imap 1.0.2

use std::borrow::Borrow;
use std::collections::hash_set::Iter;
use std::collections::HashSet;
use std::hash::Hash;

/// From [section 7.2.1 of RFC 3501](https://tools.ietf.org/html/rfc3501#section-7.2.1).
///
/// A list of capabilities that the server supports.
/// The capability list will include the atom "IMAP4rev1".
///
/// In addition, all servers implement the `STARTTLS`, `LOGINDISABLED`, and `AUTH=PLAIN` (described
/// in [IMAP-TLS](https://tools.ietf.org/html/rfc2595)) capabilities. See the [Security
/// Considerations section of the RFC](https://tools.ietf.org/html/rfc3501#section-11) for
/// important information.
///
/// A capability name which begins with `AUTH=` indicates that the server supports that particular
/// authentication mechanism.
///
/// The `LOGINDISABLED` capability indicates that the `LOGIN` command is disabled, and that the
/// server will respond with a [`super::Error::No`] response to any attempt to use the `LOGIN`
/// command even if the user name and password are valid.  An IMAP client MUST NOT issue the
/// `LOGIN` command if the server advertises the `LOGINDISABLED` capability.
///
/// Other capability names indicate that the server supports an extension, revision, or amendment
/// to the IMAP4rev1 protocol. Capability names either begin with `X` or they are standard or
/// standards-track [RFC 3501](https://tools.ietf.org/html/rfc3501) extensions, revisions, or
/// amendments registered with IANA.
///
/// Client implementations SHOULD NOT require any capability name other than `IMAP4rev1`, and MUST
/// ignore any unknown capability names.
pub struct Capabilities(
    // Note that this field isn't *actually* 'static.
    // Rather, it is tied to the lifetime of the `ZeroCopy` that contains this `Name`.
    pub(crate) HashSet<&'static str>,
);

impl Capabilities {
    /// Check if the server has the given capability.
    pub fn has<S: ?Sized>(&self, s: &S) -> bool
    where
        for<'a> &'a str: Borrow<S>,
        S: Hash + Eq,
    {
        self.0.contains(s)
    }

    /// Iterate over all the server's capabilities
    pub fn iter(&self) -> Iter<&str> {
        self.0.iter()
    }

    /// Returns how many capabilities the server has.
    pub fn len(&self) -> usize {
        self.0.len()
    }

    /// Returns true if the server purports to have no capabilities.
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }
}