using AxCopilot.Models;

namespace AxCopilot.Services;

/// <summary>
/// 드래프트 큐 항목의 정렬과 상태 전이를 담당한다.
/// 이후 command queue 실행기와 직접 연결될 수 있도록 queue policy를 분리한다.
/// </summary>
public sealed class DraftQueueService
{
    public sealed class DraftQueueSummary
    {
        public int TotalCount { get; init; }
        public int QueuedCount { get; init; }
        public int RunningCount { get; init; }
        public int BlockedCount { get; init; }
        public int FailedCount { get; init; }
        public int CompletedCount { get; init; }
        public DraftQueueItem? NextItem { get; init; }
        public DateTime? NextReadyAt { get; init; }
    }

    public DraftQueueItem CreateItem(string text, string priority = "next", string kind = "message")
    {
        return new DraftQueueItem
        {
            Text = text.Trim(),
            Priority = NormalizePriority(priority),
            Kind = string.IsNullOrWhiteSpace(kind) ? "message" : kind.Trim().ToLowerInvariant(),
            State = "queued",
            CreatedAt = DateTime.Now,
        };
    }

    public DraftQueueItem? GetNextQueuedItem(IEnumerable<DraftQueueItem>? items, DateTime? now = null)
    {
        var at = now ?? DateTime.Now;
        return items?
            .Where(x => CanRunNow(x, at))
            .OrderBy(GetPriorityRank)
            .ThenBy(x => x.CreatedAt)
            .FirstOrDefault();
    }

    public DraftQueueSummary GetSummary(IEnumerable<DraftQueueItem>? items, DateTime? now = null)
    {
        var at = now ?? DateTime.Now;
        var snapshot = items?.ToList() ?? [];
        var nextReadyAt = snapshot
            .Where(IsBlocked)
            .Select(x => x.NextRetryAt)
            .Where(x => x.HasValue)
            .OrderBy(x => x)
            .FirstOrDefault();

        return new DraftQueueSummary
        {
            TotalCount = snapshot.Count,
            QueuedCount = snapshot.Count(x => CanRunNow(x, at)),
            RunningCount = snapshot.Count(x => string.Equals(x.State, "running", StringComparison.OrdinalIgnoreCase)),
            BlockedCount = snapshot.Count(IsBlocked),
            FailedCount = snapshot.Count(x => string.Equals(x.State, "failed", StringComparison.OrdinalIgnoreCase)),
            CompletedCount = snapshot.Count(x => string.Equals(x.State, "completed", StringComparison.OrdinalIgnoreCase)),
            NextItem = GetNextQueuedItem(snapshot, at),
            NextReadyAt = nextReadyAt,
        };
    }

    public bool MarkRunning(DraftQueueItem? item)
    {
        if (item == null)
            return false;

        item.State = "running";
        item.LastError = null;
        item.NextRetryAt = null;
        item.AttemptCount++;
        return true;
    }

    public bool MarkCompleted(DraftQueueItem? item)
    {
        if (item == null)
            return false;

        item.State = "completed";
        item.LastError = null;
        item.NextRetryAt = null;
        return true;
    }

    public bool MarkFailed(DraftQueueItem? item, string? error)
    {
        if (item == null)
            return false;

        item.State = "failed";
        item.LastError = string.IsNullOrWhiteSpace(error) ? null : error.Trim();
        item.NextRetryAt = null;
        return true;
    }

    public bool ScheduleRetry(DraftQueueItem? item, string? error, TimeSpan? delay = null)
    {
        if (item == null)
            return false;

        item.State = "queued";
        item.LastError = string.IsNullOrWhiteSpace(error) ? null : error.Trim();
        item.NextRetryAt = DateTime.Now.Add(delay ?? GetRetryDelay(item));
        return true;
    }

    public bool ResetToQueued(DraftQueueItem? item)
    {
        if (item == null)
            return false;

        item.State = "queued";
        item.LastError = null;
        item.NextRetryAt = null;
        return true;
    }

    public TimeSpan GetRetryDelay(DraftQueueItem item)
    {
        var seconds = Math.Min(300, 15 * Math.Max(1, (int)Math.Pow(2, Math.Max(0, item.AttemptCount - 1))));
        return TimeSpan.FromSeconds(seconds);
    }

    public bool CanRunNow(DraftQueueItem item, DateTime? now = null)
    {
        var at = now ?? DateTime.Now;
        return IsQueued(item) && (!item.NextRetryAt.HasValue || item.NextRetryAt.Value <= at);
    }

    private static bool IsQueued(DraftQueueItem item)
        => string.Equals(item.State, "queued", StringComparison.OrdinalIgnoreCase);

    private static bool IsBlocked(DraftQueueItem item)
        => IsQueued(item) && item.NextRetryAt.HasValue && item.NextRetryAt.Value > DateTime.Now;

    private static string NormalizePriority(string? priority)
        => priority switch
        {
            "now" => "now",
            "later" => "later",
            _ => "next",
        };

    private static int GetPriorityRank(DraftQueueItem item)
        => NormalizePriority(item.Priority) switch
        {
            "now" => 0,
            "next" => 1,
            _ => 2,
        };
}