using System;

using System.Collections.Generic;

​

using KGySoft.CoreLibraries;

using KGySoft.Diagnostics;

​

class Example

{

    // The demo content to parse. Contains empty line, whitespaces, one key per line, one or more values per line

    private const string text = @"

        ALLUSERSPROFILE=C:\ProgramData

        ComSpec=C:\WINDOWS\system32\cmd.exe

        Path=C:\Windows\system32;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Windows\System32\OpenSSH\;C:\Program Files\dotnet\;%USERPROFILE%\AppData\Local\Microsoft\WindowsApps

        PATHEXT=.COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC

        CommonProgramFiles=C:\Program Files\Common Files

        CommonProgramFiles(x86)=C:\Program Files (x86)\Common Files

        CommonProgramW6432=C:\Program Files\Common Files

        DriverData=C:\Windows\System32\Drivers\DriverData

        ProgramData=C:\ProgramData

        ProgramFiles=C:\Program Files

        ProgramFiles(x86)=C:\Program Files (x86)

        ProgramW6432=C:\Program Files

        PSModulePath=C:\Program Files\WindowsPowerShell\Modules;C:\WINDOWS\system32\WindowsPowerShell\v1.0\Modules

        TEMP=D:\Temp

        windir=C:\WINDOWS";

​

    // The original way:

    public static string[] ByString(string content, string key)

    {

        // getting all lines, filtering the first empty line

        string[] nonEmptyLines = content.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);

​

        foreach (string line in nonEmptyLines)

        {

            // Separating key from values. We can use count: 2 because we split at the first '=' only.

            string[] keyValues = line.Split(new[] { '=' }, count: 2);

​

            // Removing white spaces and returning values if the key matches

            if (keyValues[0].TrimStart() == key)

                return keyValues[1].Split(';');

        }

​

        // key not found

        return null;

    }

​

    // The StringSegment way: almost the same code as above

    public static IList<StringSegment> ByStringSegment(string content, string key)

    {

        // getting all lines, filtering the first empty line

        IList<StringSegment> nonEmptyLines = content.AsSegment().Split(Environment.NewLine, StringSegmentSplitOptions.RemoveEmptyEntries);

​

        foreach (StringSegment line in nonEmptyLines)

        {

            // Separating key from values. We can use maxLength: 2 because we split at the first '=' only.

            IList<StringSegment> keyValues = line.Split('=', maxLength: 2);

​

            // Removing white spaces and returning values if the key matches

            if (keyValues[0].TrimStart() == key)

                return keyValues[1].Split(';');

        }

​

        // key not found

        return null;

    }

​

    // An alternative StringSegment way: uses Split only if we need all segments or we can limit max counts.

    public static IList<StringSegment> ByStringSegmentAlternative(string content, string key)

    {

        StringSegment rest = content; // same as content.AsSegment()

        while (!rest.IsNull)

        {

            // Advancing to the next line (StringSegment is immutable but the extension uses ref this parameter)

            StringSegment line = rest.ReadLine(); // see also ReadToSeparator overloads

            if (line.Length == 0)

                continue;

​

            // Separating key from values. We can use maxLength: 2 because we split at the first '=' only.

            IList<StringSegment> keyValues = line.Split('=', maxLength: 2);

​

            // Removing white spaces and returning values if the key matches

            if (keyValues[0].TrimStart() == key)

                return keyValues[1].Split(';');

        }

​

        // key not found

        return null;

    }

​

    public static void Main()

    {

        const string key = "Path";

​

        // All do the same:

        DumpValues(ByString(text, key));

        DumpValues(ByStringSegment(text, key));

        DumpValues(ByStringSegmentAlternative(text, key));

​

        // But their performance is quite different:

        new PerformanceTest { Iterations = 10_000, CpuAffinity = null }

            .AddCase(() => ByString(text, key), "String.Split+Trim")

            .AddCase(() => ByStringSegment(text, key), "StringSegment.Split+Trim")

            .AddCase(() => ByStringSegmentAlternative(text, key), "StringSegmentExtensions.ReadLine+StringSegment.Split+Trim")

            .DoTest()

            .DumpResults(Console.Out);

    }

​

    private static void DumpValues<T>(IEnumerable<T> values) => Console.WriteLine(values.Join(", "));

}

​