elefren-fork/src/page.rs

use super::{deserialise_response, FediClient, Result};
use crate::entities::itemsiter::ItemsIter;
use hyper_old_types::header::{parsing, Link, RelationType};
use reqwest::{Response, header::LINK};
use serde::Deserialize;
use url::Url;

macro_rules! pages {
    ($($direction:ident: $fun:ident),*) => {

        $(
            doc_comment::doc_comment!(concat!(
                    "Method to retrieve the ", stringify!($direction), " page of results"),
            pub async fn $fun(&mut self) -> Result<Option<Vec<T>>> {
                let url = match self.$direction.take() {
                    Some(s) => s,
                    None => return Ok(None),
                };

                let response = self.api_client.send(
                    self.api_client.http_client.get(url)
                ).await?;

                let (prev, next) = get_links(&response)?;
                self.next = next;
                self.prev = prev;

                deserialise_response(response).await
            });
         )*
    }
}

/// Owned version of the `Page` struct in this module. Allows this to be more
/// easily stored for later use
#[derive(Debug, Clone)]
pub struct OwnedPage<T: for<'de> Deserialize<'de>> {
    api_client: FediClient,
    next: Option<Url>,
    prev: Option<Url>,
    /// Initial set of items
    pub initial_items: Vec<T>,
}

impl<T: for<'de> Deserialize<'de>> OwnedPage<T> {
    pages! {
        next: next_page,
        prev: prev_page
    }
}

impl<'a, T: for<'de> Deserialize<'de>> From<Page<'a, T>> for OwnedPage<T> {
    fn from(page: Page<'a, T>) -> OwnedPage<T> {
        OwnedPage {
            api_client: page.api_client.clone(),
            next: page.next,
            prev: page.prev,
            initial_items: page.initial_items,
        }
    }
}

/// Represents a single page of API results
#[derive(Debug, Clone)]
pub struct Page<'a, T: for<'de> Deserialize<'de>> {
    api_client: &'a FediClient,
    next: Option<Url>,
    prev: Option<Url>,
    /// Initial set of items
    pub initial_items: Vec<T>,
}

impl<'a, T: for<'de> Deserialize<'de>> Page<'a, T> {
    pages! {
        next: next_page,
        prev: prev_page
    }

    pub(crate) async fn new<'m>(api_client: &'m FediClient, response: Response) -> Result<Page<'m, T>> {
        let (prev, next) = get_links(&response)?;
        Ok(Page {
            initial_items: deserialise_response(response).await?,
            next,
            prev,
            api_client: api_client,
        })
    }
}

impl<'a, T: Clone + for<'de> Deserialize<'de>> Page<'a, T> {
    /// Returns an owned version of this struct that doesn't borrow the client
    /// that created it
    pub fn into_owned(self) -> OwnedPage<T> {
        OwnedPage::from(self)
    }

    /// Returns an iterator that provides a stream of `T`s
    ///
    /// This abstracts away the process of iterating over each item in a page,
    /// then making an http call, then iterating over each item in the new
    /// page, etc. The iterator provides a stream of `T`s, calling
    /// `self.next_page()`
    /// when necessary to get
    /// more of them, until
    /// there are no more items.
    pub fn items_iter(self) -> ItemsIter<'a, T>
    where
        T: 'a,
    {
        ItemsIter::new(self)
    }
}

fn get_links(response: &Response) -> Result<(Option<Url>, Option<Url>)> {
    let mut prev = None;
    let mut next = None;

    if let Some(link_header) = response.headers().get(LINK) {
        let link_header = link_header.to_str()?;
        let link_header = link_header.as_bytes();
        let link_header: Link = parsing::from_raw_str(link_header)?;
        for value in link_header.values() {
            if let Some(relations) = value.rel() {
                if relations.contains(&RelationType::Next) {
                    next = Some(Url::parse(value.link())?);
                }

                if relations.contains(&RelationType::Prev) {
                    prev = Some(Url::parse(value.link())?);
                }
            }
        }
    }

    Ok((prev, next))
}