/* ========================================================================
 * Copyright (c) 2005-2025 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;

namespace Opc.Ua.PubSub.Configuration
{
    /// <summary>
    /// Helper class that calculates the ConfigurationVersion for MetaData
    /// </summary>
    public static class ConfigurationVersionUtils
    {
        /// <summary>
        /// The epoch date is midnight UTC (00:00) on January 1, 2000.
        /// </summary>
        private static readonly DateTime s_epochDate = new(2000, 1, 1, 0, 0, 0, DateTimeKind.Utc);

        /// <summary>
        /// Analyze and decide the right ConfigurationVersion for new MetaData
        /// </summary>
        /// <param name="oldMetaData">The historical MetaData to be compared against the new MetaData</param>
        /// <param name="newMetaData">The new MetaData </param>
        /// <exception cref="ArgumentNullException"><paramref name="newMetaData"/> is <c>null</c>.</exception>
        public static ConfigurationVersionDataType CalculateConfigurationVersion(
            DataSetMetaDataType oldMetaData,
            DataSetMetaDataType newMetaData)
        {
            if (newMetaData == null)
            {
                throw new ArgumentNullException(nameof(newMetaData));
            }

            bool hasMinorVersionChange = false;
            bool hasMajorVersionChange = false;

            if (oldMetaData == null)
            {
                // create first version of ConfigurationVersion
                hasMajorVersionChange = true;
            }
            else
            {
                /*Removing fields from the DataSet content, reordering fields, adding fields in between other fields or a
                 * DataType change in fields shall result in an update of the MajorVersion.  */
                // check if any field was deleted
                if (oldMetaData.Fields.Count > newMetaData.Fields.Count)
                {
                    hasMajorVersionChange = true;
                }
                else
                {
                    // compare fields
                    for (int i = 0; i < oldMetaData.Fields.Count; i++)
                    {
                        /*If at least one Property value of a DataSetMetaData field changes, the MajorVersion shall be updated.*/
                        if (!Utils.IsEqual(
                            oldMetaData.Fields[i].Properties,
                            newMetaData.Fields[1].Properties))
                        {
                            hasMajorVersionChange = true;
                            break;
                        }
                    }
                    if (!hasMajorVersionChange &&
                        oldMetaData.Fields.Count < newMetaData.Fields.Count)
                    {
                        /* Only the MinorVersion shall be updated if fields are added at the end of the DataSet content.*/
                        hasMinorVersionChange = true;
                    }
                }
            }

            if (hasMajorVersionChange || hasMinorVersionChange)
            {
                uint versionTime = CalculateVersionTime(DateTime.UtcNow);
                if (hasMajorVersionChange)
                {
                    // Change both minor and major version
                    return new ConfigurationVersionDataType
                    {
                        MinorVersion = versionTime,
                        MajorVersion = versionTime
                    };
                }
                // only minor version was changed
                return new ConfigurationVersionDataType
                {
                    MinorVersion = versionTime,
                    MajorVersion = newMetaData.ConfigurationVersion.MajorVersion
                };
            }

            // there is no change
            return new ConfigurationVersionDataType
            {
                MinorVersion = newMetaData.ConfigurationVersion.MinorVersion,
                MajorVersion = newMetaData.ConfigurationVersion.MajorVersion
            };
        }

        /// <summary>
        /// Calculate and return the VersionTime calculated for the input parameter
        /// </summary>
        /// <param name="timeOfConfiguration">The current time of configuration</param>
        public static uint CalculateVersionTime(DateTime timeOfConfiguration)
        {
            /*This primitive data type is a UInt32 that represents the time in seconds since the year 2000. The epoch date is midnight UTC (00:00) on January 1, 2000.

            It is used as version number based on the last change time. If the version is updated, the new value shall be greater than the previous value.
            If a Variable is initialized with a VersionTime value, the value must be either loaded from persisted configuration or time synchronization must be available to ensure a unique version is applied.
            The value 0 is used to indicate that no version information is available.*/
            return (uint)timeOfConfiguration.Subtract(s_epochDate).TotalSeconds;
        }

        /// <summary>
        /// Check if the DataSetMetaData is usable for decoding.
        /// It shall be not null and have the Fields collection defined and also the ConfigurationVersion shall be not null or Empty
        /// </summary>
        public static bool IsUsable(DataSetMetaDataType dataSetMetaData)
        {
            if (dataSetMetaData == null)
            {
                return false;
            }

            if (dataSetMetaData.Fields.IsEmpty)
            {
                return false;
            }

            if (dataSetMetaData.ConfigurationVersion == null)
            {
                return false;
            }

            if (dataSetMetaData.ConfigurationVersion.MajorVersion == 0)
            {
                return false;
            }

            if (dataSetMetaData.ConfigurationVersion.MinorVersion == 0)
            {
                return false;
            }

            return true;
        }
    }
}