# Puppet External Data Sources
#
# This is a parser function to read data from external files, this version
# uses CSV files but the concept can easily be adjust for databases, yaml
# or any other queryable data source.
#
# The object of this is to make it obvious when it's being used, rather than
# magically loading data in when an module is loaded I prefer to look at the code
# and see statements like:
#
#     $snmp_contact = extlookup("snmp_contact")
#
# The above snippet will load the snmp_contact value from CSV files, this in its
# own is useful but a common construct in puppet manifests is something like this:
#
# case $domain {
#      "myclient.com": { $snmp_contact = "John Doe <john@myclient.com>" }
#      default:        { $snmp_contact = "My Support <support@my.com>" }
# }
#
# Over time there will be a lot of this kind of thing spread all over your manifests
# and adding an additional client involves grepping through manifests to find all the
# places where you have constructs like this.
#
# This is a data problem and shouldn't be handled in code, a using this function you
# can do just that.
#
# First you configure it in site.pp:
# $extlookup_datadir = "/etc/puppet/manifests/extdata"
# $extlookup_precedence = ["%{fqdn}", "domain_%{domain}", "common"]
#
# The array tells the code how to resolve values, first it will try to find it in
# web1.myclient.com.csv then in domain_myclient.com.csv and finally in common.csv
#
# Now create the following data files in /etc/puppet/manifests/extdata
#
# domain_myclient.com.csv:
#    snmp_contact,John Doe <john@myclient.com>
#    root_contact,support@%{domain}
#    client_trusted_ips,192.168.1.130,192.168.10.0/24
#
# common.csv:
#    snmp_contact,My Support <support@my.com>
#    root_contact,support@my.com
#
# Now you can replace the case statement with the simple single line to achieve
# the exact same outcome:
#
#    $snmp_contact = extlookup("snmp_contact")
#
# The obove code shows some other features, you can use any fact or variable that
# is in scope by simply using %{varname} in your data files, you can return arrays
# by just having multiple values in the csv after the initial variable name.
#
# In the event that a variable is nowhere to be found a critical error will be raised
# that will prevent your manifest from compiling, this is to avoid accidentally putting
# in empty values etc.  You can however specify a default value:
#
#    $ntp_servers = extlookup("ntp_servers", "1.${country}.pool.ntp.org")
#
# In this case it will default to "1.${country}.pool.ntp.org" if nothing is defined in
# any data file.
#
# You can also specify an additional data file to search first before any others at use
# time, for example:
#
# $version = extlookup("rsyslog_version", "present", "packages")
#
# package{"rsyslog": ensure => $version }
#
# This will look for a version configured in packages.csv and then in the rest as configured
# by $extlookup_precedence if it's not found anywhere it will default to "present", this kind
# of use case makes puppet a lot nicer for managing large amounts of packages since you do not
# need to edit a load of manifests to do simple things like adjust a desired version number.
#
# For more information on installing and writing your own custom functions see:
#    http://reductivelabs.com/trac/puppet/wiki/WritingYourOwnFunctions
#
# For further help contact Volcane on #puppet
require 'csv'

module Puppet::Parser::Functions
    newfunction(:extlookup, :type => :rvalue) do |args|
        key = args[0]
        default = "_ExtUNSET_"
        datafile = "_ExtUNSET_"

        default = args[1] if args[1]
        datafile = args[2] if args[2]

        extlookup_datadir = lookupvar('extlookup_datadir')
        extlookup_precedence = Array.new

        # precedence values can have variables embedded in them
        # in the form %{fqdn}, you could for example do
        #
        #    $extlookup_precedence = ["hosts/%{fqdn}", "common"]
        #
        # this will result in /path/to/extdata/hosts/your.box.com.csv
        # being searched.
        #
        # we parse the precedence here because the best place to specify
        # it would be in site.pp but site.pp is only evaluated at startup
        # so $fqdn etc would have no meaning there, this way it gets evaluated
        # each run and has access to the right variables for that run
        lookupvar('extlookup_precedence').each do |prec|
            while prec =~ /%\{(.+?)\}/
                prec.gsub!(/%\{#{$1}\}/, lookupvar($1))
            end

            extlookup_precedence << prec
        end


        datafiles = Array.new

        # if we got a custom data file, put it first in the array of search files
        if datafile != ""
            datafiles << extlookup_datadir + "/#{datafile}.csv" if File.exists?(extlookup_datadir + "/#{datafile}.csv")
        end

        extlookup_precedence.each do |d|
            datafiles << extlookup_datadir + "/#{d}.csv"
        end

        desired = "_ExtUNSET_"

        datafiles.each do |file|
            parser.watch_file(file) if File.exists?(file)

            if desired == "_ExtUNSET_"
                if File.exists?(file)
                    result = CSV.read(file).find_all do |r|
                        r[0] == key
                    end


                    # return just the single result if theres just one,
                    # else take all the fields in the csv and build an array
                    if result.length > 0
                        if result[0].length == 2
                            val = result[0][1].to_s

                            # parse %{}'s in the CSV into local variables using lookupvar()
                            while val =~ /%\{(.+?)\}/
                                val.gsub!(/%\{#{$1}\}/, lookupvar($1))
                            end

                            desired = val
                        elsif result[0].length > 1
                            length = result[0].length
                            cells = result[0][1,length]

                            # Individual cells in a CSV result are a weird data type and throws
                            # puppets yaml parsing, so just map it all to plain old strings
                            desired = cells.map do |c|
                                # parse %{}'s in the CSV into local variables using lookupvar()
                                while c =~ /%\{(.+?)\}/
                                    c.gsub!(/%\{#{$1}\}/, lookupvar($1))
                                end

                                c.to_s
                            end
                        end
                    end
                end
            end
        end

        # don't accidently return nil's and such rather throw a parse error
        if desired == "_ExtUNSET_" && default == "_ExtUNSET_"
            raise Puppet::ParseError, "No match found for '#{key}' in any data file during extlookup()"
        else
            desired = default if desired == "_ExtUNSET_"
        end

        desired
    end
end

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