using System.Net.Http;
using System.Text.Json;
using ytLive.Models;
using AppLog = ytLive.Helpers.AppLog;

namespace ytLive.Services;

/// <summary>
/// Pulls a connected channel's YPP-relevant numbers from the YouTube Data API
/// (TASK 39, slice 1): subscriptions/views/videos via channels.list, and the
/// count of public uploads in the trailing 90 days via playlistItems.list on the
/// uploads playlist. Long-form watch hours and Shorts-feed views need the
/// Analytics API (a later slice behind the IChannelStatsProvider seam).
///
/// NOTE (root cause, 2026-09-23): channels.list must NOT request the
/// `auditDetails` part — that part alone requires the
/// `youtubepartner-channel-audit` scope the app doesn't (and mustn't) hold, and
/// the whole request 403s `insufficientPermissions` over it. Standing flags are
/// not exposed to ordinary apps; the drawer deep-links to YouTube Studio instead.
/// </summary>
public class ChannelStatsService
{
    private readonly YouTubeAuthService _auth;
    private readonly HttpClient _http;
    private const string ApiBase = "https://www.googleapis.com/youtube/v3";

    public ChannelStatsService(YouTubeAuthService auth, HttpClient? http = null)
    {
        _auth = auth;
        _http = http ?? new HttpClient();
    }

    private async Task<bool> EnsureToken()
    {
        if (_auth.CurrentChannel == null) return false;
        if (_auth.CurrentChannel.TokenExpiry <= DateTime.UtcNow.AddMinutes(5))
            return await _auth.RefreshToken();
        return true;
    }

    /// <summary>Captures the channel's current stats into a snapshot, or null when
    /// there's no session, a request fails, or the API returns nothing. Never throws.</summary>
    public virtual async Task<YppStatSnapshot?> CaptureCurrentAsync()
    {
        if (!await EnsureToken()) return null;

        _http.DefaultRequestHeaders.Authorization = new("Bearer", _auth.CurrentChannel!.AccessToken);

        var response = await _http.GetAsync(
            $"{ApiBase}/channels?mine=true&part=statistics,contentDetails");
        if (!response.IsSuccessStatusCode)
        {
            // Log the response body: YouTube's error.reason names the failure
            // (insufficientPermissions / quotaExceeded / …) — the bare code was
            // undiagnosable for the 2026-09-23 auditDetails 403.
            var errorBody = await response.Content.ReadAsStringAsync();
            AppLog.Write($"YPP stats: channels.list failed ({(int)response.StatusCode}): {errorBody}");
            return null;
        }

        var json = JsonSerializer.Deserialize<JsonElement>(await response.Content.ReadAsStringAsync());
        if (!json.TryGetProperty("items", out var items) || items.GetArrayLength() == 0)
            return null;

        var channel = items[0];
        var statistics = channel.GetProperty("statistics");

        var uploadsPlaylistId = channel.TryGetProperty("contentDetails", out var contentDetails)
            && contentDetails.TryGetProperty("relatedPlaylists", out var related)
            && related.TryGetProperty("uploads", out var uploads)
            ? uploads.GetString()
            : null;

        var uploadsLast90Days = uploadsPlaylistId != null
            ? await CountUploadsLast90DaysAsync(uploadsPlaylistId)
            : 0;

        return new YppStatSnapshot
        {
            CapturedAtUtc = DateTime.UtcNow,
            SubscriberCount = ReadInt64(statistics, "subscriberCount"),
            VideoCount = ReadInt64(statistics, "videoCount"),
            TotalViews = ReadInt64(statistics, "viewCount"),
            UploadsLast90Days = uploadsLast90Days,
        };
    }

    /// <summary>YouTube serializes statistics as JSON STRINGS ("350"); a tolerant
    /// read that also accepts a number (the real 403 hid this parse bug until the
    /// auditDetails removal surfaced the string shape in 2026-09-23's Good Dog).
    /// NOTE: JsonElement.TryGetInt64 THROWS on a non-Number token — ValueKind must
    /// be checked first (try-type-in, not try-catch).</summary>
    private static long ReadInt64(JsonElement parent, string name)
    {
        if (!parent.TryGetProperty(name, out var value)) return 0;
        if (value.ValueKind == JsonValueKind.Number && value.TryGetInt64(out var n)) return n;
        if (value.ValueKind == JsonValueKind.String && long.TryParse(value.GetString(), out n)) return n;
        return 0;
    }

    /// <summary>Counts uploads published within the trailing 90 days, scanning the
    /// most recent 50 from the uploads playlist (generous beyond the 3/90-day YPP
    /// requirement; the YPP tab labels it as the recent-50 window).</summary>
    private async Task<int> CountUploadsLast90DaysAsync(string uploadsPlaylistId)
    {
        var response = await _http.GetAsync(
            $"{ApiBase}/playlistItems?part=snippet&playlistId={Uri.EscapeDataString(uploadsPlaylistId)}&maxResults=50");
        if (!response.IsSuccessStatusCode)
        {
            AppLog.Write($"YPP stats: playlistItems.list failed ({(int)response.StatusCode})");
            return 0;
        }

        var json = JsonSerializer.Deserialize<JsonElement>(await response.Content.ReadAsStringAsync());
        if (!json.TryGetProperty("items", out var items)) return 0;

        var cutoff = DateTime.UtcNow.AddDays(-90);
        var count = 0;
        foreach (var item in items.EnumerateArray())
        {
            if (!item.TryGetProperty("snippet", out var snippet)
                || !snippet.TryGetProperty("publishedAt", out var published)
                || !DateTime.TryParse(published.GetString(), out var publishedAt))
            {
                continue;
            }
            if (publishedAt.ToUniversalTime() >= cutoff)
                count++;
        }
        return count;
    }
}