//! Details of the `ruma_api` procedural macro.

use proc_macro2::{Span, TokenStream};
use quote::{quote, ToTokens};
use syn::{
    braced,
    parse::{Parse, ParseStream, Result},
    Field, FieldValue, Ident, Meta, Token,
};

mod attribute;
mod metadata;
mod request;
mod response;

use self::{metadata::Metadata, request::Request, response::Response};

/// Removes `serde` attributes from struct fields.
pub fn strip_serde_attrs(field: &Field) -> Field {
    let mut field = field.clone();

    field.attrs = field
        .attrs
        .into_iter()
        .filter(|attr| {
            let meta = attr
                .interpret_meta()
                .expect("ruma_api! could not parse field attributes");

            let meta_list = match meta {
                Meta::List(meta_list) => meta_list,
                _ => return true,
            };

            if &meta_list.ident.to_string() == "serde" {
                return false;
            }

            true
        })
        .collect();

    field
}

/// The result of processing the `ruma_api` macro, ready for output back to source code.
pub struct Api {
    /// The `metadata` section of the macro.
    metadata: Metadata,
    /// The `request` section of the macro.
    request: Request,
    /// The `response` section of the macro.
    response: Response,
}

impl From<RawApi> for Api {
    fn from(raw_api: RawApi) -> Self {
        Self {
            metadata: raw_api.metadata.into(),
            request: raw_api.request.into(),
            response: raw_api.response.into(),
        }
    }
}

impl ToTokens for Api {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let description = &self.metadata.description;
        let method = &self.metadata.method;
        // We don't (currently) use this literal as a literal in the generated code. Instead we just
        // put it into doc comments, for which the span information is irrelevant. So we can work
        // with only the literal's value from here on.
        let name = &self.metadata.name.value();
        let path = &self.metadata.path;
        let rate_limited = &self.metadata.rate_limited;
        let requires_authentication = &self.metadata.requires_authentication;

        let request = &self.request;
        let request_types = quote! { #request };
        let response = &self.response;
        let response_types = quote! { #response };

        let extract_request_path = if self.request.has_path_fields() {
            quote! {
                let path_segments: Vec<&str> = request.uri().path()[1..].split('/').collect();
            }
        } else {
            TokenStream::new()
        };

        let (set_request_path, parse_request_path) = if self.request.has_path_fields() {
            let path_str = path.value();

            assert!(path_str.starts_with('/'), "path needs to start with '/'");
            assert!(
                path_str.chars().filter(|c| *c == ':').count() == self.request.path_field_count(),
                "number of declared path parameters needs to match amount of placeholders in path"
            );

            let request_path_init_fields = self.request.request_path_init_fields();

            let path_segments = path_str[1..].split('/');
            let path_segment_push = path_segments.clone().map(|segment| {
                let arg = if segment.starts_with(':') {
                    let path_var = &segment[1..];
                    let path_var_ident = Ident::new(path_var, Span::call_site());
                    quote!(&request_path.#path_var_ident.to_string())
                } else {
                    quote!(#segment)
                };

                quote! {
                    path_segments.push(#arg);
                }
            });

            let set_tokens = quote! {
                let request_path = RequestPath {
                    #request_path_init_fields
                };

                // This `unwrap()` can only fail when the url is a
                // cannot-be-base url like `mailto:` or `data:`, which is not
                // the case for our placeholder url.
                let mut path_segments = url.path_segments_mut().unwrap();
                #(#path_segment_push)*
            };

            let path_fields = path_segments
                .enumerate()
                .filter(|(_, s)| s.starts_with(':'))
                .map(|(i, segment)| {
                    let path_var = &segment[1..];
                    let path_var_ident = Ident::new(path_var, Span::call_site());
                    let path_field = self
                        .request
                        .path_field(path_var)
                        .expect("expected request to have path field");
                    let ty = &path_field.ty;

                    quote! {
                        #path_var_ident: {
                            let segment = path_segments.get(#i).unwrap().as_bytes();
                            let decoded =
                                ::url::percent_encoding::percent_decode(segment)
                                .decode_utf8_lossy();
                            #ty::deserialize(decoded.into_deserializer())
                                .map_err(|e: ::serde_json::error::Error| e)?
                        }
                    }
                });

            let parse_tokens = quote! {
                #(#path_fields,)*
            };

