using System.Net;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Options;
using Tau.Acuvim.Portal.Configuration;
using Tau.Acuvim.Portal.Data;
using Tau.Acuvim.Portal.Domain.Fleet;
using Tau.Acuvim.Portal.DTOs;

namespace Tau.Acuvim.Portal.Services;

// Background loop that pushes sites/devices/measurements to the Admin fleet ingest endpoint.
// Registered only when RunMode=Client AND FleetIngest__Enabled=true.
//
// Per tick:
//   1. Sites (full set, idempotent upsert on Admin side)
//   2. Devices (full set)
//   3. Measurements: up to 3 batches × BatchSize rows, cursor by ReceivedAt
// Then sleep IntervalSeconds.
public sealed class FleetPushService(
    IServiceProvider services,
    IOptions<FleetIngestOptions> options,
    ILogger<FleetPushService> log)
    : BackgroundService
{
    private const int MaxBatchesPerTickPerResource = 3;
    private static readonly TimeSpan MaxBackoff = TimeSpan.FromMinutes(30);

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        var interval = TimeSpan.FromSeconds(Math.Max(5, options.Value.IntervalSeconds));
        log.LogInformation("FleetPushService started. Url={Url}, interval={Interval}s",
            options.Value.Url, interval.TotalSeconds);

        // Brief startup grace so MigrateAsync + IdentityBootstrapper finish before we hit the DB.
        try { await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken); }
        catch (TaskCanceledException) { return; }

        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                await RunTickAsync(stoppingToken);
            }
            catch (Exception ex) when (ex is not TaskCanceledException)
            {
                log.LogError(ex, "FleetPushService tick failed");
            }

            try { await Task.Delay(interval, stoppingToken); }
            catch (TaskCanceledException) { break; }
        }
    }

    private async Task RunTickAsync(CancellationToken ct)
    {
        using var scope = services.CreateScope();
        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
        var client = scope.ServiceProvider.GetRequiredService<FleetPushClient>();

        if (!await ShouldRunNowAsync(db, ct))
        {
            return;
        }

        var sitesOk = await PushSitesAsync(db, client, ct);
        if (!sitesOk) return;

        var devicesOk = await PushDevicesAsync(db, client, ct);
        if (!devicesOk) return;

        await PushMeasurementsAsync(db, client, ct);
    }

    // ── Sites: full set every tick ─────────────────────────────────────────
    private async Task<bool> PushSitesAsync(AppDbContext db, FleetPushClient client, CancellationToken ct)
    {
        var state = await GetStateAsync(db, FleetPushState.ResourceSites, ct);
        var rows = await db.Sites.AsNoTracking()
            .Select(s => new FleetSiteDto(s.Id, s.Name, s.Address, s.MunicipalityId, s.IsActive))
            .ToListAsync(ct);
        if (rows.Count == 0)
        {
            await MarkSuccessAsync(db, state, cursor: DateTime.UtcNow, ct);
            return true;
        }
        var result = await client.PushSitesAsync(rows, DateTime.UtcNow, ct);
        return await HandleResultAsync(db, state, result, cursor: DateTime.UtcNow, ct);
    }

    // ── Devices: full set every tick ───────────────────────────────────────
    private async Task<bool> PushDevicesAsync(AppDbContext db, FleetPushClient client, CancellationToken ct)
    {
        var state = await GetStateAsync(db, FleetPushState.ResourceDevices, ct);
        var rows = await db.Devices.AsNoTracking()
            .Select(d => new FleetDeviceDto(d.Id, d.SiteId, d.Name, d.ExternalId, d.Description, d.IsActive))
            .ToListAsync(ct);
        if (rows.Count == 0)
        {
            await MarkSuccessAsync(db, state, cursor: DateTime.UtcNow, ct);
            return true;
        }
        var result = await client.PushDevicesAsync(rows, DateTime.UtcNow, ct);
        return await HandleResultAsync(db, state, result, cursor: DateTime.UtcNow, ct);
    }

