using System.Text;
using System.Text.Json;
using System.Text.Json.Nodes;
using Json.Schema;
using Microsoft.Extensions.Logging;

namespace NeonSprawl.Server.Game.Encounters;

/// <summary>Loads and validates <c>content/encounters/*_encounters.json</c> using the same rules as <c>scripts/validate_content.py</c> (NEO-101).</summary>
public static class EncounterDefinitionCatalogLoader
{
    /// <summary>Loads catalogs from disk or throws <see cref="InvalidOperationException"/> with actionable messages.</summary>
    public static EncounterDefinitionCatalog Load(
        string encountersDirectory,
        string encounterDefSchemaPath,
        IReadOnlySet<string> knownRewardTableIds,
        ILogger logger)
    {
        encountersDirectory = Path.GetFullPath(encountersDirectory);
        encounterDefSchemaPath = Path.GetFullPath(encounterDefSchemaPath);

        var errors = new List<string>();

        if (!File.Exists(encounterDefSchemaPath))
            errors.Add($"error: missing schema file {encounterDefSchemaPath}");

        if (!Directory.Exists(encountersDirectory))
            errors.Add($"error: missing directory {encountersDirectory}");

        if (errors.Count > 0)
            ThrowIfAny(errors);

        string[] jsonFiles = [.. Directory.GetFiles(encountersDirectory, "*_encounters.json", SearchOption.TopDirectoryOnly)
                .OrderBy(p => p, StringComparer.Ordinal)];
        if (jsonFiles.Length == 0)
            errors.Add($"error: no *_encounters.json files under {encountersDirectory}");

        if (errors.Count > 0)
            ThrowIfAny(errors);

        var schema = JsonSchema.FromText(File.ReadAllText(encounterDefSchemaPath));
        var evalOptions = new EvaluationOptions { OutputFormat = OutputFormat.List };

        var encounterIdToSourceFile = new Dictionary<string, string>(StringComparer.Ordinal);
        var rows = new Dictionary<string, EncounterDefRow>(StringComparer.Ordinal);

        foreach (var path in jsonFiles)
        {
            JsonNode? root;
            try
            {
                root = JsonNode.Parse(File.ReadAllText(path));
            }
            catch (JsonException ex)
            {
                errors.Add($"error: {path}: invalid JSON: {ex.Message}");
                continue;
            }

            if (root is not JsonObject rootObj)
            {
                errors.Add($"error: {path}: expected JSON object at root");
                continue;
            }

            var schemaVersionNode = rootObj["schemaVersion"];
            if (schemaVersionNode is not JsonValue schemaVersionValue ||
                !schemaVersionValue.TryGetValue<int>(out var schemaVersion) ||
                schemaVersion != 1)
            {
                var got = schemaVersionNode?.ToJsonString() ?? "null";
                errors.Add($"error: {path}: expected schemaVersion 1, got {got}");
                continue;
            }

            var encountersNode = rootObj["encounters"];
            if (encountersNode is not JsonArray encountersArray)
            {
                errors.Add($"error: {path}: expected top-level 'encounters' array");
                continue;
            }

            for (var i = 0; i < encountersArray.Count; i++)
            {
                var encounter = encountersArray[i];
                if (encounter is not JsonObject rowObj)
                {
                    errors.Add($"error: {path}: encounters[{i}] must be an object");
                    continue;
                }

                var eval = schema.Evaluate(rowObj, evalOptions);
                var schemaMsgs = CollectSchemaMessages(eval, path, i).OrderBy(m => m, StringComparer.Ordinal).ToList();
                if (!eval.IsValid)
                {
                    if (schemaMsgs.Count == 0)
                        schemaMsgs.Add($"error: {path} encounters[{i}] (root): schema validation failed");

                    errors.AddRange(schemaMsgs);
                }

                var rowSchemaErrors = schemaMsgs.Count;

                var eid = (rowObj["id"] as JsonValue)?.GetValue<string>();
                if (eid is not null && rowSchemaErrors == 0)
                {
                    if (encounterIdToSourceFile.TryGetValue(eid, out var prevPath))
                    {
                        errors.Add($"error: duplicate encounter id '{eid}' in {prevPath} and {path}");
                        continue;
                    }

