//! Traits for converting between structural types.
//!
//! The reason these traits exist instead of using `From` and `TryFrom` is,
//! because structural types are usually converted from
//! generic types bounded by the `Foo_SI` traits generated by the `Structural` derive macro,
//! and the `Foo_SI` trait is implemented by the `Foo` type,
//! which means that those impls would overlap with
//! the `impl From<T> for T` impl in the standard lbirary.

use std_::fmt::{self, Display};

#[cfg(feature = "std")]
use std::error::Error as StdError;

/// For conversions between structural types.
///
/// For enums,usually the from enum has to have same variants and
/// at least the same fields as the into enum.<br>
/// For structs,usually the from struct has to have at least the
/// same fields as the into struct.
///
/// # Implementations
///
/// ### Structs
///
/// This trait is usually implemented for structs by:
///
/// - Bounding the trait type parameter with the `*_SI` structural alias generated for the
/// struct by the `Structural` derive.
///
/// - Calling `into_fields` on the parameter to convert it into the fields in common with
/// the `Self` struct.
///
/// ### Enums
///
/// This trait is usually implemented for enums by:
///
/// - Bounding the trait type parameter with the `*_ESI` structural alias generated for the
/// enum by the `Structural` derive.
///
/// - Matching on all the variants of the enum with the switch macro,
/// returning the same variant.
///
/// # Struct Examples
///
/// ### Derivation
///
/// This example demonstrates how this trait can be derived for structs.
///
/// ```rust
/// use structural::{convert::FromStructural, StructuralExt, Structural, fp, make_struct};
///
/// {
///     let this = Point{x: 33, y:45};
///     assert_eq!(this.into_struc::<Entity>(), Entity{x: 33, y: 45, health: 100});
/// }
/// {
///     let this = make_struct!{x: 100, y: 200, foo: "hello"};
///     assert_eq!(this.into_struc::<Entity>(), Entity{x: 100, y: 200, health: 100});
/// }
#[cfg_attr(
    feature = "alloc",
    doc = r###"
{
    // The `Point_SI` trait was generated by the Structural derive on `Point`,
    // aliasing it's accessor trait impls.
    let this: Box<dyn Point_SI<u32>> = Box::new(Point{x: 2016, y: 2080});
    assert_eq!(this.into_struc::<Entity>(), Entity{x: 2016, y: 2080, health: 100});
}
"###
)]
///
/// #[derive(Structural)]
/// struct Point<T>{
///     pub x: T,
///     pub y: u32,
/// }
///
/// #[derive(Debug,PartialEq,Structural)]
/// #[struc(from_structural)]
/// struct Entity{
///     #[struc(public)]
///     x: u32,
///
///     #[struc(public)]
///     y: u32,
///
///     #[struc(init_with_lit = 100)]
///     health: u32,
/// }
/// ```
///
///
/// ### Semi-manual impl
///
/// You can implement the `FromStructural` trait manually by using the `z_impl_from_structural`
/// macro.
///
/// ```rust
///
/// use structural::{convert::FromStructural, StructuralExt, Structural, fp, make_struct};
///
/// {
///     let this = Point{x: 33, y:45};
///     assert_eq!(this.into_struc::<Entity>(), Entity{x: 33, y: 45, health: 100});
/// }
///
/// #[derive(Structural)]
/// struct Point<T>{
///     pub x: T,
///     pub y: u32,
/// }
///
/// #[derive(Debug,PartialEq,Structural)]
/// struct Entity{
///     #[struc(public)]
///     x: u32,
///
///     #[struc(public)]
///     y: u32,
///
///     health: u32,
/// }
///
/// // This macro implements TryFromStructural for Entity by
/// // delegating to the passed-in implementation of `FromStructural`.
/// //
/// // `TryFromStructural` cannot have a blanket impl because it would collide
/// // with user implementations.
