Add a new function "try_get_value"

* Extracts a value from a deeply-nested data structure
* Returns default if a value could not be extracted

1 files changed, 77 insertions, 0 deletions

diff --git a/lib/puppet/parser/functions/try_get_value.rb b/lib/puppet/parser/functions/try_get_value.rb
new file mode 100644
index 0000000..0c19fd9
--- /dev/null
+++ b/lib/puppet/parser/functions/try_get_value.rb
@@ -0,0 +1,77 @@
+module Puppet::Parser::Functions
+  newfunction(
+      :try_get_value,
+      :type => :rvalue,
+      :arity => -2,
+      :doc => <<-eos
+Looks up into a complex structure of arrays and hashes and returns a value
+or the default value if nothing was found.
+
+Key can contain slashes to describe path components. The function will go down
+the structure and try to extract the required value.
+
+$data = {
+  'a' => {
+    'b' => [
+      'b1',
+      'b2',
+      'b3',
+    ]
+  }
+}
+
+$value = try_get_value($data, 'a/b/2', 'not_found', '/')
+=> $value = 'b3'
+
+a -> first hash key
+b -> second hash key
+2 -> array index starting with 0
+
+not_found -> (optional) will be returned if there is no value or the path did not match. Defaults to nil.
+/ -> (optional) path delimiter. Defaults to '/'.
+
+In addition to the required "key" argument, "try_get_value" accepts default
+argument. It will be returned if no value was found or a path component is
+missing. And the fourth argument can set a variable path separator.
+  eos
+  ) do |args|
+    path_lookup = lambda do |data, path, default|
+      debug "Try_get_value: #{path.inspect} from: #{data.inspect}"
+      if data.nil?
+        debug "Try_get_value: no data, return default: #{default.inspect}"
+        break default
+      end
+      unless path.is_a? Array
+        debug "Try_get_value: wrong path, return default: #{default.inspect}"
+        break default
+      end
+      unless path.any?
+        debug "Try_get_value: value found, return data: #{data.inspect}"
+        break data
+      end
+      unless data.is_a? Hash or data.is_a? Array
+        debug "Try_get_value: incorrect data, return default: #{default.inspect}"
+        break default
+      end
+
+      key = path.shift
+      if data.is_a? Array
+        begin
+          key = Integer key
+        rescue ArgumentError
+          debug "Try_get_value: non-numeric path for an array, return default: #{default.inspect}"
+          break default
+        end
+      end
+      path_lookup.call data[key], path, default
+    end
+
+    data = args[0]
+    path = args[1] || ''
+    default = args[2]
+    separator = args[3] || '/'
+
+    path = path.split separator
+    path_lookup.call data, path, default
+  end
+end