use serde::Serialize;
use std::ops::ControlFlow;

use super::docs::Docs;
use super::{Attrs, Ident, Lifetime, LifetimeEnv, Mutability, PathType, TypeName};

/// A method declared in the `impl` associated with an FFI struct.
/// Includes both static and non-static methods, which can be distinguished
/// by inspecting [`Method::self_param`].
#[derive(Clone, PartialEq, Eq, Hash, Serialize, Debug)]
#[non_exhaustive]
pub struct Method {
    /// The name of the method as initially declared.
    pub name: Ident,

    /// Lines of documentation for the method.
    pub docs: Docs,

    /// The name of the FFI function wrapping around the method.
    pub full_path_name: Ident,

    /// The `self` param of the method, if any.
    pub self_param: Option<SelfParam>,

    /// All non-`self` params taken by the method.
    pub params: Vec<Param>,

    /// The return type of the method, if any.
    pub return_type: Option<TypeName>,

    /// The lifetimes introduced in this method and surrounding impl block.
    pub lifetime_env: LifetimeEnv,

    /// The list of `cfg` attributes (if any).
    ///
    /// These are strings instead of `syn::Attribute` or `proc_macro2::TokenStream`
    /// because those types are not `PartialEq`, `Hash`, `Serialize`, etc.
    pub attrs: Attrs,
}

impl Method {
    /// Extracts a [`Method`] from an AST node inside an `impl`.
    pub fn from_syn(
        m: &syn::ImplItemFn,
        self_path_type: PathType,
        impl_generics: Option<&syn::Generics>,
        impl_attrs: &Attrs,
    ) -> Method {
        let mut attrs = impl_attrs.clone();
        attrs.add_attrs(&m.attrs);

        let self_ident = self_path_type.path.elements.last().unwrap();
        let method_ident = &m.sig.ident;
        let concat_method_ident = format!("{self_ident}_{method_ident}");
        let extern_ident = syn::Ident::new(
            &attrs.abi_rename.apply(concat_method_ident.into()),
            m.sig.ident.span(),
        );

        let all_params = m
            .sig
            .inputs
            .iter()
            .filter_map(|a| match a {
                syn::FnArg::Receiver(_) => None,
                syn::FnArg::Typed(ref t) => Some(Param::from_syn(t, self_path_type.clone())),
            })
            .collect::<Vec<_>>();

        let self_param = m
            .sig
            .receiver()
            .map(|rec| SelfParam::from_syn(rec, self_path_type.clone()));

        let return_ty = match &m.sig.output {
            syn::ReturnType::Type(_, return_typ) => {
                // When we allow lifetime elision, this is where we would want to
                // support it so we can insert the expanded explicit lifetimes.
                Some(TypeName::from_syn(
                    return_typ.as_ref(),
                    Some(self_path_type),
                ))
            }
            syn::ReturnType::Default => None,
        };

        let lifetime_env = LifetimeEnv::from_method_item(
            m,
            impl_generics,
            self_param.as_ref(),
            &all_params[..],
            return_ty.as_ref(),
        );

        Method {
            name: Ident::from(method_ident),
            docs: Docs::from_attrs(&m.attrs),
            full_path_name: Ident::from(&extern_ident),
            self_param,
            params: all_params,
            return_type: return_ty,
            lifetime_env,
            attrs,
        }
    }

    /// Returns the parameters that the output is lifetime-bound to.
    ///
    /// # Examples
    ///
    /// Given the following method:
    /// ```ignore
    /// fn foo<'a, 'b: 'a, 'c>(&'a self, bar: Bar<'b>, baz: Baz<'c>) -> FooBar<'a> { ... }
    /// ```
    /// Then this method would return the `&'a self` and `bar: Bar<'b>` params
    /// because `'a` is in the return type, and `'b` must live at least as long
    /// as `'a`. It wouldn't include `baz: Baz<'c>` though, because the return
    /// type isn't bound by `'c` in any way.
    ///
    /// # Panics
    ///
    /// This method may panic if `TypeName::check_result_type_validity` (called by
    /// `Method::check_validity`) doesn't pass first, since the result type may
    /// contain elided lifetimes that we depend on for this method. The validity
    /// checks ensure that the return type doesn't elide any lifetimes, ensuring
    /// that this method will produce correct results.
    pub fn borrowed_params(&self) -> BorrowedParams {
        // To determine which params the return type is bound to, we just have to
        // find the params that contain a lifetime that's also in the return type.
        if let Some(ref return_type) = self.return_type {
            // The lifetimes that must outlive the return type
            let lifetimes = return_type.longer_lifetimes(&self.lifetime_env);

            let held_self_param = self.self_param.as_ref().filter(|self_param| {
                // Check if `self` is a reference with a lifetime in the return type.
                if let Some((Lifetime::Named(ref name), _)) = self_param.reference {
                    if lifetimes.contains(&name) {
                        return true;
                    }
                }
                self_param.path_type.lifetimes.iter().any(|lt| {
                    if let Lifetime::Named(name) = lt {
                        lifetimes.contains(&name)
                    } else {
                        false
                    }
                })
            });

