using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using LocalizationTool.Models;

namespace LocalizationTool.Services
{
    /// <summary>
    /// CSV 导入导出（逗号分隔，Excel 可直接打开编辑）。
    /// 列结构与主界面表格一致：第一列"中文原文"，其后为各语言代码列（en-US、ja-JP…）。
    /// 导出 UTF-8 带 BOM（Excel 中文不乱码）；导入兼容 UTF-8 与 ANSI（GB18030）。
    /// </summary>
    public static class CsvExchange
    {
        /// <summary>导出表格行到 CSV 文件。langs 决定语言列（与表格当前勾选列一致）。</summary>
        public static void Export(string path, IEnumerable<RowVm> rows, List<PackFile> langs)
        {
            var sb = new StringBuilder();
            sb.AppendLine(JoinCsv(new[] { "中文原文" }.Concat(langs.Select(l => l.LanguageCode))));

            foreach (var r in rows)
            {
                var fields = new List<string> { r.Key };
                foreach (var l in langs)
                    fields.Add(r.Cells.TryGetValue(l.LanguageCode, out var c) ? c.Value : "");
                sb.AppendLine(JoinCsv(fields));
            }

            File.WriteAllText(path, sb.ToString(), new UTF8Encoding(true));   // BOM：Excel 识别 UTF-8
        }

        /// <summary>解析 CSV 文件：返回 (表头, 数据行)。空行跳过；引号/逗号/换行转义按 RFC4180 处理。</summary>
        public static Tuple<List<string>, List<string[]>> Parse(string path)
        {
            var bytes = File.ReadAllBytes(path);
            if (bytes.Length >= 3 && bytes[0] == 0xEF && bytes[1] == 0xBB && bytes[2] == 0xBF)
                bytes = bytes.Skip(3).ToArray();

            string text;
            try { text = new UTF8Encoding(false, true).GetString(bytes); }
            catch { text = Encoding.GetEncoding("gb18030").GetString(bytes); }   // Excel 另存的 ANSI CSV

            var header = new List<string>();
            var records = new List<string[]>();

            using (var reader = new StringReader(text))
            using (var parser = new Microsoft.VisualBasic.FileIO.TextFieldParser(reader))
            {
                parser.TextFieldType = Microsoft.VisualBasic.FileIO.FieldType.Delimited;
                parser.SetDelimiters(",");
                parser.HasFieldsEnclosedInQuotes = true;

                while (!parser.EndOfData)
                {
                    string[] fields;
                    try { fields = parser.ReadFields(); }
                    catch (Microsoft.VisualBasic.FileIO.MalformedLineException)
                    {
                        throw new Exception($"第 {parser.ErrorLineNumber} 行格式错误（常见原因：引号未闭合）");
                    }
                    if (fields == null) continue;
                    if (fields.All(string.IsNullOrWhiteSpace)) continue;
                    if (header.Count == 0) { header.AddRange(fields); continue; }
                    records.Add(fields);
                }
            }

            return Tuple.Create(header, records);
        }

        private static string JoinCsv(IEnumerable<string> fields) =>
            string.Join(",", fields.Select(Escape));

        private static string Escape(string field)
        {
            field = field ?? "";
            if (field.IndexOfAny(new[] { ',', '"', '\r', '\n' }) >= 0)
                return "\"" + field.Replace("\"", "\"\"") + "\"";
            return field;
        }
    }
}