refactor(nvim): use trim usercmd function from nvim docs

dots/.config/nvim/lua/core/autocmds.lua

@@ -10,28 +10,28 @@ M.setup = function()
         end,
     })
 
-    local strip_trail_space = true
-    vim.api.nvim_create_user_command("ToggleStripTrailSpace", function()
-        strip_trail_space = not strip_trail_space
+    local trim_trailing_whitespace_on_save = true
+    vim.api.nvim_create_user_command("ToggleTrimTrailingWhitespace", function()
+        trim_trailing_whitespace_on_save = not trim_trailing_whitespace_on_save
         local intercept_state = "`Enabled`"
-        if not strip_trail_space then
+        if not trim_trailing_whitespace_on_save then
             intercept_state = "`Disabled`"
         end
-        vim.notify("Strip Trail Space set to " .. intercept_state, vim.log.levels.INFO, {
-            title = "Strip Trail Space",
+        vim.notify("Trim Trailing Whitespace Space set to " .. intercept_state, vim.log.levels.INFO, {
+            title = "Trim Trailing Whitespace",
             ---@param win integer The window handle
             on_open = function(win)
                 vim.api.nvim_set_option_value("filetype", "markdown", { buf = vim.api.nvim_win_get_buf(win) })
             end,
         })
-    end, { desc = "Toggles intercepting BufWritePre to strip trail space" })
+    end, { desc = "Toggles intercepting BufWritePre to Trim Trailing Whitespace" })
 
     -- NOTE: Remove trailing whitespace on save
     vim.api.nvim_create_autocmd("BufWritePre", {
         group = augroup,
         callback = function()
-            if strip_trail_space then
-                vim.cmd.StripTrailSpace()
+            if trim_trailing_whitespace_on_save then
+                vim.cmd.TrimTrailingWhitespace()
             end
         end,
     })

dots/.config/nvim/lua/core/cmds.lua

@@ -1,6 +1,76 @@
 local M = {}
 M.setup = function()
-    vim.api.nvim_create_user_command("StripTrailSpace", "%s/\\s\\+$//e", {})
+    -- NOTE: TrimTrailingWhitespace user command
+
+    -- If invoked as a preview callback, performs 'inccommand' preview by
+    -- highlighting trailing whitespace in the current buffer.
+    local function trim_space_preview(opts, preview_ns, preview_buf)
+        vim.cmd("highlight clear Whitespace")
+        local line1 = opts.line1
+        local line2 = opts.line2
+        local buf = vim.api.nvim_get_current_buf()
+        local lines = vim.api.nvim_buf_get_lines(buf, line1 - 1, line2, false)
+        local preview_buf_line = 0
+
+        for i, line in ipairs(lines) do
+            local start_idx, end_idx = string.find(line, "%s+$")
+
+            if start_idx and end_idx then
+                -- Highlight the match
+                vim.api.nvim_buf_add_highlight(buf, preview_ns, "Substitute", line1 + i - 2, start_idx - 1, end_idx)
+
+                -- Add lines and set highlights in the preview buffer
+                -- if inccommand=split
+                if preview_buf then
+                    local prefix = string.format("|%d| ", line1 + i - 1)
+
+                    vim.api.nvim_buf_set_lines(
+                        preview_buf,
+                        preview_buf_line,
+                        preview_buf_line,
+                        false,
+                        { prefix .. line }
+                    )
+                    vim.api.nvim_buf_add_highlight(
+                        preview_buf,
+                        preview_ns,
+                        "Substitute",
+                        preview_buf_line,
+                        #prefix + start_idx - 1,
+                        #prefix + end_idx
+                    )
+                    preview_buf_line = preview_buf_line + 1
+                end
+            end
+        end
+
+        -- Return the value of the preview type
+        return 2
+    end
+
+    -- Trims all trailing whitespace in the current buffer.
+    local function trim_space(opts)
+        local line1 = opts.line1
+        local line2 = opts.line2
+        local buf = vim.api.nvim_get_current_buf()
+        local lines = vim.api.nvim_buf_get_lines(buf, line1 - 1, line2, false)
+
+        local new_lines = {}
+        for i, line in ipairs(lines) do
+            new_lines[i] = string.gsub(line, "%s+$", "")
+        end
+        vim.api.nvim_buf_set_lines(buf, line1 - 1, line2, false, new_lines)
+    end
+
+    -- Create the user command
+    vim.api.nvim_create_user_command(
+        "TrimTrailingWhitespace",
+        trim_space,
+        { nargs = "?", range = "%", addr = "lines", preview = trim_space_preview }
+    )
+
+    -- NOTE: DiffSaved user command
+
     vim.api.nvim_create_user_command("DiffSaved", function()
         -- Thanks to sindrets: https://github.com/sindrets/dotfiles/blob/1990282dba25aaf49897f0fc70ebb50f424fc9c4/.config/nvim/lua/user/lib.lua#L175
         -- Minor alterations by me