# Evaluates an Embedded Puppet (EPP) template file and returns the rendered text
# result as a String.
#
# `epp('<MODULE NAME>/<TEMPLATE FILE>', <PARAMETER HASH>)`
#
# The first argument to this function should be a `<MODULE NAME>/<TEMPLATE FILE>`
# reference, which loads `<TEMPLATE FILE>` from `<MODULE NAME>`'s `templates`
# directory. In most cases, the last argument is optional; if used, it should be a
# [hash](/puppet/latest/reference/lang_data_hash.html) that contains parameters to
# pass to the template.
#
# - See the [template](/puppet/latest/reference/lang_template.html) documentation
# for general template usage information.
# - See the [EPP syntax](/puppet/latest/reference/lang_template_epp.html)
# documentation for examples of EPP.
#
# For example, to call the apache module's `templates/vhost/_docroot.epp`
# template and pass the `docroot` and `virtual_docroot` parameters, call the `epp`
# function like this:
#
# `epp('apache/vhost/_docroot.epp', { 'docroot' => '/var/www/html',
# 'virtual_docroot' => '/var/www/example' })`
#
# This function can also accept an absolute path, which can load a template file
# from anywhere on disk.
#
# Puppet produces a syntax error if you pass more parameters than are declared in
# the template's parameter tag. When passing parameters to a template that
# contains a parameter tag, use the same names as the tag's declared parameters.
#
# Parameters are required only if they are declared in the called template's
# parameter tag without default values. Puppet produces an error if the `epp`
# function fails to pass any required parameter.
#
# @since 4.0.0
#
Puppet::Functions.create_function(:epp, Puppet::Functions::InternalFunction) do

  dispatch :epp do
    scope_param
    param 'String', :path
    optional_param 'Hash[Pattern[/^\w+$/], Any]', :parameters
  end

  def epp(scope, path, parameters = nil)
    Puppet::Pops::Evaluator::EppEvaluator.epp(scope, path, scope.compiler.environment, parameters)
  end
end
