using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using FluentResults;
using Npgsql;

namespace pgLabII.PgUtils.ConnectionStrings;

/// <summary>
/// Parser/formatter for Npgsql-style .NET connection strings. We intentionally do not
/// rely on NpgsqlConnectionStringBuilder here because:
/// - We need a lossless, format-agnostic round-trip to our ConnectionDescriptor, including
///   unknown/extension keys and per-host port lists. NpgsqlConnectionStringBuilder normalizes
///   names, may drop unknown keys or coerce values, which breaks lossless conversions.
/// - We support multi-host with per-host ports and want to preserve the original textual
///   representation across conversions. The builder flattens/rewrites these details.
/// - We aim to keep pgLabII.PgUtils independent from Npgsql's evolving parsing rules and
///   version-specific behaviors to ensure stable UX and deterministic tests.
/// - We need symmetric formatting matching our other codecs (libpq/URL/JDBC) and consistent
///   quoting rules across formats.
/// If required, we still reference Npgsql for enums and interop types, but parsing/formatting
/// is done by this small, well-tested custom codec for full control and stability.
/// </summary>
public sealed class NpgsqlCodec : IConnectionStringCodec
{
    public ConnStringFormat Format => ConnStringFormat.Npgsql;
    public string FormatName => "Npgsql";

    public Result<ConnectionDescriptor> TryParse(string input)
    {
        try
        {
            var dict = Tokenize(input);
            var descriptor = new ConnectionDescriptorBuilder();

            // Hosts and Ports
            if (dict.TryGetValue("Host", out var hostVal) || dict.TryGetValue("Server", out hostVal) || dict.TryGetValue("Servers", out hostVal))
            {
                var hosts = SplitList(hostVal).ToList();
                List<ushort?> portsPerHost = new();
                if (dict.TryGetValue("Port", out var portVal))
                {
                    var ports = SplitList(portVal).ToList();
                    if (ports.Count == 1 && ushort.TryParse(ports[0], out var singlePort))
                    {
                        foreach (var _ in hosts) portsPerHost.Add(singlePort);
                    }
                    else if (ports.Count == hosts.Count)
                    {
                        foreach (var p in ports)
                        {
                            if (ushort.TryParse(p, NumberStyles.Integer, CultureInfo.InvariantCulture, out var up))
                                portsPerHost.Add(up);
                            else
                                portsPerHost.Add(null);
                        }
                    }
                }
                for (int i = 0; i < hosts.Count; i++)
                {
                    ushort? port = i < portsPerHost.Count ? portsPerHost[i] : null;
                    descriptor.AddHost(hosts[i], port);
                }
            }

            // Standard fields
            if (TryGetFirst(dict, out var db, "Database", "Db", "Initial Catalog", "dbname"))
                descriptor.Database = db;
            if (TryGetFirst(dict, out var user, "Username", "User ID", "User", "UID"))
                descriptor.Username = user;
            if (TryGetFirst(dict, out var pass, "Password", "PWD"))
                descriptor.Password = pass;
            if (TryGetFirst(dict, out var app, "Application Name", "ApplicationName"))
                descriptor.ApplicationName = app;
            if (TryGetFirst(dict, out var timeout, "Timeout", "Connect Timeout", "Connection Timeout"))
            {
                if (int.TryParse(timeout, NumberStyles.Integer, CultureInfo.InvariantCulture, out var t))
                    descriptor.TimeoutSeconds = t;
            }
            if (TryGetFirst(dict, out var ssl, "SSL Mode", "SslMode", "SSLMode"))
                descriptor.SslMode = ParseSslMode(ssl);

            // Preserve extras (not mapped) into Properties
            var mapped = new HashSet<string>(StringComparer.OrdinalIgnoreCase)
            {
                "Host","Server","Servers","Port","Database","Db","Initial Catalog","dbname",
                "Username","User ID","User","UID","Password","PWD","Application Name","ApplicationName",
                "Timeout","Connect Timeout","Connection Timeout","SSL Mode","SslMode","SSLMode"
            };
            foreach (var (k, v) in dict)
            {
                if (!mapped.Contains(k))
                    descriptor.Properties[k] = v;
            }

            return Result.Ok(descriptor.Build());
        }
        catch (Exception ex)
        {
            return Result.Fail<ConnectionDescriptor>(ex.Message);
        }
    }

    public Result<string> TryFormat(ConnectionDescriptor descriptor)
    {
        try
        {
            var parts = new List<string>();

            if (descriptor.Hosts != null && descriptor.Hosts.Count > 0)
            {
                var hostList = string.Join(',', descriptor.Hosts.Select(h => h.Host));
                parts.Add(FormatPair("Host", hostList));
                var ports = descriptor.Hosts.Select(h => h.Port).Where(p => p.HasValue).Select(p => p!.Value).Distinct().ToList();
                if (ports.Count == 1)
                {
                    parts.Add(FormatPair("Port", ports[0].ToString(CultureInfo.InvariantCulture)));
                }
                else if (ports.Count == 0)
                {
                    // nothing
                }
                else
                {
                    // Per-host ports if provided 1:1
                    var perHost = descriptor.Hosts.Select(h => h.Port?.ToString(CultureInfo.InvariantCulture) ?? string.Empty).ToList();
                    if (perHost.All(s => !string.IsNullOrEmpty(s)))
                        parts.Add(FormatPair("Port", string.Join(',', perHost)));
                }
            }

