/*
Crafter®.Network
Copyright (C) 2026 Catcrafts®
Catcrafts.net

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 3.0 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
*/

// CRAFTER_NETWORK_BROWSER implementation of ClientQUIC / QUICStream backed
// by the browser's WebTransport API. WebTransport is HTTP/3-based and
// expects a URL — we use https://${host}:${port}/${alpn}. Native msquic
// is not linked into the browser build.
//
// Async-only: synchronous send/receive methods on QUICStream are not
// compiled (gated out in the interface). Everything goes through the
// existing *Async / OnStream / OnDatagram callbacks. The JS bridge
// (additional/network-env.js) runs the WebTransport reader loops and
// dispatches each chunk back through the wasm exports declared below.

module;
module Crafter.Network:ClientQUIC_impl;
import :ClientQUIC;
import std;

using namespace Crafter;

namespace Crafter::NetworkBrowserBindings {
    __attribute__((import_module("env"), import_name("crafterNetworkWtConnect")))
    std::int32_t crafterNetworkWtConnect(
        const char* host, std::int32_t hostLen,
        std::int32_t port,
        const char* alpn, std::int32_t alpnLen,
        const std::uint8_t* certHash, std::int32_t certHashLen);

    __attribute__((import_module("env"), import_name("crafterNetworkWtClose")))
    void crafterNetworkWtClose(std::int32_t handle);

    __attribute__((import_module("env"), import_name("crafterNetworkWtOpenStream")))
    std::int32_t crafterNetworkWtOpenStream(std::int32_t handle, std::int32_t unidirectional);

    __attribute__((import_module("env"), import_name("crafterNetworkWtStreamWrite")))
    void crafterNetworkWtStreamWrite(std::int32_t streamId,
                                     const char* buf, std::int32_t bufLen,
                                     std::int32_t finish,
                                     std::int32_t callbackId);

    __attribute__((import_module("env"), import_name("crafterNetworkWtStreamStop")))
    void crafterNetworkWtStreamStop(std::int32_t streamId);

    __attribute__((import_module("env"), import_name("crafterNetworkWtSendDatagram")))
    void crafterNetworkWtSendDatagram(std::int32_t handle,
                                      const char* buf, std::int32_t bufLen);
}

namespace Crafter::NetworkBrowser {
    // ─── Receive state machine per stream ─────────────────────────────────
    //
    // The JS reader loop pushes every chunk it sees through
    // CrafterNetworkOnWtStreamChunk. We buffer them until the user calls
    // one of the Receive*Async variants — at which point we either
    // dispatch immediately (chunks already queued) or wait for the next
    // chunk to arrive. A FIN signal marks the end of the peer's send-
    // side; further chunks after FIN do not arrive.
    //
    // StreamState / ConnectionState live in a named namespace (not
    // anonymous) because they are referenced from the QUICStream::Impl
    // and ClientQUIC::Impl definitions below — private nested types of
    // exported classes can't have TU-local member types without a
    // diagnostic.

    enum class RecvMode { None, Once, UntilClose, UntilFull };

    struct StreamState {
        // 0 means destroyed / closed.
        std::int32_t handle = 0;

        // Buffered chunks not yet delivered to a pending callback.
        std::vector<char> buffer;
        bool finReceived = false;
        bool closed = false;

        // Pending one-shot receive.
        RecvMode mode = RecvMode::None;
        std::uint32_t target = 0;
        std::function<void(std::vector<char>)> cb;

        ClientQUIC* connection = nullptr;
    };

    struct ConnectionState {
        std::int32_t handle = 0;
        bool ready = false;
        bool closed = false;
        std::function<void(QUICStream)> onStream;
        std::function<void(std::vector<char>)> onDatagram;
    };

