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extern crate serde;

use self::serde::{ser, Serialize, Serializer};

#[derive(Debug)]
pub struct Union<T0, T1>(pub Option<T0>, pub Option<T1>);

impl<T0, T1> Union<T0, T1> {
    pub fn for0(value: T0) -> Self {
        Union(Some(value), None)
    }

    pub fn for1(value: T1) -> Self {
        Union(None, Some(value))
    }
}

impl<T0, T1> Serialize for Union<T0, T1>
where
    T0: Serialize,
    T1: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        if let Some(value) = &self.0 {
            serializer.serialize_some::<T0>(value)
        } else if let Some(value) = &self.1 {
            serializer.serialize_some::<T1>(value)
        } else {
            Err(ser::Error::custom("invalid union"))
        }
    }
}

#[derive(Debug)]
pub struct Union3<T0, T1, T2>(pub Option<T0>, pub Option<T1>, pub Option<T2>);

impl<T0, T1, T2> Union3<T0, T1, T2> {
    pub fn for0(value: T0) -> Self {
        Union3(Some(value), None, None)
    }

    pub fn for1(value: T1) -> Self {
        Union3(None, Some(value), None)
    }

    pub fn for2(value: T2) -> Self {
        Union3(None, None, Some(value))
    }
}

impl<T0, T1, T2> Serialize for Union3<T0, T1, T2>
where
    T0: Serialize,
    T1: Serialize,
    T2: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        if let Some(value) = &self.0 {
            serializer.serialize_some::<T0>(value)
        } else if let Some(value) = &self.1 {
            serializer.serialize_some::<T1>(value)
        } else if let Some(value) = &self.2 {
            serializer.serialize_some::<T2>(value)
        } else {
            Err(ser::Error::custom("invalid union"))
        }
    }
}