import APIClient
import ClientTLS
import Foundation
import HostRegistry
import SessionCore
import UIKit
import WireProtocol

/// T-iOS-15 · Production dependency graph (composition root). One immutable
/// value assembled at launch; every screen/VM receives its dependencies from
/// here — no ad-hoc URLSession/keychain access anywhere else in the App layer.
///
/// Assembly security audit (task 安全注, verified at this single point):
/// - All `G` (state-changing) HTTP goes through `APIClient` (kill via
///   SessionListViewModel's client, probe's kill round-trip inside
///   `runPairingProbe`); `URLSessionHTTPTransport` adds no headers of its own
///   EXCEPT the access-token `Cookie` (C1) — see its type doc for why that one
///   belongs at the transport and cannot bypass the Origin rule.
/// - Origin is derived solely by `HostEndpoint` (WS: URLSessionTermTransport;
///   HTTP: APIClient's route builder) — nothing here hand-assembles one.
/// - Secrets: hosts (and their access tokens) in `KeychainHostStore`
///   (AfterFirstUnlockThisDeviceOnly, hosted keychain test asserts it);
///   UserDefaults carries only the non-secret per-host lastSessionId. A token
///   never reaches a log line, a URL query, or an error description.
/// - The one other `URLSession` in the app belongs to `thumbnailTransport()`
///   below — assembled HERE, from these same providers, for the same reasons
///   (F1: the session-thumbnail pipeline is built by a SwiftUI `@State`
///   initializer that has no environment to read, and used to build a
///   credential-less transport of its own).
/// - No debug ATS overrides exist (project.yml declares NO
///   NSAllowsArbitraryLoads in any configuration — only the five §5.2 CIDR
///   exceptions), and no isSecureTextEntry-style screenshot hacks are used;
///   `UIScreen.isCaptured` detection is SKIPPED per plan (accepted residual
///   risk, local trust model).
struct AppEnvironment: Sendable {
    let hostStore: any HostStore
    let lastSessionStore: any LastSessionStore
    let http: any HTTPTransport
    /// The WS transport used when no per-host factory is injected: it carries
    /// NO access token, so it is correct only for a host that has none. Every
    /// terminal goes through `makeTermTransport(for:)`, which prefers
    /// `termTransportFactory` — production always installs one.
    let termTransport: any TermTransport
    /// Injected into `PairingViewModel` — production is `runPairingProbe`
    /// over the real transports (two-step: RO GET, then WS attach + guarded
    /// kill; only runs after the user's explicit confirm, T-iOS-12), plus the
    /// `POST /auth` token probe and the host-removal side effect (C1).
    let probe: PairingViewModel.Probe
    /// T-iOS-23 · unread last-seen watermarks (non-secret; UserDefaults).
    /// `var` + default so the memberwise init stays source-compatible for
    /// pre-P1 call sites while tests can inject an in-memory fake.
    var unreadStore: any UnreadWatermarkStore = UserDefaultsUnreadWatermarkStore()
    /// E1 · Builds the WS transport for ONE host, so the upgrade can carry that
    /// host's access token (§1.1). nil ⇒ `termTransport` for every host (the
    /// App-layer tests' `FakeTransport`); production installs the real factory.
    var termTransportFactory: (@Sendable (HostRegistry.Host) -> any TermTransport)?

    /// The WS transport a terminal on `host` must dial.
    ///
    /// E1 (HIGH) · This exists because the access-token cookie is PER HOST: the
    /// app previously shared one transport whose token was resolved
    /// host-independently, which returned nil for the mixed fleet the token
    /// feature is for (a tokened tunnel host beside an open LAN host) — the
    /// upgrade omitted the cookie, the server 401'd, and that failure is
    /// terminal with no in-app remedy. Android never had the bug because
    /// `OkHttpTermTransport` resolves `tokens.tokenFor(endpoint)`; this is the
    /// same rule.
    func makeTermTransport(for host: HostRegistry.Host) -> any TermTransport {
        termTransportFactory?(host) ?? termTransport
    }

