using System.Text.Json;
using System.Text.Json.Serialization;
using SheetMe.Core.Models;

namespace SheetMe.Core.Serialization;

/// <summary>
/// JSON 직렬화기 — 부 포맷(파일 내보내기/백업, 추후 주 포맷 승격 대비).
/// 모델 트리를 있는 그대로 담아 레거시 XML 과 동일한 정보량을 유지한다.
/// </summary>
public sealed class FormJsonSerializer : IDesignSerializer
{
    #region Member Fields
    private static readonly JsonSerializerOptions options = CreateOptions();
    #endregion

    #region Methods
    /// <summary>JSON 을 서식 문서로 역직렬화</summary>
    public FormDocument Read(string content)
        => JsonSerializer.Deserialize<FormDocument>(content, options)
            ?? throw new InvalidDataException("JSON 서식 문서를 해석할 수 없습니다.");

    /// <summary>서식 문서를 JSON 으로 직렬화</summary>
    public string Write(FormDocument document)
        => JsonSerializer.Serialize(document, options);

    private static JsonSerializerOptions CreateOptions()
    {
        var opts = new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            WriteIndented = true,
            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
            Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping,
        };
        opts.Converters.Add(new PropBagJsonConverter());
        opts.Converters.Add(new LegacyPropValueJsonConverter());
        return opts;
    }
    #endregion
}

/// <summary>PropBag JSON 컨버터 — 순서 보존을 위해 [{ "n": 이름, "v": 값 }] 배열로 직렬화</summary>
public sealed class PropBagJsonConverter : JsonConverter<PropBag>
{
    public override PropBag Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        var bag = new PropBag();
        if (reader.TokenType != JsonTokenType.StartArray)
        {
            throw new JsonException("PropBag 은 배열이어야 합니다.");
        }
        while (reader.Read() && reader.TokenType != JsonTokenType.EndArray)
        {
            if (reader.TokenType != JsonTokenType.StartObject)
            {
                throw new JsonException("PropBag 항목은 객체여야 합니다.");
            }
            string? name = null;
            LegacyPropValue? value = null;
            while (reader.Read() && reader.TokenType != JsonTokenType.EndObject)
            {
                var propName = reader.GetString();
                reader.Read();
                switch (propName)
                {
                    case "n":
                        name = reader.GetString();
                        break;
                    case "v":
                        value = JsonSerializer.Deserialize<LegacyPropValue>(ref reader, options);
                        break;
                    default:
                        reader.Skip();
                        break;
                }
            }
            if (name is not null)
            {
                bag.Set(name, value ?? new LegacyPropValue.NullValue());
            }
        }
        return bag;
    }

    public override void Write(Utf8JsonWriter writer, PropBag value, JsonSerializerOptions options)
    {
        writer.WriteStartArray();
        foreach (var (name, propValue) in value)
        {
            writer.WriteStartObject();
            writer.WriteString("n", name);
            writer.WritePropertyName("v");
            JsonSerializer.Serialize(writer, propValue, options);
            writer.WriteEndObject();
        }
        writer.WriteEndArray();
    }
}

/// <summary>LegacyPropValue 다형 JSON 컨버터 — "k" 판별자 기반</summary>
public sealed class LegacyPropValueJsonConverter : JsonConverter<LegacyPropValue>
{
    public override LegacyPropValue Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType == JsonTokenType.Null)
        {
            return new LegacyPropValue.NullValue();
        }
        if (reader.TokenType == JsonTokenType.String)
        {
            // 축약형: 문자열이면 TextValue
            return new LegacyPropValue.TextValue(reader.GetString() ?? string.Empty);
        }
        if (reader.TokenType != JsonTokenType.StartObject)
        {
            throw new JsonException("LegacyPropValue 는 문자열 또는 객체여야 합니다.");
        }

        string? kind = null;
        string? text = null;
        string? base64 = null;
        string? refName = null;
        PropBag? nested = null;
        List<LegacyItem>? items = null;

