using System.Collections.Immutable;
using System.Text;
using System.Text.RegularExpressions;

namespace StellaOps.Scanner.Analyzers.Lang.Ruby.Internal;

internal static class RubyManifestParser
{
    private static readonly Regex GemLineRegex = new(@"^\s*gem\s+(?<quote>['""])(?<name>[^'""]+)\k<quote>(?<args>.*)$", RegexOptions.Compiled);
    private static readonly Regex GroupStartRegex = new(@"^\s*group\s+(?<args>.+?)\s+do\b", RegexOptions.Compiled);
    private static readonly Regex InlineGroupRegex = new(@"(group|groups)\s*[:=]>\s*(?<value>\[.*?\]|:[A-Za-z0-9_]+)|(group|groups):\s*(?<typed>\[.*?\]|:[A-Za-z0-9_]+)", RegexOptions.Compiled);
    private static readonly Regex SymbolRegex = new(@":(?<symbol>[A-Za-z0-9_]+)", RegexOptions.Compiled);
    private static readonly Regex StringRegex = new(@"['""](?<value>[A-Za-z0-9_\-]+)['""]", RegexOptions.Compiled);

    public static IReadOnlyDictionary<string, IReadOnlyCollection<string>> ParseGroups(string manifestPath)
    {
        if (string.IsNullOrWhiteSpace(manifestPath) || !File.Exists(manifestPath))
        {
            return ImmutableDictionary<string, IReadOnlyCollection<string>>.Empty;
        }

        try
        {
            return ParseInternal(manifestPath);
        }
        catch (IOException)
        {
            return ImmutableDictionary<string, IReadOnlyCollection<string>>.Empty;
        }
        catch (UnauthorizedAccessException)
        {
            return ImmutableDictionary<string, IReadOnlyCollection<string>>.Empty;
        }
    }

    private static IReadOnlyDictionary<string, IReadOnlyCollection<string>> ParseInternal(string manifestPath)
    {
        var groupStack = new Stack<HashSet<string>>();
        var mapping = new Dictionary<string, HashSet<string>>(StringComparer.OrdinalIgnoreCase);

        foreach (var rawLine in File.ReadLines(manifestPath))
        {
            var line = StripComment(rawLine);
            if (string.IsNullOrWhiteSpace(line))
            {
                continue;
            }

            if (TryBeginGroup(line, groupStack))
            {
                continue;
            }

            if (IsGroupEnd(line) && groupStack.Count > 0)
            {
                groupStack.Pop();
                continue;
            }

            if (!TryParseGem(line, out var gemName, out var inlineGroups))
            {
                continue;
            }

            if (!mapping.TryGetValue(gemName, out var groups))
            {
                groups = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
                mapping[gemName] = groups;
            }

            if (groupStack.Count > 0)
            {
                foreach (var group in groupStack.Peek())
                {
                    groups.Add(group);
                }
            }

            foreach (var inline in inlineGroups)
            {
                groups.Add(inline);
            }

            if (groups.Count == 0)
            {
                groups.Add("default");
            }
        }

        return mapping.ToDictionary(
            static pair => pair.Key,
            static pair => (IReadOnlyCollection<string>)pair.Value
                .OrderBy(static value => value, StringComparer.OrdinalIgnoreCase)
                .ToArray(),
            StringComparer.OrdinalIgnoreCase);
    }

    private static bool TryBeginGroup(string line, Stack<HashSet<string>> stack)
    {
        var match = GroupStartRegex.Match(line);
        if (!match.Success)
        {
            return false;
        }

        var parsedGroups = ParseGroupTokens(match.Groups["args"].Value);
        var inherited = stack.Count > 0
            ? new HashSet<string>(stack.Peek(), StringComparer.OrdinalIgnoreCase)
            : new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        if (parsedGroups.Count == 0 && inherited.Count == 0)
        {
            inherited.Add("default");
        }

        foreach (var group in parsedGroups)
        {
            inherited.Add(group);
        }

        stack.Push(inherited);
        return true;
    }

    private static IReadOnlyCollection<string> ParseGroupTokens(string tokens)
    {
        if (string.IsNullOrWhiteSpace(tokens))
        {
            return Array.Empty<string>();
        }

        var normalized = tokens.Trim().Trim('(', ')');
        var results = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        foreach (var segment in normalized.Split(',', StringSplitOptions.RemoveEmptyEntries))
        {
            var token = segment.Trim();
            if (token.Length == 0)
            {
                continue;
            }

            var symbolMatch = SymbolRegex.Match(token);
            if (symbolMatch.Success)
            {
                results.Add(symbolMatch.Groups["symbol"].Value);
                continue;
            }

            var stringMatch = StringRegex.Match(token);
            if (stringMatch.Success)
            {
                results.Add(stringMatch.Groups["value"].Value);
            }
        }

        return results;
    }

    private static bool TryParseGem(string line, out string name, out IReadOnlyCollection<string> inlineGroups)
    {
        var match = GemLineRegex.Match(line);
        if (!match.Success)
        {
            name = string.Empty;
            inlineGroups = Array.Empty<string>();
            return false;
        }

        name = match.Groups["name"].Value.Trim();
        inlineGroups = ExtractInlineGroups(match.Groups["args"].Value);
        return !string.IsNullOrWhiteSpace(name);
    }

    private static IReadOnlyCollection<string> ExtractInlineGroups(string args)
    {
        if (string.IsNullOrWhiteSpace(args))
        {
            return Array.Empty<string>();
        }

        var groups = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        foreach (Match match in InlineGroupRegex.Matches(args))
        {
            if (!match.Success)
            {
                continue;
            }

            var valueGroup = match.Groups["value"].Success ? match.Groups["value"] : match.Groups["typed"];
            if (!valueGroup.Success)
            {
                continue;
            }

            var value = valueGroup.Value;
            if (string.IsNullOrWhiteSpace(value))
            {
                continue;
            }

            foreach (Match symbol in SymbolRegex.Matches(value))
            {
                if (symbol.Success)
                {
                    groups.Add(symbol.Groups["symbol"].Value);
                }
            }

            foreach (Match str in StringRegex.Matches(value))
            {
                if (str.Success)
                {
                    groups.Add(str.Groups["value"].Value);
                }
            }
        }

        return groups;
    }

    private static bool IsGroupEnd(string line)
    {
        var trimmed = line.Trim();
        if (!trimmed.StartsWith("end", StringComparison.Ordinal))
        {
            return false;
        }

        return trimmed.Length == 3 || char.IsWhiteSpace(trimmed[3]) || trimmed[3] == '#';
    }

    private static string StripComment(string line)
    {
        if (string.IsNullOrEmpty(line))
        {
            return string.Empty;
        }

        var builder = new StringBuilder(line.Length);
        var inSingle = false;
        var inDouble = false;

        for (var i = 0; i < line.Length; i++)
        {
            var ch = line[i];

            if (ch == '\'' && !inDouble)
            {
                inSingle = !inSingle;
            }
            else if (ch == '"' && !inSingle)
            {
                inDouble = !inDouble;
            }

            if (ch == '#' && !inSingle && !inDouble)
            {
                break;
            }

            builder.Append(ch);
        }

        return builder.ToString();
    }
}