using System.Globalization;

namespace Just.PreciseMath.Tests;

public class DoubleDoubleSpanFormattingTests
{
    [Theory]
    [InlineData("")]
    [InlineData("G32")]
    [InlineData("g999")]
    [InlineData("E20")]
    [InlineData("F54")]
    public void SpanFormattingMatchesExactComponentFormatting(string format)
    {
        DoubleDouble value = DoubleDouble.FromComponents(1.0, Math.ScaleB(1.0, -54));
        NumberFormatInfo provider = new() { NumberDecimalSeparator = "::", NegativeSign = "minus" };
        string expected = value.ToString(format, provider);
        char[] buffer = new char[expected.Length + 1];
        buffer[^1] = '!';
        ((ISpanFormattable)value).TryFormat(buffer.AsSpan(0, expected.Length), out int written, format, provider).ShouldBeTrue();
        written.ShouldBe(expected.Length);
        new string(buffer, 0, written).ShouldBe(expected);
        buffer[^1].ShouldBe('!');
    }

    [Fact]
    public void DefaultSpanFormattingRetainsLowComponentDigits()
    {
        Span<char> buffer = stackalloc char[64];
        DoubleDouble.FromComponents(1.0, Math.ScaleB(1.0, -54))
            .TryFormat(buffer, out int written, provider: CultureInfo.InvariantCulture).ShouldBeTrue();
        buffer[..written].ToString().ShouldBe("1.0000000000000000555111512312578");
    }

    [Fact]
    public void ShortDestinationIsUnchangedAndReportsZero()
    {
        char[] buffer = ['!', '!'];
        DoubleDouble.Pi.TryFormat(buffer, out int written, "G32", CultureInfo.InvariantCulture).ShouldBeFalse();
        written.ShouldBe(0);
        new string(buffer).ShouldBe("!!");
        DoubleDouble.One.TryFormat(Span<char>.Empty, out written, provider: CultureInfo.InvariantCulture).ShouldBeFalse();
        written.ShouldBe(0);
    }

    [Theory]
    [InlineData(-0.0)]
    [InlineData(double.NaN)]
    [InlineData(double.PositiveInfinity)]
    [InlineData(double.NegativeInfinity)]
    public void SpanFormattingPreservesSpecialValues(double high)
    {
        NumberFormatInfo provider = new() { NegativeSign = "minus", NaNSymbol = "unknown" };
        DoubleDouble value = new(high);
        Span<char> buffer = stackalloc char[64];
        value.TryFormat(buffer, out int written, "F2", provider).ShouldBeTrue();
        buffer[..written].ToString().ShouldBe(value.ToString("F2", provider));
    }

    [Theory]
    [InlineData("R")]
    [InlineData("F1000")]
    [InlineData("G-1")]
    public void InvalidFormatThrowsEvenForEmptyDestination(string format)
    {
        Should.Throw<FormatException>(() => DoubleDouble.One.TryFormat(Span<char>.Empty, out _, format, CultureInfo.InvariantCulture));
    }
}