[Xamarin.Android.Build.Tasks] Implement a new process for defining versionCode.

Context https://bugzilla.xamarin.com/show_bug.cgi?id=51620
Context https://bugzilla.xamarin.com/show_bug.cgi?id=51618
Context https://bugzilla.xamarin.com/show_bug.cgi?id=51145

Our current version system for multiple apk's for each Abi
is a bit broken [1]. If a user for example has a versionCode
set which is 123 the final version code for an x86_64 build
ends up as 327803.
This is completely transparent to the user and also does not
follow the guidance in the documentation at [1] and [2].

So we need a new system :) but as usual we have to support the
old system. So we are introducing a new system which is more
flexible. This will only apply when the `$(AndroidCreatePackagePerAbi)`
is set to `True`.

The new system has two new properties

	<AndroidVersionCodePattern/>
	<AndroidVersionCodeProperties/>

The first allows the developer to define the Pattern to be used
for the versonCode. The pattern will be made up of a format string
which will contain keys. These keys will be replaced with values
form one of the known keys or a custom user defined one.

We define a few known key values

- abi : The current target abi converted to an int where
	- 'armeabi' = 1,
	- 'armeabi-v7a' = 2,
	- 'x86' = 3,
	- 'arm64-v8a' = 4,
	- 'x86_64' = 5,

- minSDK : The minSDK value from the manifest or 11 if not present.

- versionCode : The versionCode from the manifest.

With these keys the user can define a pattern of

	{abi}{minSDK}{versionCode}

or if they way to include zero padding they can use

	{abi}{minSDK}{versionCode:D4}

similar to the left padding formats used in string.Format ().

Users can also use the `$(AndroidVersionCodeProperties)` property
to define new custom keys. This string will be in the form of a
semi-colon delimited key=value pairs. For example

	foo=12;bar=$(SomeBuildProperty)

when can then be used in the pattern.

	{abi}{foo}{bar}{versionCode}

Lets work through an example. The user defines a version code of '123'
in the manifest and enables `$(AndroidCreatePackagePerAbi)`. They define
a `$(AndroidVersionCodePattern)` of `{abi}{versionCode:D5}`.
This will result in the following version code being produced for the
'x86' build.

	300123

The first 3 is the `{abi}` value. The rest is the left zero padded
versionCode.
A slightly more complex pattern would be `{abi}{minSDK:D2}{versionCode:D4}`
which would produce

	3140123

if the minimumSdk value was set to API 14.

A more real life example mgiht be as follows. A user wants to use the `Build` value
from the AssemblyInfo.cs . They define the following target

```xml
<Target Name="_GetBuild" AfterTargets="Compile">
  <GetAssemblyIdentity AssemblyFiles="Foo.dll">
      <Output
          TaskParameter="Assemblies"
          ItemName="MasterVersion"/>
    </GetAssemblyIdentity>
    <PropertyGroup>
       <BuildVersion>$([System.Version]::Parse(%(MasterVersion.Version)).Build)</BuildVersion>
    </PropertyGroup>
</Target>
```
This extracts the build version from the built assembly. They can then define a
pattern of

	{abi}{minSDK}{build:D4}

and set the properties to

	build=$(BuildVersion)

Given similar properties from the previous example e.g abi=x86 and minSDk=14,
this will result in the follwing output (assuming the `Build` value was 3421).

	3143421

[1] https://developer.xamarin.com/guides/android/advanced_topics/build-abi-specific-apks/
[2] https://developer.android.com/google/play/publishing/multiple-apks.html#Rules

Author: dellis1972

Documentation/build_process.md

@@ -501,6 +501,68 @@ when packaing Release applications.
 
     Added in Xamarin.Android 7.1.
 
