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// This file is part of rss.
//
// Copyright © 2015-2017 The rust-syndication Developers
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the MIT License and/or Apache 2.0 License.

use std::collections::HashMap;
use std::io::{BufRead, Write};
use std::str::{self, FromStr};

use quick_xml::errors::Error as XmlError;
use quick_xml::events::attributes::Attributes;
use quick_xml::events::{Event, BytesStart, BytesEnd};
use quick_xml::reader::Reader;
use quick_xml::writer::Writer;

use category::Category;
use cloud::Cloud;
use error::Error;
use extension::{self, ExtensionMap};
use extension::dublincore::DublinCoreExtension;
use extension::itunes::ITunesChannelExtension;
use extension::util::{extension_name, parse_extension};
use fromxml::FromXml;
use image::Image;
use item::Item;
use textinput::TextInput;
use toxml::{ToXml, WriterExt};
use util::element_text;

/// Represents the channel of an RSS feed.
#[derive(Debug, Default, Clone, PartialEq, Builder)]
#[builder(setter(into), default)]
pub struct Channel {
    /// The name of the channel.
    title: String,
    /// The URL for the website corresponding to the channel.
    link: String,
    /// A description of the channel.
    description: String,
    /// The language of the channel.
    language: Option<String>,
    /// The copyright notice for the channel.
    copyright: Option<String>,
    /// The email address for the managing editor.
    managing_editor: Option<String>,
    /// The email address for the webmaster.
    webmaster: Option<String>,
    /// The publication date for the content of the channel as an RFC822 timestamp.
    pub_date: Option<String>,
    /// The date that the contents of the channel last changed as an RFC822 timestamp.
    last_build_date: Option<String>,
    /// The categories the channel belongs to.
    categories: Vec<Category>,
    /// A string indicating the program used to generate the channel.
    generator: Option<String>,
    /// A URL that points to the documentation for the RSS format.
    docs: Option<String>,
    /// The cloud to register with to be notified of updates to the channel.
    cloud: Option<Cloud>,
    /// The PICS rating for the channel.
    rating: Option<String>,
    /// The number of minutes the channel can be cached before refreshing.
    ttl: Option<String>,
    /// An image that can be displayed with the channel.
    image: Option<Image>,
    /// A text input box that can be displayed with the channel.
    text_input: Option<TextInput>,
    /// A hint to tell the aggregator which hours it can skip.
    skip_hours: Vec<String>,
    /// A hint to tell the aggregator which days it can skip.
    skip_days: Vec<String>,
    /// The items in the channel.
    items: Vec<Item>,
    /// The extensions for the channel.
    extensions: ExtensionMap,
    /// The iTunes extension for the channel.
    itunes_ext: Option<ITunesChannelExtension>,
    /// The Dublin Core extension for the channel.
    dublin_core_ext: Option<DublinCoreExtension>,
    /// The namespaces present in the RSS tag.
    namespaces: HashMap<String, String>,
}

impl Channel {
    /// Return the title of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_title("Channel Title");
    /// assert_eq!(channel.title(), "Channel Title");
    /// ```
    pub fn title(&self) -> &str {
        self.title.as_str()
    }

    /// Set the title of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_title("Channel Title");
    /// ```
    pub fn set_title<V>(&mut self, title: V)
    where
        V: Into<String>,
    {
        self.title = title.into();
    }

    /// Return the URL for the website corresponding to this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_link("http://example.com");
    /// assert_eq!(channel.link(), "http://example.com");
    /// ```
    pub fn link(&self) -> &str {
        self.link.as_str()
    }

    /// Set the URL for the website corresponding to this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_link("http://example.com");
    /// ```
    pub fn set_link<V>(&mut self, link: V)
    where
        V: Into<String>,
    {
        self.link = link.into();
    }

    /// Return the description of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_description("Channel description");
    /// assert_eq!(channel.description(), "Channel description");
    /// ```
    pub fn description(&self) -> &str {
        self.description.as_str()
    }

