using System;
using System.IO;
using System.Linq;
using System.Text.Json;

namespace Editor.UnrealImporter;

/// <summary>
/// Locates a .uproject's engine and the UnrealEditor-Cmd.exe used to run the headless export.
/// </summary>
public static class UnrealLocator
{
	public static string FindUprojectInFolder( string folder )
	{
		if ( string.IsNullOrEmpty( folder ) || !Directory.Exists( folder ) )
			return null;

		return Directory.GetFiles( folder, "*.uproject", SearchOption.TopDirectoryOnly ).FirstOrDefault();
	}

	/// <summary>Reads "EngineAssociation" (e.g. "5.5") from a .uproject. May be null.</summary>
	public static string ReadEngineAssociation( string uprojectPath )
	{
		try
		{
			using var doc = JsonDocument.Parse( File.ReadAllText( uprojectPath ) );
			if ( doc.RootElement.TryGetProperty( "EngineAssociation", out var e ) )
				return e.GetString();
		}
		catch { }

		return null;
	}

	/// <summary>
	/// Find UnrealEditor-Cmd.exe, preferring the version the project targets.
	/// Tries the registry first, then scans the standard Epic Games install root.
	/// </summary>
	public static string FindEditorCmd( string engineVersion )
	{
		var fromReg = FromRegistry( engineVersion );
		if ( fromReg != null )
			return fromReg;

		var roots = new[]
		{
			Environment.GetEnvironmentVariable( "ProgramW6432" ),
			Environment.GetEnvironmentVariable( "ProgramFiles" ),
		}.Where( x => !string.IsNullOrEmpty( x ) ).Distinct();

		foreach ( var pf in roots )
		{
			var epic = Path.Combine( pf, "Epic Games" );
			if ( !Directory.Exists( epic ) )
				continue;

			if ( !string.IsNullOrEmpty( engineVersion ) )
			{
				var exact = CmdPath( Path.Combine( epic, $"UE_{engineVersion}" ) );
				if ( File.Exists( exact ) )
					return exact;
			}

			// Fall back to the highest installed engine.
			foreach ( var dir in Directory.GetDirectories( epic, "UE_*" ).OrderByDescending( x => x ) )
			{
				var cmd = CmdPath( dir );
				if ( File.Exists( cmd ) )
					return cmd;
			}
		}

		return null;
	}

	static string CmdPath( string engineRoot )
		=> Path.Combine( engineRoot, "Engine", "Binaries", "Win64", "UnrealEditor-Cmd.exe" );

	static string FromRegistry( string engineVersion )
	{
		if ( string.IsNullOrEmpty( engineVersion ) )
			return null;

		try
		{
			using var key = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(
				$@"SOFTWARE\EpicGames\Unreal Engine\{engineVersion}" );

			if ( key?.GetValue( "InstalledDirectory" ) is string dir && !string.IsNullOrEmpty( dir ) )
			{
				var cmd = CmdPath( dir );
				if ( File.Exists( cmd ) )
					return cmd;
			}
		}
		catch { }

		return null;
	}
}