//SPDX-License-Identifier: LGPL-3.0-only
//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®

module;
#include <cerrno>

module Crafter.Network:ClientHTTP1_impl;
import :ClientHTTP1;
import :ClientTCP;
import :HTTP;
import :HTTP1;
import :Stream;
import :TLS;
import Crafter.Thread;
import std;

using namespace Crafter;

namespace {
    // Host header value. The port is elided when it is the scheme default,
    // which is what every other HTTP/1.1 client on the wire does and what
    // virtual-host matching on the far side tends to expect.
    std::string DefaultAuthority(const std::string& host, std::uint16_t port, bool secure) {
        // An IPv6 literal goes in brackets, or its colons read as the port's.
        const std::string name = host.contains(':') ? "[" + host + "]" : host;
        if (port == (secure ? 443 : 80)) return name;
        return name + ":" + std::to_string(port);
    }
}

struct ClientHTTP1::Impl {
    std::string host;
    std::uint16_t port;
    // Null for plaintext; shared by every connection this client dials, so the
    // trust store is parsed once rather than per redial.
    std::shared_ptr<TLSContext> tls;
    std::unique_ptr<ClientTCP> tcp;
    // Sits on top of `tcp` and must therefore be destroyed before it.
    std::unique_ptr<ByteStream> stream;
    std::string protocol;

    void Connect(std::chrono::milliseconds connectTimeout, std::chrono::milliseconds handshakeTimeout) {
        tcp = std::make_unique<ClientTCP>(host, port, connectTimeout);
        try {
            if (tls) {
                stream = TLSStream::Connect(tcp->socketid, tls, host, handshakeTimeout);
            } else {
                stream = std::make_unique<PlainStream>(tcp->socketid);
            }
        } catch (...) {
            // A half-built connection must not be left pooled: the next Send()
            // would treat it as reusable and read from a socket with no
            // session on it.
            tcp.reset();
            throw;
        }
        protocol = std::string(stream->Protocol());
    }

    void Close() {
        stream.reset();
        tcp.reset();
    }

    // One request/response exchange on the current connection. `received`
    // is set as soon as any response byte arrives, which is what decides
    // whether a failure is safe to replay on a new connection.
    HTTPResponse Exchange(const std::string& wire, std::string_view method,
                          const HTTP1::MessageLimits& limits,
                          std::chrono::milliseconds timeout, bool& received) {
        stream->Write(wire.data(), wire.size(), timeout);

        HTTP1::MessageParser parser(HTTP1::MessageKind::Response, limits);
        parser.SetRequestMethod(method);
        std::vector<char> chunk(16 * 1024);
        while (!parser.Complete()) {
            std::size_t read = 0;
            const StreamStatus status = stream->ReadSome(chunk.data(), chunk.size(),
                                                        timeout, read);
            if (status == StreamStatus::TimedOut) {
                throw std::runtime_error("timed out waiting for the response");
            }
            if (status == StreamStatus::Closed) {
                // Peer closed. Completes a response framed by close;
                // anything else throws out of Finish().
                parser.Finish();
                break;
            }
            received = true;
            parser.Feed(chunk.data(), read);
        }
        if (!parser.Complete()) {
            throw std::runtime_error("connection closed before a complete response arrived");
        }
        HTTPResponse response = parser.TakeResponse();
        if (!parser.KeepAlive()) Close();
        return response;
    }
};

ClientHTTP1::ClientHTTP1(const char* host, std::uint16_t port)
    : host(host), port(port), impl(std::make_unique<Impl>(std::string(host), port)) {}

ClientHTTP1::ClientHTTP1(std::string host, std::uint16_t port)
    : ClientHTTP1(host.c_str(), port) {}

ClientHTTP1::ClientHTTP1(const char* host, std::uint16_t port, TLSClientCredentials credentials)
    : host(host), port(port), impl(std::make_unique<Impl>(std::string(host), port)) {
    // Built here rather than on first Send() so bad credentials — an
    // unreadable certificate, a trust anchor that is not a certificate —
    // surface at construction, where the caller is still looking.
    impl->tls = TLSContext::Client(credentials);
}

ClientHTTP1::ClientHTTP1(std::string host, std::uint16_t port, TLSClientCredentials credentials)
    : ClientHTTP1(host.c_str(), port, std::move(credentials)) {}

