MES-ETL/ConsoleApp2/Services/CsvSource.cs

using System.Text;
using ConsoleApp2.Helpers;
using Microsoft.Extensions.Logging;

namespace ConsoleApp2.Services;

/// <summary>
/// CSV文件读取
/// </summary>
public class CsvSource
{
    private readonly string _filePath;
    private readonly StreamReader _reader;
    private readonly ILogger? _logger;
    private readonly string _tableName;

    public DataRecord Current { get; private set; }
    public string[]? Headers { get; }
    public string? CurrentRaw { get; private set; }
    public string Delimiter { get; private set; }
    public char QuoteChar { get; private set; }

    public CsvSource(string filePath, string[]? headers = null, string delimiter = ",", char quoteChar = '"',
        ILogger? logger = null)
    {
        _filePath = filePath;
        Headers = headers;
        _logger = logger;
        Delimiter = delimiter;
        QuoteChar = quoteChar;

        var fs = File.OpenRead(filePath);
        _reader = new StreamReader(fs);
        _tableName = DumpDataHelper.GetTableName(filePath);
    }

    public async ValueTask<bool> ReadAsync()
    {
        var str = await _reader.ReadLineAsync();
        if (string.IsNullOrWhiteSpace(str))
            return false;

        CurrentRaw = str;

        var fields = ParseRow2(str, QuoteChar, Delimiter);
        Current = new DataRecord(fields, _tableName, Headers);
        return true;
    }

    public string[] ParseRow(string row, char quoteChar, string delimiter)
    {
        var span = row.AsSpan();
        var result = new List<string>();

        if (span.Length == 0)
            throw new ArgumentException("The row is empty", nameof(row));

        var isInQuote = span[0] == quoteChar;
        var start = 0;
        for (var i = 1; i < span.Length; i++)
        {
            if (span[i] == quoteChar)
            {
                isInQuote = !isInQuote;
            }
            // delimiter需要足够复杂
            else if (/*!isInQuote && */span.Length > i + delimiter.Length && span[i..(i + delimiter.Length)].Equals(delimiter, StringComparison.CurrentCulture)) // field matched
            {
                string field;
                if (span[start] == quoteChar && span[i - 1] == quoteChar) // enclosed by quoteChar
                    field = span[(start + 1)..(i - 1)].ToString(); // escape quoteChar
                else
                    field = span[start..i].ToString();

                start = i + delimiter.Length;

                if (field == "\\N")
                    field = "NULL";

                result.Add(field);
                
                continue;
            }
        }

        result.Add(span[start..].ToString());


        for (var i = 0; i < result.Count; i++)
        {
            var field = result[i];
            if (DumpDataHelper.CheckHexField(field) && StringExtensions.CheckJsonHex(field))
            {
                result[i] = StringExtensions.FromHex(field);
            }
        }

        return result.ToArray();
    }
    
    public string[] ParseRow2(ReadOnlySpan<char> source, char quoteChar, string delimiter)
    {
        var result = new List<string>();
        var index = -1;
        StringBuilder current = new StringBuilder();
        bool hasQuote = false;
        bool hasSlash = false;
        while (index < source.Length-1)
        {
            index++;
            if (hasSlash == false && source[index] == '\\')
            {
                hasSlash = true;
                current.Append('\\');
                continue;
            }
            if (hasSlash ==false && source[index] == quoteChar)
            {
                hasQuote = !hasQuote;
                current.Append(source[index]);
                continue;
            }
            if (hasQuote==false && source[index] == delimiter[0])
            {
                result.Add(current.ToString());
                current.Clear();
            }
            else
            {
                current.Append(source[index]);
            }

            hasSlash = false;
        }

        result.Add(current.ToString());
        return result.ToArray();
    }
}