using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Text.Json;
using System.Text.Json.Nodes;
using Json.Schema;
using YamlDotNet.Serialization;
using YamlDotNet.Serialization.NamingConventions;

namespace StellaOps.Policy;

public sealed record PolicyScoringBindingResult(
    bool Success,
    PolicyScoringConfig? Config,
    ImmutableArray<PolicyIssue> Issues);

public static class PolicyScoringConfigBinder
{
    private const string DefaultResourceName = "StellaOps.Policy.Schemas.policy-scoring-default.json";

    private static readonly JsonSchema ScoringSchema = PolicyScoringSchema.Schema;

    private static readonly ImmutableDictionary<string, double> DefaultReachabilityBuckets = CreateDefaultReachabilityBuckets();

    private static readonly PolicyUnknownConfidenceConfig DefaultUnknownConfidence = CreateDefaultUnknownConfidence();

    private static readonly IDeserializer YamlDeserializer = new DeserializerBuilder()
        .WithNamingConvention(CamelCaseNamingConvention.Instance)
        .IgnoreUnmatchedProperties()
        .Build();

    public static PolicyScoringConfig LoadDefault()
    {
        var assembly = Assembly.GetExecutingAssembly();
        using var stream = assembly.GetManifestResourceStream(DefaultResourceName)
            ?? throw new InvalidOperationException($"Embedded resource '{DefaultResourceName}' not found.");
        using var reader = new StreamReader(stream, Encoding.UTF8, detectEncodingFromByteOrderMarks: true);
        var json = reader.ReadToEnd();
        var binding = Bind(json, PolicyDocumentFormat.Json);
        if (!binding.Success || binding.Config is null)
        {
            throw new InvalidOperationException("Failed to load default policy scoring configuration.");
        }

        return binding.Config;
    }

    public static PolicyScoringBindingResult Bind(string content, PolicyDocumentFormat format)
    {
        if (string.IsNullOrWhiteSpace(content))
        {
            var issue = PolicyIssue.Error("scoring.empty", "Scoring configuration content is empty.", "$");
            return new PolicyScoringBindingResult(false, null, ImmutableArray.Create(issue));
        }

        try
        {
            var root = Parse(content, format);
            if (root is not JsonObject obj)
            {
                var issue = PolicyIssue.Error("scoring.invalid", "Scoring configuration must be a JSON object.", "$");
                return new PolicyScoringBindingResult(false, null, ImmutableArray.Create(issue));
            }

            var issues = ImmutableArray.CreateBuilder<PolicyIssue>();
            var schemaIssues = ValidateAgainstSchema(root);
            issues.AddRange(schemaIssues);
            if (schemaIssues.Any(static issue => issue.Severity == PolicyIssueSeverity.Error))
            {
                return new PolicyScoringBindingResult(false, null, issues.ToImmutable());
            }

            var config = BuildConfig(obj, issues);
            var hasErrors = issues.Any(issue => issue.Severity == PolicyIssueSeverity.Error);
            return new PolicyScoringBindingResult(!hasErrors, config, issues.ToImmutable());
        }
        catch (JsonException ex)
        {
            var issue = PolicyIssue.Error("scoring.parse.json", $"Failed to parse scoring JSON: {ex.Message}", "$");
            return new PolicyScoringBindingResult(false, null, ImmutableArray.Create(issue));
        }
        catch (YamlDotNet.Core.YamlException ex)
        {
            var issue = PolicyIssue.Error("scoring.parse.yaml", $"Failed to parse scoring YAML: {ex.Message}", "$");
            return new PolicyScoringBindingResult(false, null, ImmutableArray.Create(issue));
        }
    }

    private static JsonNode? Parse(string content, PolicyDocumentFormat format)
    {
        return format switch
        {
            PolicyDocumentFormat.Json => JsonNode.Parse(content, new JsonNodeOptions { PropertyNameCaseInsensitive = true }),
            PolicyDocumentFormat.Yaml => ConvertYamlToJsonNode(content),
            _ => throw new ArgumentOutOfRangeException(nameof(format), format, "Unsupported scoring configuration format."),
        };
    }

    private static JsonNode? ConvertYamlToJsonNode(string content)
    {
        var yamlObject = YamlDeserializer.Deserialize<object?>(content);
        return PolicyBinderUtilities.ConvertYamlObject(yamlObject);
    }

    private static ImmutableArray<PolicyIssue> ValidateAgainstSchema(JsonNode root)
    {
        try
        {
            using var document = JsonDocument.Parse(root.ToJsonString(new JsonSerializerOptions
            {
                WriteIndented = false,
            }));

