using System.Buffers.Binary;
using System.Text;
using System.Text.RegularExpressions;

namespace StellaOps.Scanner.Analyzers.Native;

/// <summary>
/// Scans native binaries for heuristic dependency indicators.
/// Detects dlopen/LoadLibrary strings, plugin configs, and ecosystem-specific hints.
/// </summary>
public static partial class HeuristicScanner
{
    // Common shared library patterns
    private static readonly Regex ElfSonamePattern = SonameRegex();
    private static readonly Regex WindowsDllPattern = DllRegex();
    private static readonly Regex MacOsDylibPattern = DylibRegex();

    // Plugin config patterns
    private static readonly string[] PluginConfigPatterns =
    [
        "plugins.conf",
        "plugin.conf",
        "plugins.json",
        "plugin.json",
        "plugins.xml",
        "plugin.xml",
        ".so.conf",
        "modules.conf",
        "extensions.conf",
    ];

    // Go-specific patterns
    private static readonly byte[] GoCgoImportMarker = "cgo_import_dynamic"u8.ToArray();
    private static readonly byte[] GoCgoImportStatic = "cgo_import_static"u8.ToArray();

    // Rust-specific patterns
    private static readonly byte[] RustPanicPrefix = "panicked at"u8.ToArray();
    private static readonly byte[] RustCratePattern = ".rlib"u8.ToArray();

    /// <summary>
    /// Scans a binary stream for heuristic dependency indicators.
    /// </summary>
    public static HeuristicScanResult Scan(Stream stream, NativeFormat format)
    {
        ArgumentNullException.ThrowIfNull(stream);

        using var buffer = new MemoryStream();
        stream.CopyTo(buffer);
        var data = buffer.ToArray();

        var edges = new List<HeuristicEdge>();
        var pluginConfigs = new List<string>();

        // Extract printable strings and analyze them
        var strings = ExtractStrings(data, minLength: 4);

        foreach (var (str, offset) in strings)
        {
            // Check for dynamic library loading patterns
            AnalyzeDynamicLoadingString(str, offset, format, edges);

            // Check for plugin config references
            AnalyzePluginConfig(str, pluginConfigs);
        }

        // Check for Go-specific patterns
        ScanForGoPatterns(data, edges);

        // Check for Rust-specific patterns
        ScanForRustPatterns(data, edges);

        // Deduplicate edges by library name
        var uniqueEdges = edges
            .GroupBy(e => (e.LibraryName, e.ReasonCode))
            .Select(g => g.OrderByDescending(e => e.Confidence).First())
            .ToList();

        return new HeuristicScanResult(uniqueEdges, pluginConfigs.Distinct().ToList());
    }

    /// <summary>
    /// Scans specifically for dlopen/LoadLibrary style strings.
    /// </summary>
    public static IReadOnlyList<HeuristicEdge> ScanForDynamicLoading(byte[] data, NativeFormat format)
    {
        var edges = new List<HeuristicEdge>();
        var strings = ExtractStrings(data, minLength: 4);

        foreach (var (str, offset) in strings)
        {
            AnalyzeDynamicLoadingString(str, offset, format, edges);
        }

        return edges
            .GroupBy(e => e.LibraryName)
            .Select(g => g.OrderByDescending(e => e.Confidence).First())
            .ToList();
    }

    /// <summary>
    /// Scans for plugin configuration file references.
    /// </summary>
    public static IReadOnlyList<string> ScanForPluginConfigs(byte[] data)
    {
        var configs = new List<string>();
        var strings = ExtractStrings(data, minLength: 6);

        foreach (var (str, _) in strings)
        {
            AnalyzePluginConfig(str, configs);
        }

        return configs.Distinct().ToList();
    }

    private static void AnalyzeDynamicLoadingString(
        string str,
        long offset,
        NativeFormat format,
        List<HeuristicEdge> edges)
    {
        // Check for format-appropriate library patterns
        switch (format)
        {
            case NativeFormat.Elf:
                if (ElfSonamePattern.IsMatch(str))
                {
                    var confidence = DetermineConfidence(str, isPathLike: str.Contains('/'));
                    edges.Add(new HeuristicEdge(
                        str,
                        HeuristicReasonCodes.StringDlopen,
                        confidence,
                        "ELF soname pattern",
                        offset));
                }
                break;

