// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Runtime.InteropServices;

namespace Microsoft.AspNetCore.Testing;

/// <summary>
/// Skips a test if the OS is the given type (Windows) and the OS version is greater than specified.
/// E.g. Specifying Window 8 skips on Win 10, but not on Linux. Combine with OSSkipConditionAttribute as needed.
/// </summary>
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class | AttributeTargets.Assembly, AllowMultiple = true)]
public class MaximumOSVersionAttribute : Attribute, ITestCondition
{
    private readonly OperatingSystems _targetOS;
    private readonly Version _maxVersion;
    private readonly OperatingSystems _currentOS;
    private readonly Version _currentVersion;
    private readonly bool _skip;

    public MaximumOSVersionAttribute(OperatingSystems operatingSystem, string maxVersion) :
        this(operatingSystem, Version.Parse(maxVersion), GetCurrentOS(), GetCurrentOSVersion())
    {
    }

    // to enable unit testing
    internal MaximumOSVersionAttribute(OperatingSystems targetOS, Version maxVersion, OperatingSystems currentOS, Version currentVersion)
    {
        if (targetOS != OperatingSystems.Windows)
        {
            throw new NotImplementedException("Max version support is only implemented for Windows.");
        }
        _targetOS = targetOS;
        _maxVersion = maxVersion;
        _currentOS = currentOS;
        // We drop the 4th field because it is not significant and it messes up the comparisons.
        _currentVersion = new Version(currentVersion.Major, currentVersion.Minor,
            // Major and Minor are required by the parser, but if Build isn't specified then it returns -1
            // which the constructor rejects.
            currentVersion.Build == -1 ? 0 : currentVersion.Build);

        // Do not skip other OS's, Use OSSkipConditionAttribute or a separate MaximumOsVersionAttribute for that.
        _skip = _targetOS == _currentOS && _maxVersion < _currentVersion;
        SkipReason = $"This test requires {_targetOS} {_maxVersion} or earlier.";
    }

    // Since a test would be executed only if 'IsMet' is true, return false if we want to skip
    public bool IsMet => !_skip;

    public string SkipReason { get; set; }

    private static OperatingSystems GetCurrentOS()
    {
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
        {
            return OperatingSystems.Windows;
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
        {
            return OperatingSystems.Linux;
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
        {
            return OperatingSystems.MacOSX;
        }
        throw new PlatformNotSupportedException();
    }

    private static Version GetCurrentOSVersion()
    {
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
        {
            return Environment.OSVersion.Version;
        }
        else
        {
            // Not implemented, but this will still be called before the OS check happens so don't throw.
            return new Version(0, 0);
        }
    }
}
