4 files changed, 143 insertions, 4 deletions
diff --git a/src/core/main.rs b/src/core/main.rs
index cb80d74..ffe1359 100644
--- a/src/core/main.rs
+++ b/src/core/main.rs
@@ -13,11 +13,10 @@ use crate::{
 		arguments::Args,
 		exit::Exit,
 		help::build_help,
-		modules::{ConfirmAbort, ConfirmRebase, Error, ExternalEditor, Insert, List, ShowCommit},
+		modules::{ConfirmAbort, ConfirmRebase, Error, ExternalEditor, Insert, List, ShowCommit, WindowSizeError},
 		process::Process,
 	},
 	module::{ExitStatus, Modules, State},
-	window_size_error::WindowSizeError,
 };
 
 pub(super) fn load_config() -> Result<Config, Exit> {
diff --git a/src/core/modules/mod.rs b/src/core/modules/mod.rs
index 0981152..20ac7c1 100644
--- a/src/core/modules/mod.rs
+++ b/src/core/modules/mod.rs
@@ -5,6 +5,7 @@ mod external_editor;
 mod insert;
 mod list;
 mod show_commit;
+mod window_size_error;
 
 pub use self::{
 	confirm_abort::ConfirmAbort,
@@ -14,4 +15,5 @@ pub use self::{
 	insert::Insert,
 	list::List,
 	show_commit::ShowCommit,
+	window_size_error::WindowSizeError,
 };
diff --git a/src/core/modules/window_size_error/mod.rs b/src/core/modules/window_size_error/mod.rs
new file mode 100644
index 0000000..f0730f5
--- /dev/null
+++ b/src/core/modules/window_size_error/mod.rs
@@ -0,0 +1,139 @@
+use input::{Event, EventHandler, InputOptions};
+use lazy_static::lazy_static;
+use todo_file::TodoFile;
+use view::{RenderContext, ViewData, ViewLine, ViewSender};
+
+use crate::module::{Module, ProcessResult, State};
+
+const HEIGHT_ERROR_MESSAGE: &str = "Window too small, increase height to continue";
+const SHORT_ERROR_MESSAGE: &str = "Window too small";
+const SIZE_ERROR_MESSAGE: &str = "Size!";
+
+lazy_static! {
+	static ref INPUT_OPTIONS: InputOptions = InputOptions::new().movement(true).resize(false);
+}
+
+pub struct WindowSizeError {
+	return_state: State,
+	view_data: ViewData,
+}
+
+impl Module for WindowSizeError {
+	fn activate(&mut self, _: &TodoFile, previous_state: State) -> ProcessResult {
+		self.return_state = previous_state;
+		ProcessResult::new()
+	}
+
+	fn build_view_data(&mut self, context: &RenderContext, _: &TodoFile) -> &ViewData {
+		let view_width = context.width();
+		let message = if !context.is_minimum_view_width() {
+			if view_width >= SHORT_ERROR_MESSAGE.len() {
+				SHORT_ERROR_MESSAGE
+			}
+			else {
+				// not much to do if the window gets too narrow
+				SIZE_ERROR_MESSAGE
+			}
+		}
+		else if view_width >= HEIGHT_ERROR_MESSAGE.len() {
+			HEIGHT_ERROR_MESSAGE
+		}
+		else {
+			// this message will always be safe here
+			SHORT_ERROR_MESSAGE
+		};
+
+		self.view_data.update_view_data(|updater| {
+			updater.clear();
+			updater.push_line(ViewLine::from(message));
+		});
+		&mut self.view_data
+	}
+
+	fn handle_events(&mut self, event_handler: &EventHandler, _: &ViewSender, _: &mut TodoFile) -> ProcessResult {
+		let event = event_handler.read_event(&INPUT_OPTIONS, |event, _| event);
+		let mut result = ProcessResult::from(event);
+
+		if let Event::Resize(width, height) = event {
+			let render_context = RenderContext::new(width, height);
+			if !render_context.is_window_too_small() {
+				result = result.state(self.return_state);
+			}
+		}
+
+		result
+	}
+}
+
+impl WindowSizeError {
+	pub fn new() -> Self {
+		Self {
+			return_state: State::List,
+			view_data: ViewData::new(|_| {}),
+		}
+	}
+}
+
+#[cfg(test)]
+mod tests {
+	use rstest::rstest;
+	use view::assert_rendered_output;
+
+	use super::*;
+	use crate::{assert_process_result, module::testutil::module_test};
+
+	const MINIMUM_WINDOW_HEIGHT: usize = 5;
+	const MINIMUM_WINDOW_HEIGHT_ERROR_WIDTH: usize = 45;
+
+	#[rstest(
+		width, height, expected,
+		case::width_too_small_long_message(SHORT_ERROR_MESSAGE.len(), MINIMUM_WINDOW_HEIGHT + 1, "Window too small"),
+		case::width_too_small_short_message(SHORT_ERROR_MESSAGE.len() - 1, MINIMUM_WINDOW_HEIGHT + 1, "Size!"),
+		case::height_too_small_long_message(
+			MINIMUM_WINDOW_HEIGHT_ERROR_WIDTH, MINIMUM_WINDOW_HEIGHT, "Window too small, increase height to continue"
+		),
+		case::height_too_small_short_message(
+			MINIMUM_WINDOW_HEIGHT_ERROR_WIDTH - 1, MINIMUM_WINDOW_HEIGHT, "Window too small"
+		)
+	)]
+	#[allow(clippy::cast_possible_wrap)]
+	fn build_view_data(width: usize, height: usize, expected: &str) {
+		module_test(&[], &[], |mut test_context| {
+			test_context.render_context.update(width as u16, height as u16);
+			let mut module = WindowSizeError::new();
+			let view_data = test_context.build_view_data(&mut module);
+			assert_rendered_output!(view_data, "{BODY}", format!("{{Normal}}{}", expected));
+		});
+	}
+
+	#[test]
+	fn event_resize_window_still_small() {
+		module_test(&[], &[Event::Resize(1, 1)], |mut test_context| {
+			let mut module = WindowSizeError::new();
+			test_context.activate(&mut module, State::ConfirmRebase);
+			assert_process_result!(test_context.handle_event(&mut module), event = Event::Resize(1, 1));
+		});
+	}
+
+	#[test]
+	fn event_resize_window_no_longer_too_small() {
+		module_test(&[], &[Event::Resize(100, 100)], |mut test_context| {
+			let mut module = WindowSizeError::new();
+			test_context.activate(&mut module, State::ConfirmRebase);
+			assert_process_result!(
+				test_context.handle_event(&mut module),
+				event = Event::Resize(100, 100),
+				state = State::ConfirmRebase
+			);
+		});
+	}
+
+	#[test]
+	fn event_other_character() {
+		module_test(&[], &[Event::from('a')], |mut test_context| {
+			let mut module = WindowSizeError::new();
+			test_context.activate(&mut module, State::ConfirmRebase);
+			assert_process_result!(test_context.handle_event(&mut module), event = Event::from('a'));
+		});
+	}
+}
diff --git a/src/core/process/tests.rs b/src/core/process/tests.rs
index da05998..659f801 100644
--- a/src/core/process/tests.rs
+++ b/src/core/process/tests.rs
@@ -8,9 +8,8 @@ use view::{assert_rendered_output, ViewData};
 
 use super::*;
 use crate::{
-	core::modules::Error,
+	core::modules::{Error, WindowSizeError},
 	module::{testutil::module_test, Module},
-	window_size_error::WindowSizeError,
 };
 
 struct TestModule {