twitter-stream-message 0.3.0

use std::borrow::Cow;
use std::fmt;

use serde::de::{
    Deserialize,
    Deserializer,
    Error,
    IgnoredAny,
    MapAccess,
    Visitor,
};

use user::UserId;

#[derive(Clone, Debug, Eq, PartialEq, Hash)]
pub struct Warning<'a> {
    pub message: Cow<'a, str>,
    pub code: WarningCode<'a>,
}

#[derive(Clone, Debug, Eq, PartialEq, Hash)]
pub enum WarningCode<'a> {
    FallingBehind(u64),
    FollowsOverLimit(UserId),
    Custom(Cow<'a, str>),
}

impl<'de: 'a, 'a> Deserialize<'de> for Warning<'a> {
    fn deserialize<D: Deserializer<'de>>(d: D) -> Result<Self, D::Error> {
        d.deserialize_map(WarningVisitor)
    }
}

struct WarningVisitor;

impl<'a> Visitor<'a> for WarningVisitor {
    type Value = Warning<'a>;

    fn visit_map<A: MapAccess<'a>>(self, mut a: A)
        -> Result<Warning<'a>, A::Error>
    {
        use util::CowStr;

        string_enums! {
            pub enum Code<'a> {
                FallingBehind("FALLING_BEHIND"),
                FollowsOverLimit("FOLLOWS_OVER_LIMIT");
                Custom(_),
            }
        }

        let mut code = None;
        let mut message: Option<CowStr> = None;
        let mut percent_full: Option<u64> = None;
        let mut user_id: Option<UserId> = None;

        while let Some(k) = a.next_key::<CowStr>()? {
            match &*k {
                "code" => code = Some(a.next_value::<Code>()?),
                "message" => message = Some(a.next_value()?),
                "percent_full" => percent_full = Some(a.next_value()?),
                "user_id" => user_id = Some(a.next_value()?),
                _ => { a.next_value::<IgnoredAny>()?; },
            }

            macro_rules! end {
                () => {{
                    while a.next_entry::<IgnoredAny,IgnoredAny>()?.is_some() {}
                }};
            }

            match (code.as_ref(), message.as_ref(), percent_full, user_id) {
                (Some(&Code::FallingBehind), Some(_), Some(percent_full), _) =>
                {
                    end!();
                    return Ok(Warning {
                        message: message.unwrap().0,
                        code: WarningCode::FallingBehind(percent_full),
                    });
                },
                (Some(&Code::FollowsOverLimit), Some(_), _, Some(user_id)) => {
                    end!();
                    return Ok(Warning {
                        message: message.unwrap().0,
                        code: WarningCode::FollowsOverLimit(user_id),
                    });
                },
                (Some(&Code::Custom(_)), Some(_), _, _) => {
                    end!();
                    if let Some(Code::Custom(code)) = code {
                        return Ok(Warning {
                            message: message.unwrap().0,
                            code: WarningCode::Custom(code),
                        });
                    } else {
                        unreachable!();
                    }
                },
                _ => (),
            }
        }

        if code.is_none() {
            Err(A::Error::missing_field("code"))
        } else if message.is_none() {
            Err(A::Error::missing_field("message"))
        } else if code == Some(Code::FallingBehind) {
            Err(A::Error::missing_field("percent_full"))
        } else {
            Err(A::Error::missing_field("user_id"))
        }
    }

    fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "a map")
    }
}