/// structural::z_impl_from_structural!{
///     impl[F] FromStructural<F> for Entity
///     where[ F: Entity_SI ]
///     {
///         fn from_structural(from){
///             let (x, y) = from.into_fields(fp!(x, y));
///             Entity{ x, y, health: 100 }
///         }    
///     }
/// }
///
/// ```
///
/// # Enum Examples
///
/// ### Derivation
///
/// This example demonstrates how this trait can be derived for an enum with one
/// private field.
///
/// ```rust
/// use structural::{
///     convert::FromStructural,
///     for_examples::OptionLike,
///     StructuralExt, Structural, switch,
/// };
///
/// assert_eq!(Some(100).into_struc::<UberOption<_>>(), UberOption::Some(100, 0));
/// assert_eq!(None.into_struc::<UberOption<u32>>(), UberOption::None);
///
/// assert_eq!(OptionLike::Some(3).into_struc::<UberOption<_>>(), UberOption::Some(3, 0));
/// assert_eq!(OptionLike::None.into_struc::<UberOption<u32>>(), UberOption::None);
///
/// // Converting an UberOption back to itself with `FromStructural` drops the
/// // `#[struct(not_public)]` field,because it has no accessor impls.
/// assert_eq!(
///     UberOption::Some(5, 200).into_struc::<UberOption<_>>(),
///     UberOption::Some(5, 0)
/// );
/// assert_eq!(
///     UberOption::None.into_struc::<UberOption<u32>>(),
///     UberOption::None,
/// );
///
/// #[derive(Debug,Structural,PartialEq)]
/// #[struc(from_structural(bound = "T: Default"))]
/// enum UberOption<T>{
///     Some(
///         T,
///         #[struc(init_with_default)]
///         T,
///     ),
///     None,
/// }
///
/// ```
///
/// ### Semi-manual
///
/// This example demonstrates how this trait can be semi-manually
/// implemented for an enum with one
/// private field (as in a field that doesn't have accessor impls to get it).
///
/// ```rust
/// use structural::{
///     convert::FromStructural,
///     for_examples::OptionLike,
///     structural_aliases::OptionMove_ESI,
///     StructuralExt, Structural, switch,
/// };
///
/// assert_eq!(Some(100).into_struc::<UberOption<_>>(), UberOption::Some(100, 100));
/// assert_eq!(None.into_struc::<UberOption<u32>>(), UberOption::None);
///
/// assert_eq!(OptionLike::Some(3).into_struc::<UberOption<_>>(), UberOption::Some(3, 3));
/// assert_eq!(OptionLike::None.into_struc::<UberOption<u32>>(), UberOption::None);
///
/// // Converting an UberOption back to itself with `FromStructural` drops the
/// // `#[struct(not_public)]` field,because it has no accessor impls.
/// assert_eq!(
///     UberOption::Some(5, 200).into_struc::<UberOption<_>>(),
///     UberOption::Some(5, 5)
/// );
/// assert_eq!(
///     UberOption::None.into_struc::<UberOption<u32>>(),
///     UberOption::None,
/// );
///
/// #[derive(Debug,Structural,PartialEq)]
/// enum UberOption<T>{
///     Some(
///         T,
///         #[struc(not_public)]
///         T,
///     ),
///     None,
/// }
///
/// // This macro implements TryFromStructural for Entity by
/// // delegating to the passed-in implementation of `FromStructural`.
/// //
/// // `TryFromStructural` cannot have a blanket impl because it would collide
/// // with user implementations.
/// structural::z_impl_from_structural!{
///     impl[F, T] FromStructural<F> for UberOption<T>
///     where[
///         F: OptionMove_ESI<T>,
///         T: Clone,
///     ]{
///         fn from_structural(from){
///             switch!{from;
///                 Some(x) => Self::Some(x.clone(), x),
///                 None => Self::None,
///             }
///         }
///     }
/// }
///
/// ```
///
pub trait FromStructural<T>: TryFromStructural<T> {
    /// Performs the conversion
    fn from_structural(from: T) -> Self;
}

