using System;

using System.Collections.Generic;

using System.IO;

using System.Globalization;

using System.Linq;

using CsvHelper;

using CsvHelper.Configuration;

public class Program

{

    public static void Main()

    {

        // Makes a standard csv from a class, where property names are the column names.

        // It then reads that same format.

        /*

        MemoryStream csv = MakeInMemoryCsv();

        IEnumerable<RecordModel> records = ReadInMemoryCsv(csv);

        */

        // Makes a standard csv from a class, where property names are the column names.

        // It then reads that same format using the mapped field names

        // (names include standard class property names, so it works.)

        /*

        MemoryStream csv = MakeInMemoryCsv();

        IEnumerable<RecordModel> records = ReadInMemoryCsvWithFieldMap(csv);

        */

        // Makes a standard csv from an anonymous type, where non-property names are the column names.

        // It then reads that same format using the mapped field names,

        // but the mapper converts from the non-preferred column names into our preferred column names.

        MemoryStream csv = MakeInMemoryCsvWithUglyColumnNames();

        IEnumerable<RecordModel> records = ReadInMemoryCsvWithFieldMap(csv);

        foreach (var r in records)

        {

            Console.WriteLine(r);

        };

    }

    public static MemoryStream MakeInMemoryCsv() {

        var records = new List<RecordModel>

        {

            new RecordModel() { ID = "slkdfj", Name = "George" },

        };

​

        var memoryStream = new MemoryStream();

        TextWriter writer = new StreamWriter(memoryStream);

        var csv = new CsvWriter(writer, CultureInfo.InvariantCulture);

        csv.WriteRecords(records);

        csv.Flush();

        memoryStream.Seek(0, SeekOrigin.Begin);

        return memoryStream;

    }

    public static MemoryStream MakeInMemoryCsvWithUglyColumnNames() {

        var records = new[]

        {

            new { rand234 = "2345", reallyBad_ColuMnNaMe__plzFix = "George" },

            new { rand234 = "3", reallyBad_ColuMnNaMe__plzFix = "Fred" },

            new { rand234 = "23", reallyBad_ColuMnNaMe__plzFix = "Elaine" },

            new { rand234 = "5", reallyBad_ColuMnNaMe__plzFix = "Simon" },

            new { rand234 = "2", reallyBad_ColuMnNaMe__plzFix = "Ginger" },

            new { rand234 = "8", reallyBad_ColuMnNaMe__plzFix = "Roger" },

        };

​

        var memoryStream = new MemoryStream();

        TextWriter writer = new StreamWriter(memoryStream);

        var csv = new CsvWriter(writer, CultureInfo.InvariantCulture);

        csv.WriteRecords(records);

        csv.Flush();

        memoryStream.Seek(0, SeekOrigin.Begin);

        return memoryStream;

    }

    public static IEnumerable<RecordModel> ReadInMemoryCsv(MemoryStream memoryStream) {

        var reader = new StreamReader(memoryStream);

        var csv = new CsvReader(reader, CultureInfo.InvariantCulture);

        foreach (var r in csv.GetRecords<RecordModel>())

        {

            Console.WriteLine(r);

        };

        return csv.GetRecords<RecordModel>();       

    }

    public static IEnumerable<RecordModel> ReadInMemoryCsvWithFieldMap(MemoryStream memoryStream) {

        var reader = new StreamReader(memoryStream);

        var csv = new CsvReader(reader, CultureInfo.InvariantCulture);

        // the map tells CsvHelper how to map from a differently named column into our model class.

        // This also allows for dynamic-ish modeling when using a single constant or other lookup value,

        // owned by another team.

        csv.Context.RegisterClassMap<RecordModelFieldMap>();

        RecordModel record = new();

        IEnumerator<RecordModel> enumerator = csv.EnumerateRecords(record).GetEnumerator();

        bool hasRecord = enumerator.MoveNext();

        List<RecordModel> records = new();

        while (hasRecord) {

            // enumerator applies each record's data to the model we passed in.

            // We have to clone the values to maintain them across the enumerator.

            // LINQ queries that operate on the set will not work.

            records.Add(record.Clone());

            hasRecord = enumerator.MoveNext();

        }

        return records; 

    }

}

​

public class RecordModelFieldMap: ClassMap<RecordModel> {

    public RecordModelFieldMap() {

        // for property m.Name, these are the potential column names to map from

        // the first name is used when writing a csv

        Map(m => m.Name).Name("Name", "reallyBad_ColuMnNaMe__plzFix");

        Map(m => m.ID).Name("ID", "rand234");

    }

}

​

public class RecordModel {

    public string Name {get;set;}

    public string ID {get;set;}

    public override string ToString() {

        return $"Name: {Name}, ID: {ID}";   

    }

    public RecordModel Clone() {

        return new RecordModel {

            Name = this.Name,

            ID = this.ID

        };

    }

}