using System.Text;

namespace DodoSSH.Client.Terminal.Tests;

/// <summary>
/// That a session keeps the last of its output for the phone's history to read back, and knows when a
/// full-screen program has it.
/// </summary>
public sealed class OutputTailTests
{
    private static byte[] Ascii(string text) => Encoding.ASCII.GetBytes(text);

    [Fact]
    public void WhatIsHeld_IsTheLastKilobyte_InOrder()
    {
        var tail = new OutputTail();

        tail.Append(Ascii(new string('a', OutputTail.Capacity)));
        tail.Append(Ascii("stan@box:~$ ls"));

        var held = Encoding.ASCII.GetString(tail.Snapshot().Tail);

        held.Length.ShouldBe(OutputTail.Capacity);
        held.ShouldEndWith("aaastan@box:~$ ls");
    }

    [Fact]
    public void AReadLargerThanTheTail_KeepsItsEnd()
    {
        var tail = new OutputTail();

        tail.Append(Ascii(new string('x', 5000) + "the end"));

        Encoding.ASCII.GetString(tail.Snapshot().Tail).ShouldEndWith("xthe end");
    }

    [Fact]
    public void TheAlternateScreen_IsOnBetweenItsTwoSwitches()
    {
        var tail = new OutputTail();

        tail.Append(Ascii("$ vi notes\r\n\x1b[?1049h\x1b[H~\r\n~"));
        tail.Snapshot().AlternateScreen.ShouldBeTrue();

        tail.Append(Ascii("\x1b[?1049l$ "));
        tail.Snapshot().AlternateScreen.ShouldBeFalse();
    }

    [Fact]
    public void ASwitchSplitAcrossTwoReads_IsStillSeen()
    {
        var tail = new OutputTail();

        tail.Append(Ascii("$ less log\r\n\x1b[?10"));
        tail.Append(Ascii("49h"));

        tail.Snapshot().AlternateScreen.ShouldBeTrue();
    }

    [Fact]
    public void ASwitchAtTheStartOfAHugeRead_IsNotLostWithTheBytesThatFallOffTheTail()
    {
        var tail = new OutputTail();

        // A full-screen program's first frame: the switch, and then a screenful of paint.
        tail.Append(Ascii("\x1b[?1049h" + new string('#', 60_000)));

        tail.Snapshot().AlternateScreen.ShouldBeTrue();
    }

    [Fact]
    public void OtherPrivateModes_AreNotTheAlternateScreen()
    {
        var tail = new OutputTail();

        // Bracketed paste and cursor visibility, which every prompt sends.
        tail.Append(Ascii("\x1b[?2004h\x1b[?25h$ "));

        tail.Snapshot().AlternateScreen.ShouldBeFalse();
    }
}