using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.App.UI;

namespace AcDream.App.Tests.UI;

public class UiChatViewTests
{
    [Fact]
    public void ClampScroll_PinsToZero_WhenContentFitsView()
    {
        // 5 lines of content in a taller view → nothing to scroll, pinned at 0.
        Assert.Equal(0f, UiChatView.ClampScroll(50f, contentHeight: 80f, viewHeight: 200f));
        Assert.Equal(0f, UiChatView.ClampScroll(0f, contentHeight: 80f, viewHeight: 200f));
    }

    [Fact]
    public void ClampScroll_CapsAtContentMinusView_WhenOverflowing()
    {
        // Content 500, view 200 → max scrollback is 300px (oldest line at top).
        Assert.Equal(300f, UiChatView.ClampScroll(1000f, contentHeight: 500f, viewHeight: 200f));
        Assert.Equal(120f, UiChatView.ClampScroll(120f, contentHeight: 500f, viewHeight: 200f));
    }

    [Fact]
    public void ClampScroll_NeverNegative()
    {
        Assert.Equal(0f, UiChatView.ClampScroll(-50f, contentHeight: 500f, viewHeight: 200f));
    }

    // ── Char-index hit-testing (x → col) with a synthetic 10px monospace advance ──

    private static readonly Func<char, float> Mono10 = static _ => 10f;

    [Fact]
    public void CharIndexAt_ZeroOrNegative_IsColumnZero()
    {
        Assert.Equal(0, UiChatView.CharIndexAt("hello", Mono10, 0f));
        Assert.Equal(0, UiChatView.CharIndexAt("hello", Mono10, -5f));
    }

    [Fact]
    public void CharIndexAt_SnapsToGlyphMidpoint()
    {
        // glyph[0] spans 0..10 (midpoint 5), glyph[1] 10..20 (midpoint 15), ...
        Assert.Equal(0, UiChatView.CharIndexAt("hello", Mono10, 4f));   // before mid of glyph 0
        Assert.Equal(1, UiChatView.CharIndexAt("hello", Mono10, 6f));   // past mid of glyph 0
        Assert.Equal(1, UiChatView.CharIndexAt("hello", Mono10, 14f));  // before mid of glyph 1
        Assert.Equal(2, UiChatView.CharIndexAt("hello", Mono10, 16f));  // past mid of glyph 1
    }

    [Fact]
    public void CharIndexAt_PastEnd_IsLength()
    {
        Assert.Equal(5, UiChatView.CharIndexAt("hello", Mono10, 1000f));
    }

    [Fact]
    public void CharIndexAt_EmptyString_IsZero()
    {
        Assert.Equal(0, UiChatView.CharIndexAt("", Mono10, 50f));
    }

    // ── SelectedText assembly ────────────────────────────────────────────

    private static IReadOnlyList<UiChatView.Line> Lines(params string[] texts)
    {
        var list = new List<UiChatView.Line>(texts.Length);
        foreach (var t in texts)
            list.Add(new UiChatView.Line(t, new Vector4(1, 1, 1, 1)));
        return list;
    }

    [Fact]
    public void SelectedText_SingleLine_Substring()
    {
        var lines = Lines("hello world");
        var s = UiChatView.SelectedText(lines, new UiChatView.Pos(0, 6), new UiChatView.Pos(0, 11));
        Assert.Equal("world", s);
    }

    [Fact]
    public void SelectedText_SingleLine_ReversedAnchorCaret_IsNormalised()
    {
        var lines = Lines("hello world");
        // caret BEFORE anchor — Order() must normalise.
        var s = UiChatView.SelectedText(lines, new UiChatView.Pos(0, 11), new UiChatView.Pos(0, 6));
        Assert.Equal("world", s);
    }

    [Fact]
    public void SelectedText_SamePosition_IsEmpty()
    {
        var lines = Lines("hello");
        Assert.Equal("", UiChatView.SelectedText(lines, new UiChatView.Pos(0, 3), new UiChatView.Pos(0, 3)));
    }

    [Fact]
    public void SelectedText_MultiLine_JoinsWithNewline()
    {
        var lines = Lines("first line", "second line", "third line");
        // from col 6 of line 0 ("line") through col 5 of line 2 ("third")
        var s = UiChatView.SelectedText(lines, new UiChatView.Pos(0, 6), new UiChatView.Pos(2, 5));
        Assert.Equal("line\nsecond line\nthird", s);
    }

    [Fact]
    public void SelectedText_MultiLine_TwoLines_NoMiddle()
    {
        var lines = Lines("alpha", "bravo");
        var s = UiChatView.SelectedText(lines, new UiChatView.Pos(0, 2), new UiChatView.Pos(1, 3));
        Assert.Equal("pha\nbra", s);
    }

    [Fact]
    public void SelectedText_MultiLine_ReversedAnchorCaret_IsNormalised()
    {
        var lines = Lines("alpha", "bravo");
        // end before start → Order() swaps them.
        var s = UiChatView.SelectedText(lines, new UiChatView.Pos(1, 3), new UiChatView.Pos(0, 2));
        Assert.Equal("pha\nbra", s);
    }

    [Fact]
    public void SelectedText_EmptyLineList_IsEmpty()
    {
        Assert.Equal("", UiChatView.SelectedText(Array.Empty<UiChatView.Line>(),
            new UiChatView.Pos(0, 0), new UiChatView.Pos(0, 0)));
    }

    [Fact]
    public void Order_SortsByLineThenColumn()
    {
        var (s1, e1) = UiChatView.Order(new UiChatView.Pos(2, 1), new UiChatView.Pos(0, 5));
        Assert.Equal(new UiChatView.Pos(0, 5), s1);
        Assert.Equal(new UiChatView.Pos(2, 1), e1);

        var (s2, e2) = UiChatView.Order(new UiChatView.Pos(1, 8), new UiChatView.Pos(1, 2));
        Assert.Equal(new UiChatView.Pos(1, 2), s2);
        Assert.Equal(new UiChatView.Pos(1, 8), e2);
    }
}