using ClawdDotNet.Core.Audit;

namespace ClawdDotNet.Core.Analytics;

/// <summary>Filter, sort order and page of <see cref="UsageAnalytics.QueryRunsAsync"/>.</summary>
public sealed record RunQuery
{
    public DateTime FromUtc { get; init; }
    public DateTime ToUtc { get; init; }
    public IReadOnlyCollection<string> Agents { get; init; } = [];
    public IReadOnlyCollection<string> Models { get; init; } = [];
    public IReadOnlyCollection<string> Sources { get; init; } = [];
    public IReadOnlyCollection<string> Statuses { get; init; } = [];
    public decimal? MinCostUsd { get; init; }

    /// <summary>Free text over run id, agent, model, task id, task title and result.</summary>
    public string? Search { get; init; }

    /// <summary>time, agent, model, source, status, steps, prompt, completion, tokens, cost, duration.</summary>
    public string Sort { get; init; } = "time";
    public bool Descending { get; init; } = true;
    public int Offset { get; init; }
    public int Limit { get; init; } = 50;
}

public sealed record RunRow(RunReceipt Receipt, string? TaskTitle)
{
    public int TotalTokens => Receipt.PromptTokens + Receipt.CompletionTokens;
}

/// <summary>Sums over the whole filter, not only the current page.</summary>
public sealed record RunTotals(
    int Runs, long PromptTokens, long CompletionTokens, long CachedTokens,
    decimal CostUsd, int RunsWithUnknownCost, int NotRun);

public sealed record RunPage(IReadOnlyList<RunRow> Items, int Total, RunTotals Totals);

/// <summary>One stacked bar segment: <see cref="Group"/> within the bucket starting at <see cref="BucketStart"/>.</summary>
public sealed record SeriesPoint(DateTime BucketStart, string Group, int Runs, long Tokens, decimal CostUsd);

/// <summary>Something worth a marker on the time axis.</summary>
public sealed record UsageEvent(DateTime At, string Kind, string AgentId, string Text);

/// <summary>Values that occur in the range - the options of the filter dropdowns.</summary>
public sealed record UsageFacets(
    IReadOnlyList<string> Agents, IReadOnlyList<string> Models,
    IReadOnlyList<string> Sources, IReadOnlyList<string> Statuses);

/// <summary>
/// Usage analysis over run receipts (#660). Receipts rather than RunUsage: only they carry
/// run id, source, task and the runs that never happened (budget denials, #608).
///
/// <para>Filtering, sorting and bucketing happen in memory over the receipts of the
/// requested range. That keeps every rule in one testable place; the volume of a single
/// instance (a few hundred runs a day) is far below where this would matter. The range is
/// capped at <see cref="MaxReceipts"/> receipts.</para>
/// </summary>
public sealed class UsageAnalytics(
    IAuditRepository audit,
    Func<string, CancellationToken, Task<string?>>? taskTitle = null)
{
    public const int MaxReceipts = 50_000;

    /// <summary>Statuses of runs that were refused before any model call.</summary>
    private static readonly HashSet<string> NotRunStatuses =
        new(StringComparer.OrdinalIgnoreCase) { "BudgetExceeded", "ShuttingDown", "TargetBusy" };

    public async Task<RunPage> QueryRunsAsync(RunQuery q, CancellationToken ct)
    {
        var rows = await LoadAsync(q.FromUtc, q.ToUtc, ct);
        var filtered = rows.Where(r => Matches(r, q)).ToList();

        var totals = new RunTotals(
            filtered.Count,
            filtered.Sum(r => (long)r.Receipt.PromptTokens),
            filtered.Sum(r => (long)r.Receipt.CompletionTokens),
            filtered.Sum(r => (long)r.Receipt.CachedTokens),
            filtered.Sum(r => r.Receipt.CostUsd),
            filtered.Count(r => !r.Receipt.CostIsKnown && !NotRunStatuses.Contains(r.Receipt.Status)),
            filtered.Count(r => NotRunStatuses.Contains(r.Receipt.Status)));

        var page = Sort(filtered, q.Sort, q.Descending)
            .Skip(Math.Max(0, q.Offset))
            .Take(Math.Clamp(q.Limit, 1, 500))
            .ToList();

        return new RunPage(page, filtered.Count, totals);
    }

    /// <param name="bucket"><c>hour</c> or <c>day</c>.</param>
    /// <param name="groupBy"><c>agent</c>, <c>model</c>, <c>source</c> or <c>budget</c> (#717: daily or a special budget).</param>
    /// <param name="utcOffset">Offset of the viewer's local time - a "day" is the viewer's day.</param>
    public async Task<IReadOnlyList<SeriesPoint>> SeriesAsync(
        RunQuery q, string bucket, string groupBy, TimeSpan utcOffset, CancellationToken ct)
    {
        var rows = (await LoadAsync(q.FromUtc, q.ToUtc, ct)).Where(r => Matches(r, q));

        return rows
            .GroupBy(r => (Start: BucketStart(r.Receipt.OccurredAt, bucket, utcOffset), Group: GroupKey(r.Receipt, groupBy)))
            .Select(g => new SeriesPoint(
                g.Key.Start, g.Key.Group, g.Count(),
                g.Sum(r => (long)r.TotalTokens), g.Sum(r => r.Receipt.CostUsd)))
            .OrderBy(p => p.BucketStart).ThenBy(p => p.Group, StringComparer.Ordinal)
            .ToList();
    }

    /// <summary>Budget denials and model changes - the usual explanation for a jump in a chart.</summary>
    public async Task<IReadOnlyList<UsageEvent>> EventsAsync(DateTime fromUtc, DateTime toUtc, CancellationToken ct)
    {
        var rows = await LoadAsync(fromUtc, toUtc, ct);
        var events = new List<UsageEvent>();

