use serde::de::{self, Visitor};

use crate::de::{Deserializer, Error};

pub struct MapAccess<'a, 'b> {
    de: &'a mut Deserializer<'b>,
    first: bool,
}

impl<'a, 'b> MapAccess<'a, 'b> {
    pub(crate) fn new(de: &'a mut Deserializer<'b>) -> Self {
        MapAccess { de, first: true }
    }
}

impl<'a, 'de> de::MapAccess<'de> for MapAccess<'a, 'de> {
    type Error = Error;

    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
    where
        K: de::DeserializeSeed<'de>,
    {
        let peek = match self
            .de
            .parse_whitespace()
            .ok_or(Error::EofWhileParsingObject)?
        {
            b'}' => return Ok(None),
            b',' if !self.first => {
                self.de.eat_char();
                self.de.parse_whitespace()
            }
            b => {
                if self.first {
                    self.first = false;
                    Some(b)
                } else {
                    return Err(Error::ExpectedObjectCommaOrEnd);
                }
            }
        };

        match peek.ok_or(Error::EofWhileParsingValue)? {
            b'"' => seed.deserialize(MapKey { de: &mut *self.de }).map(Some),
            b'}' => Err(Error::TrailingComma),
            _ => Err(Error::KeyMustBeAString),
        }
    }

    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
    where
        V: de::DeserializeSeed<'de>,
    {
        self.de.parse_object_colon()?;

        seed.deserialize(&mut *self.de)
    }
}

struct MapKey<'a, 'b> {
    de: &'a mut Deserializer<'b>,
}

impl<'de, 'a> de::Deserializer<'de> for MapKey<'a, 'de> {
    type Error = Error;

    fn deserialize_any<V>(self, _visitor: V) -> Result<V::Value, Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_bool<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_i8<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_i16<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_i32<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_i64<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_u8<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_u16<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_u32<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_u64<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_f32<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_f64<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_char<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        self.de.deserialize_str(visitor)
    }

    fn deserialize_string<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_bytes<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_byte_buf<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_option<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_unit<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_unit_struct<V>(
        self,
        _name: &'static str,
        _visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_newtype_struct<V>(
        self,
        _name: &'static str,
        _visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_seq<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_tuple<V>(self, _len: usize, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_tuple_struct<V>(
        self,
        _name: &'static str,
        _len: usize,
        _visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_map<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_struct<V>(
        self,
        _name: &'static str,
        _fields: &'static [&'static str],
        _visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_enum<V>(
        self,
        _name: &'static str,
        _variants: &'static [&'static str],
        _visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        unreachable!()
    }

    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        self.deserialize_str(visitor)
    }

    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        // Even if we’re ignoring the contents of the map, we still need to
        // deserialize the string here in order to chomp the key’s characters.
        self.deserialize_str(visitor)
    }
}