require 'hiera_puppet'

module Puppet::Parser::Functions
  newfunction(
    :hiera_hash,
    :type => :rvalue,
    :arity => -2,
    :doc => <<-DOC
Finds all matches of a key throughout the hierarchy and returns them in a merged hash.
If any of the matched hashes share keys, the final hash uses the value from the
highest priority match. This is called a
[hash merge lookup](https://docs.puppetlabs.com/hiera/latest/lookup_types.html#hash-merge).

The merge strategy is determined by Hiera's
[`:merge_behavior`](https://docs.puppetlabs.com/hiera/latest/configuring.html#mergebehavior)
setting.

The `hiera_hash` function takes up to three arguments, in this order:

1. A string key that Hiera searches for in the hierarchy. **Required**.
2. An optional default value to return if Hiera doesn't find anything matching the key.
    * If this argument isn't provided and this function results in a lookup failure, Puppet
    fails with a compilation error.
3. The optional name of an arbitrary
[hierarchy level](https://docs.puppetlabs.com/hiera/latest/hierarchy.html) to insert at the
top of the hierarchy. This lets you temporarily modify the hierarchy for a single lookup.
    * If Hiera doesn't find a matching key in the overriding hierarchy level, it continues
    searching the rest of the hierarchy.

**Example**: Using `hiera_hash`

~~~ yaml
# Assuming hiera.yaml
# :hierarchy:
#   - web01.example.com
#   - common

# Assuming common.yaml:
# users:
#   regular:
#     'cdouglas': 'Carrie Douglas'

# Assuming web01.example.com.yaml:
# users:
#   administrators:
#     'aberry': 'Amy Berry'
~~~

~~~ puppet
# Assuming we are not web01.example.com:

$allusers = hiera_hash('users', undef)

# $allusers contains {regular => {"cdouglas" => "Carrie Douglas"},
#                     administrators => {"aberry" => "Amy Berry"}}
~~~

You can optionally generate the default value with a
[lambda](https://docs.puppetlabs.com/puppet/latest/reference/lang_lambdas.html) that
takes one parameter.

**Example**: Using `hiera_hash` with a lambda

~~~ puppet
# Assuming the same Hiera data as the previous example:

$allusers = hiera_hash('users') | $key | { "Key \'${key}\' not found" }

# $allusers contains {regular => {"cdouglas" => "Carrie Douglas"},
#                     administrators => {"aberry" => "Amy Berry"}}
# If hiera_hash couldn't match its key, it would return the lambda result,
# "Key 'users' not found".
~~~

`hiera_hash` expects that all values returned will be hashes. If any of the values
found in the data sources are strings or arrays, Puppet raises a type mismatch error.

See
[the documentation](https://docs.puppetlabs.com/hiera/latest/puppet.html#hiera-lookup-functions)
for more information about Hiera lookup functions.

- Since 4.0.0
DOC
  ) do |*args|
    Error.is4x('hiera_hash')
  end
end

