using System;
using System.Collections.Generic;
using System.Data;
using System.Threading.Tasks;
using DataConnection.Interfaces;
using Microsoft.Data.SqlClient;

namespace DataConnection.EF.SchemaProviders;

/// <summary>
/// Provider di schema per database SQL Server
/// </summary>
public class SqlServerSchemaProvider : IDatabaseSchemaProvider
{    public async Task<IDictionary<string, IEnumerable<DbColumnInfo>>> GetDatabaseSchemaAsync(string connectionString)
    {
        var result = new Dictionary<string, IEnumerable<DbColumnInfo>>();
        
        try
        {
            Console.WriteLine($"[DEBUG] SqlServerSchemaProvider - Connection string: {connectionString?.Substring(0, Math.Min(50, connectionString?.Length ?? 0))}...");
            
            using (var connection = new SqlConnection(connectionString))
            {
                await connection.OpenAsync();
                Console.WriteLine($"[DEBUG] SqlServerSchemaProvider - Connessione aperta");
                
                // Query per ottenere la struttura delle tabelle in SQL Server
                string sql = @"
                    SELECT 
                        SCHEMA_NAME(t.schema_id) + '.' + t.name AS TableName,
                        c.name AS ColumnName,
                        tp.name AS DataType,
                        c.max_length,
                        c.precision,
                        c.scale,
                        c.is_nullable,
                        CASE WHEN pk.column_id IS NOT NULL THEN 1 ELSE 0 END AS IsPrimaryKey,
                        CASE WHEN fk.parent_column_id IS NOT NULL THEN 1 ELSE 0 END AS IsForeignKey,
                        SCHEMA_NAME(ref_t.schema_id) + '.' + ref_t.name AS ReferencedTable,
                        ref_c.name AS ReferencedColumn
                    FROM 
                        sys.tables t
                    INNER JOIN 
                        sys.columns c ON t.object_id = c.object_id
                    INNER JOIN 
                        sys.types tp ON c.user_type_id = tp.user_type_id
                    LEFT JOIN 
                        (SELECT 
                            ic.object_id, 
                            ic.column_id
                         FROM 
                            sys.indexes i
                         INNER JOIN 
                            sys.index_columns ic ON i.object_id = ic.object_id AND i.index_id = ic.index_id
                         WHERE 
                            i.is_primary_key = 1) pk ON t.object_id = pk.object_id AND c.column_id = pk.column_id
                    LEFT JOIN 
                        sys.foreign_key_columns fk ON t.object_id = fk.parent_object_id AND c.column_id = fk.parent_column_id
                    LEFT JOIN 
                        sys.tables ref_t ON fk.referenced_object_id = ref_t.object_id
                    LEFT JOIN 
                        sys.columns ref_c ON fk.referenced_object_id = ref_c.object_id AND fk.referenced_column_id = ref_c.column_id
                    WHERE
                        t.is_ms_shipped = 0
                    ORDER BY 
                        TableName, c.column_id";

                using (var command = new SqlCommand(sql, connection))
                {
                    command.CommandType = CommandType.Text;
                    
                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        string currentTable = null;
                        List<DbColumnInfo> columns = null;
                        
                        while (await reader.ReadAsync())
                        {
                            string tableName = reader.GetString(0);
                            
                            // Se stiamo passando a una nuova tabella, aggiungiamo la tabella precedente e creiamo una nuova lista
                            if (currentTable != tableName)
                            {
                                if (currentTable != null && columns != null && columns.Count > 0)
                                {
                                    result[currentTable] = columns;
                                }
                                
                                currentTable = tableName;
                                columns = new List<DbColumnInfo>();
                            }
                            
                            // Formato del tipo di dati con precisione e scala per tipi numerici o lunghezza per tipi stringa
                            string dataType = reader.GetString(2);
                            int maxLength = reader.GetInt16(3);
                            byte precision = reader.GetByte(4);
                            byte scale = reader.GetByte(5);
                            
                            // Formattazione tipo di dati per SQL Server
                            string formattedDataType = FormatSqlServerDataType(dataType, maxLength, precision, scale);
                            
                            var columnInfo = new DbColumnInfo
                            {
                                Name = reader.GetString(1),
                                DataType = formattedDataType,
                                IsNullable = reader.GetBoolean(6),
                                IsPrimaryKey = reader.GetInt32(7) == 1,
                                IsForeignKey = reader.GetInt32(8) == 1,
                                ReferencedTable = reader.IsDBNull(9) ? null : reader.GetString(9),
                                ReferencedColumn = reader.IsDBNull(10) ? null : reader.GetString(10)
                            };
                            
                            columns?.Add(columnInfo);
                        }
                          // Aggiungiamo l'ultima tabella
                        if (currentTable != null && columns != null && columns.Count > 0)
                        {
                            result[currentTable] = columns;
                        }
                        
                        Console.WriteLine($"[DEBUG] SqlServerSchemaProvider - Query completata. Trovate {result.Count} tabelle");
                        foreach (var table in result.Take(3))
                        {
                            Console.WriteLine($"[DEBUG] SqlServerSchemaProvider - Tabella: {table.Key}, Colonne: {table.Value?.Count() ?? 0}");
                        }
                    }
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Errore nel recupero dello schema del database SQL Server: {ex.Message}");
            throw;
        }
        
        return result;
    }
    
    private static string FormatSqlServerDataType(string dataType, int maxLength, byte precision, byte scale)
    {
        string formattedDataType = dataType;
        
        if (dataType == "nvarchar" || dataType == "varchar" || dataType == "char" || dataType == "nchar")
        {
            if (maxLength == -1)
                formattedDataType += "(MAX)";
            else if (dataType.StartsWith("n")) // tipi Unicode - la lunghezza è in byte, dobbiamo dividerla per 2
                formattedDataType += $"({maxLength / 2})";
            else
                formattedDataType += $"({maxLength})";
        }
        else if (dataType == "decimal" || dataType == "numeric")
        {
            formattedDataType += $"({precision},{scale})";
        }
        
        return formattedDataType;
    }
}