using System.Globalization;
using System.Reflection;
using System.Text;
using SQLInsight.Core.Findings;
using SQLInsight.Repository;

namespace SQLInsight.Web.Api;

/// <summary>
/// Read-only integration: JSON for scripts and other tools, and the Prometheus text format for Prometheus/Grafana.
/// </summary>
public static class IntegrationEndpoints
{
    /// <summary>An instance counts as up when the last contact succeeded and is this recent.</summary>
    public static readonly TimeSpan UpWindow = TimeSpan.FromMinutes(10);

    public static void Map(IEndpointRouteBuilder app)
    {
        var api = app.MapGroup("/api/v1").DisableAntiforgery().WithTags("SQLInsight Pro API v1").RequireRead();
        api.MapGet("/instances", async (InsightRepository repository, CancellationToken ct) =>
            (await repository.GetInstancesAsync(ct).ConfigureAwait(false)).Select(i => new
            {
                i.Name,
                i.ProductVersion,
                i.ProductLevel,
                i.ProductUpdateLevel,
                i.Edition,
                i.LastSeenAt,
                Up = IsUp(i),
                i.LastError,
                Findings = new { i.Critical, i.High, i.Medium, i.Low, i.Info },
                i.NotMeasurable,
            }))
            .WithSummary("Instanser med status og antal fund / Instances");

        app.MapGet("/metrics", async (InsightRepository repository, CancellationToken ct) =>
            Results.Text(await PrometheusAsync(repository, ct).ConfigureAwait(false), "text/plain; version=0.0.4; charset=utf-8")).RequireRead();
    }

    private static bool IsUp(InstanceOverview i) => !i.IsFailing && i.LastSeenAt is { } seen && DateTime.UtcNow - seen < UpWindow;

    public static async Task<string> PrometheusAsync(InsightRepository repository, CancellationToken cancellationToken)
    {
        ArgumentNullException.ThrowIfNull(repository);
        var instances = await repository.GetInstancesAsync(cancellationToken).ConfigureAwait(false);
        var findings = await repository.GetActiveFindingsAsync(cancellationToken: cancellationToken).ConfigureAwait(false);
        var metrics = await repository.GetLatestMetricsAsync(TimeSpan.FromMinutes(15), cancellationToken).ConfigureAwait(false);
        var update = await repository.GetUpdateStatusAsync(cancellationToken).ConfigureAwait(false);
        var text = new StringBuilder();

        var version = typeof(IntegrationEndpoints).Assembly.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion.Split('+')[0] ?? "0.0.0";
        Family(text, "sqlinsight_build_info", "Version of SQLInsight Pro and the rule pack in use.");
        Sample(text, "sqlinsight_build_info", [("version", version), ("rulepack", update?.RulePackVersion ?? "")], 1);

        Family(text, "sqlinsight_instance_up", "1 if the last contact with the instance succeeded within 10 minutes.");
        foreach (var i in instances)
        {
            Sample(text, "sqlinsight_instance_up", [("instance", i.Name)], IsUp(i) ? 1 : 0);
        }

        Family(text, "sqlinsight_instance_last_seen_timestamp_seconds", "Unix time of the last successful contact.");
        foreach (var i in instances.Where(i => i.LastSeenAt is not null))
        {
            Sample(text, "sqlinsight_instance_last_seen_timestamp_seconds", [("instance", i.Name)], new DateTimeOffset(DateTime.SpecifyKind(i.LastSeenAt!.Value, DateTimeKind.Utc)).ToUnixTimeSeconds());
        }

        Family(text, "sqlinsight_instance_info", "Version and edition of each instance.");
        foreach (var i in instances)
        {
            Sample(text, "sqlinsight_instance_info", [("instance", i.Name), ("version", i.ProductVersion ?? ""), ("level", $"{i.ProductLevel} {i.ProductUpdateLevel}".Trim()), ("edition", i.Edition ?? "")], 1);
        }

        Family(text, "sqlinsight_findings", "Active findings per instance and severity.");
        foreach (var i in instances)
        {
            foreach (var (severity, count) in new[] { ("critical", i.Critical), ("high", i.High), ("medium", i.Medium), ("low", i.Low), ("info", i.Info) })
            {
                Sample(text, "sqlinsight_findings", [("instance", i.Name), ("severity", severity)], count);
            }
        }

        Family(text, "sqlinsight_rule_findings", "Active findings per instance and rule.");
        foreach (var group in findings.GroupBy(f => (f.InstanceName, f.RuleId)).OrderBy(g => g.Key))
        {
            Sample(text, "sqlinsight_rule_findings",
                [("instance", group.Key.InstanceName), ("rule", group.Key.RuleId), ("severity", group.Max(f => f.Severity).ToString().ToLowerInvariant())], group.Count());
        }

        Family(text, "sqlinsight_rules_not_measurable", "Rules that could not be evaluated (version, permissions or errors).");
        foreach (var i in instances)
        {
            Sample(text, "sqlinsight_rules_not_measurable", [("instance", i.Name)], i.NotMeasurable);
        }

        Family(text, "sqlinsight_metric", "Newest sample of each collected metric (cpu.sqlserver in %, memory.ple in s, workload.* per second, …).");
        foreach (var m in metrics)
        {
            Sample(text, "sqlinsight_metric", [("instance", m.Instance), ("metric", m.Metric)], m.Value);
        }

        return text.ToString();
    }

    private static void Family(StringBuilder text, string name, string help) =>
        text.Append("# HELP ").Append(name).Append(' ').Append(help).Append('\n').Append("# TYPE ").Append(name).Append(" gauge\n");

    private static void Sample(StringBuilder text, string name, (string Name, string Value)[] labels, double value)
    {
        text.Append(name).Append('{');
        for (var i = 0; i < labels.Length; i++)
        {
            text.Append(i == 0 ? "" : ",").Append(labels[i].Name).Append("=\"").Append(Escape(labels[i].Value)).Append('"');
        }

        text.Append("} ").Append(value.ToString("R", CultureInfo.InvariantCulture)).Append('\n');
    }

    /// <summary>Label value escaping from the Prometheus text format: backslash, double quote and newline.</summary>
    public static string Escape(string value) => value.Replace("\\", "\\\\", StringComparison.Ordinal).Replace("\"", "\\\"", StringComparison.Ordinal).Replace("\n", "\\n", StringComparison.Ordinal);
}