Data-Coupler/DataConnection/DB/EF/SchemaProviders/OleDbSchemaProvider.cs

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.OleDb;
using System.Linq;
using System.Runtime.InteropServices;
using System.Threading.Tasks;
using DataConnection.Interfaces;

namespace DataConnection.EF.SchemaProviders;

/// <summary>
/// Provider di schema per database OLE DB (incluso Visual FoxPro)
/// Utilizza GetOleDbSchemaTable per ottenere metadati in modo compatibile con VFP e altri provider OLE DB
/// </summary>
public class OleDbSchemaProvider : IDatabaseSchemaProvider
{
    public async Task<IDictionary<string, IEnumerable<DbColumnInfo>>> GetDatabaseSchemaAsync(string connectionString)
    {
        var result = new Dictionary<string, IEnumerable<DbColumnInfo>>();

        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            throw new PlatformNotSupportedException("OLE DB è supportato solo su Windows.");

        try
        {
            using var connection = new OleDbConnection(connectionString);
            await Task.Run(() => connection.Open());

            Console.WriteLine($"OLE DB Schema Provider - Provider: {connection.Provider}");

            var tableNames = GetTableNamesFromConnection(connection);
            Console.WriteLine($"Trovate {tableNames.Count} tabelle");

            foreach (var tableName in tableNames)
            {
                try
                {
                    var columns = GetTableColumnsFromConnection(connection, tableName);
                    if (columns.Any())
                    {
                        result[tableName] = columns;
                        Console.WriteLine($"Tabella {tableName}: {columns.Count()} colonne");
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"Errore nel leggere le colonne della tabella {tableName}: {ex.Message}");
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Errore in OleDbSchemaProvider.GetDatabaseSchemaAsync: {ex.Message}");
            throw;
        }

        return result;
    }

    public async Task<IEnumerable<string>> GetTableNamesAsync(string connectionString)
    {
        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            return Enumerable.Empty<string>();

        try
        {
            using var connection = new OleDbConnection(connectionString);
            await Task.Run(() => connection.Open());
            return GetTableNamesFromConnection(connection);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Errore in OleDbSchemaProvider.GetTableNamesAsync: {ex.Message}");
            return Enumerable.Empty<string>();
        }
    }

    public async Task<IEnumerable<DbColumnInfo>> GetTableSchemaAsync(string connectionString, string tableName)
    {
        if (!RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            return Enumerable.Empty<DbColumnInfo>();

        try
        {
            using var connection = new OleDbConnection(connectionString);
            await Task.Run(() => connection.Open());
            return GetTableColumnsFromConnection(connection, tableName);
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Errore in OleDbSchemaProvider.GetTableSchemaAsync per {tableName}: {ex.Message}");
            return Enumerable.Empty<DbColumnInfo>();
        }
    }

    public async Task<IEnumerable<string>> GetAvailableDatabasesAsync(string connectionString)
    {
        // OLE DB file-based (VFP, Access) non supporta listing di database multipli
        try
        {
            using var connection = new OleDbConnection(connectionString);
            await Task.Run(() => connection.Open());
            var db = connection.Database;
            return string.IsNullOrEmpty(db) ? Enumerable.Empty<string>() : new[] { db };
        }
        catch
        {
            return Enumerable.Empty<string>();
        }
    }

    private static List<string> GetTableNamesFromConnection(OleDbConnection connection)
    {
        var tableNames = new List<string>();

        try
        {
            // Usa GetOleDbSchemaTable - più compatibile con VFP rispetto a GetSchema()
            var restrictions = new object?[] { null, null, null, "TABLE" };
            var tablesSchema = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, restrictions);

            if (tablesSchema != null)
            {
                foreach (DataRow row in tablesSchema.Rows)
                {
                    var tableName = row["TABLE_NAME"]?.ToString();
                    if (!string.IsNullOrEmpty(tableName))
                        tableNames.Add(tableName);
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"GetOleDbSchemaTable Tables fallito, tentativo con GetSchema: {ex.Message}");

            // Fallback a GetSchema per provider che non supportano GetOleDbSchemaTable
            try
            {
                var tablesSchema = connection.GetSchema("Tables");
                tableNames = tablesSchema.AsEnumerable()
                    .Where(row =>
                    {
                        var t = row["TABLE_TYPE"]?.ToString();
                        return t == "TABLE" || t == "BASE TABLE";
                    })
                    .Select(row => row["TABLE_NAME"]?.ToString() ?? string.Empty)
                    .Where(n => !string.IsNullOrEmpty(n))
                    .ToList();
            }
            catch (Exception ex2)
            {
                Console.WriteLine($"GetSchema Tables fallito anche: {ex2.Message}");
            }
        }

        return tableNames.OrderBy(t => t).ToList();
    }

    private static List<DbColumnInfo> GetTableColumnsFromConnection(OleDbConnection connection, string tableName)
    {
        var columns = new List<DbColumnInfo>();

        try
        {
            // Ottieni primary keys
            var primaryKeys = GetPrimaryKeys(connection, tableName);

            // Ottieni colonne via GetOleDbSchemaTable
            var restrictions = new object?[] { null, null, tableName, null };
            var columnsSchema = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Columns, restrictions);

            if (columnsSchema == null)
                return columns;

