//-----------------------------------------------------------------------
// <copyright file="MetaDataHelpers.cs" company="Microsoft Corporation">
//     Copyright (c) Microsoft Corporation.
// </copyright>
//-----------------------------------------------------------------------

namespace Microsoft.Isam.Esent.Interop
{
    using System;
    using System.Collections.Generic;
    using System.Diagnostics;
    using System.Text;
    using Microsoft.Isam.Esent.Interop.Implementation;

    /// <summary>
    /// Helper methods for the ESENT API. These methods deal with database
    /// meta-data.
    /// </summary>
    public static partial class Api
    {
        #region Simpler API. Overloads that omit unused/obsolete parameters.
        /// <summary>
        /// Initialize a new ESENT session.
        /// </summary>
        /// <param name="instance">The initialized instance to create the session in.</param>
        /// <param name="sesid">Returns the created session.</param>
        public static void BeginSession(JET_INSTANCE instance, out JET_SESID sesid)
        {
            Api.JetBeginSession(instance, out sesid, null, null);
        }

        /// <summary>
        /// Creates and attaches a database file.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="database">The path to the database file to create.</param>
        /// <param name="dbid">Returns the dbid of the new database.</param>
        /// <param name="grbit">Database creation options.</param>
        public static void CreateDatabase(JET_SESID sesid, string database, out JET_DBID dbid, CreateDatabaseGrbit grbit)
        {
            Api.JetCreateDatabase(sesid, database, null, out dbid, grbit);
        }

        /// <summary>
        /// Opens a database previously attached with <see cref="JetAttachDatabase"/>,
        /// for use with a database session. This function can be called multiple times
        /// for the same database.
        /// </summary>
        /// <param name="sesid">The session that is opening the database.</param>
        /// <param name="database">The database to open.</param>
        /// <param name="dbid">Returns the dbid of the attached database.</param>
        /// <param name="grbit">Open database options.</param>
        /// <returns>An ESENT warning code.</returns>
        public static JET_wrn OpenDatabase(
            JET_SESID sesid,
            string database,
            out JET_DBID dbid,
            OpenDatabaseGrbit grbit)
        {
            return Api.JetOpenDatabase(sesid, database, null, out dbid, grbit);
        }

        /// <summary>
        /// Opens a cursor on a previously created table.
        /// </summary>
        /// <param name="sesid">The database session to use.</param>
        /// <param name="dbid">The database to open the table in.</param>
        /// <param name="tablename">The name of the table to open.</param>
        /// <param name="grbit">Table open options.</param>
        /// <param name="tableid">Returns the opened table.</param>
        /// <returns>An ESENT warning.</returns>
        public static JET_wrn OpenTable(
            JET_SESID sesid,
            JET_DBID dbid,
            string tablename,
            OpenTableGrbit grbit,
            out JET_TABLEID tableid)
        {
            return Api.JetOpenTable(sesid, dbid, tablename, null, 0, grbit, out tableid);
        }

        #endregion

        /// <summary>
        /// Try to open a table.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="dbid">The database to look for the table in.</param>
        /// <param name="tablename">The name of the table.</param>
        /// <param name="grbit">Table open options.</param>
        /// <param name="tableid">Returns the opened tableid.</param>
        /// <returns>True if the table was opened, false if the table doesn't exist.</returns>
        public static bool TryOpenTable(
            JET_SESID sesid,
            JET_DBID dbid,
            string tablename,
            OpenTableGrbit grbit,
            out JET_TABLEID tableid)
        {
            var err = (JET_err)Impl.JetOpenTable(sesid, dbid, tablename, null, 0, grbit, out tableid);
            if (JET_err.ObjectNotFound == err)
            {
                return false;
            }

            Api.Check((int)err);
            Debug.Assert(err >= JET_err.Success, "Exception should have been thrown in case of error");
            return true;
        }

        /// <summary>
        /// Creates a dictionary which maps column names to their column IDs.
        /// </summary>
        /// <param name="sesid">The sesid to use.</param>
        /// <param name="tableid">The table to retrieve the information for.</param>
        /// <returns>A dictionary mapping column names to column IDs.</returns>
        public static IDictionary<string, JET_COLUMNID> GetColumnDictionary(JET_SESID sesid, JET_TABLEID tableid)
        {
            JET_COLUMNLIST columnlist;
            JetGetTableColumnInfo(sesid, tableid, string.Empty, out columnlist);

            // As of Sep 2015, JetGetColumnInfoW is only called for Win8+. Even though Unicode should have
            // worked in Win7, it wasn't reliable until Win8.
            Encoding encodingOfTextColumns = EsentVersion.SupportsWindows8Features ? Encoding.Unicode : LibraryHelpers.EncodingASCII;

            try
            {
                // esent treats column names as case-insensitive, so we want the dictionary to be case insensitive as well
                var dict = new Dictionary<string, JET_COLUMNID>(
                    columnlist.cRecord, StringComparer.OrdinalIgnoreCase);
                if (columnlist.cRecord > 0)
                {
                    if (Api.TryMoveFirst(sesid, columnlist.tableid))
                    {
                        do
                        {
                            string name = RetrieveColumnAsString(
                                sesid,
                                columnlist.tableid,
                                columnlist.columnidcolumnname,
                                encodingOfTextColumns,
                                RetrieveColumnGrbit.None);
                            name = StringCache.TryToIntern(name);
                            var columnidValue =
                                (uint)RetrieveColumnAsUInt32(sesid, columnlist.tableid, columnlist.columnidcolumnid);