    // Handle → state. Allocated on the heap so the pointer is stable
    // across QUICStream / ClientQUIC moves (each holds a unique_ptr<Impl>
    // that wraps a pointer into these maps via its handle).
    inline std::unordered_map<std::int32_t, StreamState*>& Streams() {
        static std::unordered_map<std::int32_t, StreamState*> m;
        return m;
    }
    inline std::unordered_map<std::int32_t, ConnectionState*>& Connections() {
        static std::unordered_map<std::int32_t, ConnectionState*> m;
        return m;
    }
    inline std::unordered_map<std::int32_t, std::function<void()>>& WriteCallbacks() {
        static std::unordered_map<std::int32_t, std::function<void()>> m;
        return m;
    }
    inline std::int32_t NextWriteCallbackId() {
        static std::int32_t counter = 0;
        return ++counter;
    }

    inline void TryDispatchRecv(StreamState& s) {
        if (s.mode == RecvMode::None) return;

        if (s.mode == RecvMode::Once) {
            if (!s.buffer.empty()) {
                auto chunk = std::move(s.buffer);
                s.buffer.clear();
                auto cb = std::move(s.cb);
                s.mode = RecvMode::None;
                if (cb) cb(std::move(chunk));
            } else if (s.finReceived || s.closed) {
                auto cb = std::move(s.cb);
                s.mode = RecvMode::None;
                if (cb) cb({});
            }
            return;
        }
        if (s.mode == RecvMode::UntilClose) {
            if (s.finReceived || s.closed) {
                auto chunk = std::move(s.buffer);
                s.buffer.clear();
                auto cb = std::move(s.cb);
                s.mode = RecvMode::None;
                if (cb) cb(std::move(chunk));
            }
            return;
        }
        if (s.mode == RecvMode::UntilFull) {
            if (s.buffer.size() >= s.target) {
                std::vector<char> chunk(s.buffer.begin(), s.buffer.begin() + s.target);
                s.buffer.erase(s.buffer.begin(), s.buffer.begin() + s.target);
                auto cb = std::move(s.cb);
                s.mode = RecvMode::None;
                if (cb) cb(std::move(chunk));
            } else if (s.finReceived || s.closed) {
                // Peer closed before we got the requested byte count —
                // deliver whatever's left. Mirrors the native variant's
                // "throws if peer closes early" only loosely (we have no
                // exception channel from JS).
                auto chunk = std::move(s.buffer);
                s.buffer.clear();
                auto cb = std::move(s.cb);
                s.mode = RecvMode::None;
                if (cb) cb(std::move(chunk));
            }
        }
    }
}

// All implementation-private state types live in Crafter::NetworkBrowser
// (above). Pull them in unqualified for readability.
using Crafter::NetworkBrowser::StreamState;
using Crafter::NetworkBrowser::ConnectionState;
using Crafter::NetworkBrowser::RecvMode;
using Crafter::NetworkBrowser::Streams;
using Crafter::NetworkBrowser::Connections;
using Crafter::NetworkBrowser::WriteCallbacks;
using Crafter::NetworkBrowser::NextWriteCallbackId;
using Crafter::NetworkBrowser::TryDispatchRecv;

// ─── QUICStream::Impl ────────────────────────────────────────────────────

struct QUICStream::Impl {
    StreamState state;
};

QUICStream::QUICStream() : impl(std::make_unique<Impl>()) {}

QUICStream::QUICStream(std::int32_t streamHandle, ClientQUIC* conn,
                       bool canSendArg, bool canReceiveArg)
    : canSend(canSendArg), canReceive(canReceiveArg),
      impl(std::make_unique<Impl>())
{
    connection = conn;
    impl->state.handle = streamHandle;
    impl->state.connection = conn;
    Streams()[streamHandle] = &impl->state;
}

QUICStream::QUICStream(QUICStream&&) noexcept = default;
QUICStream& QUICStream::operator=(QUICStream&&) noexcept = default;

QUICStream::~QUICStream() {
    if (impl && impl->state.handle != 0) {
        Streams().erase(impl->state.handle);
        Crafter::NetworkBrowserBindings::crafterNetworkWtStreamStop(impl->state.handle);
    }
}

void QUICStream::SendAsync(const void* buffer, std::uint32_t size, bool finish,
                           std::function<void()> onSent) {
    if (!impl || impl->state.handle == 0 || impl->state.closed) {
        if (onSent) onSent();
        return;
    }
    std::int32_t cbId = 0;
    if (onSent) {
        cbId = NextWriteCallbackId();
        WriteCallbacks()[cbId] = std::move(onSent);
    }
    Crafter::NetworkBrowserBindings::crafterNetworkWtStreamWrite(
        impl->state.handle,
        static_cast<const char*>(buffer),
        static_cast<std::int32_t>(size),
        finish ? 1 : 0,
        cbId);
}

