feat: add scrolling in preview window (#47)

* feat: add scrolling in preview window

refactor into two layers

* remove redundant code

* add error message for scroll_fn and send_input

* consider count for preview scrolling

README.md

@@ -142,6 +142,9 @@ j      k     next | previous (in normal mode)
 <C-v>        go to file selection as a vertical split
 <C-t>        go to a file in a new tab
 
+<C-u>        scroll up in preview window
+<C-d>        scroll down in preview window
+
 <C-c>        close telescope
 <Esc>        close telescope (in normal mode)
 ```

lua/telescope/actions.lua

@@ -34,6 +34,14 @@ function actions.get_selected_entry(prompt_bufnr)
   return actions.get_current_picker(prompt_bufnr):get_selection()
 end
 
+function actions.preview_scrolling_up(prompt_bufnr)
+  actions.get_current_picker(prompt_bufnr).previewer:scroll_fn(-30)
+end
+
+function actions.preview_scrolling_down(prompt_bufnr)
+  actions.get_current_picker(prompt_bufnr).previewer:scroll_fn(30)
+end
+
 -- TODO: It seems sometimes we get bad styling.
 local function goto_file_selection(prompt_bufnr, command)
   local picker = actions.get_current_picker(prompt_bufnr)

lua/telescope/pickers.lua

@@ -42,6 +42,9 @@ local default_mappings = {
     ["<C-x>"] = actions.goto_file_selection_split,
     ["<C-v>"] = actions.goto_file_selection_vsplit,
     ["<C-t>"] = actions.goto_file_selection_tabedit,
+
+    ["<C-u>"] = actions.preview_scrolling_up,
+    ["<C-d>"] = actions.preview_scrolling_down,
   },
 
   n = {
@@ -57,6 +60,9 @@ local default_mappings = {
 
     ["<Down>"] = actions.move_selection_next,
     ["<Up>"] = actions.move_selection_previous,
+
+    ["<C-u>"] = actions.preview_scrolling_up,
+    ["<C-d>"] = actions.preview_scrolling_down,
   },
 }
 

lua/telescope/previewers.lua

@@ -11,7 +11,7 @@ local Previewer = {}
 Previewer.__index = Previewer
 
 -- TODO: Should play with these some more, ty @clason
-local bat_options = " --style=plain --paging=never --color=always "
+local bat_options = " --style=plain --color=always "
 
 local previewer_ns = vim.api.nvim_create_namespace('telescope.previewers')
 
@@ -28,6 +28,8 @@ function Previewer:new(opts)
     state = nil,
     _setup_func = opts.setup,
     _teardown_func = opts.teardown,
+    _send_input = opts.send_input,
+    _scroll_fn = opts.scroll_fn,
     preview_fn = opts.preview_fn,
   }, Previewer)
 end
@@ -55,6 +57,22 @@ function Previewer:teardown()
   end
 end
 
+function Previewer:send_input(input)
+  if self._send_input then
+    self:_send_input(input)
+  else
+    vim.api.nvim_err_writeln("send_input is not defined for this previewer")
+  end
+end
+
+function Previewer:scroll_fn(direction)
+  if self._scroll_fn then
+    self:_scroll_fn(direction)
+  else
+    vim.api.nvim_err_writeln("scroll_fn is not defined for this previewer")
+  end
+end
+
 previewers.new = function(...)
   return Previewer:new(...)
 end
@@ -186,6 +204,22 @@ previewers.cat = defaulter(function(opts)
       }
     end,
 
+    send_input = function(self, input)
+      termcode = vim.api.nvim_replace_termcodes(input, true, false, true)
+      if self.state.termopen_id then
+        pcall(vim.fn.chansend, self.state.termopen_id, termcode)
+      end
+    end,
+
+    scroll_fn = function(self, direction)
+      if not self.state then
+        return
+      end
+      if direction > 0 then input = "d" else input = "u" end
+      local count = math.abs(direction)
+      self:send_input(count..input)
+    end,
+
     teardown = function(self)
       if not self.state then
         return