//! Module containing the DICOM Transfer Syntax data structure and related methods.
//! Similar to the DcmCodec in DCMTK, the `TransferSyntax` contains all of the necessary
//! algorithms for decoding and encoding DICOM data in a certain transfer syntax.
//!
//! This crate does not host specific transfer syntaxes. Instead, they are created in
//! other crates and registered in the global transfer syntax registry, which implements
//! [`TransferSyntaxIndex`]. For more
//! information, please see the `dicom-transfer-syntax-registry` crate.
//!
//! [`TransferSyntaxIndex`]: ./trait.TransferSyntaxIndex.html

/// Explicit VR Big Endian implementation
#[deprecated(
    since = "0.3.0",
    note = "See `decode::explicit_be` or `encode::explicit_be` instead"
)]
pub mod explicit_be;
/// Explicit VR Little Endian implementation
#[deprecated(
    since = "0.3.0",
    note = "See `decode::explicit_le` or `encode::explicit_le` instead"
)]
pub mod explicit_le;
/// Implicit VR Little Endian implementation
#[deprecated(
    since = "0.3.0",
    note = "See `decode::implicit_le` or `encode::implicit_le` instead"
)]
pub mod implicit_le;

use crate::decode::basic::BasicDecoder;
use crate::decode::DecodeFrom;
use crate::encode::{EncodeTo, EncoderFor};
use std::io::{Read, Write};

pub use byteordered::Endianness;

/// A decoder with its type erased.
pub type DynDecoder<S> = Box<dyn DecodeFrom<S>>;

/// An encoder with its type erased.
pub type DynEncoder<'w, W> = Box<dyn EncodeTo<W> + 'w>;

/// A DICOM transfer syntax specifier. The data RW adapter `A` specifies
/// custom codec capabilities when required.
#[derive(Debug)]
pub struct TransferSyntax<A = DynDataRWAdapter> {
    /// The unique identifier of the transfer syntax.
    uid: &'static str,
    /// The name of the transfer syntax.
    name: &'static str,
    /// The byte order of data.
    byte_order: Endianness,
    /// Whether the transfer syntax mandates an explicit value representation,
    /// or the VR is implicit.
    explicit_vr: bool,
    /// The transfer syntax' requirements and implemented capabilities.
    codec: Codec<A>,
}

#[cfg(feature = "inventory-registry")]
// Collect transfer syntax specifiers from other crates.
inventory::collect!(TransferSyntax);

/// Trait for containers of transfer syntax specifiers.
///
/// Types implementing this trait are held responsible for populating
/// themselves with a set of transfer syntaxes, which can be fully supported,
/// partially supported, or not supported. Usually, only one implementation
/// of this trait is used for the entire program.
pub trait TransferSyntaxIndex {
    /// Obtain a DICOM transfer syntax by its respective UID.
    ///
    /// Implementations of this method should be robust to the possible
    /// presence of a trailing null characters (`\0`) in `uid`.
    fn get(&self, uid: &str) -> Option<&TransferSyntax>;
}

impl<T: ?Sized> TransferSyntaxIndex for &T
where
    T: TransferSyntaxIndex,
{
    fn get(&self, uid: &str) -> Option<&TransferSyntax> {
        (**self).get(uid)
    }
}

#[cfg(feature = "inventory-registry")]
#[macro_export]
/// Submit a transfer syntax specifier to be supported by the
/// program's runtime. This is to be used by crates wishing to provide
/// additional support for a certain transfer syntax using the
/// main transfer syntax registry.
///
/// This macro does actually "run" anything, so place it outside of a
/// function body at the root of the crate.
macro_rules! submit_transfer_syntax {
    ($ts: expr) => {
        inventory::submit! {
            ($ts).erased()
        }
    };
}

#[cfg(not(feature = "inventory-registry"))]
#[macro_export]
/// Submit a transfer syntax specifier to be supported by the
/// program's runtime. This is to be used by crates wishing to provide
/// additional support for a certain transfer syntax using the
/// main transfer syntax registry.
///
/// This macro does actually "run" anything, so place it outside of a
/// function body at the root of the crate.
///
/// Without the `inventory-registry` feature, this request is ignored.
macro_rules! submit_transfer_syntax {
    ($ts: expr) => {
        // ignore request
    };
}

