upon 0.10.0

use std::collections::BTreeMap;
use std::fmt::Display;

use serde::ser::{Error as _, Impossible};

use crate::{to_value, Error, Result, Value};

#[derive(Default)]
pub struct SerializeMap {
    map: BTreeMap<String, Value>,
    next_key: Option<String>,
}

impl SerializeMap {
    pub fn new() -> Self {
        Self {
            map: BTreeMap::new(),
            next_key: None,
        }
    }
}

impl serde::ser::SerializeMap for SerializeMap {
    type Ok = Value;
    type Error = Error;

    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
    where
        T: ?Sized + serde::Serialize,
    {
        self.next_key = Some(key.serialize(MapKeySerializer)?);
        Ok(())
    }

    fn serialize_value<T>(&mut self, value: &T) -> Result<()>
    where
        T: ?Sized + serde::Serialize,
    {
        let key = self.next_key.take().unwrap();
        self.map.insert(key, to_value(value)?);
        Ok(())
    }

    fn end(self) -> Result<Self::Ok> {
        Ok(Value::Map(self.map))
    }
}

impl serde::ser::SerializeStruct for SerializeMap {
    type Ok = Value;
    type Error = Error;

    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
    where
        T: ?Sized + serde::Serialize,
    {
        serde::ser::SerializeMap::serialize_entry(self, key, value)
    }

    fn end(self) -> Result<Self::Ok> {
        serde::ser::SerializeMap::end(self)
    }
}

pub struct MapKeySerializer;

impl serde::ser::Serializer for MapKeySerializer {
    type Ok = String;
    type Error = Error;

    type SerializeSeq = Impossible<String, Error>;
    type SerializeTuple = Impossible<String, Error>;
    type SerializeTupleStruct = Impossible<String, Error>;
    type SerializeTupleVariant = Impossible<String, Error>;
    type SerializeMap = Impossible<String, Error>;
    type SerializeStruct = Impossible<String, Error>;
    type SerializeStructVariant = Impossible<String, Error>;

    fn serialize_bool(self, _v: bool) -> Result<Self::Ok> {
        Err(err_not_string())
    }

    fn serialize_i8(self, v: i8) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_i16(self, v: i16) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_i32(self, v: i32) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_i64(self, v: i64) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_u8(self, v: u8) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_u16(self, v: u16) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_u32(self, v: u32) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_u64(self, v: u64) -> Result<Self::Ok> {
        Ok(v.to_string())
    }

    fn serialize_f32(self, _v: f32) -> Result<Self::Ok> {
        Err(err_not_string())
    }

    fn serialize_f64(self, _v: f64) -> Result<Self::Ok> {
        Err(err_not_string())
    }

    fn serialize_char(self, v: char) -> Result<Self::Ok> {
        Ok(String::from(v))
    }

    fn serialize_str(self, v: &str) -> Result<Self::Ok> {
        Ok(v.to_owned())
    }

    fn serialize_bytes(self, _v: &[u8]) -> Result<Self::Ok> {
        Err(err_not_string())
    }

    fn serialize_none(self) -> Result<Self::Ok> {
        Err(err_not_string())
    }

    fn serialize_some<T>(self, _value: &T) -> Result<Self::Ok>
    where
        T: ?Sized + serde::Serialize,
    {
        Err(err_not_string())
    }

    fn serialize_unit(self) -> Result<Self::Ok> {
        Err(err_not_string())
    }

    fn serialize_unit_struct(self, _name: &'static str) -> Result<Self::Ok> {
        Err(err_not_string())
    }

    fn serialize_unit_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
    ) -> Result<Self::Ok> {
        Ok(variant.to_owned())
    }

    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<Self::Ok>
    where
        T: ?Sized + serde::Serialize,
    {
        value.serialize(self)
    }

    fn serialize_newtype_variant<T>(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        _value: &T,
    ) -> Result<Self::Ok>
    where
        T: ?Sized + serde::Serialize,
    {
        Err(err_not_string())
    }

    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
        Err(err_not_string())
    }

    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
        Err(err_not_string())
    }

    fn serialize_tuple_struct(
        self,
        _name: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeTupleStruct> {
        Err(err_not_string())
    }

    fn serialize_tuple_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeTupleVariant> {
        Err(err_not_string())
    }

    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
        Err(err_not_string())
    }

    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
        Err(err_not_string())
    }

    fn serialize_struct_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeStructVariant> {
        Err(err_not_string())
    }

    fn collect_str<T>(self, value: &T) -> Result<Self::Ok>
    where
        T: ?Sized + Display,
    {
        Ok(value.to_string())
    }
}

fn err_not_string() -> Error {
    Error::custom("map key must be a string")
}