                            var columnid = new JET_COLUMNID { Value = columnidValue };
                            dict.Add(name, columnid);
                        }
                        while (TryMoveNext(sesid, columnlist.tableid));
                    }
                }

                return dict;
            }
            finally
            {
                // Close the temporary table used to return the results
                JetCloseTable(sesid, columnlist.tableid);
            }
        }

        /// <summary>
        /// Get the columnid of the specified column.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="tableid">The table containing the column.</param>
        /// <param name="columnName">The name of the column.</param>
        /// <returns>The id of the column.</returns>
        public static JET_COLUMNID GetTableColumnid(JET_SESID sesid, JET_TABLEID tableid, string columnName)
        {
            JET_COLUMNDEF columndef;
            JetGetTableColumnInfo(sesid, tableid, columnName, out columndef);
            return columndef.columnid;
        }

        /// <summary>
        /// Iterates over all the columns in the table, returning information about each one.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="tableid">The table to retrieve column information for.</param>
        /// <returns>An iterator over ColumnInfo for each column in the table.</returns>
        public static IEnumerable<ColumnInfo> GetTableColumns(JET_SESID sesid, JET_TABLEID tableid)
        {
            return new GenericEnumerable<ColumnInfo>(() => new TableidColumnInfoEnumerator(sesid, tableid));
        }

        /// <summary>
        /// Iterates over all the columns in the table, returning information about each one.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="dbid">The database containing the table.</param>
        /// <param name="tablename">The name of the table.</param>
        /// <returns>An iterator over ColumnInfo for each column in the table.</returns>
        public static IEnumerable<ColumnInfo> GetTableColumns(JET_SESID sesid, JET_DBID dbid, string tablename)
        {
            if (null == tablename)
            {
                throw new ArgumentNullException("tablename");
            }

            return new GenericEnumerable<ColumnInfo>(() => new TableColumnInfoEnumerator(sesid, dbid, tablename));
        }

        /// <summary>
        /// Iterates over all the indexes in the table, returning information about each one.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="tableid">The table to retrieve index information for.</param>
        /// <returns>An iterator over an IndexInfo for each index in the table.</returns>
        public static IEnumerable<IndexInfo> GetTableIndexes(JET_SESID sesid, JET_TABLEID tableid)
        {
            return new GenericEnumerable<IndexInfo>(() => new TableidIndexInfoEnumerator(sesid, tableid));
        }

        /// <summary>
        /// Iterates over all the indexs in the table, returning information about each one.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="dbid">The database containing the table.</param>
        /// <param name="tablename">The name of the table.</param>
        /// <returns>An iterator over an IndexInfo for each index in the table.</returns>
        public static IEnumerable<IndexInfo> GetTableIndexes(JET_SESID sesid, JET_DBID dbid, string tablename)
        {
            if (null == tablename)
            {
                throw new ArgumentNullException("tablename");
            }

            return new GenericEnumerable<IndexInfo>(() => new TableIndexInfoEnumerator(sesid, dbid, tablename));
        }

        /// <summary>
        /// Returns the names of the tables in the database.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="dbid">The database containing the table.</param>
        /// <returns>An iterator over the names of the tables in the database.</returns>
        public static IEnumerable<string> GetTableNames(JET_SESID sesid, JET_DBID dbid)
        {
            return new GenericEnumerable<string>(() => new TableNameEnumerator(sesid, dbid));
        }

        /// <summary>
        /// Retrieves information about indexes on a table.
        /// </summary>
        /// <param name="sesid">The session to use.</param>
        /// <param name="tableid">The table to retrieve index information about.</param>
        /// <param name="indexname">The name of the index.</param>
        /// <param name="result">Filled in with information about indexes on the table.</param>
        /// <param name="infoLevel">The type of information to retrieve.</param>
        /// <returns>true if there was no error, false if the index wasn't found. Throws for other Jet errors.</returns>
        public static bool TryJetGetTableIndexInfo(
            JET_SESID sesid,
            JET_TABLEID tableid,
            string indexname,
            out JET_INDEXID result,
            JET_IdxInfo infoLevel)
        {
            int err = Impl.JetGetTableIndexInfo(sesid, tableid, indexname, out result, infoLevel);

            if ((JET_err)err == JET_err.IndexNotFound)
            {
                return false;
            }

            Api.Check(err);

            return true;
        }

        /// <summary>
        /// Determines the name of the current index of a given cursor.
        /// </summary>
        /// <remarks>
        /// This name is also used to later re-select that index as the current index using
        /// <see cref="JetSetCurrentIndex"/>.  It can also be used to discover the properties of that index using
        /// JetGetTableIndexInfo.
        /// 
        /// The returned name of the index will be null if the current index is the clustered index and no primary
        /// index was explicitly defined.
        /// </remarks>
        /// <param name="sesid">The session to use.</param>
        /// <param name="tableid">The cursor to get the index name for.</param>
        /// <returns>Returns the name of the index.</returns>
        public static string JetGetCurrentIndex(JET_SESID sesid, JET_TABLEID tableid)
        {
            string indexName;
            Api.JetGetCurrentIndex(sesid, tableid, out indexName, SystemParameters.NameMost);

            return string.IsNullOrEmpty(indexName) ? null : indexName;
        }
    }
}