// JsSerializer.cs
// SPDX-License-Identifier: GPL-3.0-or-later
// SPDX-FileCopyrightText: 2025 Catswords OSS and WelsonJS Contributors
// https://github.com/gnh1201/welsonjs
// 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Text;

namespace WelsonJS.Launcher
{
    public sealed class JsSerializer : IDisposable
    {
        private readonly JsCore _core;
        private readonly bool _ownsCore;

        public JsSerializer() : this(new JsCore(), true) { }

        public JsSerializer(JsCore core, bool ownsCore)
        {
            if (core == null) throw new ArgumentNullException("core");
            _core = core;
            _ownsCore = ownsCore;
        }

        public bool IsValid(string json)
        {
            if (json == null) throw new ArgumentNullException("json");
            string script =
                "(function(){try{JSON.parse(" + Q(json) + ");return '1';}catch(_){return '0';}})()";
            string r = _core.EvaluateToString(script);
            return r == "1";
        }

        public string Minify(string json)
        {
            if (json == null) throw new ArgumentNullException("json");
            string script = "JSON.stringify(JSON.parse(" + Q(json) + "))";
            return _core.EvaluateToString(script);
        }

        public string Pretty(string json, int space)
        {
            if (json == null) throw new ArgumentNullException("json");
            space = Clamp(space, 0, 10);
            string script = "JSON.stringify(JSON.parse(" + Q(json) + "),null," + space.ToString(CultureInfo.InvariantCulture) + ")";
            return _core.EvaluateToString(script);
        }

        public string Normalize(string json)
        {
            return Minify(json);
        }

        /// <summary>
        /// Extracts a value by a simple path of property names (numeric segment as string = array index).
        /// Returns the selected value as a JSON string.
        /// </summary>
        public string Extract(string json, params string[] path)
        {
            if (path == null) path = new string[0];
            object[] mixed = new object[path.Length];
            for (int i = 0; i < path.Length; i++) mixed[i] = path[i];
            return Extract(json, mixed);
        }

        /// <summary>
        /// Extracts by a mixed path. Segments can be strings (object keys) or integers (array indices).
        /// Returns the selected value as a JSON string (e.g., a JS string returns with quotes).
        /// Usage: Extract(json, "items", 0, "name")
        /// </summary>
        public string Extract(string json, params object[] path)
        {
            if (json == null) throw new ArgumentNullException("json");
            if (path == null) path = new object[0];

            string jsPath = BuildJsPath(path);

            var sb = new StringBuilder();
            sb.Append("(function(){var v=JSON.parse(").Append(Q(json)).Append(");");
            sb.Append("var p=").Append(jsPath).Append(";");
            sb.Append("for(var i=0;i<p.length;i++){var k=p[i];");
            sb.Append("if(Array.isArray(v) && typeof k==='number'){ v=v[k]; }");
            sb.Append("else { v=(v==null?null:v[k]); }}");
            sb.Append("return JSON.stringify(v);})()");
            return _core.EvaluateToString(sb.ToString());
        }

        public string Serialize(object value, int space)
        {
            space = Clamp(space, 0, 10);
            string expr = BuildJsExpression(value, new HashSet<object>(ReferenceEqualityComparer.Instance), 0);
            string script = "JSON.stringify((" + expr + "),null," + space.ToString(CultureInfo.InvariantCulture) + ")";
            return _core.EvaluateToString(script);
        }

        private static int Clamp(int v, int min, int max)
        {
            if (v < min) return min;
            if (v > max) return max;
            return v;
        }

        /// <summary>
        /// Encode a .NET string as a JS double-quoted string literal.
        /// </summary>
        private static string Q(string s)
        {
            if (s == null) return "null";
            var sb = new StringBuilder(s.Length + 16);
            sb.Append('"');
            for (int i = 0; i < s.Length; i++)
            {
                char ch = s[i];
                switch (ch)
                {
                    case '\\': sb.Append(@"\\"); break;
                    case '"': sb.Append("\\\""); break;
                    case '\b': sb.Append(@"\b"); break;
                    case '\f': sb.Append(@"\f"); break;
                    case '\n': sb.Append(@"\n"); break;
                    case '\r': sb.Append(@"\r"); break;
                    case '\t': sb.Append(@"\t"); break;
                    default:
                        if (char.IsControl(ch))
                        {
                            sb.Append("\\u");
                            sb.Append(((int)ch).ToString("X4"));
                        }
                        else
                        {
                            sb.Append(ch);
                        }
                        break;
                }
            }
            sb.Append('"');
            return sb.ToString();
        }

