use std::fmt;

use crate::buffer::BufWriter;

use crate::ser::{self, Error, ForwardNamedToSeqProduct, Serialize, SerializeArray, SerializeMap, SerializeSeqProduct};
use crate::AlgebraicValue;

/// Defines the BSATN serialization data format.
pub struct Serializer<'a, W> {
    writer: &'a mut W,
}

impl<'a, W> Serializer<'a, W> {
    /// Returns a serializer using the given `writer`.
    pub fn new(writer: &'a mut W) -> Self {
        Self { writer }
    }

    /// Reborrows the serializer.
    #[inline]
    fn reborrow(&mut self) -> Serializer<'_, W> {
        Serializer { writer: self.writer }
    }
}

/// An error during BSATN serialization.
#[derive(Debug)]
pub struct BsatnError {
    /// The error message for the BSATN error.
    custom: String,
}

impl fmt::Display for BsatnError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(&self.custom)
    }
}
impl std::error::Error for BsatnError {}

impl Error for BsatnError {
    fn custom<T: fmt::Display>(msg: T) -> Self {
        let custom = msg.to_string();
        Self { custom }
    }
}

/// Writes `len` converted to a `u32` to `writer`.
///
/// Errors if `len` would not fit in a `u32`.
fn put_len(writer: &mut impl BufWriter, len: usize) -> Result<(), BsatnError> {
    let len = len.try_into().map_err(|_| BsatnError::custom("len too long"))?;
    writer.put_u32(len);
    Ok(())
}

impl<W: BufWriter> ser::Serializer for Serializer<'_, W> {
    type Ok = ();
    type Error = BsatnError;
    type SerializeArray = Self;
    type SerializeMap = Self;
    type SerializeSeqProduct = Self;
    type SerializeNamedProduct = ForwardNamedToSeqProduct<Self>;

    fn serialize_bool(self, v: bool) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u8(v as u8);
        Ok(())
    }
    fn serialize_u8(self, v: u8) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u8(v);
        Ok(())
    }
    fn serialize_u16(self, v: u16) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u16(v);
        Ok(())
    }
    fn serialize_u32(self, v: u32) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u32(v);
        Ok(())
    }
    fn serialize_u64(self, v: u64) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u64(v);
        Ok(())
    }
    fn serialize_u128(self, v: u128) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u128(v);
        Ok(())
    }
    fn serialize_i8(self, v: i8) -> Result<Self::Ok, Self::Error> {
        self.writer.put_i8(v);
        Ok(())
    }
    fn serialize_i16(self, v: i16) -> Result<Self::Ok, Self::Error> {
        self.writer.put_i16(v);
        Ok(())
    }
    fn serialize_i32(self, v: i32) -> Result<Self::Ok, Self::Error> {
        self.writer.put_i32(v);
        Ok(())
    }
    fn serialize_i64(self, v: i64) -> Result<Self::Ok, Self::Error> {
        self.writer.put_i64(v);
        Ok(())
    }
    fn serialize_i128(self, v: i128) -> Result<Self::Ok, Self::Error> {
        self.writer.put_i128(v);
        Ok(())
    }
    fn serialize_f32(self, v: f32) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u32(v.to_bits());
        Ok(())
    }
    fn serialize_f64(self, v: f64) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u64(v.to_bits());
        Ok(())
    }
    fn serialize_str(self, v: &str) -> Result<Self::Ok, Self::Error> {
        self.serialize_bytes(v.as_bytes())
    }
    fn serialize_bytes(self, v: &[u8]) -> Result<Self::Ok, Self::Error> {
        put_len(self.writer, v.len())?; // N.B. `v.len() > u32::MAX` isn't allowed.
        self.writer.put_slice(v);
        Ok(())
    }
    fn serialize_array(self, len: usize) -> Result<Self::SerializeArray, Self::Error> {
        put_len(self.writer, len)?; // N.B. `len > u32::MAX` isn't allowed.
        Ok(self)
    }
    fn serialize_map(self, len: usize) -> Result<Self::SerializeMap, Self::Error> {
        put_len(self.writer, len)?; // N.B. `len > u32::MAX` isn't allowed.
        Ok(self)
    }
    fn serialize_seq_product(self, _len: usize) -> Result<Self::SerializeSeqProduct, Self::Error> {
        Ok(self)
    }
    fn serialize_named_product(self, len: usize) -> Result<Self::SerializeNamedProduct, Self::Error> {
        // Serialize named like unnamed.
        self.serialize_seq_product(len).map(ForwardNamedToSeqProduct::new)
    }
    fn serialize_variant<T: super::Serialize + ?Sized>(
        self,
        tag: u8,
        _name: Option<&str>,
        value: &T,
    ) -> Result<Self::Ok, Self::Error> {
        self.writer.put_u8(tag);
        value.serialize(self)
    }

