using System.Text.Json;
using System.Text.Json.Nodes;
using StellaOps.Findings.Ledger.Domain;
using StellaOps.Findings.Ledger.Hashing;
using StellaOps.Findings.Ledger.Infrastructure.Policy;

namespace StellaOps.Findings.Ledger.Services;

public static class LedgerProjectionReducer
{
    public static ProjectionReduceResult Reduce(
        LedgerEventRecord record,
        FindingProjection? current,
        PolicyEvaluationResult evaluation)
    {
        ArgumentNullException.ThrowIfNull(record);
        ArgumentNullException.ThrowIfNull(evaluation);

        var eventObject = record.EventBody["event"]?.AsObject()
            ?? throw new InvalidOperationException("Ledger event payload is missing 'event' object.");
        var payload = eventObject["payload"] as JsonObject;

        var status = evaluation.Status ?? DetermineStatus(record.EventType, payload, current?.Status);
        var severity = evaluation.Severity ?? DetermineSeverity(payload, current?.Severity);
        var riskScore = evaluation.RiskScore ?? current?.RiskScore;
        var riskSeverity = evaluation.RiskSeverity ?? current?.RiskSeverity;
        var riskProfileVersion = evaluation.RiskProfileVersion ?? current?.RiskProfileVersion;
        var riskExplanationId = evaluation.RiskExplanationId ?? current?.RiskExplanationId;
        var riskEventSequence = evaluation.RiskEventSequence ?? current?.RiskEventSequence ?? record.SequenceNumber;

        var labels = CloneLabels(evaluation.Labels);
        MergeLabels(labels, payload);

        var explainRef = evaluation.ExplainRef ?? DetermineExplainRef(payload, current?.ExplainRef);
        var rationale = CloneArray(evaluation.Rationale);
        if (rationale.Count == 0 && !string.IsNullOrWhiteSpace(explainRef))
        {
            rationale.Add(explainRef);
        }

        var updatedAt = record.RecordedAt;

        var provisional = new FindingProjection(
            record.TenantId,
            record.FindingId,
            record.PolicyVersion,
            status,
            severity,
            riskScore,
            riskSeverity,
            riskProfileVersion,
            riskExplanationId,
            riskEventSequence,
            labels,
            record.EventId,
            explainRef,
            rationale,
            updatedAt,
            string.Empty);

        var cycleHash = ProjectionHashing.ComputeCycleHash(provisional);
        var projection = provisional with { CycleHash = cycleHash };

        var historyEntry = new FindingHistoryEntry(
            record.TenantId,
            record.FindingId,
            record.PolicyVersion,
            record.EventId,
            projection.Status,
            projection.Severity,
            record.ActorId,
            DetermineComment(payload),
            record.OccurredAt);

        var actionEntry = CreateActionEntry(record, payload);
        return new ProjectionReduceResult(projection, historyEntry, actionEntry);
    }

    private static string DetermineStatus(string eventType, JsonObject? payload, string? currentStatus)
    {
        var candidate = ExtractString(payload, "status") ?? currentStatus;

        return eventType switch
        {
            LedgerEventConstants.EventFindingCreated => candidate ?? "affected",
            LedgerEventConstants.EventFindingStatusChanged => candidate ?? currentStatus ?? "affected",
            LedgerEventConstants.EventFindingClosed => candidate ?? "closed",
            LedgerEventConstants.EventFindingAcceptedRisk => candidate ?? "accepted_risk",
            _ => candidate ?? currentStatus ?? "affected"
        };
    }

    private static decimal? DetermineSeverity(JsonObject? payload, decimal? current)
    {
        if (payload is null)
        {
            return current;
        }

        if (payload.TryGetPropertyValue("severity", out var severityNode))
        {
            if (TryConvertDecimal(severityNode, out var severity))
            {
                return severity;
            }

            if (severityNode is JsonValue value && value.TryGetValue(out string? severityString)
                && decimal.TryParse(severityString, out var severityFromString))
            {
                return severityFromString;
            }
        }

