From 858247b9a262dae0eea9b544f55d8a9bdacafa33 Mon Sep 17 00:00:00 2001
From: Jairon Terrero <jairon@passivelogic.com>
Date: Mon, 9 Sep 2024 13:19:59 -0600
Subject: [PATCH] feature: Adds a unitless `percent` unit

---
 Sources/Units/Registry.swift               |  4 ++
 Sources/Units/Unit/DefaultUnits.swift      |  9 ++++
 Sources/Units/Unit/Unit+DefaultUnits.swift |  4 ++
 Tests/UnitsTests/MeasurementTests.swift    | 58 ++++++++++++++++++++++
 4 files changed, 75 insertions(+)

diff --git a/Sources/Units/Registry.swift b/Sources/Units/Registry.swift
index 34d44a8..a6ace57 100644
--- a/Sources/Units/Registry.swift
+++ b/Sources/Units/Registry.swift
@@ -379,5 +379,9 @@ class Registry {
         DefaultUnits.imperialGallon,
         DefaultUnits.imperialPeck,
         DefaultUnits.metricCup,
+
+        // MARK: Unitless
+
+        DefaultUnits.percent
     ]
 }
diff --git a/Sources/Units/Unit/DefaultUnits.swift b/Sources/Units/Unit/DefaultUnits.swift
index fde7e7e..e87d857 100644
--- a/Sources/Units/Unit/DefaultUnits.swift
+++ b/Sources/Units/Unit/DefaultUnits.swift
@@ -1271,4 +1271,13 @@ enum DefaultUnits {
         dimension: [.Length: 3],
         coefficient: 0.00025
     )
+
+    // MARK: Unitless
+
+    static let percent = try! DefinedUnit(
+        name: "percent",
+        symbol: "%",
+        dimension: [:],
+        coefficient: 0.01
+    )
 }
diff --git a/Sources/Units/Unit/Unit+DefaultUnits.swift b/Sources/Units/Unit/Unit+DefaultUnits.swift
index 0da43d2..3807b1a 100644
--- a/Sources/Units/Unit/Unit+DefaultUnits.swift
+++ b/Sources/Units/Unit/Unit+DefaultUnits.swift
@@ -278,4 +278,8 @@ public extension Unit {
     static let imperialGallon = Unit(definedBy: DefaultUnits.imperialGallon)
     static let imperialPeck = Unit(definedBy: DefaultUnits.imperialPeck)
     static let metricCup = Unit(definedBy: DefaultUnits.metricCup)
+
+    // MARK: Unitless
+
+    static let percent = Unit(definedBy: DefaultUnits.percent)
 }
diff --git a/Tests/UnitsTests/MeasurementTests.swift b/Tests/UnitsTests/MeasurementTests.swift
index c26f943..ddafedc 100644
--- a/Tests/UnitsTests/MeasurementTests.swift
+++ b/Tests/UnitsTests/MeasurementTests.swift
@@ -210,6 +210,64 @@ final class MeasurementTests: XCTestCase {
         )
     }
 
+    func testPercent() throws {
+        XCTAssertEqual(
+            1.measured(in: .percent),
+            1.measured(in: .percent)
+        )
+
+        XCTAssertNotEqual(
+            100.measured(in: .percent),
+            1.measured(in: .none)
+        )
+
+        try {
+            let percent1 = 5.measured(in: .percent)
+            let percent2 = 5.measured(in: .percent)
+            XCTAssertEqual(
+                try percent1 + percent2,
+                10.measured(in: .percent),
+                accuracy: accuracy
+            )
+        }()
+
+        try {
+            let percent1 = 5.measured(in: .percent)
+            let value2 = 5.measured(in: .none)
+            XCTAssertThrowsError(try percent1 + value2)
+        }()
+
+        XCTAssertTrue(
+            2.measured(in: .percent).isDimensionallyEquivalent(
+                to: 2.measured(in: .percent)
+            )
+        )
+
+        XCTAssertTrue(
+            2.measured(in: .percent).isDimensionallyEquivalent(
+                to: 2.measured(in: .none)
+            )
+        )
+
+        XCTAssertEqual(
+            try 1.measured(in: .percent).convert(to: .none),
+            0.01.measured(in: .none),
+            accuracy: accuracy
+        )
+
+        XCTAssertEqual(
+            try 1.measured(in: .none).convert(to: .percent),
+            100.measured(in: .percent),
+            accuracy: accuracy
+        )
+
+        _ = {
+            let measurement = 1.measured(in: .percent) / 2.measured(in: .second)
+            XCTAssertEqual(measurement.unit, Unit.percent / Unit.second)
+            XCTAssertEqual(measurement.value, 0.5, accuracy: accuracy)
+        }()
+    }
+
     func testComplexArithmetic() throws {
         XCTAssertEqual(
             try 1.measured(in: .mile / .mile) * 1.measured(in: .mile) - 1.measured(in: .mile),