HellionChat/HellionChat/Themes/ThemeJsonLoader.cs

using System.Text.Json;
using HellionChat.Util;

namespace HellionChat.Themes;

internal static class ThemeJsonLoader
{
    public const int SupportedSchemaVersion = 2;

    // Returns null when the file declares an older schemaVersion. Hard-cut
    // policy from the v2.x style refactor: v1 user themes are not migrated,
    // they're silently ignored so the loader stays free of legacy mapping
    // code. Any other malformed input still throws FormatException.
    public static Theme? LoadFromString(string json)
    {
        if (string.IsNullOrWhiteSpace(json))
            throw new FormatException("Theme JSON is empty");

        JsonDocument doc;
        try
        {
            doc = JsonDocument.Parse(json);
        }
        catch (JsonException ex)
        {
            throw new FormatException("Theme JSON is not valid JSON", ex);
        }

        using (doc)
        {
            var root = doc.RootElement;

            var schemaVersion = ReadInt(root, "schemaVersion");
            if (schemaVersion < SupportedSchemaVersion)
                return null;
            if (schemaVersion > SupportedSchemaVersion)
                throw new FormatException(
                    $"Unsupported schemaVersion {schemaVersion}; this build reads up to {SupportedSchemaVersion}"
                );

            var slug = ReadString(root, "slug");
            var name = ReadString(root, "name");
            var author = ReadString(root, "author");
            var description = ReadString(root, "description");

            var colors = ReadColors(root.GetProperty("colors"));
            var layout = ReadLayout(root.GetProperty("layout"));
            var typography = ReadTypography(root);

            ThemeChatColors? chatColors = null;
            if (
                root.TryGetProperty("chatChannels", out var ch)
                && ch.ValueKind == JsonValueKind.Object
            )
                chatColors = ReadChatColors(ch);

            return new Theme(
                slug,
                name,
                author,
                description,
                colors,
                layout,
                typography,
                IsBuiltIn: false,
                ChatColors: chatColors
            );
        }
    }

    private static ThemeChatColors ReadChatColors(JsonElement el)
    {
        var dict = new Dictionary<HellionChat.Code.ChatType, uint>();
        foreach (var prop in el.EnumerateObject())
        {
            // Property name is the ChatType name (e.g. "Say", "Tell"), value is hex like theme colours.
            // Unknown channel names are silently skipped for forward-compat with future SE channels.
            if (
                !Enum.TryParse<HellionChat.Code.ChatType>(
                    prop.Name,
                    ignoreCase: true,
                    out var channel
                )
            )
                continue;
            if (prop.Value.ValueKind != JsonValueKind.String)
                continue;
            var hex = prop.Value.GetString();
            if (string.IsNullOrWhiteSpace(hex))
                continue;
            dict[channel] = HellionChat.Util.ColourUtil.HexToRgba(hex);
        }
        return new ThemeChatColors(dict);
    }

    public static Theme? LoadFromFile(string path)
    {
        // FileShare.Read lets concurrent readers and well-behaved editors share
        // the handle; atomic-replace editors still raise IOException, caught upstream.
        using var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
        using var reader = new StreamReader(stream);
        var json = reader.ReadToEnd();
        return LoadFromString(json);
    }