ClientHTTP1::ClientHTTP1(ClientHTTP1&&) noexcept = default;
ClientHTTP1::~ClientHTTP1() = default;

bool ClientHTTP1::Connected() const noexcept {
    return impl && impl->tcp != nullptr;
}

bool ClientHTTP1::Secure() const noexcept {
    return impl && impl->tls != nullptr;
}

std::string_view ClientHTTP1::Protocol() const noexcept {
    return impl ? std::string_view(impl->protocol) : std::string_view();
}

void ClientHTTP1::Disconnect() {
    if (impl) impl->Close();
}

HTTPResponse ClientHTTP1::Send(const HTTPRequest& request) {
    HTTPRequest prepared = request;
    if (prepared.authority.empty()) {
        prepared.authority = DefaultAuthority(host, port, Secure());
    }
    const std::string wire = HTTP1::SerializeRequest(prepared);
    const std::string method = prepared.method.empty() ? std::string("GET") : prepared.method;

    // Two attempts at most, and the second one only for the keep-alive
    // race: the peer may have closed a pooled connection at the same moment
    // we wrote to it, which is indistinguishable from success until the
    // read fails. Nothing is replayed once a response byte has arrived.
    for (int attempt = 0;; ++attempt) {
        const bool reused = impl->tcp != nullptr;
        if (!reused) impl->Connect(connectTimeout, handshakeTimeout);

        bool received = false;
        try {
            return impl->Exchange(wire, method, limits, timeout, received);
        } catch (const std::exception&) {
            impl->Close();
            if (attempt == 0 && reused && !received) continue;
            throw;
        }
    }
}

void ClientHTTP1::SendAsync(const HTTPRequest& request,
                            std::function<void(HTTPResponse)> onSuccess,
                            std::function<void(std::string)> onError) {
    HTTPRequest copy = request;
    ThreadPool::Enqueue([this, copy = std::move(copy),
                         onSuccess = std::move(onSuccess),
                         onError = std::move(onError)]() mutable {
        try {
            HTTPResponse response = this->Send(copy);
            if (onSuccess) onSuccess(std::move(response));
        } catch (const std::exception& e) {
            if (onError) onError(e.what());
        } catch (...) {
            if (onError) onError("unknown error");
        }
    });
}

namespace {
    // The five parts urllib.parse.urlsplit cuts a URL into. FetchHTTP1 needs
    // the splitting, the joining (urljoin) and the reassembly to resolve a
    // Location the way urllib does, and nothing else of urllib.parse.
    struct SplitURL {
        std::string scheme;
        std::string netloc;
        std::string path;
        std::string query;
        std::string fragment;
    };

    bool IsAsciiAlpha(char c) {
        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
    }

    bool IsSchemeChar(char c) {
        return IsAsciiAlpha(c) || (c >= '0' && c <= '9') || c == '+' || c == '-' || c == '.';
    }

    std::string ToLowerAsciiCopy(std::string_view text) {
        std::string lower(text);
        for (char& c : lower) {
            if (c >= 'A' && c <= 'Z') c = static_cast<char>(c - 'A' + 'a');
        }
        return lower;
    }

    // str.split('/'): every piece, empty ones included, and [""] for "".
    std::vector<std::string> SplitSlashes(std::string_view text) {
        std::vector<std::string> pieces;
        std::size_t start = 0;
        while (true) {
            const std::size_t slash = text.find('/', start);
            if (slash == std::string_view::npos) {
                pieces.emplace_back(text.substr(start));
                return pieces;
            }
            pieces.emplace_back(text.substr(start, slash - start));
            start = slash + 1;
        }
    }

    // urlsplit: tabs and newlines dropped anywhere, leading controls and
    // spaces stripped, the scheme lowercased.
    SplitURL Split(std::string_view input) {
        std::string url;
        url.reserve(input.size());
        for (const char c : input) {
            if (c != '\t' && c != '\r' && c != '\n') url.push_back(c);
        }
        std::size_t start = 0;
        while (start < url.size() && static_cast<unsigned char>(url[start]) <= 0x20) ++start;
        url.erase(0, start);

        SplitURL parts;
        const std::size_t colon = url.find(':');
        if (colon != std::string::npos && colon > 0 && IsAsciiAlpha(url[0])
            && std::ranges::all_of(std::string_view(url).substr(0, colon), IsSchemeChar)) {
            parts.scheme = ToLowerAsciiCopy(std::string_view(url).substr(0, colon));
            url.erase(0, colon + 1);
        }
        if (url.starts_with("//")) {
            std::size_t end = url.find_first_of("/?#", 2);
            if (end == std::string::npos) end = url.size();
            parts.netloc = url.substr(2, end - 2);
            url.erase(0, end);
            if (parts.netloc.contains('[') != parts.netloc.contains(']')) {
                throw std::invalid_argument("FetchHTTP1: unbalanced brackets in the host of " + std::string(input));
            }
        }
        if (const std::size_t hash = url.find('#'); hash != std::string::npos) {
            parts.fragment = url.substr(hash + 1);
            url.erase(hash);
        }
        if (const std::size_t question = url.find('?'); question != std::string::npos) {
            parts.query = url.substr(question + 1);
            url.erase(question);
        }
        parts.path = std::move(url);
        return parts;
    }

