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use std::fmt;
use std::marker::PhantomData;
use serde::ser::{Serialize, Serializer, SerializeSeq};
use serde::de::{Deserialize, Deserializer, Visitor, SeqAccess};

use super::{ManyToMany, ERROR};

impl<L, R> Serialize for ManyToMany<L, R>
where
    L: std::hash::Hash + Eq + Clone + Serialize,
    R: std::hash::Hash + Eq + Clone + Serialize
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let keys = self.get_left_keys();
        let mut seq = serializer.serialize_seq(None)?;
        
        for left in keys {
            let values = self.get_left(left).expect(ERROR);
            for value in values {
                seq.serialize_element(&(left, value))?;
            }
        }

        seq.end()
    }
}

struct ManyToManyVisitor<L: std::hash::Hash + Eq + Clone, R: std::hash::Hash + Eq + Clone> {
    marker: PhantomData<fn() -> ManyToMany<L, R>>
}

impl<L: std::hash::Hash + Eq + Clone, R: std::hash::Hash + Eq + Clone> ManyToManyVisitor<L, R> {
    fn new() -> Self {
        ManyToManyVisitor {
            marker: PhantomData
        }
    }
}

impl<'de, L, R> Visitor<'de> for ManyToManyVisitor<L, R>
where
    L: std::hash::Hash + Eq + Clone + Deserialize<'de>,
    R: std::hash::Hash + Eq + Clone + Deserialize<'de>
{
    type Value = ManyToMany<L, R>;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        formatter.write_str("many-to-many map")
    }

    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
    where
            A: SeqAccess<'de>, {
        let mut map = ManyToMany::new();

        while let Some((left, right)) = seq.next_element()? as Option<(L, R)> {
            map.insert(left, right);
        }

        Ok(map)
    }
}

impl<'de, L, R> Deserialize<'de> for ManyToMany<L, R>
where
    L: std::hash::Hash + Eq + Clone + Deserialize<'de>,
    R: std::hash::Hash + Eq + Clone + Deserialize<'de>
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        deserializer.deserialize_seq(ManyToManyVisitor::new())
    }
}