using System.Runtime.InteropServices;
using System.Text;

namespace Lskj.AgentPet.Host;

internal static class WindowsCredentialStore
{
    internal const string DefaultAstrBotTarget = "Langsu.Lserp.AstrBot.ApiKey";
    private const uint CredentialTypeGeneric = 1;
    private const int MaximumSecretBytes = 2048;

    public static void PopulateAstrBotApiKey(IDictionary<string, string?> environment)
    {
        ArgumentNullException.ThrowIfNull(environment);
        if (environment.TryGetValue("LSERP_ASTRBOT_API_KEY", out string? configured)
            && !string.IsNullOrWhiteSpace(configured)) return;

        string target = environment.TryGetValue("LSERP_ASTRBOT_CREDENTIAL_TARGET", out string? custom)
            && !string.IsNullOrWhiteSpace(custom)
            ? custom.Trim()
            : DefaultAstrBotTarget;
        if (target.Length is < 8 or > 128) return;

        string? secret = ReadGenericSecret(target);
        if (!string.IsNullOrWhiteSpace(secret)) environment["LSERP_ASTRBOT_API_KEY"] = secret;
    }

    private static string? ReadGenericSecret(string target)
    {
        if (!OperatingSystem.IsWindows()) return null;
        if (!CredRead(target, CredentialTypeGeneric, 0, out nint address) || address == 0)
            return null;
        try
        {
            NativeCredential credential = Marshal.PtrToStructure<NativeCredential>(address);
            if (credential.CredentialBlob == 0
                || credential.CredentialBlobSize is 0 or > MaximumSecretBytes)
                return null;
            byte[] bytes = new byte[credential.CredentialBlobSize];
            Marshal.Copy(credential.CredentialBlob, bytes, 0, bytes.Length);
            return Encoding.Unicode.GetString(bytes).TrimEnd('\0').Trim();
        }
        finally
        {
            CredFree(address);
        }
    }

    [DllImport("advapi32.dll", EntryPoint = "CredReadW", CharSet = CharSet.Unicode, SetLastError = true)]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool CredRead(
        string target,
        uint type,
        int reservedFlag,
        out nint credential);

    [DllImport("advapi32.dll", SetLastError = false)]
    private static extern void CredFree(nint buffer);

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    private struct NativeCredential
    {
        public uint Flags;
        public uint Type;
        public nint TargetName;
        public nint Comment;
        public System.Runtime.InteropServices.ComTypes.FILETIME LastWritten;
        public uint CredentialBlobSize;
        public nint CredentialBlob;
        public uint Persist;
        public uint AttributeCount;
        public nint Attributes;
        public nint TargetAlias;
        public nint UserName;
    }
}