MainForm.cs

#region License and Terms
//
// NCrontab - Crontab for .NET
// Copyright (c) 2008 Atif Aziz. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using NCrontab;

namespace NCrontabViewer;

public partial class MainForm : Form
{
    static readonly char[] Separators = [' '];

    DateTime lastChangeTime;
    bool dirty;
    CrontabSchedule? crontab;
    bool isSixPart;
    DateTime startTime;
    int totalOccurrenceCount;

    public MainForm()
    {
        InitializeComponent();
    }

    // ReSharper disable once InconsistentNaming
    void CronBox_Changed(object sender, EventArgs args)
    {
        this.lastChangeTime = DateTime.Now;
        this.dirty = true;
        this.isSixPart = false;
        this.crontab = null;
    }

    // ReSharper disable once InconsistentNaming
    void Timer_Tick(object sender, EventArgs args)
    {
        var changeLapse = DateTime.Now - this.lastChangeTime;

        if (!this.dirty || changeLapse <= TimeSpan.FromMilliseconds(500))
            return;

        this.dirty = false;
        DoCrontabbing();
    }

    void DoCrontabbing()
    {
        this.resultBox.Clear();
        this.errorProvider.SetError(this.cronBox, null);
        this.statusBarPanel.Text = "Ready";
        this.moreButton.Enabled = false;

        const string defaultCustomFormat = "dd/MM/yyyy HH:mm";

        if (this.crontab == null)
        {
            try
            {
                var expression = this.cronBox.Text.Trim();

                if (expression.Length == 0)
                    return;

                this.isSixPart = expression.Split(Separators, StringSplitOptions.RemoveEmptyEntries).Length == 6;
                this.crontab = CrontabSchedule.Parse(expression, new CrontabSchedule.ParseOptions { IncludingSeconds = this.isSixPart });

                this.totalOccurrenceCount = 0;

                this.startTime = DateTime.ParseExact(this.startTimePicker.Text,
                                                     this.startTimePicker.CustomFormat ?? defaultCustomFormat, CultureInfo.InvariantCulture,
                                                     DateTimeStyles.AssumeLocal) - (this.isSixPart ? TimeSpan.FromSeconds(1): TimeSpan.FromMinutes(1));
            }
            catch (CrontabException e)
            {
                this.errorProvider.SetError(this.cronBox, e.Message);

                var traceBuilder = new StringBuilder();

                Exception traceException = e;
                Exception lastException;

                do
                {
                    _ = traceBuilder.Append(traceException.Message)
                                    .Append("\r\n");
                    lastException = traceException;
                    traceException = traceException.GetBaseException();
                }
                while (lastException != traceException);

                this.resultBox.Text = traceBuilder.ToString();
                return;
            }

        }

        var endTime = DateTime.ParseExact(this.endTimePicker.Text,
            this.endTimePicker.CustomFormat ?? defaultCustomFormat, CultureInfo.InvariantCulture,
            DateTimeStyles.AssumeLocal);

        var sb = new StringBuilder();

        var count = 0;
        const int maxCount = 500;
        var info = DateTimeFormatInfo.CurrentInfo;
        var dayWidth = info.AbbreviatedDayNames.Max(s => s.Length);
        var monthWidth = info.AbbreviatedMonthNames.Max(s => s.Length);
        var timeComponent = this.isSixPart ? "HH:mm:ss" : "HH:mm";
        var timeFormat = $"{{0,-{dayWidth}:ddd}} {{0:dd}}, {{0,-{monthWidth}:MMM}} {{0:yyyy {timeComponent}}}";
        var lastTimeString = new string('?', string.Format(null, timeFormat, DateTime.MinValue).Length);

        foreach (var occurrence in this.crontab.GetNextOccurrences(this.startTime, endTime))
        {
            if (count + 1 > maxCount)
                break;

            this.startTime = occurrence;
            this.totalOccurrenceCount++;
            count++;

            var timeString = string.Format(null, timeFormat, occurrence);

            _ = sb.Append(timeString)
                  .Append(" | ");

            var index = Diff(lastTimeString, timeString, 0, dayWidth, sb);
            _ = sb.Append(' ');
            index = Diff(lastTimeString, timeString, index + 1, 2, sb);
            _ = sb.Append(", ");
            index = Diff(lastTimeString, timeString, index + 2, monthWidth, sb);
            _ = sb.Append(' ');
            index = Diff(lastTimeString, timeString, index + 1, 4, sb);
            _ = sb.Append(' ');
            index = Diff(lastTimeString, timeString, index + 1, 2, sb);
            _ = sb.Append(':');
            index = Diff(lastTimeString, timeString, index + 1, 2, sb);
            if (this.isSixPart)
            {
                _ = sb.Append(':');
                _ = Diff(lastTimeString, timeString, index + 1, 2, sb);
            }

            lastTimeString = timeString;

            _ = sb.Append("\r\n");
        }

        this.moreButton.Enabled = count == maxCount;

        this.statusBarPanel.Text = $"Last count = {count:N0}, Total = {this.totalOccurrenceCount:N0}";

        this.resultBox.Text = sb.ToString();
        this.resultBox.Select(0, 0);
        this.resultBox.ScrollToCaret();
    }

    static int Diff(string oldString, string newString, int index, int length, StringBuilder builder)
    {
#pragma warning disable IDE0045 // Convert to conditional expression (has side-effects)
        if (string.CompareOrdinal(oldString, index, newString, index, length) == 0)
            _ = builder.Append('-', length);
        else
            _ = builder.Append(newString, index, length);
#pragma warning restore IDE0045 // Convert to conditional expression

        return index + length;
    }

    // ReSharper disable once InconsistentNaming
    void More_Click(object sender, EventArgs e) => DoCrontabbing();
}