overlays
    let forget: (() -> Void)?
}

extension FocusedValues {
    @Entry var serverWindow: ServerFocus?
}

struct ServerWindow: View {
    @Binding var origin: String?
    @ViewState private var overlays = Overlays()
    @ViewState private var form = ConnectForm()
    @ViewState private var slot = WindowSlot()
    @Environment(\.openWindow) private var openWindow
    @Environment(\.dismiss) private var dismissWindow

    private var connection: Connection? {
        origin.flatMap { Servers.shared.connections[$0] }
    }

    private var focus: ServerFocus {
        var forgetting: (() -> Void)?
        if connection != nil {
            forgetting = forget
        }
        return ServerFocus(origin: connection?.origin.absoluteString, store: connection?.store, overlays: overlays, forget: forgetting)
    }

    private var frameColor: Color {
        connection.map { Servers.shared.color($0.origin.absoluteString) } ?? Palette.bg
    }

    @ViewBuilder
    private var content: some View {
        if let connection {
            switch connection.phase {
            case .starting:
                Color.clear
            case .failed(let message):
                FatalView(message: message)
            case .running(let store):
                MainView()
                    .environment(store)
            }
        } else {
            ConnectView(form: form) { connected in
                let key = connected.absoluteString
                if Servers.shared.shown.contains(key) {
                    openWindow(id: "main", value: key)
                    dismissWindow()
                    return
                }
                origin = key
            }
        }
    }

    private var framed: some View {
        content
            .foregroundStyle(Palette.text)
            .tint(Palette.accent)
            .background(Palette.bg)
            .padding(connection == nil ? 0 : 3)
            .background(frameColor)
            .environment(overlays)
            .font(Fonts.font(13))
            .frame(minWidth: 640, minHeight: 400)
    }

    var body: some View {
        framed
            .navigationTitle(connection?.origin.host() ?? "byre")
            .background {
                WindowReader(found: joinTabs)
            }
            .focusedSceneValue(\.serverWindow, focus)
            .onChange(of: origin, initial: true) { old, new in
                moved(old, new)
            }
            .onChange(of: Servers.shared.origins) { old, new in
                adopt(new.filter { !old.contains($0) })
            }
            .onAppear(perform: appeared)
            .onDisappear {
                if let origin {
                    Servers.shared.shown.remove(origin)
                    release(origin)
                }
            }
    }

    private func moved(_ old: String?, _ new: String?) {
        let servers = Servers.shared
        if let old {
            servers.shown.remove(old)
            release(old)
        }
        if let new {
            servers.shown.insert(new)
            servers.windows[new] = slot
        }
        servers.arrange(slot.window?.tabGroup)
    }

    private func release(_ origin: String) {
        if Servers.shared.windows[origin] === slot {
            Servers.shared.windows[origin] = nil
        }
    }

    private func appeared() {
        let servers = Servers.shared
        let openWindow = openWindow
        servers.openWindow = { origin in
            if let origin {
                openWindow(id: "main", value: origin)
            } else {
                openWindow(id: "main")
            }
        }
        if !servers.launched {
            servers.launched = true
            adopt(servers.origins)
            for o in servers.origins where !servers.shown.contains(o) {
                openWindow(id: "main", value: o)
            }
        }
        Notifier.shared.deliver()
    }

    private func joinTabs(_ window: NSWindow) {
        window.tabbingMode = .preferred
        slot.window = window
        DispatchQueue.main.async {
            let host = NSApp.windows.first { $0 !== window && $0.isVisible && $0.tabbingIdentifier == window.tabbingIdentifier }
            if let host, !(host.tabbedWindows ?? []).contains(window) {
                host.addTabbedWindow(window, ordered: .above)
            }
            Servers.shared.arrange(window.tabGroup)
        }
    }

    private func adopt(_ candidates: [String]) {
        guard origin == nil, form.serverText.isEmpty, !form.connecting, let next = candidates.first(where: { !Servers.shared.shown.contains($0) }) else {
            return
        }
        origin = next
        Servers.shared.shown.insert(next)
    }

    private func forget() {
        guard let current = origin else {
            return
        }
        form.serverText = current
        origin = nil
        Servers.shared.remove(current)
    }
}