[Feature] Encapsulate interface logic (#1320)

* Provide a utility function for aligning text

* Replace lvim banner with one using only ASCII chars

* Use strings.format instead of .. operator

* Center text in the popup based on its dimentions

* Minor improvements

* Provide a popup factory function

* Add function documentation

* Improve text alignment

* Print marker only if provider list is not empty

* Format client capabilities as list

* Pretty format lsp client capabilities

* Add a metatable to popup.lua

* Improve rendering when no lsp is available

* Take cmdheight into acount when computing popup size and pos

Co-authored-by: kylo252 <59826753+kylo252@users.noreply.github.com>

lua/interface/popup.lua

@@ -0,0 +1,62 @@
+local Popup = {}
+
+--- Create a new floating window
+-- @param config The configuration passed to vim.api.nvim_open_win
+-- @param win_opts The options registered with vim.api.nvim_win_set_option
+-- @param buf_opts The options registered with vim.api.nvim_buf_set_option
+-- @return A new popup
+function Popup:new(opts)
+  opts = opts or {}
+  opts.layout = opts.layout or {}
+  opts.win_opts = opts.win_opts or {}
+  opts.buf_opts = opts.buf_opts or {}
+
+  Popup.__index = Popup
+
+  local editor_layout = {
+    height = vim.o.lines - vim.o.cmdheight - 2, -- Add margin for status and buffer line
+    width = vim.o.columns,
+  }
+  local popup_layout = {
+    relative = "editor",
+    height = math.floor(editor_layout.height * 0.9),
+    width = math.floor(editor_layout.width * 0.8),
+    style = "minimal",
+    border = "rounded",
+  }
+  popup_layout.row = math.floor((editor_layout.height - popup_layout.height) / 2)
+  popup_layout.col = math.floor((editor_layout.width - popup_layout.width) / 2)
+
+  local obj = {
+    buffer = vim.api.nvim_create_buf(false, true),
+    layout = vim.tbl_deep_extend("force", popup_layout, opts.layout),
+    win_opts = opts.win_opts,
+    buf_opts = opts.buf_opts,
+  }
+
+  setmetatable(obj, Popup)
+
+  return obj
+end
+
+--- Display the popup with the provided content
+-- @param content_provider A function accepting the popup's layout and returning the content to display
+function Popup:display(content_provider)
+  self.win_id = vim.api.nvim_open_win(self.buffer, true, self.layout)
+  vim.lsp.util.close_preview_autocmd({ "BufHidden", "BufLeave" }, self.win_id)
+
+  local lines = content_provider(self.layout)
+  vim.api.nvim_buf_set_lines(self.bufnr, 0, -1, false, lines)
+
+  -- window options
+  for key, value in pairs(self.win_opts) do
+    vim.api.nvim_win_set_option(self.win_id, key, value)
+  end
+
+  -- buffer options
+  for key, value in pairs(self.buf_opts) do
+    vim.api.nvim_buf_set_option(self.buffer, key, value)
+  end
+end
+
+return Popup