using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace UnrealBuildTool
{
	/// <summary>
	/// Holds information about the current engine version
	/// </summary>
	[Serializable]
	public class BuildVersion
	{
		/// <summary>
		/// The major engine version (4 for UE4)
		/// </summary>
		public int MajorVersion;

		/// <summary>
		/// The minor engine version
		/// </summary>
		public int MinorVersion;

		/// <summary>
		/// The hotfix/patch version
		/// </summary>
		public int PatchVersion;

		/// <summary>
		/// The changelist that the engine is being built from
		/// </summary>
		public int Changelist;

		/// <summary>
		/// The changelist that the engine maintains compatibility with
		/// </summary>
		public int CompatibleChangelist;

		/// <summary>
		/// Whether the changelist numbers are a licensee changelist
		/// </summary>
		public int IsLicenseeVersion;

		/// <summary>
		/// Whether the current build is a promoted build, that is, built strictly from a clean sync of the given changelist
		/// </summary>
		public int IsPromotedBuild;

		/// <summary>
		/// Name of the current branch, with '/' characters escaped as '+'
		/// </summary>
		public string BranchName;

		/// <summary>
		/// Returns the value which can be used as the compatible changelist. Requires that the regular changelist is also set, and defaults to the 
		/// regular changelist if a specific compatible changelist is not set.
		/// </summary>
		public int EffectiveCompatibleChangelist
		{
			get { return (Changelist != 0 && CompatibleChangelist != 0)? CompatibleChangelist : Changelist; }
		}

		/// <summary>
		/// Try to read a version file from disk
		/// </summary>
		/// <param name="Version">The version information</param>
		/// <returns>True if the version was read sucessfully, false otherwise</returns>
		public static bool TryRead(out BuildVersion Version)
		{
			return TryRead(GetDefaultFileName(), out Version);
		}

		/// <summary>
		/// Try to read a version file from disk
		/// </summary>
		/// <param name="FileName">Path to the version file</param>
		/// <param name="Version">The version information</param>
		/// <returns>True if the version was read sucessfully, false otherwise</returns>
		public static bool TryRead(string FileName, out BuildVersion Version)
		{
			JsonObject Object;
			if (!JsonObject.TryRead(FileName, out Object))
			{
				Version = null;
				return false;
			}
			return TryParse(Object, out Version);
		}

		/// <summary>
		/// Get the default path to the build.version file on disk
		/// </summary>
		/// <returns>Path to the Build.version file</returns>
		public static string GetDefaultFileName()
		{
			return FileReference.Combine(UnrealBuildTool.EngineDirectory, "Build", "Build.version").FullName;
		}

		/// <summary>
		/// Parses a build version from a JsonObject
		/// </summary>
		/// <param name="Object">The object to read from</param>
		/// <param name="Version">The resulting version field</param>
		/// <returns>True if the build version could be read, false otherwise</returns>
		public static bool TryParse(JsonObject Object, out BuildVersion Version)
		{
			BuildVersion NewVersion = new BuildVersion();
			if (!Object.TryGetIntegerField("MajorVersion", out NewVersion.MajorVersion) || !Object.TryGetIntegerField("MinorVersion", out NewVersion.MinorVersion) || !Object.TryGetIntegerField("PatchVersion", out NewVersion.PatchVersion))
			{
				Version = null;
				return false;
			}

			Object.TryGetIntegerField("Changelist", out NewVersion.Changelist);
			Object.TryGetIntegerField("CompatibleChangelist", out NewVersion.CompatibleChangelist);
			Object.TryGetIntegerField("IsLicenseeVersion", out NewVersion.IsLicenseeVersion);
			Object.TryGetIntegerField("IsPromotedBuild", out NewVersion.IsPromotedBuild);
			Object.TryGetStringField("BranchName", out NewVersion.BranchName);

			Version = NewVersion;
			return true;
		}

		/// <summary>
		/// Exports this object as Json
		/// </summary>
		/// <param name="FileName">The filename to write to</param>
		/// <returns>True if the build version could be read, false otherwise</returns>
		public void Write(string FileName)
		{
			using (JsonWriter Writer = new JsonWriter(FileName))
			{
				Writer.WriteObjectStart();
				WriteProperties(Writer);
				Writer.WriteObjectEnd();
			}
		}

		/// <summary>
		/// Exports this object as Json
		/// </summary>
		/// <param name="Writer">The json writer to receive the version settings</param>
		/// <returns>True if the build version could be read, false otherwise</returns>
		public void WriteProperties(JsonWriter Writer)
		{
			Writer.WriteValue("MajorVersion", MajorVersion);
			Writer.WriteValue("MinorVersion", MinorVersion);
			Writer.WriteValue("PatchVersion", PatchVersion);
			Writer.WriteValue("Changelist", Changelist);
			Writer.WriteValue("CompatibleChangelist", CompatibleChangelist);
			Writer.WriteValue("IsLicenseeVersion", IsLicenseeVersion);
			Writer.WriteValue("IsPromotedBuild", IsPromotedBuild);
			Writer.WriteValue("BranchName", BranchName);
		}
	}
}