            var result = ScoringSchema.Evaluate(document.RootElement, new EvaluationOptions
            {
                OutputFormat = OutputFormat.List,
                RequireFormatValidation = true,
            });

            if (result.IsValid)
            {
                return ImmutableArray<PolicyIssue>.Empty;
            }

            var issues = ImmutableArray.CreateBuilder<PolicyIssue>();
            var seen = new HashSet<string>(StringComparer.Ordinal);
            CollectSchemaIssues(result, issues, seen);
            return issues.ToImmutable();
        }
        catch (JsonException ex)
        {
            return ImmutableArray.Create(PolicyIssue.Error("scoring.schema.normalize", $"Failed to normalize scoring configuration for schema validation: {ex.Message}", "$"));
        }
    }

    private static void CollectSchemaIssues(EvaluationResults result, ImmutableArray<PolicyIssue>.Builder issues, HashSet<string> seen)
    {
        if (result.Errors is { Count: > 0 })
        {
            foreach (var pair in result.Errors)
            {
                var keyword = SanitizeKeyword(pair.Key);
                var path = ConvertPointerToPath(result.InstanceLocation?.ToString() ?? "#");
                var message = pair.Value ?? "Schema violation.";
                var key = $"{path}|{keyword}|{message}";
                if (seen.Add(key))
                {
                    issues.Add(PolicyIssue.Error($"scoring.schema.{keyword}", message, path));
                }
            }
        }

        if (result.Details is null)
        {
            return;
        }

        foreach (var detail in result.Details)
        {
            CollectSchemaIssues(detail, issues, seen);
        }
    }

    private static string ConvertPointerToPath(string pointer)
    {
        if (string.IsNullOrEmpty(pointer) || pointer == "#")
        {
            return "$";
        }

        if (pointer[0] == '#')
        {
            pointer = pointer.Length > 1 ? pointer[1..] : string.Empty;
        }

        if (string.IsNullOrEmpty(pointer))
        {
            return "$";
        }

        var segments = pointer.Split('/', StringSplitOptions.RemoveEmptyEntries);
        var builder = new StringBuilder("$");
        foreach (var segment in segments)
        {
            var unescaped = segment.Replace("~1", "/").Replace("~0", "~");
            if (int.TryParse(unescaped, out var index))
            {
                builder.Append('[').Append(index).Append(']');
            }
            else
            {
                builder.Append('.').Append(unescaped);
            }
        }

        return builder.ToString();
    }

    private static string SanitizeKeyword(string keyword)
    {
        if (string.IsNullOrWhiteSpace(keyword))
        {
            return "unknown";
        }

        var builder = new StringBuilder(keyword.Length);
        foreach (var ch in keyword)
        {
            if (char.IsLetterOrDigit(ch))
            {
                builder.Append(char.ToLowerInvariant(ch));
            }
            else if (ch is '.' or '_' or '-')
            {
                builder.Append(ch);
            }
            else
            {
                builder.Append('_');
            }
        }

        return builder.Length == 0 ? "unknown" : builder.ToString();
    }

    private static PolicyScoringConfig BuildConfig(JsonObject obj, ImmutableArray<PolicyIssue>.Builder issues)
    {
        var version = ReadString(obj, "version", issues, required: true) ?? PolicyScoringConfig.BaselineVersion;

        var severityWeights = ReadSeverityWeights(obj, issues);
        var quietPenalty = ReadDouble(obj, "quietPenalty", issues, defaultValue: 45);
        var warnPenalty = ReadDouble(obj, "warnPenalty", issues, defaultValue: 15);
        var ignorePenalty = ReadDouble(obj, "ignorePenalty", issues, defaultValue: 35);
        var trustOverrides = ReadTrustOverrides(obj, issues);
        var reachabilityBuckets = ReadReachabilityBuckets(obj, issues);
        var unknownConfidence = ReadUnknownConfidence(obj, issues);

        return new PolicyScoringConfig(
            version,
            severityWeights,
            quietPenalty,
            warnPenalty,
            ignorePenalty,
            trustOverrides,
            reachabilityBuckets,
            unknownConfidence);
    }

    private static ImmutableDictionary<string, double> CreateDefaultReachabilityBuckets()
    {
        var builder = ImmutableDictionary.CreateBuilder<string, double>(StringComparer.OrdinalIgnoreCase);
        builder["entrypoint"] = 1.0;
        builder["direct"] = 0.85;
        builder["indirect"] = 0.6;
        builder["runtime"] = 0.45;
        builder["unreachable"] = 0.25;
        builder["unknown"] = 0.5;
        return builder.ToImmutable();
    }