    /// Set the description of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_description("Channel description");
    /// ```
    pub fn set_description<V>(&mut self, description: V)
    where
        V: Into<String>,
    {
        self.description = description.into();
    }

    /// Return the language of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_language("en-US".to_string());
    /// assert_eq!(channel.language(), Some("en-US"));
    /// ```
    pub fn language(&self) -> Option<&str> {
        self.language.as_ref().map(|s| s.as_str())
    }

    /// Set the language of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_language("en-US".to_string());
    /// ```
    pub fn set_language<V>(&mut self, language: V)
    where
        V: Into<Option<String>>,
    {
        self.language = language.into();
    }

    /// Return the copyright notice for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_copyright("© 2017 John Doe".to_string());
    /// assert_eq!(channel.copyright(), Some("© 2017 John Doe"));
    /// ```
    pub fn copyright(&self) -> Option<&str> {
        self.copyright.as_ref().map(|s| s.as_str())
    }

    /// Set the copyright notice for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_copyright("© 2017 John Doe".to_string());
    /// ```
    pub fn set_copyright<V>(&mut self, copyright: V)
    where
        V: Into<Option<String>>,
    {
        self.copyright = copyright.into();
    }

    /// Return the email address for the managing editor of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_managing_editor("johndoe@example.com".to_string());
    /// assert_eq!(channel.managing_editor(), Some("johndoe@example.com"));
    /// ```
    pub fn managing_editor(&self) -> Option<&str> {
        self.managing_editor.as_ref().map(|s| s.as_str())
    }

    /// Set the email address for the managing editor of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_managing_editor("johndoe@example.com".to_string());
    /// assert_eq!(channel.managing_editor(), Some("johndoe@example.com"));
    /// ```
    pub fn set_managing_editor<V>(&mut self, managing_editor: V)
    where
        V: Into<Option<String>>,
    {
        self.managing_editor = managing_editor.into();
    }

    /// Return the email address for webmaster of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_webmaster("johndoe@example.com".to_string());
    /// assert_eq!(channel.webmaster(), Some("johndoe@example.com"));
    /// ```
    pub fn webmaster(&self) -> Option<&str> {
        self.webmaster.as_ref().map(|s| s.as_str())
    }

    /// Set the email address for webmaster of this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_webmaster("johndoe@example.com".to_string());
    /// ```
    pub fn set_webmaster<V>(&mut self, webmaster: V)
    where
        V: Into<Option<String>>,
    {
        self.webmaster = webmaster.into();
    }

    /// Return the publication date for the content of this channel as an RFC822 timestamp.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_pub_date("Mon, 1 Jan 2017 12:00:00 GMT".to_string());
    /// assert_eq!(channel.pub_date(), Some("Mon, 1 Jan 2017 12:00:00 GMT"));
    /// ```
    pub fn pub_date(&self) -> Option<&str> {
        self.pub_date.as_ref().map(|s| s.as_str())
    }

    /// Set the publication date for the content of this channel as an RFC822 timestamp.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_pub_date("Mon, 1 Jan 2017 12:00:00 GMT".to_string());
    /// ```
    pub fn set_pub_date<V>(&mut self, pub_date: V)
    where
        V: Into<Option<String>>,
    {
        self.pub_date = pub_date.into();
    }

    /// Return the time that the content of this channel was last changed as an RFC822 timestamp.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_last_build_date("Mon, 1 Jan 2017 12:00:00 GMT".to_string());
    /// assert_eq!(channel.last_build_date(), Some("Mon, 1 Jan 2017 12:00:00 GMT"));
    /// ```
    pub fn last_build_date(&self) -> Option<&str> {
        self.last_build_date.as_ref().map(|s| s.as_str())
    }

    /// Set the time that the content of this channel was last changed as an RFC822 timestamp.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_last_build_date("Mon, 1 Jan 2017 12:00:00 GMT".to_string());
    /// ```
    pub fn set_last_build_date<V>(&mut self, last_build_date: V)
    where
        V: Into<Option<String>>,
    {
        self.last_build_date = last_build_date.into();
    }