/// For conversions between structural types.
///
/// This trait has a blanket implementations for all types that implement `FromStructural`.
///
/// # Example
///
/// This example demonstrates how you can use `IntoStructural` as a bound.
///
/// ```rust
/// use structural::convert::IntoStructural;
///
/// assert_eq!( into_other((0, 1, 2), [3, 4]), [[0, 1], [3, 4]] );
///
/// fn into_other<T, U>(left: T, right: U)-> [U;2]
/// where
///     T: IntoStructural<U>,
/// {
///     [left.into_structural(), right]
/// }
///
/// ```
///
pub trait IntoStructural<T>: Sized {
    /// Performs the conversion
    fn into_structural(self) -> T;
}

impl<This, T> IntoStructural<T> for This
where
    T: FromStructural<This>,
{
    fn into_structural(self) -> T {
        T::from_structural(self)
    }
}

///////////////////////////////////////////////////////////////////////////////

/// For fallible conversions between structural types.
///
/// Usually conversions between enums require the from enum to have at least the
/// fields and variants of the into enum.
///
/// All the examples in this crate are for enums,
/// since converting from an enum to another with a subset of the variants in the
/// first is the motivating usecase for defining this trait.
///
/// # Implementations
///
/// ### Enums
///
/// This trait is usually implemented for enums by:
///
/// - Bounding the trait's type parameter with the `*_SI` structural alias generated for the
/// enum by the `Structural` derive.
///
/// - Matching on all the variants of the enum with the switch macro,
/// returning `Ok` with a variant if the parameter matches that enum variant.
/// If the parameter doesn't match any of the enum variants,an error is returned.
///
/// # Enum Examples
///
/// ### Derived
///
/// This example demonstrates how this trait can be derived.
///
/// ```rust
/// use structural::{
///     convert::{EmptyTryFromError, TryFromError},
///     for_examples::{Enum3, Enum4},
///     Structural, StructuralExt, switch,
/// };
///
/// use std::cmp::Ordering;
///
/// assert_eq!(
///     Enum3::Foo(3, 5).try_into_struc::<Variants>(),
///     Ok(Variants::Foo(3)),
/// );
/// assert_eq!(
///     Enum3::Bar(Ordering::Less, None).try_into_struc::<Variants>(),
///     Ok(Variants::Bar),
/// );
/// assert_eq!(
///     Enum3::Baz{foom: "hi"}.try_into_struc::<Variants>(),
///     Ok(Variants::Baz{foom: "hi"}),
/// );
///
/// let qux=Enum4::Qux { uh: [0; 4], what: (false, false) };
/// assert_eq!(
///     qux.try_into_struc::<Variants>(),
///     Err(TryFromError::with_empty_error(qux)),
/// );
///
///
/// #[derive(Structural, Copy, Clone, Debug, PartialEq)]
/// // This attribute tells the `Structural` derive to generate the
/// // `TryFromStructural` and `FromStructural` impls
/// #[struc(from_structural)]
/// enum Variants {
///     Foo(u8),
///     Bar,
///     Baz { foom: &'static str },
/// }
///
///  
/// ```
///
/// ### Semi-manual impl
///
/// This example demonstrates how this trait can be implemented with the
/// `z_impl_try_from_structural_for_enum` macro.
///
/// ```rust
/// use structural::{
///     convert::{EmptyTryFromError, TryFromError},
///     for_examples::{Enum3, Enum4},
///     Structural, StructuralExt, switch,
/// };
///
/// use std::cmp::Ordering;
///
/// assert_eq!(
///     Enum3::Foo(3, 5).try_into_struc::<Variants>(),
///     Ok(Variants::Foo(3)),
/// );
/// assert_eq!(
///     Enum3::Bar(Ordering::Less, None).try_into_struc::<Variants>(),
///     Ok(Variants::Bar),
/// );
/// assert_eq!(
///     Enum3::Baz{foom: "hi"}.try_into_struc::<Variants>(),
///     Ok(Variants::Baz{foom: "hi"}),
/// );
///
/// let qux=Enum4::Qux { uh: [0; 4], what: (false, false) };
/// assert_eq!(
///     qux.try_into_struc::<Variants>(),
///     Err(TryFromError::with_empty_error(qux)),
/// );
///
///
/// #[derive(Structural, Copy, Clone, Debug, PartialEq)]