    // ── Measurements: cursor-driven batches up to MaxBatchesPerTickPerResource ─
    private async Task PushMeasurementsAsync(AppDbContext db, FleetPushClient client, CancellationToken ct)
    {
        var state = await GetStateAsync(db, FleetPushState.ResourceMeasurements, ct);
        var cursor = state.LastCursor ?? DateTime.MinValue.ToUniversalTime();
        int batchSize = options.Value.BatchSize;

        for (int i = 0; i < MaxBatchesPerTickPerResource; i++)
        {
            var rows = await db.PowerMeasurements.AsNoTracking()
                .Where(m => m.ReceivedAt > cursor)
                .OrderBy(m => m.ReceivedAt)
                .Take(batchSize)
                .Select(m => new FleetMeasurementDto(
                    m.Time, m.DeviceId, m.ActivePowerKw,
                    m.ReactivePowerKvar, m.ApparentPowerKva, m.PowerFactor,
                    m.VoltageV, m.FrequencyHz,
                    m.EnergyImportedKwh, m.EnergyExportedKwh,
                    m.Source, m.ReceivedAt))
                .ToListAsync(ct);

            if (rows.Count == 0) break;

            var newCursor = rows[^1].ReceivedAt;
            var result = await client.PushMeasurementsAsync(rows, newCursor, ct);

            if (result.StatusCode == HttpStatusCode.RequestEntityTooLarge)
            {
                batchSize = Math.Max(100, batchSize / 2);
                log.LogWarning("Ingest returned 413; halving batch size to {BatchSize}", batchSize);
                continue;
            }

            var ok = await HandleResultAsync(db, state, result, cursor: newCursor, ct);
            if (!ok) return;

            cursor = newCursor;
            if (rows.Count < batchSize) break;
        }
    }

    // ── State helpers ──────────────────────────────────────────────────────
    private static async Task<FleetPushState> GetStateAsync(AppDbContext db, string resourceType, CancellationToken ct)
    {
        var row = await db.FleetPushState.FirstOrDefaultAsync(x => x.ResourceType == resourceType, ct);
        if (row is null)
        {
            row = new FleetPushState { ResourceType = resourceType };
            db.FleetPushState.Add(row);
            await db.SaveChangesAsync(ct);
        }
        return row;
    }

    private static async Task MarkSuccessAsync(AppDbContext db, FleetPushState state, DateTime cursor, CancellationToken ct)
    {
        state.LastCursor = cursor;
        state.LastSyncedAt = DateTime.UtcNow;
        state.LastError = null;
        state.ConsecutiveFailures = 0;
        await db.SaveChangesAsync(ct);
    }

    private async Task<bool> HandleResultAsync(
        AppDbContext db, FleetPushState state, FleetPushResult result, DateTime cursor, CancellationToken ct)
    {
        if (result.Succeeded)
        {
            await MarkSuccessAsync(db, state, cursor, ct);
            if (result.Rejected > 0)
            {
                log.LogWarning("Ingest accepted={Accepted} rejected={Rejected} for {Resource}",
                    result.Accepted, result.Rejected, state.ResourceType);
            }
            return true;
        }

        state.LastError = result.Error;
        state.ConsecutiveFailures++;
        state.LastSyncedAt = DateTime.UtcNow;
        await db.SaveChangesAsync(ct);

        var backoff = result.RetryAfter ?? BackoffFor(state.ConsecutiveFailures);
        log.LogWarning("Push failed for {Resource}: {Error}. Failures={N}, next attempt after ~{Backoff}.",
            state.ResourceType, result.Error, state.ConsecutiveFailures, backoff);

        // Stop this tick; the next interval handles the retry naturally.
        return false;
    }

    private static TimeSpan BackoffFor(int failures)
    {
        var baseMinutes = Math.Min(Math.Pow(2, Math.Max(0, failures - 1)), 30);
        return TimeSpan.FromMinutes(baseMinutes);
    }

    // Block when we're in a long backoff window — only attempt if enough time has passed
    // since LastSyncedAt to cover the backoff. Cheap: read one row.
    private async Task<bool> ShouldRunNowAsync(AppDbContext db, CancellationToken ct)
    {
        var maxFailures = await db.FleetPushState.AsNoTracking()
            .Select(x => new { x.LastSyncedAt, x.ConsecutiveFailures })
            .ToListAsync(ct);
        if (maxFailures.Count == 0) return true;

        foreach (var row in maxFailures)
        {
            if (row.ConsecutiveFailures == 0) return true;
            if (row.LastSyncedAt is null) return true;
            var since = DateTime.UtcNow - row.LastSyncedAt.Value;
            var backoff = BackoffFor(row.ConsecutiveFailures);
            if (since >= backoff) return true;
        }
        return false;
    }
}