using System;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Text.Json;
using System.Collections.Generic;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Routing;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using SNote.Models;
using SNote.Server.Data;
using SNote.Server.Security;

namespace SNote.Server.Endpoints;

public static class SyncEndpoints
{
    public static void MapSyncEndpoints(this IEndpointRouteBuilder routes)
    {
        // 0. Heartbeat ping endpoint
        routes.MapGet("/api/sync/ping", () => Results.Ok(new { status = "Healthy" }));

        // 1. Handshake Endpoint: Receive registration of downstream peers
        routes.MapPost("/api/sync/register-peer", async (RegisterPeerRequest req, HttpContext context, PeerCache peerCache, CertificateManager certManager) =>
        {
            if (string.IsNullOrWhiteSpace(req.PeerUrl))
            {
                return Results.BadRequest("Peer URL is required.");
            }

            // Authenticate server-to-server JWT
            if (!AuthHelper.IsServerAuthenticated(context, certManager))
            {
                return Results.Json(new { error = "Unauthorized server connection handshake." }, statusCode: 401);
            }

            peerCache.RegisterPeer(req.PeerUrl);
            return Results.Ok(new { message = "Server peer registered successfully." });
        });

        // 2. Full Database pulling (bootstrapping new server node)
        routes.MapPost("/api/sync/pull-database", async (HttpContext context, ServerDbContext db, IConfiguration config, CertificateManager certManager) =>
        {
            var enablePull = config.GetValue<bool>("EnableFullDbPull", false);
            if (!enablePull)
            {
                return Results.Json(new { error = "Full database pulling is disabled on this server." }, statusCode: 403);
            }

            if (!AuthHelper.IsServerAuthenticated(context, certManager))
            {
                return Results.Json(new { error = "Unauthorized server node." }, statusCode: 401);
            }

            var users = await db.Users.ToListAsync();
            var nodes = await db.Nodes.ToListAsync();
            var nodeKeys = await db.NodeKeys.ToListAsync();
            var pendingShares = await db.PendingShares.ToListAsync();
            var aclEntries = await db.AclEntries.ToListAsync();
            var peerServers = await db.PeerServers.ToListAsync();

            var dump = new DatabaseDumpPayload(users, nodes, nodeKeys, pendingShares, aclEntries, peerServers);
            return Results.Ok(dump);
        });

        // 3. Synchronize nodes states
        routes.MapPost("/api/sync/nodes", async (SyncExchangeRequest req, HttpContext context, ServerDbContext db, CertificateManager certManager) =>
        {
            if (!AuthHelper.IsServerAuthenticated(context, certManager))
            {
                return Results.Unauthorized();
            }

            var toPush = new List<SyncPushItem>();
            var toRequest = new List<string>();

            var localNodes = await db.Nodes.ToListAsync();
            var localNodeUuids = localNodes.Select(n => n.Uuid).ToHashSet();

            foreach (var remoteItem in req.Items)
            {
                var localNode = localNodes.FirstOrDefault(n => n.Uuid == remoteItem.Uuid);
                if (localNode == null)
                {
                    toRequest.Add(remoteItem.Uuid);
                }
                else
                {
                    if (localNode.UpdatedAt > remoteItem.UpdatedAt)
                    {
                        var acls = await db.AclEntries.Where(a => a.NodeUuid == localNode.Uuid).ToListAsync();
                        var keys = await db.NodeKeys.Where(k => k.NodeUuid == localNode.Uuid).ToListAsync();
                        toPush.Add(new SyncPushItem(localNode, acls, keys));
                    }
                    else if (localNode.UpdatedAt < remoteItem.UpdatedAt)
                    {
                        toRequest.Add(remoteItem.Uuid);
                    }
                }
            }

            var remoteUuids = req.Items.Select(i => i.Uuid).ToHashSet();
            foreach (var localNode in localNodes)
            {
                if (!remoteUuids.Contains(localNode.Uuid))
                {
                    var acls = await db.AclEntries.Where(a => a.NodeUuid == localNode.Uuid).ToListAsync();
                    var keys = await db.NodeKeys.Where(k => k.NodeUuid == localNode.Uuid).ToListAsync();
                    toPush.Add(new SyncPushItem(localNode, acls, keys));
                }
            }

            return Results.Ok(new SyncExchangeResponse(toPush, toRequest));
        });

