using System;

using System.Text.RegularExpressions;

using System.Linq; // To extract properties (Value, Length) of matches.

using System.Collections.Generic; // For the Dictionary.

public class Program

{

    public static void Main()

    {

        string strContent =

            @"[Name]

Jhon

​

[Age]

45

​

[MobileNumber]

1020304050

​

Billing address                     Delivery address 

Somewhere else in the               Here

 world                              India

Not India

​

(nothing)";

        // The INI-style fields are easily parsed with Regex.

        string[] fields = { "Name", "Age", "MobileNumber" };

        foreach(var field in fields)

        {

            var match = Regex.Match(strContent, "\\["+field+"\\]\n(.*)");

            if(!match.Success) continue;

            Console.WriteLine(field+": "+match.Groups[1].Value);

        }

        // The tabular fields.

        // They start with a header line containing all the field names (separated by at least 2 spaces),

        // then 1 or more data lines where each field value is aligned with the corresponding field name in the header line.

        // Lookup for a known field, either at the start of a line, or after a field separator of at least 2 spaces.

        var headerMatch = Regex.Match(strContent, "(?:^|.*  )Billing address(?:  .*|$)", RegexOptions.Multiline);

        // Split the line to get the individual fields.

        var fieldsMatches = Regex.Matches(headerMatch.Value+"  ", "([^ ](?:[^ ]+| [^ ]+)*)  +", RegexOptions.Multiline);

        var fieldNames = fieldsMatches.Select(m => m.Value.Trim()).ToArray();

        var fieldPos = fieldsMatches.Select(m => m.Index).ToArray();

        var fieldLengths = fieldsMatches.Select(m => m.Length).ToArray();

        // Get the lines following the header line, until an empty line or the end of the block.

        var dataLines = Regex.Match(strContent.Substring(headerMatch.Index + headerMatch.Length), "(?:\n.+)*");

        // For each line, loop to isolate individual fields.

        var fieldVals = new Dictionary<string, string>();

        foreach(var fieldName in fieldNames)

            fieldVals.Add(fieldName, "");

        foreach(Match line in Regex.Matches(dataLines.Value, ".+"))

        {

            var fieldNum = 0;

            var ls = line.Value;

            foreach(var fieldName in fieldNames)

            {

                var pos = fieldPos[fieldNum];

                var length = fieldLengths[fieldNum];

                string fragment = ls.Length <= pos ? "" : ls.Substring(pos, pos + length > ls.Length ? ls.Length - pos : length);

                fragment = fragment.TrimEnd();

                // For multiline field values, separate each segment from the previous with a newline,

                // except if it starts with a space in which case it is just the wrapped tail of the previous (à la LDIF).

                var concatenator = fieldVals[fieldName].Length > 0 && fragment.Length > 0 && fragment.Substring(0, 1) != " " ? "\n" : "";

                fieldVals[fieldName] += concatenator+fragment;

                ++fieldNum;

            }

        }

        foreach(var field in fieldVals)

            Console.WriteLine(field.Key+": "+field.Value.Replace("\n", " <newline> "));

    }

}