            (set_tokens, parse_tokens)
        } else {
            let set_tokens = quote! {
                url.set_path(metadata.path);
            };
            let parse_tokens = TokenStream::new();
            (set_tokens, parse_tokens)
        };

        let set_request_query = if self.request.has_query_fields() {
            let request_query_init_fields = self.request.request_query_init_fields();

            quote! {
                let request_query = RequestQuery {
                    #request_query_init_fields
                };

                url.set_query(Some(&::serde_urlencoded::to_string(request_query)?));
            }
        } else {
            TokenStream::new()
        };

        let extract_request_query = if self.request.has_query_fields() {
            quote! {
                let request_query: RequestQuery =
                    ::serde_urlencoded::from_str(&request.uri().query().unwrap_or(""))?;
            }
        } else {
            TokenStream::new()
        };

        let parse_request_query = if self.request.has_query_fields() {
            self.request.request_init_query_fields()
        } else {
            TokenStream::new()
        };

        let add_headers_to_request = if self.request.has_header_fields() {
            let add_headers = self.request.add_headers_to_request();
            quote! {
                let headers = http_request.headers_mut();
                #add_headers
            }
        } else {
            TokenStream::new()
        };

        let extract_request_headers = if self.request.has_header_fields() {
            quote! {
                let headers = request.headers();
            }
        } else {
            TokenStream::new()
        };

        let parse_request_headers = if self.request.has_header_fields() {
            self.request.parse_headers_from_request()
        } else {
            TokenStream::new()
        };

        let create_http_request = if let Some(field) = self.request.newtype_body_field() {
            let field_name = field
                .ident
                .as_ref()
                .expect("expected field to have an identifier");

            quote! {
                let request_body = RequestBody(request.#field_name);

                let mut http_request = ::http::Request::new(::serde_json::to_vec(&request_body)?);
            }
        } else if self.request.has_body_fields() {
            let request_body_init_fields = self.request.request_body_init_fields();

            quote! {
                let request_body = RequestBody {
                    #request_body_init_fields
                };

                let mut http_request = ::http::Request::new(::serde_json::to_vec(&request_body)?);
            }
        } else {
            quote! {
                let mut http_request = ::http::Request::new(Vec::new());
            }
        };

        let extract_request_body = if let Some(field) = self.request.newtype_body_field() {
            let ty = &field.ty;
            quote! {
                let request_body: #ty =
                    ::serde_json::from_slice(request.body().as_slice())?;
            }
        } else if self.request.has_body_fields() {
            quote! {
                let request_body: RequestBody =
                    ::serde_json::from_slice(request.body().as_slice())?;
            }
        } else {
            TokenStream::new()
        };

        let parse_request_body = if let Some(field) = self.request.newtype_body_field() {
            let field_name = field
                .ident
                .as_ref()
                .expect("expected field to have an identifier");

            quote! {
                #field_name: request_body,
            }
        } else if self.request.has_body_fields() {
            self.request.request_init_body_fields()
        } else {
            TokenStream::new()
        };

        let try_deserialize_response_body = if let Some(field) = self.response.newtype_body_field()
        {
            let field_type = &field.ty;

            quote! {
                ::serde_json::from_slice::<#field_type>(http_response.into_body().as_slice())?
            }
        } else if self.response.has_body_fields() {
            quote! {
                ::serde_json::from_slice::<ResponseBody>(http_response.into_body().as_slice())?
            }
        } else {
            quote! {
                ()
            }
        };

        let extract_response_headers = if self.response.has_header_fields() {
            quote! {
                let mut headers = http_response.headers().clone();
            }
        } else {
            TokenStream::new()
        };

        let response_init_fields = if self.response.has_fields() {
            self.response.init_fields()
        } else {
            TokenStream::new()
        };

        let serialize_response_headers = self.response.apply_header_fields();

        let try_serialize_response_body = if self.response.has_body() {
            let body = self.response.to_body();
            quote! {
                ::serde_json::to_vec(&#body)?
            }
        } else {
            quote! {
                "{}".as_bytes().to_vec()
            }
        };

        let endpoint_doc = format!("The `{}` API endpoint.\n\n{}", name, description.value());
        let request_doc = format!("Data for a request to the `{}` API endpoint.", name);
        let response_doc = format!("Data in the response from the `{}` API endpoint.", name);

        let api = quote! {
            use ::ruma_api::Endpoint as _;
            use ::serde::Deserialize as _;
            use ::serde::de::{Error as _, IntoDeserializer as _};

            use ::std::convert::{TryInto as _};

