YouTube-Manager/Manager.YouTube/Parsers/HtmlParser.cs

using System.Text.Json.Nodes;
using DotBased.Monads;
using HtmlAgilityPack;
using Manager.YouTube.Models.Parser;

namespace Manager.YouTube.Parsers;

public static class HtmlParser
{
    public static Result<(string, bool)> GetStateJson(string html)
    {
        if (string.IsNullOrWhiteSpace(html))
        {
            return ResultError.Fail("html cannot be empty!");
        }

        var htmlDocument = new HtmlDocument();
        htmlDocument.LoadHtml(html);

        const string setFunction = "ytcfg.set({";
        var scriptNode = htmlDocument.DocumentNode.SelectSingleNode($"//script[contains(., '{setFunction}')]");
        if (string.IsNullOrWhiteSpace(scriptNode.InnerText))
            return ResultError.Fail($"Could not find {setFunction} in html script nodes!");
        
        var json = ExtractJson(scriptNode.InnerText, "ytcfg.set(");

        if (string.IsNullOrWhiteSpace(json))
        {
            return ResultError.Fail($"Could not find {setFunction} in html script nodes!");
        }

        var isPremiumUser = html.Contains("logo-type=\"YOUTUBE_PREMIUM_LOGO\"", StringComparison.OrdinalIgnoreCase);

        return (json, isPremiumUser);
    }

    public static Result<YouTubeVideoData> GetVideoDataFromHtml(string html)
    {
        if (string.IsNullOrWhiteSpace(html))
        {
            return ResultError.Fail("html cannot be empty!");
        }
        var htmlDocument = new HtmlDocument();
        htmlDocument.LoadHtml(html);

        const string initialYoutubeData = "var ytInitialPlayerResponse = {";
        var initialPlayerDataNode = htmlDocument.DocumentNode.SelectSingleNode($"//script[contains(., '{initialYoutubeData}')]");
        if (string.IsNullOrWhiteSpace(initialPlayerDataNode.InnerText))
        {
            return ResultError.Fail("Could not find {initialPlayerData} in html script nodes!");
        }
        var initialPlayerDataString = ExtractJson(initialPlayerDataNode.InnerText, "var ytInitialPlayerResponse = ");
        if (string.IsNullOrWhiteSpace(initialPlayerDataString))
        {
            return ResultError.Fail("Failed to extract initial player date from JSON.");
        }
        var parsedPlayerInitialData = JsonNode.Parse(initialPlayerDataString);
        
        const string initialData = "var ytInitialData = {";
        var initialDataNode = htmlDocument.DocumentNode.SelectSingleNode($"//script[contains(., '{initialData}')]");
        if (string.IsNullOrWhiteSpace(initialDataNode.InnerText))
        {
            return ResultError.Fail("Could not find {initialData} in html script nodes!");
        }
        
        var initialDataJsonString = ExtractJson(initialDataNode.InnerText, "var ytInitialData = ");
        if (string.IsNullOrWhiteSpace(initialDataJsonString))
        {
            return ResultError.Fail("Failed to extract initial player date from JSON.");
        }
        var parsedInitialData = JsonNode.Parse(initialDataJsonString);

        try
        {
            return new YouTubeVideoData
            {
                YouTubePlayerData = parsedPlayerInitialData?.AsObject(),
                YouTubeInitialData = parsedInitialData?.AsObject()
            };
        }
        catch (Exception e)
        {
            return ResultError.Error(e, "Could not parse youtube player data.");
        }
    }

    static string? ExtractJson(string input, string marker)
    {
        var start = input.IndexOf(marker, StringComparison.Ordinal);
        if (start < 0) return null;

        start += marker.Length;

        // Skip until first '{'
        while (start < input.Length && input[start] != '{')
            start++;

        if (start >= input.Length) return null;

        var depth = 0;
        var i = start;

        for (; i < input.Length; i++)
        {
            if (input[i] == '{') depth++;
            else if (input[i] == '}')
            {
                depth--;
                if (depth != 0) continue;
                i++;
                break;
            }
        }

        return input[start..i];
    }
}