                    encounterIdToSourceFile[eid] = path;

                    var rewardTableId = (rowObj["rewardTableId"] as JsonValue)?.GetValue<string>();
                    if (rewardTableId is not null && !knownRewardTableIds.Contains(rewardTableId))
                    {
                        errors.Add(
                            $"error: {path} encounters[{i}]: rewardTableId '{rewardTableId}' is not in reward table catalogs");
                    }

                    rows[eid] = ParseRow(rowObj);
                }
            }
        }

        ThrowIfAny(errors);

        var e5m3 = PrototypeE5M3EncounterCatalogRules.TryGetE5M3GateError(encounterIdToSourceFile);
        if (e5m3 is not null)
        {
            errors.Add(e5m3);
            ThrowIfAny(errors);
        }

        var npcCrossRef = PrototypeE5M3EncounterCatalogRules.TryGetNpcInstanceCrossRefError(rows);
        if (npcCrossRef is not null)
        {
            errors.Add(npcCrossRef);
            ThrowIfAny(errors);
        }

        if (logger.IsEnabled(LogLevel.Information))
        {
            logger.LogInformation(
                "Loaded encounter catalog from {EncountersDirectory}: {EncounterCount} encounter(s) across {CatalogFileCount} JSON catalog file(s).",
                encountersDirectory,
                rows.Count,
                jsonFiles.Length);
        }

        return new EncounterDefinitionCatalog(encountersDirectory, rows, jsonFiles.Length);
    }

    private static EncounterDefRow ParseRow(JsonObject rowObj)
    {
        var id = (rowObj["id"] as JsonValue)!.GetValue<string>();
        var displayName = (rowObj["displayName"] as JsonValue)!.GetValue<string>();
        var completionCriteria = rowObj["completionCriteria"] as JsonObject
                                 ?? throw new InvalidOperationException("expected completionCriteria object");
        var completionCriteriaKind = (completionCriteria["kind"] as JsonValue)!.GetValue<string>();
        var requiredNpcInstanceIds = ParseStringArray(rowObj["requiredNpcInstanceIds"] as JsonArray);
        var rewardTableId = (rowObj["rewardTableId"] as JsonValue)!.GetValue<string>();

        return new EncounterDefRow(id, displayName, completionCriteriaKind, requiredNpcInstanceIds, rewardTableId);
    }

    private static IReadOnlyList<string> ParseStringArray(JsonArray? array)
    {
        if (array is null)
            return [];

        var values = new List<string>(array.Count);
        foreach (var node in array)
        {
            if (node is JsonValue value && value.TryGetValue<string>(out var s))
                values.Add(s);
        }

        return values;
    }

    private static List<string> CollectSchemaMessages(EvaluationResults eval, string filePath, int index)
    {
        var sink = new List<string>();
        AppendSchemaMessages(eval, filePath, index, sink);
        return sink;
    }

    private static void AppendSchemaMessages(EvaluationResults r, string filePath, int index, List<string> sink)
    {
        if (r.HasDetails)
        {
            foreach (var d in r.Details!)
                AppendSchemaMessages(d, filePath, index, sink);
        }

        if (!r.HasErrors)
            return;

        foreach (var kv in r.Errors!)
        {
            var loc = r.InstanceLocation?.ToString();
            if (string.IsNullOrEmpty(loc) || loc == "#")
                loc = "(root)";

            sink.Add($"error: {filePath} encounters[{index}] {loc}: {kv.Key} — {kv.Value}");
        }
    }

    private static void ThrowIfAny(List<string> errors)
    {
        if (errors.Count == 0)
            return;

        var sb = new StringBuilder();
        sb.AppendLine("Encounter catalog validation failed:");
        foreach (var e in errors.OrderBy(x => x, StringComparer.Ordinal))
            sb.AppendLine(e);

        throw new InvalidOperationException(sb.ToString().TrimEnd());
    }
}