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// Copyright 2019-2024 ChainSafe Systems
// SPDX-License-Identifier: Apache-2.0, MIT
// Copyright 2018-2020 Alec Mocatta
// SPDX-License-Identifier: Apache-2.0, MIT

//! Wrapper that uses the `Range` HTTP header to resume get requests.
//!
//! Most of the code can be attributed to `Alec Mocatta` and comes from the crate
//! <https://crates.io/crates/reqwest_resume/>
//! Some modifications have been done to update the code regarding `tokio`,
//! replace the `hyperx` dependency with `hyper` and add two unit tests.

use crate::utils::net::global_http_client;
use bytes::Bytes;
use futures::{ready, FutureExt as _, Stream, TryFutureExt as _};
use std::{
    pin::Pin,
    task::{Context, Poll},
    time::Duration,
};
use tokio::time::sleep;

/// A `Client` to make Requests with.
///
/// See [`reqwest::Client`].
#[derive(Debug)]
pub struct Client(reqwest::Client);
impl Client {
    /// Constructs a new `Client` using the global Forest HTTP client.
    pub fn new() -> Self {
        Self(global_http_client())
    }
    /// Convenience method to make a `GET` request to a URL.
    ///
    /// See [`reqwest::Client::get()`].
    pub fn get(&self, url: reqwest::Url) -> RequestBuilder {
        RequestBuilder(self.0.clone(), reqwest::Method::GET, url)
    }
}

/// A builder to construct the properties of a Request.
///
/// See [`reqwest::RequestBuilder`].
#[derive(Debug)]
pub struct RequestBuilder(reqwest::Client, reqwest::Method, reqwest::Url);
impl RequestBuilder {
    /// Constructs the Request and sends it the target URL, returning a Response.
    ///
    /// See [`reqwest::RequestBuilder::send()`].
    pub async fn send(self) -> reqwest::Result<Response> {
        let RequestBuilder(client, method, url) = self;

        let response = loop {
            let builder = client.request(method.clone(), url.clone());
            match builder.send().await {
                Err(err) if !err.is_builder() && !err.is_redirect() && !err.is_status() => {
                    sleep(Duration::from_secs(1)).await
                }
                x => break x?,
            }
        };
        let accept_byte_ranges = response
            .headers()
            .get(http::header::ACCEPT_RANGES)
            .map(http::HeaderValue::as_bytes)
            == Some(b"bytes");
        let resp = Response {
            client,
            method,
            url,
            response,
            accept_byte_ranges,
            pos: 0,
        };
        Ok(resp)
    }
}

/// A Response to a submitted Request.
///
/// See [`reqwest::Response`].
#[derive(Debug)]
pub struct Response {
    client: reqwest::Client,
    method: reqwest::Method,
    url: reqwest::Url,
    response: reqwest::Response,
    accept_byte_ranges: bool,
    pos: u64,
}
impl Response {
    /// Convert the response into a `Stream` of `Bytes` from the body.
    ///
    /// See [`reqwest::Response::bytes_stream()`].
    pub fn bytes_stream(self) -> impl Stream<Item = reqwest::Result<Bytes>> + Send {
        Decoder {
            client: self.client,
            method: self.method,
            url: self.url,
            decoder: Box::pin(self.response.bytes_stream()),
            accept_byte_ranges: self.accept_byte_ranges,
            pos: self.pos,
        }
    }

    pub fn response(&self) -> &reqwest::Response {
        &self.response
    }
}

struct Decoder {
    client: reqwest::Client,
    method: reqwest::Method,
    url: reqwest::Url,
    decoder: Pin<Box<dyn Stream<Item = reqwest::Result<Bytes>> + Send>>,
    accept_byte_ranges: bool,
    pos: u64,
}
impl Stream for Decoder {
    type Item = reqwest::Result<Bytes>;

    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
        loop {
            match ready!(self.decoder.as_mut().poll_next(cx)) {
                Some(Err(err)) => {
                    if !self.accept_byte_ranges {
                        break Poll::Ready(Some(Err(err)));
                    }
                    let builder = self.client.request(self.method.clone(), self.url.clone());
                    let mut headers = http::HeaderMap::new();
                    let value = http::HeaderValue::from_str(&std::format!("bytes={}-", self.pos))
                        .expect("unreachable");
                    headers.insert(http::header::RANGE, value);
                    let builder = builder.headers(headers);
                    // https://developer.mozilla.org/en-US/docs/Web/HTTP/Range_requests
                    self.decoder = Box::pin(
                        sleep(Duration::from_secs(1))
                            .then(|()| builder.send())
                            .map_ok(reqwest::Response::bytes_stream)
                            .try_flatten_stream(),
                    );
                }
                Some(Ok(n)) => {
                    self.pos += n.len() as u64;
                    break Poll::Ready(Some(Ok(n)));
                }
                None => break Poll::Ready(None),
            }
        }
    }
}

/// Shortcut method to quickly make a GET request.
///
/// See [`reqwest::get`].
pub async fn get(url: reqwest::Url) -> reqwest::Result<Response> {
    Client::new().get(url).send().await
}

#[cfg(test)]
mod tests;