Align selections via & (#1101)

* align lines

* remove log statement

* use selections to align

* fix a clippy issue

* only accept 1,2,3 as user count

* Update helix-term/src/commands.rs

Co-authored-by: Ivan Tham <pickfire@riseup.net>

* return if user count is not correct

* add doc

Co-authored-by: Ivan Tham <pickfire@riseup.net>

3 files changed, 73 insertions, 1 deletions

diff --git a/book/src/keymap.md b/book/src/keymap.md
index c88ed767..fbe77267 100644
--- a/book/src/keymap.md
+++ b/book/src/keymap.md
@@ -92,6 +92,7 @@
 | `s`      | Select all regex matches inside selections                        | `select_regex`                       |
 | `S`      | Split selection into subselections on regex matches               | `split_selection`                    |
 | `Alt-s`  | Split selection on newlines                                       | `split_selection_on_newline`         |
+| `&`      | Align selection in columns                                        | `align_selections`                   |
 | `_`      | Trim whitespace from the selection                                | `trim_selections`                    |
 | `;`      | Collapse selection onto a single cursor                           | `collapse_selection`                 |
 | `Alt-;`  | Flip selection cursor and anchor                                  | `flip_selections`                    |
diff --git a/helix-term/src/commands.rs b/helix-term/src/commands.rs
index fde505fd..a7179c30 100644
--- a/helix-term/src/commands.rs
+++ b/helix-term/src/commands.rs
@@ -314,6 +314,7 @@ impl Command {
         join_selections, "Join lines inside selection",
         keep_selections, "Keep selections matching regex",
         remove_selections, "Remove selections matching regex",
+        align_selections, "Align selections in column",
         keep_primary_selection, "Keep primary selection",
         remove_primary_selection, "Remove primary selection",
         completion, "Invoke completion popup",
@@ -657,6 +658,76 @@ fn trim_selections(cx: &mut Context) {
     };
 }
 
+// align text in selection
+fn align_selections(cx: &mut Context) {
+    let align_style = cx.count();
+    if align_style > 3 {
+        cx.editor.set_error(
+            "align only accept 1,2,3 as count to set left/center/right align".to_string(),
+        );
+        return;
+    }
+
+    let (view, doc) = current!(cx.editor);
+    let text = doc.text().slice(..);
+    let selection = doc.selection(view.id);
+    let mut column_widths = vec![];
+    let mut last_line = text.len_lines();
+    let mut column = 0;
+    // first of all, we need compute all column's width, let use max width of the selections in a column
+    for sel in selection {
+        let (l1, l2) = sel.line_range(text);
+        if l1 != l2 {
+            cx.editor
+                .set_error("align cannot work with multi line selections".to_string());
+            return;
+        }
+        // if the selection is not in the same line with last selection, we set the column to 0
+        column = if l1 != last_line { 0 } else { column + 1 };
+        last_line = l1;
+
+        if column < column_widths.len() {
+            if sel.to() - sel.from() > column_widths[column] {
+                column_widths[column] = sel.to() - sel.from();
+            }
+        } else {
+            // a new column, current selection width is the temp width of the column
+            column_widths.push(sel.to() - sel.from());
+        }
+    }
+    last_line = text.len_lines();
+    // once we get the with of each column, we transform each selection with to it's column width based on the align style
+    let transaction = Transaction::change_by_selection(doc.text(), selection, |range| {
+        let l = range.cursor_line(text);
+        column = if l != last_line { 0 } else { column + 1 };
+        last_line = l;
+
+        (
+            range.from(),
+            range.to(),
+            Some(
+                align_fragment_to_width(&range.fragment(text), column_widths[column], align_style)
+                    .into(),
+            ),
+        )
+    });
+
+    doc.apply(&transaction, view.id);
+    doc.append_changes_to_history(view.id);
+}
+
+fn align_fragment_to_width(fragment: &str, width: usize, align_style: usize) -> String {
+    let trimed = fragment.trim_matches(|c| c == ' ');
+    let mut s = " ".repeat(width - trimed.chars().count());
+    match align_style {
+        1 => s.insert_str(0, trimed),           // left align
+        2 => s.insert_str(s.len() / 2, trimed), // center align
+        3 => s.push_str(trimed),                // right align
+        n => unimplemented!("{}", n),
+    }
+    s
+}
+
 fn goto_window(cx: &mut Context, align: Align) {
     let (view, doc) = current!(cx.editor);
 
diff --git a/helix-term/src/keymap.rs b/helix-term/src/keymap.rs
index bf3b594e..7f6d0c6b 100644
--- a/helix-term/src/keymap.rs
+++ b/helix-term/src/keymap.rs
@@ -604,7 +604,7 @@ impl Default for Keymaps {
             // "q" => record_macro,
             // "Q" => replay_macro,
 
-            // & align selections
+            "&" => align_selections,
             "_" => trim_selections,
 
             "(" => rotate_selections_backward,