/// enum Variants {
///     Foo(u8),
///     Bar,
///     Baz { foom: &'static str },
/// }
///
/// // This macro implements FromStructural in terms of TryFromStructural,
/// //
/// // In order to implement FromStructural,
/// // this macro assumes that the TryFromStructural implementation written by users:
/// //   - Matches on all the variants of the enum
/// //   - Returns `Ok` for all the variants of the enum that were matches by name.
/// structural::z_impl_try_from_structural_for_enum!{
///     impl[F] TryFromStructural<F> for Variants
///     // `Variants_SI` was generated by the `Structural` derive for `Variants`
///     // aliasing its accessor trait impls,
///     // and allows `F` to have more variants than `Foo`,`Bar`,and `Baz`.
///     where[ F: Variants_SI, ]
///     {
///         type Error = EmptyTryFromError;
///
///         fn try_from_structural(this){
///             switch! {this;
///                 Foo(x) => Ok(Self::Foo(x)),
///                 Bar => Ok(Self::Bar),
///                 Baz{foom} => Ok(Self::Baz{foom}),
///                 _ => Err(TryFromError::with_empty_error(this)),
///             }
///         }
///     }
///
///     // `Variants_ESI` was generated by the `Structural` derive for `Variants`
///     // aliasing its accessor trait impls,
///     // and requires `F` to only have the `Foo`,`Bar`,and `Baz` variants.
///     FromStructural
///     where[ F: Variants_ESI, ]
/// }
///  
/// ```
///
/// # Example: Manual implementation
///
/// ```rust
/// use structural::{
///     convert::{EmptyTryFromError, FromStructural, TryFromError, TryFromStructural},
///     for_examples::{Enum3, Enum4},
///     Structural, StructuralExt, switch,
/// };
///
/// use std::cmp::Ordering;
///
/// assert_eq!(
///     Enum3::Foo(3, 5).try_into_struc::<Variants>(),
///     Ok(Variants::Foo(3)),
/// );
/// assert_eq!(
///     Enum3::Bar(Ordering::Less, None).try_into_struc::<Variants>(),
///     Ok(Variants::Bar),
/// );
/// assert_eq!(
///     Enum3::Baz{foom: "hi"}.try_into_struc::<Variants>(),
///     Ok(Variants::Baz{foom: "hi"}),
/// );
///
/// let qux=Enum4::Qux { uh: [0; 4], what: (false, false) };
/// assert_eq!(
///     qux.try_into_struc::<Variants>(),
///     Err(TryFromError::with_empty_error(qux)),
/// );
///
///
/// #[derive(Structural, Copy, Clone, Debug, PartialEq)]
/// enum Variants {
///     Foo(u8),
///     Bar,
///     Baz { foom: &'static str },
/// }
///  
/// impl<F> FromStructural<F> for Variants
/// where
///     // `Variants_ESI` was generated by the `Structural` derive for `Variants`
///     // aliasing its accessor trait impls,
///     // and requires `F` to only have the `Foo`,`Bar`,and `Baz` variants.
///     F: Variants_ESI,
/// {
///     fn from_structural(this: F) -> Self {
///         switch! {this;
///             Foo(x) => Self::Foo(x),
///             Bar => Self::Bar,
///             Baz{foom} => Self::Baz{foom},
///         }
///     }
/// }
///
/// impl<F> TryFromStructural<F> for Variants
/// where
///     // `Variants_SI` was generated by the `Structural` derive for `Variants`
///     // aliasing its accessor trait impls,
///     // and allows `F` to have more variants than `Foo`,`Bar`,and `Baz`.
///     F: Variants_SI,
/// {
///     type Error = EmptyTryFromError;
///
///     fn try_from_structural(this: F) -> Result<Self, TryFromError<F, Self::Error>> {
///         switch! {this;
///             Foo(x) => Ok(Self::Foo(x)),
///             Bar => Ok(Self::Bar),
///             Baz{foom} => Ok(Self::Baz{foom}),
///             _ => Err(TryFromError::with_empty_error(this)),
///         }
///     }
/// }
///  
/// ```
///
pub trait TryFromStructural<T>: Sized {
    /// The error parameter of `TryFromError`,
    /// returned from `try_into_structural` on conversion error.
    type Error;

