Add a method to check status & get the current price (#5)

* add helper method

* fix paren

* update example and docs

Co-authored-by: Jayant Krishnamurthy <[email protected]>

Author: jayantk

README.md

@@ -4,3 +4,37 @@ A rust API for desribing on-chain pyth account structures.  A primer on pyth acc
 
 
 Contains a library for use in on-chain program development and an off-chain example program for loading and printing product reference data and aggregate prices from all devnet pyth accounts.
+
+### Running the Example
+
+The example program prints the product reference data and current price information for Pyth on Solana devnet.
+Run the following commands to try this example program:
+
+```
+cargo build --examples
+cargo run --example get_accounts
+```
+
+The output of this command is a listing of Pyth's accounts, such as:
+
+```
+product_account .. 6MEwdxe4g1NeAF9u6KDG14anJpFsVEa2cvr5H6iriFZ8
+  symbol.......... SRM/USD
+  asset_type...... Crypto
+  quote_currency.. USD
+  description..... SRM/USD
+  generic_symbol.. SRMUSD
+  base............ SRM
+  price_account .. 992moaMQKs32GKZ9dxi8keyM2bUmbrwBZpK4p2K6X5Vs
+    price ........ 7398000000
+    conf ......... 3200000
+    price_type ... price
+    exponent ..... -9
+    status ....... trading
+    corp_act ..... nocorpact
+    num_qt ....... 1
+    valid_slot ... 91340924
+    publish_slot . 91340925
+    twap ......... 7426390900
+    twac ......... 2259870
+```

examples/get_accounts.rs

@@ -107,18 +107,30 @@ fn main() {
         loop {
           let pd = clnt.get_account_data( &px_pkey ).unwrap();
           let pa = cast::<Price>( &pd );
+
+          let maybe_price = pa.get_current_price();
           assert_eq!( pa.magic, MAGIC, "not a valid pyth account" );
           assert_eq!( pa.atype, AccountType::Price as u32,
                      "not a valid pyth price account" );
           assert_eq!( pa.ver, VERSION_2,
                       "unexpected pyth price account version" );
           println!( "  price_account .. {:?}", px_pkey );
+          match maybe_price {
+            Some((price, confidence, _)) => {
+              println!("    price ........ {}", price);
+              println!("    conf ......... {}", confidence);
+            }
+            None => {
+              println!("    price ........ unavailable");
+              println!("    conf ......... unavailable");
+            }
+          }
+
           println!( "    price_type ... {}", get_price_type(&pa.ptype));
           println!( "    exponent ..... {}", pa.expo );
           println!( "    status ....... {}", get_status(&pa.agg.status));
           println!( "    corp_act ..... {}", get_corp_act(&pa.agg.corp_act));
-          println!( "    price ........ {}", pa.agg.price );
-          println!( "    conf ......... {}", pa.agg.conf );
+
           println!( "    num_qt ....... {}", pa.num_qt );
           println!( "    valid_slot ... {}", pa.valid_slot );
           println!( "    publish_slot . {}", pa.agg.pub_slot );

src/lib.rs

@@ -131,6 +131,27 @@ pub struct Price
   pub comp       : [PriceComp;32] // price components one per quoter
 }
 
+impl Price {
+  /**
+   * Get the current price and confidence interval as fixed-point numbers. Returns a triple of
+   * the current price, confidence interval, and the exponent for both numbers (i.e., the number
+   * of decimal places.)
+   * For example:
+   *
+   * get_current_price() -> Some((12345, 267, -2)) // represents 123.45 +- 2.67
+   * get_current_price() -> Some((123, 1, 2)) // represents 12300 +- 100
+   *
+   * Returns None if price information is currently unavailable.
+   */
+  pub fn get_current_price(&self) -> Option<(i64, u64, i32)> {
+    if !matches!(self.agg.status, PriceStatus::Trading) {
+      None
+    } else {
+      Some((self.agg.price, self.agg.conf, self.expo))
+    }
+  }
+}
+
 struct AccKeyU64
 {
   pub val: [u64;4]