From 3f519376b24467ddbc544094bee77cd747d66038 Mon Sep 17 00:00:00 2001
From: Jet Pham <55770902+jetpham@users.noreply.github.com>
Date: Sat, 7 Jun 2025 12:41:57 -0700
Subject: [PATCH] feat: add a finite state machine for debouncing

---
 src/gpio.rs | 64 ++++++++++++++++++++++++++++++++++++++++++++---------
 src/main.rs |  4 +++-
 2 files changed, 57 insertions(+), 11 deletions(-)

diff --git a/src/gpio.rs b/src/gpio.rs
index 6bdb95d..db2f630 100644
--- a/src/gpio.rs
+++ b/src/gpio.rs
@@ -1,4 +1,4 @@
-use std::time::Duration;
+use std::time::{Duration, Instant};
 use std::fmt;
 use serde::{Serialize, Deserialize};
 
@@ -11,6 +11,14 @@ pub enum CircuitEvent {
     Closed,
 }
 
+#[derive(Debug, PartialEq)]
+enum FsmState {
+    Idle,
+    DebouncingHigh,
+    High,
+    DebouncingLow,
+}
+
 impl fmt::Display for CircuitEvent {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
@@ -23,32 +31,68 @@ impl fmt::Display for CircuitEvent {
 pub struct GpioMonitor {
     pin: InputPin,
     poll_interval: Duration,
+    debounce_delay: Duration,
+    state: FsmState,
+    last_potential_transition_time: Instant,
 }
 
 impl GpioMonitor {
-    pub fn new(pin_number: u8, poll_interval: Duration) -> Result<Self> {
+    pub fn new(pin_number: u8, poll_interval: Duration, debounce_delay: Duration) -> Result<Self> {
         let gpio = Gpio::new()
             .context("Failed to initialize GPIO")?;
         let pin = gpio.get(pin_number)
             .context(format!("Failed to get GPIO pin {}", pin_number))?
             .into_input_pullup();
 
-        Ok(Self { pin, poll_interval })
+        Ok(Self { 
+            pin, 
+            poll_interval,
+            debounce_delay,
+            state: FsmState::Idle,
+            last_potential_transition_time: Instant::now(),
+        })
     }
 
     pub async fn monitor<F>(&mut self, mut callback: F) -> Result<()>
     where
         F: FnMut(CircuitEvent) + Send + 'static,
     {
-        let mut previous_state = self.get_current_state();
-        callback(previous_state); // Send initial state
-
         loop {
-            let current_state = self.get_current_state();
+            let current_switch_reading = self.get_current_state() == CircuitEvent::Closed;
+            let time_since_last_change = self.last_potential_transition_time.elapsed();
 
-            if current_state != previous_state {
-                callback(current_state);
-                previous_state = current_state;
+            match self.state {
+                FsmState::Idle => {
+                    if current_switch_reading {
+                        self.state = FsmState::DebouncingHigh;
+                        self.last_potential_transition_time = Instant::now();
+                    }
+                }
+                
+                FsmState::DebouncingHigh => {
+                    if !current_switch_reading {
+                        self.state = FsmState::Idle;
+                    } else if time_since_last_change >= self.debounce_delay {
+                        self.state = FsmState::High;
+                        callback(CircuitEvent::Closed);
+                    }
+                }
+                
+                FsmState::High => {
+                    if !current_switch_reading {
+                        self.state = FsmState::DebouncingLow;
+                        self.last_potential_transition_time = Instant::now();
+                    }
+                }
+                
+                FsmState::DebouncingLow => {
+                    if current_switch_reading {
+                        self.state = FsmState::High;
+                    } else if time_since_last_change >= self.debounce_delay {
+                        self.state = FsmState::Idle;
+                        callback(CircuitEvent::Open);
+                    }
+                }
             }
 
             tokio::time::sleep(self.poll_interval).await;
diff --git a/src/main.rs b/src/main.rs
index bcaf0ff..9c2fa04 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,6 +13,7 @@ use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt};
 
 const DEFAULT_GPIO_PIN: u8 = 17;
 const DEFAULT_POLL_INTERVAL_MS: u64 = 100;
+const DEFAULT_DEBOUNCE_DELAY_SECS: u64 = 5;
 const LOG_DIR: &str = "logs";
 const LOG_PREFIX: &str = "noisebell";
 const LOG_SUFFIX: &str = "log";
@@ -54,7 +55,8 @@ async fn main() -> Result<()> {
     info!("initializing gpio monitor");
     let mut gpio_monitor = gpio::GpioMonitor::new(
         DEFAULT_GPIO_PIN,
-        Duration::from_millis(DEFAULT_POLL_INTERVAL_MS)
+        Duration::from_millis(DEFAULT_POLL_INTERVAL_MS),
+        Duration::from_secs(DEFAULT_DEBOUNCE_DELAY_SECS)
     )?;
 
     // Set up the callback for state changes