    // urlunsplit, for the http(s) URLs FetchHTTP1 puts back together.
    std::string Unsplit(const SplitURL& parts) {
        std::string url = parts.path;
        if (!parts.netloc.empty()) {
            if (!url.empty() && url.front() != '/') url.insert(url.begin(), '/');
            url = "//" + parts.netloc + url;
        } else if (url.starts_with("//")) {
            url = "//" + url;
        } else if ((parts.scheme == "http" || parts.scheme == "https") && (url.empty() || url.front() == '/')) {
            url = "//" + url;
        }
        if (!parts.scheme.empty()) url = parts.scheme + ":" + url;
        if (!parts.query.empty()) url += "?" + parts.query;
        if (!parts.fragment.empty()) url += "#" + parts.fragment;
        return url;
    }

    // urljoin, for a reference found in a redirect: RFC 3986 resolution the
    // way Python does it, a `..` that would climb above the root dropped.
    std::string Join(std::string_view base, std::string_view reference) {
        if (base.empty()) return std::string(reference);
        if (reference.empty()) return std::string(base);
        const SplitURL from = Split(base);
        SplitURL to = Split(reference);
        if (to.scheme.empty()) to.scheme = from.scheme;
        const bool relative = to.scheme == "http" || to.scheme == "https";
        if (to.scheme != from.scheme || !relative) return std::string(reference);
        if (!to.netloc.empty()) return Unsplit(to);
        to.netloc = from.netloc;
        if (to.path.empty()) {
            to.path = from.path;
            if (to.query.empty()) to.query = from.query;
            return Unsplit(to);
        }

        std::vector<std::string> baseParts = SplitSlashes(from.path);
        // The base's last segment is a file, not a directory: it does not
        // take part in resolving.
        if (!baseParts.back().empty()) baseParts.pop_back();
        std::vector<std::string> segments;
        if (to.path.starts_with('/')) {
            segments = SplitSlashes(to.path);
        } else {
            segments = std::move(baseParts);
            std::vector<std::string> more = SplitSlashes(to.path);
            segments.insert(segments.end(), more.begin(), more.end());
            // Empty segments between the first and the last would come back
            // as doubled slashes.
            if (segments.size() > 2) {
                std::vector<std::string> kept { segments.front() };
                for (std::size_t i = 1; i + 1 < segments.size(); ++i) {
                    if (!segments[i].empty()) kept.push_back(segments[i]);
                }
                kept.push_back(segments.back());
                segments = std::move(kept);
            }
        }
        std::vector<std::string> resolved;
        for (const std::string& segment : segments) {
            if (segment == "..") {
                if (!resolved.empty()) resolved.pop_back();
            } else if (segment != ".") {
                resolved.push_back(segment);
            }
        }
        // A reference ending in a directory step keeps its trailing slash.
        if (segments.back() == "." || segments.back() == "..") resolved.emplace_back();
        std::string path;
        for (std::size_t i = 0; i < resolved.size(); ++i) {
            if (i > 0) path += '/';
            path += resolved[i];
        }
        to.path = path.empty() ? std::string("/") : path;
        return Unsplit(to);
    }

    // urllib quotes a Location before it follows it, keeping every ASCII
    // letter, digit and punctuation mark: what it escapes are spaces,
    // controls and bytes outside ASCII.
    std::string QuoteLocation(std::string_view location) {
        std::string quoted;
        for (const char c : location) {
            const unsigned char byte = static_cast<unsigned char>(c);
            if (byte > 0x20 && byte < 0x7f) {
                quoted.push_back(c);
            } else {
                quoted += std::format("%{:02X}", byte);
            }
        }
        return quoted;
    }

    struct FetchTarget {
        bool secure = false;
        // Without brackets: what the socket and TLS verification are given.
        std::string host;
        std::uint16_t port = 0;
        // The URL's host[:port] as written, for the Host header.
        std::string authority;
        // Path and query: the request target.
        std::string target;
    };

