affn-derive 0.1.4

use proc_macro2::TokenStream as TokenStream2;
use quote::quote;
use syn::{DeriveInput, Expr, Lit, Meta};

/// Attributes parsed from `#[frame(...)]`.
#[derive(Default)]
pub(crate) struct FrameAttributes {
    /// Custom frame name (defaults to struct name).
    pub name: Option<String>,
    /// Polar angle name for SphericalNaming (e.g., "dec", "lat", "alt").
    pub polar: Option<String>,
    /// Azimuthal angle name for SphericalNaming (e.g., "ra", "lon", "az").
    pub azimuth: Option<String>,
    /// Distance name for SphericalNaming (defaults to "distance").
    pub distance: Option<String>,
    /// Whether to generate inherent impls on Direction<F> and Position<C,F,U>.
    /// Only valid when the frame is defined in the same crate as Direction/Position.
    pub inherent: bool,
    /// Ellipsoid type name for HasEllipsoid impl (e.g., "Wgs84").
    pub ellipsoid: Option<syn::Ident>,
}

pub(crate) fn derive_reference_frame_impl(input: DeriveInput) -> syn::Result<TokenStream2> {
    let name = &input.ident;

    let attrs = parse_frame_attributes(&input)?;

    let name_expr = match &attrs.name {
        Some(custom_name) => quote! { #custom_name },
        None => {
            let name_str = name.to_string();
            quote! { #name_str }
        }
    };

    // Generate SphericalNaming impl (always) + inherent methods (when `inherent` flag set)
    let spherical_impl = match (&attrs.polar, &attrs.azimuth) {
        (Some(polar), Some(azimuth)) => {
            let distance = attrs.distance.as_deref().unwrap_or("distance");

            let polar_ident = syn::Ident::new(polar, proc_macro2::Span::call_site());
            let azimuth_ident = syn::Ident::new(azimuth, proc_macro2::Span::call_site());

            // SphericalNaming is always generated (trait impl, not inherent)
            let naming_impl = quote! {
                impl ::affn::frames::SphericalNaming for #name {
                    fn polar_name() -> &'static str {
                        #polar
                    }
                    fn azimuth_name() -> &'static str {
                        #azimuth
                    }
                    fn distance_name() -> &'static str {
                        #distance
                    }
                }
            };

            // Inherent impls: only generated when `inherent` flag is set.
            // These require Direction/Position to be in the same crate as the frame.
            let inherent_impl = if attrs.inherent {
                // Determine constructor parameter order:
                // IAU convention: polar first for alt/az, azimuth first for everything else
                let polar_first = polar == "alt";

                let (first_param, second_param) = if polar_first {
                    (&polar_ident, &azimuth_ident)
                } else {
                    (&azimuth_ident, &polar_ident)
                };

                // The core spherical constructors always take (polar, azimuth).
                let (polar_arg, azimuth_arg) = (&polar_ident, &azimuth_ident);

                let polar_doc = format!("Returns the {} angle in degrees.", polar);
                let azimuth_doc = format!("Returns the {} angle in degrees.", azimuth);
                let dir_new_doc = format!(
                    "Creates a new direction from {} and {} (canonicalized).",
                    first_param, second_param
                );
                let pos_new_doc = format!(
                    "Creates a new position from {}, {}, and distance (canonicalized).",
                    first_param, second_param
                );

                // Ellipsoidal getters: only for frames with an associated
                // ellipsoid.  We do NOT generate a constructor —
                // `ellipsoidal::Position` already has its own `new()`.
                let ellipsoidal_getters = if attrs.ellipsoid.is_some() {
                    let distance_ident = syn::Ident::new(distance, proc_macro2::Span::call_site());
                    let distance_doc = format!(
                        "Returns the {} (height above the reference ellipsoid).",
                        distance
                    );

                    quote! {
                        // ── EllipsoidalPosition<C, F, U>: inherent named getters ──

                        impl<C, U> ::affn::ellipsoidal::Position<C, #name, U>
                        where
                            C: ::affn::centers::ReferenceCenter,
                            U: ::qtty::length::LengthUnit,
                        {
                            #[doc = #polar_doc]
                            #[inline]
                            pub fn #polar_ident(&self) -> ::qtty::angular::Degrees {
                                self.lat
                            }

                            #[doc = #azimuth_doc]
                            #[inline]
                            pub fn #azimuth_ident(&self) -> ::qtty::angular::Degrees {
                                self.lon
                            }

                            #[doc = #distance_doc]
                            #[inline]
                            pub fn #distance_ident(&self) -> ::qtty::Quantity<U> {
                                self.height
                            }
                        }
                    }
                } else {
                    quote! {}
                };

                quote! {
                    // ── Direction<F>: inherent named constructor + getters ──

                    impl ::affn::spherical::Direction<#name> {
                        #[doc = #dir_new_doc]
                        #[inline]
                        pub fn new(
                            #first_param: ::qtty::angular::Degrees,
                            #second_param: ::qtty::angular::Degrees,
                        ) -> Self {
                            let (polar, azimuth) =
                                ::affn::spherical::canonicalize_polar_azimuth(#polar_arg, #azimuth_arg);
                            Self::new_unchecked(polar, azimuth)
                        }

