use std::collections::{hash_map, HashMap};

use serde::de::{
    self, DeserializeSeed, EnumAccess, Error as DeError, MapAccess, SeqAccess, VariantAccess,
    Visitor,
};
use serde::Deserialize;

use crate::debug as fmtdebug;
use crate::dec::*;
use crate::serde::error::{Error, Result};

/// Serde deserializer for nettext
pub struct Deserializer<'de, 'a>(Term<'de, 'a>);

impl<'de, 'a> Deserializer<'de, 'a> {
    pub fn from_term(input: &'a Term<'de, 'a>) -> Deserializer<'de, 'a> {
        Deserializer(Term(input.0.mkref()))
    }
}

/// Deserialize nettext from bytes
pub fn from_bytes<'a, T>(s: &'a [u8]) -> Result<T>
where
    T: Deserialize<'a>,
{
    let term = decode(s)?;
    let mut deserializer = Deserializer::from_term(&term);
    T::deserialize(&mut deserializer)
}

/// Deserialize nettext from decoded term
pub fn from_term<'a, T>(term: &'a Term<'a, 'a>) -> Result<T>
where
    T: Deserialize<'a>,
{
    let mut deserializer = Deserializer::from_term(term);
    T::deserialize(&mut deserializer)
}

// ----

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

    fn deserialize_any<V>(self, _visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        Err(Error::custom(format!(
            "deserialize_any not supported, at: `{}`",
            self.0
        )))
    }

    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let value = match self.0.string()? {
            "true" => true,
            "false" => false,
            _ => return Err(Error::custom("Invalid boolean litteral")),
        };
        visitor.visit_bool(value)
    }

    fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_i8(self.0.string()?.parse()?)
    }

    fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_i16(self.0.string()?.parse()?)
    }

    fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_i32(self.0.string()?.parse()?)
    }

    fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_i64(self.0.string()?.parse()?)
    }

    fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_u8(self.0.string()?.parse()?)
    }

    fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_u16(self.0.string()?.parse()?)
    }

    fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_u32(self.0.string()?.parse()?)
    }

    fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_u64(self.0.string()?.parse()?)
    }

    fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_f32(self.0.string()?.parse()?)
    }

    fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_f64(self.0.string()?.parse()?)
    }

    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let s = String::from_utf8(self.0.bytes()?)?;
        let mut chars = s.chars();
        let c = chars
            .next()
            .ok_or_else(|| Error::custom("invalid char: empty string"))?;
        if chars.next().is_some() {
            Err(Error::custom("invalid char: too many chars"))
        } else {
            visitor.visit_char(c)
        }
    }

    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let s = String::from_utf8(self.0.bytes()?)?;
        visitor.visit_string(s)
    }

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

    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_byte_buf(self.0.bytes()?)
    }

    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_byte_buf(self.0.bytes()?)
    }

    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        if self.0.dict_of::<0, &[u8]>([], false).is_ok() {
            visitor.visit_none()
        } else {
            visitor.visit_some(self)
        }
    }

    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        if self.0.dict_of::<0, &[u8]>([], false).is_ok() {
            visitor.visit_unit()
        } else {
            Err(Error::custom(format!(
                "Expected unit, got: `{}`",
                fmtdebug(self.0.raw())
            )))
        }
    }

    fn deserialize_unit_struct<V>(self, name: &'static str, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        if self.0.string()? == name {
            visitor.visit_unit()
        } else {
            Err(Error::custom(format!(
                "Expected {}, got: `{}`",
                name,
                fmtdebug(self.0.raw())
            )))
        }
    }

    fn deserialize_newtype_struct<V>(self, name: &'static str, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let [variant, args] = self.0.seq_of_first()?;
        if variant.string()? == name {
            visitor.visit_newtype_struct(&mut Deserializer(args))
        } else {
            Err(Error::custom(format!(
                "Expected {}, got: `{}`",
                name,
                fmtdebug(variant.raw())
            )))
        }
    }

    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_seq(&mut Seq(&self.0.list()?))
    }

    fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_seq(&mut Seq(&self.0.seq()))
    }

    fn deserialize_tuple_struct<V>(
        self,
        name: &'static str,
        _len: usize,
        visitor: V,
    ) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let [variant, args] = self.0.seq_of_first()?;
        if variant.string()? == name {
            visitor.visit_seq(&mut Seq(&args.seq()))
        } else {
            Err(Error::custom(format!(
                "Expected {}, got: `{}`",
                name,
                fmtdebug(variant.raw())
            )))
        }
    }

