/*
 *
 * Copyright 2015, Google Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
 *     * Neither the name of Google Inc. nor the names of its
 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

// The gRPC protocol is an RPC protocol on top of HTTP2.
//
// While the most common type of RPC receives only one request message and returns only one response
// message, the protocol also supports RPCs that return multiple individual messages in a streaming
// fashion, RPCs that accept a stream of request messages, or RPCs with both streaming requests and
// responses.
//
// Conceptually, each gRPC call consists of a bidirectional stream of binary messages, with RPCs of
// the "non-streaming type" sending only one message in the corresponding direction (the protocol
// doesn't make any distinction).
//
// Each RPC uses a different HTTP2 stream, and thus multiple simultaneous RPCs can be multiplexed
// transparently on the same TCP connection.

#import <Foundation/Foundation.h>
#import <RxLibrary/GRXWriter.h>

#pragma mark gRPC errors

// Domain of NSError objects produced by gRPC.
extern NSString *const kGRPCErrorDomain;

// gRPC error codes.
// Note that a few of these are never produced by the gRPC libraries, but are of general utility for
// server applications to produce.
typedef NS_ENUM(NSUInteger, GRPCErrorCode) {
  // The operation was cancelled (typically by the caller).
  GRPCErrorCodeCancelled = 1,

  // Unknown error. Errors raised by APIs that do not return enough error information may be
  // converted to this error.
  GRPCErrorCodeUnknown = 2,

  // The client specified an invalid argument. Note that this differs from FAILED_PRECONDITION.
  // INVALID_ARGUMENT indicates arguments that are problematic regardless of the state of the
  // server (e.g., a malformed file name).
  GRPCErrorCodeInvalidArgument = 3,

  // Deadline expired before operation could complete. For operations that change the state of the
  // server, this error may be returned even if the operation has completed successfully. For
  // example, a successful response from the server could have been delayed long enough for the
  // deadline to expire.
  GRPCErrorCodeDeadlineExceeded = 4,

  // Some requested entity (e.g., file or directory) was not found.
  GRPCErrorCodeNotFound = 5,

  // Some entity that we attempted to create (e.g., file or directory) already exists.
  GRPCErrorCodeAlreadyExists = 6,

  // The caller does not have permission to execute the specified operation. PERMISSION_DENIED isn't
  // used for rejections caused by exhausting some resource (RESOURCE_EXHAUSTED is used instead for
  // those errors). PERMISSION_DENIED doesn't indicate a failure to identify the caller
  // (UNAUTHENTICATED is used instead for those errors).
  GRPCErrorCodePermissionDenied = 7,

  // The request does not have valid authentication credentials for the operation (e.g. the caller's
  // identity can't be verified).
  GRPCErrorCodeUnauthenticated = 16,

  // Some resource has been exhausted, perhaps a per-user quota.
  GRPCErrorCodeResourceExhausted = 8,

  // The RPC was rejected because the server is not in a state required for the procedure's
  // execution. For example, a directory to be deleted may be non-empty, etc.
  // The client should not retry until the server state has been explicitly fixed (e.g. by
  // performing another RPC). The details depend on the service being called, and should be found in
  // the NSError's userInfo.
  GRPCErrorCodeFailedPrecondition = 9,

  // The RPC was aborted, typically due to a concurrency issue like sequencer check failures,
  // transaction aborts, etc. The client should retry at a higher-level (e.g., restarting a read-
  // modify-write sequence).
  GRPCErrorCodeAborted = 10,

  // The RPC was attempted past the valid range. E.g., enumerating past the end of a list.
  // Unlike INVALID_ARGUMENT, this error indicates a problem that may be fixed if the system state
  // changes. For example, an RPC to get elements of a list will generate INVALID_ARGUMENT if asked
  // to return the element at a negative index, but it will generate OUT_OF_RANGE if asked to return
  // the element at an index past the current size of the list.
  GRPCErrorCodeOutOfRange = 11,

  // The procedure is not implemented or not supported/enabled in this server.
  GRPCErrorCodeUnimplemented = 12,

  // Internal error. Means some invariant expected by the server application or the gRPC library has
  // been broken.
  GRPCErrorCodeInternal = 13,

  // The server is currently unavailable. This is most likely a transient condition and may be
  // corrected by retrying with a backoff.
  GRPCErrorCodeUnavailable = 14,

  // Unrecoverable data loss or corruption.
  GRPCErrorCodeDataLoss = 15,
};

// Keys used in |NSError|'s |userInfo| dictionary to store the response headers and trailers sent by
// the server.
extern id const kGRPCHeadersKey;
extern id const kGRPCTrailersKey;

#pragma mark GRPCCall

// The container of the request headers of an RPC conforms to this protocol, which is a subset of
// NSMutableDictionary's interface. It will become a NSMutableDictionary later on.
// The keys of this container are the header names, which per the HTTP standard are case-
// insensitive. They are stored in lowercase (which is how HTTP/2 mandates them on the wire), and
// can only consist of ASCII characters.
// A header value is a NSString object (with only ASCII characters), unless the header name has the
// suffix "-bin", in which case the value has to be a NSData object.
@protocol GRPCRequestHeaders <NSObject>

@property(nonatomic, readonly) NSUInteger count;

- (id)objectForKeyedSubscript:(NSString *)key;
- (void)setObject:(id)obj forKeyedSubscript:(NSString *)key;

- (void)removeAllObjects;
- (void)removeObjectForKey:(NSString *)key;

@end

// Represents a single gRPC remote call.
@interface GRPCCall : GRXWriter

// These HTTP headers will be passed to the server as part of this call. Each HTTP header is a
// name-value pair with string names and either string or binary values.
//
// The passed dictionary has to use NSString keys, corresponding to the header names. The value
// associated to each can be a NSString object or a NSData object. E.g.:
//
// call.requestHeaders = @{@"authorization": @"Bearer ..."};
//
// call.requestHeaders[@"my-header-bin"] = someData;
//
// After the call is started, trying to modify this property is an error.
//
// The property is initialized to an empty NSMutableDictionary.
@property(atomic, readonly) id<GRPCRequestHeaders> requestHeaders;

// This dictionary is populated with the HTTP headers received from the server. This happens before
// any response message is received from the server. It has the same structure as the request
// headers dictionary: Keys are NSString header names; names ending with the suffix "-bin" have a
// NSData value; the others have a NSString value.
//
// The value of this property is nil until all response headers are received, and will change before
// any of -writeValue: or -writesFinishedWithError: are sent to the writeable.
@property(atomic, readonly) NSDictionary *responseHeaders;

// Same as responseHeaders, but populated with the HTTP trailers received from the server before the
// call finishes.
//
// The value of this property is nil until all response trailers are received, and will change
// before -writesFinishedWithError: is sent to the writeable.
@property(atomic, readonly) NSDictionary *responseTrailers;

// The request writer has to write NSData objects into the provided Writeable. The server will
// receive each of those separately and in order as distinct messages.
// A gRPC call might not complete until the request writer finishes. On the other hand, the request
// finishing doesn't necessarily make the call to finish, as the server might continue sending
// messages to the response side of the call indefinitely (depending on the semantics of the
// specific remote method called).
// To finish a call right away, invoke cancel.
- (instancetype)initWithHost:(NSString *)host
                        path:(NSString *)path
              requestsWriter:(GRXWriter *)requestsWriter NS_DESIGNATED_INITIALIZER;

// Finishes the request side of this call, notifies the server that the RPC should be cancelled, and
// finishes the response side of the call with an error of code CANCELED.
- (void)cancel;

// TODO(jcanizales): Let specify a deadline. As a category of GRXWriter?
@end