use crate::parsing::{Implementation, ParsedField, ParsedNodeFn};

use proc_macro_error2::emit_error;
use quote::quote;
use syn::{spanned::Spanned, GenericParam, Type};

pub fn validate_node_fn(parsed: &ParsedNodeFn) -> syn::Result<()> {
	let validators: &[fn(&ParsedNodeFn)] = &[
		// Add more validators here as needed
		validate_implementations_for_generics,
		validate_primary_input_expose,
	];

	for validator in validators {
		validator(parsed);
	}

	Ok(())
}

fn validate_primary_input_expose(parsed: &ParsedNodeFn) {
	if let Some(ParsedField::Regular { exposed: true, pat_ident, .. }) = parsed.fields.first() {
		emit_error!(
			pat_ident.span(),
			"Unnecessary #[expose] attribute on primary input `{}`. Primary inputs are always exposed.",
			pat_ident.ident;
			help = "You can safely remove the #[expose] attribute from this field.";
			note = "The function's second argument, `{}`, is the node's primary input and it's always exposed by default", pat_ident.ident
		);
	}
}

fn validate_implementations_for_generics(parsed: &ParsedNodeFn) {
	let has_skip_impl = parsed.attributes.skip_impl;

	if !has_skip_impl && !parsed.fn_generics.is_empty() {
		for field in &parsed.fields {
			match field {
				ParsedField::Regular { ty, implementations, pat_ident, .. } => {
					if contains_generic_param(ty, &parsed.fn_generics) && implementations.is_empty() {
						emit_error!(
							ty.span(),
							"Generic type `{}` in field `{}` requires an #[implementations(...)] attribute",
							quote!(#ty),
							pat_ident.ident;
							help = "Add #[implementations(ConcreteType1, ConcreteType2)] to field '{}'", pat_ident.ident;
							help = "Or use #[skip_impl] if you want to manually implement the node"
						);
					}
				}
				ParsedField::Node {
					input_type,
					output_type,
					implementations,
					pat_ident,
					..
				} => {
					if (contains_generic_param(input_type, &parsed.fn_generics) || contains_generic_param(output_type, &parsed.fn_generics)) && implementations.is_empty() {
						emit_error!(
							pat_ident.span(),
							"Generic types in Node field `{}` require an #[implementations(...)] attribute",
							pat_ident.ident;
							help = "Add #[implementations(InputType1 -> OutputType1, InputType2 -> OutputType2)] to field '{}'", pat_ident.ident;
							help = "Or use #[skip_impl] if you want to manually implement the node"
						);
					}
					// Additional check for Node implementations
					for impl_ in implementations {
						validate_node_implementation(impl_, input_type, output_type, &parsed.fn_generics);
					}
				}
			}
		}
	}
}

fn validate_node_implementation(impl_: &Implementation, input_type: &Type, output_type: &Type, fn_generics: &[GenericParam]) {
	if contains_generic_param(&impl_.input, fn_generics) || contains_generic_param(&impl_.output, fn_generics) {
		emit_error!(
			impl_.input.span(),
			"Implementation types `{}` and `{}` must be concrete, not generic",
			quote!(#input_type), quote!(#output_type);
			help = "Replace generic types with concrete types in the implementation"
		);
	}
}

fn contains_generic_param(ty: &Type, fn_generics: &[GenericParam]) -> bool {
	struct GenericParamChecker<'a> {
		fn_generics: &'a [GenericParam],
		found: bool,
	}

	impl<'a> syn::visit::Visit<'a> for GenericParamChecker<'a> {
		fn visit_ident(&mut self, ident: &'a syn::Ident) {
			if self
				.fn_generics
				.iter()
				.any(|param| if let GenericParam::Type(type_param) = param { type_param.ident == *ident } else { false })
			{
				self.found = true;
			}
		}
	}

	let mut checker = GenericParamChecker { fn_generics, found: false };
	syn::visit::visit_type(&mut checker, ty);
	checker.found
}