//! Support for decoding RPC Responses.

use std::sync::Arc;

use serde::{Deserialize, Serialize};

use super::{AnyRequestId, JsonAnyObj};

use crate::{

    conn::ErrorResponse,

    util::{Utf8CString, define_from_for_arc},

};

/// An unparsed and unvalidated response, as received from Arti.

///

/// (It will have no internal newlines, and a single NL at the end.)

#[derive(Clone, Debug, derive_more::AsRef)]

pub(crate) struct UnparsedResponse {

    /// The body of this response.

    msg: String,

}

impl UnparsedResponse {

    /// Construct a new UnparsedResponse.

}

/// A response that we have validated for correct syntax,

/// re-encoded in canonical form,

/// and enough to find the information we need about it

/// to deliver it to the application.

#[derive(Clone, Debug)]

pub(crate) struct ValidatedResponse {

    /// The re-encoded text of this response.

    pub(crate) msg: Utf8CString,

    /// The metadata from this response.

    pub(crate) meta: ResponseMeta,

}

/// An error that occurred when trying to decode an RPC response.

#[derive(Clone, Debug, thiserror::Error)]

#[non_exhaustive]

pub(crate) enum DecodeResponseError {

    /// We couldn't decode a response as json.

    #[error("Arti sent a message that didn't conform to the RPC protocol")]

    JsonProtocolViolation(#[source] Arc<serde_json::Error>),

    /// There was something (other than json encoding) wrong with a response.

    #[error("Arti sent a message that didn't conform to the RPC protocol: {0}")]

    ProtocolViolation(&'static str),

    /// We decoded the response, but rather than having an `id`,

    /// it had an error message from Arti with no id.  We treat this as fatal.

    #[error("Arti reported a fatal error: {0}")]

    Fatal(ErrorResponse),

}

define_from_for_arc!( serde_json::Error => DecodeResponseError [JsonProtocolViolation] );

impl UnparsedResponse {

    /// If this response is well-formed, and it corresponds to a single request,

    /// re-encode it and return it as a ValidatedResponse.

        // We're using serde_json::Value in order to preserve any unrecognized fields

        // in the response when we re-encode it.

        //

        // The alternative would be to preserve unrecognized fields using serde(flatten) and a

        // JsonMap in each struct.  But that creates a risk of forgetting to do so in some

        // struct that we create in the future.

            // (This should be impossible; serde_json rejects NULs.)

            Err(_) => {

            }

        };

    /// Return the inner `str` for this unparsed message.

}

impl ValidatedResponse {

    /// Return true if no additional response should arrive for this request.

        use ResponseKind as K;

        }

    /// Return the request ID associated with this response.

}

/// Metadata extracted from a response while decoding it.

#[derive(Clone, Debug)]

#[cfg_attr(test, derive(Eq, PartialEq))]

pub(crate) struct ResponseMeta {

    /// The request ID for this response.

    pub(crate) id: AnyRequestId,

    /// The kind of response that was received.

    pub(crate) kind: ResponseKind,

}

/// A kind of response received from Arti.

//

// TODO: Possibly unify or derive from ResponseMetaBodyDe?

#[derive(Clone, Debug, Eq, PartialEq)]

pub(crate) enum ResponseKind {

    /// Arti reports that an error has occurred.

    Error,

    /// Arti reports that the request completed successfully.

    Success,

    /// Arti reports an incremental update for the request.

    Update,

}

/// Serde-only type: decodes enough fields from a response in order to validate it

/// and route it to the application.

#[derive(Deserialize, Debug)]

struct Response {

    /// The request ID for this response.

    ///

    /// This field is mandatory for any non-Error response.

    id: Option<AnyRequestId>,

    /// The body as decoded for this response.

    #[serde(flatten)]

    body: ResponseBody,

}

/// Inner type to implement `Response``

#[derive(Deserialize, Debug)]

enum ResponseBody {

    /// Arti reports that an error has occurred.