    FetchTarget ParseTarget(std::string_view url) {
        const SplitURL parts = Split(url);
        if (parts.scheme != "http" && parts.scheme != "https") {
            throw std::invalid_argument("FetchHTTP1: not an http:// or https:// URL: " + std::string(url));
        }
        FetchTarget target;
        target.secure = parts.scheme == "https";
        std::string hostinfo = parts.netloc;
        if (const std::size_t at = hostinfo.rfind('@'); at != std::string::npos) hostinfo.erase(0, at + 1);
        std::string port;
        if (hostinfo.starts_with('[')) {
            const std::size_t close = hostinfo.find(']');
            target.host = hostinfo.substr(1, close - 1);
            const std::string rest = hostinfo.substr(close + 1);
            if (rest.starts_with(':')) {
                port = rest.substr(1);
            } else if (!rest.empty()) {
                throw std::invalid_argument("FetchHTTP1: unexpected text after the IPv6 host in " + std::string(url));
            }
        } else {
            const std::size_t colon = hostinfo.find(':');
            target.host = hostinfo.substr(0, colon);
            if (colon != std::string::npos) port = hostinfo.substr(colon + 1);
        }
        if (target.host.empty()) {
            throw std::invalid_argument("FetchHTTP1: no host in " + std::string(url));
        }
        if (port.empty()) {
            target.port = target.secure ? 443 : 80;
        } else {
            std::uint32_t value = 0;
            const auto [end, error] = std::from_chars(port.data(), port.data() + port.size(), value);
            if (error != std::errc() || end != port.data() + port.size() || value > 65535) {
                throw std::invalid_argument("FetchHTTP1: bad port '" + port + "' in " + std::string(url));
            }
            target.port = static_cast<std::uint16_t>(value);
        }
        target.authority = hostinfo;
        target.target = parts.path.empty() ? std::string("/") : parts.path;
        if (!target.target.starts_with('/')) target.target.insert(target.target.begin(), '/');
        if (!parts.query.empty()) target.target += "?" + parts.query;
        return target;
    }

    std::int32_t StatusCode(const HTTPResponse& response) {
        std::int32_t code = 0;
        std::from_chars(response.status.data(), response.status.data() + response.status.size(), code);
        return code;
    }
}

FetchResultHTTP1 Crafter::FetchHTTP1(std::string_view url, const FetchOptionsHTTP1& options) {
    std::string current(url);
    std::string method = options.method.empty() ? std::string("GET") : options.method;
    std::unordered_map<std::string, std::string> headers = options.headers;
    std::string body = options.body;
    // How often the chain has been sent to each URL: urllib's loop check.
    std::map<std::string, std::uint32_t> visited;
    FetchResultHTTP1 result;
    while (true) {
        const FetchTarget target = ParseTarget(current);
        ClientHTTP1 client = target.secure ? ClientHTTP1(target.host, target.port, options.credentials)
                                           : ClientHTTP1(target.host, target.port);
        client.connectTimeout = options.connectTimeout;
        client.handshakeTimeout = options.handshakeTimeout;
        client.timeout = options.timeout;
        client.limits = options.limits;

        HTTPRequest request;
        request.method = method;
        request.scheme = target.secure ? "https" : "http";
        request.authority = target.authority;
        request.path = target.target;
        request.headers = headers;
        request.body = body;
        result.response = client.Send(request);
        result.url = current;

        const std::int32_t code = StatusCode(result.response);
        const bool redirect = code == 301 || code == 302 || code == 303 || code == 307 || code == 308;
        if (!redirect) return result;
        // The methods urllib redirects; any other comes back as the redirect.
        const bool followed = method == "GET" || method == "HEAD" || (method == "POST" && code <= 303);
        if (!followed) return result;
        auto location = result.response.headers.find("location");
        if (location == result.response.headers.end()) location = result.response.headers.find("uri");
        if (location == result.response.headers.end()) return result;

        std::string next = QuoteLocation(location->second);
        SplitURL parts = Split(next);
        if (!parts.scheme.empty() && parts.scheme != "http" && parts.scheme != "https") return result;
        if (parts.path.empty() && !parts.netloc.empty()) {
            parts.path = "/";
            next = Unsplit(parts);
        }
        next = Join(current, next);

        const auto seen = visited.find(next);
        const std::uint32_t times = seen == visited.end() ? 0 : seen->second;
        if (times >= options.maxRepeats || visited.size() >= options.maxRedirects) {
            result.limited = true;
            return result;
        }
        visited[next] = times + 1;
        ++result.redirects;

        // What urllib sends next: a GET, or a HEAD for a HEAD, without the
        // body or the headers that described it.
        if (method != "HEAD") method = "GET";
        body.clear();
        headers.erase("content-length");
        headers.erase("content-type");
        current = std::move(next);
    }
}