/// A description and possible implementation regarding
/// the encoding and decoding requirements of a transfer syntax.
/// This is also used as a means to describe whether pixel data is encapsulated
/// and whether this implementation supports it.
#[derive(Debug, Clone, PartialEq)]
pub enum Codec<A> {
    /// No codec is given, nor is it required.
    None,
    /// Custom encoding and decoding of the entire data set is required, but
    /// not supported. This could be used by a stub of
    /// _Deflated Explicit VR Little Endian_, for example.
    Unsupported,
    /// Custom encoding and decoding of the pixel data set is required, but
    /// not supported. The program should still be able to parse DICOM
    /// data sets and fetch the pixel data in its encapsulated form.
    EncapsulatedPixelData,
    /// A pixel data encapsulation codec is required and provided for reading
    /// and writing pixel data.
    PixelData(A),
    /// A full, custom data set codec is required and provided.
    Dataset(A),
}

/// An alias for a transfer syntax specifier with no pixel data encapsulation
/// nor data set deflating.
pub type AdapterFreeTransferSyntax = TransferSyntax<NeverAdapter>;

/// An adapter of byte read and write streams.
pub trait DataRWAdapter<R, W> {
    /// The type of the adapted reader.
    type Reader: Read;
    /// The type of the adapted writer.
    type Writer: Write;

    /// Adapt a byte reader.
    fn adapt_reader(&self, reader: R) -> Self::Reader
    where
        R: Read;

    /// Adapt a byte writer.
    fn adapt_writer(&self, writer: W) -> Self::Writer
    where
        W: Write;
}

/// Alias type for a dynamically dispatched data adapter.
pub type DynDataRWAdapter = Box<
    dyn DataRWAdapter<
            Box<dyn Read>,
            Box<dyn Write>,
            Reader = Box<dyn Read>,
            Writer = Box<dyn Write>,
        > + Send
        + Sync,
>;

impl<'a, T, R, W> DataRWAdapter<R, W> for &'a T
where
    T: DataRWAdapter<R, W>,
    R: Read,
    W: Write,
{
    type Reader = <T as DataRWAdapter<R, W>>::Reader;
    type Writer = <T as DataRWAdapter<R, W>>::Writer;

    /// Adapt a byte reader.
    fn adapt_reader(&self, reader: R) -> Self::Reader
    where
        R: Read,
    {
        (**self).adapt_reader(reader)
    }

    /// Adapt a byte writer.
    fn adapt_writer(&self, writer: W) -> Self::Writer
    where
        W: Write,
    {
        (**self).adapt_writer(writer)
    }
}

/** An immaterial type representing an adapted which is never required,
 * and as such is never instantiated. Most transfer syntaxes use this,
 * as they do not have to adapt readers and writers for encoding and decoding.
 */
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub enum NeverAdapter {}

impl<R, W> DataRWAdapter<R, W> for NeverAdapter {
    type Reader = Box<dyn Read>;
    type Writer = Box<dyn Write>;

    fn adapt_reader(&self, _reader: R) -> Self::Reader
    where
        R: Read,
    {
        unreachable!()
    }

    fn adapt_writer(&self, _writer: W) -> Self::Writer
    where
        W: Write,
    {
        unreachable!()
    }
}

impl<A> TransferSyntax<A> {
    /** Create a new transfer syntax descriptor.
     *
     * Note that only transfer syntax implementors are expected to construct
     * TS descriptors from scratch. For a practical usage of transfer syntaxes,
     * one should look up an existing transfer syntax registry by UID.
     */
    pub const fn new(
        uid: &'static str,
        name: &'static str,
        byte_order: Endianness,
        explicit_vr: bool,
        codec: Codec<A>,
    ) -> Self {
        TransferSyntax {
            uid,
            name,
            byte_order,
            explicit_vr,
            codec,
        }
    }

    /// Obtain this transfer syntax' unique identifier.
    pub const fn uid(&self) -> &'static str {
        self.uid
    }

    /// Obtain the name of this transfer syntax.
    pub const fn name(&self) -> &'static str {
        self.name
    }

    /// Obtain this transfer syntax' expected endianness.
    pub const fn endianness(&self) -> Endianness {
        self.byte_order
    }

    /// Obtain this transfer syntax' codec specification.
    pub fn codec(&self) -> &Codec<A> {
        &self.codec
    }

    /// Check whether this transfer syntax specifier provides a complete
    /// implementation.
    pub fn fully_supported(&self) -> bool {
        matches!(
            self.codec,
            Codec::None | Codec::Dataset(_) | Codec::PixelData(_),
        )
    }

    /// Check whether no codecs are required for this transfer syntax,
    /// meaning that a complete implementation is available
    /// and no pixel data conversion is required.
    pub fn is_codec_free(&self) -> bool {
        matches!(self.codec, Codec::None)
    }