void QUICStream::RecieveAsync(std::function<void(std::vector<char>)> cb) {
    if (!impl) { if (cb) cb({}); return; }
    impl->state.mode = RecvMode::Once;
    impl->state.cb = std::move(cb);
    TryDispatchRecv(impl->state);
}

void QUICStream::RecieveUntilCloseAsync(std::function<void(std::vector<char>)> cb) {
    if (!impl) { if (cb) cb({}); return; }
    impl->state.mode = RecvMode::UntilClose;
    impl->state.cb = std::move(cb);
    TryDispatchRecv(impl->state);
}

void QUICStream::RecieveUntilFullAsync(std::uint32_t bufferSize,
                                       std::function<void(std::vector<char>)> cb) {
    if (!impl) { if (cb) cb({}); return; }
    impl->state.mode = RecvMode::UntilFull;
    impl->state.target = bufferSize;
    impl->state.cb = std::move(cb);
    TryDispatchRecv(impl->state);
}

void QUICStream::Stop() {
    if (impl && impl->state.handle != 0) {
        Crafter::NetworkBrowserBindings::crafterNetworkWtStreamStop(impl->state.handle);
        Streams().erase(impl->state.handle);
        impl->state.handle = 0;
        impl->state.closed = true;
    }
}

// ─── ClientQUIC::Impl ────────────────────────────────────────────────────

struct ClientQUIC::Impl {
    ConnectionState state;
};

namespace {
    QUICStream MakeStreamFromHandle(std::int32_t streamId, ClientQUIC* conn,
                                    bool canSend, bool canReceive) {
        return QUICStream{streamId, conn, canSend, canReceive};
    }
}

ClientQUIC::ClientQUIC(const char* host, std::uint16_t port, std::string alpnArg,
                       QUICClientCredentials creds)
    : alpn(std::move(alpnArg)), impl(std::make_unique<Impl>()) {
    // Zeroed hash means "no pinning" — JS passes an empty array, browser
    // falls back to its trust store. A non-zero hash is forwarded as a
    // serverCertificateHashes entry (Chrome only, < 14 day cert validity).
    const std::uint8_t* hashPtr = nullptr;
    std::int32_t hashLen = 0;
    for (std::uint8_t b : creds.serverCertificateHash) {
        if (b != 0) { hashPtr = creds.serverCertificateHash.data(); hashLen = 32; break; }
    }
    std::string hostStr = host;
    impl->state.handle = Crafter::NetworkBrowserBindings::crafterNetworkWtConnect(
        hostStr.data(), static_cast<std::int32_t>(hostStr.size()),
        static_cast<std::int32_t>(port),
        alpn.data(), static_cast<std::int32_t>(alpn.size()),
        hashPtr, hashLen);
    // wasm builds run with -fno-exceptions; a failed JS-side allocation
    // leaves the connection in a closed state and the first operation will
    // produce a sentinel result (OpenStream returns a default-constructed
    // QUICStream, SendDatagram silently drops, OnStream/OnDatagram never
    // fire). The constructor cannot signal the failure synchronously.
    if (impl->state.handle == 0) {
        impl->state.closed = true;
    } else {
        Connections()[impl->state.handle] = &impl->state;
    }
}

ClientQUIC::ClientQUIC(std::string host, std::uint16_t port, std::string alpnArg,
                       QUICClientCredentials creds)
    : ClientQUIC(host.c_str(), port, std::move(alpnArg), std::move(creds)) {}

ClientQUIC::ClientQUIC(ClientQUIC&&) noexcept = default;

ClientQUIC::~ClientQUIC() {
    if (impl && impl->state.handle != 0) {
        Connections().erase(impl->state.handle);
        Crafter::NetworkBrowserBindings::crafterNetworkWtClose(impl->state.handle);
    }
}

QUICStream ClientQUIC::OpenStream(bool unidirectional) {
    if (!impl || impl->state.handle == 0 || impl->state.closed) {
        return QUICStream{};  // default-constructed: closed sentinel
    }
    std::int32_t streamId = Crafter::NetworkBrowserBindings::crafterNetworkWtOpenStream(
        impl->state.handle, unidirectional ? 1 : 0);
    if (streamId == 0) {
        return QUICStream{};
    }
    return MakeStreamFromHandle(streamId, this,
                                /*canSend=*/true,
                                /*canReceive=*/!unidirectional);
}

