lib/plugins/aws/package/compile/events/cloudWatchLog/index.js/AwsCompileCloudWatchLogEvents/compileCloudWatchLogEvents
class AwsCompileCloudWatchLogEvents:  compileCloudWatchLogEvents() {
    const logGroupNames = [];

    this.serverless.service.getAllFunctions().forEach(functionName => {
      const functionObj = this.serverless.service.getFunction(functionName);
      let cloudWatchLogNumberInFunction = 0;

      if (functionObj.events) {
        const logGroupNamesThisFunction = [];

        functionObj.events.forEach(event => {
          if (event.cloudwatchLog) {
            cloudWatchLogNumberInFunction++;
            let LogGroupName;
            let FilterPattern;

            if (typeof event.cloudwatchLog === 'object') {
              if (!event.cloudwatchLog.logGroup) {
                const errorMessage = [
                  'Missing "logGroup" property for cloudwatchLog event ',
                  `in function ${functionName} Please check the docs for more info.`,
                ].join('');
                throw new this.serverless.classes.Error(errorMessage);
              }

              if (event.cloudwatchLog.filter && typeof event.cloudwatchLog.filter !== 'string') {
                const errorMessage = [
                  `"filter" property for cloudwatchLog event in function ${functionName} `,
                  'should be string. Please check the docs for more info.',
                ].join('');
                throw new this.serverless.classes.Error(errorMessage);
              }

              LogGroupName = event.cloudwatchLog.logGroup.replace(/\r?\n/g, '');
              FilterPattern = event.cloudwatchLog.filter
                ? event.cloudwatchLog.filter.replace(/\r?\n/g, '')
                : '';
            } else if (typeof event.cloudwatchLog === 'string') {
              LogGroupName = event.cloudwatchLog.replace(/\r?\n/g, '');
              FilterPattern = '';
            } else {
              const errorMessage = [
                `cloudwatchLog event of function "${functionName}" is not an object or a string`,
                ' Please check the docs for more info.',
              ].join('');
              throw new this.serverless.classes.Error(errorMessage);
            }

            if (_.indexOf(logGroupNames, LogGroupName) !== -1) {
              const errorMessage = [
                `"${LogGroupName}" logGroup for cloudwatchLog event is duplicated.`,
                ' This property can only be set once per CloudFormation stack.',
              ].join('');
              throw new this.serverless.classes.Error(errorMessage);
            }
            logGroupNames.push(LogGroupName);
            logGroupNamesThisFunction.push(LogGroupName);

            const lambdaLogicalId = this.provider.naming.getLambdaLogicalId(functionName);
            const cloudWatchLogLogicalId = this.provider.naming.getCloudWatchLogLogicalId(
              functionName,
              cloudWatchLogNumberInFunction
            );
            const lambdaPermissionLogicalId = this.provider.naming.getLambdaCloudWatchLogPermissionLogicalId(
              functionName
            );

            // unescape quotes once when the first quote is detected escaped
            const idxFirstSlash = FilterPattern.indexOf('\\');
            const idxFirstQuote = FilterPattern.indexOf('"');
            if (idxFirstSlash >= 0 && idxFirstQuote >= 0 && idxFirstQuote > idxFirstSlash) {
              FilterPattern = FilterPattern.replace(/\\("|\\|')/g, (match, g) => g);
            }

            const cloudWatchLogRuleTemplate = `
              {
                "Type": "AWS::Logs::SubscriptionFilter",
                "DependsOn": "${lambdaPermissionLogicalId}",
                "Properties": {
                  "LogGroupName": "${LogGroupName}",
                  "FilterPattern": ${JSON.stringify(FilterPattern)},
                  "DestinationArn": { "Fn::GetAtt": ["${lambdaLogicalId}", "Arn"] }
                }
              }
            `;

            const commonSuffixOfLogGroupName = this.longestCommonSuffix(logGroupNamesThisFunction);

            const permissionTemplate = `
            {
              "Type": "AWS::Lambda::Permission",
              "Properties": {
                "FunctionName": { "Fn::GetAtt": ["${lambdaLogicalId}", "Arn"] },
                "Action": "lambda:InvokeFunction",
                "Principal": {
                  "Fn::Join": [ "", [
                  "logs.",
                  { "Ref": "AWS::Region" },
                  ".amazonaws.com"
                  ] ]
                },
                "SourceArn": {
                  "Fn::Join": [ "", [
                  "arn:",
                  { "Ref": "AWS::Partition" },
                  ":logs:",
                  { "Ref": "AWS::Region" },
                  ":",
                  { "Ref": "AWS::AccountId" },
                  ":log-group:",
                  "${commonSuffixOfLogGroupName}",
                  ":*"
                  ] ]
                }
              }
            }
          `;

            const newCloudWatchLogRuleObject = {
              [cloudWatchLogLogicalId]: JSON.parse(cloudWatchLogRuleTemplate),
            };

            const newPermissionObject = {
              [lambdaPermissionLogicalId]: JSON.parse(permissionTemplate),
            };

            _.merge(
              this.serverless.service.provider.compiledCloudFormationTemplate.Resources,
              newCloudWatchLogRuleObject,
              newPermissionObject
            );
          }
        });
      }
    });
  }