        // 4. Receive full node pushes during sync
        routes.MapPost("/api/sync/push", async (List<SyncPushItem> items, HttpContext context, ServerDbContext db, CertificateManager certManager) =>
        {
            if (!AuthHelper.IsServerAuthenticated(context, certManager))
            {
                return Results.Unauthorized();
            }

            foreach (var item in items)
            {
                var localNode = await db.Nodes.FirstOrDefaultAsync(n => n.Uuid == item.Node.Uuid);
                if (localNode == null)
                {
                    db.Nodes.Add(item.Node);
                    db.AclEntries.AddRange(item.AclEntries);
                    db.NodeKeys.AddRange(item.NodeKeys);
                }
                else if (localNode.UpdatedAt < item.Node.UpdatedAt)
                {
                    localNode.Name = item.Node.Name;
                    localNode.Type = item.Node.Type;
                    localNode.Content = item.Node.Content;
                    localNode.OwnerUsername = item.Node.OwnerUsername;
                    localNode.UpdatedAt = item.Node.UpdatedAt;
                    localNode.IsDeleted = item.Node.IsDeleted;

                    var existingAcls = await db.AclEntries.Where(a => a.NodeUuid == item.Node.Uuid).ToListAsync();
                    db.AclEntries.RemoveRange(existingAcls);
                    db.AclEntries.AddRange(item.AclEntries);

                    var existingKeys = await db.NodeKeys.Where(k => k.NodeUuid == item.Node.Uuid).ToListAsync();
                    db.NodeKeys.RemoveRange(existingKeys);
                    db.NodeKeys.AddRange(item.NodeKeys);
                }
            }

            await db.SaveChangesAsync();
            return Results.Ok(new { message = "Synced elements updated successfully." });
        });

        // 5. Receive broadcast of changes (broadcasts single node updates)
        routes.MapPost("/api/sync/broadcast", async (SyncPushItem item, HttpContext context, ServerDbContext db, PeerCache peerCache, CertificateManager certManager, HttpClient httpClient) =>
        {
            if (!AuthHelper.IsServerAuthenticated(context, certManager))
            {
                return Results.Unauthorized();
            }

            var broadcastId = item.BroadcastId;
            if (!string.IsNullOrEmpty(broadcastId))
            {
                // Loop check: if already processed, ignore!
                if (!peerCache.TryProcessBroadcast(broadcastId))
                {
                    return Results.Ok(new { message = "Broadcast already processed (loop detected).", updated = false });
                }
            }

            var localNode = await db.Nodes.FirstOrDefaultAsync(n => n.Uuid == item.Node.Uuid);
            bool updated = false;

            if (localNode == null)
            {
                db.Nodes.Add(item.Node);
                db.AclEntries.AddRange(item.AclEntries);
                db.NodeKeys.AddRange(item.NodeKeys);
                updated = true;
            }
            else if (localNode.UpdatedAt < item.Node.UpdatedAt)
            {
                localNode.Name = item.Node.Name;
                localNode.Type = item.Node.Type;
                localNode.Content = item.Node.Content;
                localNode.OwnerUsername = item.Node.OwnerUsername;
                localNode.UpdatedAt = item.Node.UpdatedAt;
                localNode.IsDeleted = item.Node.IsDeleted;

                var existingAcls = await db.AclEntries.Where(a => a.NodeUuid == item.Node.Uuid).ToListAsync();
                db.AclEntries.RemoveRange(existingAcls);
                db.AclEntries.AddRange(item.AclEntries);

                var existingKeys = await db.NodeKeys.Where(k => k.NodeUuid == item.Node.Uuid).ToListAsync();
                db.NodeKeys.RemoveRange(existingKeys);
                db.NodeKeys.AddRange(item.NodeKeys);

                updated = true;
            }

            if (updated)
            {
                await db.SaveChangesAsync();