+-   **AndroidVersionCodePattern** – A string property which allows
+    the developer to customize the `versionCode` in the manifest when splitting
+    up the apk by abi.
+    See [Creating the Version Code for the APK](https://developer.xamarin.com/guides/android/advanced_topics/build-abi-specific-apks/#Creating_the_Version_Code_for_the_APK)
+    for information on deciding a `versionCode`.
+    
+    Some examples, if `abi` is `armeabi` and `versionCode` in the manifest
+    is `123`
+
+        {abi}{versionCode}
+
+    will prodice a versionCode of `1123`.
+    If `abi` is `x86_64` and `versionCode` in the manifest
+    is `44`. This will produce `544`.
+
+    If we include a left padding format string 
+
+        {abi}{versionCode:0000}
+
+    it would produde `50044` because we are left padding the `versionCode`
+    with `0`. Alternatively you can use the decimal padding such as
+
+        {abi}{versionCode:D4}
+
+    which does the same as the previous example. 
+
+    Only '0' and 'Dx' padding format strings are supported since the value
+    MUST be an integer.
+    
+    Pre defined key items
+        
+    -   **abi**  – Inserts the targetted abi for the app
+        -   1 – `armeabi`
+        -   2 – `armeabi-v7a`
+        -   3 – `x86`
+        -   4 – `arm64-v8a`
+        -   5 – `x86_64`
+
+    -   **minSDK**  – Inserts the minimum supported Sdk
+        value from the `AndroidManifest.xml` or `11` if none is
+        defined.
+
+    -   **versionCode** – Uses the version code direrctly from 
+        `Properties\AndroidManifest.xml`. 
+
+    You can define custom items using the [AndroidVersionCodeProperties](#AndroidVersionCodeProperties) 
+    property.
+
+    Added in Xamarin.Android 7.2.
+
+-   **AndroidVersionCodeProperties** – A string property which allows
+    the developer to define custom items to use with the [AndroidVersionCodePattern](#AndroidVersionCodePattern).
+    They are in the form of a `key=value` pair. All items in the `value` should
+    be integer values. 
+
+            screen=23;target=$(_SupportedApiLevel)
+
+    As you can see you can make use of existing or custom MSBuild properties
+    in the string. 
+
+    Added in Xamarin.Android 7.2.
+
 ## Binding Project Build Properties
 
 The following MSBuild properties are used with

src/Xamarin.Android.Build.Tasks/Tasks/Aapt.cs

@@ -76,6 +76,19 @@ public class Aapt : AsyncTask
 
 		public bool ExplicitCrunch { get; set; }
 
+		// pattern to use for the version code. Used in CreatePackagePerAbi
+		// eg. {abi:00}{dd}{version}
+		// known keyworks
+		//  {abi} the value for the current abi
+		//  {version} the version code from the manifest.
+		public string VersionCodePattern { get; set; }
+
+		// Name=Value pair seperated by ';'
+		// e.g screen=21;abi=11
+		public string VersionCodeProperties { get; set; }
+
+		public string AndroidSdkPlatform { get; set; }
+
 		Dictionary<string,string> resource_name_case_map = new Dictionary<string,string> ();
 
 		bool ManifestIsUpToDate (string manifestFile)
@@ -190,6 +203,8 @@ public override bool Execute ()
 			Log.LogDebugMessage ("  ExtraArgs: {0}", ExtraArgs);
 			Log.LogDebugMessage ("  CreatePackagePerAbi: {0}", CreatePackagePerAbi);
 			Log.LogDebugMessage ("  ResourceNameCaseMap: {0}", ResourceNameCaseMap);
+			Log.LogDebugMessage ("  VersionCodePattern: {0}", VersionCodePattern);
+			Log.LogDebugMessage ("  VersionCodeProperties: {0}", VersionCodeProperties);
 			if (CreatePackagePerAbi)
 				Log.LogDebugMessage ("  SupportedAbis: {0}", SupportedAbis);
 
