using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;

namespace StellaOps.Provcache;

public sealed partial class ProvcacheService
{
    /// <inheritdoc />
    public async Task<ProvcacheServiceResult> GetAsync(
        string veriKey,
        bool bypassCache = false,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(veriKey);

        if (bypassCache && _options.AllowCacheBypass)
        {
            _logger.LogDebug("Cache bypass requested for VeriKey {VeriKey}", veriKey);
            return ProvcacheServiceResult.Bypassed();
        }
        var sw = Stopwatch.StartNew();
        using var activity = ProvcacheTelemetry.StartGetActivity(veriKey);

        try
        {
            var result = await _store.GetAsync(veriKey, cancellationToken).ConfigureAwait(false);
            sw.Stop();

            RecordMetrics(result.IsHit, sw.Elapsed.TotalMilliseconds);

            if (result.IsHit && result.Entry is not null)
            {
                if (result.Entry.ExpiresAt <= _timeProvider.GetUtcNow())
                {
                    _logger.LogDebug("Cache entry for VeriKey {VeriKey} is expired", veriKey);
                    ProvcacheTelemetry.RecordRequest("get", "expired");
                    return ProvcacheServiceResult.Expired(result.Entry, sw.Elapsed.TotalMilliseconds);
                }

                _logger.LogDebug(
                    "Cache hit for VeriKey {VeriKey} from {Source} in {ElapsedMs}ms",
                    veriKey,
                    result.Source,
                    sw.Elapsed.TotalMilliseconds);

                ProvcacheTelemetry.MarkCacheHit(activity, result.Source ?? "valkey");
                ProvcacheTelemetry.RecordHit(result.Source ?? "valkey");
                ProvcacheTelemetry.RecordRequest("get", ProvcacheTelemetry.ResultHit);
                ProvcacheTelemetry.RecordLatency("get", sw.Elapsed);

                return ProvcacheServiceResult.Hit(result.Entry, result.Source!, sw.Elapsed.TotalMilliseconds);
            }

            var dbEntry = await _repository.GetAsync(veriKey, cancellationToken).ConfigureAwait(false);
            sw.Stop();

            if (dbEntry is not null)
            {
                if (dbEntry.ExpiresAt <= _timeProvider.GetUtcNow())
                {
                    _logger.LogDebug("Database entry for VeriKey {VeriKey} is expired", veriKey);
                    ProvcacheTelemetry.RecordRequest("get", "expired");
                    return ProvcacheServiceResult.Expired(dbEntry, sw.Elapsed.TotalMilliseconds);
                }

                await _store.SetAsync(dbEntry, cancellationToken).ConfigureAwait(false);

                _logger.LogDebug(
                    "Cache backfill for VeriKey {VeriKey} from postgres in {ElapsedMs}ms",
                    veriKey,
                    sw.Elapsed.TotalMilliseconds);

                ProvcacheTelemetry.MarkCacheHit(activity, "postgres");
                ProvcacheTelemetry.RecordHit("postgres");
                ProvcacheTelemetry.RecordRequest("get", ProvcacheTelemetry.ResultHit);
                ProvcacheTelemetry.RecordLatency("get", sw.Elapsed);

                return ProvcacheServiceResult.Hit(dbEntry, "postgres", sw.Elapsed.TotalMilliseconds);
            }

            ProvcacheTelemetry.MarkCacheMiss(activity);
            ProvcacheTelemetry.RecordMiss();
            ProvcacheTelemetry.RecordRequest("get", ProvcacheTelemetry.ResultMiss);
            ProvcacheTelemetry.RecordLatency("get", sw.Elapsed);

            _logger.LogDebug("Cache miss for VeriKey {VeriKey} in {ElapsedMs}ms", veriKey, sw.Elapsed.TotalMilliseconds);
            return ProvcacheServiceResult.Miss(sw.Elapsed.TotalMilliseconds);
        }
        catch (Exception ex)
        {
            ProvcacheTelemetry.MarkError(activity, ex.Message);
            ProvcacheTelemetry.RecordRequest("get", ProvcacheTelemetry.ResultError);
            _logger.LogError(ex, "Error getting cache entry for VeriKey {VeriKey}", veriKey);
            return ProvcacheServiceResult.Miss(sw.Elapsed.TotalMilliseconds);
        }
    }
}