use serde::{
    de::{self, DeserializeSeed, Deserializer, EnumAccess, SeqAccess, VariantAccess, Visitor},
    forward_to_deserialize_any,
    ser::{self, Impossible, Serialize, SerializeSeq, SerializeTupleVariant, Serializer},
};
use std::fmt;

/// A wrapper for serializing and deserializing enums in the way Yojson expects. Based off of
/// [this](https://github.com/serde-rs/serde/issues/979#issuecomment-350340431).
pub struct EnumAsArray<T>(pub T);

fn expected_enum<T, E>() -> Result<T, E>
where
    E: ser::Error,
{
    Err(ser::Error::custom(
        "EnumAsArray expected to operate on an enum type",
    ))
}

impl<S> Serializer for EnumAsArray<S>
where
    S: Serializer,
{
    type Ok = S::Ok;
    type Error = S::Error;

    type SerializeSeq = Impossible<Self::Ok, Self::Error>;
    type SerializeTuple = Impossible<Self::Ok, Self::Error>;
    type SerializeTupleStruct = Impossible<Self::Ok, Self::Error>;
    type SerializeTupleVariant = EnumAsArray<S::SerializeSeq>;
    type SerializeMap = Impossible<Self::Ok, Self::Error>;
    type SerializeStruct = Impossible<Self::Ok, Self::Error>;
    type SerializeStructVariant = Impossible<Self::Ok, Self::Error>;

    fn serialize_bool(self, _v: bool) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_i8(self, _v: i8) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_i16(self, _v: i16) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_i32(self, _v: i32) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_i64(self, _v: i64) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_u8(self, _v: u8) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_u16(self, _v: u16) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_u32(self, _v: u32) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_u64(self, _v: u64) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_f32(self, _v: f32) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_f64(self, _v: f64) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_char(self, _v: char) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_str(self, _v: &str) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_bytes(self, _v: &[u8]) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_none(self) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_some<T: ?Sized + Serialize>(self, _value: &T) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_unit_struct(self, _name: &'static str) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_unit_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
    ) -> Result<Self::Ok, Self::Error> {
        let mut seq = self.0.serialize_seq(Some(1))?;
        seq.serialize_element(variant)?;
        seq.end()
    }
    fn serialize_newtype_struct<T: ?Sized + Serialize>(
        self,
        _name: &'static str,
        _value: &T,
    ) -> Result<Self::Ok, Self::Error> {
        expected_enum()
    }
    fn serialize_newtype_variant<T: ?Sized + Serialize>(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
        value: &T,
    ) -> Result<Self::Ok, Self::Error> {
        let mut seq = self.0.serialize_seq(Some(2))?;
        seq.serialize_element(variant)?;
        seq.serialize_element(value)?;
        seq.end()
    }
    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
        expected_enum()
    }
    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Self::Error> {
        expected_enum()
    }
    fn serialize_tuple_struct(
        self,
        _name: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
        expected_enum()
    }
    fn serialize_tuple_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
        len: usize,
    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
        let mut seq = self.0.serialize_seq(Some(1 + len))?;
        seq.serialize_element(variant)?;
        Ok(EnumAsArray(seq))
    }
    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
        expected_enum()
    }
    fn serialize_struct(
        self,
        _name: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeStruct, Self::Error> {
        expected_enum()
    }
    fn serialize_struct_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeStructVariant, Self::Error> {
        Err(ser::Error::custom(
            "enum_as_array::serialize does not support struct variants",
        ))
    }
}

impl<S> SerializeTupleVariant for EnumAsArray<S>
where
    S: SerializeSeq,
{
    type Ok = S::Ok;
    type Error = S::Error;

    fn serialize_field<T: ?Sized + Serialize>(&mut self, value: &T) -> Result<(), Self::Error> {
        self.0.serialize_element(value)
    }
    fn end(self) -> Result<Self::Ok, Self::Error> {
        self.0.end()
    }
}

impl<'de, D> Deserializer<'de> for EnumAsArray<D>
where
    D: Deserializer<'de>,
{
    type Error = D::Error;

    fn deserialize_any<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        Err(de::Error::custom(
            "EnumAsArray expected to operate on an enum type",
        ))
    }

    fn deserialize_enum<V>(
        self,
        _name: &'static str,
        _variants: &'static [&'static str],
        visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        self.0.deserialize_seq(EnumAsArray(visitor))
    }

    forward_to_deserialize_any! {
        bool i8 i16 i32 i64 u8 u16 u32 u64 f32 f64 char str string bytes
        byte_buf option unit unit_struct newtype_struct seq tuple
        tuple_struct map struct identifier ignored_any
    }
}

impl<'de, V> Visitor<'de> for EnumAsArray<V>
where
    V: Visitor<'de>,
{
    type Value = V::Value;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        self.0.expecting(formatter)
    }

    fn visit_seq<A>(self, seq: A) -> Result<Self::Value, A::Error>
    where
        A: SeqAccess<'de>,
    {
        self.0.visit_enum(EnumAsArray(seq))
    }
}

impl<'de, A> EnumAccess<'de> for EnumAsArray<A>
where
    A: SeqAccess<'de>,
{
    type Error = A::Error;
    type Variant = Self;

    fn variant_seed<V>(mut self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
    where
        V: DeserializeSeed<'de>,
    {
        match self.0.next_element_seed(seed)? {
            Some(first) => Ok((first, self)),
            None => Err(de::Error::custom("expected at least one element")),
        }
    }
}

impl<'de, A> VariantAccess<'de> for EnumAsArray<A>
where
    A: SeqAccess<'de>,
{
    type Error = A::Error;

    fn unit_variant(self) -> Result<(), Self::Error> {
        Ok(())
    }

    fn newtype_variant_seed<T>(mut self, seed: T) -> Result<T::Value, Self::Error>
    where
        T: DeserializeSeed<'de>,
    {
        match self.0.next_element_seed(seed)? {
            Some(newtype) => Ok(newtype),
            None => Err(de::Error::custom("missing newtype variant value")),
        }
    }

    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        visitor.visit_seq(self.0)
    }

    fn struct_variant<V>(
        self,
        _fields: &'static [&'static str],
        _visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        Err(de::Error::custom(
            "EnumAsArray does not support struct variants",
        ))
    }
}