using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using StellaOps.Scanner.Analyzers.OS;
using StellaOps.Scanner.Analyzers.OS.Abstractions;
using StellaOps.Scanner.Analyzers.OS.Analyzers;
using StellaOps.Scanner.Analyzers.OS.Helpers;

namespace StellaOps.Scanner.Analyzers.OS.Dpkg;

internal sealed class DpkgPackageAnalyzer : OsPackageAnalyzerBase
{
    private static readonly IReadOnlyList<OSPackageRecord> EmptyPackages =
        new ReadOnlyCollection<OSPackageRecord>(System.Array.Empty<OSPackageRecord>());

    private readonly DpkgStatusParser _parser = new();

    public DpkgPackageAnalyzer(ILogger<DpkgPackageAnalyzer> logger)
        : base(logger)
    {
    }

    public override string AnalyzerId => "dpkg";

    protected override ValueTask<IReadOnlyList<OSPackageRecord>> ExecuteCoreAsync(OSPackageAnalyzerContext context, CancellationToken cancellationToken)
    {
        var statusPath = Path.Combine(context.RootPath, "var", "lib", "dpkg", "status");
        if (!File.Exists(statusPath))
        {
            Logger.LogInformation("dpkg status file not found at {Path}; skipping analyzer.", statusPath);
            return ValueTask.FromResult<IReadOnlyList<OSPackageRecord>>(EmptyPackages);
        }

        using var stream = File.OpenRead(statusPath);
        var entries = _parser.Parse(stream, cancellationToken);

        var infoDirectory = Path.Combine(context.RootPath, "var", "lib", "dpkg", "info");
        var records = new List<OSPackageRecord>();

        foreach (var entry in entries)
        {
            if (!IsInstalled(entry.Status))
            {
                continue;
            }

            if (string.IsNullOrWhiteSpace(entry.Name) || string.IsNullOrWhiteSpace(entry.Version) || string.IsNullOrWhiteSpace(entry.Architecture))
            {
                continue;
            }

            var versionParts = PackageVersionParser.ParseDebianVersion(entry.Version);
            var sourceName = ParseSource(entry.Source) ?? entry.Name;
            var distribution = entry.Origin;
            if (distribution is null && entry.Metadata.TryGetValue("origin", out var originValue))
            {
                distribution = originValue;
            }
            distribution ??= "debian";

            var purl = PackageUrlBuilder.BuildDebian(distribution!, entry.Name, entry.Version, entry.Architecture);

            var vendorMetadata = new Dictionary<string, string?>(StringComparer.Ordinal)
            {
                ["source"] = entry.Source,
                ["homepage"] = entry.Homepage,
                ["maintainer"] = entry.Maintainer,
                ["origin"] = entry.Origin,
                ["priority"] = entry.Priority,
                ["section"] = entry.Section,
            };

            foreach (var kvp in entry.Metadata)
            {
                vendorMetadata[$"dpkg:{kvp.Key}"] = kvp.Value;
            }

            var dependencies = entry.Depends.Concat(entry.PreDepends).ToArray();
            var provides = entry.Provides.ToArray();

            var fileEvidence = BuildFileEvidence(infoDirectory, entry, cancellationToken);

            var cveHints = CveHintExtractor.Extract(entry.Description, string.Join(' ', dependencies), string.Join(' ', provides));

            var record = new OSPackageRecord(
                AnalyzerId,
                purl,
                entry.Name,
                versionParts.UpstreamVersion,
                entry.Architecture,
                PackageEvidenceSource.DpkgStatus,
                epoch: versionParts.Epoch,
                release: versionParts.Revision,
                sourcePackage: sourceName,
                license: entry.License,
                cveHints: cveHints,
                provides: provides,
                depends: dependencies,
                files: fileEvidence,
                vendorMetadata: vendorMetadata);

            records.Add(record);
        }

        records.Sort();
        return ValueTask.FromResult<IReadOnlyList<OSPackageRecord>>(records);
    }

    private static bool IsInstalled(string? status)
        => status?.Contains("install ok installed", System.StringComparison.OrdinalIgnoreCase) == true;

    private static string? ParseSource(string? sourceField)
    {
        if (string.IsNullOrWhiteSpace(sourceField))
        {
            return null;
        }

