using System;
using System.Globalization;
using System.Net.Http;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;
using ytLive.Helpers;

namespace ytLive.Services;

/// <summary>
/// TASK 39·2: the two numbers YouTube only publishes through the **Analytics** API — long-form watch
/// hours (trailing 12 months) and Shorts-feed views (trailing 90 days).
/// <para>This is the one place the app needs a scope beyond <c>auth/youtube</c>: the Analytics API
/// requires <c>yt-analytics.readonly</c>, which means a one-time Google re-consent. Until that scope is
/// granted, the drawer says so instead of inventing numbers.</para>
/// <para>Values are estimates: Analytics lags, and YouTube's own validity filtering decides what counts
/// towards eligibility.</para>
/// </summary>
public interface IWatchMetricsSource
{
    /// <summary>Estimated public long-form watch hours over the trailing 12 months, or null when the
    /// Analytics scope is not granted / the read failed.</summary>
    Task<long?> GetLongFormWatchHoursAsync(CancellationToken cancellationToken = default);

    /// <summary>Shorts-feed views over the trailing 90 days, or null.</summary>
    Task<long?> GetShortsViewsAsync(CancellationToken cancellationToken = default);
}

public sealed class YouTubeAnalyticsService : IWatchMetricsSource
{
    private const string ApiBase = "https://youtubeanalytics.googleapis.com/v2/reports";

    private readonly YouTubeAuthService _auth;
    private readonly HttpClient _http;
    private readonly Func<DateTime> _now;

    public YouTubeAnalyticsService(YouTubeAuthService auth, HttpClient? http = null, Func<DateTime>? now = null)
    {
        _auth = auth;
        _http = http ?? new HttpClient();
        _now = now ?? (() => DateTime.UtcNow);
    }

    public async Task<long?> GetLongFormWatchHoursAsync(CancellationToken cancellationToken = default)
    {
        // Minutes watched for long-form videos over the trailing year → hours.
        var minutes = await QueryTotalAsync(
            "estimatedMinutesWatched", "creatorContentType==video", 365, cancellationToken).ConfigureAwait(false);
        return minutes is null ? null : (long)Math.Round(minutes.Value / 60.0);
    }

    public async Task<long?> GetShortsViewsAsync(CancellationToken cancellationToken = default)
        => await QueryTotalAsync("views", "creatorContentType==shorts", 90, cancellationToken)
            .ConfigureAwait(false);

    private async Task<long?> QueryTotalAsync(
        string metric, string filter, int days, CancellationToken cancellationToken)
    {
        if (!_auth.HasAnalyticsScope) return null;
        if (_auth.CurrentChannel?.AccessToken is not { } token) return null;

        var end = _now().Date;
        var start = end.AddDays(-days);
        var url = $"{ApiBase}?ids=channel==MINE" +
                  $"&startDate={start.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)}" +
                  $"&endDate={end.ToString("yyyy-MM-dd", CultureInfo.InvariantCulture)}" +
                  $"&metrics={Uri.EscapeDataString(metric)}" +
                  $"&filters={Uri.EscapeDataString(filter)}";

        try
        {
            _http.DefaultRequestHeaders.Authorization = new("Bearer", token);
            var response = await _http.GetAsync(url, cancellationToken).ConfigureAwait(false);
            if (!response.IsSuccessStatusCode)
            {
                AppLog.Write($"Analytics query failed ({metric}): {(int)response.StatusCode}");
                return null;
            }

            var json = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
            return ParseTotal(json);
        }
        catch (Exception ex)
        {
            AppLog.Write($"Analytics query failed ({metric}): {ex.Message}");
            return null;
        }
    }

    /// <summary>Pure: the Analytics API answers with columnHeaders + rows; a channel with no data in the
    /// window returns no rows at all, which must read as "no data" rather than zero.</summary>
    internal static long? ParseTotal(string json)
    {
        using var document = JsonDocument.Parse(json);
        if (!document.RootElement.TryGetProperty("rows", out var rows)) return null;
        if (rows.ValueKind != JsonValueKind.Array || rows.GetArrayLength() == 0) return null;
        var row = rows[0];
        if (row.ValueKind != JsonValueKind.Array || row.GetArrayLength() == 0) return null;
        var value = row[0];
        return value.ValueKind == JsonValueKind.Number && value.TryGetInt64(out var total) ? total : null;
    }
}