    /// Return the categories that this channel belongs to.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Category};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_categories(vec![Category::default()]);
    /// assert_eq!(channel.categories().len(), 1);
    /// ```
    pub fn categories(&self) -> &[Category] {
        &self.categories
    }

    /// Return a mutable slice of the categories that this channel belongs to.
    pub fn categories_mut(&mut self) -> &mut [Category] {
        &mut self.categories
    }

    /// Set the categories that this channel belongs to.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Category};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_categories(vec![Category::default()]);
    /// ```
    pub fn set_categories<V>(&mut self, categories: V)
    where
        V: Into<Vec<Category>>,
    {
        self.categories = categories.into();
    }

    /// Return a string indicating the program used to generate the channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_generator("Program Name".to_string());
    /// assert_eq!(channel.generator(), Some("Program Name"));
    /// ```
    pub fn generator(&self) -> Option<&str> {
        self.generator.as_ref().map(|s| s.as_str())
    }

    /// Set a string indicating the program used to generate the channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_generator("Program Name".to_string());
    /// ```
    pub fn set_generator<V>(&mut self, generator: V)
    where
        V: Into<Option<String>>,
    {
        self.generator = generator.into();
    }

    /// Return a URL that points to the documentation of the RSS format used in this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_docs("https://cyber.harvard.edu/rss/rss.html".to_string());
    /// assert_eq!(channel.docs(), Some("https://cyber.harvard.edu/rss/rss.html"));
    /// ```
    pub fn docs(&self) -> Option<&str> {
        self.docs.as_ref().map(|s| s.as_str())
    }

    /// Set a URL that points to the documentation of the RSS format used in this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_docs("https://cyber.harvard.edu/rss/rss.html".to_string());
    /// ```
    pub fn set_docs<V>(&mut self, docs: V)
    where
        V: Into<Option<String>>,
    {
        self.docs = docs.into();
    }

    /// Return the information used to register with a cloud for notifications of updates to the
    /// channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Cloud};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_cloud(Cloud::default());
    /// assert!(channel.cloud().is_some());
    /// ```
    pub fn cloud(&self) -> Option<&Cloud> {
        self.cloud.as_ref()
    }

    /// Set the information used to register with a cloud for notifications of updates to the
    /// channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Cloud};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_cloud(Cloud::default());
    /// ```
    pub fn set_cloud<V>(&mut self, cloud: V)
    where
        V: Into<Option<Cloud>>,
    {
        self.cloud = cloud.into();
    }

    /// Return the time to live of this channel. This indicates the number of minutes the
    /// channel can be cached before needing to be refreshed.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_ttl("60".to_string());
    /// assert_eq!(channel.ttl(), Some("60"));
    /// ```
    pub fn ttl(&self) -> Option<&str> {
        self.ttl.as_ref().map(|s| s.as_str())
    }

    /// Set the time to live of this channel. This indicates the number of minutes the
    /// channel can be cached before needing to be refreshed.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_ttl("60".to_string());
    /// ```
    pub fn set_ttl<V>(&mut self, ttl: V)
    where
        V: Into<Option<String>>,
    {
        self.ttl = ttl.into();
    }

    /// Return the image to be displayed with this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Image};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_image(Image::default());
    /// assert!(channel.image().is_some());
    /// ```
    pub fn image(&self) -> Option<&Image> {
        self.image.as_ref()
    }

    /// Set the image to be displayed with this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Image};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_image(Image::default());
    /// ```
    pub fn set_image<V>(&mut self, image: V)
    where
        V: Into<Option<Image>>,
    {
        self.image = image.into();
    }

    /// Return the [PICS](https://www.w3.org/PICS/) rating for this channel.
    pub fn rating(&self) -> Option<&str> {
        self.rating.as_ref().map(|s| s.as_str())
    }

