using System;
using System.Collections.Generic;
using System.Numerics;

namespace AcDream.App.UI.Layout;

/// <summary>
/// Shared multi-segment rich-text composer for the chargen description
/// boxes (Campaign CC gate round 1 Batch C — GF-2/GF-3/GF-11a, and the
/// Summary how-to text). Ports retail's
/// <c>UIElement_Text::SetStringInfoWithFont</c> /
/// <c>AppendStringInfoWithFont @ 0x00469D70</c> composition model: a text
/// box is built from an ORDERED list of string segments, each carrying its
/// OWN font-color palette index
/// (<c>UIElement_Text::AppendStringInfoWithFont</c>'s
/// <c>SetFontColorHelper</c> -&gt; <c>InqProperty(0x1B)</c> array lookup —
/// see <see cref="AcDream.App.UI.UiText.FontColorPalette"/>).
///
/// <para>
/// The description pages used to bypass this entirely: they assigned a raw
/// <c>LinesProvider</c> lambda returning ONE unwrapped <see cref="AcDream.App.UI.UiText.Line"/>
/// per composed string, with no word-wrap. Historical symptom (Batch C):
/// for the Town page an unwrapped single line meant the town-specific
/// SUFFIX of the composed string rendered far outside the box's clipped
/// viewport, so switching towns looked like "the text never changes" even
/// though the underlying string genuinely did (only its INVISIBLE tail
/// differed). Escape decoding (the DAT's literal two-character <c>"\n"</c>,
/// Batch C's other symptom) has since moved to the string source
/// (<see cref="DatStringResolver"/> → <see cref="RetailStringEscapes"/>,
/// the 2026-08-17 systemic round) — segments reach this composer with real
/// line breaks already in place.
/// </para>
/// </summary>
internal static class DatRichText
{
    /// <summary>One composed segment: text plus the color it should render
    /// in. A null or empty <see cref="Text"/> is silently skipped (mirrors
    /// retail's own null-string-info no-op guards throughout this text
    /// composition family).</summary>
    public readonly record struct Segment(string? Text, Vector4 Color);

    /// <summary>
    /// Word-wraps every segment (independently, so
    /// each segment's wrapped lines keep ITS OWN color), then concatenates
    /// the results in order. No separator is inserted between segments —
    /// retail's own composition calls concatenate directly
    /// (<c>AppendStringInfoWithFont</c>/<c>append_n_chars</c> with no
    /// interposed literal), so any blank-line spacing between sections
    /// comes from the authored DAT string content itself, not from code
    /// here.
    /// </summary>
    public static IReadOnlyList<UiText.Line> Compose(
        UiText target,
        IReadOnlyList<Segment> segments)
    {
        ArgumentNullException.ThrowIfNull(target);
        ArgumentNullException.ThrowIfNull(segments);

        var lines = new List<UiText.Line>();
        // R2-1 (Campaign CC gate round 1 Batch E): the wrap width must shrink
        // by the SAME left+right inset the draw path now applies (Padding
        // plus the four retail margins, UiText.MarginLeft's own doc) — the
        // Batch-C regression's second half: text wasn't just drawing at the
        // wrong X, it was also wrapping to the FULL box width instead of the
        // authored interior width, overflowing the visible right edge too.
        float maximumWidth = MathF.Max(
            1f,
            target.Width - (target.Padding + target.MarginLeft) - (target.Padding + target.MarginRight));
        Func<string, float> measure = target.DatFont is { } font
            ? font.MeasureWidth
            : static value => value.Length * 8f;

        foreach (Segment segment in segments)
        {
            if (string.IsNullOrEmpty(segment.Text))
                continue;

            // Escape decoding (the DAT's literal two-character "\n") happens
            // at the string source (DatStringResolver → RetailStringEscapes,
            // 2026-08-17 systemic round — retail's own placement), so
            // segments arrive with real line breaks; WrapWords preserves
            // them and drops any stray CR itself.
            foreach (string wrapped in UiText.WrapWords(segment.Text, measure, maximumWidth))
                lines.Add(new UiText.Line(wrapped, segment.Color));
        }

        return lines;
    }

    /// <summary>
    /// Resolves <paramref name="target"/>'s own authored font-color
    /// palette (dat property <c>0x1B</c>) entry at <paramref name="index"/>,
    /// falling back to <paramref name="fallback"/> when the palette is
    /// absent or too short. Mirrors the same fallback shape
    /// <c>CharacterStatController.BuildSelectedTitleRuns</c> already uses
    /// for its own palette-indexed colors.
    /// </summary>
    public static Vector4 PaletteColor(UiText target, int index, Vector4 fallback) =>
        index >= 0 && index < target.FontColorPalette.Count
            ? target.FontColorPalette[index]
            : fallback;
}