@@ -244,8 +259,15 @@ protected string GenerateCommandLineCommands (string ManifestFile, string curren
 			Directory.CreateDirectory (manifestDir);
 			manifestFile = Path.Combine (manifestDir, Path.GetFileName (ManifestFile));
 			ManifestDocument manifest = new ManifestDocument (ManifestFile, this.Log);
-			if (currentAbi != null)	
-				manifest.SetAbi (currentAbi);
+			manifest.SdkVersion = AndroidSdkPlatform;
+			if (currentAbi != null) {
+				if (!string.IsNullOrEmpty (VersionCodePattern))
+					manifest.CalculateVersionCode (currentAbi, VersionCodePattern, VersionCodeProperties);
+				else
+					manifest.SetAbi (currentAbi);
+			} else if ((manifest.VersionCode == "1" || string.IsNullOrEmpty (manifest.VersionCode)) && !string.IsNullOrEmpty (VersionCodePattern)) {
+				manifest.CalculateVersionCode (null, VersionCodePattern, VersionCodeProperties);
+			}
 			manifest.ApplicationName = ApplicationName;
 			manifest.Save (manifestFile);
 

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/ManifestTest.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Linq;
 using NUnit.Framework;
 using Xamarin.ProjectTools;
@@ -264,6 +264,144 @@ public void DirectBootAwareAttribute ()
 			}
 		}
 
