/*
 *
 * Copyright 2015 gRPC authors.
 *
 * 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.
 *
 */

#import "GRPCHost.h"

#include <grpc/grpc.h>
#include <grpc/grpc_security.h>
#import <GRPCClient/GRPCCall.h>
#ifdef GRPC_COMPILE_WITH_CRONET
#import <GRPCClient/GRPCCall+ChannelArg.h>
#import <GRPCClient/GRPCCall+Cronet.h>
#endif

#import "GRPCChannel.h"
#import "GRPCCompletionQueue.h"
#import "GRPCConnectivityMonitor.h"
#import "NSDictionary+GRPC.h"
#import "version.h"

NS_ASSUME_NONNULL_BEGIN

static NSMutableDictionary *kHostCache;

// This connectivity monitor flushes the host cache when connectivity status
// changes or when connection switch between Wifi and Cellular data, so that a
// new call will use a new channel. Otherwise, a new call will still use the
// cached channel which is no longer available and will cause gRPC to hang.
static GRPCConnectivityMonitor *connectivityMonitor = nil;

@implementation GRPCHost {
  // TODO(mlumish): Investigate whether caching channels with strong links is a good idea.
  GRPCChannel *_channel;
}

+ (nullable instancetype)hostWithAddress:(NSString *)address {
  return [[self alloc] initWithAddress:address];
}

- (void)dealloc {
  if (_channelCreds != nil) {
    grpc_channel_credentials_release(_channelCreds);
  }
}

// Default initializer.
- (nullable instancetype)initWithAddress:(NSString *)address {
  if (!address) {
    return nil;
  }

  // To provide a default port, we try to interpret the address. If it's just a host name without
  // scheme and without port, we'll use port 443. If it has a scheme, we pass it untouched to the C
  // gRPC library.
  // TODO(jcanizales): Add unit tests for the types of addresses we want to let pass untouched.
  NSURL *hostURL = [NSURL URLWithString:[@"https://" stringByAppendingString:address]];
  if (hostURL.host && !hostURL.port) {
    address = [hostURL.host stringByAppendingString:@":443"];
  }

  // Look up the GRPCHost in the cache.
  static dispatch_once_t cacheInitialization;
  dispatch_once(&cacheInitialization, ^{
    kHostCache = [NSMutableDictionary dictionary];
  });
  @synchronized(kHostCache) {
    GRPCHost *cachedHost = kHostCache[address];
    if (cachedHost) {
      return cachedHost;
    }

    if ((self = [super init])) {
      _address = address;
      _secure = YES;
      kHostCache[address] = self;
    }
    // Keep a single monitor to flush the cache if the connectivity status changes
    // Thread safety guarded by @synchronized(kHostCache)
    if (!connectivityMonitor) {
      connectivityMonitor =
      [GRPCConnectivityMonitor monitorWithHost:hostURL.host];
      void (^handler)(void) = ^{
        [GRPCHost flushChannelCache];
      };
      [connectivityMonitor handleLossWithHandler:handler
                         wifiStatusChangeHandler:handler];
    }
  }
  return self;
}

+ (void)flushChannelCache {
  @synchronized(kHostCache) {
    [kHostCache enumerateKeysAndObjectsUsingBlock:^(id  _Nonnull key,
                                                    GRPCHost * _Nonnull host,
                                                    BOOL * _Nonnull stop) {
      [host disconnect];
    }];
  }
}

+ (void)resetAllHostSettings {
  @synchronized (kHostCache) {
    kHostCache = [NSMutableDictionary dictionary];
  }
}

- (nullable grpc_call *)unmanagedCallWithPath:(NSString *)path
                                   serverName:(NSString *)serverName
                                      timeout:(NSTimeInterval)timeout
                              completionQueue:(GRPCCompletionQueue *)queue {
  GRPCChannel *channel;
  // This is racing -[GRPCHost disconnect].
  @synchronized(self) {
    if (!_channel) {
      _channel = [self newChannel];
    }
    channel = _channel;
  }
  return [channel unmanagedCallWithPath:path
                             serverName:serverName
                                timeout:timeout
                        completionQueue:queue];
}

- (BOOL)setTLSPEMRootCerts:(nullable NSString *)pemRootCerts
            withPrivateKey:(nullable NSString *)pemPrivateKey
             withCertChain:(nullable NSString *)pemCertChain
                     error:(NSError **)errorPtr {
  static NSData *kDefaultRootsASCII;
  static NSError *kDefaultRootsError;
  static dispatch_once_t loading;
  dispatch_once(&loading, ^{
    NSString *defaultPath = @"gRPCCertificates.bundle/roots"; // .pem
    // Do not use NSBundle.mainBundle, as it's nil for tests of library projects.
    NSBundle *bundle = [NSBundle bundleForClass:self.class];
    NSString *path = [bundle pathForResource:defaultPath ofType:@"pem"];
    NSError *error;
    // Files in PEM format can have non-ASCII characters in their comments (e.g. for the name of the
    // issuer). Load them as UTF8 and produce an ASCII equivalent.
    NSString *contentInUTF8 = [NSString stringWithContentsOfFile:path
                                                        encoding:NSUTF8StringEncoding
                                                           error:&error];
    if (contentInUTF8 == nil) {
      kDefaultRootsError = error;
      return;
    }
    kDefaultRootsASCII = [contentInUTF8 dataUsingEncoding:NSASCIIStringEncoding
                                     allowLossyConversion:YES];
  });

