#include <mbgl/storage/asset_request.hpp>
#include <mbgl/storage/response.hpp>
#include <mbgl/platform/platform.hpp>
#include <mbgl/util/std.hpp>

#include <uv.h>

#include <limits>

namespace mbgl {

struct AssetRequestBaton {
    AssetRequestBaton(AssetRequest *request_, const std::string &path, uv_loop_t *loop);
    ~AssetRequestBaton();

    void cancel();
    static void fileOpened(uv_fs_t *req);
    static void fileStated(uv_fs_t *req);
    static void fileRead(uv_fs_t *req);
    static void fileClosed(uv_fs_t *req);
    static void notifyError(uv_fs_t *req);
    static void cleanup(uv_fs_t *req);

    const std::thread::id threadId;
    AssetRequest *request = nullptr;
    uv_fs_t req;
    uv_file fd = -1;
    bool canceled = false;
    std::string body;
    uv_buf_t buffer;
};

AssetRequestBaton::AssetRequestBaton(AssetRequest *request_, const std::string &path, uv_loop_t *loop)
    : threadId(std::this_thread::get_id()), request(request_) {
    req.data = this;
    uv_fs_open(loop, &req, path.c_str(), O_RDONLY, S_IRUSR, fileOpened);
}

AssetRequestBaton::~AssetRequestBaton() {
}

void AssetRequestBaton::cancel() {
    canceled = true;

    // uv_cancel fails frequently when the request has already been started.
    // In that case, we have to let it complete and check the canceled bool
    // instead.
    uv_cancel((uv_req_t *)&req);
}

void AssetRequestBaton::notifyError(uv_fs_t *req) {
    AssetRequestBaton *ptr = reinterpret_cast<AssetRequestBaton *>(req->data);
    assert(std::this_thread::get_id() == ptr->threadId);

    if (ptr->request && req->result < 0 && !ptr->canceled && req->result != UV_ECANCELED) {
        ptr->request->response = util::make_unique<Response>();
        ptr->request->response->code = req->result == UV_ENOENT ? 404 : 500;
#if UV_VERSION_MAJOR == 0 && UV_VERSION_MINOR <= 10
        ptr->request->response->message = uv_strerror(uv_last_error(req->loop));
#else
        ptr->request->response->message = uv_strerror(int(req->result));
#endif
        ptr->request->notify();
    }
}

void AssetRequestBaton::fileOpened(uv_fs_t *req) {
    AssetRequestBaton *ptr = reinterpret_cast<AssetRequestBaton *>(req->data);
    assert(std::this_thread::get_id() == ptr->threadId);

    if (req->result < 0) {
        // Opening failed or was canceled. There isn't much left we can do.
        notifyError(req);
        cleanup(req);
    } else {
        const uv_file fd = uv_file(req->result);

        // We're going to reuse this handle, so we need to cleanup first.
        uv_fs_req_cleanup(req);

        if (ptr->canceled || !ptr->request) {
            // Either the AssetRequest object has been destructed, or the
            // request was canceled.
            uv_fs_close(req->loop, req, fd, fileClosed);
        } else {
            ptr->fd = fd;
            uv_fs_fstat(req->loop, req, fd, fileStated);
        }
    }
}

void AssetRequestBaton::fileStated(uv_fs_t *req) {
    AssetRequestBaton *ptr = reinterpret_cast<AssetRequestBaton *>(req->data);
    assert(std::this_thread::get_id() == ptr->threadId);

    if (req->result != 0 || ptr->canceled || !ptr->request) {
        // Stating failed or was canceled. We already have an open file handle
        // though, which we'll have to close.
        notifyError(req);

