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

internal static class RustCargoLockParser
{
    public static IReadOnlyList<RustCargoPackage> Parse(string path, CancellationToken cancellationToken)
    {
        if (string.IsNullOrWhiteSpace(path))
        {
            throw new ArgumentException("Lock path is required", nameof(path));
        }

        var info = new FileInfo(path);
        if (!info.Exists)
        {
            return Array.Empty<RustCargoPackage>();
        }

        var packages = new List<RustCargoPackage>();
        using var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read);
        using var reader = new StreamReader(stream);

        RustCargoPackageBuilder? builder = null;
        string? currentArrayKey = null;
        var arrayValues = new List<string>();

        while (!reader.EndOfStream)
        {
            cancellationToken.ThrowIfCancellationRequested();

            var line = reader.ReadLine();
            if (line is null)
            {
                break;
            }

            var trimmed = TrimComments(line.AsSpan());
            if (trimmed.Length == 0)
            {
                continue;
            }

            if (IsPackageHeader(trimmed))
            {
                FlushCurrent(builder, packages);
                builder = new RustCargoPackageBuilder();
                currentArrayKey = null;
                arrayValues.Clear();
                continue;
            }

            if (builder is null)
            {
                continue;
            }

            if (currentArrayKey is not null)
            {
                if (trimmed[0] == ']')
                {
                    builder.SetArray(currentArrayKey, arrayValues);
                    currentArrayKey = null;
                    arrayValues.Clear();
                    continue;
                }

                var value = ExtractString(trimmed);
                if (!string.IsNullOrEmpty(value))
                {
                    arrayValues.Add(value);
                }

                continue;
            }

            if (trimmed[0] == '[')
            {
                // Entering a new table; finish any pending package and skip section.
                FlushCurrent(builder, packages);
                builder = null;
                continue;
            }

            var equalsIndex = trimmed.IndexOf('=');
            if (equalsIndex < 0)
            {
                continue;
            }

            var key = trimmed[..equalsIndex].Trim();
            var valuePart = trimmed[(equalsIndex + 1)..].Trim();
            if (valuePart.Length == 0)
            {
                continue;
            }

            if (valuePart[0] == '[')
            {
                currentArrayKey = key.ToString();
                arrayValues.Clear();

                if (valuePart.Length > 1 && valuePart[^1] == ']')
                {
                    var inline = valuePart[1..^1].Trim();
                    if (inline.Length > 0)
                    {
                        foreach (var token in SplitInlineArray(inline.ToString()))
                        {
                            var parsedValue = ExtractString(token.AsSpan());
                            if (!string.IsNullOrEmpty(parsedValue))
                            {
                                arrayValues.Add(parsedValue);
                            }
                        }
                    }

                    builder.SetArray(currentArrayKey, arrayValues);
                    currentArrayKey = null;
                    arrayValues.Clear();
                }

                continue;
            }

            var parsed = ExtractString(valuePart);
            if (parsed is not null)
            {
                builder.SetField(key, parsed);
            }
        }

        if (currentArrayKey is not null && arrayValues.Count > 0)
        {
            builder?.SetArray(currentArrayKey, arrayValues);
        }

        FlushCurrent(builder, packages);
        return packages;
    }

    private static ReadOnlySpan<char> TrimComments(ReadOnlySpan<char> line)
    {
        var index = line.IndexOf('#');
        if (index >= 0)
        {
            line = line[..index];
        }

        return line.Trim();
    }

    private static bool IsPackageHeader(ReadOnlySpan<char> value)
        => value.SequenceEqual("[[package]]".AsSpan());

    private static IEnumerable<string> SplitInlineArray(string value)
    {
        var start = 0;
        var inString = false;

        for (var i = 0; i < value.Length; i++)
        {
            var current = value[i];

            if (current == '"')
            {
                inString = !inString;
            }

            if (current == ',' && !inString)
            {
                var item = value.AsSpan(start, i - start).Trim();
                if (item.Length > 0)
                {
                    yield return item.ToString();
                }

                start = i + 1;
            }
        }

        if (start < value.Length)
        {
            var item = value.AsSpan(start).Trim();
            if (item.Length > 0)
            {
                yield return item.ToString();
            }
        }
    }

    private static string? ExtractString(ReadOnlySpan<char> value)
    {
        if (value.Length == 0)
        {
            return null;
        }

        if (value[0] == '"' && value[^1] == '"')
        {
            var inner = value[1..^1];
            return inner.ToString();
        }

        var trimmed = value.Trim();
        return trimmed.Length == 0 ? null : trimmed.ToString();
    }

    private static void FlushCurrent(RustCargoPackageBuilder? builder, List<RustCargoPackage> packages)
    {
        if (builder is null || !builder.HasData)
        {
            return;
        }

        if (builder.TryBuild(out var package))
        {
            packages.Add(package);
        }
    }

    private sealed class RustCargoPackageBuilder
    {
        private readonly SortedSet<string> _dependencies = new(StringComparer.Ordinal);

        private string? _name;
        private string? _version;
        private string? _source;
        private string? _checksum;

        public bool HasData => !string.IsNullOrWhiteSpace(_name);

        public void SetField(ReadOnlySpan<char> key, string value)
        {
            if (key.SequenceEqual("name".AsSpan()))
            {
                _name ??= value.Trim();
            }
            else if (key.SequenceEqual("version".AsSpan()))
            {
                _version ??= value.Trim();
            }
            else if (key.SequenceEqual("source".AsSpan()))
            {
                _source ??= value.Trim();
            }
            else if (key.SequenceEqual("checksum".AsSpan()))
            {
                _checksum ??= value.Trim();
            }
        }

        public void SetArray(string key, IEnumerable<string> values)
        {
            if (!string.Equals(key, "dependencies", StringComparison.Ordinal))
            {
                return;
            }

            foreach (var entry in values)
            {
                if (string.IsNullOrWhiteSpace(entry))
                {
                    continue;
                }

                var normalized = entry.Trim();
                if (normalized.Length > 0)
                {
                    _dependencies.Add(normalized);
                }
            }
        }

        public bool TryBuild(out RustCargoPackage package)
        {
            if (string.IsNullOrWhiteSpace(_name))
            {
                package = null!;
                return false;
            }

            package = new RustCargoPackage(
                _name!,
                _version ?? string.Empty,
                _source,
                _checksum,
                _dependencies.ToArray());

            return true;
        }
    }
}

internal sealed record RustCargoPackage(
    string Name,
    string Version,
    string? Source,
    string? Checksum,
    IReadOnlyList<string> Dependencies);