From fffdc8aab1086eb60bc9537fafb725ba876c46f2 Mon Sep 17 00:00:00 2001
From: Melody Horn <melody@boringcactus.com>
Date: Sat, 4 Dec 2021 20:37:59 -0700
Subject: slightly improve ETA calculation

---
 index.html     |  2 +-
 src/history.rs | 64 +++++++++++++++++++++++++++++++++++++++-------------------
 2 files changed, 44 insertions(+), 22 deletions(-)

diff --git a/index.html b/index.html
index 4359092..cb5aa8c 100644
--- a/index.html
+++ b/index.html
@@ -31,7 +31,7 @@
     <h2>For tracking your Login Queue (Extreme) raid progression.</h2>
     <p>
         Share your FFXIV window, and then this tool will try to calculate how much longer you probably have to wait.
-        (The actual calculation isn't very sophisticated, but it's better than nothing.)
+        (The actual calculation isn't very well-designed, but it's better than nothing.)
         (Also this is incredibly janky; if anything breaks or misbehaves try reloading the page.)
     </p>
     <h2><button id="bootbutton">Start!</button></h2>
diff --git a/src/history.rs b/src/history.rs
index f8ffec2..6031499 100644
--- a/src/history.rs
+++ b/src/history.rs
@@ -1,6 +1,7 @@
 // god is dead and we have killed him and consequently std::time::Instant doesn't work on wasm
 
 use chrono::prelude::*;
+use chrono::Duration;
 use wasm_bindgen::prelude::*;
 
 struct Reading {
@@ -18,36 +19,57 @@ pub enum NoETA {
     Fuck,
 }
 
+// Duration doesn't impl Mul<f32> so we have to do percents
+const RECENCY_PERCENT: i32 = 20;
+
 impl History {
     pub fn record(&mut self, queue_size: u32) {
-        self.data.push(Reading {
-            time: Local::now(),
-            queue_size,
-        });
+        let redundant = match self.data.last() {
+            Some(last) => queue_size == last.queue_size,
+            None => false,
+        };
+        if !redundant {
+            self.data.push(Reading {
+                time: Local::now(),
+                queue_size,
+            });
+        }
     }
 
     pub fn completion_time(&self) -> Result<js_sys::Date, NoETA> {
-        // TODO make this not suck
-        let &Reading {
-            time: first_time,
-            queue_size: first_size,
-            ..
-        } = self.data.first().ok_or(NoETA::Pending)?;
+        let weighted_average_step_time = self
+            .data
+            .iter()
+            .zip(self.data.iter().skip(1))
+            .map(|(one, two)| {
+                // queue velocity should ideally be measured in distance per time,
+                // but the units wind up fucky (reciprocal duration not implemented)
+                // so instead we use time per distance
+                if one.time > two.time {
+                    return Err(NoETA::Fuck);
+                }
+                let delta_time = two.time - one.time;
+                let delta_queue = match one.queue_size.checked_sub(two.queue_size) {
+                    Some(d) => d,
+                    None => return Err(NoETA::Fuck),
+                };
+                Ok(delta_time / delta_queue as i32)
+            })
+            .reduce(|previous, current| match (previous, current) {
+                (Ok(previous), Ok(current)) => {
+                    let previous_term = previous * (100 - RECENCY_PERCENT) / 100;
+                    let current_term = current * RECENCY_PERCENT / 100;
+                    Ok(previous_term + current_term)
+                }
+                (Err(e), _) => Err(e),
+                (_, Err(e)) => Err(e),
+            })
+            .ok_or(NoETA::Pending)??;
         let &Reading {
             time: last_time,
             queue_size: last_size,
         } = self.data.last().ok_or(NoETA::Pending)?;
-        let overall_time_elapsed = last_time - first_time;
-        if overall_time_elapsed.is_zero() {
-            return Err(NoETA::Pending);
-        }
-        let overall_queue_motion = match first_size.checked_sub(last_size) {
-            Some(0) => return Err(NoETA::Pending),
-            Some(x) => x,
-            None => return Err(NoETA::Fuck),
-        };
-        let duration_per_step = overall_time_elapsed / overall_queue_motion as i32;
-        let remaining_duration = duration_per_step * last_size as i32;
+        let remaining_duration = weighted_average_step_time * last_size as i32;
         let completion_time = last_time + remaining_duration;
         let completion_time_gmt = completion_time.timestamp_millis();
         Ok(js_sys::Date::new(&JsValue::from(
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