using System.Text;
using MesETL.App.HostedServices.Abstractions;
using Microsoft.Extensions.Logging;

namespace MesETL.App.Services.ETL;

/// <summary>
/// CSV文件读取
/// </summary>
public class CsvReader : IDataReader
{
    protected readonly string? FilePath;
    protected readonly Lazy<StreamReader> Reader;
    protected readonly ILogger? Logger;
    protected readonly string TableName;

    public DataRecord Current { get; protected set; } = null!;
    public string[] Headers { get; }
    public string Delimiter { get; }
    public char QuoteChar { get; }
    
    public CsvReader(Stream stream, string tableName, string[] headers, string delimiter = ",", char quoteChar = '"', ILogger? logger = null)
    : this(tableName, headers, delimiter, quoteChar, logger)
    {
        Reader = new Lazy<StreamReader>(() => new StreamReader(stream));
    }

    public CsvReader(string filePath, string tableName, string[] headers, string delimiter = ",", char quoteChar = '"', ILogger? logger = null)
    : this(tableName, headers, delimiter, quoteChar, logger)
    {
        var fs = File.OpenRead(filePath);
        FilePath = filePath;
        Reader = new Lazy<StreamReader>(() => new StreamReader(fs));
    }

    private CsvReader(string tableName, string[] headers, string delimiter = ",", char quoteChar = '"', ILogger? logger = null)
    {
        TableName = tableName;
        Headers = headers;
        Logger = logger;
        Delimiter = delimiter;
        QuoteChar = quoteChar;
        Reader = null!;
    }

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

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

    public string[] ParseRow(ReadOnlySpan<char> source, char quoteChar, string delimiter)
    {
        var result = new List<string>();
        var index = -1;
        var current = new StringBuilder();
        var hasQuote = false;
        var 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();
    }

    public virtual void Dispose()
    {
        if(Reader.IsValueCreated)
            Reader.Value.Dispose();
    }
}