//! Core module for ADN functionality.
//! Brings [`Mentionable`]/[`Factory`]/[`Origin`] concepts from the original implementation in Python.
//! Allows for more generic behaviour via [`Context`], as opposed to original async-only.

use std::{error::Error, fmt::Display, rc::Rc};

use crate::func::*;

/// Execution context.
pub trait Context {
    /// Type to provide for [Monad]ic representation of computation, mostly that of resolution ([`Resolution`]).
    type T: Monad;

    /// Type to represent resolution errors mainly arising in [`Resolver::resolve`].
    type LookupError<'a>: 'a + Error;

    /// Get [type@Hash] of a slice, mostly for use in [`Point`].
    fn hash(s: &[u8]) -> Hash;
}

/// Failure yielded by [`Origin`].
#[derive(Debug)]
pub enum ResolutionError<L, P> {
    Lookup(L),
    Parse(P),
}

/// See [`ResolutionResult`].
pub type ResolutionFailure<'a, Ctx, A> = ResolutionError<
    <Ctx as Context>::LookupError<'a>,
    <<A as Mentionable<'a, Ctx>>::Fctr as Factory<'a, Ctx>>::ParseError,
>;

/// Result yielded by [`Origin`].
pub type ResolutionResult<'a, Ctx, A> = Result<Rc<A>, ResolutionFailure<'a, Ctx, A>>;

/// Helper alias for [`WeakFunctor::F`] of [`Context::T`].
pub type Wrapped<'a, Ctx, A> = <<Ctx as Context>::T as WeakFunctor>::F<'a, A>;

/// Wrapped result returned by [`Origin`].
pub type Resolution<'a, Ctx, A> = Wrapped<'a, Ctx, ResolutionResult<'a, Ctx, A>>;

/// Fixed [type@Hash] length.
pub const HASH_SIZE: usize = 32;

/// Zeroed out array of the same length as [`type@Hash`].
/// Used in [`crate::std::nullable`].
pub const HASH_ZEROS: [u8; HASH_SIZE] = [0; HASH_SIZE];

/// For use in [`Point`]/[`Address`].
pub type Hash = [u8; HASH_SIZE];

/// Serialisation mechanism that is chosen over bytestring concatenation
/// both for performance and simplicity.
///
/// See [`Serializable`].
pub trait Serializer {
    /// Writes bytes from a slice. Should advance value of [`Serializer::tell()`] by `buf.len()`.
    fn write(&mut self, buf: &[u8]);
    /// Current position of the stream. It's expected to be used by [`crate::std::inlining`]
    fn tell(&self) -> usize;
}

impl Serializer for Vec<u8> {
    fn write(&mut self, buf: &[u8]) {
        self.extend(buf);
    }

    fn tell(&self) -> usize {
        self.len()
    }
}

/// See [`Serializer`].
pub trait Serializable {
    /// Expected to use [`Serializer::write`].
    fn serialize(&self, serializer: &mut dyn Serializer);
}

/// Fundamental trait for ADN objects.
pub trait Mentionable<'a, Ctx: 'a + Context>: 'a + Serializable {
    /// Type of the associated factory.
    type Fctr: Factory<'a, Ctx, Mtbl = Self>;

    /// Value of the associated factory.
    fn factory(&self) -> Self::Fctr;
    /// See implementation for the definition.
    /// Hash of all the references' points concatenated, ordered, non-unique.
    /// Used for walking over object trees to ensure two objects with different references don't collide.
    fn topology(&self) -> Hash {
        let mut vec = Vec::new();
        for point in self.points() {
            vec.extend(point.point);
        }
        Ctx::hash(&vec)
    }
    /// References ([Point]s) to other objects.
    fn points(&self) -> Vec<Point<'a, Ctx, TypelessMentionable<'a, Ctx>>>;
}

/// Short-hand for the type of values returned by [`Resolver::resolve`].
pub type HashResolution<'a, Ctx> = Wrapped<
    'a,
    Ctx,
    Result<(Vec<u8>, Rc<dyn Resolver<'a, Ctx>>), <Ctx as Context>::LookupError<'a>>,
>;

/// Value accepted by [`Resolver::resolve`]. Includes index to make it order-sensitive.
#[derive(Clone, Copy, Debug)]
pub struct Address {
    pub point: Hash,
    /// Index of the point in the [`Mentionable::points()`].
    pub index: usize,
}

/// Trait representing the "rainbow table" behaviour.
pub trait Resolver<'a, Ctx: 'a + Context>: 'a {
    /// Successfully returned value should be the inverse of the point passed
    /// with topology header ([`Mentionable::topology()`]) omitted.
    fn resolve(self: Rc<Self>, address: Address) -> HashResolution<'a, Ctx>;
}

