fix: report truncated pane reads

refs #1717

3 files changed, 83 insertions, 34 deletions

diff --git a/src/app/api/agents.rs b/src/app/api/agents.rs
index ffb9cb63..f1977ce4 100644
--- a/src/app/api/agents.rs
+++ b/src/app/api/agents.rs
@@ -117,7 +117,7 @@ impl App {
         else {
             return agent_not_found(id, &params.target);
         };
-        let text = crate::app::api_helpers::read_terminal_snapshot(
+        let snapshot = crate::app::api_helpers::read_terminal_snapshot(
             pane,
             params.source,
             params.format,
@@ -137,9 +137,9 @@ impl App {
                         .unwrap(),
                     source: params.source,
                     format: params.format,
-                    text,
+                    text: snapshot.text,
                     revision: 0,
-                    truncated: false,
+                    truncated: snapshot.truncated,
                 },
             },
         )
diff --git a/src/app/api/panes.rs b/src/app/api/panes.rs
index 43206d1e..253fd627 100644
--- a/src/app/api/panes.rs
+++ b/src/app/api/panes.rs
@@ -1179,7 +1179,7 @@ impl App {
         else {
             return pane_not_found(id, &params.pane_id);
         };
-        let text = crate::app::api_helpers::read_terminal_snapshot(
+        let snapshot = crate::app::api_helpers::read_terminal_snapshot(
             pane,
             params.source,
             params.format,
@@ -1195,9 +1195,9 @@ impl App {
                     tab_id: self.public_tab_id(ws_idx, tab_idx).unwrap(),
                     source: params.source,
                     format: params.format,
-                    text,
+                    text: snapshot.text,
                     revision: 0,
-                    truncated: false,
+                    truncated: snapshot.truncated,
                 },
             },
         )
@@ -2002,6 +2002,28 @@ mod tests {
     }
 
     #[tokio::test]
+    async fn api_pane_read_reports_when_older_rows_are_omitted() {
+        let (mut app, public_pane_id, _pane_id) = app_with_scrollback_runtime();
+
+        let response = app.handle_pane_read(
+            "req".into(),
+            PaneReadParams {
+                pane_id: public_pane_id,
+                source: crate::api::schema::ReadSource::Recent,
+                lines: Some(2),
+                format: crate::api::schema::ReadFormat::Text,
+                strip_ansi: true,
+            },
+        );
+        let success: SuccessResponse = serde_json::from_str(&response).unwrap();
+        let ResponseResult::PaneRead { read } = success.result else {
+            panic!("expected pane read response");
+        };
+        assert!(read.text.contains("line 19"));
+        assert!(read.truncated);
+    }
+
+    #[tokio::test]
     async fn api_pane_send_keys_preserves_legacy_control_c_aliases() {
         let (mut app, pane_id, mut rx) = app_with_send_key_runtime(3);
 
diff --git a/src/app/api_helpers.rs b/src/app/api_helpers.rs
index 6c393dac..e0091b39 100644
--- a/src/app/api_helpers.rs
+++ b/src/app/api_helpers.rs
@@ -106,50 +106,77 @@ pub(super) fn read_terminal_snapshot(
     source: crate::api::schema::ReadSource,
     format: crate::api::schema::ReadFormat,
     lines: Option<u32>,
-) -> String {
+) -> crate::pane::TerminalReadSnapshot {
     use crate::api::schema::{ReadFormat, ReadSource};
 