        /// <summary>
        /// Builds a JS array literal representing the path.
        /// Numeric segments are emitted as numbers; others as strings.
        /// </summary>
        private static string BuildJsPath(object[] segments)
        {
            if (segments == null || segments.Length == 0) return "[]";

            var sb = new StringBuilder();
            sb.Append('[');
            for (int i = 0; i < segments.Length; i++)
            {
                if (i > 0) sb.Append(',');

                object seg = segments[i];

                // Treat integral types as numbers for array indexing
                if (seg is sbyte || seg is byte ||
                    seg is short || seg is ushort ||
                    seg is int || seg is uint ||
                    seg is long || seg is ulong)
                {
                    sb.Append(Convert.ToString(seg, CultureInfo.InvariantCulture));
                }
                else
                {
                    string str = (seg == null) ? string.Empty : Convert.ToString(seg, CultureInfo.InvariantCulture);
                    sb.Append(Q(str));
                }
            }
            sb.Append(']');
            return sb.ToString();
        }

        private static bool IsNumeric(object v)
        {
            if (v == null) return false;
            Type t = v.GetType();
            t = Nullable.GetUnderlyingType(t) ?? t;
            return t == typeof(byte) || t == typeof(sbyte) ||
                   t == typeof(short) || t == typeof(ushort) ||
                   t == typeof(int) || t == typeof(uint) ||
                   t == typeof(long) || t == typeof(ulong) ||
                   t == typeof(float) || t == typeof(double) ||
                   t == typeof(decimal);
        }

        private static bool IsImmutableLike(object v)
        {
            return v is string || v is bool ||
                   v is byte || v is sbyte ||
                   v is short || v is ushort ||
                   v is int || v is uint ||
                   v is long || v is ulong ||
                   v is float || v is double || v is decimal ||
                   v is Guid || v is DateTime || v is DateTimeOffset;
        }

        /// <summary>
        /// Builds a safe JS expression for a .NET value (no engine calls here).
        /// Engine will stringify the produced expression via JSON.stringify.
        /// </summary>
        private static string BuildJsExpression(object value, HashSet<object> seen, int depth)
        {
            if (depth > 64) return "null"; // depth guard

            if (value == null) return "null";

            // Primitives
            if (value is string) return Q((string)value);
            if (value is bool) return ((bool)value) ? "true" : "false";
            if (IsNumeric(value))
                return Convert.ToString(value, CultureInfo.InvariantCulture);

            // Common value-like types → stringify as JS strings
            if (value is Guid)
                return Q(((Guid)value).ToString());
            if (value is DateTime)
                return Q(((DateTime)value).ToUniversalTime().ToString("o", CultureInfo.InvariantCulture));
            if (value is DateTimeOffset)
                return Q(((DateTimeOffset)value).ToUniversalTime().ToString("o", CultureInfo.InvariantCulture));
            if (value is byte[])
                return Q(Convert.ToBase64String((byte[])value));

            // Prevent circular refs for reference types
            if (!IsImmutableLike(value) && !seen.Add(value))
                return "null";

            // IDictionary (string keys only)
            if (value is IDictionary)
            {
                var map = (IDictionary)value;
                var sb = new StringBuilder();
                sb.Append('{');
                bool first = true;
                foreach (DictionaryEntry kv in map)
                {
                    string key = kv.Key as string;
                    if (key == null) continue; // JSON keys must be strings
                    if (!first) sb.Append(',');
                    first = false;
                    sb.Append(Q(key)).Append(':')
                      .Append(BuildJsExpression(kv.Value, seen, depth + 1));
                }
                sb.Append('}');
                return sb.ToString();
            }

            // IEnumerable → array
            if (value is IEnumerable)
            {
                var seq = (IEnumerable)value;
                var sb = new StringBuilder();
                sb.Append('[');
                bool first = true;
                foreach (object item in seq)
                {
                    if (!first) sb.Append(',');
                    first = false;
                    sb.Append(BuildJsExpression(item, seen, depth + 1));
                }
                sb.Append(']');
                return sb.ToString();
            }

            // Fallback → ToString() as JS string
            string s = value.ToString();
            return Q(s ?? string.Empty);
        }

        public void Dispose()
        {
            if (_ownsCore)
                _core.Dispose();
        }

        /// <summary>
        /// Reference equality comparer for cycle detection (works on .NET Framework).
        /// </summary>
        private sealed class ReferenceEqualityComparer : IEqualityComparer<object>
        {
            private ReferenceEqualityComparer() { }
            public static readonly ReferenceEqualityComparer Instance = new ReferenceEqualityComparer();
            bool IEqualityComparer<object>.Equals(object x, object y) { return object.ReferenceEquals(x, y); }
            int IEqualityComparer<object>.GetHashCode(object obj)
            {
                return System.Runtime.CompilerServices.RuntimeHelpers.GetHashCode(obj);
            }
        }
    }
}