feat: Themes (#79)

Big shoutout to @rockerBOO  for the idea and basically all the impl!

* feat: Add dropdown layout strategy

* Adding more docs. Working better with options

* Refactor borders

* Fix for spaces

* Add preview to layout. Add Themes.

* feat: themes

Co-authored-by: TJ DeVries <devries.timothyj@gmail.com>

lua/telescope/pickers/layout_strategies.lua

@@ -1,6 +1,32 @@
+--[[
+
+Layout strategies are different functions to position telescope.
+
+horizontal:
+- Supports `prompt_position`, `preview_cutoff`
+
+vertical:
+
+flex: Swap between `horizontal` and `vertical` strategies based on the window width
+- Supports `vertical` or `horizontal` features
+
+dropdown:
+
+
+Layout strategies are callback functions
+
+-- @param self: Picker
+-- @param columns: number Columns in the vim window
+-- @param lines: number Lines in the vim window
+-- @param prompt_title: string
+function(self, columns, lines, prompt_title)
+end
+
+--]]
 
 local layout_strategies = {}
-
+local log = require("telescope.log")
+local resolve = require("telescope.config.resolve")
 --[[
    +-----------------+---------------------+
    |                 |                     |
@@ -19,7 +45,6 @@ layout_strategies.horizontal = function(self, max_columns, max_lines, prompt_tit
 
   -- TODO: Test with 120 width terminal
   -- TODO: Test with self.width
-
   local width_padding = 10
 
   -- TODO: Determine config settings.
@@ -40,6 +65,7 @@ layout_strategies.horizontal = function(self, max_columns, max_lines, prompt_tit
   end
 
   local other_width = max_columns - preview.width - (2 * width_padding)
+
   results.width = other_width
   prompt.width = other_width
 
@@ -80,11 +106,69 @@ layout_strategies.horizontal = function(self, max_columns, max_lines, prompt_tit
   return {
     preview = preview.width > 0 and preview,
     results = results,
-    prompt = prompt,
-  }
+    prompt = prompt
+}
 end
 
+--[[
+    +-----------------+
+    |     Prompt      |
+    +-----------------+
+    |     Result      |
+    |     Result      |
+    |     Result      |
+    +-----------------+
+--]]
 
+-- Check if there are any borders. Right now it's a little raw as
+-- there are a few things that contribute to the border
+local is_borderless = function(opts)
+  if opts.window.border == false then return true end
+end
+
+layout_strategies.center = function(self, columns, lines, prompt_title)
+  local initial_options = self:_get_initial_window_options(prompt_title)
+  local preview = initial_options.preview
+  local results = initial_options.results
+  local prompt = initial_options.prompt
+
+  local max_results = self.max_results or 15
+  local width = self.width or 70
+
+  local max_width = (width > columns and columns or width)
+
+  prompt.height = 1
+  results.height = max_results
+
+  prompt.width = max_width
+  results.width = max_width
+  preview.width = max_width
+
+  local bs = 1 -- border size
+
+  if is_borderless(self) then bs = 0 end
+
+  prompt.line = (lines / 2) - ((max_results + (bs * 2)) / 2)
+  results.line = prompt.line + prompt.height + (bs * 2)
+
+  preview.line = 1
+  preview.height = math.floor(prompt.line - 2)
+
+  if not self.previewer or columns < self.preview_cutoff then
+    preview.height = 0
+  end
+
+  -- Get left column, after centering, appling the width, and the border size
+  results.col = (columns / 2) - (width / 2) + (bs * 2)
+  prompt.col = results.col
+  preview.col = results.col
+
+  return {
+    preview = self.previewer and preview,
+    results = results,
+    prompt = prompt
+  }
+end
 
 --[[
     +-----------------+