From b020fb294425df7853a1931498278ee362104ee8 Mon Sep 17 00:00:00 2001
From: Adam Rocska <adam.rocska@adams.solutions>
Date: Thu, 30 Apr 2020 13:27:23 +0200
Subject: [PATCH] Finally got a concept on how to program this in a
 non-convoluted way. - Extended UInt8 with a nice and juicy bitmask helper
 function - Foundation for a ControlByte type

Signed-off-by: Adam Rocska <adam.rocska@adams.solutions>
---
 Sources/MaxMindDBReader/ControlByte.swift     | 17 ++++++++++
 Sources/MaxMindDBReader/UInt8.swift           |  9 +++++
 .../ControlByteTest.swift                     | 33 ++++++++++++++++++
 Tests/MaxMindDBReaderTests/UInt8Test.swift    | 34 +++++++++++++++++++
 4 files changed, 93 insertions(+)
 create mode 100644 Sources/MaxMindDBReader/ControlByte.swift
 create mode 100644 Sources/MaxMindDBReader/UInt8.swift
 create mode 100644 Tests/MaxMindDBReaderTests/ControlByteTest.swift
 create mode 100644 Tests/MaxMindDBReaderTests/UInt8Test.swift

diff --git a/Sources/MaxMindDBReader/ControlByte.swift b/Sources/MaxMindDBReader/ControlByte.swift
new file mode 100644
index 0000000..0821cfb
--- /dev/null
+++ b/Sources/MaxMindDBReader/ControlByte.swift
@@ -0,0 +1,17 @@
+import Foundation
+
+struct ControlByte {
+
+  let type: DataType
+
+  init?(firstByte: UInt8, secondByte: UInt8 = 0b0000_0000) {
+    let typeDefinitionOnFirstByte = firstByte &>> 5
+    guard let type = typeDefinitionOnFirstByte != 0b0000_0000
+                     ? DataType(rawValue: typeDefinitionOnFirstByte)
+                     : DataType(rawValue: secondByte + 7)
+      else {
+      return nil
+    }
+    self.type = type
+  }
+}
diff --git a/Sources/MaxMindDBReader/UInt8.swift b/Sources/MaxMindDBReader/UInt8.swift
new file mode 100644
index 0000000..bc9ef48
--- /dev/null
+++ b/Sources/MaxMindDBReader/UInt8.swift
@@ -0,0 +1,9 @@
+import Foundation
+
+extension UInt8 {
+
+  @inlinable func areBitsSet(bitMask: UInt8) -> Bool {
+    return (self & bitMask) > 0
+  }
+
+}
diff --git a/Tests/MaxMindDBReaderTests/ControlByteTest.swift b/Tests/MaxMindDBReaderTests/ControlByteTest.swift
new file mode 100644
index 0000000..9d28297
--- /dev/null
+++ b/Tests/MaxMindDBReaderTests/ControlByteTest.swift
@@ -0,0 +1,33 @@
+import Foundation
+import XCTest
+@testable import MaxMindDBReader
+
+class ControlByteTest: XCTestCase {
+  func testInit() {
+    let dataTypes = (1...255).compactMap({ DataType(rawValue: $0) })
+
+    let nonExtendedTypes = dataTypes.filter({ $0.rawValue <= 7 }).map({ $0.rawValue })
+    let extendedTypes = dataTypes.filter({ $0.rawValue > 7 }).map({ $0.rawValue })
+    precondition(nonExtendedTypes.count > 0, "nonExtendedTypes can't be empty.")
+    precondition(extendedTypes.count > 0, "extendedTypes can't be empty.")
+    for nonExtendedType in nonExtendedTypes {
+      XCTAssertEqual(
+        DataType(rawValue: nonExtendedType),
+        ControlByte(firstByte: nonExtendedType &<< 5)?.type
+      )
+      XCTAssertEqual(
+        DataType(rawValue: nonExtendedType),
+        ControlByte(
+          firstByte: nonExtendedType &<< 5,
+          secondByte: 0b1111_1111
+        )?.type
+      )
+    }
+    for extendedType in extendedTypes {
+      XCTAssertEqual(
+        DataType(rawValue: extendedType),
+        ControlByte(firstByte: 0b0000_0000, secondByte: extendedType - 7)?.type
+      )
+    }
+  }
+}
diff --git a/Tests/MaxMindDBReaderTests/UInt8Test.swift b/Tests/MaxMindDBReaderTests/UInt8Test.swift
new file mode 100644
index 0000000..d29e318
--- /dev/null
+++ b/Tests/MaxMindDBReaderTests/UInt8Test.swift
@@ -0,0 +1,34 @@
+import Foundation
+import XCTest
+@testable import MaxMindDBReader
+
+class UInt8Test: XCTestCase {
+
+  func testAreBitsSet() {
+    XCTAssertTrue(UInt8(0b0010_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertTrue(UInt8(0b0110_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertTrue(UInt8(0b1110_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertTrue(UInt8(0b1111_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertTrue(UInt8(0b1111_1000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertTrue(UInt8(0b1111_1100).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertTrue(UInt8(0b1111_1110).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertTrue(UInt8(0b1111_1111).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b0000_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b0100_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b1100_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b1101_0000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b1101_1000).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b1101_1100).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b1101_1110).areBitsSet(bitMask: 0b0010_0000))
+    XCTAssertFalse(UInt8(0b1101_1111).areBitsSet(bitMask: 0b0010_0000))
+
+    XCTAssertTrue(UInt8(0b1100_0000).areBitsSet(bitMask: 0b1100_0000))
+    XCTAssertTrue(UInt8(0b1110_0000).areBitsSet(bitMask: 0b1100_0000))
+    XCTAssertTrue(UInt8(0b1111_0000).areBitsSet(bitMask: 0b1100_0000))
+    XCTAssertTrue(UInt8(0b1111_1000).areBitsSet(bitMask: 0b1100_0000))
+    XCTAssertTrue(UInt8(0b1111_1100).areBitsSet(bitMask: 0b1100_0000))
+    XCTAssertTrue(UInt8(0b1111_1110).areBitsSet(bitMask: 0b1100_0000))
+    XCTAssertTrue(UInt8(0b1111_1111).areBitsSet(bitMask: 0b1100_0000))
+  }
+
+}