# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   cloudwatch_log_group_retention_period_check
# 
# Description:
#   This control checks whether an Amazon CloudWatch Log Group retention period is set to a value greater than or equal to 365 days.
# 
# Reports on:
#   AWS::Logs::LogGroup
# 
# Evaluates:
#   AWS CloudFormation, AWS CloudFormation hook
# 
# Rule Parameters:
#   None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document does not contain any CloudWatch log group resources
#     Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudWatch log group resource
#       And: 'RetentionInDays' has been provided and set to a non integer value or
#            integer value less than 365
#     Then: FAIL
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains a CloudWatch log group resource
#       And: 'RetentionInDays' has not been provided
#     Then: PASS
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation Hook Document
#       And: The input document contains a CloudWatch log group resource
#       And: 'RetentionInDays' has been provided and set to an integer value greater than or equal to 365
#     Then: PASS

#
# Constants
#
let CLOUDWATCH_LOGS_TYPE = "AWS::Logs::LogGroup"
let MINIMUM_RETENTION_IN_DAYS = 365
let INPUT_DOCUMENT = this

#
# Assignments
#
let cloudwatch_log_groups = Resources.*[ Type == %CLOUDWATCH_LOGS_TYPE ]

#
# Primary Rules
#
rule cloudwatch_log_group_retention_period_check when is_cfn_template(%INPUT_DOCUMENT)
                                                      %cloudwatch_log_groups not empty {
    check(%cloudwatch_log_groups.Properties)
        <<
        [CT.CLOUDWATCH.PR.2]: Require an Amazon CloudWatch log group to be retained for at least one year
        [FIX]: Omit the field value of 'RetentionInDays' to adopt the default retention setting of 'Never expire', or set 'RetentionInDays' to an integer value greater than or equal to 365.
        >>
}

rule cloudwatch_log_group_retention_period_check when is_cfn_hook(%INPUT_DOCUMENT, %CLOUDWATCH_LOGS_TYPE) {
    check(%INPUT_DOCUMENT.%CLOUDWATCH_LOGS_TYPE.resourceProperties)
        <<
        [CT.CLOUDWATCH.PR.2]: Require an Amazon CloudWatch log group to be retained for at least one year
        [FIX]: Omit the field value of 'RetentionInDays' to adopt the default retention setting of 'Never expire', or set 'RetentionInDays' to an integer value greater than or equal to 365.
        >>
}

#
# Parameterized Rules
#
rule check(cloudwatch_log_group){
    %cloudwatch_log_group {
        # Scenario 3
        RetentionInDays not exists or

        # Scenarios 2 and 4
        RetentionInDays >= %MINIMUM_RETENTION_IN_DAYS
    }
}

#
# Utility Rules
#
rule is_cfn_template(doc) {
    %doc {
        AWSTemplateFormatVersion exists  or
        Resources exists
    }
}

rule is_cfn_hook(doc, RESOURCE_TYPE) {
    %doc.%RESOURCE_TYPE.resourceProperties exists
}