using System.Globalization;

namespace Nonemm.Core;

/// Checks a signal report before it goes in the log. Most modes exchange RST;
/// the weak-signal modes exchange a signal-to-noise ratio in decibels instead.
public static class SignalReport
{
    private const int Weakest = -50;
    private const int Strongest = 50;

    public static bool IsPlausible(string text, Mode mode)
    {
        string report = text.Trim();
        return mode.ReportsDecibels ? IsDecibels(report) : IsRst(report);
    }

    /// What to type, for an error message.
    public static string Example(Mode mode) => mode.ReportsDecibels
        ? "-12"
        : mode.Category == ModeCategory.Phone ? "59" : "599";

    /// Readability 1 to 5, strength 1 to 9 and, on CW and the digital modes,
    /// tone 1 to 9. Two figures pass on every mode: phone sends two, and an
    /// operator on CW may drop the tone.
    private static bool IsRst(string report) =>
        report.Length is 2 or 3
        && report[0] is >= '1' and <= '5'
        && report[1] is >= '1' and <= '9'
        && (report.Length == 2 || report[2] is >= '1' and <= '9');

    private static bool IsDecibels(string report) =>
        int.TryParse(report, NumberStyles.AllowLeadingSign,
            CultureInfo.InvariantCulture, out int decibels)
        && decibels >= Weakest
        && decibels <= Strongest;
}