    ///

    /// In this case, we decode the error to make sure it's well-formed.

    #[serde(rename = "error")]

    Error(RpcError),

    /// Arti reports that the request completed successfully.

    #[serde(rename = "result")]

    Success(JsonAnyObj),

    /// Arti reports an incremental update for the request.

    #[serde(rename = "update")]

    Update(JsonAnyObj),

}

impl<'a> From<&'a ResponseBody> for ResponseKind {

        use ResponseBody as RMB;

        use ResponseKind as RK;

        // TODO RPC: If we keep the current set of types,

        // we should have this discriminant code be macro-generated.

        }

}

/// Error returned from [`ResponseMeta::try_from_response`] when a response

/// has no Id field, and therefore indicates a fatal protocol error.

#[derive(thiserror::Error, Debug, Clone)]

#[error("Response was fatal (it had no ID)")]

struct ResponseWasFatal;

impl ResponseMeta {

    /// Try to extract a `ResponseMeta` from a response.

    ///

    /// Return `Err(ResponseWasFatal)` if the ID was missing on an error, and `Err(Err(_))` on any

    /// other problem.

        use DecodeResponseError as E;

        use ResponseBody as Body;

                // No ID, so this is a fatal response.

                // Re-encode the response.

            }

        }

}

/// Try to decode `s` as an error response, and return its error.

///

/// (Gives an error if this is not an error response)

//

// TODO RPC: Eventually we should try to refactor this out if we can; it is only called in one

// place.

    }

/// An error sent by Arti, decoded into its parts.

#[derive(Clone, Debug, Deserialize, Serialize)]

#[cfg_attr(test, derive(PartialEq, Eq))]

pub struct RpcError {

    /// A human-readable message from Arti.

    message: String,

    /// An error code representing the underlying problem.

    code: RpcErrorCode,

    /// One or more `ErrorKind`s, encoded as strings.

    kinds: Vec<String>,

}

impl RpcError {

    /// Return the human-readable message that Arti sent as part of this error.

    /// Return the numeric error code from this error.

    /// Return an iterator over the ErrorKinds for this error.

    //

    // Note: This is not a great API for FFI purposes.

    // But FFI code should get errors as a String, so that's probably fine.

}

caret::caret_int! {

    #[derive(serde::Deserialize, serde::Serialize)]

    pub struct RpcErrorCode(i32) {

        /// "The JSON sent is not a valid Request object."

        INVALID_REQUEST = -32600,

        /// "The method does not exist ."

        NO_SUCH_METHOD = -32601,

        /// "Invalid method parameter(s)."

        INVALID_PARAMS = -32602,

        /// "The server suffered some kind of internal problem"

        INTERNAL_ERROR = -32603,

        /// "Some requested object was not valid"

        OBJECT_ERROR = 1,

        /// "Some other error occurred"

        REQUEST_ERROR = 2,

        /// This method exists, but wasn't implemented on this object.

        METHOD_NOT_IMPL = 3,

    }

}

#[cfg(test)]

mod test {

    // @@ begin test lint list maintained by maint/add_warning @@

    #![allow(clippy::bool_assert_comparison)]

    #![allow(clippy::clone_on_copy)]

    #![allow(clippy::dbg_macro)]

    #![allow(clippy::mixed_attributes_style)]

    #![allow(clippy::print_stderr)]

    #![allow(clippy::print_stdout)]

    #![allow(clippy::single_char_pattern)]

    #![allow(clippy::unwrap_used)]

    #![allow(clippy::unchecked_time_subtraction)]

    #![allow(clippy::useless_vec)]

    #![allow(clippy::needless_pass_by_value)]

    #![allow(clippy::string_slice)] // See arti#2571

    //! <!-- @@ end test lint list maintained by maint/add_warning @@ -->

    use super::*;

    /// Helper: Decode a string into a Response, then convert it into

    /// a ResponseMeta.

