using System.Text.Json;
using SPMS.Application.DTOs.Message;
using SPMS.Application.Interfaces;
using SPMS.Domain.Common;

namespace SPMS.Application.Services;

public class MessageValidationService : IMessageValidationService
{
    private const int MaxTitleLength = 100;
    private const int MaxBodyLength = 2000;
    private const int MaxDataSizeBytes = 4096;
    private static readonly string[] AllowedLinkTypes = ["deeplink", "web", "none"];

    public MessageValidationResultDto Validate(MessageValidateRequestDto request)
    {
        var errors = new List<FieldError>();

        ValidateTitle(request.Title, errors);
        ValidateBody(request.Body, errors);
        ValidateImageUrl(request.ImageUrl, errors);
        ValidateLinkUrl(request.LinkUrl, errors);
        ValidateLinkType(request.LinkType, errors);
        ValidateData(request.Data, errors);

        return new MessageValidationResultDto
        {
            IsValid = errors.Count == 0,
            Errors = errors
        };
    }

    private static void ValidateTitle(string title, List<FieldError> errors)
    {
        if (string.IsNullOrWhiteSpace(title))
        {
            errors.Add(new FieldError { Field = "title", Message = "제목은 필수입니다." });
            return;
        }

        if (title.Length > MaxTitleLength)
            errors.Add(new FieldError { Field = "title", Message = $"제목은 {MaxTitleLength}자를 초과할 수 없습니다." });
    }

    private static void ValidateBody(string body, List<FieldError> errors)
    {
        if (string.IsNullOrWhiteSpace(body))
        {
            errors.Add(new FieldError { Field = "body", Message = "본문은 필수입니다." });
            return;
        }

        if (body.Length > MaxBodyLength)
            errors.Add(new FieldError { Field = "body", Message = $"본문은 {MaxBodyLength}자를 초과할 수 없습니다." });
    }

    private static void ValidateImageUrl(string? imageUrl, List<FieldError> errors)
    {
        if (string.IsNullOrWhiteSpace(imageUrl))
            return;

        if (!Uri.TryCreate(imageUrl, UriKind.Absolute, out var uri) ||
            (uri.Scheme != "http" && uri.Scheme != "https"))
            errors.Add(new FieldError { Field = "image_url", Message = "유효한 URL 형식이 아닙니다." });
    }

    private static void ValidateLinkUrl(string? linkUrl, List<FieldError> errors)
    {
        if (string.IsNullOrWhiteSpace(linkUrl))
            return;

        if (!Uri.TryCreate(linkUrl, UriKind.Absolute, out _))
            errors.Add(new FieldError { Field = "link_url", Message = "유효한 URL 형식이 아닙니다." });
    }

    private static void ValidateLinkType(string? linkType, List<FieldError> errors)
    {
        if (string.IsNullOrWhiteSpace(linkType))
            return;

        if (!AllowedLinkTypes.Contains(linkType.ToLowerInvariant()))
            errors.Add(new FieldError { Field = "link_type", Message = "link_type은 deeplink, web, none 중 하나여야 합니다." });
    }

    private static void ValidateData(object? data, List<FieldError> errors)
    {
        if (data is null)
            return;

        // object? → JSON 문자열로 변환
        string jsonString;
        if (data is JsonElement jsonElement)
        {
            if (jsonElement.ValueKind == JsonValueKind.Null || jsonElement.ValueKind == JsonValueKind.Undefined)
                return;

            if (jsonElement.ValueKind != JsonValueKind.Object)
            {
                errors.Add(new FieldError { Field = "data", Message = "data는 JSON 객체여야 합니다." });
                return;
            }

            jsonString = jsonElement.GetRawText();
        }
        else if (data is string strData)
        {
            if (string.IsNullOrWhiteSpace(strData))
                return;

            try
            {
                using var doc = JsonDocument.Parse(strData);
                if (doc.RootElement.ValueKind != JsonValueKind.Object)
                {
                    errors.Add(new FieldError { Field = "data", Message = "data는 JSON 객체여야 합니다." });
                    return;
                }
            }
            catch (JsonException)
            {
                errors.Add(new FieldError { Field = "data", Message = "유효한 JSON 형식이 아닙니다." });
                return;
            }

            jsonString = strData;
        }
        else
        {
            // 기타 타입은 직렬화하여 검증
            jsonString = JsonSerializer.Serialize(data);
        }

        if (System.Text.Encoding.UTF8.GetByteCount(jsonString) > MaxDataSizeBytes)
            errors.Add(new FieldError { Field = "data", Message = $"data는 {MaxDataSizeBytes / 1024}KB를 초과할 수 없습니다." });
    }
}