using System;
using System.Collections.Generic;
using System.Buffers.Binary;
using System.IO;
using System.Threading;
using Microsoft.Data.Sqlite;
using Microsoft.Extensions.Logging;
using StellaOps.Scanner.Analyzers.OS.Rpm.Internal;

namespace StellaOps.Scanner.Analyzers.OS.Rpm;

internal sealed class RpmDatabaseReader : IRpmDatabaseReader
{
    private readonly ILogger _logger;
    private readonly RpmHeaderParser _parser = new();

    public RpmDatabaseReader(ILogger logger)
    {
        _logger = logger;
    }

    public IReadOnlyList<RpmHeader> ReadHeaders(string rootPath, CancellationToken cancellationToken)
    {
        var sqlitePath = ResolveSqlitePath(rootPath);
        if (sqlitePath is null)
        {
            _logger.LogWarning("rpmdb.sqlite not found under root {RootPath}; attempting legacy rpmdb fallback.", rootPath);
            return ReadLegacyHeaders(rootPath, cancellationToken);
        }

        var headers = new List<RpmHeader>();
        try
        {
            var connectionString = new SqliteConnectionStringBuilder
            {
                DataSource = sqlitePath,
                Mode = SqliteOpenMode.ReadOnly,
            }.ToString();

            using var connection = new SqliteConnection(connectionString);
            connection.Open();

            using var command = connection.CreateCommand();
            command.CommandText = "SELECT * FROM Packages";

            using var reader = command.ExecuteReader();
            while (reader.Read())
            {
                cancellationToken.ThrowIfCancellationRequested();
                var blob = ExtractHeaderBlob(reader);
                if (blob is null)
                {
                    continue;
                }

                try
                {
                    headers.Add(_parser.Parse(blob));
                }
                catch (Exception ex)
                {
                    _logger.LogWarning(ex, "Failed to parse RPM header record (pkgKey={PkgKey}).", TryGetPkgKey(reader));
                }
            }
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Unable to read rpmdb.sqlite at {Path}.", sqlitePath);
            return ReadLegacyHeaders(rootPath, cancellationToken);
        }

        if (headers.Count == 0)
        {
            return ReadLegacyHeaders(rootPath, cancellationToken);
        }

        return headers;
    }

    private static string? ResolveSqlitePath(string rootPath)
    {
        var candidates = new[]
        {
            Path.Combine(rootPath, "var", "lib", "rpm", "rpmdb.sqlite"),
            Path.Combine(rootPath, "usr", "lib", "sysimage", "rpm", "rpmdb.sqlite"),
        };

        foreach (var candidate in candidates)
        {
            if (File.Exists(candidate))
            {
                return candidate;
            }
        }

        return null;
    }

    private IReadOnlyList<RpmHeader> ReadLegacyHeaders(string rootPath, CancellationToken cancellationToken)
    {
        var packagesPath = ResolveLegacyPackagesPath(rootPath);
        if (packagesPath is null)
        {
            _logger.LogWarning("Legacy rpmdb Packages file not found under root {RootPath}; rpm analyzer will skip.", rootPath);
            return Array.Empty<RpmHeader>();
        }

        byte[] data;
        try
        {
            data = File.ReadAllBytes(packagesPath);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Unable to read legacy rpmdb Packages file at {Path}.", packagesPath);
            return Array.Empty<RpmHeader>();
        }

        // Detect BerkeleyDB format and use appropriate extraction method
        if (BerkeleyDbReader.IsBerkeleyDb(data))
        {
            _logger.LogDebug("Detected BerkeleyDB format for rpmdb at {Path}; using BDB extraction.", packagesPath);
            return ReadBerkeleyDbHeaders(data, packagesPath, cancellationToken);
        }

        // Fall back to raw RPM header scanning for non-BDB files
        return ReadRawRpmHeaders(data, packagesPath, cancellationToken);
    }

    private IReadOnlyList<RpmHeader> ReadBerkeleyDbHeaders(byte[] data, string packagesPath, CancellationToken cancellationToken)
    {
        var results = new List<RpmHeader>();
        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        // Try page-aware extraction first
        var headerBlobs = BerkeleyDbReader.ExtractValues(data);
        if (headerBlobs.Count == 0)
        {
            // Fall back to overflow-aware extraction for fragmented data
            headerBlobs = BerkeleyDbReader.ExtractValuesWithOverflow(data);
        }

        foreach (var blob in headerBlobs)
        {
            cancellationToken.ThrowIfCancellationRequested();

            try
            {
                var header = _parser.Parse(blob);
                var key = $"{header.Name}::{header.Version}::{header.Release}::{header.Architecture}";
                if (seen.Add(key))
                {
                    results.Add(header);
                }
            }
            catch (Exception ex)
            {
                _logger.LogDebug(ex, "Failed to parse RPM header blob from BerkeleyDB.");
            }
        }