            #[doc = #endpoint_doc]
            #[derive(Debug)]
            pub struct Endpoint;

            #[doc = #request_doc]
            #request_types

            impl ::std::convert::TryFrom<::http::Request<Vec<u8>>> for Request {
                type Error = ::ruma_api::Error;

                #[allow(unused_variables)]
                fn try_from(request: ::http::Request<Vec<u8>>) -> Result<Self, Self::Error> {
                    #extract_request_path
                    #extract_request_query
                    #extract_request_headers
                    #extract_request_body

                    Ok(Request {
                        #parse_request_path
                        #parse_request_query
                        #parse_request_headers
                        #parse_request_body
                    })
                }
            }

            impl ::std::convert::TryFrom<Request> for ::http::Request<Vec<u8>> {
                type Error = ::ruma_api::Error;

                #[allow(unused_mut, unused_variables)]
                fn try_from(request: Request) -> Result<Self, Self::Error> {
                    let metadata = Endpoint::METADATA;

                    // Use dummy homeserver url which has to be overwritten in
                    // the calling code. Previously (with http::Uri) this was
                    // not required, but Url::parse only accepts absolute urls.
                    let mut url = ::url::Url::parse("http://invalid-host-please-change/").unwrap();

                    { #set_request_path }
                    { #set_request_query }

                    #create_http_request

                    *http_request.method_mut() = ::http::Method::#method;
                    *http_request.uri_mut() = url.into_string().parse().unwrap();

                    { #add_headers_to_request }

                    Ok(http_request)
                }
            }

            #[doc = #response_doc]
            #response_types

            impl ::std::convert::TryFrom<Response> for ::http::Response<Vec<u8>> {
                type Error = ::ruma_api::Error;

                #[allow(unused_variables)]
                fn try_from(response: Response) -> Result<Self, Self::Error> {
                    let response = ::http::Response::builder()
                        .header(::http::header::CONTENT_TYPE, "application/json")
                        #serialize_response_headers
                        .body(#try_serialize_response_body)
                        .unwrap();
                    Ok(response)
                }
            }

            impl ::std::convert::TryFrom<::http::Response<Vec<u8>>> for Response {
                type Error = ::ruma_api::Error;

                #[allow(unused_variables)]
                fn try_from(http_response: ::http::Response<Vec<u8>>) -> Result<Self, Self::Error> {
                    if http_response.status().is_success() {
                        #extract_response_headers

                        let response_body = #try_deserialize_response_body;
                        Ok(Response {
                            #response_init_fields
                        })
                    } else {
                        Err(http_response.status().clone().into())
                    }
                }
            }

            impl ::ruma_api::Endpoint for Endpoint {
                type Request = Request;
                type Response = Response;

                /// Metadata for the `#name` endpoint.
                const METADATA: ::ruma_api::Metadata = ::ruma_api::Metadata {
                    description: #description,
                    method: ::http::Method::#method,
                    name: #name,
                    path: #path,
                    rate_limited: #rate_limited,
                    requires_authentication: #requires_authentication,
                };
            }
        };

        api.to_tokens(tokens);
    }
}

/// Custom keyword macros for syn.
mod kw {
    use syn::custom_keyword;

    custom_keyword!(metadata);
    custom_keyword!(request);
    custom_keyword!(response);
}

/// The entire `ruma_api!` macro structure directly as it appears in the source code..
pub struct RawApi {
    /// The `metadata` section of the macro.
    pub metadata: Vec<FieldValue>,
    /// The `request` section of the macro.
    pub request: Vec<Field>,
    /// The `response` section of the macro.
    pub response: Vec<Field>,
}

impl Parse for RawApi {
    fn parse(input: ParseStream<'_>) -> Result<Self> {
        input.parse::<kw::metadata>()?;
        let metadata;
        braced!(metadata in input);

        input.parse::<kw::request>()?;
        let request;
        braced!(request in input);

        input.parse::<kw::response>()?;
        let response;
        braced!(response in input);

        Ok(Self {
            metadata: metadata
                .parse_terminated::<FieldValue, Token![,]>(FieldValue::parse)?
                .into_iter()
                .collect(),
            request: request
                .parse_terminated::<Field, Token![,]>(Field::parse_named)?
                .into_iter()
                .collect(),
            response: response
                .parse_terminated::<Field, Token![,]>(Field::parse_named)?
                .into_iter()
                .collect(),
        })
    }
}