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

using System.Collections.Concurrent;
using Microsoft.DotNet.NativeWrapper;

namespace Microsoft.DotNet.DotNetSdkResolver
{

    //  Thread safety note:
    //  This class is used by the MSBuild SDK resolvers, which can be called on multiple threads.
    public class NETCoreSdkResolver
    {
        private readonly Func<string, string?> _getEnvironmentVariable;
        private readonly VSSettings _vsSettings;

        // Caches of minimum versions, compatible SDKs are static to benefit multiple IDE evaluations.
        private static readonly ConcurrentDictionary<string, Version> s_minimumMSBuildVersions
            = new();

        private static readonly ConcurrentDictionary<CompatibleSdkKey, CompatibleSdkValue> s_compatibleSdks
            = new();

        public NETCoreSdkResolver()
            : this(Environment.GetEnvironmentVariable, VSSettings.Ambient)
        {
        }

        public NETCoreSdkResolver(Func<string, string?> getEnvironmentVariable, VSSettings vsSettings)
        {
            _getEnvironmentVariable = getEnvironmentVariable;
            _vsSettings = vsSettings;
        }

        private sealed class CompatibleSdkKey : IEquatable<CompatibleSdkKey>
        {
            public readonly string? DotnetExeDirectory;
            public readonly Version MSBuildVersion;

            public CompatibleSdkKey(string? dotnetExeDirectory, Version msbuildVersion)
            {
                DotnetExeDirectory = dotnetExeDirectory;
                MSBuildVersion = msbuildVersion;
            }

            public bool Equals(CompatibleSdkKey? other)
            {
                return other != null
                    && DotnetExeDirectory == other.DotnetExeDirectory
                    && MSBuildVersion == other.MSBuildVersion;
            }

            public override bool Equals(object? obj)
            {
                return Equals(obj as CompatibleSdkValue);
            }

            public override int GetHashCode()
            {
                int h1 = DotnetExeDirectory!.GetHashCode();
                int h2 = MSBuildVersion.GetHashCode();
                return unchecked(((h1 << 5) + h1) ^ h2);
            }
        }

        private sealed class CompatibleSdkValue
        {
            public readonly string? MostRecentCompatible;
            public readonly string? MostRecentCompatibleNonPreview;

            public CompatibleSdkValue(string? mostRecentCompatible, string? mostRecentCompatibleNonPreview)
            {
                MostRecentCompatible = mostRecentCompatible;
                MostRecentCompatibleNonPreview = mostRecentCompatibleNonPreview;
            }
        }

        private string? GetMostCompatibleSdk(string? dotnetExeDirectory, Version msbuildVersion, int minimumSdkMajorVersion = 0)
        {
            CompatibleSdkValue sdks = GetMostCompatibleSdks(dotnetExeDirectory, msbuildVersion, minimumSdkMajorVersion);
            if (_vsSettings.DisallowPrerelease())
            {
                return sdks.MostRecentCompatibleNonPreview;
            }

            return sdks.MostRecentCompatible;
        }

        private CompatibleSdkValue GetMostCompatibleSdks(string? dotnetExeDirectory, Version msbuildVersion, int minimumSdkMajorVersion)
        {
            return s_compatibleSdks.GetOrAdd(
                new CompatibleSdkKey(dotnetExeDirectory, msbuildVersion),
                key =>
                {
                    string? mostRecent = null;
                    string? mostRecentNonPreview = null;

                    string[] availableSdks = NETCoreSdkResolverNativeWrapper.GetAvailableSdks(key.DotnetExeDirectory)!;
                    for (int i = availableSdks.Length - 1; i >= 0; i--)
                    {
                        string netcoreSdkDir = availableSdks[i];
                        string netcoreSdkVersion = new DirectoryInfo(netcoreSdkDir).Name;
                        Version minimumMSBuildVersion = GetMinimumMSBuildVersion(netcoreSdkDir);

                        if (key.MSBuildVersion < minimumMSBuildVersion)
                        {
                            continue;
                        }

                        if (minimumSdkMajorVersion != 0 && int.TryParse(netcoreSdkVersion.Split('.')[0], out int sdkMajorVersion) && sdkMajorVersion < minimumSdkMajorVersion)
                        {
                            continue;
                        }

                        if (mostRecent == null)
                        {
                            mostRecent = netcoreSdkDir;
                        }

                        if (netcoreSdkVersion.IndexOf('-') < 0)
                        {
                            mostRecentNonPreview = netcoreSdkDir;
                            break;
                        }
                    }

                    return new CompatibleSdkValue(mostRecent, mostRecentNonPreview);
                });
        }

        public Version GetMinimumMSBuildVersion(string netcoreSdkDir)
        {
            return s_minimumMSBuildVersions.GetOrAdd(
                netcoreSdkDir,
                dir =>
                {
                    string minimumVersionFilePath = Path.Combine(netcoreSdkDir, "minimumMSBuildVersion");
                    if (!File.Exists(minimumVersionFilePath))
                    {
                        // smallest version that had resolver support and also
                        // greater than or equal to the version required by any 
                        // .NET Core SDK that did not have this file.
                        return new Version(15, 3, 0);
                    }

                    return Version.Parse(File.ReadLines(minimumVersionFilePath).First().Trim());
                });
        }

        public SdkResolutionResult ResolveNETCoreSdkDirectory(string? globalJsonStartDir, Version msbuildVersion, bool isRunningInVisualStudio, string? dotnetExeDir)
        {
            var result = NETCoreSdkResolverNativeWrapper.ResolveSdk(dotnetExeDir, globalJsonStartDir, _vsSettings.DisallowPrerelease());

            string? mostCompatible = result.ResolvedSdkDirectory;
            if (result.ResolvedSdkDirectory == null
                && result.GlobalJsonPath != null
                && isRunningInVisualStudio)
            {
                result.FailedToResolveSDKSpecifiedInGlobalJson = true;
                // We need the SDK to be version 5 or higher to ensure that we generate a build error when we fail to resolve the SDK specified by global.json
                mostCompatible = GetMostCompatibleSdk(dotnetExeDir, msbuildVersion, 5);
            }
            else if (result.ResolvedSdkDirectory != null
                     && result.GlobalJsonPath == null
                     && msbuildVersion < GetMinimumMSBuildVersion(result.ResolvedSdkDirectory))
            {
                mostCompatible = GetMostCompatibleSdk(dotnetExeDir, msbuildVersion);
            }

            if (mostCompatible != null)
            {
                result.ResolvedSdkDirectory = mostCompatible;
            }

            return result;
        }
    }
}