using System.Text.Json;

namespace JournalBot.Shared;

public sealed record QueueStatus(int Pending, int Failed);

public sealed class RuntimeReader
{
    private readonly string _root;
    public RuntimeReader(string runtimeRoot) => _root = runtimeRoot;

    private string Queue(string sub) => Path.Combine(_root, "queue", sub);

    public IReadOnlyList<QueueItem> ReadHistory()
    {
        var dir = Queue("done");
        if (!Directory.Exists(dir)) return Array.Empty<QueueItem>();
        var items = new List<QueueItem>();
        foreach (var f in Directory.EnumerateFiles(dir, "*.json"))
        {
            try
            {
                var item = JsonSerializer.Deserialize<QueueItem>(
                    File.ReadAllText(f, System.Text.Encoding.UTF8));
                if (item is not null) items.Add(item);
            }
            catch (JsonException) { /* skip malformed */ }
        }
        // Newest first by processed_at (fallback received_at).
        return items
            .OrderByDescending(i => i.ProcessedAt ?? i.ReceivedAt, StringComparer.Ordinal)
            .ToList();
    }

    public QueueStatus ReadStatus()
    {
        int Count(string sub) => Directory.Exists(Queue(sub))
            ? Directory.EnumerateFiles(Queue(sub), "*.json").Count()
            : 0;
        return new QueueStatus(Count("pending"), Count("failed"));
    }

    public IReadOnlyList<string> TailLog(string fileName, int lines)
    {
        var path = Path.Combine(_root, "logs", fileName);
        if (!File.Exists(path)) return Array.Empty<string>();
        var all = File.ReadAllLines(path, System.Text.Encoding.UTF8);
        return all.Length <= lines ? all : all[^lines..];
    }
}