{%- macro files_switch(source_files,
                       lookup=None,
                       default_files_switch=['id', 'os_family'],
                       indent_width=6,
                       use_subpath=False) %}
  {#-
    Returns a valid value for the "source" parameter of a "file.managed"
    state function. This makes easier the usage of the Template Override and
    Files Switch (TOFS) pattern.

    Params:
      * source_files: ordered list of files to look for
      * lookup: key under '<tplroot>:tofs:source_files' to prepend to the
        list of source files
      * default_files_switch: if there's no config (e.g. pillar)
        '<tplroot>:tofs:files_switch' this is the ordered list of grains to
        use as selector switch of the directories under
        "<path_prefix>/files"
      * indent_width: indentation of the result value to conform to YAML
      * use_subpath: defaults to `False` but if set, lookup the source file
        recursively from the current state directory up to `tplroot`

    Example (based on a `tplroot` of `xxx`):

    If we have a state:

      Deploy configuration:
        file.managed:
          - name: /etc/yyy/zzz.conf
          - source: {{ files_switch(['/etc/yyy/zzz.conf', '/etc/yyy/zzz.conf.jinja'],
                                    lookup='Deploy configuration'
                    ) }}
          - template: jinja

    In a minion with id=theminion and os_family=RedHat, it's going to be
    rendered as:

      Deploy configuration:
        file.managed:
          - name: /etc/yyy/zzz.conf
          - source:
            - salt://xxx/files/theminion/etc/yyy/zzz.conf
            - salt://xxx/files/theminion/etc/yyy/zzz.conf.jinja
            - salt://xxx/files/RedHat/etc/yyy/zzz.conf
            - salt://xxx/files/RedHat/etc/yyy/zzz.conf.jinja
            - salt://xxx/files/default/etc/yyy/zzz.conf
            - salt://xxx/files/default/etc/yyy/zzz.conf.jinja
          - template: jinja
  #}
  {#- Get the `tplroot` from `tpldir` #}
  {%- set tplroot = tpldir.split('/')[0] %}
  {%- set path_prefix = salt['config.get'](tplroot ~ ':tofs:path_prefix', tplroot) %}
  {%- set files_dir = salt['config.get'](tplroot ~ ':tofs:dirs:files', 'files') %}
  {%- set files_switch_list = salt['config.get'](
      tplroot ~ ':tofs:files_switch',
      default_files_switch
  ) %}
  {#- Lookup source_files (v2), files (v1), or fallback to an empty list #}
  {%- set src_files = salt['config.get'](
      tplroot ~ ':tofs:source_files:' ~ lookup,
      salt['config.get'](tplroot ~ ':tofs:files:' ~ lookup, [])
  ) %}
  {#- Append the default source_files #}
  {%- set src_files = src_files + source_files %}
  {#- Only add to [''] when supporting older TOFS implementations #}
  {%- set path_prefix_exts = [''] %}
  {%- if use_subpath and tplroot != tpldir %}
    {#- Walk directory tree to find {{ files_dir }} #}
    {%- set subpath_parts = tpldir.lstrip(tplroot).lstrip('/').split('/') %}
    {%- for path in subpath_parts %}
      {%- set subpath = subpath_parts[0:loop.index] | join('/') %}
      {%- do path_prefix_exts.append('/' ~ subpath) %}
    {%- endfor %}
  {%- endif %}
  {%- for path_prefix_ext in path_prefix_exts|reverse %}
    {%- set path_prefix_inc_ext = path_prefix ~ path_prefix_ext %}
    {#- For older TOFS implementation, use `files_switch` from the config #}
    {#- Use the default, new method otherwise #}
    {%- set fsl = salt['config.get'](
        tplroot ~ path_prefix_ext|replace('/', ':') ~ ':files_switch',
        files_switch_list
    ) %}
    {#- Append an empty value to evaluate as `default` in the loop below #}
    {%- if '' not in fsl %}
      {%- set fsl = fsl + [''] %}
    {%- endif %}
    {%- for fs in fsl %}
      {%- for src_file in src_files %}
        {%- if fs %}
          {%- set fs_dirs = salt['config.get'](fs, fs) %}
        {%- else %}
          {%- set fs_dirs = salt['config.get'](tplroot ~ ':tofs:dirs:default', 'default') %}
        {%- endif %}
        {#- Force the `config.get` lookup result as a list where necessary #}
        {#- since we need to also handle grains that are lists #}
        {%- if fs_dirs is string %}
          {%- set fs_dirs = [fs_dirs] %}
        {%- endif %}
        {%- for fs_dir in fs_dirs %}
          {%- set url = [
              '- salt:/',
              path_prefix_inc_ext.strip('/'),
              files_dir.strip('/'),
              fs_dir.strip('/'),
              src_file.strip('/'),
          ] | select | join('/') %}
{{ url | indent(indent_width, true) }}
        {%- endfor %}
      {%- endfor %}
    {%- endfor %}
  {%- endfor %}
{%- endmacro %}