Conform to IteratorProtocol for scanning.

I've left the old callback implementations in for now, undecided whether these should be removed. The nice thing about the callback method is that it's more compact, however the logic behind it is less clear.

Sources/SwiftRPLidar/SwiftRPLidar.swift

@@ -96,6 +96,8 @@ public class SwiftRPLidar {
     private var motorRunning = false
     private let measurementDelayus: UInt32
     
+    private(set) var isScanning = false
+    private(set) var dataSize: UInt8 = 5
     /**
      A class to interact with the RPLidar A1 and A2.
      
@@ -154,7 +156,7 @@ public class SwiftRPLidar {
     }
     
     /**
-        Gets information about the connected lidar.
+     Gets information about the connected lidar.
      
      - returns (model, firmware, hardware, serialNumber)
      */
@@ -204,6 +206,7 @@ public class SwiftRPLidar {
      */
     public func stop() throws{
         try sendCommand(Constants.STOP.asData())
+        isScanning = false
     }
     
     /**
@@ -224,6 +227,31 @@ public class SwiftRPLidar {
      - throws If the input data is in the incorrect format, or the health retrieved errors.
      */
     public func iterMeasurements(maxBufferMeasurements: Int = 500, _ onMeasure: MeasurementHandler) throws {
+        if !isScanning {
+            throw RPLidarError.SCAN_ERROR(message: "You must start scanning!")
+        }
+        var read = true
+        while read {
+            do {
+                let raw = try receiveMeasurementAndClearBuffer(dataSize: dataSize, maxBufferMeasurements: maxBufferMeasurements)
+                if raw.count > 0 {
+                    read = try onMeasure(processScan(raw: raw))
+                }
+                if measurementDelayus > 0 {
+                    usleep(measurementDelayus)
+                }
+            } catch RPLidarError.INCORRECT_DESCRIPTOR_FORMAT {
+                print("Incorrect Descriptor, skipping scan")
+            } catch RPLidarError.SCAN_ERROR(let message) {
+                print("Scan processing failed, skipping scan: \(message)")
+            }
+        }
+    }
+    
+    /**
+     Send the command to the lidar to start scanning. This should be called before using any iterator.
+     */
+    public func startScanning() throws -> UInt8  {
         try startMotor()
         let (status, _) = try getHealth()
         if status == .ERROR{
@@ -239,29 +267,30 @@ public class SwiftRPLidar {
         if dataSize != 5 || isSingle || dataType != Constants.SCAN_TYPE {
             throw RPLidarError.INCORRECT_DESCRIPTOR_FORMAT
         }
-        var read = true
-        while read {
-            do {
-                let raw = try readResponse(Int(dataSize))
-                if maxBufferMeasurements > 0 {
-                    let dataInWaiting = serialPort.inWaiting
-                    if dataInWaiting > maxBufferMeasurements {
-                        print("Too many measurements in the input buffer. Clearing Buffer")
-                        _ = try serialPort.readData(ofLength: dataInWaiting / Int(dataSize) * Int(dataSize))
-                    }
-                }
-                if raw.count > 0 {
-                    read = try onMeasure(processScan(raw: raw))
-                }
-                if measurementDelayus > 0 {
-                    usleep(measurementDelayus)
-                }
-            } catch RPLidarError.INCORRECT_DESCRIPTOR_FORMAT {
-                print("Incorrect Descriptor, skipping scan")
-            } catch RPLidarError.SCAN_ERROR(let message) {
-                print("Scan processing failed, skipping scan: \(message)")
+        isScanning = true
+        self.dataSize = dataSize
+        return dataSize
+    }
+    
+    /**
+     Receive a measurement from the lidar. If the data in waiting exceeds the buffer, clear it.
+     - parameters:
+     dataSize: The length of the data in bytes for a single lidar measurement.
+     maxBufferMeasurements: The maximum length allowed in the buffer before it should be cleared.
+     */
+    public func receiveMeasurementAndClearBuffer(dataSize: UInt8, maxBufferMeasurements: Int = 500) throws -> Data{
+        if !isScanning {
+            throw RPLidarError.SCAN_ERROR(message: "Haven't started scanning")
+        }
+        let raw = try readResponse(Int(dataSize))
+        if maxBufferMeasurements > 0 {
+            let dataInWaiting = serialPort.inWaiting
+            if dataInWaiting > maxBufferMeasurements {
+                print("Too many measurements in the input buffer. Clearing Buffer")
+                _ = try serialPort.readData(ofLength: dataInWaiting / Int(dataSize) * Int(dataSize))
             }
         }
+        return raw
     }
     
