Extend :Rg to support visual select mode

Also move away from using the telescope builtin grep for word under
cursor mapping by extending the `:Rg` command to work in the following
circumstances:

* `:Rg text to search for`
* `:Rg` word under cursor
* `'<,'>Rg` visual selection

plugin/commands.lua

@@ -116,16 +116,31 @@ end, {
   complete = 'file',
 })
 
--- :Rg grep for the given string and fuzzy find the results, bang to enable
--- regex in given string
--- FIXME: Support visual select modes
+-- :Rg grep for the given string, word under the cursor, or visual selection
+-- then fuzzy find the results. Bang to enable regex in given string.
 vim.api.nvim_create_user_command('Rg', function(opts)
-  local grep_opts = { search = opts.args }
+  print(vim.inspect(opts))
+  local search = opts.args
+  if opts.range == 2 then
+    local lines = vim.fn.getline(vim.fn.line("'<"), vim.fn.line("'>"))
+    local start_col = vim.fn.col("'<")
+    local end_col = vim.fn.col("'>")
+    if #lines == 1 then
+      lines[1] = string.sub(lines[1], start_col, end_col)
+    else
+      lines[1] = string.sub(lines[1], start_col)
+      lines[#lines] = string.sub(lines[#lines], 1, end_col)
+    end
+    search = table.concat(lines, "\n")
+  elseif #search == 0 then
+    search = vim.fn.expand('<cword>')
+  end
+  local grep_opts = { search = search}
   if opts.bang then
     grep_opts['use_regex'] = true
   end
   require('telescope.builtin').grep_string(grep_opts)
-end, { bang = true, nargs = '*' })
+end, { bang = true, range = true, nargs = '*' })
 
 vim.api.nvim_create_user_command('PreProcIfWrap', function(opts)
   local buffer = vim.api.nvim_get_current_buf()