use proc_macro::TokenStream;
use quote::quote;
use std::collections::HashSet;
use syn::spanned::Spanned;

pub fn derive_params(input: TokenStream) -> TokenStream {
    let ast = syn::parse_macro_input!(input as syn::DeriveInput);

    let struct_name = &ast.ident;
    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
    let fields = match ast.data {
        syn::Data::Struct(syn::DataStruct {
            fields: syn::Fields::Named(named_fields),
            ..
        }) => named_fields,
        _ => {
            return syn::Error::new(
                ast.span(),
                "Deriving Params is only supported on structs with named fields",
            )
            .to_compile_error()
            .into()
        }
    };

    // We only care about fields with `id`, `persist`, and `nested` attributes. For the `id` fields
    // we'll build a mapping function that creates a hashmap containing pointers to those
    // parameters. For the `persist` function we'll create functions that serialize and deserialize
    // those fields individually (so they can be added and removed independently of eachother) using
    // JSON. The `nested` fields should also implement the `Params` trait and their fields will be
    // inherited and added to this field's lists.
    let mut param_mapping_self_tokens = Vec::new();
    let mut field_serialize_tokens = Vec::new();
    let mut field_deserialize_tokens = Vec::new();
    let mut nested_params_field_idents: Vec<syn::Ident> = Vec::new();
    let mut nested_params_group_names: Vec<String> = Vec::new();

    // We'll also enforce that there are no duplicate keys at compile time
    // TODO: This doesn't work for nested fields since we don't know anything about the fields on
    //       the nested structs
    let mut param_ids = HashSet::new();
    let mut persist_ids = HashSet::new();
    for field in fields.named {
        let field_name = match &field.ident {
            Some(ident) => ident,
            _ => continue,
        };

        // These two attributes are mutually exclusive
        let mut id_attr: Option<String> = None;
        let mut persist_attr: Option<String> = None;
        // And the `#[nested = "..."]` attribute contains a group name we should use
        let mut nested_attr: Option<String> = None;
        for attr in &field.attrs {
            if attr.path.is_ident("id") {
                match attr.parse_meta() {
                    Ok(syn::Meta::NameValue(syn::MetaNameValue {
                        lit: syn::Lit::Str(s),
                        ..
                    })) => {
                        if id_attr.is_none() {
                            id_attr = Some(s.value());
                        } else {
                            return syn::Error::new(attr.span(), "Duplicate id attribute")
                                .to_compile_error()
                                .into();
                        }
                    }
                    _ => {
                        return syn::Error::new(
                            attr.span(),
                            "The id attribute should be a key-value pair with a string argument: #[id = \"foo_bar\"]",
                        )
                        .to_compile_error()
                        .into()
                    }
                };
            } else if attr.path.is_ident("persist") {
                match attr.parse_meta() {
                    Ok(syn::Meta::NameValue(syn::MetaNameValue {
                        lit: syn::Lit::Str(s),
                        ..
                    })) => {
                        if persist_attr.is_none() {
                            persist_attr = Some(s.value());
                        } else {
                            return syn::Error::new(attr.span(), "Duplicate persist attribute")
                                .to_compile_error()
                                .into();
                        }
                    }
                    _ => {
                        return syn::Error::new(
                            attr.span(),
                            "The persist attribute should be a key-value pair with a string argument: #[persist = \"foo_bar\"]",
                        )
                        .to_compile_error()
                        .into()
                    }
                };
            } else if attr.path.is_ident("nested") {
                match attr.parse_meta() {
                    Ok(syn::Meta::NameValue(syn::MetaNameValue {
                        lit: syn::Lit::Str(s),
                        ..
                    })) => {
                        let s = s.value();
                        if s.is_empty() {
                            return syn::Error::new(attr.span(), "Group names cannot be empty")
                                .to_compile_error()
                                .into();
                        } else if s.contains('/') {
                            return syn::Error::new(attr.span(), "Group names may not contain slashes")
                                .to_compile_error()
                                .into();
                        } else if nested_attr.is_some() {
                            return syn::Error::new(attr.span(), "Duplicate nested attribute")
                                .to_compile_error()
                                .into();
                        } else {
                            nested_attr = Some(s);
                        }
                    }
                    _ => {
                        return syn::Error::new(
                            attr.span(),
                            "The nested attribute should be a key-value pair with a string argument: #[nested = \"Group Name\"]",
                        )
                        .to_compile_error()
                        .into()
                    }
                };
            }
        }

        match (id_attr, persist_attr) {
            (Some(param_id), None) => {
                if !param_ids.insert(param_id.clone()) {
                    return syn::Error::new(
                        field.span(),
                        "Multiple fields with the same parameter ID found",
                    )
                    .to_compile_error()
                    .into();
                }

