using System.Numerics;
using Dalamud.Bindings.ImGui;
using Dalamud.Interface;
using HellionChat.Util;

namespace HellionChat.Ui.StyleEngine.Widgets;

// The band above the conversation: which channel you are in on the left, where
// you are and what time it is on the right.
//
// Set apart by small caps with wide tracking rather than by size. That is a
// deliberate departure from the mockup, which asks for one pixel smaller than
// body text: one pixel would cost a whole additional font handle at full glyph
// range, because tab names are free user input and can be CJK. Tracking carries
// the same weight in every palette and costs nothing.
//
// The tab name draws in the body face for the same reason. Only the world and the
// clock use the meta face, whose glyph range is ASCII plus a middle dot.
internal static class ChannelHeader
{
    private const float InsetRaw = 14f;
    private const float PadYRaw = 7f;
    private const float TrackRaw = 1.8f;
    private const float DetailTrackRaw = 0.9f;
    private const float IconGapRaw = 8f;

    // Measured, never a fixed 32px: the band has to hold a line of text, and the
    // font comes from Config, which display scaling does not feed into.
    internal static float Height =>
        ImGui.GetTextLineHeight() + MathF.Round(PadYRaw * 2f * Metrics.Scale);

    internal static void Draw(Tab tab, ChannelHeaderMode mode, FontManager fonts, string detail)
    {
        var scale = Metrics.Scale;
        var width = ImGui.GetContentRegionAvail().X;
        var height = Height;
        var origin = ImGui.GetCursorScreenPos();

        var theme = Plugin.Instance.ThemeRegistry.Active;
        var surface = theme.Colors.Surface;

        var name = tab.Name.ToUpperInvariant();
        var track = TrackRaw * scale;
        var detailTrack = DetailTrackRaw * scale;

        // Measure before deciding, the way the status bar does. Icon and gap are
        // part of the name run because they are dropped together with it.
        float nameRun;
        using (fonts.RegularFont!.Push())
            nameRun = DrawListExtensions.MeasureTrackedText(name, track);

        var iconWidth = MeasureIcon(fonts, Components.Sidebar.ResolveTabIcon(tab));
        nameRun += iconWidth + IconGapRaw * scale;

        float detailRun;
        using (fonts.MetaFont!.Push())
            detailRun = DrawListExtensions.MeasureTrackedText(detail, detailTrack);

        var inset = InsetRaw * scale;
        var plan = ChannelHeaderLayout.Plan(
            mode,
            width - inset * 2f,
            ImGui.GetContentRegionAvail().Y - height,
            nameRun,
            detailRun
        );

        if (!plan.ShowHeader)
            return;

        var dl = ImGui.GetWindowDrawList();
        var bottomRight = origin + new Vector2(width, height);
        dl.AddRectFilled(origin, bottomRight, ColourUtil.RgbaToAbgr(surface));
        dl.AddLine(
            new Vector2(origin.X, bottomRight.Y - 1f),
            new Vector2(bottomRight.X, bottomRight.Y - 1f),
            ColourUtil.RgbaToAbgr(theme.Colors.Border),
            MathF.Max(1f, scale)
        );

        var textY = origin.Y + MathF.Round(PadYRaw * scale);

        if (plan.ShowName)
        {
            var accent = ColourUtil.RgbaToAbgr(
                ColourUtil.EnsureContrast(theme.Colors.Accent, surface, 4.5f)
            );
            var x = origin.X + inset;

            using (fonts.FontAwesome.Push())
            {
                var glyph = Components.Sidebar.ResolveTabIcon(tab).ToIconString();
                dl.AddText(new Vector2(x, textY), accent, glyph);
                x += ImGui.CalcTextSize(glyph).X + IconGapRaw * scale;
            }

            using (fonts.RegularFont.Push())
                dl.DrawTrackedText(new Vector2(x, textY), name, accent, track);
        }

        if (plan.ShowDetail)
        {
            var muted = ColourUtil.RgbaToAbgr(
                ColourUtil.EnsureContrast(theme.Colors.TextMuted, surface, 4.5f)
            );

            // The meta face is smaller, so it would hang from the top edge
            // without the drop -- ImGui aligns by top, not by baseline.
            float bodyAscent;
            using (fonts.RegularFont.Push())
                bodyAscent = ImGui.GetFont().Ascent;

            float metaAscent;
            using (fonts.MetaFont.Push())
                metaAscent = ImGui.GetFont().Ascent;

            var drop = BaselineMath.OffsetFor(bodyAscent, metaAscent, scale);

            using (fonts.MetaFont.Push())
                dl.DrawTrackedText(
                    new Vector2(bottomRight.X - inset - detailRun, textY + drop),
                    detail,
                    muted,
                    detailTrack
                );
        }

        // ItemSize rather than a cursor move: it advances the cursor AND extends
        // CursorMaxPos, which is what the enclosing layout measures.
        ImGui.SetCursorScreenPos(origin);
        ImGuiP.ItemSize(new Vector2(width, height - ImGui.GetStyle().ItemSpacing.Y));
    }

    private static float MeasureIcon(FontManager fonts, FontAwesomeIcon icon)
    {
        using (fonts.FontAwesome.Push())
            return ImGui.CalcTextSize(icon.ToIconString()).X;
    }
}