            // Collect all the params that contain a named lifetime that's also
            // in the return type.
            let held_params = self
                .params
                .iter()
                .filter_map(|param| {
                    let mut lt_kind = LifetimeKind::ReturnValue;
                    param
                        .ty
                        .visit_lifetimes(&mut |lt, _| {
                            // Thanks to `TypeName::visit_lifetimes`, we can
                            // traverse the lifetimes without allocations and
                            // short-circuit if we find a match.
                            match lt {
                                Lifetime::Named(name) if lifetimes.contains(&name) => {
                                    return ControlFlow::Break(());
                                }
                                Lifetime::Static => {
                                    lt_kind = LifetimeKind::Static;
                                    return ControlFlow::Break(());
                                }
                                _ => {}
                            };
                            ControlFlow::Continue(())
                        })
                        .is_break()
                        .then(|| (param, lt_kind))
                })
                .collect();

            BorrowedParams(held_self_param, held_params)
        } else {
            BorrowedParams(None, vec![])
        }
    }

    /// Checks whether the method qualifies for special writeable handling.
    /// To qualify, a method must:
    ///  - not return any value
    ///  - have the last argument be an `&mut diplomat_runtime::DiplomatWriteable`
    ///
    /// Typically, methods of this form will be transformed in the bindings to a
    /// method that doesn't take the writeable as an argument but instead creates
    /// one locally and just returns the final string.
    pub fn is_writeable_out(&self) -> bool {
        let return_compatible = self
            .return_type
            .as_ref()
            .map(|return_type| match return_type {
                TypeName::Unit => true,
                TypeName::Result(ok, _, _) => {
                    matches!(ok.as_ref(), TypeName::Unit)
                }
                _ => false,
            })
            .unwrap_or(true);

        return_compatible && self.params.last().map(Param::is_writeable).unwrap_or(false)
    }

    /// Checks if any parameters are writeable (regardless of other compatibilities for writeable output)
    pub fn has_writeable_param(&self) -> bool {
        self.params.iter().any(|p| p.is_writeable())
    }

    /// Returns the documentation block
    pub fn docs(&self) -> &Docs {
        &self.docs
    }
}

/// The `self` parameter taken by a [`Method`].
#[derive(Clone, PartialEq, Eq, Hash, Serialize, Debug)]
#[non_exhaustive]
pub struct SelfParam {
    /// The lifetime and mutability of the `self` param, if it's a reference.
    pub reference: Option<(Lifetime, Mutability)>,

    /// The type of the parameter, which will be a named reference to
    /// the associated struct,
    pub path_type: PathType,
}

impl SelfParam {
    pub fn to_typename(&self) -> TypeName {
        let typ = TypeName::Named(self.path_type.clone());
        if let Some((ref lifetime, ref mutability)) = self.reference {
            return TypeName::Reference(lifetime.clone(), *mutability, Box::new(typ));
        }
        typ
    }

    pub fn from_syn(rec: &syn::Receiver, path_type: PathType) -> Self {
        SelfParam {
            reference: rec
                .reference
                .as_ref()
                .map(|(_, lt)| (lt.into(), Mutability::from_syn(&rec.mutability))),
            path_type,
        }
    }
}

/// A parameter taken by a [`Method`], not including `self`.
#[derive(Clone, PartialEq, Eq, Hash, Serialize, Debug)]
#[non_exhaustive]
pub struct Param {
    /// The name of the parameter in the original method declaration.
    pub name: Ident,

    /// The type of the parameter.
    pub ty: TypeName,
}

impl Param {
    /// Check if this parameter is a Writeable
    pub fn is_writeable(&self) -> bool {
        match self.ty {
            TypeName::Reference(_, Mutability::Mutable, ref w) => **w == TypeName::Writeable,
            _ => false,
        }
    }

    pub fn from_syn(t: &syn::PatType, self_path_type: PathType) -> Self {
        let ident = match t.pat.as_ref() {
            syn::Pat::Ident(ident) => ident,
            _ => panic!("Unexpected param type"),
        };

        Param {
            name: (&ident.ident).into(),
            ty: TypeName::from_syn(&t.ty, Some(self_path_type)),
        }
    }
}

/// The type of lifetime.
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum LifetimeKind {
    /// Param must live at least as long as the returned object.
    ReturnValue,
    /// Param must live for the duration of the program.
    Static,
}