/// Trait representing a readable stream used for parsing.
///
/// See [`Serializer`], [`Factory::deserialize`].
pub trait Deserializer {
    /// Read at most `n` bytes.
    fn read_n(&mut self, n: usize) -> &[u8];
    /// Read til the end of the stream.
    fn read_all(&mut self) -> &[u8];
    /// See [`Serializer::tell`].
    fn tell(&self) -> usize;
}

/// Short-hand for the type of vaalues returned by [`Factory::deserialize`].
pub type ParseResult<'a, Ctx, F> =
    Result<<F as Factory<'a, Ctx>>::Mtbl, <F as Factory<'a, Ctx>>::ParseError>;

/// Trait representing deserialisation rules for [Mentionable]s.
/// Crucial for [`TypelessMentionable`] and therefore [`Mentionable::points`].
pub trait Factory<'a, Ctx: 'a + Context>: Clone + 'a {
    /// Type of the associated objects.
    type Mtbl: Mentionable<'a, Ctx, Fctr = Self>;
    /// Type of an error that [`Factory::deserialize`] can fail with.
    type ParseError: 'a + Error;

    /// See [`Deserializer`], [`Resolver`].
    fn deserialize(
        &self,
        deserializer: &mut dyn Deserializer,
        resolver: Rc<dyn Resolver<'a, Ctx>>,
    ) -> ParseResult<'a, Ctx, Self>;
    /// Called by finite stream parsers if there's any data left.
    fn unexpected_tail(&self, tail: &[u8]) -> Self::ParseError;
}

/// Represents a potentially resolvable [`Mentionable`].
pub trait Origin<'a, Ctx: 'a + Context>: 'a {
    /// Type of the associated object.
    type Mtbl: Mentionable<'a, Ctx>;
    /// Value of the associated factory.
    fn factory(&self) -> <Self::Mtbl as Mentionable<'a, Ctx>>::Fctr;
    /// Try resolving the value.
    fn resolve(self: Rc<Self>) -> Resolution<'a, Ctx, Self::Mtbl>;
}

struct LocalOrigin<A>(Rc<A>);

impl<'a, Ctx: 'a + Context, A: Mentionable<'a, Ctx>> Origin<'a, Ctx> for LocalOrigin<A> {
    type Mtbl = A;

    fn factory(&self) -> A::Fctr {
        self.0.factory()
    }

    fn resolve(self: Rc<Self>) -> Resolution<'a, Ctx, Self::Mtbl> {
        Ctx::T::pure(Ok(self.0.clone()))
    }
}

impl<A> From<A> for LocalOrigin<A> {
    fn from(value: A) -> Self {
        LocalOrigin(value.into())
    }
}

/// The main way to represent a reference in ADN.
pub struct Point<'a, Ctx: 'a + Context, A: Mentionable<'a, Ctx>> {
    pub point: Hash,
    pub origin: Rc<dyn Origin<'a, Ctx, Mtbl = A>>,
}

impl<'a, Ctx: 'a + Context, A: Mentionable<'a, Ctx>> Clone for Point<'a, Ctx, A> {
    fn clone(&self) -> Self {
        Self {
            point: self.point,
            origin: self.origin.clone(),
        }
    }
}

impl<'a, Ctx: 'a + Context, A: Mentionable<'a, Ctx>> Point<'a, Ctx, A> {
    fn prepare_bytes_for_hashing(mentioned: &A) -> Vec<u8> {
        let mut vec = mentioned.topology().to_vec();
        mentioned.serialize(&mut vec);
        vec
    }

    fn from_fields(point: Hash, origin: Rc<dyn Origin<'a, Ctx, Mtbl = A>>) -> Self {
        Point { point, origin }
    }

    fn from_values<O: Origin<'a, Ctx, Mtbl = A>>(point: Hash, origin: O) -> Self {
        Self::from_fields(point, Rc::new(origin))
    }

    /// See [`Origin::resolve`].
    pub fn resolve(&self) -> Resolution<'a, Ctx, A> {
        self.origin.clone().resolve()
    }

    fn from_mentionable(mentionable: A) -> Self {
        Self::from_values(
            Ctx::hash(Self::prepare_bytes_for_hashing(&mentionable).as_slice()),
            LocalOrigin::from(mentionable),
        )
    }
}

impl<'a, Ctx: 'a + Context, A: Mentionable<'a, Ctx>> From<A> for Point<'a, Ctx, A> {
    fn from(value: A) -> Self {
        Self::from_mentionable(value)
    }
}

type TypelessSerialize<'a> = dyn 'a + Fn(&mut dyn Serializer);