            // Ordina per posizione ordinale
            var rows = columnsSchema.AsEnumerable()
                .OrderBy(r => r.IsNull("ORDINAL_POSITION") ? 0 : Convert.ToInt32(r["ORDINAL_POSITION"]))
                .ToList();

            foreach (DataRow row in rows)
            {
                var columnName = row["COLUMN_NAME"]?.ToString();
                if (string.IsNullOrEmpty(columnName))
                    continue;

                // DATA_TYPE è un int (OleDbType enum value)
                int oleDbTypeInt = row.IsNull("DATA_TYPE") ? 0 : Convert.ToInt32(row["DATA_TYPE"]);
                var dataType = MapOleDbTypeToString(oleDbTypeInt);

                // Formato con dimensioni
                var columnSize = row.IsNull("CHARACTER_MAXIMUM_LENGTH") ? 0 : Convert.ToInt32(row["CHARACTER_MAXIMUM_LENGTH"]);
                var numericPrecision = row.IsNull("NUMERIC_PRECISION") ? 0 : Convert.ToInt32(row["NUMERIC_PRECISION"]);
                var numericScale = row.IsNull("NUMERIC_SCALE") ? 0 : Convert.ToInt32(row["NUMERIC_SCALE"]);

                var formattedType = FormatDataType(dataType, columnSize, numericPrecision, numericScale);

                bool isNullable = true;
                if (!row.IsNull("IS_NULLABLE"))
                    isNullable = Convert.ToBoolean(row["IS_NULLABLE"]);

                columns.Add(new DbColumnInfo
                {
                    Name = columnName,
                    DataType = formattedType,
                    IsNullable = isNullable,
                    IsPrimaryKey = primaryKeys.Contains(columnName, StringComparer.OrdinalIgnoreCase)
                });
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Errore nel recuperare le colonne per {tableName}: {ex.Message}");
        }

        return columns;
    }

    private static HashSet<string> GetPrimaryKeys(OleDbConnection connection, string tableName)
    {
        var primaryKeys = new HashSet<string>(StringComparer.OrdinalIgnoreCase);

        try
        {
            var restrictions = new object?[] { null, null, tableName };
            var pkSchema = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Primary_Keys, restrictions);

            if (pkSchema != null)
            {
                foreach (DataRow row in pkSchema.Rows)
                {
                    var col = row["COLUMN_NAME"]?.ToString();
                    if (!string.IsNullOrEmpty(col))
                        primaryKeys.Add(col);
                }
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Primary keys non disponibili per {tableName}: {ex.Message}");

            // Fallback: prova con Indexes
            try
            {
                var restrictions = new object?[] { null, null, null, null, tableName };
                var idxSchema = connection.GetOleDbSchemaTable(OleDbSchemaGuid.Indexes, restrictions);

                if (idxSchema != null)
                {
                    foreach (DataRow row in idxSchema.Rows)
                    {
                        if (row["PRIMARY_KEY"] is bool pk && pk)
                        {
                            var col = row["COLUMN_NAME"]?.ToString();
                            if (!string.IsNullOrEmpty(col))
                                primaryKeys.Add(col);
                        }
                    }
                }
            }
            catch { /* Se anche questo fallisce, ignora */ }
        }

        return primaryKeys;
    }

    private static string MapOleDbTypeToString(int oleDbTypeInt)
    {
        // Mappa OleDbType enum (int) a nome leggibile
        // https://learn.microsoft.com/en-us/dotnet/api/system.data.oledb.oledbtype
        return oleDbTypeInt switch
        {
            2 => "SmallInt",
            3 => "Integer",
            4 => "Single",
            5 => "Double",
            6 => "Currency",
            7 => "Date",
            8 => "VarChar",      // BSTR
            9 => "IDispatch",
            10 => "Error",
            11 => "Boolean",
            12 => "Variant",
            13 => "IUnknown",
            14 => "Decimal",
            16 => "TinyInt",
            17 => "UnsignedTinyInt",
            18 => "UnsignedSmallInt",
            19 => "UnsignedInt",
            20 => "BigInt",
            21 => "UnsignedBigInt",
            64 => "DateTime",
            65 => "FileTime",
            72 => "Guid",
            128 => "Binary",
            129 => "Char",
            130 => "NVarChar",    // WChar
            131 => "Decimal",    // Numeric
            132 => "UserDefined",
            133 => "Date",
            134 => "Time",
            135 => "DateTime",   // DBTimeStamp
            136 => "Variant",    // Chapter
            138 => "PropVariant",
            139 => "VarNumeric",
            200 => "VarChar",
            201 => "LongVarChar",
            202 => "NVarChar",   // VarWChar
            203 => "NText",      // LongVarWChar
            204 => "VarBinary",
            205 => "Image",      // LongVarBinary
            _ => $"Type({oleDbTypeInt})"
        };
    }

    private static string FormatDataType(string dataType, int columnSize, int numericPrecision, int numericScale)
    {
        var upper = dataType.ToUpperInvariant();

        if (upper.Contains("DECIMAL") || upper.Contains("NUMERIC"))
        {
            if (numericPrecision > 0)
                return $"{dataType}({numericPrecision},{numericScale})";
        }
        else if (upper.Contains("CHAR") || upper.Contains("VARCHAR") || upper.Contains("TEXT") || upper.Contains("BINARY"))
        {
            if (columnSize > 0 && columnSize < 8000)
                return $"{dataType}({columnSize})";
            else if (columnSize >= 8000)
                return $"{dataType}(MAX)";
        }

        return dataType;
    }
}