+		static object [] VersionCodeTestSource = new object [] {
+			new object[] {
+				/* seperateApk */ false,
+				/* abis */ "armeabi-v7a",
+				/* versionCode */ "123",
+				/* pattern */ null,
+				/* props */ null,
+				/* shouldBuild */ true,
+				/* expected */ "123",
+			},
+			new object[] {
+				/* seperateApk */ false,
+				/* abis */ "armeabi-v7a",
+				/* versionCode */ "123",
+				/* pattern */ "{abi}{versionCode}",
+				/* props */ null,
+				/* shouldBuild */ true,
+				/* expected */ "123",
+			},
+			new object[] {
+				/* seperateApk */ false,
+				/* abis */ "armeabi-v7a",
+				/* versionCode */ "1",
+				/* pattern */ "{abi}{versionCode}",
+				/* props */ "versionCode=123",
+				/* shouldBuild */ true,
+				/* expected */ "123",
+			},
+			new object[] {
+				/* seperateApk */ false,
+				/* abis */ "armeabi-v7a;x86",
+				/* versionCode */ "123",
+				/* pattern */ "{abi}{versionCode}",
+				/* props */ null,
+				/* shouldBuild */ true,
+				/* expected */ "123",
+			},
+			new object[] {
+				/* seperateApk */ true,
+				/* abis */ "armeabi-v7a;x86",
+				/* versionCode */ "123",
+				/* pattern */ null,
+				/* props */ null,
+				/* shouldBuild */ true,
+				/* expected */ "131195;196731",
+			},
+			new object[] {
+				/* seperateApk */ true,
+				/* abis */ "armeabi-v7a;x86",
+				/* versionCode */ "123",
+				/* pattern */ "{abi}{versionCode}",
+				/* props */ null,
+				/* shouldBuild */ true,
+				/* expected */ "2123;3123",
+			},
+			new object[] {
+				/* seperateApk */ true,
+				/* abis */ "armeabi-v7a;x86",
+				/* versionCode */ "12",
+				/* pattern */ "{abi}{minSDK:00}{versionCode:000}",
+				/* props */ null,
+				/* shouldBuild */ true,
+				/* expected */ "211012;311012",
+			},
+			new object[] {
+				/* seperateApk */ true,
+				/* abis */ "armeabi-v7a;x86",
+				/* versionCode */ "12",
+				/* pattern */ "{abi}{minSDK:00}{screen}{versionCode:000}",
+				/* props */ "screen=24",
+				/* shouldBuild */ true,
+				/* expected */ "21124012;31124012",
+			},
+			new object[] {
+				/* seperateApk */ true,
+				/* abis */ "armeabi-v7a;x86",
+				/* versionCode */ "12",
+				/* pattern */ "{abi}{minSDK:00}{screen}{foo:0}{versionCode:000}",
+				/* props */ "screen=24;foo=$(Foo)",
+				/* shouldBuild */ true,
+				/* expected */ "211241012;311241012",
+			},
+			new object[] {
+				/* seperateApk */ true,
+				/* abis */ "armeabi-v7a;x86",
+				/* versionCode */ "12",
+				/* pattern */ "{abi}{minSDK:00}{screen}{foo:00}{versionCode:000}",
+				/* props */ "screen=24;foo=$(Foo)",
+				/* shouldBuild */ false,
+				/* expected */ "2112401012;3112401012",
+			},
+		};
+
+		[Test]
+		[TestCaseSource("VersionCodeTestSource")]
+		public void VersionCodeTests (bool seperateApk, string abis, string versionCode, string versionCodePattern, string versionCodeProperties, bool shouldBuild, string expectedVersionCode)
+		{
+			var proj = new XamarinAndroidApplicationProject () {
+				IsRelease = true,
+			};
+			proj.SetProperty ("Foo", "1");
+			proj.SetProperty (proj.ReleaseProperties, KnownProperties.AndroidCreatePackagePerAbi, seperateApk);
+			if (!string.IsNullOrEmpty (abis))
+				proj.SetProperty (proj.ReleaseProperties, KnownProperties.AndroidSupportedAbis, abis);
+			if (!string.IsNullOrEmpty (versionCodePattern))
+				proj.SetProperty (proj.ReleaseProperties, "AndroidVersionCodePattern", versionCodePattern);
+			else
+				proj.RemoveProperty (proj.ReleaseProperties, "AndroidVersionCodePattern");
+			if (!string.IsNullOrEmpty (versionCodeProperties))
+				proj.SetProperty (proj.ReleaseProperties, "AndroidVersionCodeProperties", versionCodeProperties);
+			else
+				proj.RemoveProperty (proj.ReleaseProperties, "AndroidVersionCodeProperties");
+			proj.AndroidManifest = proj.AndroidManifest.Replace ("android:versionCode=\"1\"", $"android:versionCode=\"{versionCode}\"");
+			using (var builder = CreateApkBuilder (Path.Combine ("temp", "VersionCodeTests"), false, false)) {
+				builder.ThrowOnBuildFailure = false;
+				Assert.AreEqual (shouldBuild, builder.Build (proj), shouldBuild ? "Build should have succeeded." : "Build should have failed.");
+				if (!shouldBuild)
+					return;
+				var abiItems = seperateApk ? abis.Split (';') : new string[1];
+				var expectedItems = expectedVersionCode.Split (';');
+				XNamespace aNS = "http://schemas.android.com/apk/res/android";
+				Assert.AreEqual (abiItems.Length, expectedItems.Length, "abis parameter should have matching elements for expected");
+				for (int i = 0; i < abiItems.Length; i++) {
+					var path = seperateApk ? Path.Combine ("android", abiItems[i], "AndroidManifest.xml") : Path.Combine ("android", "manifest", "AndroidManifest.xml");
+					var manifest = builder.Output.GetIntermediaryAsText (Root, path);
+					var doc = XDocument.Parse (manifest);
+					var nsResolver = new XmlNamespaceManager (new NameTable ());
+					nsResolver.AddNamespace ("android", "http://schemas.android.com/apk/res/android");
+					var m = doc.XPathSelectElement ("/manifest") as XElement;
+					Assert.IsNotNull (m, "no manifest element found");
+					var vc = m.Attribute (aNS + "versionCode");
+					Assert.IsNotNull (vc, "no versionCode attribute found");
+					StringAssert.AreEqualIgnoringCase (expectedItems[i], vc.Value,
+						$"Version Code is incorrect. Found {vc.Value} expect {expectedItems[i]}");
+				}
+			}
+		}
+
 		[Test]
 		public void ManifestPlaceholders ()
 		{

src/Xamarin.Android.Build.Tasks/Utilities/ManifestDocument.cs

@@ -29,6 +29,8 @@ internal class ManifestDocument
 	{
 		public static XNamespace AndroidXmlNamespace = "http://schemas.android.com/apk/res/android";
 
+		const int maxVersionCode = 2100000000;
+
 		static XNamespace androidNs = AndroidXmlNamespace;
 
