Air Quality: Sort of correct limits for pollutants.

1Weather/Model/ModelObjects/Health/Health.swift

@@ -23,8 +23,13 @@ public struct AirQuality: Equatable, Hashable {
         return progressValue
     }
     public var status: HealthStatus {
-        get {
-            HealthStatus(value: index)
+        switch index {
+        case 0...50: return .good
+        case 51...100: return .moderate
+        case 101...150: return .unhealthyForSensitiveGroups
+        case 151...200: return .unhealthy
+        case 201...300: return .veryUnhealthy
+        default: return .hazardous
         }
     }
 }
@@ -37,23 +42,6 @@ public enum HealthStatus: String {
     case veryUnhealthy = "health.airquality.status.veryUnhealthy"
     case hazardous = "health.airquality.status.hazardous"
     
-    public init(value: Double) {
-        switch value {
-        case 0...50:
-            self = .good
-        case 51...100:
-            self = .moderate
-        case 101...150:
-            self = .unhealthyForSensitiveGroups
-        case 151...200:
-            self = .unhealthy
-        case 201...300:
-            self = .veryUnhealthy
-        default:
-            self = .hazardous
-        }
-    }
-    
     public var localized: String {
         return self.rawValue.localized()
     }
@@ -192,13 +180,123 @@ public struct Pollutant: Equatable, Hashable {
     public let name: String
     public let value: Double
     public var progress:CGFloat {
-        var progressValue = max(0, CGFloat(value / 500))
+        guard let hazardousLevelStart = self.hazardousLevelStart else {
+            return 0.1 // not great, not terrible
+        }
+        
+        var progressValue = max(0, CGFloat(value / hazardousLevelStart))
         progressValue = min(1, progressValue)
         return progressValue
     }
-    public var status: HealthStatus {
-        get {
-            HealthStatus(value: value)
+    
+    public init(name: String, value: Double) {
+        self.name = name
+        self.value = value
+        var statusValue = HealthStatus.good
+        
+        let shortName = name.trimmingCharacters(in: .whitespacesAndNewlines).replacingOccurrences(of: " ", with: "").lowercased()
+        if let statusLimits: [HealthStatus: Double] = Pollutant.upperLimits[shortName] {
+            let statusesSequence: [HealthStatus] = [.good, .moderate, .unhealthyForSensitiveGroups, .unhealthy, .veryUnhealthy, .hazardous]
+            for possibleStatus: HealthStatus in statusesSequence {
+                if let limit: Double = statusLimits[possibleStatus] {
+                    if value < limit {
+                        statusValue = possibleStatus
+                        break
+                    }
+                }
+                else {
+                    assertionFailure("No limit for status \(possibleStatus) of pollutant \(name)") // should never happen.
+                    statusValue = possibleStatus
+                    continue
+                }
+            }
+            if let veryUnhealthyUpperLimit = statusLimits[.veryUnhealthy] {
+                hazardousLevelStart = veryUnhealthyUpperLimit
+            }
+            else {
+                assertionFailure("No limit for status \(HealthStatus.veryUnhealthy) of pollutant \(name)") // should never happen.
+                hazardousLevelStart = nil
+            }
         }
+        else {
+            assertionFailure("No limits for Pollutant \(name)!")
+            statusValue = .good
+            hazardousLevelStart = nil
+        }
+        self.status = statusValue
     }
+    
+    public private (set) var status: HealthStatus
+    private let hazardousLevelStart: Double?
+    
+    /// Preferably these should be configurable from the server.
+    /// See https://en.wikipedia.org/wiki/Air_quality_index
+    /// The "AQI Category, Pollutants and Health Breakpoints" table.
+    private static let upperLimits: [String: [HealthStatus: Double]] = [
+        "pm10": [
+            .good: 50.0,
+            .moderate: 100.0,
+            .unhealthyForSensitiveGroups: 250.0,
+            .unhealthy: 350.0,
+            .veryUnhealthy: 430.0,
+            .hazardous: Double.infinity
+        ],
+        "pm2.5": [
+            .good: 30.0,
+            .moderate: 60.0,
+            .unhealthyForSensitiveGroups: 90.0,
+            .unhealthy: 120.0,
+            .veryUnhealthy: 250.0,
+            .hazardous: Double.infinity
+        ],
+        "no2": [
+            .good: 40.0,
+            .moderate: 80.0,
+            .unhealthyForSensitiveGroups: 180.0,
+            .unhealthy: 280.0,
+            .veryUnhealthy: 400.0,
+            .hazardous: Double.infinity
+        ],
+        "o3": [
+            .good: 50.0,
+            .moderate: 100.0,
+            .unhealthyForSensitiveGroups: 168.0,
+            .unhealthy: 208.0,
+            .veryUnhealthy: 748.0,
+            .hazardous: Double.infinity
+        ],
+        "co": [
+            .good: 1.0,
+            .moderate: 2.0,
+            .unhealthyForSensitiveGroups: 10.0,
+            .unhealthy: 17.0,
+            .veryUnhealthy: 34.0,
+            .hazardous: Double.infinity
+        ],
+        "so2": [
+            .good: 40.0,
+            .moderate: 80.0,
+            .unhealthyForSensitiveGroups: 380.0,
+            .unhealthy: 800.0,
+            .veryUnhealthy: 1600.0,
+            .hazardous: Double.infinity
+        ],
+        "nh3": [
+            .good: 200.0,
+            .moderate: 400.0,
+            .unhealthyForSensitiveGroups: 800.0,
+            .unhealthy: 1200.0,
+            .veryUnhealthy: 1800.0,
+            .hazardous: Double.infinity
+        ],
+        "pb": [
+            .good: 0.5,
+            .moderate: 1.0,
+            .unhealthyForSensitiveGroups: 2.0,
+            .unhealthy: 3.0,
+            .veryUnhealthy: 3.5,
+            .hazardous: Double.infinity
+        ]
+    ]
 }
+