// 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.Text;

namespace Microsoft.Interop
{
    internal static class ComInterfaceGeneratorHelpers
    {
        private static readonly IMarshallingGeneratorResolver s_managedToUnmanagedDisabledMarshallingGeneratorResolver = CreateGeneratorResolver(EnvironmentFlags.DisableRuntimeMarshalling, MarshalDirection.ManagedToUnmanaged);
        private static readonly IMarshallingGeneratorResolver s_unmanagedToManagedDisabledMarshallingGeneratorResolver = CreateGeneratorResolver(EnvironmentFlags.DisableRuntimeMarshalling, MarshalDirection.UnmanagedToManaged);
        private static readonly IMarshallingGeneratorResolver s_managedToUnmanagedEnabledMarshallingGeneratorResolver = CreateGeneratorResolver(EnvironmentFlags.None, MarshalDirection.ManagedToUnmanaged);
        private static readonly IMarshallingGeneratorResolver s_unmanagedToManagedEnabledMarshallingGeneratorResolver = CreateGeneratorResolver(EnvironmentFlags.None, MarshalDirection.UnmanagedToManaged);

        private static IMarshallingGeneratorResolver CreateGeneratorResolver(EnvironmentFlags env, MarshalDirection direction)
            => DefaultMarshallingGeneratorResolver.Create(env, direction, TypeNames.GeneratedComInterfaceAttribute_ShortName,
                [
                    new StructAsHResultMarshallerFactory(),
                    new ManagedHResultExceptionGeneratorResolver(),
                    new ComInterfaceDispatchMarshallingResolver(),
                ]);

        public static IMarshallingGeneratorResolver GetGeneratorResolver(EnvironmentFlags env, MarshalDirection direction)
            => (env.HasFlag(EnvironmentFlags.DisableRuntimeMarshalling), direction) switch
            {
                (true, MarshalDirection.ManagedToUnmanaged) => s_managedToUnmanagedDisabledMarshallingGeneratorResolver,
                (true, MarshalDirection.UnmanagedToManaged) => s_unmanagedToManagedDisabledMarshallingGeneratorResolver,
                (false, MarshalDirection.ManagedToUnmanaged) => s_managedToUnmanagedEnabledMarshallingGeneratorResolver,
                (false, MarshalDirection.UnmanagedToManaged) => s_unmanagedToManagedEnabledMarshallingGeneratorResolver,
                _ => throw new UnreachableException(),
            };

        public static string CreateEmbeddedDataBlobExpression(ReadOnlySpan<byte> bytes)
        {
            // Three digits and ", " per byte; the brackets replace one separator.
            var builder = new StringBuilder(Math.Max(2, checked(bytes.Length * 5)));
            builder.Append('[');
            for (int i = 0; i < bytes.Length; i++)
            {
                if (i != 0)
                {
                    builder.Append(", ");
                }
                builder.Append(bytes[i]);
            }
            builder.Append(']');
            return builder.ToString();
        }
    }
}