    /// Performs the conversion
    fn try_from_structural(from: T) -> Result<Self, TryFromError<T, Self::Error>>;
}

/// For fallible conversions between structural types.
///
/// This trait has a blanket implementations for all types that implement `TryFromStructural`.
///
/// # Example
///
/// This example demonstrates how you can use `TryIntoStructural` as a bound.
///
/// ```rust
/// use structural::{
///     convert::TryIntoStructural,
///     for_examples::{Enum2, Enum3}
/// };
///
/// use std::cmp::{Ordering::{Less, Equal, Greater}, PartialEq};
///
/// compare_eq(Enum3::Foo(3, 5), Enum2::Foo(3, 5)      , true  );
/// compare_eq(Enum3::Foo(5, 8), Enum2::Foo(5, 8)      , true  );
/// compare_eq(Enum3::Foo(3, 5), Enum2::Foo(4, 5)      , false );
/// compare_eq(Enum3::Foo(3, 5), Enum2::Bar(Less, None), false );
///
/// compare_eq(Enum3::Bar(Less, None), Enum2::Foo(3, 5)       , false );
/// compare_eq(Enum3::Bar(Less, None), Enum2::Bar(Less, None) , true  );
/// compare_eq(Enum3::Bar(Equal,None), Enum2::Bar(Equal, None), true  );
/// compare_eq(Enum3::Bar(Less, None), Enum2::Bar(Equal, None), false );
///
/// // `Enum3::Baz{..}` is never equal to an `Enum2`,because it doesn't have a `Baz` variant.
/// compare_eq(Enum3::Baz{foom: "hello"}, Enum2::Foo(3, 5)       , false );
/// compare_eq(Enum3::Baz{foom: "hello"}, Enum2::Bar(Less, None) , false );
///
/// fn compare_eq<T, U>(left: T, right: U, expected: bool)
/// where
///     T: TryIntoStructural<U>,
///     U: PartialEq,
/// {
///     let is_equal = match left.try_into_structural() {
///         Ok(left) => left==right,
///         Err(_) => false,
///     };
///
///     assert_eq!( is_equal, expected );
/// }
///
/// ```
///
pub trait TryIntoStructural<T>: Sized {
    /// The error parameter of `TryFromError`,
    /// returned from `try_into_structural` on conversion error.
    type Error;

    /// Performs the conversion
    fn try_into_structural(self) -> Result<T, TryFromError<Self, Self::Error>>;
}

impl<This, T> TryIntoStructural<T> for This
where
    T: TryFromStructural<This>,
{
    type Error = T::Error;

    fn try_into_structural(self) -> Result<T, TryFromError<Self, Self::Error>> {
        T::try_from_structural(self)
    }
}

///////////////////////////////////////////////////////////////////////////////

/// The error type returned by  `TryFromStructural` and `TryIntoStructural`.
#[derive(Debug, Clone, PartialEq)]
pub struct TryFromError<T, E> {
    /// The paramter of `TryFromStructural::try_from_structural`
    /// (or self in `TryIntoStructural::try_into_structural`)
    /// that failed to be conevrted.
    pub from: T,
    /// The `TryFromStructural::Error` associated type.
    pub error: E,
}

impl<T, E> TryFromError<T, E> {
    /// Constructs this error.
    pub fn new(from: T, error: E) -> Self {
        Self { from, error }
    }
}

impl<T> TryFromError<T, EmptyTryFromError> {
    /// Constructs this error,with `EmptyTryFromError` as the error.
    pub fn with_empty_error(from: T) -> Self {
        Self {
            from,
            error: EmptyTryFromError,
        }
    }
}

impl<T, E> Display for TryFromError<T, E>
where
    E: Display,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        Display::fmt(&self.error, f)
    }
}

#[cfg(feature = "std")]
#[allow(deprecated)]
impl<T, E> StdError for TryFromError<T, E>
where
    T: fmt::Debug,
    E: StdError,
{
    fn source(&self) -> Option<&(dyn StdError + 'static)> {
        self.error.source()
    }
    fn description(&self) -> &str {
        self.error.description()
    }
    fn cause(&self) -> Option<&dyn StdError> {
        self.error.cause()
    }
}

///////////////////////////////////////////////////////////////////////////////

/// The "default" error for the `TryFromStructural::Error` associated type,
/// for when there are no details for how the conversion failed.
#[derive(Debug, Clone, PartialEq)]
pub struct EmptyTryFromError;

impl Display for EmptyTryFromError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        Display::fmt("failed TryIntoStructural conversion", f)
    }
}

#[cfg(feature = "std")]
impl StdError for EmptyTryFromError {}