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/reward-tables/*_reward_tables.json</c> using the same rules as <c>scripts/validate_content.py</c> (NEO-101).</summary>
public static class RewardTableDefinitionCatalogLoader
{
    /// <summary>Loads catalogs from disk or throws <see cref="InvalidOperationException"/> with actionable messages.</summary>
    public static RewardTableDefinitionCatalog Load(
        string rewardTablesDirectory,
        string rewardTableSchemaPath,
        string rewardGrantRowSchemaPath,
        IReadOnlySet<string> knownItemIds,
        ILogger logger)
    {
        rewardTablesDirectory = Path.GetFullPath(rewardTablesDirectory);
        rewardTableSchemaPath = Path.GetFullPath(rewardTableSchemaPath);
        rewardGrantRowSchemaPath = Path.GetFullPath(rewardGrantRowSchemaPath);

        var errors = new List<string>();

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

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

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

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

        var jsonFiles = Directory.GetFiles(rewardTablesDirectory, "*_reward_tables.json", SearchOption.TopDirectoryOnly)
            .OrderBy(p => p, StringComparer.Ordinal)
            .ToArray();
        if (jsonFiles.Length == 0)
            errors.Add($"error: no *_reward_tables.json files under {rewardTablesDirectory}");

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

        var grantRowSchema = JsonSchema.FromText(File.ReadAllText(rewardGrantRowSchemaPath));
        SchemaRegistry.Global.Register(grantRowSchema);
        var tableSchema = JsonSchema.FromText(File.ReadAllText(rewardTableSchemaPath));
        SchemaRegistry.Global.Register(tableSchema);

        var evalOptions = new EvaluationOptions { OutputFormat = OutputFormat.List };

        var rewardTableIdToSourceFile = new Dictionary<string, string>(StringComparer.Ordinal);
        var rows = new Dictionary<string, RewardTableDefRow>(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 rewardTablesNode = rootObj["rewardTables"];
            if (rewardTablesNode is not JsonArray rewardTablesArray)
            {
                errors.Add($"error: {path}: expected top-level 'rewardTables' array");
                continue;
            }

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

                var eval = tableSchema.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} rewardTables[{i}] (root): schema validation failed");

                    errors.AddRange(schemaMsgs);
                }

                var rowSchemaErrors = schemaMsgs.Count;

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

                    rewardTableIdToSourceFile[rid] = path;
                    CrossCheckFixedGrants(rowObj, path, i, knownItemIds, errors);
                    rows[rid] = ParseRow(rowObj);
                }
            }
        }

        ThrowIfAny(errors);

        var e5m3 = PrototypeE5M3RewardTableCatalogRules.TryGetE5M3GateError(rewardTableIdToSourceFile);
        if (e5m3 is not null)
        {
            errors.Add(e5m3);
            ThrowIfAny(errors);
        }

        var grantContent = PrototypeE5M3RewardTableCatalogRules.TryGetGrantContentGateError(rows);
        if (grantContent is not null)
        {
            errors.Add(grantContent);
            ThrowIfAny(errors);
        }

        if (logger.IsEnabled(LogLevel.Information))
        {
            logger.LogInformation(
                "Loaded reward table catalog from {RewardTablesDirectory}: {RewardTableCount} reward table(s) across {CatalogFileCount} JSON catalog file(s).",
                rewardTablesDirectory,
                rows.Count,
                jsonFiles.Length);
        }

        return new RewardTableDefinitionCatalog(rewardTablesDirectory, rows, jsonFiles.Length);
    }

    private static void CrossCheckFixedGrants(
        JsonObject rowObj,
        string path,
        int tableIndex,
        IReadOnlySet<string> knownItemIds,
        List<string> errors)
    {
        if (rowObj["fixedGrants"] is not JsonArray grantsArray)
            return;

        var seenGrantItemIds = new HashSet<string>(StringComparer.Ordinal);
        for (var j = 0; j < grantsArray.Count; j++)
        {
            if (grantsArray[j] is not JsonObject grantObj)
                continue;

            var itemId = (grantObj["itemId"] as JsonValue)?.GetValue<string>();
            if (itemId is null)
                continue;

            if (!seenGrantItemIds.Add(itemId))
            {
                errors.Add(
                    $"error: {path} rewardTables[{tableIndex}].fixedGrants[{j}]: duplicate itemId '{itemId}'");
            }

            if (!knownItemIds.Contains(itemId))
            {
                errors.Add(
                    $"error: {path} rewardTables[{tableIndex}].fixedGrants[{j}]: itemId '{itemId}' is not in item catalogs");
            }
        }
    }

    private static RewardTableDefRow ParseRow(JsonObject rowObj)
    {
        var id = (rowObj["id"] as JsonValue)!.GetValue<string>();
        var displayName = (rowObj["displayName"] as JsonValue)!.GetValue<string>();
        var fixedGrants = ParseGrantRows(rowObj["fixedGrants"] as JsonArray);

        return new RewardTableDefRow(id, displayName, fixedGrants);
    }

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

        var rows = new List<RewardGrantRow>(array.Count);
        foreach (var node in array)
        {
            if (node is not JsonObject grantObj)
                continue;

            var itemId = (grantObj["itemId"] as JsonValue)!.GetValue<string>();
            var quantity = (grantObj["quantity"] as JsonValue)!.GetValue<int>();
            rows.Add(new RewardGrantRow(itemId, quantity));
        }

        return rows;
    }

    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} rewardTables[{index}] {loc}: {kv.Key} — {kv.Value}");
        }
    }

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

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

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