using System.Globalization;
using System.Text;
using FluentResults;

namespace pgLabII.PgUtils.ConnectionStrings;

/// <summary>
/// Codec for PostgreSQL URL format: postgresql://[user[:password]@]host[:port][,hostN[:portN]]/[database]?param=value&...
/// - Supports multi-host by comma-separated host:port entries in authority part.
/// - Supports IPv6 literals in square brackets, e.g. [::1]:5432.
/// - Percent-decodes user, password, database, and query param values on parse.
/// - Percent-encodes user, password, database, and query values on format.
/// - Maps sslmode, application_name, connect_timeout into descriptor fields; others preserved in Properties.
/// </summary>
public sealed class UrlCodec : IConnectionStringCodec
{
    public ConnStringFormat Format => ConnStringFormat.Url;
    public string FormatName => "URL";

    public Result<ConnectionDescriptor> TryParse(string input)
    {
        try
        {
            if (string.IsNullOrWhiteSpace(input))
                return Result.Fail<ConnectionDescriptor>("Empty URL");

            // Accept schemes postgresql:// or postgres://
            if (!input.StartsWith("postgresql://", StringComparison.OrdinalIgnoreCase) &&
                !input.StartsWith("postgres://", StringComparison.OrdinalIgnoreCase))
                return Result.Fail<ConnectionDescriptor>("URL must start with postgresql:// or postgres://");

            // We cannot rely entirely on System.Uri for multi-host. We'll manually split scheme and the rest.
            var span = input.AsSpan();
            int schemeSep = input.IndexOf("//", StringComparison.Ordinal);
            if (schemeSep < 0)
                return Result.Fail<ConnectionDescriptor>("Invalid URL: missing //");
            var scheme = input.Substring(0, schemeSep - 1); // includes ':'
            var rest = input.Substring(schemeSep + 2);

            // Split off path and query/fragment
            string authorityAndMaybeMore = rest;
            string pathAndQuery = string.Empty;
            int slashIdx = rest.IndexOf('/');
            if (slashIdx >= 0)
            {
                authorityAndMaybeMore = rest.Substring(0, slashIdx);
                pathAndQuery = rest.Substring(slashIdx); // starts with '/'
            }

            string userInfo = string.Empty;
            string authority = authorityAndMaybeMore;
            int atIdx = authorityAndMaybeMore.IndexOf('@');
            if (atIdx >= 0)
            {
                userInfo = authorityAndMaybeMore.Substring(0, atIdx);
                authority = authorityAndMaybeMore.Substring(atIdx + 1);
            }

            var builder = new ConnectionDescriptorBuilder();

            // Parse userinfo
            if (!string.IsNullOrEmpty(userInfo))
            {
                var up = userInfo.Split(':', 2);
                if (up.Length > 0 && up[0].Length > 0)
                    builder.Username = Uri.UnescapeDataString(up[0]);
                if (up.Length > 1)
                    builder.Password = Uri.UnescapeDataString(up[1]);
            }

            // Parse hosts (maybe comma-separated)
            foreach (string hostPart in CodecCommon.SplitHosts(authority))
            {
                CodecCommon.ParseHostPort(hostPart, out string host, out ushort? port);
                if (!string.IsNullOrEmpty(host))
                    builder.AddHost(host, port);
            }

            // Parse path (database) and query
            string database = string.Empty;
            string query = string.Empty;
            if (!string.IsNullOrEmpty(pathAndQuery))
            {
                // pathAndQuery like /db?x=y
                int qIdx = pathAndQuery.IndexOf('?');
                string path = qIdx >= 0 ? pathAndQuery[..qIdx] : pathAndQuery;
                query = qIdx >= 0 ? pathAndQuery[(qIdx + 1)..] : string.Empty;
                if (path.Length > 0)
                {
                    // strip leading '/'
                    if (path[0] == '/') 
                        path = path[1..];
                    if (path.Length > 0)
                        database = Uri.UnescapeDataString(path);
                }
            }
            if (!string.IsNullOrEmpty(database)) builder.Database = database;

            var queryDict = CodecCommon.ParseQuery(query);