        uv_fs_req_cleanup(req);
        uv_fs_close(req->loop, req, ptr->fd, fileClosed);
    } else {
#if UV_VERSION_MAJOR == 0 && UV_VERSION_MINOR <= 10
        const uv_statbuf_t *stat = static_cast<const uv_statbuf_t *>(req->ptr);
#else
        const uv_stat_t *stat = static_cast<const uv_stat_t *>(req->ptr);
#endif
        if (stat->st_size > std::numeric_limits<int>::max()) {
            // File is too large for us to open this way because uv_buf's only support unsigned
            // ints as maximum size.
            if (ptr->request) {
                ptr->request->response = util::make_unique<Response>();
                ptr->request->response->code = UV_EFBIG;
#if UV_VERSION_MAJOR == 0 && UV_VERSION_MINOR <= 10
                ptr->request->response->message = uv_strerror(uv_err_t {UV_EFBIG, 0});
#else
                ptr->request->response->message = uv_strerror(UV_EFBIG);
#endif
                ptr->request->notify();
            }

            uv_fs_req_cleanup(req);
            uv_fs_close(req->loop, req, ptr->fd, fileClosed);
        } else {
            const unsigned int size = (unsigned int)(stat->st_size);
            ptr->body.resize(size);
            ptr->buffer = uv_buf_init(const_cast<char *>(ptr->body.data()), size);
            uv_fs_req_cleanup(req);
#if UV_VERSION_MAJOR == 0 && UV_VERSION_MINOR <= 10
            uv_fs_read(req->loop, req, ptr->fd, ptr->buffer.base, ptr->buffer.len, -1, fileRead);
#else
            uv_fs_read(req->loop, req, ptr->fd, &ptr->buffer, 1, 0, fileRead);
#endif
        }
    }
}

void AssetRequestBaton::fileRead(uv_fs_t *req) {
    AssetRequestBaton *ptr = reinterpret_cast<AssetRequestBaton *>(req->data);
    assert(std::this_thread::get_id() == ptr->threadId);

    if (req->result < 0 || ptr->canceled || !ptr->request) {
        // Reading failed or was canceled. We already have an open file handle
        // though, which we'll have to close.
        notifyError(req);
    } else {
        // File was successfully read.
        if (ptr->request) {
            ptr->request->response = util::make_unique<Response>();
            ptr->request->response->code = 200;
            ptr->request->response->data = std::move(ptr->body);
            ptr->request->notify();
        }
    }

    uv_fs_req_cleanup(req);
    uv_fs_close(req->loop, req, ptr->fd, fileClosed);
}

void AssetRequestBaton::fileClosed(uv_fs_t *req) {
    assert(std::this_thread::get_id() == (reinterpret_cast<AssetRequestBaton *>(req->data))->threadId);

    if (req->result < 0) {
        // Closing the file failed. But there isn't anything we can do.
    }

    cleanup(req);
}

void AssetRequestBaton::cleanup(uv_fs_t *req) {
    AssetRequestBaton *ptr = reinterpret_cast<AssetRequestBaton *>(req->data);
    assert(std::this_thread::get_id() == ptr->threadId);

    if (ptr->request) {
        ptr->request->ptr = nullptr;
    }

    uv_fs_req_cleanup(req);
    delete ptr;
    ptr = nullptr;
}


AssetRequest::AssetRequest(const std::string &path_, uv_loop_t *loop)
    : BaseRequest(path_) {
    if (!path.empty() && path[0] == '/') {
        // This is an absolute path. We don't allow this. Note that this is not a way to absolutely
        // prevent access to resources outside the application bundle; e.g. there could be symlinks
        // in the application bundle that link to outside. We don't care about these.
        response = util::make_unique<Response>();
        response->code = 403;
        response->message = "Path is outside the application bundle";
        notify();
    } else {
        // Note: The AssetRequestBaton object is deleted in AssetRequestBaton::cleanup().
        ptr = new AssetRequestBaton(this, platform::applicationRoot() + "/" + path, loop);
    }
}

void AssetRequest::cancel() {
    assert(std::this_thread::get_id() == threadId);

    if (ptr) {
        ptr->cancel();

        // When deleting a AssetRequest object with a uv_fs_* call is in progress, we are making sure
        // that the callback doesn't accidentally reference this object again.
        ptr->request = nullptr;
        ptr = nullptr;
    }

    notify();
}

AssetRequest::~AssetRequest() {
    assert(std::this_thread::get_id() == threadId);
    cancel();

    // Note: The AssetRequestBaton object is deleted in AssetRequestBaton::cleanup().
}

}