using System.Collections.Concurrent;
using Luna.Identity.Abstractions;

namespace Luna.Identity;

public class UserIdentityService(IPairingCodeGenerator pairingCodeGenerator) : IUserIdentityService
{
    // Todo: User creation
    private readonly UserIdentity currentUser = new(
        UserId: Guid.NewGuid().ToString(),
        UserName: "Erik");
    
    private readonly ConcurrentDictionary<string, IList<PairingCode>> pairingCodes = new();
    private readonly ConcurrentDictionary<string, IList<ChannelLink>> linkedChannels = new();

    public UserIdentity GetCurrentUser() => currentUser;

    public string StartChannelLink(string userId, string channelType)
    {
        if (!pairingCodes.ContainsKey(userId))
            pairingCodes[userId] = new List<PairingCode>();

        var existingCode = pairingCodes[userId]
            .SingleOrDefault(c => c.ChannelType == channelType);

        switch (existingCode)
        {
            case {} when !IsPairingCodeExpired(existingCode):
                return existingCode.Code;
            case {} when IsPairingCodeExpired(existingCode):
                pairingCodes[userId].Remove(existingCode);
                return CreateNewPairingCode(userId, channelType);
            default:
                return CreateNewPairingCode(userId, channelType);
        }
    }

    public void CompleteChannelLink(string userId, string channelType, string code)
    {
        if (!linkedChannels.ContainsKey(userId))
            linkedChannels[userId] = new List<ChannelLink>();
        
        if (linkedChannels[userId].Any(channel => channel.ChannelType == channelType && channel.UserId == userId))
            throw new InvalidOperationException($"Channel {channelType} already linked to user with id {userId}");
        
        if (!pairingCodes.TryGetValue(userId, out var userCodes))
            throw new InvalidOperationException($"No active pairing codes for user with id {userId}");

        var userCode = userCodes.SingleOrDefault(c => c.ChannelType == channelType && c.Code == code);
        if (userCode is null)
            throw new InvalidOperationException($"Pairing code {code} did not match any active codes for channel {channelType}");

        if (IsPairingCodeExpired(userCode))
            throw new InvalidOperationException($"Pairing code {code} is already expired");
        
        linkedChannels[userId].Add(new ChannelLink(
            ChannelType: channelType,
            ChannelUserId: userId,
            UserId: userId,
            LinkedAt: DateTimeOffset.UtcNow));
    }
    
    public bool IsChannelLinked(string userId, string channelType) 
        => linkedChannels.TryGetValue(userId, out var channelLinks) 
                && channelLinks.Any(link => link.ChannelType == channelType && link.UserId == userId);


    private bool IsPairingCodeExpired(PairingCode code)
        => code.CreatedAt + code.TimeToLive < DateTimeOffset.UtcNow;

    private string CreateNewPairingCode(string userId, string channelType)
    {
        var code = pairingCodeGenerator.Generate(channelType, userId);
        pairingCodes[userId].Add(code);

        return code.Code;
    }
}