//! RPC dispatcher.
use std::collections::HashMap;

use anyhow::{bail, Result};
use thiserror::Error;

use crate::{common::sgx::QuotePolicy, consensus::state::keymanager::Status as KeyManagerStatus};

use super::{
    context::Context,
    types::{Body, Kind, Request, Response},
};

/// Dispatch error.
#[derive(Error, Debug)]
enum DispatchError {
    #[error("method not found: {method:?}")]
    MethodNotFound { method: String },
    #[error("invalid RPC kind: {method:?} ({kind:?})")]
    InvalidRpcKind { method: String, kind: Kind },
}

/// RPC handler.
pub trait Handler {
    /// Returns the list of RPC methods supported by this handler.
    fn methods(&'static self) -> Vec<Method>;
}

/// Descriptor of a RPC API method.
#[derive(Clone, Debug)]
pub struct MethodDescriptor {
    /// Method name.
    pub name: String,
    /// Specifies which kind of RPC is allowed to call the method.
    pub kind: Kind,
}

/// Handler for a RPC method.
pub trait MethodHandler<Rq, Rsp> {
    /// Invoke the method implementation and return a response.
    fn handle(&self, ctx: &Context, request: &Rq) -> Result<Rsp>;
}

impl<Rq, Rsp, F> MethodHandler<Rq, Rsp> for F
where
    Rq: 'static,
    Rsp: 'static,
    F: Fn(&Context, &Rq) -> Result<Rsp> + 'static,
{
    fn handle(&self, ctx: &Context, request: &Rq) -> Result<Rsp> {
        (*self)(ctx, request)
    }
}

/// Dispatcher for a RPC method.
pub trait MethodHandlerDispatch {
    /// Get method descriptor.
    fn get_descriptor(&self) -> &MethodDescriptor;

    /// Dispatch request.
    fn dispatch(&self, ctx: &Context, request: Request) -> Result<Response>;
}

struct MethodHandlerDispatchImpl<Rq, Rsp> {
    /// Method descriptor.
    descriptor: MethodDescriptor,
    /// Method handler.
    handler: Box<dyn MethodHandler<Rq, Rsp> + Send + Sync>,
}

impl<Rq, Rsp> MethodHandlerDispatch for MethodHandlerDispatchImpl<Rq, Rsp>
where
    Rq: cbor::Decode + 'static,
    Rsp: cbor::Encode + 'static,
{
    fn get_descriptor(&self) -> &MethodDescriptor {
        &self.descriptor
    }

    fn dispatch(&self, ctx: &Context, request: Request) -> Result<Response> {
        let request = cbor::from_value(request.args)?;
        let response = self.handler.handle(ctx, &request)?;

        Ok(Response {
            body: Body::Success(cbor::to_value(response)),
        })
    }
}

/// RPC method dispatcher implementation.
pub struct Method {
    /// Method dispatcher.
    dispatcher: Box<dyn MethodHandlerDispatch + Send + Sync>,
}

impl Method {
    /// Create a new enclave method descriptor.
    pub fn new<Rq, Rsp, Handler>(method: MethodDescriptor, handler: Handler) -> Self
    where
        Rq: cbor::Decode + 'static,
        Rsp: cbor::Encode + 'static,
        Handler: MethodHandler<Rq, Rsp> + Send + Sync + 'static,
    {
        Method {
            dispatcher: Box::new(MethodHandlerDispatchImpl {
                descriptor: method,
                handler: Box::new(handler),
            }),
        }
    }

    /// Return method name.
    fn get_name(&self) -> &String {
        &self.dispatcher.get_descriptor().name
    }

    /// Return RPC call kind.
    fn get_kind(&self) -> Kind {
        self.dispatcher.get_descriptor().kind
    }

    /// Dispatch a request.
    fn dispatch(&self, ctx: &mut Context, request: Request) -> Result<Response> {
        self.dispatcher.dispatch(ctx, request)
    }
}

/// Key manager status update handler callback.
pub type KeyManagerStatusHandler = dyn Fn(KeyManagerStatus) + Send + Sync;
/// Key manager quote policy update handler callback.
pub type KeyManagerQuotePolicyHandler = dyn Fn(QuotePolicy) + Send + Sync;

/// RPC call dispatcher.
#[derive(Default)]
pub struct Dispatcher {
    /// Registered RPC methods.
    methods: HashMap<String, Method>,
    /// Registered key manager status handler.
    km_status_handler: Option<Box<KeyManagerStatusHandler>>,
    /// Registered key manager quote policy handler.
    km_quote_policy_handler: Option<Box<KeyManagerQuotePolicyHandler>>,
}

impl Dispatcher {
    /// Register a new method in the dispatcher.
    pub fn add_method(&mut self, method: Method) {
        self.methods.insert(method.get_name().clone(), method);
    }

    /// Register new methods in the dispatcher.
    pub fn add_methods(&mut self, methods: Vec<Method>) {
        for method in methods {
            self.add_method(method);
        }
    }

    /// Dispatch request.
    pub fn dispatch(&self, mut ctx: Context, request: Request, kind: Kind) -> Response {
        match self.dispatch_fallible(&mut ctx, request, kind) {
            Ok(response) => response,
            Err(error) => Response {
                body: Body::Error(format!("{error}")),
            },
        }
    }

    fn dispatch_fallible(
        &self,
        ctx: &mut Context,
        request: Request,
        kind: Kind,
    ) -> Result<Response> {
        let method = match self.methods.get(&request.method) {
            Some(method) => method,
            None => bail!(DispatchError::MethodNotFound {
                method: request.method,
            }),
        };

        if method.get_kind() != kind {
            bail!(DispatchError::InvalidRpcKind {
                method: request.method,
                kind,
            });
        };

        method.dispatch(ctx, request)
    }

    /// Handle key manager status update.
    pub fn handle_km_status_update(&self, status: KeyManagerStatus) {
        if let Some(handler) = self.km_status_handler.as_ref() {
            handler(status)
        }
    }

    /// Handle key manager quote policy update.
    pub fn handle_km_quote_policy_update(&self, policy: QuotePolicy) {
        if let Some(handler) = self.km_quote_policy_handler.as_ref() {
            handler(policy)
        }
    }

    /// Update key manager status update handler.
    pub fn set_keymanager_status_update_handler(
        &mut self,
        f: Option<Box<KeyManagerStatusHandler>>,
    ) {
        self.km_status_handler = f;
    }

    /// Update key manager quote policy update handler.
    pub fn set_keymanager_quote_policy_update_handler(
        &mut self,
        f: Option<Box<KeyManagerQuotePolicyHandler>>,
    ) {
        self.km_quote_policy_handler = f;
    }
}