            if (!string.IsNullOrEmpty(descriptor.Database))
                parts.Add(FormatPair("Database", descriptor.Database));
            if (!string.IsNullOrEmpty(descriptor.Username))
                parts.Add(FormatPair("Username", descriptor.Username));
            if (!string.IsNullOrEmpty(descriptor.Password))
                parts.Add(FormatPair("Password", descriptor.Password));
            if (descriptor.SslMode.HasValue)
                parts.Add(FormatPair("SSL Mode", FormatSslMode(descriptor.SslMode.Value)));
            if (!string.IsNullOrEmpty(descriptor.ApplicationName))
                parts.Add(FormatPair("Application Name", descriptor.ApplicationName));
            if (descriptor.TimeoutSeconds.HasValue)
                parts.Add(FormatPair("Timeout", descriptor.TimeoutSeconds.Value.ToString(CultureInfo.InvariantCulture)));

            var emittedKeys = new HashSet<string>(parts.Select(p => p.Split('=')[0].Trim()), StringComparer.OrdinalIgnoreCase);
            foreach (var kv in descriptor.Properties)
            {
                if (!emittedKeys.Contains(kv.Key))
                    parts.Add(FormatPair(kv.Key, kv.Value));
            }

            return Result.Ok(string.Join(";", parts));
        }
        catch (Exception ex)
        {
            return Result.Fail<string>(ex.Message);
        }
    }

    private static IEnumerable<string> SplitList(string s)
    {
        return s.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
    }

    private static bool TryGetFirst(Dictionary<string, string> dict, out string value, params string[] keys)
    {
        foreach (var k in keys)
        {
            if (dict.TryGetValue(k, out value)) return true;
        }
        value = string.Empty;
        return false;
    }

    private static SslMode ParseSslMode(string s)
    {
        switch (s.Trim().ToLowerInvariant())
        {
            case "disable": return SslMode.Disable;
            case "allow": return SslMode.Allow;
            case "prefer": return SslMode.Prefer;
            case "require": return SslMode.Require;
            case "verify-ca":
            case "verifyca": return SslMode.VerifyCA;
            case "verify-full":
            case "verifyfull": return SslMode.VerifyFull;
            default: throw new ArgumentException($"Not a valid SSL Mode: {s}");
        }
    }

    private static string FormatSslMode(SslMode mode)
    {
        return mode switch
        {
            SslMode.Disable => "Disable",
            SslMode.Allow => "Allow",
            SslMode.Prefer => "Prefer",
            SslMode.Require => "Require",
            SslMode.VerifyCA => "VerifyCA",
            SslMode.VerifyFull => "VerifyFull",
            _ => "Prefer"
        };
    }

    // Npgsql/.NET connection string grammar: semicolon-separated key=value; values with special chars are wrapped in quotes, internal quotes doubled
    private static string FormatPair(string key, string? value)
    {
        value ??= string.Empty;
        var needsQuotes = NeedsQuoting(value);
        if (!needsQuotes) return key + "=" + value;
        return key + "=\"" + EscapeQuoted(value) + "\"";
    }

    private static bool NeedsQuoting(string value)
    {
        if (value.Length == 0) return true;
        foreach (var c in value)
        {
            if (char.IsWhiteSpace(c) || c == ';' || c == '=' || c == '"') return true;
        }
        return false;
    }

    private static string EscapeQuoted(string value)
    {
        // Double the quotes per standard DbConnectionString rules
        return value.Replace("\"", "\"\"");
    }

    private static Dictionary<string, string> Tokenize(string input)
    {
        // Simple tokenizer for .NET connection strings: key=value pairs separated by semicolons; values may be quoted with double quotes
        var dict = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
        int i = 0;
        void SkipWs() { while (i < input.Length && char.IsWhiteSpace(input[i])) i++; }

        while (true)
        {
            SkipWs();
            if (i >= input.Length) break;

            // read key
            int keyStart = i;
            while (i < input.Length && input[i] != '=') i++;
            if (i >= input.Length) { break; }
            var key = input.Substring(keyStart, i - keyStart).Trim();
            i++; // skip '='
            SkipWs();

            // read value
            string value;
            if (i < input.Length && input[i] == '"')
            {
                i++; // skip opening quote
                var sb = new StringBuilder();
                while (i < input.Length)
                {
                    char c = input[i++];
                    if (c == '"')
                    {
                        if (i < input.Length && input[i] == '"')
                        {
                            // doubled quote -> literal quote
                            sb.Append('"');
                            i++;
                            continue;
                        }
                        else
                        {
                            break; // end quoted value
                        }
                    }
                    else
                    {
                        sb.Append(c);
                    }
                }
                value = sb.ToString();
            }
            else
            {
                int valStart = i;
                while (i < input.Length && input[i] != ';') i++;
                value = input.Substring(valStart, i - valStart).Trim();
            }

            dict[key] = value;

            // skip to next, if ; present, consume one
            while (i < input.Length && input[i] != ';') i++;
            if (i < input.Length && input[i] == ';') i++;
        }

        return dict;
    }

    private sealed class ConnectionDescriptorBuilder
    {
        public List<HostEndpoint> Hosts { get; } = new();
        public string? Database { get; set; }
        public string? Username { get; set; }
        public string? Password { get; set; }
        public SslMode? SslMode { get; set; }
        public string? ApplicationName { get; set; }
        public int? TimeoutSeconds { get; set; }
        public Dictionary<string, string> Properties { get; } = new(StringComparer.OrdinalIgnoreCase);

        public void AddHost(string host, ushort? port)
        {
            if (string.IsNullOrWhiteSpace(host)) return;
            Hosts.Add(new HostEndpoint { Host = host.Trim(), Port = port });
        }

        public ConnectionDescriptor Build()
        {
            return new ConnectionDescriptor
            {
                Hosts = Hosts,
                Database = Database,
                Username = Username,
                Password = Password,
                SslMode = SslMode,
                ApplicationName = ApplicationName,
                TimeoutSeconds = TimeoutSeconds,
                Properties = Properties
            };
        }
    }
}