// Copyright 2016 The Grin Developers
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! RESTful API server to easily expose services as RESTful JSON/HTTP endpoints.
//! Fairly constrained on what the service API must look like by design.
//!
//! To use it, just have your service(s) implement the ApiEndpoint trait and
//! register them on a ApiServer.

use std::error::Error;
use std::fmt::{self, Display, Debug, Formatter};
use std::io::Read;
use std::net::ToSocketAddrs;
use std::ops::Index;
use std::string::ToString;
use std::str::FromStr;

use iron::{Iron, Request, Response, IronResult, IronError, status, headers};
use iron::method::Method;
use iron::modifiers::Header;
use iron::middleware::Handler;
use router::Router;
use serde::{Serialize, Deserialize};
use serde_json;

/// Errors that can be returned by an ApiEndpoint implementation.
#[derive(Debug)]
pub enum ApiError {
	Internal(String),
	Argument(String),
}

impl Display for ApiError {
	fn fmt(&self, f: &mut Formatter) -> fmt::Result {
		match *self {
			ApiError::Argument(ref s) => write!(f, "Bad arguments: {}", s),
			ApiError::Internal(ref s) => write!(f, "Internal error: {}", s),
		}
	}
}

impl Error for ApiError {
	fn description(&self) -> &str {
		match *self {
			ApiError::Argument(_) => "Bad arguments.",
			ApiError::Internal(_) => "Internal error.",
		}
	}
}

impl From<ApiError> for IronError {
	fn from(e: ApiError) -> IronError {
		match e {
			ApiError::Argument(_) => IronError::new(e, status::Status::BadRequest),
			ApiError::Internal(_) => IronError::new(e, status::Status::InternalServerError),
		}
	}
}

pub type ApiResult<T> = ::std::result::Result<T, ApiError>;

/// Trait to implement to expose a service as a RESTful HTTP endpoint. Each
/// method corresponds to a specific relative URL and HTTP method following
/// basic REST principles:
///
/// * create: POST /
/// * get:    GET /:id
/// * update: PUT /:id
/// * delete: DELETE /:id
///
/// The methods method defines which operation the endpoint implements, they're
/// all optional by default. It also allows the framework to automatically
/// define the OPTIONS HTTP method.
///
/// The type accepted by create and update, and returned by get, must implement
/// the serde Serialize and Deserialize traits. The identifier type returned by
/// create and accepted by all other methods must have a string representation.
pub trait ApiEndpoint: Clone + Send + Sync + 'static {
	type ID: ToString + FromStr;
	type T: Serialize + Deserialize;

	fn methods(&self) -> Vec<Method>;

	#[allow(unused_variables)]
	fn create(&self, o: Self::T) -> ApiResult<Self::ID> {
		unimplemented!()
	}

	#[allow(unused_variables)]
	fn delete(&self, id: Self::ID) -> ApiResult<()> {
		unimplemented!()
	}

	#[allow(unused_variables)]
	fn update(&self, id: Self::ID, o: Self::T) -> ApiResult<()> {
		unimplemented!()
	}

	#[allow(unused_variables)]
	fn get(&self, id: Self::ID) -> ApiResult<Self::T> {
		unimplemented!()
	}
}

// Wrapper required to define the implementation below, Rust doesn't let us
// define the parametric implementation for trait from another crate.
struct ApiWrapper<E>(E);

impl<E> Handler for ApiWrapper<E>
	where E: ApiEndpoint,
	      <<E as ApiEndpoint>::ID as FromStr>::Err: Debug + Send + Error
{
	fn handle(&self, req: &mut Request) -> IronResult<Response> {
		match req.method {
			Method::Get => {
				let res = self.0.get(extract_param(req, "id")?)?;
				let res_json = serde_json::to_string(&res)
          .map_err(|e| IronError::new(e, status::InternalServerError))?;
				Ok(Response::with((status::Ok, res_json)))
			}
			Method::Put => {
				let id = extract_param(req, "id")?;
				let t: E::T = serde_json::from_reader(req.body.by_ref())
          .map_err(|e| IronError::new(e, status::BadRequest))?;
				self.0.update(id, t)?;
				Ok(Response::with(status::NoContent))
			}
			Method::Delete => {
				let id = extract_param(req, "id")?;
				self.0.delete(id)?;
				Ok(Response::with(status::NoContent))
			}
			Method::Post => {
				let t: E::T = serde_json::from_reader(req.body.by_ref())
          .map_err(|e| IronError::new(e, status::BadRequest))?;
				let id = self.0.create(t)?;
				Ok(Response::with((status::Created, id.to_string())))
			}
			_ => Ok(Response::with(status::MethodNotAllowed)),
		}
	}
}