    /// Set the [PICS](https://www.w3.org/PICS/) rating for this channel.
    pub fn set_rating<V>(&mut self, rating: V)
    where
        V: Into<Option<String>>,
    {
        self.rating = rating.into();
    }

    /// Return the information for a text box to be displayed with this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, TextInput};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_text_input(TextInput::default());
    /// assert!(channel.text_input().is_some());
    /// ```
    pub fn text_input(&self) -> Option<&TextInput> {
        self.text_input.as_ref()
    }

    /// Set the information for a text box to be displayed with this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, TextInput};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_text_input(TextInput::default());
    /// ```
    pub fn set_text_input<V>(&mut self, text_input: V)
    where
        V: Into<Option<TextInput>>,
    {
        self.text_input = text_input.into();
    }

    /// Return the hours that aggregators can skip for refreshing content.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let skip_hours = vec![6, 7, 8, 14, 22];
    ///
    /// let mut channel = Channel::default();
    /// channel.set_skip_hours(vec!["1".to_string()]);
    /// assert_eq!(channel.skip_hours().len(), 1);
    /// ```
    pub fn skip_hours(&self) -> &[String] {
        &self.skip_hours
    }

    /// Return a mutable slice of the hours that aggregators can skip for refreshing content.
    pub fn skip_hours_mut(&mut self) -> &mut [String] {
        &mut self.skip_hours
    }

    /// Set the hours that aggregators can skip for refreshing content.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_skip_hours(vec!["1".to_string()]);
    /// ```
    pub fn set_skip_hours<V>(&mut self, skip_hours: V)
    where
        V: Into<Vec<String>>,
    {
        self.skip_hours = skip_hours.into();
    }

    /// Return the days that aggregators can skip for refreshing content.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_skip_days(vec!["Monday".to_string()]);
    /// assert_eq!(channel.skip_days().len(), 1);
    /// ```
    pub fn skip_days(&self) -> &[String] {
        &self.skip_days
    }

    /// Return a mutable slice of the days that aggregators can skip for refreshing content.
    pub fn skip_days_mut(&mut self) -> &mut [String] {
        &mut self.skip_days
    }

    /// Set the days that aggregators can skip for refreshing content.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_skip_days(vec!["Monday".to_string()]);
    /// ```
    pub fn set_skip_days<V>(&mut self, skip_days: V)
    where
        V: Into<Vec<String>>,
    {
        self.skip_days = skip_days.into();
    }

    /// Return the items in this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Item};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_items(vec![Item::default()]);
    /// assert_eq!(channel.items().len(), 1);
    /// ```
    pub fn items(&self) -> &[Item] {
        &self.items
    }

    /// Return a mutable slice of the items in this channel.
    pub fn items_mut(&mut self) -> &mut [Item] {
        &mut self.items
    }

    /// Set the items in this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::{Channel, Item};
    ///
    /// let mut channel = Channel::default();
    /// channel.set_items(vec![Item::default()]);
    /// ```
    pub fn set_items<V>(&mut self, items: V)
    where
        V: Into<Vec<Item>>,
    {
        self.items = items.into();
    }

    /// Return the iTunes extension for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    /// use rss::extension::itunes::ITunesChannelExtension;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_itunes_ext(ITunesChannelExtension::default());
    /// assert!(channel.itunes_ext().is_some());
    /// ```
    pub fn itunes_ext(&self) -> Option<&ITunesChannelExtension> {
        self.itunes_ext.as_ref()
    }

    /// Set the iTunes extension for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    /// use rss::extension::itunes::ITunesChannelExtension;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_itunes_ext(ITunesChannelExtension::default());
    /// ```
    pub fn set_itunes_ext<V>(&mut self, itunes_ext: V)
    where
        V: Into<Option<ITunesChannelExtension>>,
    {
        self.itunes_ext = itunes_ext.into();
    }