     /**
@@ -290,6 +319,16 @@ public class SwiftRPLidar {
         }
     }
     
+    /**
+     Make an iterator that can be used to iterate over batches of measurements.
+     - parameters:
+     withLength: Minimum number of measurements to process in an iteration.
+     maxBufferMeasurements: The maximum number of measurements allowed in the buffer before clearing it.
+     */
+    public func makeScanIterator(withLength minLength: Int = 5, maxBufferMeasurements: Int = 500) -> LidarScanIterator {
+        return LidarScanIterator(lidar: self, measurementsPerBatch: minLength, maxBufferMeasurements: maxBufferMeasurements)
+    }
+    
     private func setPwm(_ pwm: Int) throws{
         assert(0 <= pwm && pwm <= Constants.MAX_MOTOR_PWM)
         try self.sendPayloadCommand(Constants.SET_PWM_BYTE, payload: pwm.asData())
@@ -361,3 +400,84 @@ extension UInt8 {
     }
 }
 
+// MARK: Iterator Extensions
+
+extension SwiftRPLidar: Sequence {
+    public typealias Element = LidarScan
+    public typealias Iterator = LidarMeasurementIterator
+    
+    public func makeIterator() -> LidarMeasurementIterator {
+        return LidarMeasurementIterator(lidar: self, maxBufferMeasurements: 500)
+    }
+}
+
+
+/**
+ Iterator for individual lidar measurements.
+ A scan may be nil when data is not received from serialPort, or when the lidar is not ready for scanning.
+ */
+public struct LidarMeasurementIterator {
+    let lidar: SwiftRPLidar
+    let maxBufferMeasurements: Int
+}
+
+extension LidarMeasurementIterator: IteratorProtocol{
+    public typealias Element = LidarScan
+    
+    public mutating func next() -> LidarScan? {
+        if lidar.isScanning {
+            do {
+                let raw = try lidar.receiveMeasurementAndClearBuffer(dataSize: lidar.dataSize, maxBufferMeasurements: maxBufferMeasurements)
+                if raw.count > 0 {
+                    return try processScan(raw: raw)
+                }
+            } catch {
+                print("Failed to process lidar scan")
+            }
+        } else {
+            print("You must start scanning!")
+        }
+        return nil
+    }
+}
+
+/**
+ Iterator for batches of lidar measurements.
+ */
+public struct LidarScanIterator {
+    let lidar: SwiftRPLidar
+    let measurementsPerBatch: Int
+    let maxBufferMeasurements: Int
+    public typealias Element = [LidarScan]
+}
+
+extension LidarScanIterator: Sequence {
+    public typealias Iterator = LidarScanIterator
+    
+    public func makeIterator() -> LidarScanIterator {
+        return LidarScanIterator(lidar: lidar, measurementsPerBatch: measurementsPerBatch, maxBufferMeasurements: maxBufferMeasurements)
+    }
+}
+
+extension LidarScanIterator: IteratorProtocol {
+    
+    public mutating func next() -> [LidarScan]? {
+        
+        if lidar.isScanning {
+            var allScans: [LidarScan] = []
+            do {
+                while allScans.count < measurementsPerBatch {
+                    let raw = try lidar.receiveMeasurementAndClearBuffer(dataSize: lidar.dataSize, maxBufferMeasurements: maxBufferMeasurements)
+                    if raw.count > 0 {
+                        allScans.append(try processScan(raw: raw))
+                    }
+                }
+                return allScans
+            } catch {
+                print("Failed to process scan")
+            }
+        }
+        return nil
+    }
+}
+