using System.Security.Cryptography;

namespace WebDrop.Core;

public sealed partial class ChannelService
{
    private static (byte[]? Hash, byte[]? Salt) HashJoinPassword(string? password)
    {
        if (string.IsNullOrEmpty(password)) return (null, null);
        if (password.Length is < 8 or > 256) throw new WebDropException(ErrorCode.BadRequest);
        var salt = RandomNumberGenerator.GetBytes(16);
        return (Rfc2898DeriveBytes.Pbkdf2(password, salt, 210_000, HashAlgorithmName.SHA256, 32), salt);
    }

    private static void CheckAdmission(IResourceTx tx, Channel channel, Credentials creds, string? password)
    {
        string account = creds.AccountName ?? throw new WebDropException(ErrorCode.AccountRequired);
        if (account == channel.CreatorAccount) return;
        if (tx.IsJoinDenied(channel.Id, account)) throw new WebDropException(ErrorCode.Forbidden);
        if (tx.HasInvitation(channel.Id, account)) return;
        if (tx.GetChannelMember(channel.Id, account) is not null) return;
        if (channel.Settings.JoinPolicy == JoinPolicy.Invite) throw new WebDropException(ErrorCode.InvitationRequired);
        if (channel.JoinPasswordHash is null) return;
        if (string.IsNullOrEmpty(password)) throw new WebDropException(ErrorCode.ChannelPasswordRequired);
        if (password.Length > 256) throw new WebDropException(ErrorCode.ChannelPasswordInvalid);
        var actual = Rfc2898DeriveBytes.Pbkdf2(password, channel.JoinPasswordSalt!, 210_000, HashAlgorithmName.SHA256, 32);
        if (!CryptographicOperations.FixedTimeEquals(actual, channel.JoinPasswordHash)) throw new WebDropException(ErrorCode.ChannelPasswordInvalid);
    }

    public IReadOnlyList<ChannelInvitation> Invitations(Id16 id, Credentials creds) => store.Read(tx =>
    {
        var (_, principal) = Authenticate(tx, id, creds, Membership.None);
        if (principal.Role != Role.Owner) RequireMemberPermission(tx, id, creds, WorkspacePermission.RemoveMembers);
        return tx.ListInvitations(id);
    });

    /// <summary>非空间主的调用方:必须是已加入的成员,且所在身份组被授予该权限</summary>
    private Principal RequireMemberPermission(IResourceTx tx, Id16 id, Credentials creds, string permission)
    {
        var (_, principal) = Authenticate(tx, id, creds, Membership.Required);
        if (!HasWorkspacePermission(tx.GetWorkspace(id), principal, permission)) throw new WebDropException(ErrorCode.Forbidden);
        return principal;
    }

    public IReadOnlyList<ChannelInvitation> UserInvitations(string username) => store.Read(tx => tx.ListUserInvitations(username));

    public void RevokeInvitation(Id16 id, Credentials creds, string username)
    {
        store.Write(tx =>
        {
            var (_, principal) = Authenticate(tx, id, creds, Membership.None);
            if (tx.GetChannelMember(id, username)?.Role == "owner") throw new WebDropException(ErrorCode.Forbidden);
            if (principal.Role != Role.Owner)
            {
                // 被授权的成员不能移除自己,也不能移除同样有移除权限的人
                var acting = RequireMemberPermission(tx, id, creds, WorkspacePermission.RemoveMembers);
                if (username == acting.AccountName || HasWorkspacePermission(tx.GetWorkspace(id), new Principal(Role.Write, username), WorkspacePermission.RemoveMembers)) throw new WebDropException(ErrorCode.Forbidden);
            }
            tx.DeleteInvitation(id, username);
            tx.DeleteKeyPackage(id, username);
            tx.DeleteChannelMember(id, username);
            var crypto = tx.GetWorkspaceCrypto(id);
            crypto.Access.RemoveAll(a => a.Username == username);
            crypto.Envelopes.RemoveAll(e => e.Username == username);
            crypto.Revision++;
            tx.PutWorkspaceCrypto(id, crypto);
            tx.DenyAccount(id, username);
            return 0;
        });
        events.MembersChanged(id);
    }

    /// <summary>空间里所有成员的账号(不做鉴权,供已经通过鉴权的接口补全成员资料)</summary>
    public IReadOnlyList<string> MemberAccounts(Id16 id) => store.Read(tx => tx.ListChannelMembers(id).Select(m => m.Username).ToList());

    public IReadOnlyList<ChannelMember> Members(Id16 id, Credentials creds) => store.Read(tx =>
    {
        var (_, principal) = Authenticate(tx, id, creds, Membership.None);
        if (principal.Role != Role.Owner) _ = Authenticate(tx, id, creds, Membership.Required);
        return tx.ListChannelMembers(id);
    });

    public IReadOnlyList<ChannelKeyPackage> AccountChannels(string username) =>
        store.Read(tx => tx.ListUserKeyPackages(username, clock.NowMs));

    public void SaveOwnerKeyPackage(Id16 id, Credentials creds, string payload)
    {
        if (payload is null || payload.Length is < 1 or > 16_384) throw new WebDropException(ErrorCode.BadRequest);
        store.Write(tx =>
        {
            var (_, principal) = Authenticate(tx, id, creds, Membership.None);
            RequireOwner(principal);
            tx.PutKeyPackage(id, principal.AccountName!, payload, clock.NowMs);
            return 0;
        });
    }
}