        if (results.Count == 0)
        {
            _logger.LogWarning("No RPM headers parsed from BerkeleyDB rpmdb at {Path}.", packagesPath);
        }
        else
        {
            _logger.LogDebug("Extracted {Count} RPM headers from BerkeleyDB rpmdb at {Path}.", results.Count, packagesPath);
        }

        return results;
    }

    private IReadOnlyList<RpmHeader> ReadRawRpmHeaders(byte[] data, string packagesPath, CancellationToken cancellationToken)
    {
        var headerBlobs = new List<byte[]>();

        if (BerkeleyDbReader.IsBerkeleyDb(data))
        {
            headerBlobs.AddRange(BerkeleyDbReader.ExtractValues(data));
            if (headerBlobs.Count == 0)
            {
                headerBlobs.AddRange(BerkeleyDbReader.ExtractValuesWithOverflow(data));
            }
        }
        else
        {
            headerBlobs.AddRange(ExtractRpmHeadersFromRaw(data, cancellationToken));
        }

        if (headerBlobs.Count == 0)
        {
            _logger.LogWarning("No RPM headers parsed from legacy rpmdb Packages at {Path}.", packagesPath);
            return Array.Empty<RpmHeader>();
        }

        var results = new List<RpmHeader>(headerBlobs.Count);
        var seen = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        foreach (var blob in headerBlobs)
        {
            cancellationToken.ThrowIfCancellationRequested();

            try
            {
                var header = _parser.Parse(blob);
                var key = $"{header.Name}::{header.Version}::{header.Release}::{header.Architecture}";
                if (seen.Add(key))
                {
                    results.Add(header);
                }
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Failed to parse RPM header from legacy rpmdb blob.");
            }
        }

        return results;
    }

    private static string? ResolveLegacyPackagesPath(string rootPath)
    {
        var candidates = new[]
        {
            Path.Combine(rootPath, "var", "lib", "rpm", "Packages"),
            Path.Combine(rootPath, "usr", "lib", "sysimage", "rpm", "Packages"),
        };

        foreach (var candidate in candidates)
        {
            if (File.Exists(candidate))
            {
                return candidate;
            }
        }

        return null;
    }

    private static IEnumerable<byte[]> ExtractRpmHeadersFromRaw(byte[] data, CancellationToken cancellationToken)
    {
        var magicBytes = new byte[] { 0x8e, 0xad, 0xe8, 0xab };
        var seenOffsets = new HashSet<int>();
        var offset = 0;

        while (offset <= data.Length - magicBytes.Length)
        {
            cancellationToken.ThrowIfCancellationRequested();
            var candidateIndex = FindNextMagic(data, magicBytes, offset);
            if (candidateIndex < 0)
            {
                yield break;
            }

            if (!seenOffsets.Add(candidateIndex))
            {
                offset = candidateIndex + 1;
                continue;
            }

            if (TryExtractHeaderSlice(data, candidateIndex, out var slice))
            {
                yield return slice;
            }

            offset = candidateIndex + 1;
        }
    }

    private static bool TryExtractHeaderSlice(byte[] data, int offset, out byte[] slice)
    {
        slice = Array.Empty<byte>();

        if (offset + 16 >= data.Length)
        {
            return false;
        }

        try
        {
            var span = data.AsSpan(offset);
            var indexCount = BinaryPrimitives.ReadInt32BigEndian(span.Slice(8, 4));
            var storeSize = BinaryPrimitives.ReadInt32BigEndian(span.Slice(12, 4));

            if (indexCount <= 0 || storeSize <= 0)
            {
                return false;
            }

            var totalLength = 16 + (indexCount * 16) + storeSize;
            if (totalLength <= 0 || offset + totalLength > data.Length)
            {
                return false;
            }

            slice = new byte[totalLength];
            Buffer.BlockCopy(data, offset, slice, 0, totalLength);
            return true;
        }
        catch
        {
            return false;
        }
    }

    private static int FindNextMagic(byte[] data, byte[] magic, int startIndex)
    {
        for (var i = startIndex; i <= data.Length - magic.Length; i++)
        {
            if (data[i] == magic[0] &&
                data[i + 1] == magic[1] &&
                data[i + 2] == magic[2] &&
                data[i + 3] == magic[3])
            {
                return i;
            }
        }

        return -1;
    }

    private static byte[]? ExtractHeaderBlob(SqliteDataReader reader)
    {
        for (var i = 0; i < reader.FieldCount; i++)
        {
            if (reader.GetFieldType(i) == typeof(byte[]))
            {
                return reader.GetFieldValue<byte[]>(i);
            }
        }

        return null;
    }

    private static object? TryGetPkgKey(SqliteDataReader reader)
    {
        try
        {
            var ordinal = reader.GetOrdinal("pkgKey");
            if (ordinal >= 0)
            {
                return reader.GetValue(ordinal);
            }
        }
        catch
        {
        }

        return null;
    }
}