                // These are pairs of `(parameter_id, param_ptr, param_group)`. The specific
                // parameter types know how to convert themselves into the correct ParamPtr variant.
                // Top-level parameters have no group, and we'll prefix the group name specified in
                // the `#[nested = "..."]` attribute to fields coming from nested groups
                param_mapping_self_tokens.push(
                    quote! { (String::from(#param_id), self.#field_name.as_ptr(), String::new()) },
                );
            }
            (None, Some(persist_key)) => {
                if !persist_ids.insert(persist_key.clone()) {
                    return syn::Error::new(
                        field.span(),
                        "Multiple persisted fields with the same ID found",
                    )
                    .to_compile_error()
                    .into();
                }

                // We don't know anything about the field types, but because we can generate this
                // function we get type erasure for free since we only need to worry about byte
                // vectors
                field_serialize_tokens.push(quote! {
                    match ::nih_plug::param::internals::PersistentField::map(
                        &self.#field_name,
                        ::nih_plug::param::internals::serialize_field,
                    ) {
                        Ok(data) => {
                            serialized.insert(String::from(#persist_key), data);
                        }
                        Err(err) => {
                            ::nih_plug::nih_debug_assert_failure!(
                                "Could not serialize '{}': {}",
                                #persist_key,
                                err
                            )
                        }
                    };
                });
                field_deserialize_tokens.push(quote! {
                    #persist_key => {
                        match ::nih_plug::param::internals::deserialize_field(&data) {
                            Ok(deserialized) => {
                                ::nih_plug::param::internals::PersistentField::set(
                                    &self.#field_name,
                                    deserialized,
                                );
                            }
                            Err(err) => {
                                ::nih_plug::nih_debug_assert_failure!(
                                    "Could not deserialize '{}': {}",
                                    #persist_key,
                                    err
                                )
                            }
                        };
                    }
                });
            }
            (Some(_), Some(_)) => {
                return syn::Error::new(
                    field.span(),
                    "The id and persist attributes are mutually exclusive",
                )
                .to_compile_error()
                .into();
            }
            (None, None) => (),
        }

        if let Some(nested_group_name) = nested_attr {
            nested_params_field_idents.push(field_name.clone());
            // FIXME: Generate the insertion code here
            nested_params_group_names.push(nested_group_name);
        }
    }

    quote! {
        unsafe impl #impl_generics Params for #struct_name #ty_generics #where_clause {
            fn param_map(&self) -> Vec<(String, nih_plug::prelude::ParamPtr, String)> {
                // This may not be in scope otherwise, used to call .as_ptr()
                use ::nih_plug::param::Param;

                let mut param_map = vec![#(#param_mapping_self_tokens),*];

                let nested_params_fields: &[&dyn Params] = &[#(&self.#nested_params_field_idents),*];
                let nested_params_groups: &[String] = &[#(String::from(#nested_params_group_names)),*];
                for (nested_params, group_name) in
                    nested_params_fields.into_iter().zip(nested_params_groups)
                {
                    let nested_param_map = nested_params.param_map();
                    let prefixed_nested_param_map =
                        nested_param_map
                            .into_iter()
                            .map(|(param_id, param_ptr, nested_group_name)| {
                                (
                                    param_id,
                                    param_ptr,
                                    if nested_group_name.is_empty() {
                                        group_name.to_string()
                                    } else {
                                        format!("{}/{}", group_name, nested_group_name)
                                    }
                                )
                            });

                    param_map.extend(prefixed_nested_param_map);
                }

                param_map
            }

            fn serialize_fields(&self) -> ::std::collections::HashMap<String, String> {
                let mut serialized = ::std::collections::HashMap::new();
                #(#field_serialize_tokens)*

                let nested_params_fields: &[&dyn Params] = &[#(&self.#nested_params_field_idents),*];
                for nested_params in nested_params_fields {
                    serialized.extend(nested_params.serialize_fields());
                }

                serialized
            }

            fn deserialize_fields(&self, serialized: &::std::collections::HashMap<String, String>) {
                for (field_name, data) in serialized {
                    match field_name.as_str() {
                        #(#field_deserialize_tokens)*
                        _ => ::nih_plug::nih_debug_assert_failure!("Unknown serialized field name: {} (this may not be accurate)", field_name),
                    }
                }

                // FIXME: The above warning will course give false postiives when using nested
                //        parameter structs. An easy fix would be to use
                //        https://doc.rust-lang.org/std/collections/struct.HashMap.html#method.drain_filter
                //        once that gets stabilized.
                let nested_params_fields: &[&dyn Params] = &[#(&self.#nested_params_field_idents),*];
                for nested_params in nested_params_fields {
                    nested_params.deserialize_fields(serialized);
                }
            }
        }
    }
    .into()
}