                // Relay broadcast to all peers (upstream + downstream) with loop prevention!
                if (!string.IsNullOrEmpty(broadcastId))
                {
                    _ = Task.Run(async () =>
                    {
                        await BroadcastNodeChangeAsync(item.Node.Uuid, db, peerCache, certManager, httpClient, broadcastId);
                    });
                }
            }

            return Results.Ok(new { message = "Broadcast processed.", updated });
        });
    }

    // Handshake: Tells the destination server who we are and registers us
    public static async Task RegisterPeerWithDestinationAsync(string destinationUrl, string localUrl, CertificateManager certManager, HttpClient httpClient)
    {
        try
        {
            Console.WriteLine($"[Handshake] Registering our address '{localUrl}' with destination '{destinationUrl}'...");
            var cleanDest = destinationUrl.TrimEnd('/') + "/api/sync/register-peer";

            var payload = new RegisterPeerRequest(localUrl);
            var json = JsonSerializer.Serialize(payload);
            var request = new HttpRequestMessage(HttpMethod.Post, cleanDest)
            {
                Content = new StringContent(json, Encoding.UTF8, "application/json")
            };

            // Generate server-to-server JWT signature
            var token = AuthHelper.GenerateServerToken(certManager);
            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);

            var response = await httpClient.SendAsync(request);
            if (response.IsSuccessStatusCode)
            {
                Console.WriteLine("[Handshake] Successfully registered with destination server.");
            }
            else
            {
                Console.WriteLine($"[Handshake] Handshake failed: {response.StatusCode}");
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"[Handshake] Handshake error: {ex.Message}");
        }
    }

    // Broadcast a node change to both database and dynamic in-memory cached peer servers
    public static async Task BroadcastNodeChangeAsync(string nodeUuid, ServerDbContext db, PeerCache peerCache, CertificateManager certManager, HttpClient httpClient, string? broadcastId = null)
    {
        var node = await db.Nodes.FirstOrDefaultAsync(n => n.Uuid == nodeUuid);
        if (node == null) return;

        var acls = await db.AclEntries.Where(a => a.NodeUuid == nodeUuid).ToListAsync();
        var keys = await db.NodeKeys.Where(k => k.NodeUuid == nodeUuid).ToListAsync();

        var bId = string.IsNullOrEmpty(broadcastId) ? Guid.NewGuid().ToString() : broadcastId;
        
        // Register it locally in PeerCache so we don't process it ourselves if it loops back
        peerCache.TryProcessBroadcast(bId);

        var payload = new SyncPushItem(node, acls, keys, bId);
        var json = JsonSerializer.Serialize(payload);

        // Fetch database configured peers
        var dbPeers = await db.PeerServers.Select(p => p.Url).ToListAsync();
        
        // Fetch dynamically handshake-registered in-memory peers
        var dynamicPeers = peerCache.GetPeers();
        
        // Combine peers
        var allPeers = dbPeers.Union(dynamicPeers, StringComparer.OrdinalIgnoreCase).ToList();

        foreach (var peerUrl in allPeers)
        {
            try
            {
                var request = new HttpRequestMessage(HttpMethod.Post, $"{peerUrl.TrimEnd('/')}/api/sync/broadcast");
                request.Content = new StringContent(json, Encoding.UTF8, "application/json");

                var token = AuthHelper.GenerateServerToken(certManager);
                request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);

                var response = await httpClient.SendAsync(request);
                Console.WriteLine($"Broadcast to {peerUrl}: {response.StatusCode}");
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Failed to broadcast change to {peerUrl}: {ex.Message}");
            }
        }
    }

