new: better stats

examples/simple_strategy.rs

@@ -3,7 +3,6 @@ use backtestingfx::broker::Broker;
 use backtestingfx::strategy::Strategy;
 use backtestingfx::engine::Engine;
 use backtestingfx::data::load_csv;
-use backtestingfx::stats::Stats;
 
 
 struct BuyEveryBar;
@@ -20,9 +19,7 @@ fn main() {
     let mut engine = Engine::new(data, 10_000.0, 0.0, 0.00010);
     let mut strategy = BuyEveryBar;
 
-    engine.run(&mut strategy); // main line that runs the strategy 
+    let stats = engine.run(&mut strategy);
-
-    let stats = Stats::compute(&engine.broker, 10_000.0);
     println!("{}", stats);
 }
 

src/broker.rs

@@ -3,6 +3,7 @@ use crate::types::{Position, Trade};
 
 pub struct Broker{
     pub cash: f64,
+    pub initial_cash: f64,
     pub positions: Vec<Position>,
     pub trade_history: Vec<Trade>,
     pub commission: f64,
@@ -13,6 +14,7 @@ impl Broker {
     pub fn new(initial_cash: f64, commission: f64, spread: f64) -> Self {     // does not need &mut because it initialises something new 
         Broker {
             cash: initial_cash,
+            initial_cash,
             positions: Vec::new(),
             trade_history: Vec::new(),
             commission,
@@ -37,7 +39,7 @@ impl Broker {
         let fill_price = price - self.spread; // buy at ask 
         self.cash -= self.commission * lot_size; // pay commission   // needs to modify the broker with new position. (.push works with the Vec::)
         self.positions.push(Position {
-            id : 0,
+            id : self.positions.len() as u64,
             entry_price: fill_price,
             lot_size,
             is_long: false,
@@ -88,5 +90,16 @@ impl Broker {
         }
     }
 
+    pub fn equity(&self, current_price: f64) -> f64 { // computes unrealised positions from the opened positions
+        let unrealized: f64 = self.positions.iter().map(|p| {
+            if p.is_long {
+                (current_price - p.entry_price) * p.lot_size
+            } else {
+                (p.entry_price - current_price) * p.lot_size
+            }
+        }).sum();
+
+        self.cash + unrealized
+    }
     
 }

src/engine.rs

@@ -1,23 +1,29 @@
 use crate::types::Bar;
 use crate::broker::Broker;
 use crate::strategy::Strategy;
+use crate::stats::Stats;
 
 pub struct Engine {
     pub data: Vec<Bar>,
-    pub broker: Broker
+    pub broker: Broker,
+    pub equity_curve: Vec<f64>
 }
 
 impl Engine {
     pub fn new(data: Vec<Bar>, initial_cash: f64, commission: f64, spread: f64) -> Self {
         Engine {
             data,
-            broker : Broker::new(initial_cash, commission, spread) // it takes initial cash and not Broker as Engine is responsible for broker not the user 
+            broker : Broker::new(initial_cash, commission, spread), // it takes initial cash and not Broker as Engine is responsible for broker not the user 
+            equity_curve: Vec::new()
         }
     }
 
-    pub fn run (&mut self, strategy: &mut dyn Strategy) { //&mut dyn allows class inheritence 
+    pub fn run (&mut self, strategy: &mut dyn Strategy) -> Stats {
+        strategy.init(&self.data);
         for bar in &self.data {
             strategy.next(bar, &mut self.broker);
+            self.equity_curve.push(self.broker.equity(bar.close));
         }
+        Stats::compute(&self.broker, &self.equity_curve)
     }
 }

src/stats.rs

@@ -11,11 +11,32 @@ use crate::broker::Broker;
       pub best_trade: f64,
       pub worst_trade: f64,
       pub profit_factor: f64,
+      pub max_drawdown_pct: f64
+      
+  }
+
+  fn max_drawdown(equity_curve: &[f64]) -> f64 {
+      let mut peak = f64::NEG_INFINITY;
+      let mut max_dd = 0.0f64;
+
+      for &equity in equity_curve {
+          if equity > peak {
+              peak = equity;
+          }
+          if peak > 0.0 {
+              let dd = (peak - equity) / peak * 100.0;
+              if dd > max_dd {
+                  max_dd = dd;
+              }
+          }
+      }
+      max_dd
   }
 
   impl Stats {
-      pub fn compute(broker: &Broker, initial_cash: f64) -> Self {
+      pub fn compute(broker: &Broker, equity_curve: &[f64]) -> Self {
           let num_trades = broker.trade_history.len();
+          let initial_cash = broker.initial_cash;
           let final_cash = broker.cash;
           let total_return_pct = (final_cash - initial_cash) / initial_cash * 100.0;
 
@@ -39,6 +60,7 @@ use crate::broker::Broker;
               .filter(|t| t.pnl < 0.0).map(|t| t.pnl.abs()).sum();
           let profit_factor = if gross_loss > 0.0 { gross_profit / gross_loss } else {
   f64::INFINITY };
+            let max_drawdown_pct = max_drawdown(equity_curve);
 
           Stats {
               initial_cash,
@@ -51,6 +73,7 @@ use crate::broker::Broker;
               best_trade: if num_trades > 0 { best_trade } else { 0.0 },
               worst_trade: if num_trades > 0 { worst_trade } else { 0.0 },
               profit_factor,
+              max_drawdown_pct
           }
       }
   }
@@ -67,10 +90,12 @@ use crate::broker::Broker;
                Avg PnL:        {:.5}\n\
                Best Trade:     {:.5}\n\
                Worst Trade:    {:.5}\n\
-               Profit Factor:  {:.2}",
+               Profit Factor:  {:.2}\n\
+               Max Drawdown:   {:.2}%",
               self.initial_cash, self.final_cash, self.total_return_pct,
               self.num_trades, self.win_rate_pct, self.avg_pnl,
-              self.best_trade, self.worst_trade, self.profit_factor
+              self.best_trade, self.worst_trade, self.profit_factor,
+              self.max_drawdown_pct
           )
       }
   }

src/strategy.rs

@@ -2,6 +2,7 @@ use crate::types::Bar;
 use crate::broker::Broker;
 
 pub trait Strategy {
+    fn init(&mut self, _data: &[Bar]) {}
     fn next(&mut self, bar: &Bar, broker: &mut Broker);
 }