#[derive(Default, Debug)]
/// Parameters in a method that might be borrowed in the return type.
#[non_exhaustive]
pub struct BorrowedParams<'a>(
    pub Option<&'a SelfParam>,
    pub Vec<(&'a Param, LifetimeKind)>,
);

impl BorrowedParams<'_> {
    /// Returns an [`Iterator`] through the names of the parameters that are borrowed
    /// for the lifetime of the return value, accepting an `Ident` that the `self`
    /// param will be called if present.
    pub fn return_names<'a>(&'a self, self_name: &'a Ident) -> impl Iterator<Item = &'a Ident> {
        self.0.iter().map(move |_| self_name).chain(
            self.1
                .iter()
                .filter(|(_, ltk)| (*ltk == LifetimeKind::ReturnValue))
                .map(|(param, _)| &param.name),
        )
    }

    /// Returns an [`Iterator`] through the names of the parameters that are borrowed for a
    /// static lifetime.
    pub fn static_names(&self) -> impl Iterator<Item = &'_ Ident> {
        self.1
            .iter()
            .filter(|(_, ltk)| (*ltk == LifetimeKind::Static))
            .map(|(param, _)| &param.name)
    }

    /// Returns `true` if a provided param name is included in the borrowed params,
    /// otherwise `false`.
    ///
    /// This method doesn't check the `self` parameter. Use
    /// [`BorrowedParams::borrows_self`] instead.
    pub fn contains(&self, param_name: &Ident) -> bool {
        self.1.iter().any(|(param, _)| &param.name == param_name)
    }

    /// Returns `true` if there are no borrowed parameters, otherwise `false`.
    pub fn is_empty(&self) -> bool {
        self.0.is_none() && self.1.is_empty()
    }

    /// Returns `true` if the `self` param is borrowed, otherwise `false`.
    pub fn borrows_self(&self) -> bool {
        self.0.is_some()
    }

    /// Returns `true` if there are any borrowed params, otherwise `false`.
    pub fn borrows_params(&self) -> bool {
        !self.1.is_empty()
    }

    /// Returns the number of borrowed params.
    pub fn len(&self) -> usize {
        self.1.len() + usize::from(self.0.is_some())
    }
}

#[cfg(test)]
mod tests {
    use insta;

    use syn;

    use crate::ast::{Attrs, Ident, Method, Path, PathType};

    #[test]
    fn static_methods() {
        insta::assert_yaml_snapshot!(Method::from_syn(
            &syn::parse_quote! {
                /// Some docs.
                #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
                fn foo(x: u64, y: MyCustomStruct) {

                }
            },
            PathType::new(Path::empty().sub_path(Ident::from("MyStructContainingMethod"))),
            None,
            &Attrs::default()
        ));

        insta::assert_yaml_snapshot!(Method::from_syn(
            &syn::parse_quote! {
                /// Some docs.
                /// Some more docs.
                ///
                /// Even more docs.
                #[diplomat::rust_link(foo::Bar::batz, FnInEnum)]
                fn foo(x: u64, y: MyCustomStruct) -> u64 {
                    x
                }
            },
            PathType::new(Path::empty().sub_path(Ident::from("MyStructContainingMethod"))),
            None,
            &Attrs::default()
        ));
    }

    #[test]
    fn cfged_method() {
        insta::assert_yaml_snapshot!(Method::from_syn(
            &syn::parse_quote! {
                /// Some docs.
                #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
                #[cfg(any(feature = "foo", not(feature = "bar")))]
                fn foo(x: u64, y: MyCustomStruct) {

                }
            },
            PathType::new(Path::empty().sub_path(Ident::from("MyStructContainingMethod"))),
            None,
            &Attrs::default()
        ));
    }

    #[test]
    fn nonstatic_methods() {
        insta::assert_yaml_snapshot!(Method::from_syn(
            &syn::parse_quote! {
                fn foo(&self, x: u64, y: MyCustomStruct) {

                }
            },
            PathType::new(Path::empty().sub_path(Ident::from("MyStructContainingMethod"))),
            None,
            &Attrs::default()
        ));

        insta::assert_yaml_snapshot!(Method::from_syn(
            &syn::parse_quote! {
                #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
                fn foo(&mut self, x: u64, y: MyCustomStruct) -> u64 {
                    x
                }
            },
            PathType::new(Path::empty().sub_path(Ident::from("MyStructContainingMethod"))),
            None,
            &Attrs::default()
        ));
    }

    macro_rules! assert_borrowed_params {
        ([$($return_param:ident),*] $(, [$($static_param:ident),*])? => $($tokens:tt)* ) => {{
            let method = Method::from_syn(
                &syn::parse_quote! { $($tokens)* },
                PathType::new(Path::empty().sub_path(Ident::from("MyStructContainingMethod"))),
                None,
                &Attrs::default()
            );

