using System.Collections.Immutable;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Scripting;

namespace ZB.MOM.WW.ScadaBridge.ScriptAnalysis.Tests;

/// <summary>
/// Pins the per-compile native-metadata fix (2026-08-12 follow-up to 5a781c70):
/// Roslyn's default ScriptMetadataResolver re-resolves the transitive assembly
/// closure through MetadataReference.CreateFromFile on EVERY script compile —
/// each call minting a fresh AssemblyMetadata → PEReader → NativeHeapMemoryBlock.
/// The decorator memoizes so each distinct assembly is resolved once per process.
/// </summary>
public class CachingScriptMetadataResolverTests
{
    private sealed class CountingResolver : MetadataReferenceResolver
    {
        public int MissingCalls;
        public int ReferenceCalls;
        public override bool ResolveMissingAssemblies => true;

        public override PortableExecutableReference? ResolveMissingAssembly(
            MetadataReference definition, AssemblyIdentity referenceIdentity)
        {
            Interlocked.Increment(ref MissingCalls);
            return MetadataReference.CreateFromFile(typeof(object).Assembly.Location);
        }

        public override ImmutableArray<PortableExecutableReference> ResolveReference(
            string reference, string? baseFilePath, MetadataReferenceProperties properties)
        {
            Interlocked.Increment(ref ReferenceCalls);
            return [MetadataReference.CreateFromFile(typeof(object).Assembly.Location)];
        }

        public override bool Equals(object? other) => ReferenceEquals(this, other);
        public override int GetHashCode() => 0;
    }

    private static readonly AssemblyIdentity SomeIdentity = new("System.Fake", new Version(1, 0, 0, 0));
    private static readonly MetadataReference SomeDefinition =
        MetadataReference.CreateFromFile(typeof(object).Assembly.Location);

    [Fact]
    public void ResolveMissingAssembly_SameIdentityTwice_ResolvesOnceAndSharesInstance()
    {
        var inner = new CountingResolver();
        var sut = new CachingScriptMetadataResolver(inner);

        var first = sut.ResolveMissingAssembly(SomeDefinition, SomeIdentity);
        var second = sut.ResolveMissingAssembly(SomeDefinition, SomeIdentity);

        Assert.Equal(1, inner.MissingCalls);
        Assert.Same(first, second); // one AssemblyMetadata/PEReader/native block, not two
    }

    [Fact]
    public void ResolveMissingAssembly_DistinctIdentities_ResolveIndependently()
    {
        var inner = new CountingResolver();
        var sut = new CachingScriptMetadataResolver(inner);

        sut.ResolveMissingAssembly(SomeDefinition, SomeIdentity);
        sut.ResolveMissingAssembly(SomeDefinition, new AssemblyIdentity("System.Other", new Version(1, 0, 0, 0)));

        Assert.Equal(2, inner.MissingCalls);
    }

    [Fact]
    public void ResolveReference_SameArgsTwice_ResolvesOnceAndSharesInstances()
    {
        var inner = new CountingResolver();
        var sut = new CachingScriptMetadataResolver(inner);

        var first = sut.ResolveReference("System.Xml", baseFilePath: null, MetadataReferenceProperties.Assembly);
        var second = sut.ResolveReference("System.Xml", baseFilePath: null, MetadataReferenceProperties.Assembly);

        Assert.Equal(1, inner.ReferenceCalls);
        Assert.Same(first[0], second[0]);
    }

    [Fact]
    public void Instance_IsProcessWideSingleton()
        => Assert.Same(CachingScriptMetadataResolver.Instance, CachingScriptMetadataResolver.Instance);

    [Fact]
    public void ResolveMissingAssemblies_DelegatesToInner()
    {
        var sut = new CachingScriptMetadataResolver(new CountingResolver());
        Assert.True(sut.ResolveMissingAssemblies);
    }
}