using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace Graphic
{
    public partial class Form1 : Form
    {
        private static readonly float MAX_Y_AXIS_HEIGHT = 1e5F;
        private static readonly float MIN_Y_AXIS_HEIGHT = -1e5F;
        private static readonly float MAX_X_AXIS_WIDTH = 1e5F;
        private static readonly float MIN_X_AXIS_WIDTH = -1e5F;

        public Form1()
        {
            InitializeComponent();
        }

        /*
         * Отрисовка графика по нажатию кнопки
         */
        private void Button1_Click(object sender, EventArgs e)
        {
            var formula = textBox1.Text;
            Function function = new Function(formula);
            pictureBox1.Refresh();
            BuildGraph(function, GetPoints(function, double.Parse(textBox2.Text), double.Parse(textBox3.Text), double.Parse(textBox4.Text)));
        }

        /*
         * Запрет ввода пробелов
         */
        private void TextBox1_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (!char.IsWhiteSpace(e.KeyChar)) return;
            else e.Handled = true;
        }

        /*
         * Построение графика функции
         */
        private void BuildGraph(Function function, List<Pair> points)
        {
            label5.Text = function.MethodChord(-10, 10, 0.01).ToString();

            float coef_y = 1, coef_x = 1;
            float max_y = 0, min_y = float.MaxValue;
            float max_x = 0, min_x = float.MaxValue;

            for (var i = 0; i < points.Count; i++)
            {
                if (points[i].second > max_y)
                    max_y = points[i].second;
                if (points[i].second < min_y)
                    min_y = points[i].second;
                if (points[i].first > max_x)
                    max_x = points[i].first;
                if (points[i].first < min_x)
                    min_x = points[i].first;
            }

            coef_x = pictureBox1.Width/ Math.Abs(min_x - max_x);
            if (float.IsInfinity(max_y))
                coef_y = pictureBox1.Height / Math.Abs(100500F);
            else
                coef_y = pictureBox1.Height / Math.Abs(max_y);

            using (Graphics gr = pictureBox1.CreateGraphics())
            {
                gr.TranslateTransform((pictureBox1.Right + pictureBox1.Left) / 2, (pictureBox1.Bottom + pictureBox1.Top) / 2);
                Pen pen = new Pen(Color.Black, 1);
                Brush brush = new SolidBrush(pictureBox1.BackColor);

                pen.Width = 0.01F;
                gr.DrawLine(pen, 0, MIN_Y_AXIS_HEIGHT, 0, MAX_Y_AXIS_HEIGHT); //Ось x
                gr.DrawLine(pen, MIN_X_AXIS_WIDTH, 0, MAX_X_AXIS_WIDTH, 0); //Ось y

                pen.Color = Color.Red;
                gr.ScaleTransform(coef_x, coef_y);

                float last_x = points[0].first;
                float last_y = -points[0].second;
                for (var i = 1; i < points.Count; i++)
                {
                    float next_x = points[i].first;
                    float next_y = -points[i].second;

                    if (next_y > MAX_Y_AXIS_HEIGHT)
                    {
                        last_x = points[i].first;
                        last_y = MIN_Y_AXIS_HEIGHT;
                        continue;
                    }
                    if (next_y < MIN_Y_AXIS_HEIGHT)
                    {
                        last_x = points[i].first;
                        last_y = MAX_Y_AXIS_HEIGHT;
                        continue;
                    }

                    gr.DrawLine(pen, last_x, last_y, next_x, next_y);

                    last_x = next_x;
                    last_y = next_y;
                }

                pen.Dispose();
            }
        }

        /*
         * Возращает набор точек, используя функцию
         */
        private List<Pair> GetPoints(Function function, double start, double end, double step)
        {
            List<Pair> points = new List<Pair>();
            for (double val = start; val <= end; val += step)
            {
                double next_y = function.GetValue(val);
                points.Add(new Pair((float)val, (float)next_y));
            }
            return points;
        }
    }
}