From c4dc35828252336fcd64d0cf1b7e35683701bc5c Mon Sep 17 00:00:00 2001
From: Wez Furlong <wez@wezfurlong.org>
Date: Tue, 27 Apr 2021 06:20:37 -0700
Subject: [PATCH] add truncate_left_to_width

refs: #647
---
 config/src/lua.rs                             | 31 +++++++++++++++++++
 docs/changelog.md                             |  2 +-
 .../lua/wezterm/truncate_left_to_width.md     | 15 +++++++++
 docs/config/lua/wezterm/truncate_to_width.md  |  3 ++
 4 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 docs/config/lua/wezterm/truncate_left_to_width.md

diff --git a/config/src/lua.rs b/config/src/lua.rs
index ac70896c4..87457365d 100644
--- a/config/src/lua.rs
+++ b/config/src/lua.rs
@@ -151,6 +151,37 @@ pub fn make_lua_context(config_file: &Path) -> anyhow::Result<Lua> {
             )?,
         )?;
 
+        wezterm_mod.set(
+            "truncate_left_to_width",
+            lua.create_function(
+                |_, (s, max_width, min_width): (String, usize, Option<usize>)| {
+                    let mut result = vec![];
+                    let mut len = 0;
+                    for g in s.graphemes(true).rev() {
+                        let g_len = grapheme_column_width(g);
+                        if g_len + len > max_width {
+                            break;
+                        }
+                        result.push(g);
+                        len += g_len;
+                    }
+
+                    if let Some(min_width) = min_width {
+                        while len < min_width {
+                            if len >= max_width {
+                                break;
+                            }
+                            result.push(" ");
+                            len += 1;
+                        }
+                    }
+
+                    result.reverse();
+                    Ok(result.join(""))
+                },
+            )?,
+        )?;
+
         wezterm_mod.set("font", lua.create_function(font)?)?;
         wezterm_mod.set(
             "font_with_fallback",
diff --git a/docs/changelog.md b/docs/changelog.md
index d3c60aff2..949c0ec53 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -46,7 +46,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Fixed: tabs would remain hovered after moving the mouse down into the main terminal area [#591](https://github.com/wez/wezterm/issues/591)
 * New: [tab_bar_at_bottom](config/lua/config/tab_bar_at_bottom.md) setting to put the tab bar at the bottom of the window [#278](https://github.com/wez/wezterm/issues/278)
 * New: [wezterm.column_width](config/lua/wezterm/column_width.md) function for measuring the displayed width of a string
-* New: [wezterm.truncate_to_width](config/lua/wezterm/truncate_to_width.md) function for truncating/padding a string based on its displayed width
+* New: [wezterm.truncate_to_width](config/lua/wezterm/truncate_to_width.md) and [wezterm.truncate_left_to_width](config/lua/wezterm/truncate_left_to_width.md) function for truncating/padding a string based on its displayed width
 
 ### 20210405-110924-a5bb5be8
 
diff --git a/docs/config/lua/wezterm/truncate_left_to_width.md b/docs/config/lua/wezterm/truncate_left_to_width.md
new file mode 100644
index 000000000..1c487eaa2
--- /dev/null
+++ b/docs/config/lua/wezterm/truncate_left_to_width.md
@@ -0,0 +1,15 @@
+# wezterm.truncate_left_to_width(string, max_width, min_width)
+
+*Since: nightly builds only*
+
+Returns a copy of `string` that is no longer than `max_width` columns
+(as measured by [wezterm.column_width](column_width.md)), and, optionally,
+no shorter than `min_width` columns, padding out with spaces.
+
+Truncation and padding occur on the left hand side of the string.
+
+For example, `wezterm.truncate_to_width("hello", 3)` returns `"llo"`,
+and `wezterm.truncate_to_width("a", 10, 5)` returns "    a"`.
+
+See also: [wezterm.truncate_to_width](truncate_to_width.md)
+
diff --git a/docs/config/lua/wezterm/truncate_to_width.md b/docs/config/lua/wezterm/truncate_to_width.md
index 632b31f6a..a78a26502 100644
--- a/docs/config/lua/wezterm/truncate_to_width.md
+++ b/docs/config/lua/wezterm/truncate_to_width.md
@@ -6,6 +6,9 @@ Returns a copy of `string` that is no longer than `max_width` columns
 (as measured by [wezterm.column_width](column_width.md)), and, optionally,
 no shorter than `min_width` columns, padding out with spaces.
 
+Truncation and padding occur on the right hand side of the string.
+
 For example, `wezterm.truncate_to_width("hello", 3)` returns `"hel"`,
 and `wezterm.truncate_to_width("a", 10, 5)` returns "a    "`.
 
+See also: [wezterm.truncate_left_to_width](truncate_left_to_width.md)