            case NativeFormat.Pe:
                if (WindowsDllPattern.IsMatch(str))
                {
                    var confidence = DetermineConfidence(str, isPathLike: str.Contains('\\') || str.Contains('/'));
                    edges.Add(new HeuristicEdge(
                        str,
                        HeuristicReasonCodes.StringLoadLibrary,
                        confidence,
                        "PE DLL pattern",
                        offset));
                }
                break;

            case NativeFormat.MachO:
                if (MacOsDylibPattern.IsMatch(str) || str.EndsWith(".dylib", StringComparison.OrdinalIgnoreCase))
                {
                    var confidence = DetermineConfidence(str, isPathLike: str.Contains('/'));
                    edges.Add(new HeuristicEdge(
                        str,
                        HeuristicReasonCodes.StringDlopen,
                        confidence,
                        "Mach-O dylib pattern",
                        offset));
                }
                break;
        }

        // Check for cross-platform dlopen-style patterns
        // Require at least 1 character between "lib" and ".so" (e.g., "libx.so" minimum)
        if (str.StartsWith("lib", StringComparison.Ordinal) && str.Contains(".so"))
        {
            var soIndex = str.IndexOf(".so", StringComparison.Ordinal);
            if (soIndex > 3 && !edges.Any(e => e.LibraryName == str))
            {
                var confidence = DetermineConfidence(str, isPathLike: str.Contains('/'));
                edges.Add(new HeuristicEdge(
                    str,
                    HeuristicReasonCodes.StringDlopen,
                    confidence,
                    "Generic soname pattern",
                    offset));
            }
        }
    }

    private static HeuristicConfidence DetermineConfidence(string libraryName, bool isPathLike)
    {
        // Higher confidence for path-like strings (more likely to be actual dlopen args)
        if (isPathLike)
        {
            return HeuristicConfidence.High;
        }

        // Medium confidence for standard naming conventions
        if (libraryName.StartsWith("lib", StringComparison.Ordinal) ||
            libraryName.EndsWith(".dll", StringComparison.OrdinalIgnoreCase) ||
            libraryName.EndsWith(".dylib", StringComparison.OrdinalIgnoreCase))
        {
            return HeuristicConfidence.Medium;
        }

        // Lower confidence for generic matches
        return HeuristicConfidence.Low;
    }

    private static void AnalyzePluginConfig(string str, List<string> configs)
    {
        foreach (var pattern in PluginConfigPatterns)
        {
            if (str.EndsWith(pattern, StringComparison.OrdinalIgnoreCase) ||
                str.Contains(pattern, StringComparison.OrdinalIgnoreCase))
            {
                // Extract just the filename if it's a path
                var filename = str;
                var lastSlash = str.LastIndexOfAny(['/', '\\']);
                if (lastSlash >= 0 && lastSlash < str.Length - 1)
                {
                    filename = str[(lastSlash + 1)..];
                }

                configs.Add(filename);
                break;
            }
        }
    }

    private static void ScanForGoPatterns(byte[] data, List<HeuristicEdge> edges)
    {
        // Look for cgo_import_dynamic markers
        var cgoImportOffsets = FindAllOccurrences(data, GoCgoImportMarker);
        foreach (var offset in cgoImportOffsets)
        {
            // Extract the library name following the marker
            var libraryName = ExtractFollowingString(data, offset + GoCgoImportMarker.Length);
            if (!string.IsNullOrEmpty(libraryName) && IsValidLibraryName(libraryName))
            {
                edges.Add(new HeuristicEdge(
                    libraryName,
                    HeuristicReasonCodes.GoCgoImport,
                    HeuristicConfidence.High,
                    "Go CGO import directive",
                    offset));
            }
        }

        // Look for cgo_import_static markers
        var staticOffsets = FindAllOccurrences(data, GoCgoImportStatic);
        foreach (var offset in staticOffsets)
        {
            var libraryName = ExtractFollowingString(data, offset + GoCgoImportStatic.Length);
            if (!string.IsNullOrEmpty(libraryName) && IsValidLibraryName(libraryName))
            {
                edges.Add(new HeuristicEdge(
                    libraryName,
                    HeuristicReasonCodes.GoCgoImport,
                    HeuristicConfidence.High,
                    "Go CGO static import",
                    offset));
            }
        }
    }

    private static void ScanForRustPatterns(byte[] data, List<HeuristicEdge> edges)
    {
        // Look for Rust panic messages that might indicate FFI usage
        var panicOffsets = FindAllOccurrences(data, RustPanicPrefix);
        if (panicOffsets.Count > 0)
        {
            // Binary is likely Rust - look for linked libraries in a more targeted way
            var strings = ExtractStrings(data, minLength: 4);
            foreach (var (str, offset) in strings)
            {
                // Look for extern "C" FFI patterns
                if (str.Contains("libstd-") || str.Contains("libcore-"))
                {
                    continue; // Skip Rust standard library
                }