/// See [`Mentionable::points`].
pub struct TypelessMentionable<'a, Ctx: 'a + Context> {
    t_serialize: Box<TypelessSerialize<'a>>,
    t_factory: TypelessFactory<'a, Ctx>,
    t_topology: Hash,
    t_points: Vec<Point<'a, Ctx, TypelessMentionable<'a, Ctx>>>,
}

type TypelessParsed<'a, Ctx> = Result<TypelessMentionable<'a, Ctx>, Box<dyn 'a + Error>>;

type TypelessDeserialize<'a, Ctx> =
    dyn 'a + Fn(&mut dyn Deserializer, Rc<dyn Resolver<'a, Ctx>>) -> TypelessParsed<'a, Ctx>;

type TypelessUnexpectedTail<'a> = dyn 'a + Fn(&[u8]) -> TypelessError<'a>;

/// See [`Mentionable::points`]/[`TypelessMentionable`].
pub struct TypelessFactory<'a, Ctx: 'a + Context> {
    t_deserialize: Rc<TypelessDeserialize<'a, Ctx>>,
    t_unexpected_tail: Rc<TypelessUnexpectedTail<'a>>,
}

impl<'a, Ctx: 'a + Context> Serializable for TypelessMentionable<'a, Ctx> {
    fn serialize(&self, serializer: &mut dyn Serializer) {
        (self.t_serialize)(serializer);
    }
}

impl<'a, Ctx: 'a + Context> Mentionable<'a, Ctx> for TypelessMentionable<'a, Ctx> {
    type Fctr = TypelessFactory<'a, Ctx>;

    fn factory(&self) -> Self::Fctr {
        self.t_factory.clone()
    }

    fn topology(&self) -> Hash {
        self.t_topology
    }

    fn points(&self) -> Vec<Point<'a, Ctx, TypelessMentionable<'a, Ctx>>> {
        self.t_points.clone()
    }
}

impl<'a, Ctx: 'a + Context> Clone for TypelessFactory<'a, Ctx> {
    fn clone(&self) -> Self {
        Self {
            t_deserialize: self.t_deserialize.clone(),
            t_unexpected_tail: self.t_unexpected_tail.clone(),
        }
    }
}

/// See [`Mentionable::points`]/[`TypelessFactory`].
#[derive(Debug)]
pub struct TypelessError<'a>(Box<dyn 'a + Error>);

impl<'a> Display for TypelessError<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.write_fmt(format_args!("typeless error: {}", self.0))
    }
}

impl<'a> Error for TypelessError<'a> {}

impl<'a, Ctx: 'a + Context> Factory<'a, Ctx> for TypelessFactory<'a, Ctx> {
    type Mtbl = TypelessMentionable<'a, Ctx>;

    type ParseError = TypelessError<'a>;

    fn deserialize(
        &self,
        deserializer: &mut dyn Deserializer,
        resolver: Rc<dyn Resolver<'a, Ctx>>,
    ) -> ParseResult<'a, Ctx, Self> {
        match (self.t_deserialize)(deserializer, resolver) {
            Ok(mentionable) => Ok(mentionable),
            Err(error) => Err(TypelessError(error)),
        }
    }

    fn unexpected_tail(&self, tail: &[u8]) -> Self::ParseError {
        (self.t_unexpected_tail)(tail)
    }
}

impl<'a, Ctx: 'a + Context> TypelessMentionable<'a, Ctx> {
    pub fn from_typed<A: Mentionable<'a, Ctx>>(mentionable: Rc<A>) -> Self {
        let factory = TypelessFactory::from_typed(mentionable.factory());
        let topology = mentionable.topology();
        let points = mentionable.points();
        TypelessMentionable {
            t_serialize: Box::new(move |serializer| mentionable.serialize(serializer)),
            t_factory: factory,
            t_topology: topology,
            t_points: points,
        }
    }
}

impl<'a, Ctx: 'a + Context> TypelessFactory<'a, Ctx> {
    pub fn from_typed<F: Factory<'a, Ctx>>(factory: F) -> Self {
        let tail_factory = factory.clone();
        TypelessFactory {
            t_deserialize: Rc::new(move |deserializer, resolver| {
                match factory.deserialize(deserializer, resolver) {
                    Ok(mentionable) => Ok(TypelessMentionable::from_typed(Rc::new(mentionable))),
                    Err(error) => Err(Box::new(error)),
                }
            }),
            t_unexpected_tail: Rc::new(move |tail| {
                TypelessError::from_typed(tail_factory.unexpected_tail(tail))
            }),
        }
    }
}

impl<'a> TypelessError<'a> {
    pub fn from_typed<E: 'a + Error>(error: E) -> Self {
        TypelessError(Box::new(error))
    }
}