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

namespace AcDream.App.Tests.UI;

public class UiTextTests
{
    [Fact]
    public void ClampScroll_PinsToZero_WhenContentFitsView()
    {
        // 5 lines of content in a taller view → nothing to scroll, pinned at 0.
        Assert.Equal(0f, UiText.ClampScroll(50f, contentHeight: 80f, viewHeight: 200f));
        Assert.Equal(0f, UiText.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, UiText.ClampScroll(1000f, contentHeight: 500f, viewHeight: 200f));
        Assert.Equal(120f, UiText.ClampScroll(120f, contentHeight: 500f, viewHeight: 200f));
    }

    [Fact]
    public void ClampScroll_NeverNegative()
    {
        Assert.Equal(0f, UiText.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, UiText.CharIndexAt("hello", Mono10, 0f));
        Assert.Equal(0, UiText.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, UiText.CharIndexAt("hello", Mono10, 4f));   // before mid of glyph 0
        Assert.Equal(1, UiText.CharIndexAt("hello", Mono10, 6f));   // past mid of glyph 0
        Assert.Equal(1, UiText.CharIndexAt("hello", Mono10, 14f));  // before mid of glyph 1
        Assert.Equal(2, UiText.CharIndexAt("hello", Mono10, 16f));  // past mid of glyph 1
    }

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

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

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

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

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

    [Fact]
    public void SelectedText_SamePosition_IsEmpty()
    {
        var lines = Lines("hello");
        Assert.Equal("", UiText.SelectedText(lines, new UiText.Pos(0, 3), new UiText.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 = UiText.SelectedText(lines, new UiText.Pos(0, 6), new UiText.Pos(2, 5));
        Assert.Equal("line\nsecond line\nthird", s);
    }

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

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

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

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

    // ── VOffset: vertical positioning for single-line mode ───────────────────

    /// <summary>
    /// VJustify.Center: vertical offset = (height - lineHeight) / 2.
    /// This is the original formula used by both the Centered and RightAligned paths
    /// before VerticalJustify was introduced. Must remain unchanged (backward compat).
    /// </summary>
    [Fact]
    public void VOffset_Center_ReturnsHalfHeightMinusLineHeight()
    {
        float y = UiText.VOffset(height: 55f, lineHeight: 12f, padding: 0f, VJustify.Center);
        Assert.Equal((55f - 12f) * 0.5f, y);
    }

    /// <summary>
    /// VJustify.Top: vertical offset = padding (top of the content area).
    /// Used for footer title elements whose dat box is the full footer height (55 px)
    /// but the text should render near the top.
    /// </summary>
    [Fact]
    public void VOffset_Top_ReturnsPadding()
    {
        float y = UiText.VOffset(height: 55f, lineHeight: 12f, padding: 0f, VJustify.Top);
        Assert.Equal(0f, y);

        float yWithPadding = UiText.VOffset(height: 55f, lineHeight: 12f, padding: 4f, VJustify.Top);
        Assert.Equal(4f, yWithPadding);
    }

    /// <summary>
    /// VJustify.Bottom: vertical offset = height - lineHeight - padding.
    /// </summary>
    [Fact]
    public void VOffset_Bottom_ReturnsHeightMinusLineHeightMinusPadding()
    {
        float y = UiText.VOffset(height: 55f, lineHeight: 12f, padding: 2f, VJustify.Bottom);
        Assert.Equal(55f - 12f - 2f, y);
    }

    /// <summary>
    /// Center with non-zero padding: padding does NOT affect the center formula —
    /// VJustify.Center always uses (height - lineHeight) / 2 regardless of padding,
    /// matching the original behavior.
    /// </summary>
    [Fact]
    public void VOffset_Center_IgnoresPadding()
    {
        float yNoPad  = UiText.VOffset(height: 40f, lineHeight: 12f, padding: 0f, VJustify.Center);
        float yWithPad = UiText.VOffset(height: 40f, lineHeight: 12f, padding: 4f, VJustify.Center);
        Assert.Equal(yNoPad, yWithPad);   // Center is padding-independent
        Assert.Equal((40f - 12f) * 0.5f, yNoPad);
    }
}