using System.Collections.Concurrent;
using System.Collections.Immutable;
using System.Security;

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

internal static class RustLicenseScanner
{
    private static readonly ConcurrentDictionary<string, RustLicenseIndex> IndexCache = new(StringComparer.Ordinal);

    public static RustLicenseIndex GetOrCreate(string rootPath, CancellationToken cancellationToken)
    {
        if (string.IsNullOrWhiteSpace(rootPath) || !Directory.Exists(rootPath))
        {
            return RustLicenseIndex.Empty;
        }

        var normalizedRoot = NormalizeRoot(rootPath);
        return IndexCache.GetOrAdd(
            normalizedRoot,
            static (_, state) => BuildIndex(state.RootPath, state.CancellationToken),
            (RootPath: rootPath, CancellationToken: cancellationToken));
    }

    private static RustLicenseIndex BuildIndex(string rootPath, CancellationToken cancellationToken)
    {
        var byName = new Dictionary<string, List<RustLicenseInfo>>(StringComparer.Ordinal);
        var enumeration = new EnumerationOptions
        {
            MatchCasing = MatchCasing.CaseSensitive,
            IgnoreInaccessible = true,
            RecurseSubdirectories = true,
            AttributesToSkip = FileAttributes.Device | FileAttributes.ReparsePoint,
        };

        foreach (var cargoTomlPath in Directory.EnumerateFiles(rootPath, "Cargo.toml", enumeration))
        {
            cancellationToken.ThrowIfCancellationRequested();

            if (IsUnderTargetDirectory(cargoTomlPath))
            {
                continue;
            }

            if (!TryParseCargoToml(rootPath, cargoTomlPath, out var info))
            {
                continue;
            }

            var normalizedName = RustCrateBuilder.NormalizeName(info.Name);
            if (!byName.TryGetValue(normalizedName, out var entries))
            {
                entries = new List<RustLicenseInfo>();
                byName[normalizedName] = entries;
            }

            entries.Add(info);
        }

        foreach (var entry in byName.Values)
        {
            entry.Sort(static (left, right) =>
            {
                var versionCompare = string.Compare(left.Version, right.Version, StringComparison.OrdinalIgnoreCase);
                if (versionCompare != 0)
                {
                    return versionCompare;
                }

                return string.Compare(left.CargoTomlRelativePath, right.CargoTomlRelativePath, StringComparison.Ordinal);
            });
        }

        return new RustLicenseIndex(byName);
    }

    private static bool TryParseCargoToml(string rootPath, string cargoTomlPath, out RustLicenseInfo info)
    {
        info = default!;

        try
        {
            using var stream = new FileStream(cargoTomlPath, FileMode.Open, FileAccess.Read, FileShare.Read);
            using var reader = new StreamReader(stream, leaveOpen: false);

            string? name = null;
            string? version = null;
            string? licenseExpression = null;
            string? licenseFile = null;
            var inPackageSection = false;

            while (reader.ReadLine() is { } line)
            {
                line = StripComment(line).Trim();
                if (line.Length == 0)
                {
                    continue;
                }

                if (line.StartsWith("[", StringComparison.Ordinal))
                {
                    inPackageSection = string.Equals(line, "[package]", StringComparison.OrdinalIgnoreCase);
                    if (!inPackageSection && line.StartsWith("[dependency", StringComparison.OrdinalIgnoreCase))
                    {
                        // Exiting package section.
                        break;
                    }

                    continue;
                }

                if (!inPackageSection)
                {
                    continue;
                }

                if (TryParseStringAssignment(line, "name", out var parsedName))
                {
                    name ??= parsedName;
                    continue;
                }

                if (TryParseStringAssignment(line, "version", out var parsedVersion))
                {
                    version ??= parsedVersion;
                    continue;
                }

                if (TryParseStringAssignment(line, "license", out var parsedLicense))
                {
                    licenseExpression ??= parsedLicense;
                    continue;
                }

                if (TryParseStringAssignment(line, "license-file", out var parsedLicenseFile))
                {
                    licenseFile ??= parsedLicenseFile;
                    continue;
                }
            }

            if (string.IsNullOrWhiteSpace(name))
            {
                return false;
            }