                // Look for native library references
                if ((str.StartsWith("lib", StringComparison.Ordinal) && str.Contains(".so")) ||
                    str.EndsWith(".dll", StringComparison.OrdinalIgnoreCase))
                {
                    // Only add if it looks like an FFI dependency
                    if (!str.Contains("rust") && !str.Contains("std"))
                    {
                        edges.Add(new HeuristicEdge(
                            str,
                            HeuristicReasonCodes.RustFfi,
                            HeuristicConfidence.Medium,
                            "Rust FFI library reference",
                            offset));
                    }
                }
            }
        }

        // Look for .rlib references
        var rlibOffsets = FindAllOccurrences(data, RustCratePattern);
        if (rlibOffsets.Count > 0)
        {
            // This is a Rust binary - we've already processed above
        }
    }

    private static List<(string Value, long Offset)> ExtractStrings(byte[] data, int minLength)
    {
        var results = new List<(string, long)>();
        var currentString = new StringBuilder();
        var stringStart = -1L;

        for (var i = 0; i < data.Length; i++)
        {
            var b = data[i];

            // Check for printable ASCII
            if (b >= 0x20 && b < 0x7F)
            {
                if (currentString.Length == 0)
                {
                    stringStart = i;
                }
                currentString.Append((char)b);
            }
            else
            {
                // End of string
                if (currentString.Length >= minLength)
                {
                    results.Add((currentString.ToString(), stringStart));
                }
                currentString.Clear();
            }
        }

        // Don't forget the last string
        if (currentString.Length >= minLength)
        {
            results.Add((currentString.ToString(), stringStart));
        }

        return results;
    }

    private static string? ExtractFollowingString(byte[] data, int startOffset)
    {
        // Skip whitespace and null bytes
        var i = startOffset;
        while (i < data.Length && (data[i] == 0 || data[i] == ' ' || data[i] == '\t'))
        {
            i++;
        }

        var sb = new StringBuilder();
        while (i < data.Length && data[i] >= 0x20 && data[i] < 0x7F)
        {
            sb.Append((char)data[i]);
            i++;
            if (sb.Length > 256) break; // Sanity limit
        }

        var result = sb.ToString().Trim();
        return string.IsNullOrEmpty(result) ? null : result;
    }

    private static List<int> FindAllOccurrences(byte[] data, byte[] pattern)
    {
        var results = new List<int>();
        if (pattern.Length == 0 || data.Length < pattern.Length)
        {
            return results;
        }

        for (var i = 0; i <= data.Length - pattern.Length; i++)
        {
            var match = true;
            for (var j = 0; j < pattern.Length; j++)
            {
                if (data[i + j] != pattern[j])
                {
                    match = false;
                    break;
                }
            }

            if (match)
            {
                results.Add(i);
            }
        }

        return results;
    }

    private static bool IsValidLibraryName(string name)
    {
        if (string.IsNullOrWhiteSpace(name) || name.Length < 3)
        {
            return false;
        }

        // Basic validation - should contain alphanumeric and common separators
        return name.All(c => char.IsLetterOrDigit(c) || c == '.' || c == '_' || c == '-' || c == '/');
    }

    [GeneratedRegex(@"^(/[a-zA-Z0-9_/.-]+/)?lib[a-zA-Z0-9_+-]+\.so(\.[0-9]+)*$", RegexOptions.Compiled)]
    private static partial Regex SonameRegex();

    [GeneratedRegex(@"^[a-zA-Z0-9_+-]+\.dll$", RegexOptions.IgnoreCase | RegexOptions.Compiled)]
    private static partial Regex DllRegex();

    [GeneratedRegex(@"^(@rpath/|@loader_path/|@executable_path/|/)?[a-zA-Z0-9_+-]+\.dylib$", RegexOptions.Compiled)]
    private static partial Regex DylibRegex();
}