    private static PolicyUnknownConfidenceConfig CreateDefaultUnknownConfidence()
    {
        var bands = ImmutableArray.Create(
            new PolicyUnknownConfidenceBand("high", 0.65, "Fresh unknowns with recent telemetry."),
            new PolicyUnknownConfidenceBand("medium", 0.35, "Unknowns aging toward action required."),
            new PolicyUnknownConfidenceBand("low", 0.0, "Stale unknowns that must be triaged."));
        return new PolicyUnknownConfidenceConfig(0.8, 0.05, 0.2, bands);
    }

    private static ImmutableDictionary<string, double> ReadReachabilityBuckets(JsonObject obj, ImmutableArray<PolicyIssue>.Builder issues)
    {
        if (!obj.TryGetPropertyValue("reachabilityBuckets", out var node))
        {
            issues.Add(PolicyIssue.Warning("scoring.reachability.default", "reachabilityBuckets not specified; defaulting to baseline weights.", "$.reachabilityBuckets"));
            return DefaultReachabilityBuckets;
        }

        if (node is not JsonObject bucketsObj)
        {
            issues.Add(PolicyIssue.Error("scoring.reachability.type", "reachabilityBuckets must be an object.", "$.reachabilityBuckets"));
            return DefaultReachabilityBuckets;
        }

        var builder = ImmutableDictionary.CreateBuilder<string, double>(StringComparer.OrdinalIgnoreCase);
        foreach (var pair in bucketsObj)
        {
            if (pair.Value is null)
            {
                issues.Add(PolicyIssue.Warning("scoring.reachability.null", $"Bucket '{pair.Key}' is null; defaulting to 0.", $"$.reachabilityBuckets.{pair.Key}"));
                builder[pair.Key] = 0;
                continue;
            }

            var value = ExtractDouble(pair.Value, issues, $"$.reachabilityBuckets.{pair.Key}");
            builder[pair.Key] = value;
        }

        if (builder.Count == 0)
        {
            issues.Add(PolicyIssue.Warning("scoring.reachability.empty", "No reachability buckets defined; using defaults.", "$.reachabilityBuckets"));
            return DefaultReachabilityBuckets;
        }

        return builder.ToImmutable();
    }

    private static PolicyUnknownConfidenceConfig ReadUnknownConfidence(JsonObject obj, ImmutableArray<PolicyIssue>.Builder issues)
    {
        if (!obj.TryGetPropertyValue("unknownConfidence", out var node))
        {
            issues.Add(PolicyIssue.Warning("scoring.unknown.default", "unknownConfidence not specified; defaulting to baseline decay settings.", "$.unknownConfidence"));
            return DefaultUnknownConfidence;
        }

        if (node is not JsonObject configObj)
        {
            issues.Add(PolicyIssue.Error("scoring.unknown.type", "unknownConfidence must be an object.", "$.unknownConfidence"));
            return DefaultUnknownConfidence;
        }

        var initial = DefaultUnknownConfidence.Initial;
        if (configObj.TryGetPropertyValue("initial", out var initialNode))
        {
            initial = ExtractDouble(initialNode, issues, "$.unknownConfidence.initial");
        }
        else
        {
            issues.Add(PolicyIssue.Warning("scoring.unknown.initial.default", "initial not specified; using baseline value.", "$.unknownConfidence.initial"));
        }

        var decay = DefaultUnknownConfidence.DecayPerDay;
        if (configObj.TryGetPropertyValue("decayPerDay", out var decayNode))
        {
            decay = ExtractDouble(decayNode, issues, "$.unknownConfidence.decayPerDay");
        }
        else
        {
            issues.Add(PolicyIssue.Warning("scoring.unknown.decay.default", "decayPerDay not specified; using baseline value.", "$.unknownConfidence.decayPerDay"));
        }

        var floor = DefaultUnknownConfidence.Floor;
        if (configObj.TryGetPropertyValue("floor", out var floorNode))
        {
            floor = ExtractDouble(floorNode, issues, "$.unknownConfidence.floor");
        }
        else
        {
            issues.Add(PolicyIssue.Warning("scoring.unknown.floor.default", "floor not specified; using baseline value.", "$.unknownConfidence.floor"));
        }

        var bands = ReadConfidenceBands(configObj, issues);
        if (bands.IsDefaultOrEmpty)
        {
            bands = DefaultUnknownConfidence.Bands;
        }