            // Map known params
            if (queryDict.TryGetValue("sslmode", out var sslVal))
                builder.SslMode = CodecCommon.ParseSslModeLoose(sslVal);
            if (queryDict.TryGetValue("application_name", out var app))
                builder.ApplicationName = app;
            if (queryDict.TryGetValue("connect_timeout", out var tout) && int.TryParse(tout, NumberStyles.Integer, CultureInfo.InvariantCulture, out var ts))
                builder.TimeoutSeconds = ts;

            // Preserve extras
            foreach (var (k, v) in queryDict)
            {
                if (!IsMappedQueryKey(k))
                    builder.Properties[k] = v;
            }

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

    public Result<string> TryFormat(ConnectionDescriptor descriptor)
    {
        try
        {
            var sb = new StringBuilder();
            sb.Append("postgresql://");

            // userinfo
            if (!string.IsNullOrEmpty(descriptor.Username))
            {
                sb.Append(Uri.EscapeDataString(descriptor.Username));
                if (!string.IsNullOrEmpty(descriptor.Password))
                {
                    sb.Append(':');
                    sb.Append(Uri.EscapeDataString(descriptor.Password));
                }
                sb.Append('@');
            }

            // hosts
            if (descriptor.Hosts.Count > 0)
            {
                var hostParts = new List<string>(descriptor.Hosts.Count);
                foreach (var h in descriptor.Hosts)
                {
                    var host = h.Host ?? string.Empty;
                    bool isIpv6 = host.Contains(':') && !host.StartsWith("[") && !host.EndsWith("]");
                    if (isIpv6)
                        host = "[" + host + "]";
                    if (h.Port.HasValue)
                        host += ":" + h.Port.Value.ToString(CultureInfo.InvariantCulture);
                    hostParts.Add(host);
                }
                sb.Append(string.Join(',', hostParts));
            }

            // path (database)
            sb.Append('/');
            if (!string.IsNullOrEmpty(descriptor.Database))
                sb.Append(Uri.EscapeDataString(descriptor.Database));

            // query
            var queryPairs = new List<string>();
            if (descriptor.SslMode.HasValue)
                queryPairs.Add("sslmode=" + Uri.EscapeDataString(CodecCommon.FormatSslModeUrlLike(descriptor.SslMode.Value)));
            if (!string.IsNullOrEmpty(descriptor.ApplicationName))
                queryPairs.Add("application_name=" + Uri.EscapeDataString(descriptor.ApplicationName));
            if (descriptor.TimeoutSeconds.HasValue)
                queryPairs.Add("connect_timeout=" + Uri.EscapeDataString(descriptor.TimeoutSeconds.Value.ToString(CultureInfo.InvariantCulture)));

            // Add extra properties not already emitted
            var emitted = new HashSet<string>(queryPairs.Select(p => p.Split('=')[0]), StringComparer.OrdinalIgnoreCase);
            foreach (var kv in descriptor.Properties)
            {
                if (emitted.Contains(kv.Key)) continue;
                queryPairs.Add(Uri.EscapeDataString(kv.Key) + "=" + Uri.EscapeDataString(kv.Value ?? string.Empty));
            }

            if (queryPairs.Count > 0)
            {
                sb.Append('?');
                sb.Append(string.Join('&', queryPairs));
            }

            return Result.Ok(sb.ToString());
        }
        catch (Exception ex)
        {
            return Result.Fail<string>(ex.Message);
        }
    }

    private static bool IsMappedQueryKey(string key)
        => key.Equals("sslmode", StringComparison.OrdinalIgnoreCase)
           || key.Equals("application_name", StringComparison.OrdinalIgnoreCase)
           || key.Equals("connect_timeout", StringComparison.OrdinalIgnoreCase);
}