use syn;
use syn::*;
use quote::Tokens;

use ::util::*;


#[derive(Default, Debug)]
struct ObjAttrs {
    name: Option<String>,
    description: Option<String>,
}

impl ObjAttrs {
    fn from_input(input: &DeriveInput) -> ObjAttrs {
        let mut res = ObjAttrs::default();

        // Check attributes for name and description.
        if let Some(items) = get_graphl_attr(&input.attrs) {
            for item in items {
                if let Some(val) = keyed_item_value(item, "name", true) {
                    res.name = Some(val);
                    continue;
                }
                if let Some(val) = keyed_item_value(item, "description", true) {
                    res.description = Some(val);
                    continue;
                }
                panic!(format!(
                    "Unknown attribute for #[derive(GraphQLInputObject)]: {:?}",
                    item));
            }
        }
        res
    }
}

#[derive(Default)]
struct ObjFieldAttrs {
    name: Option<String>,
    description: Option<String>,
    default: Option<String>,
}

impl ObjFieldAttrs {
    fn from_input(variant: &Field) -> ObjFieldAttrs {
        let mut res = ObjFieldAttrs::default();

        // Check attributes for name and description.
        if let Some(items) = get_graphl_attr(&variant.attrs) {
            for item in items {
                if let Some(val) = keyed_item_value(item, "name", true) {
                    res.name = Some(val);
                    continue;
                }
                if let Some(val) = keyed_item_value(item, "description", true) {
                    res.description = Some(val);
                    continue;
                }
                if let Some(val) = keyed_item_value(item, "default", true) {
                    res.default = Some(val);
                    continue;
                }
                panic!(format!(
                    "Unknown attribute for #[derive(GraphQLInputObject)]: {:?}",
                    item));
            }
        }
        res
    }
}

pub fn impl_input_object(ast: &syn::DeriveInput) -> Tokens {
    let fields = match ast.body {
        Body::Struct(ref data) => {
            match data {
                &VariantData::Struct(ref fields) => fields,
                _ => {
                    panic!("#[derive(GraphQLInputObject)] may only be used on regular structs with fields");
                },
            }
        },
        Body::Enum(_) => {
            panic!("#[derive(GraphlQLInputObject)] may only be applied to structs, not to enums");
        },
    };

    // Parse attributes.
    let ident = &ast.ident;
    let attrs = ObjAttrs::from_input(ast);
    let name = attrs.name.unwrap_or(ast.ident.to_string());

    let mut meta_fields = Vec::<Tokens>::new();
    let mut from_inputs = Vec::<Tokens>::new();
    let mut to_inputs = Vec::<Tokens>::new();

    for field in fields {
        let field_ty = &field.ty;
        let field_attrs = ObjFieldAttrs::from_input(field);
        let field_ident = field.ident.as_ref().unwrap();

        // Build value.
        let name = match field_attrs.name {
            Some(ref name) => {
                // Custom name specified.
                name.to_string()
            },
            None => {
                // Note: auto camel casing when no custom name specified.
                ::util::to_camel_case(field_ident.as_ref())
            },
        };
        let descr = match field_attrs.description {
            Some(s) => quote!{ Some(#s.to_string())  },
            None => quote!{ None },
        };

        let default = match field_attrs.default {
            Some(ref def) => {
                match syn::parse_token_trees(def) {
                    Ok(t) => Some(quote!{ #(#t)* }),
                    Err(_) => {
                        panic!("#graphql(default = ?) must be a valid Rust expression inside a string");
                    },
                }
            },
            None => None,
        };

        let meta_field = match default {
            Some(ref def) => {
                quote!{
                    registry.arg_with_default::<#field_ty>( #name, &#def),
                }
            },
            None => {
                quote!{
                    registry.arg::<#field_ty>(#name),
                }
            }
        };
        meta_fields.push(meta_field);

        // Buil from_input clause.

        let from_input_default = match default {
            Some(ref def) => {
                quote!{
                    Some(&&::juniper::InputValue::Null) | None if true => #def,
                }
            },
            None => quote!{},
        };

        let from_input = quote!{
            #field_ident: {
                // TODO: investigate the unwraps here, they seem dangerous!
                match obj.get(#name) {
                    #from_input_default
                    Some(v) => ::juniper::FromInputValue::from(v).unwrap(),
                    _ => ::juniper::FromInputValue::from(&::juniper::InputValue::null()).unwrap()
                }
            },
        };
        from_inputs.push(from_input);

        // Build to_input clause.
        let to_input = quote!{
            (#name, self.#field_ident.to()),
        };
        to_inputs.push(to_input);
    }

    quote! {
        impl ::juniper::GraphQLType for #ident {
            type Context = ();

            fn name() -> Option<&'static str> {
                Some(#name)
            }

            fn meta<'r>(registry: &mut ::juniper::Registry<'r>) -> ::juniper::meta::MetaType<'r> {
                let fields = &[
                    #(#meta_fields)*
                ];
                registry.build_input_object_type::<#ident>(fields).into_meta()
            }
        }

        impl ::juniper::FromInputValue for #ident {
            fn from(value: &::juniper::InputValue) -> Option<#ident> {
                if let Some(obj) = value.to_object_value() {
                    let item = #ident {
                        #(#from_inputs)*
                    };
                    Some(item)
                }
                else {
                    None
                }
            }
        }

        impl ::juniper::ToInputValue for #ident {
            fn to(&self) -> ::juniper::InputValue {
                ::juniper::InputValue::object(vec![
                    #(#to_inputs)*
                ].into_iter().collect())
            }
        }
    }
}