using System.Text.RegularExpressions;
using BlueLaminate.Scraper.Wiki;
using HtmlAgilityPack;

namespace BlueLaminate.Scraper.Weapons;

/// <summary>
/// Scrapes the CS2 weapon catalogue from the wiki's "Weapons" page.
///
/// Layout: the page has one "tabber" per weapon category, each immediately
/// preceded by a section heading (the category / Type). Inside each tabber the
/// "Global Offensive &amp; Counter-Strike 2" tab holds a gallery of captions —
/// one per weapon, optionally suffixed with "(CT)" or "(T)" for team-locked
/// weapons.
/// </summary>
public sealed class WeaponWikiScraper
{
    private const string Page = "Weapons";
    private const string Cs2TabHash = "Global_Offensive_&_Counter-Strike_2";

    // Matches a trailing "(CT)" / "(T)" team annotation, capturing the team.
    private static readonly Regex TeamAnnotation =
        new(@"\s*\((CT|T)\)\s*$", RegexOptions.Compiled);

    // The wiki labels the default knife "Stock Knife"; drop the prefix.
    private static readonly Regex StockPrefix =
        new(@"^Stock\s+", RegexOptions.Compiled);

    private readonly WikiPageFetcher _fetcher;

    public WeaponWikiScraper(WikiPageFetcher fetcher) => _fetcher = fetcher;

    public async Task<IReadOnlyList<ScrapedWeapon>> ScrapeAsync(CancellationToken ct = default)
    {
        var doc = await _fetcher.LoadAsync(Page, ct);

        // Headings and tabbers in document order so each tabber inherits the
        // most recent heading as its category.
        var nodes = doc.DocumentNode.SelectNodes(
            "//h2 | //h3 | //h4 | "
            + "//div[contains(concat(' ', normalize-space(@class), ' '), ' tabber ')]");

        var aggregator = new WeaponAggregator();
        string? currentType = null;

        if (nodes is not null)
        {
            foreach (var node in nodes)
            {
                if (node.Name is "h2" or "h3" or "h4")
                {
                    currentType = HeadingText(node);
                    continue;
                }

                if (currentType is null)
                    continue;

                foreach (var caption in Cs2Captions(node))
                    aggregator.Add(caption, currentType);
            }
        }

        return aggregator.Build();
    }

    /// <summary>Caption texts from the CS2 tab of a single tabber, if present.</summary>
    private static IEnumerable<string> Cs2Captions(HtmlNode tabber)
    {
        var tabs = tabber.SelectNodes(
            ".//li[contains(concat(' ', normalize-space(@class), ' '), ' wds-tabs__tab ')]");
        if (tabs is null)
            yield break;

        var index = -1;
        for (var i = 0; i < tabs.Count; i++)
        {
            // HtmlAgilityPack returns attribute values un-decoded, and the wiki
            // entity-encodes the "&" in this hash (&amp;).
            var hash = HtmlEntity.DeEntitize(tabs[i].GetAttributeValue("data-hash", string.Empty));
            if (hash == Cs2TabHash)
            {
                index = i;
                break;
            }
        }

        if (index < 0)
            yield break;

        var contents = tabber.SelectNodes(
            ".//div[contains(concat(' ', normalize-space(@class), ' '), ' wds-tab__content ')]");
        if (contents is null || index >= contents.Count)
            yield break;

        var captions = contents[index].SelectNodes(
            ".//div[contains(concat(' ', normalize-space(@class), ' '), ' lightbox-caption ')]");
        if (captions is null)
            yield break;

        foreach (var caption in captions)
            yield return WikiText.Normalize(caption.InnerText);
    }

    private static string HeadingText(HtmlNode heading)
    {
        var headline = heading.SelectSingleNode(
            ".//span[contains(concat(' ', normalize-space(@class), ' '), ' mw-headline ')]");
        return WikiText.Normalize((headline ?? heading).InnerText);
    }

    /// <summary>
    /// Collapses the per-caption rows into one weapon per name, tracking which
    /// teams it appeared for so a weapon shown as both "(CT)" and "(T)" (or with
    /// no annotation) resolves to "Both".
    /// </summary>
    private sealed class WeaponAggregator
    {
        private sealed class Entry
        {
            public required string Type { get; init; }
            public bool SawCt;
            public bool SawT;
            public bool SawUnannotated;
        }

        private readonly Dictionary<string, Entry> _byName = new();
        private readonly List<string> _order = new();

        public void Add(string caption, string type)
        {
            if (string.IsNullOrEmpty(caption))
                return;

            var match = TeamAnnotation.Match(caption);
            var name = TeamAnnotation.Replace(caption, string.Empty);
            name = StockPrefix.Replace(name, string.Empty).Trim();
            if (name.Length == 0)
                return;

            if (!_byName.TryGetValue(name, out var entry))
            {
                entry = new Entry { Type = type };
                _byName[name] = entry;
                _order.Add(name);
            }

            if (!match.Success)
                entry.SawUnannotated = true;
            else if (match.Groups[1].Value == "CT")
                entry.SawCt = true;
            else
                entry.SawT = true;
        }

        public IReadOnlyList<ScrapedWeapon> Build()
        {
            var result = new List<ScrapedWeapon>(_order.Count);
            foreach (var name in _order)
            {
                var e = _byName[name];
                var team =
                    e.SawUnannotated || (e.SawCt && e.SawT) ? "Both"
                    : e.SawCt ? "CT"
                    : e.SawT ? "T"
                    : "Both";
                result.Add(new ScrapedWeapon(name, e.Type, team));
            }
            return result;
        }
    }
}