    /// Return the Dublin Core extension for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    /// use rss::extension::dublincore::DublinCoreExtension;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_dublin_core_ext(DublinCoreExtension::default());
    /// assert!(channel.dublin_core_ext().is_some());
    /// ```
    pub fn dublin_core_ext(&self) -> Option<&DublinCoreExtension> {
        self.dublin_core_ext.as_ref()
    }

    /// Set the Dublin Core extension for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    /// use rss::extension::dublincore::DublinCoreExtension;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_dublin_core_ext(DublinCoreExtension::default());
    /// ```
    pub fn set_dublin_core_ext<V>(&mut self, dublin_core_ext: V)
    where
        V: Into<Option<DublinCoreExtension>>,
    {
        self.dublin_core_ext = dublin_core_ext.into();
    }

    /// Return the extensions for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::HashMap;
    /// use rss::Channel;
    /// use rss::extension::{ExtensionMap, Extension};
    ///
    /// let extension = Extension::default();
    ///
    /// let mut item_map = HashMap::<String, Vec<Extension>>::new();
    /// item_map.insert("ext:name".to_string(), vec![extension]);
    ///
    /// let mut extension_map = ExtensionMap::default();
    /// extension_map.insert("ext".to_string(), item_map);
    ///
    /// let mut channel = Channel::default();
    /// channel.set_extensions(extension_map);
    /// assert_eq!(channel.extensions()
    ///                   .get("ext")
    ///                   .and_then(|m| m.get("ext:name"))
    ///                   .map(|v| v.len()),
    ///            Some(1));
    /// ```
    pub fn extensions(&self) -> &ExtensionMap {
        &self.extensions
    }

    /// Set the extensions for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    /// use rss::extension::ExtensionMap;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_extensions(ExtensionMap::default());
    /// ```
    pub fn set_extensions<V>(&mut self, extensions: V)
    where
        V: Into<ExtensionMap>,
    {
        self.extensions = extensions.into()
    }

    /// Return the namespaces for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::HashMap;
    /// use rss::Channel;
    ///
    /// let mut namespaces = HashMap::new();
    /// namespaces.insert("ext".to_string(), "http://example.com".to_string());
    ///
    /// let mut channel = Channel::default();
    /// channel.set_namespaces(namespaces);
    /// assert_eq!(channel.namespaces().get("ext").map(|s| s.as_str()), Some("http://example.com"));
    /// ```
    pub fn namespaces(&self) -> &HashMap<String, String> {
        &self.namespaces
    }

    /// Set the namespaces for this channel.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::collections::HashMap;
    /// use rss::Channel;
    ///
    /// let mut channel = Channel::default();
    /// channel.set_namespaces(HashMap::new());
    /// ```
    pub fn set_namespaces<V>(&mut self, namespaces: V)
    where
        V: Into<HashMap<String, String>>,
    {
        self.namespaces = namespaces.into()
    }
}

impl Channel {
    /// Attempt to read an RSS channel from a URL.
    ///
    /// Note: The `from_url` method can only be used by enabling the `from_url` feature in
    /// your `Cargo.toml` as follows:
    ///
    /// ```toml
    /// [dependencies]
    /// rss = { version = "*", features = ["from_url"] }
    /// ```
    ///
    /// # Examples
    ///
    /// ```
    /// use rss::Channel;
    /// let channel = Channel::from_url("https://feedpress.me/usererror.xml");
    /// ```
    #[cfg(feature = "from_url")]
    pub fn from_url(url: &str) -> Result<Channel, Error> {
        use std::io::Read;

        let mut content = String::new();
        ::reqwest::get(url)?.read_to_string(&mut content)?;
        Ok(Channel::from_str(content.as_str())?)
    }

    /// Attempt to read an RSS channel from a reader.
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// let reader: BufRead = ...;
    /// let channel = Channel::read_from(reader).unwrap();
    /// ```
    pub fn read_from<R: BufRead>(reader: R) -> Result<Channel, Error> {
        let mut reader = Reader::from_reader(reader);
        reader.trim_text(true).expand_empty_elements(true);
        let mut namespaces = HashMap::new();
        let mut buf = Vec::new();
        let mut skip_buf = Vec::new();

        let mut channel: Option<Channel> = None;