-    let requested_lines = lines.unwrap_or(80).min(1000) as usize;
-    let text = match (format, source) {
-        (ReadFormat::Text, ReadSource::Visible) => terminal.visible_text(),
-        (ReadFormat::Text, ReadSource::Recent) => terminal.recent_text(requested_lines),
+    let line_limit = lines.map(|lines| lines.min(1000) as usize);
+    let recent_lines = line_limit.unwrap_or(80);
+    match (format, source) {
+        (ReadFormat::Text, ReadSource::Visible) => {
+            limit_snapshot_lines(terminal.visible_text(), line_limit)
+        }
+        (ReadFormat::Text, ReadSource::Recent) => terminal.recent_text_snapshot(recent_lines),
         (ReadFormat::Text, ReadSource::RecentUnwrapped) => {
-            terminal.recent_unwrapped_text(requested_lines)
+            terminal.recent_unwrapped_text_snapshot(recent_lines)
+        }
+        (ReadFormat::Text, ReadSource::Detection) => {
+            limit_snapshot_lines(terminal.detection_text(), line_limit)
+        }
+        (ReadFormat::Ansi, ReadSource::Visible) => {
+            limit_snapshot_lines(terminal.visible_ansi(), line_limit)
         }
-        (ReadFormat::Text, ReadSource::Detection) => terminal.detection_text(),
-        (ReadFormat::Ansi, ReadSource::Visible) => terminal.visible_ansi(),
-        (ReadFormat::Ansi, ReadSource::Recent) => terminal.recent_ansi(requested_lines),
+        (ReadFormat::Ansi, ReadSource::Recent) => terminal.recent_ansi_snapshot(recent_lines),
         (ReadFormat::Ansi, ReadSource::RecentUnwrapped) => {
-            terminal.recent_unwrapped_ansi(requested_lines)
+            terminal.recent_unwrapped_ansi_snapshot(recent_lines)
+        }
+        (ReadFormat::Ansi, ReadSource::Detection) => {
+            limit_snapshot_lines(terminal.detection_text(), line_limit)
         }
-        (ReadFormat::Ansi, ReadSource::Detection) => terminal.detection_text(),
-    };
-
-    if lines.is_some() && matches!(source, ReadSource::Visible | ReadSource::Detection) {
-        last_lines(&text, requested_lines)
-    } else {
-        text
     }
 }
 
-fn last_lines(text: &str, count: usize) -> String {
-    if text.is_empty() || count == 0 {
-        return String::new();
-    }
+fn limit_snapshot_lines(text: String, limit: Option<usize>) -> crate::pane::TerminalReadSnapshot {
+    let Some(limit) = limit else {
+        return crate::pane::TerminalReadSnapshot {
+            text,
+            truncated: false,
+        };
+    };
     let lines: Vec<_> = text.split_inclusive('\n').collect();
-    lines[lines.len().saturating_sub(count)..].concat()
+    crate::pane::TerminalReadSnapshot {
+        text: lines[lines.len().saturating_sub(limit)..].concat(),
+        truncated: lines.len() > limit,
+    }
 }
 
 #[cfg(test)]
 mod read_snapshot_tests {
-    use super::last_lines;
+    use super::limit_snapshot_lines;
+
+    #[test]
+    fn line_limit_preserves_endings_and_reports_omitted_lines() {
+        let snapshot = limit_snapshot_lines("one\ntwø\n三\n".into(), Some(2));
+        assert_eq!(snapshot.text, "twø\n三\n");
+        assert!(snapshot.truncated);
+
+        let snapshot = limit_snapshot_lines("one\ntwo\nthree".into(), Some(1));
+        assert_eq!(snapshot.text, "three");
+        assert!(snapshot.truncated);
+
+        let snapshot = limit_snapshot_lines("one\ntwo".into(), Some(0));
+        assert_eq!(snapshot.text, "");
+        assert!(snapshot.truncated);
+
+        let snapshot = limit_snapshot_lines("".into(), Some(2));
+        assert_eq!(snapshot.text, "");
+        assert!(!snapshot.truncated);
+    }
 
     #[test]
-    fn last_lines_preserves_real_line_endings_and_unicode() {
-        assert_eq!(last_lines("one\ntwø\n三\n", 2), "twø\n三\n");
-        assert_eq!(last_lines("one\ntwo\nthree", 1), "three");
-        assert_eq!(last_lines("one\ntwo", 0), "");
-        assert_eq!(last_lines("", 2), "");
+    fn omitted_line_limit_returns_the_complete_snapshot() {
+        let snapshot = limit_snapshot_lines("one\ntwo\n".into(), None);
+        assert_eq!(snapshot.text, "one\ntwo\n");
+        assert!(!snapshot.truncated);
     }
 }