Support the case where a PiJuice isn't present

PiJuiceSharp/AbsentPiJuiceStatus.cs

@@ -0,0 +1,72 @@
+
+namespace PiJuiceSharp
+{
+    /// <summary>
+    /// A placeholder implementation of <see cref="IPiJuiceStatus"/> that returns default values for when no PiJuice
+    /// interface is present at all.
+    /// </summary>
+    public sealed class AbsentPiJuiceStatus : IPiJuiceStatus
+    {
+        public void Dispose()
+        {
+        }
+
+        public float GetBatteryCurrent()
+        {
+            return 0F;
+        }
+
+        public int GetBatteryTemperature()
+        {
+            return 0;
+        }
+
+        public float GetBatteryVoltage()
+        {
+            return 0F;
+        }
+
+        public int GetChargeLevel()
+        {
+            return 0;
+        }
+
+        public Dictionary<string, object> GetFaultStatus()
+        {
+            return new();
+        }
+
+        public float GetGpioCurrent()
+        {
+            return 0F;
+        }
+
+        public float GetGpioVoltage()
+        {
+            return 0F;
+        }
+
+        public LedBlinkState GetLedBlinkState(Led led)
+        {
+            return new();
+        }
+
+        public Color GetLedState(Led led)
+        {
+            return new();
+        }
+
+        public StatusInfo GetStatus()
+        {
+            return new StatusInfo(false, false, BatteryStatus.NoPiJuice, PowerInputStatus.NotPresent, PowerInputStatus.NotPresent);
+        }
+
+        public void SetLedBlinkState(Led led, LedBlinkState state)
+        {
+        }
+
+        public void SetLedState(Led led, Color color)
+        {
+        }
+    }
+}

PiJuiceSharp/IPiJuiceStatus.cs

@@ -0,0 +1,19 @@
+
+namespace PiJuiceSharp
+{
+    public interface IPiJuiceStatus : IDisposable
+    {
+        float GetBatteryCurrent();
+        int GetBatteryTemperature();
+        float GetBatteryVoltage();
+        int GetChargeLevel();
+        Dictionary<string, object> GetFaultStatus();
+        float GetGpioCurrent();
+        float GetGpioVoltage();
+        LedBlinkState GetLedBlinkState(Led led);
+        Color GetLedState(Led led);
+        StatusInfo GetStatus();
+        void SetLedBlinkState(Led led, LedBlinkState state);
+        void SetLedState(Led led, Color color);
+    }
+}

PiJuiceSharp/PiJuiceInterface.cs

@@ -1,4 +1,5 @@
 using System.Device.I2c;
+using System.Diagnostics.CodeAnalysis;
 
 namespace PiJuiceSharp
 {
@@ -8,14 +9,27 @@ public sealed class PiJuiceInterface : IDisposable
         private readonly I2cDevice i2cDevice;
         private readonly int address;
 
-
-        public PiJuiceInterface(int busId = 1, int deviceAddress = 0x14)
+        private PiJuiceInterface(int busId = 1, int deviceAddress = 0x14)
         {
             var settings = new I2cConnectionSettings(busId, deviceAddress);
             this.i2cDevice = I2cDevice.Create(settings);
             this.address = deviceAddress;
         }
 
+        public static bool TryConnect([NotNullWhen(true)] out PiJuiceInterface? piJuiceInterface)
+        {
+            try
+            {
+                piJuiceInterface = new PiJuiceInterface();
+                return true;
+            }
+            catch (IOException)
+            {
+                piJuiceInterface = null;
+                return false;
+            }
+        }
+
         public void Dispose()
         {
             this.i2cDevice?.Dispose();

PiJuiceSharp/PiJuiceSharp.csproj

@@ -24,7 +24,7 @@
 		<EnableNETAnalyzers>True</EnableNETAnalyzers>
 		<AnalysisLevel>latest-all</AnalysisLevel>
 		<EnforceCodeStyleInBuild>True</EnforceCodeStyleInBuild>
-		<Version>0.2.0</Version>
+		<Version>0.3.0</Version>
 		<TreatWarningsAsErrors>True</TreatWarningsAsErrors>
 	</PropertyGroup>
 

PiJuiceSharp/PiJuiceStatus.cs

@@ -1,7 +1,7 @@
 
 namespace PiJuiceSharp
 {
-    public sealed class PiJuiceStatus : IDisposable
+    public sealed class PiJuiceStatus : IPiJuiceStatus
     {
         private const byte STATUS_CMD = 0x40;
         private const byte CHARGE_LEVEL_CMD = 0x41;
@@ -15,11 +15,23 @@ public sealed class PiJuiceStatus : IDisposable
         private const byte LED_BLINK_CMD = 0x68;
         private readonly PiJuiceInterface piJuiceInterface;
 
-        public PiJuiceStatus(PiJuiceInterface piJuiceInterface)
+        private PiJuiceStatus(PiJuiceInterface piJuiceInterface)
         {
             this.piJuiceInterface = piJuiceInterface;
         }
 