            var expressions = ImmutableArray<string>.Empty;
            if (!string.IsNullOrWhiteSpace(licenseExpression))
            {
                expressions = ImmutableArray.Create(licenseExpression!);
            }

            var files = ImmutableArray<RustLicenseFileReference>.Empty;
            if (!string.IsNullOrWhiteSpace(licenseFile))
            {
                var directory = Path.GetDirectoryName(cargoTomlPath) ?? string.Empty;
                var absolute = Path.GetFullPath(Path.Combine(directory, licenseFile!));
                if (File.Exists(absolute))
                {
                    var relative = NormalizeRelativePath(rootPath, absolute);
                    if (RustFileHashCache.TryGetSha256(absolute, out var sha256))
                    {
                        files = ImmutableArray.Create(new RustLicenseFileReference(relative, sha256));
                    }
                    else
                    {
                        files = ImmutableArray.Create(new RustLicenseFileReference(relative, null));
                    }
                }
            }

            var cargoRelative = NormalizeRelativePath(rootPath, cargoTomlPath);

            info = new RustLicenseInfo(
                name!.Trim(),
                string.IsNullOrWhiteSpace(version) ? null : version!.Trim(),
                expressions,
                files,
                cargoRelative);

            return true;
        }
        catch (IOException)
        {
            return false;
        }
        catch (UnauthorizedAccessException)
        {
            return false;
        }
        catch (SecurityException)
        {
            return false;
        }
    }

    private static string NormalizeRoot(string rootPath)
    {
        var full = Path.GetFullPath(rootPath);
        return OperatingSystem.IsWindows()
            ? full.ToLowerInvariant()
            : full;
    }

    private static bool TryParseStringAssignment(string line, string key, out string? value)
    {
        value = null;

        if (!line.StartsWith(key, StringComparison.Ordinal))
        {
            return false;
        }

        var remaining = line[key.Length..].TrimStart();
        if (remaining.Length == 0 || remaining[0] != '=')
        {
            return false;
        }

        remaining = remaining[1..].TrimStart();
        if (remaining.Length < 2 || remaining[0] != '"' || remaining[^1] != '"')
        {
            return false;
        }

        value = remaining[1..^1];
        return true;
    }

    private static string StripComment(string line)
    {
        var index = line.IndexOf('#');
        return index < 0 ? line : line[..index];
    }

    private static bool IsUnderTargetDirectory(string path)
    {
        var segment = $"{Path.DirectorySeparatorChar}target{Path.DirectorySeparatorChar}";
        return path.Contains(segment, OperatingSystem.IsWindows() ? StringComparison.OrdinalIgnoreCase : StringComparison.Ordinal);
    }

    private static string NormalizeRelativePath(string rootPath, string absolutePath)
    {
        var relative = Path.GetRelativePath(rootPath, absolutePath);
        if (string.IsNullOrWhiteSpace(relative) || relative == ".")
        {
            return ".";
        }

        return relative.Replace('\\', '/');
    }
}

internal sealed class RustLicenseIndex
{
    private readonly Dictionary<string, List<RustLicenseInfo>> _byName;

    public static readonly RustLicenseIndex Empty = new(new Dictionary<string, List<RustLicenseInfo>>(StringComparer.Ordinal));

    public RustLicenseIndex(Dictionary<string, List<RustLicenseInfo>> byName)
    {
        _byName = byName ?? throw new ArgumentNullException(nameof(byName));
    }

    public RustLicenseInfo? Find(string crateName, string? version)
    {
        if (string.IsNullOrWhiteSpace(crateName))
        {
            return null;
        }

        var normalized = RustCrateBuilder.NormalizeName(crateName);
        if (!_byName.TryGetValue(normalized, out var list) || list.Count == 0)
        {
            return null;
        }

        if (!string.IsNullOrWhiteSpace(version))
        {
            var match = list.FirstOrDefault(entry => string.Equals(entry.Version, version, StringComparison.OrdinalIgnoreCase));
            if (match is not null)
            {
                return match;
            }
        }

        return list[0];
    }
}

internal sealed record RustLicenseInfo(
    string Name,
    string? Version,
    ImmutableArray<string> Expressions,
    ImmutableArray<RustLicenseFileReference> Files,
    string CargoTomlRelativePath);

internal sealed record RustLicenseFileReference(string RelativePath, string? Sha256);