using System;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

namespace Wunnell.Windows.Forms
{
    /// <summary>
    /// Represents a Windows control that allows the user to select a date
    /// and a time and to display the date and time with a specified format.
    /// </summary>
    /// <remarks>
    /// The <b>NullableDateTimePicker</b> extends the <b>DateTimePicker</b> control by adding support for binding null
    /// values through the <see cref="DataValue"/> property.  When a check box is displayed in the control and
    /// is not checked, the control is displayed blank instead of with greyed text.  This represents a null value.
    /// </remarks>
    [ToolboxBitmap(typeof(DateTimePicker))]
    public class NullableDateTimePicker : System.Windows.Forms.DateTimePicker
    {
#region Constants

        /// <summary>
        /// The default value for the Format property.
        /// </summary>
        const DateTimePickerFormat DEFAULT_FORMAT = DateTimePickerFormat.Long;

#endregion // Constants

#region Variables

        /// <summary>
        /// The custom format string used to format the date and/or time in the control.
        /// </summary>
        private string _customFormat;
        /// <summary>
        /// Determines whether dates and times are displayed using standard or custom formatting.
        /// </summary>
        private DateTimePickerFormat _format;
        private object oldDataValue;

#endregion // Variables

#region Properties

        /// <summary>
        /// Gets or sets a value indicating whether the <see cref="Value"/> property has been
        /// set with a valid date/time value and the displayed value is able to be updated.
        /// </summary>
        /// <value>
        /// <b>true</b> if the <b>Value</b> property has been set with a valid <b>DateTime</b> value and
        /// the displayed value is able to be updated; otherwise, <b>false</b>. The default is <b>true</b>.
        /// </value>
        /// <remarks>
        /// This property is used to obtain the state of the check box that is displayed if the <see cref="ShowCheckBox"/>
        /// property value is <b>true</b>.  If the <b>Checked</b> property value is <b>true</b>, the
        /// <see cref="NullableDateTimePicker"/> control displays the properly formatted <b>Value</b> property value and the
        /// <see cref="DataValue"/> property value is the same as the <b>Value</b> property value; otherwise, if the <b>ShowCheckBox</b>
        /// property value is true, the control is blank and the <b>DataValue</b> property value is <b>DBNull.Value</b>.
        /// </remarks>
        public new bool Checked
        {
            get
            {
                return base.Checked;
            }
            set
            {
                if (base.Checked != value)
                {
                    base.Checked = value;
                    this.SetBaseFormat();
                }
            }
        }

        /// <summary>
        /// Gets or sets the custom date/time format string.
        /// </summary>
        /// <value>
        /// A string that represents the custom date/time format. The default is a null reference (<b>Nothing</b> in Visual Basic).
        /// </value>
        public new string CustomFormat
        {
            get
            {
                return this._customFormat;
            }
            set
            {
                if (value != this._customFormat)
                {
                    this._customFormat = value;
                    this.SetBaseFormat();
                }
            }
        }

        /// <summary>
        /// Gets or sets the data value of the control.
        /// </summary>
        /// <value>
        /// The date and time contained in the control if there is no checkbox displayed
        /// or the displayed check box is checked; otherwise, <b>DBNull.Value</b>.
        /// </value>
        /// <remarks>
        /// This property is intended to be bound to <b>DataRow</b> fields, allowing null values from databases to be
        /// entered and displayed.  It accepts a null reference (<b>Nothing</b> in Visual Basic) or <b>DBNull.Value</b>
        /// to clear the date/time value contained in the control or a <b>DateTime</b> object to set it.
        /// </remarks>
        [
            Bindable(BindableSupport.Yes),
            Browsable(false)
        ]
        public object DataValue
        {
            get
            {
                if (base.Checked || !base.ShowCheckBox)
                {
                    // Return the actual date and time when there is not an unchecked check box.
                    return base.Value;
                }
                else
                {
                    // Return a null database value when there is an unchecked check box.
                    return DBNull.Value;
                }
            }
            set
            {

                if (value == null || value == DBNull.Value)
                {
                    // Uncheck the control to indicate a null value.
                    this.Checked = false;
                }
                else if (value is DateTime)
                {
                    try
                    {
                        // Set the specified value.
                        this.Value = (DateTime)value;
                    }
                    catch (Exception ex)
                    {
                        // Most likely the value assigned was outside the limits set by MinDate and MaxDate
                        throw new ArgumentException(string.Format("'{0}' is an invalid value for 'DataValue'.  See the inner exception for more information.", value.ToString()),
                                                    ex);
                    }

