using System.Text.RegularExpressions;
using StellaOps.BinaryIndex.Core.Models;
using StellaOps.BinaryIndex.FixIndex.Models;

namespace StellaOps.BinaryIndex.FixIndex.Parsers;

/// <summary>
/// Parses RPM spec file changelog sections for CVE mentions.
/// </summary>
/// <remarks>
/// RPM changelog format:
/// %changelog
/// * Mon Jan 01 2024 Packager &lt;email&gt; - 1.2.3-4
/// - Fix CVE-2024-1234
/// </remarks>
public sealed partial class RpmChangelogParser : IChangelogParser
{
    [GeneratedRegex(@"\bCVE-\d{4}-\d{4,7}\b", RegexOptions.Compiled)]
    private static partial Regex CvePatternRegex();

    [GeneratedRegex(@"^\*\s+\w{3}\s+\w{3}\s+\d{1,2}\s+\d{4}\s+(.+?)\s+-\s+(\S+)", RegexOptions.Compiled)]
    private static partial Regex EntryHeaderPatternRegex();

    [GeneratedRegex(@"^%changelog\s*$", RegexOptions.Compiled | RegexOptions.IgnoreCase)]
    private static partial Regex ChangelogStartPatternRegex();

    [GeneratedRegex(@"^%\w+", RegexOptions.Compiled)]
    private static partial Regex SectionStartPatternRegex();

    /// <summary>
    /// Parses the top entry of an RPM spec changelog for CVE mentions.
    /// </summary>
    public IEnumerable<FixEvidence> ParseTopEntry(
        string specContent,
        string distro,
        string release,
        string sourcePkg)
    {
        if (string.IsNullOrWhiteSpace(specContent))
            yield break;

        var lines = specContent.Split('\n');
        var inChangelog = false;
        var inFirstEntry = false;
        string? currentVersion = null;
        var entryLines = new List<string>();

        foreach (var line in lines)
        {
            // Detect %changelog start
            if (ChangelogStartPatternRegex().IsMatch(line))
            {
                inChangelog = true;
                continue;
            }

            if (!inChangelog)
                continue;

            // Exit on new section (e.g., %files, %prep)
            if (SectionStartPatternRegex().IsMatch(line) && !ChangelogStartPatternRegex().IsMatch(line))
                break;

            // Detect entry header: * Day Mon DD YYYY Author <email> - version
            var headerMatch = EntryHeaderPatternRegex().Match(line);
            if (headerMatch.Success)
            {
                if (inFirstEntry)
                {
                    // We've hit the second entry, stop processing
                    break;
                }

                inFirstEntry = true;
                currentVersion = headerMatch.Groups[2].Value;
                entryLines.Add(line);
                continue;
            }

            if (inFirstEntry)
            {
                entryLines.Add(line);
            }
        }

        if (currentVersion == null || entryLines.Count == 0)
            yield break;

        var entryText = string.Join('\n', entryLines);
        var cves = CvePatternRegex().Matches(entryText)
            .Select(m => m.Value)
            .Distinct()
            .ToList();

        foreach (var cve in cves)
        {
            yield return new FixEvidence
            {
                Distro = distro,
                Release = release,
                SourcePkg = sourcePkg,
                CveId = cve,
                State = FixState.Fixed,
                FixedVersion = currentVersion,
                Method = FixMethod.Changelog,
                Confidence = 0.75m, // RPM changelogs are less structured than Debian
                Evidence = new ChangelogEvidence
                {
                    File = "*.spec",
                    Version = currentVersion,
                    Excerpt = entryText.Length > 2000 ? entryText[..2000] : entryText,
                    LineNumber = null
                },
                CreatedAt = DateTimeOffset.UtcNow
            };
        }
    }

    /// <summary>
    /// Parses the full RPM spec changelog for all CVE mentions with their versions.
    /// </summary>
    public IEnumerable<FixEvidence> ParseAllEntries(
        string specContent,
        string distro,
        string release,
        string sourcePkg)
    {
        if (string.IsNullOrWhiteSpace(specContent))
            yield break;

        var lines = specContent.Split('\n');
        var inChangelog = false;
        string? currentVersion = null;
        var currentEntry = new List<string>();

        foreach (var line in lines)
        {
            // Detect %changelog start
            if (ChangelogStartPatternRegex().IsMatch(line))
            {
                inChangelog = true;
                continue;
            }

            if (!inChangelog)
                continue;

            // Exit on new section
            if (SectionStartPatternRegex().IsMatch(line) && !ChangelogStartPatternRegex().IsMatch(line))
            {
                // Process last entry
                if (currentVersion != null && currentEntry.Count > 0)
                {
                    foreach (var fix in ExtractCvesFromEntry(currentEntry, currentVersion, distro, release, sourcePkg))
                        yield return fix;
                }
                break;
            }

            // Detect entry header
            var headerMatch = EntryHeaderPatternRegex().Match(line);
            if (headerMatch.Success)
            {
                // Process previous entry
                if (currentVersion != null && currentEntry.Count > 0)
                {
                    foreach (var fix in ExtractCvesFromEntry(currentEntry, currentVersion, distro, release, sourcePkg))
                        yield return fix;
                }

                currentVersion = headerMatch.Groups[2].Value;
                currentEntry = [line];
                continue;
            }

            if (currentVersion != null)
            {
                currentEntry.Add(line);
            }
        }

        // Process final entry if exists
        if (currentVersion != null && currentEntry.Count > 0)
        {
            foreach (var fix in ExtractCvesFromEntry(currentEntry, currentVersion, distro, release, sourcePkg))
                yield return fix;
        }
    }

    private IEnumerable<FixEvidence> ExtractCvesFromEntry(
        List<string> entryLines,
        string version,
        string distro,
        string release,
        string sourcePkg)
    {
        var entryText = string.Join('\n', entryLines);
        var cves = CvePatternRegex().Matches(entryText)
            .Select(m => m.Value)
            .Distinct();

        foreach (var cve in cves)
        {
            yield return new FixEvidence
            {
                Distro = distro,
                Release = release,
                SourcePkg = sourcePkg,
                CveId = cve,
                State = FixState.Fixed,
                FixedVersion = version,
                Method = FixMethod.Changelog,
                Confidence = 0.75m,
                Evidence = new ChangelogEvidence
                {
                    File = "*.spec",
                    Version = version,
                    Excerpt = entryText.Length > 2000 ? entryText[..2000] : entryText,
                    LineNumber = null
                },
                CreatedAt = DateTimeOffset.UtcNow
            };
        }
    }
}