fn extract_param<ID>(req: &mut Request, param: &'static str) -> IronResult<ID>
	where ID: ToString + FromStr,
	      <ID as FromStr>::Err: Debug + Send + Error + 'static
{

	let id = req.extensions.get::<Router>().unwrap().find(param).unwrap_or("");
	id.parse::<ID>().map_err(|e| IronError::new(e, status::BadRequest))
}

/// HTTP server allowing the registration of ApiEndpoint implementations.
pub struct ApiServer {
	root: String,
	router: Router,
}

impl ApiServer {
	/// Creates a new ApiServer that will serve ApiEndpoint implementations
	/// under the root URL.
	pub fn new(root: String) -> ApiServer {
		ApiServer {
			root: root,
			router: Router::new(),
		}
	}

	/// Starts the ApiServer at the provided address.
	pub fn start<A: ToSocketAddrs>(self, addr: A) -> Result<(), String> {
		Iron::new(self.router).http(addr).map(|_| ()).map_err(|e| e.to_string())
	}

	/// Register a new API endpoint, providing a relative URL for the new
	/// endpoint.
	pub fn register_endpoint<E>(&mut self, subpath: String, endpoint: E)
		where E: ApiEndpoint,
		      <<E as ApiEndpoint>::ID as FromStr>::Err: Debug + Send + Error
	{

		assert_eq!(subpath.chars().nth(0).unwrap(), '/');

		// declare a route for each method actually implemented by the endpoint
		let route_postfix = &subpath[1..];
		let root = self.root.clone() + &subpath;
		for m in endpoint.methods() {
			let full_path = match m {
				Method::Get => root.clone() + "/:id",
				Method::Put => root.clone() + "/:id",
				Method::Delete => root.clone() + "/:id",
				Method::Post => root.clone(),
				_ => panic!(format!("Unsupported method: {}.", m)),
			};
			self.router.route(m.clone(),
			                  full_path,
			                  ApiWrapper(endpoint.clone()),
			                  m.to_string() + "_" + route_postfix);
		}

		// support for the HTTP Options method by differentiating what's on the
		// root resource vs the id resource
		let (root_opts, sub_opts) = endpoint.methods().iter().fold((vec![], vec![]),
		                                                           |mut acc, m| {
			if *m == Method::Post {
				acc.0.push(m.clone());
			} else {
				acc.1.push(m.clone());
			}
			acc
		});
		self.router.options(root.clone(),
		                    move |_: &mut Request| {
			                    Ok(Response::with((status::Ok,
			                                       Header(headers::Allow(root_opts.clone())))))
			                   },
		                    "option_".to_string() + route_postfix);
		self.router.options(root.clone() + "/:id",
		                    move |_: &mut Request| {
			                    Ok(Response::with((status::Ok,
			                                       Header(headers::Allow(sub_opts.clone())))))
			                   },
		                    "option_id_".to_string() + route_postfix);
	}
}


#[cfg(test)]
mod test {
	use super::*;
	use rest::*;

	#[derive(Serialize, Deserialize)]
	pub struct Animal {
		name: String,
		legs: u32,
		lethal: bool,
	}

	#[derive(Clone)]
	pub struct TestApi;

	impl ApiEndpoint for TestApi {
		type ID = String;
		type T = Animal;

		fn methods(&self) -> Vec<Method> {
			vec![Method::Get]
		}

		fn get(&self, name: String) -> Result<Animal> {
			Ok(Animal {
				name: name,
				legs: 4,
				lethal: false,
			})
		}
	}

	#[test]
	fn req_chain_json() {
		let mut apis = ApiServer::new("/v1".to_string());
		apis.register_endpoint("/animal".to_string(), TestApi);
	}
}