    static func production() -> AppEnvironment {
        // C-iOS-2 (MEDIUM no-relaunch fix) · Resolve the installed device client
        // identity LAZILY from the keychain on each connect/challenge, injected
        // into BOTH transports + the probe as a provider. This way a certificate
        // imported from the "设备证书" screen takes effect on the NEXT connection
        // without relaunching — a snapshot captured here would stay stale. A
        // missing cert is the normal pre-install state (→ nil); genuine faults
        // are logged, not fatal (`loadedIdentityOrNil`). mTLS challenges only
        // fire for tunnel hosts, so a `nil` result is inert for local hosts.
        let identityProvider = keychainIdentityProvider()
        let hostStore = KeychainHostStore()
        // C1 · ONE access-token source for the whole app, reading the same
        // Keychain records the pairing flow writes. Both transports consult it
        // per request/connect, so a token typed mid-run applies immediately —
        // no relaunch, and no token snapshot captured at composition.
        let tokens = AccessTokenSource(store: hostStore)
        let http = URLSessionHTTPTransport(
            identityProvider: identityProvider,
            tokenForOrigin: { origin in await tokens.token(forOrigin: origin) }
        )
        // E1 · ONE transport per host: the upgrade's Cookie is this host's token
        // and never another's. The provider is re-consulted on every connect
        // (rotation applies on the next reconnect, no relaunch).
        let termTransportFactory: @Sendable (HostRegistry.Host) -> any TermTransport = { host in
            URLSessionTermTransport(
                identityProvider: identityProvider,
                tokenProvider: { tokens.wsToken(for: host) }
            )
        }
        return AppEnvironment(
            hostStore: hostStore,
            lastSessionStore: UserDefaultsLastSessionStore(),
            http: http,
            termTransport: URLSessionTermTransport(identityProvider: identityProvider),
            probe: PairingViewModel.Probe(
                verifyHost: { endpoint, token in
                    // The candidate token has to reach BOTH probe legs. HTTP
                    // takes it as a parameter (APIClient stamps the Cookie); the
                    // WS leg gets a PROBE-SCOPED transport carrying exactly this
                    // candidate — the frozen `TermTransport.connect` has no
                    // credential parameter, and the host is not paired yet, so
                    // the shared transport could not resolve it from the store.
                    let ws = URLSessionTermTransport(
                        identityProvider: identityProvider,
                        tokenProvider: { token?.rawValue }
                    )
                    return await runPairingProbe(
                        endpoint: endpoint, http: http, ws: ws,
                        accessToken: token?.rawValue
                    )
                },
                validateToken: { endpoint, token in
                    await probeAccessToken(endpoint: endpoint, http: http, token: token)
                },
                unregisterPush: { host in
                    await PushHostDeregistration.run(for: host)
                }
            ),
            termTransportFactory: termTransportFactory
        )
    }

    /// C-iOS-2 · The lazy, Keychain-backed device-identity provider: resolved
    /// per TLS client-certificate challenge (never snapshotted), so a certificate
    /// imported mid-run is presented on the NEXT handshake without a relaunch.
    /// ONE definition, shared by `production()` and `thumbnailTransport()`.
    static func keychainIdentityProvider() -> @Sendable () -> ClientIdentity? {
        let identityStore = KeychainClientIdentityStore()
        return { identityStore.loadedIdentityOrNil() }
    }

    /// F1 · The HTTP transport `SessionThumbnailPipeline.live()` fetches
    /// `GET /live-sessions/:id/preview` over — assembled HERE, at the
    /// composition root, from the SAME two credential providers `production()`
    /// installs on the app-wide transport: the lazy mTLS identity AND the
    /// per-origin access token.
    ///
    /// WHY IT EXISTS (the bug it fixes): the pipeline used to build its own
    /// `URLSessionHTTPTransport` with an identity provider but **no token
    /// source**, so on a `WEBTERM_TOKEN`-gated host every preview came back 401.
    /// The pipeline never throws by design — a failed preview IS a placeholder —
    /// so the whole session list silently degraded to placeholder thumbnails with
    /// nothing on screen saying why. It is assembled here rather than in the
    /// component because the pipeline is created by a SwiftUI `@State`
    /// initializer that has no `AppEnvironment` to read from.
    ///
    /// It is a SEPARATE `URLSession` from `production().http` for the same reason
    /// (no environment at that call site), and that costs nothing: both are
    /// `.ephemeral` (preview bytes are raw ring-buffer terminal output and must
    /// never touch a disk cache — T-iOS-19) and both resolve their credentials
    /// per request, so neither can hold a stale token.
    ///
    /// - Parameters:
    ///   - hostStore: where the per-host tokens live — Keychain in production,
    ///     an in-memory double in tests.
    ///   - identityProvider: the mTLS identity source (see above).
    static func thumbnailTransport(
        hostStore: any HostStore = KeychainHostStore(),
        identityProvider: @escaping @Sendable () -> ClientIdentity?
            = AppEnvironment.keychainIdentityProvider()
    ) -> URLSessionHTTPTransport {
        let tokens = AccessTokenSource(store: hostStore)
        return URLSessionHTTPTransport(
            identityProvider: identityProvider,
            tokenForOrigin: { origin in await tokens.token(forOrigin: origin) }
        )
    }

    /// Away-digest source for a session engine: wraps `APIClient.events` per
    /// host (the engine never holds an HTTP client — plan §3.2). The token rides
    /// along at the transport, so this stays token-free.
    func makeEventsSource(endpoint: HostEndpoint)
        -> @Sendable (UUID) async throws -> [TimelineEvent] {
        let client = APIClient(endpoint: endpoint, http: http)
        return { id in try await client.events(id: id) }
    }
}

// MARK: - Access-token source (C1 · ios-completion §1.1)