    /// Check whether reading and writing of data sets is unsupported.
    /// If this is `true`, encoding and decoding will not be available.
    pub fn unsupported(&self) -> bool {
        matches!(self.codec, Codec::Unsupported)
    }

    /// Check whether reading and writing the pixel data is unsupported.
    /// If this is `true`, encoding and decoding of the data set will still
    /// be possible, but the pixel data will only be available in its
    /// encapsulated form.
    pub fn unsupported_pixel_encapsulation(&self) -> bool {
        matches!(
            self.codec,
            Codec::Unsupported | Codec::EncapsulatedPixelData
        )
    }

    /// Retrieve the appropriate data element decoder for this transfer syntax.
    /// Can yield none if decoding is not supported.
    ///
    /// The resulting decoder does not consider pixel data encapsulation or
    /// data set compression rules. This means that the consumer of this method
    /// needs to adapt the reader before using the decoder.
    pub fn decoder<'s>(&self) -> Option<DynDecoder<dyn Read + 's>> {
        self.decoder_for()
    }

    /// Retrieve the appropriate data element decoder for this transfer syntax
    /// and given reader type (this method is not object safe).
    /// Can yield none if decoding is not supported.
    ///
    /// The resulting decoder does not consider pixel data encapsulation or
    /// data set compression rules. This means that the consumer of this method
    /// needs to adapt the reader before using the decoder.
    pub fn decoder_for<S>(&self) -> Option<DynDecoder<S>>
    where
        Self: Sized,
        S: ?Sized + Read,
    {
        match (self.byte_order, self.explicit_vr) {
            (Endianness::Little, false) => Some(Box::new(
                implicit_le::ImplicitVRLittleEndianDecoder::default(),
            )),
            (Endianness::Little, true) => Some(Box::new(
                explicit_le::ExplicitVRLittleEndianDecoder::default(),
            )),
            (Endianness::Big, true) => {
                Some(Box::new(explicit_be::ExplicitVRBigEndianDecoder::default()))
            }
            _ => None,
        }
    }

    /// Retrieve the appropriate data element encoder for this transfer syntax.
    /// Can yield none if encoding is not supported. The resulting encoder does not
    /// consider pixel data encapsulation or data set compression rules.
    pub fn encoder<'w>(&self) -> Option<DynEncoder<'w, dyn Write + 'w>> {
        self.encoder_for()
    }

    /// Retrieve the appropriate data element encoder for this transfer syntax
    /// and the given writer type (this method is not object safe).
    /// Can yield none if encoding is not supported. The resulting encoder does not
    /// consider pixel data encapsulation or data set compression rules.
    pub fn encoder_for<'w, W: 'w>(&self) -> Option<DynEncoder<'w, W>>
    where
        Self: Sized,
        W: ?Sized + Write,
    {
        match (self.byte_order, self.explicit_vr) {
            (Endianness::Little, false) => Some(Box::new(EncoderFor::new(
                implicit_le::ImplicitVRLittleEndianEncoder::default(),
            ))),
            (Endianness::Little, true) => Some(Box::new(EncoderFor::new(
                explicit_le::ExplicitVRLittleEndianEncoder::default(),
            ))),
            (Endianness::Big, true) => Some(Box::new(EncoderFor::new(
                explicit_be::ExplicitVRBigEndianEncoder::default(),
            ))),
            _ => None,
        }
    }

    /// Obtain a dynamic basic decoder, based on this transfer syntax' expected endianness.
    pub fn basic_decoder(&self) -> BasicDecoder {
        BasicDecoder::from(self.endianness())
    }

    /// Type-erase the pixel data or data set codec.
    pub fn erased(self) -> TransferSyntax
    where
        A: Send + Sync + 'static,
        A: DataRWAdapter<
            Box<dyn Read>,
            Box<dyn Write>,
            Reader = Box<dyn Read>,
            Writer = Box<dyn Write>,
        >,
    {
        let codec = match self.codec {
            Codec::Dataset(a) => Codec::Dataset(Box::new(a) as DynDataRWAdapter),
            Codec::PixelData(a) => Codec::PixelData(Box::new(a) as DynDataRWAdapter),
            Codec::EncapsulatedPixelData => Codec::EncapsulatedPixelData,
            Codec::Unsupported => Codec::Unsupported,
            Codec::None => Codec::None,
        };

        TransferSyntax {
            uid: self.uid,
            name: self.name,
            byte_order: self.byte_order,
            explicit_vr: self.explicit_vr,
            codec,
        }
    }
}