 		XDocument doc;
@@ -68,6 +70,19 @@ public string VersionCode {
 				doc.Root.SetAttributeValue (androidNs + "versionCode", value);
 			}
 		}
+		public string MinimumSdk {
+			get {
+				var uses = doc.Root.Element ("uses-sdk");
+				if (uses?.Attribute (androidNs + "minSdkVersion") == null) {
+					int minSdkVersion;
+					if (!int.TryParse (SdkVersionName, out minSdkVersion))
+						minSdkVersion = 11;
+					return Math.Min (minSdkVersion, 11).ToString ();
+				} else {
+					return uses.Attribute (androidNs + "minSdkVersion").Value;
+				}
+			}
+		}
 		TaskLoggingHelper log;
 
 		public ManifestDocument (string templateFilename, TaskLoggingHelper log) : base ()
@@ -839,11 +854,45 @@ public void SetAbi (string abi)
 			int code = 1;
 			if (!string.IsNullOrEmpty (VersionCode)) {
 				code = Convert.ToInt32 (VersionCode);
-				if (code > 0xffff || code < 0)
-					throw new ArgumentOutOfRangeException ("VersionCode", "VersionCode is outside 0, 65535 interval");
+				if (code > maxVersionCode || code < 0)
+					throw new ArgumentOutOfRangeException ("VersionCode", $"VersionCode is outside 0, {maxVersionCode} interval");
 			}
 			code |= GetAbiCode (abi) << 16;
 			VersionCode = code.ToString ();
 		}
+
+		public void CalculateVersionCode (string currentAbi, string versionCodePattern, string versionCodeProperties)
+		{
+			var regex = new Regex ("\\{(?<key>([A-Za-z]+)):?[D0-9]*[\\}]");
+			var kvp = new Dictionary<string, int> ();
+			foreach (var item in versionCodeProperties?.Split (new char [] { ';', ':' }) ?? new string [0]) {
+				var keyValue = item.Split (new char [] { '=' });
+				int val;
+				if (!int.TryParse (keyValue [1], out val))
+					continue;
+				kvp.Add (keyValue [0], val);
+			}
+			if (!kvp.ContainsKey ("abi") && !string.IsNullOrEmpty (currentAbi))
+				kvp.Add ("abi", GetAbiCode (currentAbi));
+			if (!kvp.ContainsKey ("versionCode"))
+				kvp.Add ("versionCode", int.Parse (VersionCode));
+			if (!kvp.ContainsKey ("minSDK")) {
+				kvp.Add ("minSDK", int.Parse (MinimumSdk));
+			}
+			var versionCode = String.Empty;
+			foreach (Match match in regex.Matches (versionCodePattern)) {
+				var key = match.Groups ["key"].Value;
+				var format = match.Value.Replace (key, "0");
+				if (!kvp.ContainsKey (key))
+					continue;
+				versionCode += string.Format (format, kvp [key]);
+			}
+			int code;
+			if (!int.TryParse (versionCode, out code))
+				throw new ArgumentOutOfRangeException ("VersionCode", $"VersionCode {versionCode} is invalid. It must be an integer value.");
+			if (code > maxVersionCode || code < 0)
+				throw new ArgumentOutOfRangeException ("VersionCode", $"VersionCode {code} is outside 0, {maxVersionCode} interval");
+			VersionCode = versionCode;
+		}
 	}
 }

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -1807,6 +1807,9 @@ because xbuild doesn't support framework reference assemblies.
     CreatePackagePerAbi="$(AndroidCreatePackagePerAbi)"
     YieldDuringToolExecution="$(YieldDuringToolExecution)"
     ExplicitCrunch="$(AndroidExplicitCrunch)"
+    VersionCodePattern="$(AndroidVersionCodePattern)"
+    VersionCodeProperties="$(AndroidVersionCodeProperties)"
+    AndroidSdkPlatform="$(_AndroidApiLevel)"
      />
   <Touch Files="$(_PackagedResources)" />
   <!-- LibraryProjectJars must not be used for aapt in BuildApk*, or it will *bundle* the jar! -->