void ClientQUIC::SendDatagram(const void* buffer, std::uint32_t size) {
    if (!impl || impl->state.handle == 0 || impl->state.closed) return;
    Crafter::NetworkBrowserBindings::crafterNetworkWtSendDatagram(
        impl->state.handle,
        static_cast<const char*>(buffer),
        static_cast<std::int32_t>(size));
}

void ClientQUIC::OnStream(std::function<void(QUICStream)> cb) {
    if (impl) impl->state.onStream = std::move(cb);
}

void ClientQUIC::OnDatagram(std::function<void(std::vector<char>)> cb) {
    if (impl) impl->state.onDatagram = std::move(cb);
}

void ClientQUIC::Stop() {
    if (impl && impl->state.handle != 0) {
        Crafter::NetworkBrowserBindings::crafterNetworkWtClose(impl->state.handle);
        Connections().erase(impl->state.handle);
        impl->state.handle = 0;
        impl->state.closed = true;
    }
}

// ─── WASM exports the JS bridge dispatches back through ──────────────────

extern "C" {
    __attribute__((export_name("CrafterNetworkOnWtReady")))
    void CrafterNetworkOnWtReady(std::int32_t connectionHandle) {
        auto it = Connections().find(connectionHandle);
        if (it == Connections().end()) return;
        it->second->ready = true;
    }

    __attribute__((export_name("CrafterNetworkOnWtClosed")))
    void CrafterNetworkOnWtClosed(std::int32_t connectionHandle,
                                  char* messagePtr, std::int32_t /*messageLen*/) {
        std::free(messagePtr);
        auto it = Connections().find(connectionHandle);
        if (it == Connections().end()) return;
        it->second->closed = true;
        it->second->ready = false;
        // The JS bridge dispatches CrafterNetworkOnWtStreamChunk(_, nullptr, 0,
        // fin=1) for each stream that belonged to this connection so pending
        // receivers terminate. We don't iterate stream state here.
    }

    __attribute__((export_name("CrafterNetworkOnWtIncomingStream")))
    void CrafterNetworkOnWtIncomingStream(std::int32_t connectionHandle,
                                          std::int32_t streamId,
                                          std::int32_t bidirectional) {
        auto it = Connections().find(connectionHandle);
        if (it == Connections().end() || !it->second->onStream) {
            // No registered handler — close the stream JS-side to free
            // resources. Mirrors what the native msquic backend does
            // when a stream arrives before OnStream is registered (it
            // queues, but in the browser we don't have a backing buffer
            // to queue against without leaking).
            Crafter::NetworkBrowserBindings::crafterNetworkWtStreamStop(streamId);
            return;
        }
        QUICStream stream = MakeStreamFromHandle(streamId, /*conn=*/nullptr,
                                                 /*canSend=*/bidirectional != 0,
                                                 /*canReceive=*/true);
        it->second->onStream(std::move(stream));
    }

    __attribute__((export_name("CrafterNetworkOnWtStreamChunk")))
    void CrafterNetworkOnWtStreamChunk(std::int32_t streamId,
                                       char* dataPtr, std::int32_t dataLen,
                                       std::int32_t fin) {
        auto it = Streams().find(streamId);
        if (it == Streams().end()) { std::free(dataPtr); return; }
        StreamState& s = *it->second;
        if (dataPtr && dataLen > 0) {
            s.buffer.insert(s.buffer.end(), dataPtr, dataPtr + dataLen);
        }
        std::free(dataPtr);
        if (fin) s.finReceived = true;
        TryDispatchRecv(s);
    }

    __attribute__((export_name("CrafterNetworkOnWtStreamWriteComplete")))
    void CrafterNetworkOnWtStreamWriteComplete(std::int32_t callbackId) {
        auto it = WriteCallbacks().find(callbackId);
        if (it == WriteCallbacks().end()) return;
        auto cb = std::move(it->second);
        WriteCallbacks().erase(it);
        if (cb) cb();
    }

    __attribute__((export_name("CrafterNetworkOnWtDatagram")))
    void CrafterNetworkOnWtDatagram(std::int32_t connectionHandle,
                                    char* dataPtr, std::int32_t dataLen) {
        auto it = Connections().find(connectionHandle);
        if (it == Connections().end() || !it->second->onDatagram) {
            std::free(dataPtr);
            return;
        }
        std::vector<char> data(dataPtr, dataPtr + dataLen);
        std::free(dataPtr);
        it->second->onDatagram(std::move(data));
    }
}