    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        visitor.visit_map(&mut Dict::from_term(&self.0)?)
    }

    fn deserialize_struct<V>(
        self,
        name: &'static str,
        _fields: &'static [&'static str],
        visitor: V,
    ) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let [variant, data] = self.0.seq_of()?;
        if variant.string()? != name {
            return Err(Error::custom(format!(
                "Expected {}, got: `{}`",
                name,
                fmtdebug(variant.raw())
            )));
        }

        Deserializer(data).deserialize_map(visitor)
    }

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

    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let s = self.0.string()?;
        match s.split_once('.') {
            Some((_a, b)) => visitor.visit_borrowed_str(b),
            None => visitor.visit_borrowed_str(s),
        }
    }

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

pub struct Seq<'de, 'a>(&'a [Term<'de, 'a>]);

impl<'de, 'a> SeqAccess<'de> for &'a mut Seq<'de, 'a> {
    type Error = Error;

    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>>
    where
        T: DeserializeSeed<'de>,
    {
        // Check if there are no more elements.
        if self.0.is_empty() {
            return Ok(None);
        }
        let first = Term(self.0[0].0.mkref());
        self.0 = &self.0[1..];

        seed.deserialize(&mut Deserializer::from_term(&first))
            .map(Some)
    }
}

pub struct Dict<'de, 'a>(
    &'a HashMap<&'de [u8], AnyTerm<'de, 'a>>,
    Option<&'de [u8]>,
    hash_map::Keys<'a, &'de [u8], AnyTerm<'de, 'a>>,
);

impl<'de, 'a> Dict<'de, 'a> {
    fn from_term(t: &'a Term<'de, 'a>) -> Result<Dict<'de, 'a>> {
        match t.0.mkref() {
            AnyTerm::DictRef(_, d) => Ok(Dict(d, None, d.keys())),
            _ => Err(Error::custom("expected a DICT")),
        }
    }
}

impl<'de, 'a> MapAccess<'de> for &'a mut Dict<'de, 'a> {
    type Error = Error;

    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>>
    where
        K: DeserializeSeed<'de>,
    {
        match self.2.next() {
            None => Ok(None),
            Some(k) => {
                self.1 = Some(k);
                seed.deserialize(&mut Deserializer(Term(AnyTerm::Str(k))))
                    .map(Some)
            }
        }
    }

    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value>
    where
        V: DeserializeSeed<'de>,
    {
        let k = self
            .1
            .ok_or_else(|| Error::custom("invald mapaccess order"))?;
        let v = self
            .0
            .get(k)
            .ok_or_else(|| Error::custom("invald mapaccess order"))?;
        seed.deserialize(&mut Deserializer(Term(v.mkref())))
    }
}

// ----

struct Enum<'de, 'a>(&'a Term<'de, 'a>);

impl<'de, 'a> EnumAccess<'de> for Enum<'de, 'a> {
    type Error = Error;
    type Variant = Self;

    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant)>
    where
        V: DeserializeSeed<'de>,
    {
        let variant = &self.0.seq()[0];
        let variant = seed.deserialize(&mut Deserializer(Term(variant.0.mkref())))?;
        Ok((variant, self))
    }
}

impl<'de, 'a> VariantAccess<'de> for Enum<'de, 'a> {
    type Error = Error;

    fn unit_variant(self) -> Result<()> {
        if self.0.seq().len() > 1 {
            Err(Error::custom("Spurrious data in unit variant"))
        } else {
            Ok(())
        }
    }

    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value>
    where
        T: DeserializeSeed<'de>,
    {
        let [_, rest] = self.0.seq_of_first()?;
        seed.deserialize(&mut Deserializer(rest))
    }

    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let [_, rest] = self.0.seq_of_first()?;
        visitor.visit_seq(&mut Seq(&rest.seq()))
    }

    fn struct_variant<V>(self, _fields: &'static [&'static str], visitor: V) -> Result<V::Value>
    where
        V: Visitor<'de>,
    {
        let [_, rest] = self.0.seq_of_first()?;
        visitor.visit_map(&mut Dict::from_term(&rest)?)
    }
}