use std::convert::Infallible;
use std::fmt;
use std::fmt::Write;

use percent_encoding::{AsciiSet, NON_ALPHANUMERIC, utf8_percent_encode};

use crate::filters::{FastWritable, HtmlSafeOutput};

// Urlencode char encoding set. Only the characters in the unreserved set don't
// have any special purpose in any part of a URI and can be safely left
// unencoded as specified in https://tools.ietf.org/html/rfc3986.html#section-2.3
const URLENCODE_STRICT_SET: &AsciiSet = &NON_ALPHANUMERIC
    .remove(b'_')
    .remove(b'.')
    .remove(b'-')
    .remove(b'~');

// Same as URLENCODE_STRICT_SET, but preserves forward slashes for encoding paths
const URLENCODE_SET: &AsciiSet = &URLENCODE_STRICT_SET.remove(b'/');

/// Percent-encodes the argument for safe use in URI; does not encode `/`.
///
/// This should be safe for all parts of URI (paths segments, query keys, query
/// values). In the rare case that the server can't deal with forward slashes in
/// the query string, use [`urlencode_strict`], which encodes them as well.
///
/// Encodes all characters except ASCII letters, digits, and `_.-~/`. In other
/// words, encodes all characters which are not in the unreserved set,
/// as specified by [RFC3986](https://tools.ietf.org/html/rfc3986#section-2.3),
/// with the exception of `/`.
///
/// ```none,ignore
/// <a href="/metro{{ "/stations/Château d'Eau"|urlencode }}">Station</a>
/// <a href="/page?text={{ "look, unicode/emojis ✨"|urlencode }}">Page</a>
/// ```
///
/// To encode `/` as well, see [`urlencode_strict`](./fn.urlencode_strict.html).
///
/// [`urlencode_strict`]: ./fn.urlencode_strict.html
///
/// ```
/// # #[cfg(feature = "code-in-doc")] {
/// # use askama::Template;
/// /// ```jinja
/// /// <div>{{ example|urlencode }}</div>
/// /// ```
/// #[derive(Template)]
/// #[template(ext = "html", in_doc = true)]
/// struct Example<'a> {
///     example: &'a str,
/// }
///
/// assert_eq!(
///     Example { example: "hello?world" }.to_string(),
///     "<div>hello%3Fworld</div>"
/// );
/// # }
/// ```
#[inline]
pub fn urlencode<T>(s: T) -> Result<HtmlSafeOutput<UrlencodeFilter<T>>, Infallible> {
    Ok(HtmlSafeOutput(UrlencodeFilter(s, URLENCODE_SET)))
}

/// Percent-encodes the argument for safe use in URI; encodes `/`.
///
/// Use this filter for encoding query keys and values in the rare case that
/// the server can't process them unencoded.
///
/// Encodes all characters except ASCII letters, digits, and `_.-~`. In other
/// words, encodes all characters which are not in the unreserved set,
/// as specified by [RFC3986](https://tools.ietf.org/html/rfc3986#section-2.3).
///
/// ```none,ignore
/// <a href="/page?text={{ "look, unicode/emojis ✨"|urlencode_strict }}">Page</a>
/// ```
///
/// If you want to preserve `/`, see [`urlencode`](./fn.urlencode.html).
///
/// ```
/// # #[cfg(feature = "code-in-doc")] {
/// # use askama::Template;
/// /// ```jinja
/// /// <a href='{{ example|urlencode_strict }}'>Example</a>
/// /// ```
/// #[derive(Template)]
/// #[template(ext = "html", in_doc = true)]
/// struct Example<'a> {
///     example: &'a str,
/// }
///
/// assert_eq!(
///     Example { example: "/hello/world" }.to_string(),
///     "<a href='%2Fhello%2Fworld'>Example</a>"
/// );
/// # }
/// ```
#[inline]
pub fn urlencode_strict<T>(s: T) -> Result<HtmlSafeOutput<UrlencodeFilter<T>>, Infallible> {
    Ok(HtmlSafeOutput(UrlencodeFilter(s, URLENCODE_STRICT_SET)))
}

pub struct UrlencodeFilter<T>(pub T, pub &'static AsciiSet);

impl<T: fmt::Display> fmt::Display for UrlencodeFilter<T> {
    #[inline]
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(UrlencodeWriter(f, self.1), "{}", self.0)
    }
}

impl<T: FastWritable> FastWritable for UrlencodeFilter<T> {
    #[inline]
    fn write_into<W: fmt::Write + ?Sized>(&self, f: &mut W) -> crate::Result<()> {
        self.0.write_into(&mut UrlencodeWriter(f, self.1))
    }
}

struct UrlencodeWriter<W>(W, &'static AsciiSet);

impl<W: fmt::Write> fmt::Write for UrlencodeWriter<W> {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        for s in utf8_percent_encode(s, self.1) {
            self.0.write_str(s)?;
        }
        Ok(())
    }
}

#[test]
#[cfg(feature = "alloc")]
fn test_urlencoding() {
    use alloc::string::ToString;

    // Unreserved (https://tools.ietf.org/html/rfc3986.html#section-2.3)
    // alpha / digit
    assert_eq!(urlencode("AZaz09").unwrap().to_string(), "AZaz09");
    assert_eq!(urlencode_strict("AZaz09").unwrap().to_string(), "AZaz09");
    // other
    assert_eq!(urlencode("_.-~").unwrap().to_string(), "_.-~");
    assert_eq!(urlencode_strict("_.-~").unwrap().to_string(), "_.-~");

    // Reserved (https://tools.ietf.org/html/rfc3986.html#section-2.2)
    // gen-delims
    assert_eq!(
        urlencode(":/?#[]@").unwrap().to_string(),
        "%3A/%3F%23%5B%5D%40"
    );
    assert_eq!(
        urlencode_strict(":/?#[]@").unwrap().to_string(),
        "%3A%2F%3F%23%5B%5D%40"
    );
    // sub-delims
    assert_eq!(
        urlencode("!$&'()*+,;=").unwrap().to_string(),
        "%21%24%26%27%28%29%2A%2B%2C%3B%3D"
    );
    assert_eq!(
        urlencode_strict("!$&'()*+,;=").unwrap().to_string(),
        "%21%24%26%27%28%29%2A%2B%2C%3B%3D"
    );

    // Other
    assert_eq!(
        urlencode("žŠďŤňĚáÉóŮ").unwrap().to_string(),
        "%C5%BE%C5%A0%C4%8F%C5%A4%C5%88%C4%9A%C3%A1%C3%89%C3%B3%C5%AE"
    );
    assert_eq!(
        urlencode_strict("žŠďŤňĚáÉóŮ").unwrap().to_string(),
        "%C5%BE%C5%A0%C4%8F%C5%A4%C5%88%C4%9A%C3%A1%C3%89%C3%B3%C5%AE"
    );

    // Ferris
    assert_eq!(urlencode("🦀").unwrap().to_string(), "%F0%9F%A6%80");
    assert_eq!(urlencode_strict("🦀").unwrap().to_string(), "%F0%9F%A6%80");
}