/// The app's single read path for per-host access tokens.
///
/// Reads the `HostStore` (Keychain) on demand rather than caching a value at
/// composition: pairing writes a token into the same records, and a snapshot
/// taken at launch would make "type the token, then connect" require a relaunch.
/// A Keychain read is a sub-millisecond `SecItemCopyMatching` + JSON decode, so
/// per-request resolution is affordable at the app's polling cadence.
///
/// SECURITY (§5.3): the token is returned as a `String` for exactly one use — a
/// `Cookie` header value. It is never logged, never interpolated into a URL, and
/// the values it returns are `AccessToken`-validated (§1.1 charset), which is
/// what makes header injection impossible.
final class AccessTokenSource: @unchecked Sendable {
    private let store: any HostStore
    private let lock = NSLock()
    /// Origin → token, rebuilt from the store on every `token(forOrigin:)`.
    /// See `wsToken(for:)`. Guarded by `lock`; `nonisolated` state is the reason
    /// this type is `@unchecked Sendable` (an actor cannot serve the WS
    /// provider, which is synchronous).
    private var snapshot: [String: String] = [:]

    init(store: any HostStore) {
        self.store = store
    }

    /// This host's token, matched by ORIGIN (`HostEndpoint.originHeader` — the
    /// single derivation point, plan §5.1), or nil when the host has none / is
    /// unknown / the store read fails. A failed read degrades to "no token"
    /// rather than throwing: the request then gets the server's 401, which the
    /// UI already explains, instead of the app breaking outright.
    func token(forOrigin origin: String) async -> String? {
        let hosts = (try? await store.loadAll()) ?? []
        updateSnapshot(from: hosts)
        return hosts.first { $0.endpoint.originHeader == origin }?.accessToken?.rawValue
    }

    /// The token a WS upgrade to `host` must present (§1.1) — for the one caller
    /// that can be given neither an `await` nor a parameter: SessionCore's
    /// frozen `tokenProvider: @Sendable () -> String?`, which the per-host
    /// transport closes over (`AppEnvironment.makeTermTransport(for:)`).
    ///
    /// Two reads, in this order, and both are THIS host's own value — no answer
    /// derived from any other host can ever be returned (§5.3):
    /// 1. the latest value the store returned for this origin (so a token
    ///    rotated mid-run applies on the next connect, no relaunch);
    /// 2. the `host` record itself, which the coordinator read from the same
    ///    Keychain store when the session was opened — this is what makes the
    ///    FIRST connect correct even before any HTTP request has warmed the
    ///    snapshot (a cold-start terminal must not depend on that race), and
    ///    what keeps a failed store read from silently dropping the cookie.
    ///
    /// Consequence of (2), stated plainly: a token DELETED from the store keeps
    /// riding until this terminal is reopened. That is still this host's own
    /// value — the server just answers 401 if it is no longer valid — and it is
    /// the price of never dropping the cookie on a cold connect.
    func wsToken(for host: HostRegistry.Host) -> String? {
        let origin = host.endpoint.originHeader
        return lock.withLock { snapshot[origin] } ?? host.accessToken?.rawValue
    }

    private func updateSnapshot(from hosts: [HostRegistry.Host]) {
        let resolved = hosts.reduce(into: [String: String]()) { map, host in
            guard let token = host.accessToken?.rawValue else { return }
            map[host.endpoint.originHeader] = token
        }
        lock.withLock { snapshot = resolved }
    }
}

/// `POST /auth` (§1.1) as the pairing flow needs it: the four documented
/// outcomes, or a typed transport failure. Lives here (composition root) because
/// it is the seam between `APIClient`'s throwing API and the VM's total switch.
private func probeAccessToken(
    endpoint: HostEndpoint,
    http: any HTTPTransport,
    token: AccessToken
) async -> Result<AccessTokenProbeResult, PairingViewModel.TokenProbeFailure> {
    do {
        let client = APIClient(endpoint: endpoint, http: http)
        return .success(try await client.probeAccessToken(token.rawValue))
    } catch APIClientError.malformedToken {
        return .failure(.malformed)
    } catch let apiError as APIClientError {
        // `.message` is user-facing copy about the STATUS, never about the token.
        return .failure(.unreachable(apiError.message))
    } catch {
        return .failure(.unreachable((error as NSError).localizedDescription))
    }
}

// MARK: - Host removal → APNs de-registration (C1 · fixes the dead hook)

/// Bridge from "the user removed a host" to `PushRegistrar.handleHostRemoved`.
///
/// The registrar owns the in-memory APNs device token (deliberately never
/// persisted — iOS re-delivers it on every registration), so the de-registration
/// can only be done by the LIVE instance. That instance is created and held by
/// `PushAppDelegate` (`makePushWiring`), which the system builds after this
/// composition root — hence the resolution happens at CALL time through
/// `UIApplication.shared.delegate`, the platform's own object, rather than any
/// singleton of ours.
///
/// nil delegate / nil registrar (unit tests, XCUITest, a build where push was
/// never wired) is a deliberate no-op: removal must never depend on push.
enum PushHostDeregistration {
    @MainActor
    static func run(for host: HostRegistry.Host) async {
        guard let delegate = UIApplication.shared.delegate as? PushAppDelegate,
              let registrar = delegate.registrar else {
            return
        }
        await registrar.handleHostRemoved(host)
    }
}