                    // Explicitly check the control in case the specified value was the same as the current Value property.
                    this.Checked = true;
                }
                else
                {
                    // An invalid type of object was assigned.
                    throw new ArgumentException(string.Format("'{0}' is an invalid type for 'DataValue'.  'DataValue' accepts only a null reference, DBNull.Value or a 'DateTime' object.",
                                                              value.GetType().Name));
                }
            }
        }

        /// <summary>
        /// Gets or sets the format of the date and time displayed in the control.
        /// </summary>
        /// <value>
        /// One of the <b>DateTimePickerFormat</b> values. The default is <b>Long</b>.
        /// </value>
        [DefaultValue(DEFAULT_FORMAT)]
        public new DateTimePickerFormat Format
        {
            get
            {
                return this._format;
            }
            set
            {
                if (value != this._format)
                {
                    this._format = value;
                    this.SetBaseFormat();
                }
            }
        }

        /// <summary>
        /// Gets or sets a value indicating whether a check box is displayed to the left of the selected date.
        /// </summary>
        /// <value>
        /// <b>true</b> if a check box is displayed to the left of the selected date; otherwise, <b>false</b>. The default is <b>false</b>.
        /// </value>
        public new bool ShowCheckBox
        {
            get
            {
                return base.ShowCheckBox;
            }
            set
            {
                if (value != base.ShowCheckBox)
                {
                    base.ShowCheckBox = value;
                    this.SetBaseFormat();
                }
            }
        }

#endregion // Properties

#region Constructors

        /// <summary>
        /// Initializes a new instance of the <see cref="NullableDateTimePicker"/> class.
        /// </summary>
        public NullableDateTimePicker()
            : base()
        {
            this._customFormat = base.CustomFormat;
            this._format = base.Format;
        }

#endregion // Constructors

#region Events

        /// <summary>
        /// Occurs when the <see cref="DataValue"/> property changes.
        /// </summary>
        /// <remarks>
        /// This event is raised whenever the apparent value of the control changes.
        /// This may occur when the <see cref="Checked"/>, <see cref="ShowCheckBox"/> or <b>Value</b> property changes.
        /// </remarks>
        [
            Category("Action"),
            Description("Occurs when the apparent value of the control changes.")
        ]
        public event EventHandler DataValueChanged;

#endregion // Events

#region Methods

        /// <summary>
        /// Raises the <b>DataValueChanged</b> event.
        /// </summary>
        /// <param name="e">
        /// An <b>EventArgs</b> that contains the event data.
        /// </param>
        protected virtual void OnDataValueChanged(EventArgs e)
        {
            // Refresh the previous value.
            this.oldDataValue = this.DataValue;

            if (this.DataValueChanged != null)
            {
                // Raise the DataValueChanged event
                this.DataValueChanged(this, e);
            }
        }

        /// <summary>
        /// Raises the <b>ValueChanged</b> event.
        /// </summary>
        /// <param name="e">
        /// An <b>EventArgs</b> that contains the event data.
        /// </param>
        protected override void OnValueChanged(EventArgs e)
        {
            this.SetBaseFormat();
            base.OnValueChanged(e);
        }

        /// <summary>
        /// Sets the <b>Format</b> and <b>CustomFormat</b> base properties to either
        /// hide or display the date and/or time value contained in the control.
        /// </summary>
        private void SetBaseFormat()
        {
            string customFormat;
            DateTimePickerFormat format;

            if (base.Checked || !base.ShowCheckBox)
            {
                // Use the actual format values.
                customFormat = this._customFormat;
                format = this._format;
            }
            else
            {
                // Set the format to hide the text.
                customFormat = " ";
                format = DateTimePickerFormat.Custom;
            }

            if (base.CustomFormat != customFormat)
            {
                base.CustomFormat = customFormat;
            }

            if (base.Format != format)
            {
                base.Format = format;
            }

            bool dataValueChanged;

            if (this.oldDataValue is DateTime && this.DataValue is DateTime)
            {
                // Compare the old and current values as DateTime instances.
                dataValueChanged = ((DateTime)this.oldDataValue != (DateTime)this.DataValue);
            }
            else
            {
                // Compare the old and current values as Object instances.
                dataValueChanged = (this.oldDataValue != this.DataValue);
            }

            if (dataValueChanged)
            {
                this.OnDataValueChanged(EventArgs.Empty);
            }
        }

#endregion // Methods
    }
}