path: root/ecs-macros/src/lib.rs

use std::path::PathBuf as FsPathBuf;

use proc_macro::TokenStream;
use quote::{quote, ToTokens};
use syn::spanned::Spanned;
use syn::{
    parse,
    Attribute,
    Generics,
    Ident,
    Item,
    ItemEnum,
    ItemStruct,
    ItemUnion,
    Path,
};
use toml::value::{Table as TomlTable, Value as TomlValue};

macro_rules! syn_path {
    ($first_segment: ident $(::$segment: ident)*) => {
        ::syn::Path {
            leading_colon: None,
            segments: ::syn::punctuated::Punctuated::from_iter([
                syn_path_segment!($first_segment),
                $(syn_path_segment!($segment),)*
            ])
        }
    };
}

macro_rules! syn_path_segment {
    ($segment: ident) => {
        ::syn::PathSegment {
            ident: ::proc_macro2::Ident::new(
                stringify!($segment),
                ::proc_macro2::Span::call_site(),
            ),
            arguments: ::syn::PathArguments::None,
        }
    };
}

#[proc_macro_derive(Component, attributes(component))]
pub fn component_derive(input: TokenStream) -> TokenStream
{
    let item: TypeItem = parse::<Item>(input).unwrap().try_into().unwrap();

    let item_ident = item.ident();

    let (impl_generics, type_generics, where_clause) = item.generics().split_for_impl();

    let ecs_path = find_engine_ecs_crate_path().unwrap_or_else(|| syn_path!(ecs));

    quote! {
        impl #impl_generics #ecs_path::component::Component for #item_ident #type_generics
        #where_clause
        {
            type Component = Self;

            type RefMut<'component> =
                #ecs_path::system::ComponentRefMut<'component, Self>;

            type Ref<'component> =
                #ecs_path::system::ComponentRef<'component, Self>;

            fn id(&self) -> #ecs_path::component::Id
            {
                #ecs_path::component::Id::of::<Self>()
            }

            fn as_any_mut(&mut self) -> &mut dyn std::any::Any
            {
                self
            }

            fn as_any(&self) -> &dyn std::any::Any
            {
                self
            }
        }

        impl #impl_generics #ecs_path::system::Input for #item_ident #type_generics
        #where_clause
        {
        }

        impl #impl_generics #ecs_path::type_name::TypeName for #item_ident #type_generics
        #where_clause
        {
            fn type_name(&self) -> &'static str
            {
                std::any::type_name::<Self>()
            }
        }
    }
    .into()
}

#[proc_macro_derive(Sole, attributes(sole))]
pub fn sole_derive(input: TokenStream) -> TokenStream
{
    let item: TypeItem = parse::<Item>(input).unwrap().try_into().unwrap();

    let item_ident = item.ident();

    let sole_attr = item.attribute::<SoleAttribute>("sole").unwrap_or_default();

    let drop_last = sole_attr.drop_last;

    let (impl_generics, type_generics, where_clause) = item.generics().split_for_impl();

    let ecs_path = find_engine_ecs_crate_path().unwrap_or_else(|| syn_path!(ecs));

    quote! {
        impl #impl_generics #ecs_path::sole::Sole for #item_ident #type_generics
        #where_clause
        {
            fn drop_last(&self) -> bool
            {
                #drop_last
            }

            fn as_any_mut(&mut self) -> &mut dyn std::any::Any
            {
                self
            }

            fn as_any(&self) -> &dyn std::any::Any
            {
                self
            }
        }

        impl #impl_generics #ecs_path::type_name::TypeName for #item_ident #type_generics
        #where_clause
        {
            fn type_name(&self) -> &'static str
            {
                std::any::type_name::<Self>()
            }
        }
    }
    .into()
}

trait FromAttribute: Sized
{
    fn from_attribute(attribute: &Attribute) -> Result<Self, syn::Error>;
}

enum TypeItem
{
    Struct(ItemStruct),
    Enum(ItemEnum),
    Union(ItemUnion),
}

impl TypeItem
{
    fn ident(&self) -> &Ident
    {
        match self {
            Self::Struct(struct_item) => &struct_item.ident,
            Self::Enum(enum_item) => &enum_item.ident,
            Self::Union(union_item) => &union_item.ident,
        }
    }

    fn attribute<Attr: FromAttribute>(&self, attr_ident: &str) -> Option<Attr>
    {
        let item_attrs = match &self {
            Self::Struct(struct_item) => &struct_item.attrs,
            &Self::Enum(enum_item) => &enum_item.attrs,
            &Self::Union(union_item) => &union_item.attrs,
        };

        let mut attr: Option<&Attribute> = None;

        for item_attr in item_attrs {
            if attr.is_some() {
                panic!("Expected only one {} attribute", attr_ident);
            }

            if item_attr.path().get_ident()? == attr_ident {
                attr = Some(item_attr);
            }
        }

        Some(Attr::from_attribute(attr?).unwrap())
    }

    fn generics(&self) -> &Generics
    {
        match self {
            Self::Struct(struct_item) => &struct_item.generics,
            Self::Enum(enum_item) => &enum_item.generics,
            Self::Union(union_item) => &union_item.generics,
        }
    }
}

impl TryFrom<Item> for TypeItem
{
    type Error = syn::Error;

    fn try_from(item: Item) -> Result<Self, Self::Error>
    {
        match item {
            Item::Struct(struct_item) => Ok(Self::Struct(struct_item)),
            Item::Enum(enum_item) => Ok(Self::Enum(enum_item)),
            Item::Union(union_item) => Ok(Self::Union(union_item)),
            _ => Err(syn::Error::new(
                item.span(),
                "Expected a struct, a enum or a union",
            )),
        }
    }
}

impl ToTokens for TypeItem
{
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream)
    {
        match self {
            Self::Struct(struct_item) => struct_item.to_tokens(tokens),
            Self::Enum(enum_item) => enum_item.to_tokens(tokens),
            Self::Union(union_item) => union_item.to_tokens(tokens),
        }
    }
}

#[derive(Debug, Default)]
struct SoleAttribute
{
    drop_last: bool,
}

impl FromAttribute for SoleAttribute
{
    fn from_attribute(attribute: &Attribute) -> Result<Self, syn::Error>
    {
        let mut drop_last = false;

        attribute.parse_nested_meta(|meta| {
            if meta
                .path
                .get_ident()
                .is_some_and(|flag| flag == "drop_last")
            {
                drop_last = true;

                return Ok(());
            }

            Err(meta.error("Unrecognized token"))
        })?;

        Ok(Self { drop_last })
    }
}

fn find_engine_ecs_crate_path() -> Option<Path>
{
    let cargo_manifest_dir = FsPathBuf::from(std::env::var("CARGO_MANIFEST_DIR").ok()?);

    let crate_manifest = std::fs::read_to_string(cargo_manifest_dir.join("Cargo.toml"))
        .ok()?
        .parse::<TomlTable>()
        .expect("Failed to parse crate manifest file");

    let crate_dependencies = match crate_manifest.get("dependencies")? {
        TomlValue::Table(dependencies) => Some(dependencies),
        _ => None,
    }?;

    crate_dependencies.iter().find_map(|(crate_dep_name, _)| {
        if crate_dep_name == "engine" {
            return Some(syn_path!(engine::ecs));
        }

        None
    })
}