    unsafe fn serialize_bsatn(self, ty: &crate::AlgebraicType, bsatn: &[u8]) -> Result<Self::Ok, Self::Error> {
        debug_assert!(AlgebraicValue::decode(ty, &mut { bsatn }).is_ok());
        self.writer.put_slice(bsatn);
        Ok(())
    }

    unsafe fn serialize_bsatn_in_chunks<'a, I: Clone + Iterator<Item = &'a [u8]>>(
        self,
        ty: &crate::AlgebraicType,
        total_bsatn_len: usize,
        bsatn: I,
    ) -> Result<Self::Ok, Self::Error> {
        debug_assert!(total_bsatn_len <= isize::MAX as usize);
        debug_assert!(AlgebraicValue::decode(ty, &mut &*concat_bytes_slow(total_bsatn_len, bsatn.clone())).is_ok());

        for chunk in bsatn {
            self.writer.put_slice(chunk);
        }
        Ok(())
    }

    unsafe fn serialize_str_in_chunks<'a, I: Clone + Iterator<Item = &'a [u8]>>(
        self,
        total_len: usize,
        string: I,
    ) -> Result<Self::Ok, Self::Error> {
        debug_assert!(total_len <= isize::MAX as usize);
        debug_assert!(String::from_utf8(concat_bytes_slow(total_len, string.clone())).is_ok());

        // We need to len-prefix to make this BSATN.
        put_len(self.writer, total_len)?;

        for chunk in string {
            self.writer.put_slice(chunk);
        }
        Ok(())
    }
}

/// Concatenates `chunks` into a `Vec<u8>`.
fn concat_bytes_slow<'a>(cap: usize, chunks: impl Iterator<Item = &'a [u8]>) -> Vec<u8> {
    let mut bytes = Vec::with_capacity(cap);
    for chunk in chunks {
        bytes.extend(chunk);
    }
    assert_eq!(bytes.len(), cap);
    bytes
}

impl<W: BufWriter> SerializeArray for Serializer<'_, W> {
    type Ok = ();
    type Error = BsatnError;

    fn serialize_element<T: super::Serialize + ?Sized>(&mut self, elem: &T) -> Result<(), Self::Error> {
        elem.serialize(self.reborrow())
    }

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

impl<W: BufWriter> SerializeMap for Serializer<'_, W> {
    type Ok = ();
    type Error = BsatnError;

    fn serialize_entry<K: Serialize + ?Sized, V: Serialize + ?Sized>(
        &mut self,
        key: &K,
        value: &V,
    ) -> Result<(), Self::Error> {
        key.serialize(self.reborrow())?;
        value.serialize(self.reborrow())
    }

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

impl<W: BufWriter> SerializeSeqProduct for Serializer<'_, W> {
    type Ok = ();
    type Error = BsatnError;

    fn serialize_element<T: super::Serialize + ?Sized>(&mut self, elem: &T) -> Result<(), Self::Error> {
        elem.serialize(self.reborrow())
    }
    fn end(self) -> Result<Self::Ok, Self::Error> {
        Ok(())
    }
}