using System.Collections.Concurrent;
using PlotLine.Models;

namespace PlotLine.Services;

public interface IWritingWorkspacePresenceService
{
    Task<WritingWorkspaceStatus> RegisterAsync(int userId, string connectionId, WritingWindowRegistration registration, WordCompanionPresenceStatus wordStatus);
    Task<WritingWorkspaceStatus> HeartbeatAsync(int userId, string connectionId, WritingWindowHeartbeat heartbeat, WordCompanionPresenceStatus wordStatus);
    Task<WritingWorkspaceStatus?> DisconnectAsync(string connectionId, WordCompanionPresenceStatus? wordStatus);
    Task<WritingWorkspaceStatus> GetStatusAsync(int userId, WritingWorkspaceScope scope, WordCompanionPresenceStatus wordStatus);
    Task<IReadOnlyList<WritingWorkspaceStatus>> MarkStaleOfflineAsync(Func<int, Task<WordCompanionPresenceStatus>> wordStatusForUser);
    Task<string?> GetConnectionIdForRoleAsync(int userId, WritingWorkspaceScope scope, string role);
}

public sealed class WritingWorkspacePresenceService : IWritingWorkspacePresenceService
{
    private static readonly TimeSpan ActiveTimeout = TimeSpan.FromSeconds(45);
    private readonly ConcurrentDictionary<string, WindowRecord> windowsById = new(StringComparer.Ordinal);
    private readonly ConcurrentDictionary<string, string> windowIdsByConnection = new(StringComparer.Ordinal);

    public Task<WritingWorkspaceStatus> RegisterAsync(int userId, string connectionId, WritingWindowRegistration registration, WordCompanionPresenceStatus wordStatus)
    {
        var now = DateTime.UtcNow;
        var windowId = Clean(registration.BrowserWindowID);
        if (windowId is null)
        {
            windowId = Guid.NewGuid().ToString("N");
        }

        var record = windowsById.AddOrUpdate(
            WindowKey(userId, windowId),
            _ => new WindowRecord
            {
                BrowserWindowID = windowId,
                UserID = userId,
                ConnectedUtc = now
            },
            (_, existing) => existing);

        Apply(record, connectionId, registration.ProjectID, registration.BookID, registration.CurrentRoute, registration.WritingRole, registration.DisplayLabel, now);
        windowIdsByConnection[connectionId] = WindowKey(userId, windowId);
        return Task.FromResult(BuildStatus(userId, new WritingWorkspaceScope { ProjectID = record.ProjectID, BookID = record.BookID }, wordStatus));
    }

    public Task<WritingWorkspaceStatus> HeartbeatAsync(int userId, string connectionId, WritingWindowHeartbeat heartbeat, WordCompanionPresenceStatus wordStatus)
    {
        var registration = new WritingWindowRegistration
        {
            BrowserWindowID = heartbeat.BrowserWindowID,
            ProjectID = heartbeat.ProjectID,
            BookID = heartbeat.BookID,
            CurrentRoute = heartbeat.CurrentRoute,
            WritingRole = heartbeat.WritingRole,
            DisplayLabel = heartbeat.DisplayLabel
        };
        return RegisterAsync(userId, connectionId, registration, wordStatus);
    }

    public Task<WritingWorkspaceStatus?> DisconnectAsync(string connectionId, WordCompanionPresenceStatus? wordStatus)
    {
        if (!windowIdsByConnection.TryRemove(connectionId, out var key)
            || !windowsById.TryGetValue(key, out var record)
            || !string.Equals(record.ConnectionID, connectionId, StringComparison.Ordinal))
        {
            return Task.FromResult<WritingWorkspaceStatus?>(null);
        }

        record.IsActive = false;
        record.ConnectionID = string.Empty;
        var status = BuildStatus(record.UserID, new WritingWorkspaceScope { ProjectID = record.ProjectID, BookID = record.BookID }, wordStatus ?? new WordCompanionPresenceStatus { UserID = record.UserID });
        return Task.FromResult<WritingWorkspaceStatus?>(status);
    }

    public Task<WritingWorkspaceStatus> GetStatusAsync(int userId, WritingWorkspaceScope scope, WordCompanionPresenceStatus wordStatus)
        => Task.FromResult(BuildStatus(userId, scope, wordStatus));

    public async Task<IReadOnlyList<WritingWorkspaceStatus>> MarkStaleOfflineAsync(Func<int, Task<WordCompanionPresenceStatus>> wordStatusForUser)
    {
        var now = DateTime.UtcNow;
        var changedScopes = new Dictionary<string, (int UserID, int? ProjectID, int? BookID)>(StringComparer.Ordinal);
        foreach (var record in windowsById.Values)
        {
            if (!record.IsActive || now - record.LastSeenUtc <= ActiveTimeout)
            {
                continue;
            }

            record.IsActive = false;
            if (!string.IsNullOrWhiteSpace(record.ConnectionID))
            {
                windowIdsByConnection.TryRemove(record.ConnectionID, out _);
                record.ConnectionID = string.Empty;
            }

            changedScopes[ScopeKey(record.UserID, record.ProjectID, record.BookID)] = (record.UserID, record.ProjectID, record.BookID);
        }