                        #[doc = #polar_doc]
                        #[inline]
                        pub fn #polar_ident(&self) -> ::qtty::angular::Degrees {
                            self.polar
                        }

                        #[doc = #azimuth_doc]
                        #[inline]
                        pub fn #azimuth_ident(&self) -> ::qtty::angular::Degrees {
                            self.azimuth
                        }
                    }

                    // ── Position<C, F, U>: inherent named getters (any center) ──

                    impl<C, U> ::affn::spherical::Position<C, #name, U>
                    where
                        C: ::affn::centers::ReferenceCenter,
                        U: ::qtty::length::LengthUnit,
                    {
                        #[doc = #polar_doc]
                        #[inline]
                        pub fn #polar_ident(&self) -> ::qtty::angular::Degrees {
                            self.polar
                        }

                        #[doc = #azimuth_doc]
                        #[inline]
                        pub fn #azimuth_ident(&self) -> ::qtty::angular::Degrees {
                            self.azimuth
                        }
                    }

                    // ── Position<C, F, U>: named constructor (only Params = ()) ──

                    impl<C, U> ::affn::spherical::Position<C, #name, U>
                    where
                        C: ::affn::centers::ReferenceCenter<Params = ()>,
                        U: ::qtty::length::LengthUnit,
                    {
                        #[doc = #pos_new_doc]
                        #[inline]
                        pub fn new<T: Into<::qtty::Quantity<U>>>(
                            #first_param: ::qtty::angular::Degrees,
                            #second_param: ::qtty::angular::Degrees,
                            distance: T,
                        ) -> Self {
                            Self::new_with_params((), #polar_arg, #azimuth_arg, distance.into())
                        }
                    }

                    #ellipsoidal_getters
                }
            } else {
                quote! {}
            };

            quote! {
                #naming_impl
                #inherent_impl
            }
        }
        (Some(_), None) => {
            return Err(syn::Error::new_spanned(
                &input.ident,
                "`polar` attribute requires `azimuth` to also be specified",
            ));
        }
        (None, Some(_)) => {
            return Err(syn::Error::new_spanned(
                &input.ident,
                "`azimuth` attribute requires `polar` to also be specified",
            ));
        }
        (None, None) => quote! {},
    };

    // Generate HasEllipsoid impl when `ellipsoid = "..."` is specified
    let ellipsoid_impl = match &attrs.ellipsoid {
        Some(ellipsoid_ident) => quote! {
            impl ::affn::ellipsoid::HasEllipsoid for #name {
                type Ellipsoid = ::affn::ellipsoid::#ellipsoid_ident;
            }
        },
        None => quote! {},
    };

    // When SphericalNaming names are available, also override ReferenceFrame::spherical_names()
    // so that Display impls on spherical types can use domain names without requiring
    // a SphericalNaming bound.
    let spherical_names_method = match (&attrs.polar, &attrs.azimuth) {
        (Some(polar), Some(azimuth)) => {
            let distance = attrs.distance.as_deref().unwrap_or("distance");
            quote! {
                fn spherical_names() -> ::core::option::Option<(&'static str, &'static str, &'static str)> {
                    ::core::option::Option::Some((#polar, #azimuth, #distance))
                }
            }
        }
        _ => quote! {},
    };

    let expanded = quote! {
        impl ::affn::frames::ReferenceFrame for #name {
            fn frame_name() -> &'static str {
                #name_expr
            }
            #spherical_names_method
        }

        #spherical_impl
        #ellipsoid_impl
    };

    Ok(expanded)
}

pub(crate) fn parse_frame_attributes(input: &DeriveInput) -> syn::Result<FrameAttributes> {
    let mut attrs = FrameAttributes::default();

    for attr in &input.attrs {
        if attr.path().is_ident("frame") {
            let nested = attr.parse_args_with(
                syn::punctuated::Punctuated::<Meta, syn::Token![,]>::parse_terminated,
            )?;

            for meta in nested {
                match &meta {
                    Meta::Path(path) if path.is_ident("inherent") => {
                        attrs.inherent = true;
                    }
                    Meta::NameValue(nv) => {
                        let value_str = extract_string_literal(&nv.value)?;

                        if nv.path.is_ident("name") {
                            attrs.name = Some(value_str);
                        } else if nv.path.is_ident("polar") {
                            attrs.polar = Some(value_str);
                        } else if nv.path.is_ident("azimuth") {
                            attrs.azimuth = Some(value_str);
                        } else if nv.path.is_ident("distance") {
                            attrs.distance = Some(value_str);
                        } else if nv.path.is_ident("ellipsoid") {
                            attrs.ellipsoid =
                                Some(syn::Ident::new(&value_str, proc_macro2::Span::call_site()));
                        }
                    }
                    _ => {}
                }
            }
        }
    }

    Ok(attrs)
}

/// Extract a string literal from an expression, or return an error.
fn extract_string_literal(expr: &Expr) -> syn::Result<String> {
    if let Expr::Lit(expr_lit) = expr {
        if let Lit::Str(lit_str) = &expr_lit.lit {
            return Ok(lit_str.value());
        }
    }
    Err(syn::Error::new_spanned(expr, "expected string literal"))
}