dtemplate.pl

use Mojolicious::Lite;

# I don't think defaulting both dir and page works, so separate root handler is necessary below
get '/*dir/:page' => {dir => ''} => sub {
  my $c = shift;

  # attempt to render the requested page
  my @parts = (split(m{/}, $c->stash('dir')), $c->stash('page'));
  $c->stash(template => join '/', @parts);
  return if $c->render_maybe;

  # attempt to render _index pages in the containing directories
  $parts[-1] = '_index';
  while (1) {
    $c->stash(template => join '/', @parts);
    return if $c->render_maybe;
    last if @parts < 2;
    splice @parts, -2, 1;
  }

  # no _index page found
  $c->render(status => 404, text => 'Not found');
};

get '/' => '_index';

app->start;

__DATA__

@@ some/path/this.html.ep

Hello from the page some/path/this.html

@@ some/path/_index.html.ep

Hello from some/path

@@ some/_index.html.ep

Hello from some/

@@ _index.html.ep

Hello from /