        // for parsing RSS 0.9, 1.0 feeds
        let mut items: Option<Vec<Item>> = None;
        let mut image: Option<Image> = None;
        let mut text_input: Option<TextInput> = None;

        // find opening element
        loop {
            match reader.read_event(&mut buf)? {
                Event::Start(element) => {
                    if element.name() == b"rss" || element.name() == b"rdf:RDF" {
                        for attr in element.attributes().with_checks(false) {
                            if let Ok(attr) = attr {

                                if !attr.key.starts_with(b"xmlns:") ||
                                    attr.key == b"xmlns:itunes" ||
                                    attr.key == b"xmlns:dc"
                                {
                                    continue;
                                }

                                let key = str::from_utf8(&attr.key[6..])?.to_string();
                                let value = attr.unescape_and_decode_value(&reader)?;
                                namespaces.insert(key, value);
                            }
                        }

                        break;
                    } else {
                        return Err(Error::InvalidStartTag);
                    }
                }
                Event::Eof => return Err(Error::Eof),
                _ => continue,
            }
        }

        loop {
            match reader.read_event(&mut buf)? {
                Event::Start(element) => {
                    match element.name() {
                        b"channel" => {
                            let inner = Channel::from_xml(&mut reader, element.attributes())?;
                            channel = Some(inner);
                        }
                        b"item" => {
                            let item = Item::from_xml(&mut reader, element.attributes())?;
                            if items.is_none() {
                                items = Some(Vec::new());
                            }
                            items.as_mut().unwrap().push(item);
                        }
                        b"image" => {
                            let inner = Image::from_xml(&mut reader, element.attributes())?;
                            image = Some(inner);
                        }
                        b"textinput" => {
                            let inner = TextInput::from_xml(&mut reader, element.attributes())?;
                            text_input = Some(inner);
                        }
                        name => reader.read_to_end(name, &mut skip_buf)?,
                    }
                }
                Event::End(_) | Event::Eof => break,
                _ => {}
            }
            buf.clear();
        }

        if let Some(mut channel) = channel {
            if let Some(mut items) = items {
                channel.items.append(&mut items);
            }

            if image.is_some() {
                channel.image = image;
            }

            if text_input.is_some() {
                channel.text_input = text_input;
            }

            channel.namespaces = namespaces;

            Ok(channel)
        } else {
            Err(Error::Eof)
        }
    }

    /// Attempt to write the RSS channel as XML to a writer.
    ///
    /// # Example
    ///
    /// ```rust,ignore
    /// let channel: Channel = ...;
    /// let writer: Write = ...;
    /// channel.write_to(writer).unwrap();
    /// ```
    pub fn write_to<W: Write>(&self, writer: W) -> Result<W, Error> {
        let mut writer = ::quick_xml::Writer::new(writer);

        let name = b"rss";
        let mut element = BytesStart::borrowed(name, name.len());
        element.push_attribute(("version", "2.0"));

        let mut itunes_ns = self.itunes_ext.is_some();
        let mut dc_ns = self.dublin_core_ext.is_some();

        if !itunes_ns || !dc_ns {
            for item in &self.items {
                if !itunes_ns {
                    itunes_ns = item.itunes_ext().is_some();
                }

                if !dc_ns {
                    dc_ns = item.dublin_core_ext().is_some();
                }

                if itunes_ns && dc_ns {
                    break;
                }
            }
        }

        if itunes_ns {
            element.push_attribute(("xmlns:itunes", extension::itunes::NAMESPACE));
        }

        if dc_ns {
            element.push_attribute(("xmlns:dc", extension::dublincore::NAMESPACE));
        }
        for (name, url) in &self.namespaces {
            element.push_attribute((format!("xmlns:{}", &**name).as_bytes(), url.as_bytes()));
        }

        writer.write_event(Event::Start(element))?;

        self.to_xml(&mut writer)?;

        writer.write_event(Event::End(BytesEnd::borrowed(name)))?;

