Add confirmation prompts for modifications of lots of tasks

cli/src/invocation/cmd/modify.rs

@@ -1,15 +1,58 @@
 use crate::argparse::{Filter, Modification};
-use crate::invocation::{apply_modification, filtered_tasks, summarize_task};
+use crate::invocation::util::{confirm, summarize_task};
+use crate::invocation::{apply_modification, filtered_tasks};
+use crate::settings::Settings;
 use taskchampion::Replica;
 use termcolor::WriteColor;
 
+/// confirm modification of more than `modificationt_count_prompt` tasks, defaulting to 3
+fn check_modification<W: WriteColor>(
+    w: &mut W,
+    settings: &Settings,
+    affected_tasks: usize,
+) -> Result<bool, crate::Error> {
+    let setting = settings.modification_count_prompt.unwrap_or(3);
+    if setting == 0 || affected_tasks <= setting as usize {
+        return Ok(true);
+    }
+
+    let prompt = format!("Operation will modify {} tasks; continue?", affected_tasks,);
+    if confirm(&prompt)? {
+        return Ok(true);
+    }
+
+    writeln!(w, "Cancelled")?;
+
+    // only show this help if the setting is not set
+    if settings.modification_count_prompt.is_none() {
+        writeln!(
+            w,
+            "Set the `modification_count_prompt` setting to avoid this prompt:"
+        )?;
+        writeln!(
+            w,
+            "    ta config set modification_count_prompt {}",
+            affected_tasks + 1
+        )?;
+        writeln!(w, "Set it to 0 to disable the prompt entirely")?;
+    }
+    Ok(false)
+}
+
 pub(crate) fn execute<W: WriteColor>(
     w: &mut W,
     replica: &mut Replica,
+    settings: &Settings,
     filter: Filter,
     modification: Modification,
 ) -> Result<(), crate::Error> {
-    for task in filtered_tasks(replica, &filter)? {
+    let tasks = filtered_tasks(replica, &filter)?;
+
+    if !check_modification(w, settings, tasks.size_hint().0)? {
+        return Ok(());
+    }
+
+    for task in tasks {
         let mut task = task.into_mut(replica);
 
         apply_modification(&mut task, &modification)?;
@@ -34,6 +77,7 @@ mod test {
     fn test_modify() {
         let mut w = test_writer();
         let mut replica = test_replica();
+        let settings = Settings::default();
 
         let task = replica
             .new_task(Status::Pending, s!("old description"))
@@ -46,7 +90,7 @@ mod test {
             description: DescriptionMod::Set(s!("new description")),
             ..Default::default()
         };
-        execute(&mut w, &mut replica, filter, modification).unwrap();
+        execute(&mut w, &mut replica, &settings, filter, modification).unwrap();
 
         // check that the task appeared..
         let task = replica.get_task(task.get_uuid()).unwrap().unwrap();