            let borrowed_params = method.borrowed_params();
            // The ident parser in syn doesn't allow `self`, so we use "this" as a placeholder
            // and then change it.
            let mut actual_return: Vec<&str> = borrowed_params.return_names(&Ident::THIS).map(|ident| ident.as_str()).collect();
            if borrowed_params.0.is_some() {
                actual_return[0] = "self";
            }
            let expected_return: &[&str] = &[$(stringify!($return_param)),*];
            assert_eq!(actual_return, expected_return);
            let actual_static: Vec<&str> = borrowed_params.static_names().map(|ident| ident.as_str()).collect();
            let expected_static: &[&str] = &[$($(stringify!($static_param)),*)?];
            assert_eq!(actual_static, expected_static);
        }};
    }

    #[test]
    fn static_params_held_by_return_type() {
        assert_borrowed_params! { [first, second] =>
            #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
            fn foo<'a, 'b>(first: &'a First, second: &'b Second, third: &Third) -> Foo<'a, 'b> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [hold] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn transitivity<'a, 'b: 'a, 'c: 'b, 'd: 'c, 'e: 'd, 'x>(hold: &'x One<'e>, nohold: &One<'x>) -> Box<Foo<'a>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [hold] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn a_le_b_and_b_le_a<'a: 'b, 'b: 'a>(hold: &'b Bar, nohold: &'c Bar) -> Box<Foo<'a>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [a, b, c, d] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn many_dependents<'a, 'b: 'a, 'c: 'a, 'd: 'b, 'x, 'y>(a: &'x One<'a>, b: &'b One<'a>, c: &Two<'x, 'c>, d: &'x Two<'d, 'y>, nohold: &'x Two<'x, 'y>) -> Box<Foo<'a>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [hold] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn return_outlives_param<'short, 'long: 'short>(hold: &Two<'long, 'short>, nohold: &'short One<'short>) -> Box<Foo<'long>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [hold] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn transitivity_deep_types<'a, 'b: 'a, 'c: 'b, 'd: 'c>(hold: Option<Box<Bar<'d>>>, nohold: &'a Box<Option<Baz<'a>>>) -> Result<Box<Foo<'b>>, Error> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [top, left, right, bottom] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn diamond_top<'top, 'left: 'top, 'right: 'top, 'bottom: 'left + 'right>(top: One<'top>, left: One<'left>, right: One<'right>, bottom: One<'bottom>) -> Box<Foo<'top>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [left, bottom] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn diamond_left<'top, 'left: 'top, 'right: 'top, 'bottom: 'left + 'right>(top: One<'top>, left: One<'left>, right: One<'right>, bottom: One<'bottom>) -> Box<Foo<'left>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [right, bottom] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn diamond_right<'top, 'left: 'top, 'right: 'top, 'bottom: 'left + 'right>(top: One<'top>, left: One<'left>, right: One<'right>, bottom: One<'bottom>) -> Box<Foo<'right>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [bottom] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn diamond_bottom<'top, 'left: 'top, 'right: 'top, 'bottom: 'left + 'right>(top: One<'top>, left: One<'left>, right: One<'right>, bottom: One<'bottom>) -> Box<Foo<'bottom>> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [a, b, c, d] =>
            #[diplomat::rust_link(Foo, FnInStruct)]
            fn diamond_and_nested_types<'a, 'b: 'a, 'c: 'b, 'd: 'b + 'c, 'x, 'y>(a: &'x One<'a>, b: &'y One<'b>, c: &One<'c>, d: &One<'d>, nohold: &One<'x>) -> Box<Foo<'a>> {
                unimplemented!()
            }
        }
    }

    #[test]
    fn nonstatic_params_held_by_return_type() {
        assert_borrowed_params! { [self] =>
            #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
            fn foo<'a>(&'a self) -> Foo<'a> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [self, foo, bar] =>
            #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
            fn foo<'x, 'y>(&'x self, foo: &'x Foo, bar: &Bar<'y>, baz: &Baz) -> Foo<'x, 'y> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [self, bar] =>
            #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
            fn foo<'a, 'b>(&'a self, bar: Bar<'b>) -> Foo<'a, 'b> {
                unimplemented!()
            }
        }

        assert_borrowed_params! { [self, bar], [baz] =>
            #[diplomat::rust_link(foo::Bar::batz, FnInStruct)]
            fn foo<'a, 'b>(&'a self, bar: Bar<'b>, baz: &'static str) -> Foo<'a, 'b, 'static> {
                unimplemented!()
            }
        }
    }
}