        return current;
    }

    private static void MergeLabels(JsonObject target, JsonObject? payload)
    {
        if (payload is null)
        {
            return;
        }

        if (payload.TryGetPropertyValue("labels", out var labelsNode) && labelsNode is JsonObject labelUpdates)
        {
            foreach (var property in labelUpdates)
            {
                if (property.Value is null || property.Value.GetValueKind() == JsonValueKind.Null)
                {
                    target.Remove(property.Key);
                }
                else
                {
                    target[property.Key] = property.Value.DeepClone();
                }
            }
        }

        if (payload.TryGetPropertyValue("labelsRemove", out var removeNode) && removeNode is JsonArray removeArray)
        {
            foreach (var item in removeArray)
            {
                if (item is JsonValue value && value.TryGetValue(out string? key) && !string.IsNullOrWhiteSpace(key))
                {
                    target.Remove(key);
                }
            }
        }
    }

    private static string? DetermineExplainRef(JsonObject? payload, string? current)
    {
        var explainRef = ExtractString(payload, "explainRef") ?? ExtractString(payload, "explain_ref");
        return explainRef ?? current;
    }

    private static string? DetermineComment(JsonObject? payload)
    {
        return ExtractString(payload, "comment")
            ?? ExtractString(payload, "justification")
            ?? ExtractString(payload, "note");
    }

    private static TriageActionEntry? CreateActionEntry(LedgerEventRecord record, JsonObject? payload)
    {
        var actionType = record.EventType switch
        {
            LedgerEventConstants.EventFindingStatusChanged => "status_change",
            LedgerEventConstants.EventFindingCommentAdded => "comment",
            LedgerEventConstants.EventFindingAssignmentChanged => "assign",
            LedgerEventConstants.EventFindingRemediationPlanAdded => "remediation_plan",
            LedgerEventConstants.EventFindingAcceptedRisk => "accept_risk",
            LedgerEventConstants.EventFindingAttachmentAdded => "attach_evidence",
            LedgerEventConstants.EventFindingClosed => "close",
            _ => null
        };

        if (actionType is null)
        {
            return null;
        }

        var payloadClone = payload?.DeepClone()?.AsObject() ?? new JsonObject();
        return new TriageActionEntry(
            record.TenantId,
            record.EventId,
            record.EventId,
            record.FindingId,
            actionType,
            payloadClone,
            record.RecordedAt,
            record.ActorId);
    }

    private static JsonObject CloneLabels(JsonObject? source)
    {
        return source is null ? new JsonObject() : (JsonObject)source.DeepClone();
    }

    private static JsonArray CloneArray(JsonArray source)
    {
        ArgumentNullException.ThrowIfNull(source);

        var clone = new JsonArray();
        foreach (var item in source)
        {
            clone.Add(item?.DeepClone());
        }

        return clone;
    }

    private static string? ExtractString(JsonObject? obj, string propertyName)
    {
        if (obj is null)
        {
            return null;
        }

        if (!obj.TryGetPropertyValue(propertyName, out var node) || node is null)
        {
            return null;
        }

        if (node is JsonValue value && value.TryGetValue(out string? result))
        {
            return string.IsNullOrWhiteSpace(result) ? null : result;
        }

        return node.ToString();
    }

    private static bool TryConvertDecimal(JsonNode? node, out decimal value)
    {
        switch (node)
        {
            case null:
                value = default;
                return false;
            case JsonValue jsonValue when jsonValue.TryGetValue(out decimal decimalValue):
                value = decimalValue;
                return true;
            case JsonValue jsonValue when jsonValue.TryGetValue(out double doubleValue):
                value = Convert.ToDecimal(doubleValue);
                return true;
            default:
                if (decimal.TryParse(node.ToString(), out var parsed))
                {
                    value = parsed;
                    return true;
                }

                value = default;
                return false;
        }
    }
}