    // Periodically pings downstream peer servers in PeerCache to ensure they are online
    public static async Task StartHeartbeatPingerAsync(PeerCache peerCache, CertificateManager certManager, HttpClient httpClient, System.Threading.CancellationToken token)
    {
        Console.WriteLine("[Heartbeat] Starting periodic downstream heartbeat pinger...");
        while (!token.IsCancellationRequested)
        {
            try
            {
                // Wait for 30 seconds
                await Task.Delay(30000, token);

                var peers = peerCache.GetPeers();
                if (peers.Count == 0) continue;

                var jwtToken = AuthHelper.GenerateServerToken(certManager);

                foreach (var peerUrl in peers)
                {
                    try
                    {
                        var request = new HttpRequestMessage(HttpMethod.Get, $"{peerUrl.TrimEnd('/')}/api/sync/ping");
                        request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", jwtToken);
                        
                        // Set a short timeout (e.g. 5 seconds) to avoid blocking
                        using var cts = new System.Threading.CancellationTokenSource(TimeSpan.FromSeconds(5));
                        using var linkedCts = System.Threading.CancellationTokenSource.CreateLinkedTokenSource(token, cts.Token);

                        var response = await httpClient.SendAsync(request, linkedCts.Token);
                        if (!response.IsSuccessStatusCode)
                        {
                            Console.WriteLine($"[Heartbeat] Peer {peerUrl} ping failed with status code: {response.StatusCode}. Evicting...");
                            peerCache.RemovePeer(peerUrl);
                        }
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine($"[Heartbeat] Peer {peerUrl} is unreachable ({ex.Message}). Evicting...");
                        peerCache.RemovePeer(peerUrl);
                    }
                }
            }
            catch (TaskCanceledException)
            {
                break;
            }
            catch (Exception ex)
            {
                Console.WriteLine($"[Heartbeat] Error in heartbeat loop: {ex.Message}");
            }
        }
    }

    public static async Task SyncWithDestinationServerAsync(string peerUrl, ServerDbContext db, CertificateManager certManager, HttpClient httpClient)
    {
        try
        {
            var token = AuthHelper.GenerateServerToken(certManager);

            var localNodes = await db.Nodes.ToListAsync();
            var reqItems = localNodes.Select(n => new SyncNodeState(n.Uuid, n.UpdatedAt, n.IsDeleted)).ToList();

            var request = new HttpRequestMessage(HttpMethod.Post, $"{peerUrl.TrimEnd('/')}/api/sync/nodes");
            request.Content = new StringContent(JsonSerializer.Serialize(new SyncExchangeRequest(reqItems)), Encoding.UTF8, "application/json");
            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);

            var response = await httpClient.SendAsync(request);
            if (!response.IsSuccessStatusCode) return;

            var result = JsonSerializer.Deserialize<SyncExchangeResponse>(await response.Content.ReadAsStringAsync(), new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
            if (result == null) return;

            if (result.ToPush != null && result.ToPush.Count > 0)
            {
                foreach (var item in result.ToPush)
                {
                    var local = await db.Nodes.FirstOrDefaultAsync(n => n.Uuid == item.Node.Uuid);
                    if (local == null)
                    {
                        db.Nodes.Add(item.Node);
                        db.AclEntries.AddRange(item.AclEntries);
                        db.NodeKeys.AddRange(item.NodeKeys);
                    }
                    else if (local.UpdatedAt < item.Node.UpdatedAt)
                    {
                        local.Name = item.Node.Name;
                        local.Type = item.Node.Type;
                        local.Content = item.Node.Content;
                        local.OwnerUsername = item.Node.OwnerUsername;
                        local.UpdatedAt = item.Node.UpdatedAt;
                        local.IsDeleted = item.Node.IsDeleted;

                        var existingAcls = await db.AclEntries.Where(a => a.NodeUuid == item.Node.Uuid).ToListAsync();
                        db.AclEntries.RemoveRange(existingAcls);
                        db.AclEntries.AddRange(item.AclEntries);

