new builtin - autocommands (#302)

* feat: new builtin - Autocommands finder

* fix: remove decorators to avoid confusion.

* make preview split same hl-group as border

* use highlight instead of marker character for preview selection hl

lua/telescope/previewers.lua

@@ -770,6 +770,51 @@ previewers.man = defaulter(function(_)
   }
 end)
 
+previewers.autocommands = defaulter(function(_)
+return previewers.new_buffer_previewer {
+  setup = function()
+    return {}
+  end,
+
+  teardown = function(self)
+    if self.state and self.state.hl_id then
+      pcall(vim.fn.matchdelete, self.state.hl_id, self.state.hl_win)
+      self.state.hl_id = nil
+    end
+  end,
+
+  preview_fn = function(self, entry, status)
+    local results = vim.tbl_filter(
+      function (x) return x.group == entry.group end,
+      status.picker.finder.results
+      )
+    local display = {}
+    table.insert(display, string.format(" augroup: %s - [ %d entries ]", entry.group, #results))
+    -- TODO: calculate banner width/string in setup()
+    -- TODO: get column characters to be the same HL group as border
+    table.insert(display, string.rep("─", vim.fn.getwininfo(status.preview_win)[1].width))
+
+    local selected_row
+    for idx, item in ipairs(results) do
+      if item == entry then
+        selected_row = idx
+      end
+      table.insert(display,
+        string.format("  %-14s▏%-08s %s", item.event, item.ft_pattern, item.command)
+      )
+    end
+
+    with_preview_window(status, nil, function()
+      -- TODO: set filetype in setup()
+      vim.api.nvim_buf_set_option(status.preview_bufnr, "filetype", "vim")
+      vim.api.nvim_buf_set_lines(status.preview_bufnr, 0, -1, false, display)
+      vim.api.nvim_buf_add_highlight(status.preview_bufnr, 0, "TelescopeBorder", 1, 0, -1)
+      vim.api.nvim_buf_add_highlight(status.preview_bufnr, 0, "TelescopeSelection", selected_row + 1, 0, -1)
+    end)
+  end,
+}
+end, {})
+
 previewers.display_content = defaulter(function(_)
   return previewers.new_buffer_previewer {
     preview_fn = function(self, entry, status)