using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace LagerFileView
{
    public partial class MainView:Form
    {
        public string FilePath { get; set; }

        public int LineNo { get; set; }

        public int PageSize { get; set; } = 1000;

        public CancellationTokenSource CancelSource { get; set; } = new CancellationTokenSource();

        public MainView() {
            InitializeComponent();
        }

        private void butOpenFile_Click(object sender,EventArgs e) {
            this.CancelSource.Cancel();
            using(var fileDlg = new OpenFileDialog()) {
                fileDlg.Filter = "文本文件 (*.txt;*.log)|*.txt;*.log|所有文件 (*.*)|*.*";
                if(fileDlg.ShowDialog() == DialogResult.OK) {
                    this.FilePath = fileDlg.FileName;
                    this.labStatus.Text = "找到文件，正在打开...";
                    this.CancelSource = new CancellationTokenSource();
                    OpenFileTask(this.CancelSource.Token);
                }
            }
        }

        private void OpenFileTask(CancellationToken cancellation) {
            this.trbFileText.Clear();
            Task.Factory.StartNew(() => {
                using var fs = new FileStream(this.FilePath,FileMode.Open,FileAccess.Read);
                using var reader = new StreamReader(fs);
                string? line;
                int cl = 0;
                int start = this.PageSize * this.LineNo;
                int end = start + this.PageSize;
                while((line = reader.ReadLine()) != null) {
                    if(cancellation.IsCancellationRequested) {
                        break;
                    }
                    if(cl < start) {
                        cl++;
                        continue;
                    }
                    if(cl > end) {
                        break;
                    }
                    this.Invoke(() => {
                        this.trbFileText.AppendText(line + "\n");
                    });
                    cl++;
                }
                this.labStatus.Text = $"已打开第{start}行至{cl}行";
            });

        }

        private void moveLast_Click(object sender,EventArgs e) {
            this.LineNo--;
            this.LineNo = Math.Max(0,this.LineNo);
            this.CancelSource.Cancel();
            this.CancelSource = new CancellationTokenSource();
            OpenFileTask(this.CancelSource.Token);
        }

        private void moveNext_Click(object sender,EventArgs e) {
            this.LineNo++;
            this.CancelSource.Cancel();
            this.CancelSource = new CancellationTokenSource();
            OpenFileTask(this.CancelSource.Token);

        }
    }
}