    fn response_meta(s: &str) -> Result<ResponseMeta, DecodeResponseError> {

        match ResponseMeta::try_from_response(&serde_json::from_str::<Response>(s)?) {

            Ok(v) => v,

            Err(_) => {

                let utf8 = Utf8CString::try_from(s.to_string())

                    .map_err(|_| DecodeResponseError::ProtocolViolation("not utf8cstr?"))?;

                Err(DecodeResponseError::Fatal(

                    ErrorResponse::from_validated_string(utf8),

                ))

            }

        }

    }

    #[test]

    fn response_meta_good() {

        use ResponseKind as RK;

        use ResponseMeta as RM;

        for (s, expected) in [

            (

                r#"{"id":7, "result": {}}"#,

                RM {

                    id: 7.into(),

                    kind: RK::Success,

                },

            ),

            (

                r#"{"id":"hi", "update": {"here":["goes", "nothing"]}}"#,

                RM {

                    id: "hi".to_string().into(),

                    kind: RK::Update,

                },

            ),

            (

                r#"{"id": 6, "error": {"message":"iffy wobbler", "code":999, "kinds": ["BadVibes"]}}"#,

                RM {

                    id: 6.into(),

                    kind: RK::Error,

                },

            ),

            (

                r#"{"id": 6, "error": {"message":"iffy wobbler", "code":999, "kinds": ["BadVibes"], "data": {"a":"b"}}}"#,

                RM {

                    id: 6.into(),

                    kind: RK::Error,

                },

            ),

        ] {

            let got = response_meta(s).unwrap();

            assert_eq!(got, expected);

        }

    }

    #[test]

    fn response_meta_bad() {

        macro_rules! check_err {

            { $s:expr, $p:pat } => {

                let got_err = response_meta($s).unwrap_err();

                assert!(matches!(got_err, $p));

            }

        }

        use DecodeResponseError as E;

        // No ID; arti is saying we screwed up.

        check_err!(

            r#"{"error": {"message":"iffy wobbler", "code":999, "kinds": ["BadVibes"], "data": {"a":"b"}}}"#,

            E::Fatal(_)

        );

        // Missing ID on a success.

        check_err!(r#"{"result": {}}"#, E::ProtocolViolation(_));

        // Missing ID on an update.

        check_err!(r#"{"update": {}}"#, E::ProtocolViolation(_));

        // No recognized type.

        check_err!(r#"{"id": 7, "flupdate": {}}"#, E::JsonProtocolViolation(_));

        // Couldn't parse.

        check_err!(r#"{{{{{"#, E::JsonProtocolViolation(_));

        // Error is no good.

        check_err!(

            r#"{"id": 77 "error": {"message":"iffy wobbler"}}"#,

            E::JsonProtocolViolation(_)

        );

    }

    #[test]

    fn bad_json() {

        // we rely on the json parser rejecting some things.

        for s in [

            "{ ",         // not complete

            "",           // Empty.

            "{ \0 }",     // contains nul byte.

            "{ \"\0\" }", // string contains nul byte.

        ] {

            let r: Result<serde_json::Value, _> = serde_json::from_str(s);

            assert!(dbg!(r.err()).is_some());

        }

    }

    #[test]

    fn re_encode() {

        let response = r#"{

            "id": 6,

            "error": {

                "message":"iffy wobbler",

                "code":999,

                "kinds": ["BadVibes"],

                "data": {"a":"b"},

                "explosion": 22

             },

             "xyzzy":"plugh"

        }"#;

        let json_orig: serde_json::Value = serde_json::from_str(response).unwrap();

        let resp = UnparsedResponse::new(response.into());

        let valid = resp.try_validate().unwrap();

        let msg: &str = valid.msg.as_ref();

        let json_reencoded: serde_json::Value = serde_json::from_str(msg).unwrap();

        // To make sure all fields were preserved, we have to compare the json objects for equality;

        // we cannot rely on the order of the fields.

        assert_eq!(json_orig, json_reencoded);

    }

}