        while (reader.Read() && reader.TokenType != JsonTokenType.EndObject)
        {
            var propName = reader.GetString();
            reader.Read();
            switch (propName)
            {
                case "k": kind = reader.GetString(); break;
                case "text": text = reader.GetString(); break;
                case "b64": base64 = reader.GetString(); break;
                case "ref": refName = reader.GetString(); break;
                case "props": nested = JsonSerializer.Deserialize<PropBag>(ref reader, options); break;
                case "items":
                    items = new List<LegacyItem>();
                    if (reader.TokenType != JsonTokenType.StartArray)
                    {
                        throw new JsonException("items 는 배열이어야 합니다.");
                    }
                    while (reader.Read() && reader.TokenType != JsonTokenType.EndArray)
                    {
                        string? aqn = null;
                        LegacyPropValue? itemValue = null;
                        while (reader.Read() && reader.TokenType != JsonTokenType.EndObject)
                        {
                            var itemProp = reader.GetString();
                            reader.Read();
                            switch (itemProp)
                            {
                                case "aqn": aqn = reader.GetString(); break;
                                case "v": itemValue = JsonSerializer.Deserialize<LegacyPropValue>(ref reader, options); break;
                                default: reader.Skip(); break;
                            }
                        }
                        items.Add(new LegacyItem { Aqn = aqn ?? string.Empty, Value = itemValue ?? new LegacyPropValue.NullValue() });
                    }
                    break;
                default: reader.Skip(); break;
            }
        }

        return kind switch
        {
            "text" => new LegacyPropValue.TextValue(text ?? string.Empty),
            "null" => new LegacyPropValue.NullValue(),
            "nested" => new LegacyPropValue.NestedValue { Children = nested ?? new PropBag() },
            "items" => new LegacyPropValue.ItemsValue { Items = items ?? new List<LegacyItem>() },
            "binary" => new LegacyPropValue.BinaryValue { Base64 = base64 ?? string.Empty },
            "ref" => new LegacyPropValue.ReferenceValue { Name = refName ?? string.Empty },
            _ => throw new JsonException($"알 수 없는 LegacyPropValue 종류: {kind}"),
        };
    }

    public override void Write(Utf8JsonWriter writer, LegacyPropValue value, JsonSerializerOptions options)
    {
        switch (value)
        {
            case LegacyPropValue.TextValue text:
                // 가장 흔한 형태는 축약(문자열)으로 — JSON 가독성
                writer.WriteStringValue(text.Value);
                break;

            case LegacyPropValue.NullValue:
                writer.WriteStartObject();
                writer.WriteString("k", "null");
                writer.WriteEndObject();
                break;

            case LegacyPropValue.NestedValue nested:
                writer.WriteStartObject();
                writer.WriteString("k", "nested");
                writer.WritePropertyName("props");
                JsonSerializer.Serialize(writer, nested.Children, options);
                writer.WriteEndObject();
                break;

            case LegacyPropValue.ItemsValue items:
                writer.WriteStartObject();
                writer.WriteString("k", "items");
                writer.WritePropertyName("items");
                writer.WriteStartArray();
                foreach (var item in items.Items)
                {
                    writer.WriteStartObject();
                    writer.WriteString("aqn", item.Aqn);
                    writer.WritePropertyName("v");
                    JsonSerializer.Serialize(writer, item.Value, options);
                    writer.WriteEndObject();
                }
                writer.WriteEndArray();
                writer.WriteEndObject();
                break;

            case LegacyPropValue.BinaryValue binary:
                writer.WriteStartObject();
                writer.WriteString("k", "binary");
                writer.WriteString("b64", binary.Base64);
                writer.WriteEndObject();
                break;

            case LegacyPropValue.ReferenceValue reference:
                writer.WriteStartObject();
                writer.WriteString("k", "ref");
                writer.WriteString("ref", reference.Name);
                writer.WriteEndObject();
                break;
        }
    }
}