HellionChat/HellionChat/Ui/AutoTellTabTint.cs

namespace HellionChat.Ui;

// Deterministic hash-based color and icon tinting for Auto-Tell sidebar tabs.
// Same tell partner (name+world) always produces the same color and icon across
// sessions. Pure string logic, no Dalamud dependency — testable without game refs.
internal static class AutoTellTabTint
{
    // Fallback for invalid input (empty name or world=0). White matches
    // TextPrimary default so the sidebar stays visually consistent.
    public const uint Fallback = 0xFFFFFFFFu;

    // 12 saturated mid-bright colors from the built-in theme pool, readable
    // on dark backgrounds. Collision risk is low at realistic 1-5 active tells.
    // RGBA format, matching ColourUtil.RgbaToAbgr convention.
    public static readonly IReadOnlyList<uint> Palette = new uint[]
    {
        0x00BED2FFu, // Arctic Cyan
        0xF97316FFu, // Ember Orange
        0xB585FFFFu, // Light Cosmic Purple
        0xE374E8FFu, // Bloom Magenta
        0x5DD39EFFu, // Mint Green
        0xF0AD4EFFu, // Warning Yellow
        0xE85C6AFFu, // Coral
        0x5CB85CFFu, // Status Green
        0x6278FFFFu, // Bloom Blue
        0xC9982EFFu, // Warm Gold
        0x9CCB7CFFu, // Soft Sage
        0xE85D04FFu, // Deep Ember
    };

    public static uint For(string name, uint world)
    {
        if (string.IsNullOrEmpty(name) || world == 0)
            return Fallback;

        return Palette[(int)(StableHash($"{name}@{world}") % Palette.Count)];
    }

    // 7 visually distinct FA glyphs that make sense in a tell context.
    // Excludes cog/comment/users — those read as system or group tabs.
    public static readonly IReadOnlyList<string> IconPool = new[]
    {
        "envelope",
        "star",
        "heart",
        "bell",
        "bookmark",
        "flag",
        "fire",
    };

    // "envelope" matches the tell context better than the old hardcoded "clock".
    public const string IconFallback = "envelope";

    public static string IconFor(string name, uint world)
    {
        if (string.IsNullOrEmpty(name) || world == 0)
            return IconFallback;

        // Reversed key ("world@name") gives icon and color independent variation
        // so the same tell partner doesn't always get the same color+icon pair.
        // 7 icons x 12 colors = 84 distinct combinations.
        return IconPool[(int)(StableHash($"{world}@{name}") % IconPool.Count)];
    }

    // FNV-1a, not string.GetHashCode. The header of this file promises the same
    // partner produces the same colour "across sessions", and GetHashCode cannot
    // keep that: .NET salts string hashing per process, so every game start
    // would reshuffle every tell tab. The tests never caught it because they
    // only ever compared two calls inside one run.
    // Returns the full uint. The old int-based version masked off the sign bit
    // before its modulo; on a uint that mask only throws away a bit of entropy.
    private static uint StableHash(string key)
    {
        const uint offsetBasis = 2166136261u;
        const uint prime = 16777619u;

        var hash = offsetBasis;
        foreach (var b in System.Text.Encoding.UTF8.GetBytes(key))
        {
            hash ^= b;
            hash *= prime;
        }

        // Avalanche step, and not optional. FNV-1a alone leaves the low bits
        // correlated for keys that differ only slightly, and the caller takes
        // exactly those bits with a modulo -- a probe over 144 near-identical
        // keys reached only 6 of the 12 colours. With fmix32 it reaches all 12.
        hash ^= hash >> 16;
        hash *= 0x7feb352du;
        hash ^= hash >> 15;
        hash *= 0x846ca68bu;
        hash ^= hash >> 16;

        return hash;
    }
}