        // One marker per agent and hour is enough for a denial streak.
        foreach (var g in rows.Where(r => r.Receipt.Status == "BudgetExceeded")
                     .GroupBy(r => (r.Receipt.AgentId, Hour: Truncate(r.Receipt.OccurredAt, TimeSpan.FromHours(1)))))
        {
            events.Add(new UsageEvent(g.Min(r => r.Receipt.OccurredAt), "budget_exceeded", g.Key.AgentId,
                $"{g.Count()} run(s) refused: daily budget exhausted"));
        }

        foreach (var agent in rows.GroupBy(r => r.Receipt.AgentId))
        {
            string? previous = null;
            foreach (var r in agent.Where(r => !string.IsNullOrWhiteSpace(r.Receipt.Model)))
            {
                if (previous is not null && previous != r.Receipt.Model)
                    events.Add(new UsageEvent(r.Receipt.OccurredAt, "model_changed", agent.Key,
                        $"{previous} → {r.Receipt.Model}"));
                previous = r.Receipt.Model;
            }
        }

        return events.OrderBy(e => e.At).ToList();
    }

    public async Task<UsageFacets> FacetsAsync(DateTime fromUtc, DateTime toUtc, CancellationToken ct)
    {
        var rows = await LoadAsync(fromUtc, toUtc, ct);
        static IReadOnlyList<string> Distinct(IEnumerable<string> values)
            => values.Where(v => !string.IsNullOrWhiteSpace(v)).Distinct().Order(StringComparer.Ordinal).ToList();

        return new UsageFacets(
            Distinct(rows.Select(r => r.Receipt.AgentId)),
            Distinct(rows.Select(r => r.Receipt.Model)),
            Distinct(rows.Select(r => r.Receipt.Source)),
            Distinct(rows.Select(r => r.Receipt.Status)));
    }

    // ─── Building blocks ───

    private async Task<IReadOnlyList<RunRow>> LoadAsync(DateTime fromUtc, DateTime toUtc, CancellationToken ct)
    {
        var receipts = await audit.ListReceiptsAsync(fromUtc, toUtc, MaxReceipts, ct);
        if (taskTitle is null)
            return receipts.Select(r => new RunRow(r, null)).ToList();

        var titles = new Dictionary<string, string?>();
        foreach (var id in receipts.Select(r => r.TaskId).OfType<string>().Distinct())
            titles[id] = await taskTitle(id, ct);

        return receipts.Select(r => new RunRow(r, r.TaskId is { } id ? titles.GetValueOrDefault(id) : null)).ToList();
    }

    internal static bool Matches(RunRow row, RunQuery q)
    {
        var r = row.Receipt;
        if (q.Agents.Count > 0 && !q.Agents.Contains(r.AgentId)) return false;
        if (q.Models.Count > 0 && !q.Models.Contains(r.Model)) return false;
        if (q.Sources.Count > 0 && !q.Sources.Contains(r.Source)) return false;
        if (q.Statuses.Count > 0 && !q.Statuses.Contains(r.Status)) return false;
        if (q.MinCostUsd is { } min && r.CostUsd < min) return false;

        if (!string.IsNullOrWhiteSpace(q.Search))
        {
            var s = q.Search.Trim();
            bool Has(string? v) => v?.Contains(s, StringComparison.OrdinalIgnoreCase) == true;
            if (!(Has(r.RunId) || Has(r.AgentId) || Has(r.Model) || Has(r.TaskId) || Has(row.TaskTitle) || Has(r.ResultRef)))
                return false;
        }
        return true;
    }

    private static IEnumerable<RunRow> Sort(IEnumerable<RunRow> rows, string sort, bool descending)
    {
        Func<RunRow, IComparable> key = (sort ?? "time").ToLowerInvariant() switch
        {
            "agent" => r => r.Receipt.AgentId,
            "model" => r => r.Receipt.Model,
            "source" => r => r.Receipt.Source,
            "status" => r => r.Receipt.Status,
            "steps" => r => r.Receipt.StepCount,
            "prompt" => r => r.Receipt.PromptTokens,
            "completion" => r => r.Receipt.CompletionTokens,
            "tokens" => r => r.TotalTokens,
            "cost" => r => r.Receipt.CostUsd,
            "duration" => r => r.Receipt.DurationMs,
            _ => r => r.Receipt.OccurredAt
        };

        // Newest first as the tie-breaker, whatever the primary order.
        return descending
            ? rows.OrderByDescending(key).ThenByDescending(r => r.Receipt.OccurredAt)
            : rows.OrderBy(key).ThenByDescending(r => r.Receipt.OccurredAt);
    }

    internal static DateTime BucketStart(DateTime occurredUtc, string bucket, TimeSpan utcOffset)
    {
        var local = DateTime.SpecifyKind(occurredUtc, DateTimeKind.Utc) + utcOffset;
        var start = bucket == "day"
            ? local.Date
            : new DateTime(local.Year, local.Month, local.Day, local.Hour, 0, 0);
        return DateTime.SpecifyKind(start - utcOffset, DateTimeKind.Utc);
    }

    private static string GroupKey(RunReceipt r, string groupBy) => groupBy switch
    {
        "model" => string.IsNullOrWhiteSpace(r.Model) ? "(unknown)" : r.Model,
        "source" => r.Source,
        // #717: A special budget is visible apart — it is outside the daily limits.
        "budget" => string.IsNullOrWhiteSpace(r.BudgetPot) ? "daily" : "special:" + r.BudgetPot,
        _ => r.AgentId
    };

    private static DateTime Truncate(DateTime value, TimeSpan unit)
        => new(value.Ticks - value.Ticks % unit.Ticks, value.Kind);
}