        Ok(writer.into_inner())
    }
}

impl ToString for Channel {
    fn to_string(&self) -> String {
        let buf = self.write_to(Vec::new()).unwrap_or_default();
        // this unwrap should be safe since the bytes written from the Channel are all valid utf8
        String::from_utf8(buf).unwrap()
    }
}

impl FromXml for Channel {
    fn from_xml<R: BufRead>(reader: &mut Reader<R>, _: Attributes) -> Result<Self, Error> {
        let mut channel = Channel::default();
        let mut buf = Vec::new();
        let mut skip_buf = Vec::new();

        loop {
            match reader.read_event(&mut buf)? {
                Event::Start(element) => {
                    match element.name() {
                        b"category" => {
                            let category = Category::from_xml(reader, element.attributes())?;
                            channel.categories.push(category);
                        }
                        b"cloud" => {
                            let cloud = Cloud::from_xml(reader, element.attributes())?;
                            channel.cloud = Some(cloud);
                        }
                        b"image" => {
                            let image = Image::from_xml(reader, element.attributes())?;
                            channel.image = Some(image);
                        }
                        b"textInput" => {
                            let text_input = TextInput::from_xml(reader, element.attributes())?;
                            channel.text_input = Some(text_input);
                        }
                        b"item" => {
                            let item = Item::from_xml(reader, element.attributes())?;
                            channel.items.push(item);
                        }
                        b"title" => {
                            if let Some(content) = element_text(reader)? {
                                channel.title = content;
                            }
                        }
                        b"link" => {
                            if let Some(content) = element_text(reader)? {
                                channel.link = content;
                            }
                        }
                        b"description" => {
                            if let Some(content) = element_text(reader)? {
                                channel.description = content;
                            }
                        }
                        b"language" => channel.language = element_text(reader)?,
                        b"copyright" => channel.copyright = element_text(reader)?,
                        b"managingEditor" => {
                            channel.managing_editor = element_text(reader)?;
                        }
                        b"webMaster" => channel.webmaster = element_text(reader)?,
                        b"pubDate" => channel.pub_date = element_text(reader)?,
                        b"lastBuildDate" => {
                            channel.last_build_date = element_text(reader)?;
                        }
                        b"generator" => channel.generator = element_text(reader)?,
                        b"rating" => channel.rating = element_text(reader)?,
                        b"docs" => channel.docs = element_text(reader)?,
                        b"ttl" => channel.ttl = element_text(reader)?,
                        b"skipHours" => {
                            loop {
                                skip_buf.clear();
                                match reader.read_event(&mut skip_buf)? {
                                    Event::Start(element) => {
                                        if element.name() == b"hour" {
                                            if let Some(content) = element_text(reader)? {
                                                channel.skip_hours.push(content);
                                            }
                                        } else {
                                            reader.read_to_end(element.name(), &mut Vec::new())?;
                                        }
                                    }
                                    Event::End(_) | Event::Eof => break,
                                    _ => {}
                                }
                            }
                        }
                        b"skipDays" => {
                            loop {
                                skip_buf.clear();
                                match reader.read_event(&mut skip_buf)? {
                                    Event::Start(element) => {
                                        if element.name() == b"day" {
                                            if let Some(content) = element_text(reader)? {
                                                channel.skip_days.push(content);
                                            }
                                        } else {
                                            reader.read_to_end(element.name(), &mut Vec::new())?;
                                        }
                                    }
                                    Event::End(_) | Event::Eof => break,
                                    _ => {}
                                }
                            }
                        }
                        n => {
                            if let Some((ns, name)) = extension_name(element.name()) {
                                parse_extension(
                                    reader,
                                    element.attributes(),
                                    ns,
                                    name,
                                    &mut channel.extensions,
                                )?;
                            } else {
                                reader.read_to_end(n, &mut skip_buf)?;
                            }
                        }
                    }
                }
                Event::End(_) => break,
                Event::Eof => return Err(Error::Eof),
                _ => {}
            }

            buf.clear();
        }

        if !channel.extensions.is_empty() {
            if let Some(map) = channel.extensions.remove("itunes") {
                channel.itunes_ext = Some(ITunesChannelExtension::from_map(map)?);
            }

            if let Some(map) = channel.extensions.remove("dc") {
                channel.dublin_core_ext = Some(DublinCoreExtension::from_map(map));
            }
        }