                        var existingKeys = await db.NodeKeys.Where(k => k.NodeUuid == item.Node.Uuid).ToListAsync();
                        db.NodeKeys.RemoveRange(existingKeys);
                        db.NodeKeys.AddRange(item.NodeKeys);
                    }
                }
                await db.SaveChangesAsync();
            }

            if (result.ToRequest != null && result.ToRequest.Count > 0)
            {
                var pushItems = new List<SyncPushItem>();
                foreach (var uuid in result.ToRequest)
                {
                    var node = await db.Nodes.FirstOrDefaultAsync(n => n.Uuid == uuid);
                    if (node != null)
                    {
                        var acls = await db.AclEntries.Where(a => a.NodeUuid == uuid).ToListAsync();
                        var keys = await db.NodeKeys.Where(k => k.NodeUuid == uuid).ToListAsync();
                        pushItems.Add(new SyncPushItem(node, acls, keys));
                    }
                }

                if (pushItems.Count > 0)
                {
                    var pushRequest = new HttpRequestMessage(HttpMethod.Post, $"{peerUrl.TrimEnd('/')}/api/sync/push");
                    pushRequest.Content = new StringContent(JsonSerializer.Serialize(pushItems), Encoding.UTF8, "application/json");
                    pushRequest.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);
                    await httpClient.SendAsync(pushRequest);
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error synchronizing with peer {peerUrl}: {ex.Message}");
        }
    }

    public static async Task BootstrapFromPeerServerAsync(string peerUrl, ServerDbContext db, CertificateManager certManager, HttpClient httpClient)
    {
        try
        {
            Console.WriteLine($"Performing full database pulling bootstrap from {peerUrl}...");
            var token = AuthHelper.GenerateServerToken(certManager);

            var request = new HttpRequestMessage(HttpMethod.Post, $"{peerUrl.TrimEnd('/')}/api/sync/pull-database");
            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);

            var response = await httpClient.SendAsync(request);
            if (!response.IsSuccessStatusCode)
            {
                Console.WriteLine($"Full database pull failed: {response.StatusCode}");
                return;
            }

            var dump = JsonSerializer.Deserialize<DatabaseDumpPayload>(await response.Content.ReadAsStringAsync(), new JsonSerializerOptions { PropertyNameCaseInsensitive = true });
            if (dump == null) return;

            db.Users.RemoveRange(await db.Users.ToListAsync());
            db.Nodes.RemoveRange(await db.Nodes.ToListAsync());
            db.NodeKeys.RemoveRange(await db.NodeKeys.ToListAsync());
            db.PendingShares.RemoveRange(await db.PendingShares.ToListAsync());
            db.AclEntries.RemoveRange(await db.AclEntries.ToListAsync());
            db.PeerServers.RemoveRange(await db.PeerServers.ToListAsync());
            await db.SaveChangesAsync();

            db.Users.AddRange(dump.Users);
            db.Nodes.AddRange(dump.Nodes);
            db.NodeKeys.AddRange(dump.NodeKeys);
            db.PendingShares.AddRange(dump.PendingShares);
            db.AclEntries.AddRange(dump.AclEntries);
            db.PeerServers.AddRange(dump.PeerServers);
            await db.SaveChangesAsync();

            Console.WriteLine("Full database pull bootstrap completed successfully!");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Error during full database pulling bootstrap: {ex.Message}");
        }
    }
}

public record RegisterPeerRequest(string PeerUrl);

public record DatabaseDumpPayload(
    List<User> Users,
    List<Node> Nodes,
    List<NodeKey> NodeKeys,
    List<PendingShare> PendingShares,
    List<AclEntry> AclEntries,
    List<PeerServer> PeerServers
);

public record SyncNodeState(string Uuid, DateTime UpdatedAt, bool IsDeleted);
public record SyncExchangeRequest(List<SyncNodeState> Items);
public record SyncPushItem(Node Node, List<AclEntry> AclEntries, List<NodeKey> NodeKeys, string? BroadcastId = null);
public record SyncExchangeResponse(List<SyncPushItem> ToPush, List<string> ToRequest);