//! Traits for working with Preserves [embedded
//! values](https://preserves.dev/preserves.html#embeddeds).

use std::io;

use super::packed;
use super::BinarySource;
use super::BytesBinarySource;
use super::Embeddable;
use super::IOValue;
use super::NestedValue;
use super::Reader;
use super::Writer;

/// Implementations parse [IOValue]s to their own particular [Embeddable] values of type `D`.
pub trait DomainParse<D: Embeddable> {
    fn parse_embedded(&mut self, v: &IOValue) -> io::Result<D>;
}

/// Implementations read and parse from `src` to produce [Embeddable] values of type `D`.
pub trait DomainDecode<D: Embeddable> {
    fn decode_embedded<'de, 'src, S: BinarySource<'de>>(
        &mut self,
        src: &'src mut S,
        read_annotations: bool,
    ) -> io::Result<D>;
}

/// Implementations unparse and write `D`s to `w`, a [writer][crate::value::writer::Writer].
pub trait DomainEncode<D: Embeddable> {
    fn encode_embedded<W: Writer>(&mut self, w: &mut W, d: &D) -> io::Result<()>;
}

impl<'a, D: Embeddable, T: DomainParse<D>> DomainParse<D> for &'a mut T {
    fn parse_embedded(&mut self, v: &IOValue) -> io::Result<D> {
        (**self).parse_embedded(v)
    }
}

impl<'a, D: Embeddable, T: DomainDecode<D>> DomainDecode<D> for &'a mut T {
    fn decode_embedded<'de, 'src, S: BinarySource<'de>>(
        &mut self,
        src: &'src mut S,
        read_annotations: bool,
    ) -> io::Result<D> {
        (**self).decode_embedded(src, read_annotations)
    }
}

/// Convenience codec: use this as embedded codec for encoding (only) when embedded values
/// should be serialized as Preserves `String`s holding their Rust [std::fmt::Debug]
/// representation.
pub struct DebugDomainEncode;

impl<D: Embeddable> DomainEncode<D> for DebugDomainEncode {
    fn encode_embedded<W: Writer>(&mut self, w: &mut W, d: &D) -> io::Result<()> {
        d.debug_encode(w)
    }
}

/// Convenience codec: use this as embedded codec for decoding (only) when embedded values are
/// expected to conform to the syntax implicit in their [std::str::FromStr] implementation.
pub struct FromStrDomainParse;

impl<Err: Into<io::Error>, D: Embeddable + std::str::FromStr<Err = Err>> DomainParse<D>
    for FromStrDomainParse
{
    fn parse_embedded(&mut self, v: &IOValue) -> io::Result<D> {
        Ok(D::from_str(v.value().to_string()?).map_err(|e| e.into())?)
    }
}

/// Use this as embedded codec when embedded data are already [IOValue]s that can be directly
/// serialized and deserialized without further transformation.
pub struct IOValueDomainCodec;

impl DomainDecode<IOValue> for IOValueDomainCodec {
    fn decode_embedded<'de, 'src, S: BinarySource<'de>>(
        &mut self,
        src: &'src mut S,
        read_annotations: bool,
    ) -> io::Result<IOValue> {
        packed::PackedReader::new(src, IOValueDomainCodec).demand_next(read_annotations)
    }
}

impl DomainEncode<IOValue> for IOValueDomainCodec {
    fn encode_embedded<W: Writer>(&mut self, w: &mut W, d: &IOValue) -> io::Result<()> {
        w.write(self, d)
    }
}

/// Use this as embedded codec to forbid use of embedded values; an [io::Error] is signalled.
pub struct NoEmbeddedDomainCodec;

impl<D: Embeddable> DomainDecode<D> for NoEmbeddedDomainCodec {
    fn decode_embedded<'de, 'src, S: BinarySource<'de>>(
        &mut self,
        _src: &'src mut S,
        _read_annotations: bool,
    ) -> io::Result<D> {
        Err(io::Error::new(
            io::ErrorKind::Unsupported,
            "Embedded values not supported here",
        ))
    }
}

impl<D: Embeddable> DomainEncode<D> for NoEmbeddedDomainCodec {
    fn encode_embedded<W: Writer>(&mut self, _w: &mut W, _d: &D) -> io::Result<()> {
        Err(io::Error::new(
            io::ErrorKind::Unsupported,
            "Embedded values not supported here",
        ))
    }
}

/// If some `C` implements [DomainDecode] but not [DomainParse], or vice versa, use `ViaCodec`
/// to promote the one to the other. Construct instances with [ViaCodec::new].
pub struct ViaCodec<C>(C);

impl<C> ViaCodec<C> {
    /// Constructs a `ViaCodec` wrapper around an underlying codec of type `C`.
    pub fn new(c: C) -> Self {
        ViaCodec(c)
    }
}

impl<D: Embeddable, C: DomainDecode<D>> DomainParse<D> for ViaCodec<C> {
    fn parse_embedded(&mut self, v: &IOValue) -> io::Result<D> {
        let bs = packed::PackedWriter::encode_iovalue(v)?;
        self.0
            .decode_embedded(&mut BytesBinarySource::new(&bs), true)
    }
}

impl<D: Embeddable, C: DomainParse<D>> DomainDecode<D> for ViaCodec<C> {
    fn decode_embedded<'de, 'src, S: BinarySource<'de>>(
        &mut self,
        src: &'src mut S,
        read_annotations: bool,
    ) -> io::Result<D> {
        let v = src
            .packed(IOValueDomainCodec)
            .demand_next(read_annotations)?;
        self.0.parse_embedded(&v)
    }
}