1 files changed, 51 insertions, 0 deletions
diff --git a/src/history.rs b/src/history.rs
new file mode 100644
index 0000000..5216d10
--- /dev/null
+++ b/src/history.rs
@@ -0,0 +1,51 @@
+// god is dead and we have killed him and consequently std::time::Instant doesn't work on wasm
+
+use chrono::prelude::*;
+use wasm_bindgen::prelude::*;
+
+struct Reading {
+    time: DateTime<Local>,
+    queue_size: u32,
+}
+
+#[derive(Default)]
+pub struct History {
+    data: Vec<Reading>,
+}
+
+impl History {
+    pub fn record(&mut self, queue_size: u32) {
+        self.data.push(Reading {
+            time: Local::now(),
+            queue_size,
+        });
+    }
+
+    pub fn completion_time(&self) -> Option<js_sys::Date> {
+        // TODO make this not suck
+        let &Reading {
+            time: first_time,
+            queue_size: first_size,
+            ..
+        } = self.data.first()?;
+        let &Reading {
+            time: last_time,
+            queue_size: last_size,
+        } = self.data.last()?;
+        let overall_time_elapsed = last_time - first_time;
+        if overall_time_elapsed.is_zero() {
+            return None;
+        }
+        let overall_queue_motion = first_size - last_size;
+        if overall_queue_motion == 0 {
+            return None;
+        }
+        let duration_per_step = overall_time_elapsed / overall_queue_motion as i32;
+        let remaining_duration = duration_per_step * last_size as i32;
+        let completion_time = last_time + remaining_duration;
+        let completion_time_gmt = completion_time.timestamp_millis();
+        Some(js_sys::Date::new(&JsValue::from(
+            completion_time_gmt as f64,
+        )))
+    }
+}