        Ok(channel)
    }
}

impl ToXml for Channel {
    fn to_xml<W: Write>(&self, writer: &mut Writer<W>) -> Result<(), XmlError> {
        let name = b"channel";

        writer
            .write_event(Event::Start(BytesStart::borrowed(name, name.len())))?;

        writer.write_text_element(b"title", &self.title)?;
        writer.write_text_element(b"link", &self.link)?;
        writer
            .write_text_element(b"description", &self.description)?;

        if let Some(language) = self.language.as_ref() {
            writer.write_text_element(b"language", language)?;
        }

        if let Some(copyright) = self.copyright.as_ref() {
            writer.write_text_element(b"copyright", copyright)?;
        }

        if let Some(managing_editor) = self.managing_editor.as_ref() {
            writer
                .write_text_element(b"managingEditor", managing_editor)?;
        }

        if let Some(webmaster) = self.webmaster.as_ref() {
            writer.write_text_element(b"webMaster", webmaster)?;
        }

        if let Some(pub_date) = self.pub_date.as_ref() {
            writer.write_text_element(b"pubDate", pub_date)?;
        }

        if let Some(last_build_date) = self.last_build_date.as_ref() {
            writer
                .write_text_element(b"lastBuildDate", last_build_date)?;
        }

        writer.write_objects(&self.categories)?;

        if let Some(generator) = self.generator.as_ref() {
            writer.write_text_element(b"generator", generator)?;
        }

        if let Some(rating) = self.rating.as_ref() {
            writer.write_text_element(b"rating", rating)?;
        }

        if let Some(docs) = self.docs.as_ref() {
            writer.write_text_element(b"docs", docs)?;
        }

        if let Some(cloud) = self.cloud.as_ref() {
            writer.write_object(cloud)?;
        }

        if let Some(ttl) = self.ttl.as_ref() {
            writer.write_text_element(b"ttl", ttl)?;
        }

        if let Some(image) = self.image.as_ref() {
            writer.write_object(image)?;
        }

        if let Some(text_input) = self.text_input.as_ref() {
            writer.write_object(text_input)?;
        }

        if !self.skip_hours.is_empty() {
            let name = b"skipHours";
            writer
                .write_event(Event::Start(BytesStart::borrowed(name, name.len())))?;
            for hour in &self.skip_hours {
                writer.write_text_element(b"hour", hour)?;
            }
            writer.write_event(Event::End(BytesEnd::borrowed(name)))?;
        }

        if !self.skip_days.is_empty() {
            let name = b"skipDays";
            writer
                .write_event(Event::Start(BytesStart::borrowed(name, name.len())))?;
            for day in &self.skip_days {
                writer.write_text_element(b"day", day)?;
            }
            writer.write_event(Event::End(BytesEnd::borrowed(name)))?;
        }

        writer.write_objects(&self.items)?;

        for map in self.extensions.values() {
            for extensions in map.values() {
                for extension in extensions {
                    extension.to_xml(writer)?;
                }
            }
        }

        if let Some(ext) = self.itunes_ext.as_ref() {
            ext.to_xml(writer)?;
        }

        if let Some(ext) = self.dublin_core_ext.as_ref() {
            ext.to_xml(writer)?;
        }

        writer.write_event(Event::End(BytesEnd::borrowed(name)))?;
        Ok(())
    }
}

impl FromStr for Channel {
    type Err = Error;

    #[inline]
    fn from_str(s: &str) -> Result<Channel, Error> {
        Channel::read_from(s.as_bytes())
    }
}