        if (initial < 0 || initial > 1)
        {
            issues.Add(PolicyIssue.Warning("scoring.unknown.initial.range", "initial confidence should be between 0 and 1. Clamping to valid range.", "$.unknownConfidence.initial"));
            initial = Math.Clamp(initial, 0, 1);
        }

        if (decay < 0 || decay > 1)
        {
            issues.Add(PolicyIssue.Warning("scoring.unknown.decay.range", "decayPerDay should be between 0 and 1. Clamping to valid range.", "$.unknownConfidence.decayPerDay"));
            decay = Math.Clamp(decay, 0, 1);
        }

        if (floor < 0 || floor > 1)
        {
            issues.Add(PolicyIssue.Warning("scoring.unknown.floor.range", "floor should be between 0 and 1. Clamping to valid range.", "$.unknownConfidence.floor"));
            floor = Math.Clamp(floor, 0, 1);
        }

        return new PolicyUnknownConfidenceConfig(initial, decay, floor, bands);
    }

    private static ImmutableArray<PolicyUnknownConfidenceBand> ReadConfidenceBands(JsonObject configObj, ImmutableArray<PolicyIssue>.Builder issues)
    {
        if (!configObj.TryGetPropertyValue("bands", out var node))
        {
            return ImmutableArray<PolicyUnknownConfidenceBand>.Empty;
        }

        if (node is not JsonArray array)
        {
            issues.Add(PolicyIssue.Error("scoring.unknown.bands.type", "unknownConfidence.bands must be an array.", "$.unknownConfidence.bands"));
            return ImmutableArray<PolicyUnknownConfidenceBand>.Empty;
        }

        var builder = ImmutableArray.CreateBuilder<PolicyUnknownConfidenceBand>();
        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        for (var index = 0; index < array.Count; index++)
        {
            var element = array[index];
            if (element is not JsonObject bandObj)
            {
                issues.Add(PolicyIssue.Warning("scoring.unknown.band.type", "Band entry must be an object.", $"$.unknownConfidence.bands[{index}]"));
                continue;
            }

            string? name = null;
            if (bandObj.TryGetPropertyValue("name", out var nameNode) && nameNode is JsonValue nameValue && nameValue.TryGetValue(out string? text))
            {
                name = text?.Trim();
            }

            if (string.IsNullOrWhiteSpace(name))
            {
                issues.Add(PolicyIssue.Error("scoring.unknown.band.name", "Band entry requires a non-empty 'name'.", $"$.unknownConfidence.bands[{index}].name"));
                continue;
            }

            if (!seen.Add(name))
            {
                issues.Add(PolicyIssue.Warning("scoring.unknown.band.duplicate", $"Duplicate band '{name}' encountered.", $"$.unknownConfidence.bands[{index}].name"));
                continue;
            }

            if (!bandObj.TryGetPropertyValue("min", out var minNode))
            {
                issues.Add(PolicyIssue.Error("scoring.unknown.band.min", $"Band '{name}' is missing 'min'.", $"$.unknownConfidence.bands[{index}].min"));
                continue;
            }

            var min = ExtractDouble(minNode, issues, $"$.unknownConfidence.bands[{index}].min");
            if (min < 0 || min > 1)
            {
                issues.Add(PolicyIssue.Warning("scoring.unknown.band.range", $"Band '{name}' min should be between 0 and 1. Clamping to valid range.", $"$.unknownConfidence.bands[{index}].min"));
                min = Math.Clamp(min, 0, 1);
            }

            string? description = null;
            if (bandObj.TryGetPropertyValue("description", out var descriptionNode) && descriptionNode is JsonValue descriptionValue && descriptionValue.TryGetValue(out string? descriptionText))
            {
                description = descriptionText?.Trim();
            }

            builder.Add(new PolicyUnknownConfidenceBand(name, min, description));
        }

        if (builder.Count == 0)
        {
            return ImmutableArray<PolicyUnknownConfidenceBand>.Empty;
        }

        return builder.ToImmutable()
            .OrderByDescending(static band => band.Min)
            .ToImmutableArray();
    }

    private static ImmutableDictionary<PolicySeverity, double> ReadSeverityWeights(JsonObject obj, ImmutableArray<PolicyIssue>.Builder issues)
    {
        if (!obj.TryGetPropertyValue("severityWeights", out var node) || node is not JsonObject severityObj)
        {
            issues.Add(PolicyIssue.Error("scoring.severityWeights.missing", "severityWeights section is required.", "$.severityWeights"));
            return ImmutableDictionary<PolicySeverity, double>.Empty;
        }

