using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Text.Json;

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

internal static class GoBuildInfoParser
{
    private const string PathPrefix = "path\t";
    private const string ModulePrefix = "mod\t";
    private const string DependencyPrefix = "dep\t";
    private const string ReplacementPrefix = "=>\t";
    private const string BuildPrefix = "build\t";

    public static bool TryParse(string goVersion, string absoluteBinaryPath, string rawModuleData, out GoBuildInfo? info)
    {
        info = null;

        if (string.IsNullOrWhiteSpace(goVersion) || string.IsNullOrWhiteSpace(rawModuleData))
        {
            return false;
        }

        string? modulePath = null;
        GoModule? mainModule = null;
        var dependencies = new List<GoModule>();
        var settings = new SortedDictionary<string, string?>(StringComparer.Ordinal);

        GoModule? lastModule = null;
        using var reader = new StringReader(rawModuleData);

        while (reader.ReadLine() is { } line)
        {
            if (string.IsNullOrWhiteSpace(line))
            {
                continue;
            }

            if (line.StartsWith(PathPrefix, StringComparison.Ordinal))
            {
                modulePath = line[PathPrefix.Length..].Trim();
                continue;
            }

            if (line.StartsWith(ModulePrefix, StringComparison.Ordinal))
            {
                mainModule = ParseModule(line.AsSpan(ModulePrefix.Length), isMain: true);
                lastModule = mainModule;
                continue;
            }

            if (line.StartsWith(DependencyPrefix, StringComparison.Ordinal))
            {
                var dependency = ParseModule(line.AsSpan(DependencyPrefix.Length), isMain: false);
                if (dependency is not null)
                {
                    dependencies.Add(dependency);
                    lastModule = dependency;
                }

                continue;
            }

            if (line.StartsWith(ReplacementPrefix, StringComparison.Ordinal))
            {
                if (lastModule is null)
                {
                    continue;
                }

                var replacement = ParseReplacement(line.AsSpan(ReplacementPrefix.Length));
                if (replacement is not null)
                {
                    lastModule.SetReplacement(replacement);
                }

                continue;
            }

            if (line.StartsWith(BuildPrefix, StringComparison.Ordinal))
            {
                var pair = ParseBuildSetting(line.AsSpan(BuildPrefix.Length));
                if (!string.IsNullOrEmpty(pair.Key))
                {
                    settings[pair.Key] = pair.Value;
                }
            }
        }

        if (mainModule is null)
        {
            return false;
        }

        if (string.IsNullOrEmpty(modulePath))
        {
            modulePath = mainModule.Path;
        }

        info = new GoBuildInfo(
            goVersion,
            absoluteBinaryPath,
            modulePath,
            mainModule,
            dependencies,
            settings);

        return true;
    }

    private static GoModule? ParseModule(ReadOnlySpan<char> span, bool isMain)
    {
        var fields = SplitFields(span, expected: 4);
        if (fields.Count == 0)
        {
            return null;
        }

        var path = fields[0];
        if (string.IsNullOrWhiteSpace(path))
        {
            return null;
        }

        var version = fields.Count > 1 ? fields[1] : null;
        var sum = fields.Count > 2 ? fields[2] : null;

        return new GoModule(path, version, sum, isMain);
    }

    private static GoModuleReplacement? ParseReplacement(ReadOnlySpan<char> span)
    {
        var fields = SplitFields(span, expected: 3);
        if (fields.Count == 0)
        {
            return null;
        }

        var path = fields[0];
        if (string.IsNullOrWhiteSpace(path))
        {
            return null;
        }

        var version = fields.Count > 1 ? fields[1] : null;
        var sum = fields.Count > 2 ? fields[2] : null;

        return new GoModuleReplacement(path, version, sum);
    }

    private static KeyValuePair<string, string?> ParseBuildSetting(ReadOnlySpan<char> span)
    {
        span = span.Trim();
        if (span.IsEmpty)
        {
            return default;
        }

        var separatorIndex = span.IndexOf('=');
        if (separatorIndex <= 0)
        {
            return default;
        }

        var rawKey = span[..separatorIndex].Trim();
        var rawValue = span[(separatorIndex + 1)..].Trim();

        var key = Unquote(rawKey.ToString());
        if (string.IsNullOrWhiteSpace(key))
        {
            return default;
        }

        var value = Unquote(rawValue.ToString());
        return new KeyValuePair<string, string?>(key, value);
    }

    private static List<string> SplitFields(ReadOnlySpan<char> span, int expected)
    {
        var fields = new List<string>(expected);
        var builder = new StringBuilder();

        for (var i = 0; i < span.Length; i++)
        {
            var current = span[i];
            if (current == '\t')
            {
                fields.Add(builder.ToString());
                builder.Clear();
                continue;
            }

            builder.Append(current);
        }

        fields.Add(builder.ToString());
        return fields;
    }

    private static string Unquote(string value)
    {
        if (string.IsNullOrEmpty(value))
        {
            return value;
        }

        value = value.Trim();
        if (value.Length < 2)
        {
            return value;
        }

        if (value[0] == '"' && value[^1] == '"')
        {
            try
            {
                return JsonSerializer.Deserialize<string>(value) ?? value;
            }
            catch (JsonException)
            {
                return value;
            }
        }

        if (value[0] == '`' && value[^1] == '`')
        {
            return value[1..^1];
        }

        return value;
    }
}