Nexus.Reader/src/NexusReader.UI.Shared/Services/PaywallParser.cs

using System;

namespace NexusReader.UI.Shared.Services;

/// <summary>
/// AOT-safe string parsing utility to isolate paywall teaser details without regex overhead.
/// </summary>
public static class PaywallParser
{
    public static bool TryParsePaywallTrigger(
        string rawText,
        out string displayTeaserText,
        out Guid lockedBookId,
        out string lockedBookTitle,
        out int localScore,
        out int globalScore)
    {
        displayTeaserText = rawText;
        lockedBookId = Guid.Empty;
        lockedBookTitle = string.Empty;
        localScore = 0;
        globalScore = 0;

        if (string.IsNullOrEmpty(rawText))
            return false;

        ReadOnlySpan<char> span = rawText.AsSpan();
        int tokenStartIndex = span.IndexOf("[PAYWALL_TRIGGER:");
        if (tokenStartIndex == -1)
            return false;

        displayTeaserText = span.Slice(0, tokenStartIndex).Trim().ToString();

        ReadOnlySpan<char> tokenContent = span.Slice(tokenStartIndex + "[PAYWALL_TRIGGER:".Length);
        int tokenEndIndex = tokenContent.IndexOf(']');
        if (tokenEndIndex == -1)
            return false;

        tokenContent = tokenContent.Slice(0, tokenEndIndex);

        int firstColonIdx = tokenContent.IndexOf(':');
        if (firstColonIdx == -1)
            return false;

        ReadOnlySpan<char> guidSpan = tokenContent.Slice(0, firstColonIdx);
        if (!Guid.TryParse(guidSpan, out lockedBookId))
            return false;

        ReadOnlySpan<char> remaining = tokenContent.Slice(firstColonIdx + 1);

        int lastColonIdx = remaining.LastIndexOf(':');
        if (lastColonIdx == -1)
            return false;

        ReadOnlySpan<char> globalScoreSpan = remaining.Slice(lastColonIdx + 1);
        if (!int.TryParse(globalScoreSpan, out globalScore))
            return false;

        remaining = remaining.Slice(0, lastColonIdx);

        int secondLastColonIdx = remaining.LastIndexOf(':');
        if (secondLastColonIdx == -1)
            return false;

        ReadOnlySpan<char> localScoreSpan = remaining.Slice(secondLastColonIdx + 1);
        if (!int.TryParse(localScoreSpan, out localScore))
            return false;

        lockedBookTitle = remaining.Slice(0, secondLastColonIdx).ToString();
        return true;
    }
}