        var parts = sourceField.Split(' ', 2, System.StringSplitOptions.TrimEntries | System.StringSplitOptions.RemoveEmptyEntries);
        return parts.Length == 0 ? null : parts[0];
    }

    private static IReadOnlyList<OSPackageFileEvidence> BuildFileEvidence(string infoDirectory, DpkgPackageEntry entry, CancellationToken cancellationToken)
    {
        if (!Directory.Exists(infoDirectory))
        {
            return Array.Empty<OSPackageFileEvidence>();
        }

        var files = new Dictionary<string, FileEvidenceBuilder>(StringComparer.Ordinal);
        void EnsureFile(string path)
        {
            if (!files.TryGetValue(path, out _))
            {
                files[path] = new FileEvidenceBuilder(path);
            }
        }

        foreach (var conffile in entry.Conffiles)
        {
            var normalized = conffile.Path.Trim();
            if (string.IsNullOrWhiteSpace(normalized))
            {
                continue;
            }

            EnsureFile(normalized);
            files[normalized].IsConfig = true;
            if (!string.IsNullOrWhiteSpace(conffile.Checksum))
            {
                files[normalized].Digests["md5"] = conffile.Checksum.Trim();
            }
        }

        foreach (var candidate in GetInfoFileCandidates(entry.Name!, entry.Architecture!))
        {
            var listPath = Path.Combine(infoDirectory, candidate + ".list");
            if (File.Exists(listPath))
            {
                foreach (var line in File.ReadLines(listPath))
                {
                    cancellationToken.ThrowIfCancellationRequested();
                    var trimmed = line.Trim();
                    if (string.IsNullOrWhiteSpace(trimmed))
                    {
                        continue;
                    }

                    EnsureFile(trimmed);
                }
            }

            var confFilePath = Path.Combine(infoDirectory, candidate + ".conffiles");
            if (File.Exists(confFilePath))
            {
                foreach (var line in File.ReadLines(confFilePath))
                {
                    cancellationToken.ThrowIfCancellationRequested();
                    if (string.IsNullOrWhiteSpace(line))
                    {
                        continue;
                    }

                    var parts = line.Split(' ', System.StringSplitOptions.RemoveEmptyEntries | System.StringSplitOptions.TrimEntries);
                    if (parts.Length == 0)
                    {
                        continue;
                    }

                    var path = parts[0];
                    EnsureFile(path);
                    files[path].IsConfig = true;
                    if (parts.Length >= 2)
                    {
                        files[path].Digests["md5"] = parts[1];
                    }
                }
            }

            var md5sumsPath = Path.Combine(infoDirectory, candidate + ".md5sums");
            if (File.Exists(md5sumsPath))
            {
                foreach (var line in File.ReadLines(md5sumsPath))
                {
                    cancellationToken.ThrowIfCancellationRequested();
                    if (string.IsNullOrWhiteSpace(line))
                    {
                        continue;
                    }

                    var parts = line.Split(' ', 2, System.StringSplitOptions.RemoveEmptyEntries | System.StringSplitOptions.TrimEntries);
                    if (parts.Length != 2)
                    {
                        continue;
                    }

                    var hash = parts[0];
                    var path = parts[1];
                    EnsureFile(path);
                    files[path].Digests["md5"] = hash;
                }
            }
        }

        if (files.Count == 0)
        {
            return Array.Empty<OSPackageFileEvidence>();
        }

        var evidence = files.Values
            .Select(builder => builder.ToEvidence())
            .OrderBy(e => e)
            .ToArray();

        return new ReadOnlyCollection<OSPackageFileEvidence>(evidence);
    }

    private static IEnumerable<string> GetInfoFileCandidates(string packageName, string architecture)
    {
        yield return packageName + ":" + architecture;
        yield return packageName;
    }

    private sealed class FileEvidenceBuilder
    {
        public FileEvidenceBuilder(string path)
        {
            Path = path;
        }

        public string Path { get; }

        public bool IsConfig { get; set; }

        public Dictionary<string, string> Digests { get; } = new(StringComparer.OrdinalIgnoreCase);

        public OSPackageFileEvidence ToEvidence()
        {
            return new OSPackageFileEvidence(Path, isConfigFile: IsConfig, digests: Digests);
        }
    }
}