        var statuses = new List<WritingWorkspaceStatus>();
        foreach (var scope in changedScopes.Values)
        {
            var wordStatus = await wordStatusForUser(scope.UserID);
            statuses.Add(BuildStatus(scope.UserID, new WritingWorkspaceScope { ProjectID = scope.ProjectID, BookID = scope.BookID }, wordStatus));
        }

        return statuses;
    }

    public Task<string?> GetConnectionIdForRoleAsync(int userId, WritingWorkspaceScope scope, string role)
    {
        var normalRole = WritingWorkspaceRoles.Normalise(role);
        var now = DateTime.UtcNow;
        var record = ActiveWindows(userId, scope, now)
            .Where(window => string.Equals(window.WritingRole, normalRole, StringComparison.Ordinal))
            .OrderByDescending(window => window.LastSeenUtc)
            .FirstOrDefault();
        return Task.FromResult(record?.ConnectionID);
    }

    private static void Apply(WindowRecord record, string connectionId, int? projectId, int? bookId, string? route, string? role, string? displayLabel, DateTime now)
    {
        record.ConnectionID = connectionId;
        record.ProjectID = Positive(projectId);
        record.BookID = Positive(bookId);
        record.CurrentRoute = Clean(route) ?? "/";
        record.WritingRole = WritingWorkspaceRoles.Normalise(role);
        record.DisplayLabel = Clean(displayLabel);
        record.IsActive = true;
        record.LastSeenUtc = now;
    }

    private WritingWorkspaceStatus BuildStatus(int userId, WritingWorkspaceScope scope, WordCompanionPresenceStatus wordStatus)
    {
        var now = DateTime.UtcNow;
        var windows = ActiveWindows(userId, scope, now)
            .Select(ToPresence)
            .OrderBy(window => window.WritingRole)
            .ThenByDescending(window => window.LastSeenUtc)
            .ToList();

        return new WritingWorkspaceStatus
        {
            UserID = userId,
            ProjectID = Positive(scope.ProjectID) ?? Positive(wordStatus.LinkedProjectID),
            BookID = Positive(scope.BookID) ?? Positive(wordStatus.LinkedBookID),
            WordCompanionConnected = wordStatus.IsConnected,
            WordDocumentOpen = wordStatus.DocumentOpen,
            WordProjectID = wordStatus.LinkedProjectID,
            WordBookID = wordStatus.LinkedBookID,
            CurrentStoryPosition = wordStatus.CurrentStoryPosition,
            Windows = windows,
            Launcher = LatestRole(windows, WritingWorkspaceRoles.Launcher),
            Context = LatestRole(windows, WritingWorkspaceRoles.Context),
            Intent = LatestRole(windows, WritingWorkspaceRoles.Intent)
        };
    }

    private IEnumerable<WindowRecord> ActiveWindows(int userId, WritingWorkspaceScope scope, DateTime now)
    {
        var projectId = Positive(scope.ProjectID);
        var bookId = Positive(scope.BookID);
        return windowsById.Values.Where(record =>
            record.UserID == userId
            && record.IsActive
            && now - record.LastSeenUtc <= ActiveTimeout
            && (!projectId.HasValue || record.ProjectID == projectId)
            && (!bookId.HasValue || record.BookID == bookId));
    }

    private static WritingWindowPresence? LatestRole(IReadOnlyList<WritingWindowPresence> windows, string role)
        => windows
            .Where(window => string.Equals(window.WritingRole, role, StringComparison.Ordinal))
            .OrderByDescending(window => window.LastSeenUtc)
            .FirstOrDefault();

    private static WritingWindowPresence ToPresence(WindowRecord record)
        => new()
        {
            BrowserWindowID = record.BrowserWindowID,
            UserID = record.UserID,
            ProjectID = record.ProjectID,
            BookID = record.BookID,
            CurrentRoute = record.CurrentRoute,
            WritingRole = record.WritingRole,
            DisplayLabel = record.DisplayLabel,
            IsActive = record.IsActive,
            ConnectedUtc = record.ConnectedUtc,
            LastSeenUtc = record.LastSeenUtc
        };

    private static string? Clean(string? value)
    {
        var cleaned = (value ?? string.Empty).Trim();
        return string.IsNullOrWhiteSpace(cleaned) ? null : cleaned;
    }

    private static int? Positive(int? value)
        => value is > 0 ? value.Value : null;

    private static string WindowKey(int userId, string windowId) => $"{userId}:{windowId}";

    private static string ScopeKey(int userId, int? projectId, int? bookId) => $"{userId}:{projectId ?? 0}:{bookId ?? 0}";

    private sealed class WindowRecord
    {
        public string BrowserWindowID { get; init; } = string.Empty;
        public int UserID { get; init; }
        public string ConnectionID { get; set; } = string.Empty;
        public int? ProjectID { get; set; }
        public int? BookID { get; set; }
        public string CurrentRoute { get; set; } = "/";
        public string WritingRole { get; set; } = WritingWorkspaceRoles.None;
        public string? DisplayLabel { get; set; }
        public bool IsActive { get; set; }
        public DateTime ConnectedUtc { get; init; }
        public DateTime LastSeenUtc { get; set; }
    }
}