+        public static IPiJuiceStatus Create()
+        {
+#pragma warning disable CA2000 // Dispose objects before losing scope - the PiJuiceInterface is disposed by the returned object
+            if (PiJuiceInterface.TryConnect(out PiJuiceInterface? piJuiceInterface))
+            {
+                return new PiJuiceStatus(piJuiceInterface);
+            }
+#pragma warning restore CA2000 // Dispose objects before losing scope
+
+            return new AbsentPiJuiceStatus();
+        }
+
         public StatusInfo GetStatus()
         {
             byte d = this.piJuiceInterface.Read(STATUS_CMD);

PiJuiceSharp/StatusInfo.cs

@@ -2,10 +2,31 @@
 {
     public enum BatteryStatus
     {
+        /// <summary>
+        /// Battery is present, but not charging
+        /// </summary>
         Normal = 0,
+
+        /// <summary>
+        /// Battery is charging from the its power input
+        /// </summary>
         ChargingFromIn = 1,
+
+        /// <summary>
+        /// Battery is charging from the 5V IO pin
+        /// </summary>
         ChargingFrom5vIo = 2,
-        NotPresent = 3
+
+        /// <summary>
+        /// The PiJuice board is present, but no battery is connected
+        /// </summary>
+        NotPresent = 3,
+
+        /// <summary>
+        /// No PiJuice board is present - no readings will be available. This is an extension to the
+        /// original PiJuice Python library.
+        /// </summary>
+        NoPiJuice = 8000,
     }
 
     public enum PowerInputStatus

PiJuiceTest/Program.cs

@@ -2,9 +2,7 @@
 
 using static System.Console;
 
-var piJuiceInterface = new PiJuiceInterface();
-
-var piJuiceStatus = new PiJuiceStatus(piJuiceInterface);
+IPiJuiceStatus piJuiceStatus = PiJuiceStatus.Create();
 
 #region Console writing function
 static void WriteHeader(string header)

README.md

@@ -2,9 +2,15 @@
 
 ![PiJuiceSharp logo](/docs/favicon-256.png)
 
-An implementation of the PiJuice client library based on the original [PiJuice Python library](https://github.com/PiSupply/PiJuice/blob/master/Software/Source/pijuice.py) in pure .NET. Currently packaged as a .NET 6 library with only a dependency on `System.Device.Gpio`.
+An implementation of the PiJuice client library based on the original [PiJuice Python library](https://github.com/PiSupply/PiJuice/blob/master/Software/Source/pijuice.py) 
+in pure .NET. Currently packaged as a .NET 6 library with only a dependency on `System.Device.Gpio`.
 
-This library currently only supports a subset of the Status APIs, and other APIs such as the RTC and Power Management are not yet implemented. Implementing others should be fairly straightforward, but I just don't have a need for them at the moment - contributions are welcome if you need to extend it!
+Only a subset of the Status APIs are currently supported, and other APIs such as the RTC and Power Management are not yet implemented. 
+Implementing others should be fairly straightforward, but I just don't have a need for them at the moment - contributions are welcome if you 
+need to extend it!
+
+This library is safe to use even if you don't know that the device will have a PiJuice attached. When a PiJuice isn't present, 
+default values will be returned for all APIs, and a value of `NoPiJuice` for `GetStatus().BatteryStatus`.
 
 ## Installation
 
@@ -14,18 +20,25 @@ You can install the library from [NuGet](https://www.nuget.org/packages/PiJuiceS
 dotnet add package PiJuiceSharp
 ```
 
-## PiJuice Status APIs
+## PiJuiceStatus
 
 You can use the `PiJuiceStatus` class to get various point-in-time status values of the PiJuice board.
 
-To construct a `PiJuiceStatus`, you need to pass in an instance of `PiJuiceInterface`.
+To construct a `PiJuiceStatus`, call `PiJuiceStatus.Create()`. This returns an implementation of `IPiJuiceStatus` which will be either a 
+fully connected `PiJuiceStatus` instance or an `AbsentPiJuiceStatus` instance which handles the case when no PiJuice was present.
 
 ``` csharp
-var piJuiceInterface = new PiJuiceInterface();
+var piJuiceStatus = PiJuiceStatus.Create();
+```
+
+If you're using dependency injection, you can configure the `IPiJuiceStatus` interface as a singleton:
 
-var piJuiceStatus = new PiJuiceStatus(piJuiceInterface);
+``` csharp
+services.AddSingleton<IPiJuiceStatus>(PiJuiceStatus.Create());
 ```
 
+## PiJuice Status APIs
+
 `GetStatus()` returns an object containing basic status information, defined as:
 
 ``` csharp
@@ -34,7 +47,8 @@ public enum BatteryStatus
         Normal = 0,
         ChargingFromIn = 1,
         ChargingFrom5vIo = 2,
-        NotPresent = 3
+        NotPresent = 3,
+        NoPiJuice = 8000
     }
 
     public enum PowerInputStatus