  NSData *rootsASCII;
  if (pemRootCerts != nil) {
    rootsASCII = [pemRootCerts dataUsingEncoding:NSASCIIStringEncoding
                            allowLossyConversion:YES];
  } else {
    if (kDefaultRootsASCII == nil) {
      if (errorPtr) {
        *errorPtr = kDefaultRootsError;
      }
      NSAssert(kDefaultRootsASCII, @"Could not read gRPCCertificates.bundle/roots.pem. This file, "
               "with the root certificates, is needed to establish secure (TLS) connections. "
               "Because the file is distributed with the gRPC library, this error is usually a sign "
               "that the library wasn't configured correctly for your project. Error: %@",
                kDefaultRootsError);
      return NO;
    }
    rootsASCII = kDefaultRootsASCII;
  }

  grpc_channel_credentials *creds;
  if (pemPrivateKey == nil && pemCertChain == nil) {
    creds = grpc_ssl_credentials_create(rootsASCII.bytes, NULL, NULL);
  } else {
    grpc_ssl_pem_key_cert_pair key_cert_pair;
    NSData *privateKeyASCII = [pemPrivateKey dataUsingEncoding:NSASCIIStringEncoding
                                       allowLossyConversion:YES];
    NSData *certChainASCII = [pemCertChain dataUsingEncoding:NSASCIIStringEncoding
                                     allowLossyConversion:YES];
    key_cert_pair.private_key = privateKeyASCII.bytes;
    key_cert_pair.cert_chain = certChainASCII.bytes;
    creds = grpc_ssl_credentials_create(rootsASCII.bytes, &key_cert_pair, NULL);
  }

  @synchronized(self) {
    if (_channelCreds != nil) {
      grpc_channel_credentials_release(_channelCreds);
    }
    _channelCreds = creds;
  }

  return YES;
}

- (NSDictionary *)channelArgs {
  NSMutableDictionary *args = [NSMutableDictionary dictionary];

  // TODO(jcanizales): Add OS and device information (see
  // https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#user-agents ).
  NSString *userAgent = @"grpc-objc/" GRPC_OBJC_VERSION_STRING;
  if (_userAgentPrefix) {
    userAgent = [_userAgentPrefix stringByAppendingFormat:@" %@", userAgent];
  }
  args[@GRPC_ARG_PRIMARY_USER_AGENT_STRING] = userAgent;

  if (_secure && _hostNameOverride) {
    args[@GRPC_SSL_TARGET_NAME_OVERRIDE_ARG] = _hostNameOverride;
  }

  if (_responseSizeLimitOverride) {
    args[@GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH] = _responseSizeLimitOverride;
  }
  // Use 10000ms initial backoff time for correct behavior on bad/slow networks  
  args[@GRPC_ARG_INITIAL_RECONNECT_BACKOFF_MS] = @10000;
  return args;
}

- (GRPCChannel *)newChannel {
  NSDictionary *args = [self channelArgs];
#ifdef GRPC_COMPILE_WITH_CRONET
  BOOL useCronet = [GRPCCall isUsingCronet];
#endif
  if (_secure) {
    GRPCChannel *channel;
    @synchronized(self) {
      if (_channelCreds == nil) {
        [self setTLSPEMRootCerts:nil withPrivateKey:nil withCertChain:nil error:nil];
      }
#ifdef GRPC_COMPILE_WITH_CRONET
      if (useCronet) {
        channel = [GRPCChannel secureCronetChannelWithHost:_address
                                               channelArgs:args];
      } else
#endif
      {
        channel = [GRPCChannel secureChannelWithHost:_address
                                         credentials:_channelCreds
                                         channelArgs:args];
      }
    }
    return channel;
  } else {
    return [GRPCChannel insecureChannelWithHost:_address channelArgs:args];
  }
}

- (NSString *)hostName {
  // TODO(jcanizales): Default to nil instead of _address when Issue #2635 is clarified.
  return _hostNameOverride ?: _address;
}

- (void)disconnect {
  // This is racing -[GRPCHost unmanagedCallWithPath:completionQueue:].
  @synchronized(self) {
    _channel = nil;
  }
}

@end

NS_ASSUME_NONNULL_END