using System;
using System.Diagnostics;

namespace MathInterpreter.Core;

/// <summary>
///     Represents a mathematical expression
/// </summary>
public sealed class MathExpression
{
    // TODO
    /*
    private double? _leftOperand;
    private Operator? _operator;
    private double? _result;
    private double? _rightOperand;
    */

    /// <summary>
    ///     Creates a new instance of <see cref="MathExpression" /> from the provided expression string.
    ///     Validates the provided expression and throws an exception if it is invalid.
    /// </summary>
    /// <param name="expressionString">The expression as a string</param>
    /// <exception cref="OperatorException">Thrown if a problem with the operator is found</exception>
    /// <exception cref="ExpressionFormatException">Thrown if a problem with the expression format is found</exception>
    /// <exception cref="NumberValueException">Thrown if a problem with the value of a number is found</exception>
    public MathExpression(string expressionString)
    {
        ValidateAndParse(expressionString.Trim().AsSpan());
    }

    /// <summary>
    ///     Gets the calculated result of the expression
    /// </summary>
    /// <exception cref="UnreachableException">
    ///     Thrown if validation during construction did not guard against an unexpected, invalid expression
    /// </exception>
    public double Result
    {
        get
        {
            // TODO
            throw new NotImplementedException();
        }
    }

    /// <summary>
    ///     Returns a string representation of the expression - this is not the originally provided string
    ///     but the cleaned up version
    /// </summary>
    /// <returns>String representation of the expression</returns>
    /// <exception cref="UnreachableException">
    ///     Thrown if validation during construction did not guard against an unexpected, invalid expression
    ///     and left this instance in an invalid state
    /// </exception>
    public override string ToString()
    {
        // TODO
        throw new NotImplementedException();
    }

    private void ValidateAndParse(ReadOnlySpan<char> expression)
    {
        // TODO
        throw new NotImplementedException();
    }
}