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codex-rs/tui/src/backtrack_helpers.rs

@@ -0,0 +1,97 @@
+use ratatui::text::Line;
+
+/// Find the header index for the Nth last user message in the transcript.
+/// Returns `None` if `n == 0` or there are fewer than `n` user messages.
+pub(crate) fn find_nth_last_user_header_index(lines: &[Line<'_>], n: usize) -> Option<usize> {
+    if n == 0 {
+        return None;
+    }
+    let mut found = 0usize;
+    for (idx, line) in lines.iter().enumerate().rev() {
+        let content: String = line
+            .spans
+            .iter()
+            .map(|s| s.content.as_ref())
+            .collect::<Vec<_>>()
+            .join("");
+        if content.trim() == "user" {
+            found += 1;
+            if found == n {
+                return Some(idx);
+            }
+        }
+    }
+    None
+}
+
+/// Extract the text content of the Nth last user message.
+/// The message body is considered to be the lines following the "user" header
+/// until the first blank line.
+pub(crate) fn nth_last_user_text(lines: &[Line<'_>], n: usize) -> Option<String> {
+    let header_idx = find_nth_last_user_header_index(lines, n)?;
+    extract_message_text_after_header(lines, header_idx)
+}
+
+/// Extract message text starting after `header_idx` until the first blank line.
+pub(crate) fn extract_message_text_after_header(
+    lines: &[Line<'_>],
+    header_idx: usize,
+) -> Option<String> {
+    let start = header_idx + 1;
+    let mut out: Vec<String> = Vec::new();
+    for line in lines.iter().skip(start) {
+        let is_blank = line
+            .spans
+            .iter()
+            .all(|s| s.content.as_ref().trim().is_empty());
+        if is_blank {
+            break;
+        }
+        let text: String = line
+            .spans
+            .iter()
+            .map(|s| s.content.as_ref())
+            .collect::<Vec<_>>()
+            .join("");
+        out.push(text);
+    }
+    if out.is_empty() { None } else { Some(out.join("\n")) }
+}
+
+/// Compute the wrapped display-line offset before `header_idx`, for a given width.
+pub(crate) fn wrapped_offset_before(
+    lines: &[Line<'_>],
+    header_idx: usize,
+    width: u16,
+) -> usize {
+    let before = &lines[0..header_idx];
+    crate::insert_history::word_wrap_lines(before, width).len()
+}
+
+/// Given a header index, return the inclusive range for the message block
+/// [header_idx, end) where end is the first blank line after the header or the
+/// end of the transcript.
+pub(crate) fn highlight_range_from_header(lines: &[Line<'_>], header_idx: usize) -> (usize, usize) {
+    let mut end = header_idx + 1;
+    while end < lines.len() {
+        let is_blank = lines[end]
+            .spans
+            .iter()
+            .all(|s| s.content.as_ref().trim().is_empty());
+        if is_blank {
+            break;
+        }
+        end += 1;
+    }
+    (header_idx, end)
+}
+
+/// Convenience: compute the highlight range for the Nth last user message.
+pub(crate) fn highlight_range_for_nth_last_user(
+    lines: &[Line<'_>],
+    n: usize,
+) -> Option<(usize, usize)> {
+    let header = find_nth_last_user_header_index(lines, n)?;
+    Some(highlight_range_from_header(lines, header))
+}
+