        var builder = ImmutableDictionary.CreateBuilder<PolicySeverity, double>();
        foreach (var severity in Enum.GetValues<PolicySeverity>())
        {
            var key = severity.ToString();
            if (!severityObj.TryGetPropertyValue(key, out var valueNode))
            {
                issues.Add(PolicyIssue.Warning("scoring.severityWeights.default", $"Severity '{key}' not specified; defaulting to 0.", $"$.severityWeights.{key}"));
                builder[severity] = 0;
                continue;
            }

            var value = ExtractDouble(valueNode, issues, $"$.severityWeights.{key}");
            builder[severity] = value;
        }

        return builder.ToImmutable();
    }

    private static double ReadDouble(JsonObject obj, string property, ImmutableArray<PolicyIssue>.Builder issues, double defaultValue)
    {
        if (!obj.TryGetPropertyValue(property, out var node))
        {
            issues.Add(PolicyIssue.Warning("scoring.numeric.default", $"{property} not specified; defaulting to {defaultValue:0.##}.", $"$.{property}"));
            return defaultValue;
        }

        return ExtractDouble(node, issues, $"$.{property}");
    }

    private static double ExtractDouble(JsonNode? node, ImmutableArray<PolicyIssue>.Builder issues, string path)
    {
        if (node is null)
        {
            issues.Add(PolicyIssue.Warning("scoring.numeric.null", $"Value at {path} missing; defaulting to 0.", path));
            return 0;
        }

        if (node is JsonValue value)
        {
            if (value.TryGetValue(out double number))
            {
                return number;
            }

            if (value.TryGetValue(out string? text) && double.TryParse(text, NumberStyles.Float, CultureInfo.InvariantCulture, out number))
            {
                return number;
            }
        }

        issues.Add(PolicyIssue.Error("scoring.numeric.invalid", $"Value at {path} is not numeric.", path));
        return 0;
    }

    private static ImmutableDictionary<string, double> ReadTrustOverrides(JsonObject obj, ImmutableArray<PolicyIssue>.Builder issues)
    {
        if (!obj.TryGetPropertyValue("trustOverrides", out var node) || node is not JsonObject trustObj)
        {
            return ImmutableDictionary<string, double>.Empty;
        }

        var builder = ImmutableDictionary.CreateBuilder<string, double>(StringComparer.OrdinalIgnoreCase);
        foreach (var pair in trustObj)
        {
            var value = ExtractDouble(pair.Value, issues, $"$.trustOverrides.{pair.Key}");
            builder[pair.Key] = value;
        }

        return builder.ToImmutable();
    }

    private static string? ReadString(JsonObject obj, string property, ImmutableArray<PolicyIssue>.Builder issues, bool required)
    {
        if (!obj.TryGetPropertyValue(property, out var node) || node is null)
        {
            if (required)
            {
                issues.Add(PolicyIssue.Error("scoring.string.missing", $"{property} is required.", $"$.{property}"));
            }
            return null;
        }

        if (node is JsonValue value && value.TryGetValue(out string? text))
        {
            return text?.Trim();
        }

        issues.Add(PolicyIssue.Error("scoring.string.invalid", $"{property} must be a string.", $"$.{property}"));
        return null;
    }
}

internal static class PolicyBinderUtilities
{
    public static JsonNode? ConvertYamlObject(object? value)
    {
        switch (value)
        {
            case null:
                return null;
            case string s when bool.TryParse(s, out var boolValue):
                return JsonValue.Create(boolValue);
            case string s:
                return JsonValue.Create(s);
            case bool b:
                return JsonValue.Create(b);
            case sbyte or byte or short or ushort or int or uint or long or ulong or float or double or decimal:
                return JsonValue.Create(Convert.ToDouble(value, CultureInfo.InvariantCulture));
            case IDictionary dictionary:
            {
                var obj = new JsonObject();
                foreach (DictionaryEntry entry in dictionary)
                {
                    if (entry.Key is null)
                    {
                        continue;
                    }

                    obj[entry.Key.ToString()!] = ConvertYamlObject(entry.Value);
                }

                return obj;
            }
            case IEnumerable enumerable:
            {
                var array = new JsonArray();
                foreach (var item in enumerable)
                {
                    array.Add(ConvertYamlObject(item));
                }

                return array;
            }
            default:
                return JsonValue.Create(value.ToString());
        }
    }
}