    private static ThemeColors ReadColors(JsonElement el) =>
        new(
            PrimaryDark: ColourUtil.HexToRgba(ReadString(el, "primaryDark")),
            Primary: ColourUtil.HexToRgba(ReadString(el, "primary")),
            PrimaryLight: ColourUtil.HexToRgba(ReadString(el, "primaryLight")),
            PrimaryGlow: ColourUtil.HexToRgba(ReadString(el, "primaryGlow")),
            AccentDark: ColourUtil.HexToRgba(ReadString(el, "accentDark")),
            Accent: ColourUtil.HexToRgba(ReadString(el, "accent")),
            AccentLight: ColourUtil.HexToRgba(ReadString(el, "accentLight")),
            Identity: ColourUtil.HexToRgba(ReadString(el, "identity")),
            WindowBg: ColourUtil.HexToRgba(ReadString(el, "windowBg")),
            ChildBg: ColourUtil.HexToRgba(ReadString(el, "childBg")),
            FrameBg: ColourUtil.HexToRgba(ReadString(el, "frameBg")),
            Surface: ColourUtil.HexToRgba(ReadString(el, "surface")),
            SurfaceHover: ColourUtil.HexToRgba(ReadString(el, "surfaceHover")),
            Border: ColourUtil.HexToRgba(ReadString(el, "border")),
            TextPrimary: ColourUtil.HexToRgba(ReadString(el, "textPrimary")),
            TextMuted: ColourUtil.HexToRgba(ReadString(el, "textMuted")),
            TextDim: ColourUtil.HexToRgba(ReadString(el, "textDim")),
            StatusSuccess: ColourUtil.HexToRgba(ReadString(el, "statusSuccess")),
            StatusDanger: ColourUtil.HexToRgba(ReadString(el, "statusDanger")),
            StatusWarning: ColourUtil.HexToRgba(ReadString(el, "statusWarning")),
            StatusInfo: ColourUtil.HexToRgba(ReadString(el, "statusInfo"))
        );

    private static ThemeLayout ReadLayout(JsonElement el) =>
        new(
            WindowRounding: ReadFloat(el, "windowRounding"),
            ChildRounding: ReadFloat(el, "childRounding"),
            PopupRounding: ReadFloat(el, "popupRounding"),
            FrameRounding: ReadFloat(el, "frameRounding"),
            GrabRounding: ReadFloat(el, "grabRounding"),
            TabRounding: ReadFloat(el, "tabRounding"),
            ScrollbarRounding: ReadFloat(el, "scrollbarRounding"),
            WindowBorderSize: ReadFloat(el, "windowBorderSize"),
            FrameBorderSize: ReadFloat(el, "frameBorderSize")
        );

    // Optional in v2 — themes without a typography block default to the
    // record's parameterless construction (both override slots null). A
    // present-but-empty object also yields the default.
    private static ThemeTypography ReadTypography(JsonElement root)
    {
        if (!root.TryGetProperty("typography", out var el) || el.ValueKind != JsonValueKind.Object)
            return new ThemeTypography();

        return new ThemeTypography(
            OverrideGlobalFontSizePt: ReadOptionalFloat(el, "overrideGlobalFontSizePt"),
            OverrideSymbolsFontSizePt: ReadOptionalFloat(el, "overrideSymbolsFontSizePt")
        );
    }

    private static string ReadString(JsonElement el, string name)
    {
        if (!el.TryGetProperty(name, out var v) || v.ValueKind != JsonValueKind.String)
            throw new FormatException($"Theme JSON missing string property '{name}'");
        return v.GetString() ?? throw new FormatException($"Theme JSON property '{name}' is null");
    }

    private static int ReadInt(JsonElement el, string name)
    {
        if (!el.TryGetProperty(name, out var v) || v.ValueKind != JsonValueKind.Number)
            throw new FormatException($"Theme JSON missing number property '{name}'");
        return v.GetInt32();
    }

    private static float ReadFloat(JsonElement el, string name)
    {
        if (!el.TryGetProperty(name, out var v) || v.ValueKind != JsonValueKind.Number)
            throw new FormatException($"Theme JSON missing number property '{name}'");
        return (float)v.GetDouble();
    }

    private static float? ReadOptionalFloat(JsonElement el, string name)
    {
        if (!el.TryGetProperty(name, out var v))
            return null;
        if (v.ValueKind == JsonValueKind.Null)
            return null;
        if (v.ValueKind != JsonValueKind.Number)
            throw new FormatException($"Theme JSON property '{name}' must be a number or null");
        return (float)v.GetDouble();
    }
}