sql-utilities/src/Strata.SqlTools.SqlServer/Breakdowns/QueryBreakdown.cs

using System.Collections;
using System.Text;
using Strata.SqlTools.SqlBreakdown.Classes;
using Strata.SqlTools.SqlBreakdown.Expressions;
using Strata.SqlTools.SqlBreakdown.Interfaces;
using Strata.SqlTools.SqlBreakdown.Interfaces.QueryEngine;
using Strata.SqlTools.SqlServer.Exceptions;
using Strata.SqlTools.Statements.SqlServer;
using Strata.SqlTools.Visitors.SqlServer;

namespace Strata.SqlTools.Breakdowns.SqlServer;

/// <summary>
/// Represents a SELECT query breakdown with all clauses (SELECT, FROM, WHERE, GROUP BY, HAVING, ORDER BY).
/// </summary>
#pragma warning disable S2325 // Methods and properties that don't access instance data should be static - False positive: These members access instance fields
public class QueryBreakdown : SqlBreakdownBase, IQueryBreakdown
{
    private const string ExpressionNullErrorMessage = "Expression cannot be null.";
    private List<IQueryParam> _parameterList;
    private List<IWithClause> _withClauses;
    protected readonly StatementParser Parser;

    // Caching fields for GetClauses() performance optimization
    private SqlClauses? _cachedClauses;
    private bool _clausesCacheDirty;

    // Backing fields for clause properties to support cache invalidation
#pragma warning disable S3604 // "Fields should not be write-only" - False positive: These fields are used as backing fields for properties that manage cache invalidation
    private ISqlExpressionClause _selectClause = new SqlExpressionClause();
    private ISqlClause _fromClause = new SqlClause();
    private ISqlExpressionClause _whereClause = new SqlExpressionClause();
    private ISqlExpressionClause _groupByClause = new SqlExpressionClause();
    private ISqlExpressionClause _havingClause = new SqlExpressionClause();
    private ISqlExpressionClause _orderByClause = new SqlExpressionClause();
#pragma warning restore S3604

    /// <summary>
    /// Initializes a new instance of the <see cref="QueryBreakdown"/> class.
    /// </summary>
    public QueryBreakdown() : base()
    {
        Parser = new StatementParser();
        _parameterList = [];
        _withClauses = [];

        // Initialize backing fields directly to avoid triggering cache invalidation
        _selectClause = new SqlExpressionClause(splitOnComma: true);
        _fromClause = new SqlClause();
        _whereClause = new SqlExpressionClause(splitOnComma: false);
        _orderByClause = new SqlExpressionClause(splitOnComma: true);
        _groupByClause = new SqlExpressionClause(splitOnComma: true);
        _havingClause = new SqlExpressionClause(splitOnComma: false);

        // Cache is dirty initially (will be built on first GetClauses() call)
        _clausesCacheDirty = true;
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="QueryBreakdown"/> class with SELECT and FROM clauses.
    /// </summary>
    /// <param name="selectClause">The SELECT clause.</param>
    /// <param name="fromClause">The FROM clause.</param>
    public QueryBreakdown(string selectClause, string fromClause) : this()
    {
        var cleanSelect = Parser.ExtractSqlComments(selectClause, out var selectComments);
        SelectClause.Clause = cleanSelect.Trim();
        SelectClause.Comment = selectComments.Count > 0 ? string.Join(" ", selectComments) : null;

        var cleanFrom = Parser.ExtractSqlComments(fromClause, out var fromComments);
        FromClause.Clause = cleanFrom.Trim();
        FromClause.Comment = fromComments.Count > 0 ? string.Join(" ", fromComments) : null;
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="QueryBreakdown"/> class with SELECT, FROM, and WHERE clauses.
    /// </summary>
    /// <param name="selectClause">The SELECT clause.</param>
    /// <param name="fromClause">The FROM clause.</param>
    /// <param name="whereClause">The WHERE clause.</param>
    public QueryBreakdown(string selectClause, string fromClause, string whereClause) : this(selectClause, fromClause)
    {
        if (!string.IsNullOrEmpty(whereClause))
        {
            var cleanWhere = Parser.ExtractSqlComments(whereClause, out var whereComments);
            WhereClause.Clause = cleanWhere.Trim();
            WhereClause.Comment = whereComments.Count > 0 ? string.Join(" ", whereComments) : null;
        }
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="QueryBreakdown"/> class with SELECT, FROM, WHERE, and ORDER BY clauses.
    /// </summary>
    /// <param name="selectClause">The SELECT clause.</param>
    /// <param name="fromClause">The FROM clause.</param>
    /// <param name="whereClause">The WHERE clause.</param>
    /// <param name="orderByClause">The ORDER BY clause.</param>
    public QueryBreakdown(string selectClause, string fromClause, string whereClause, string orderByClause)
        : this(selectClause, fromClause, whereClause)
    {
        if (!string.IsNullOrEmpty(orderByClause))
        {
            var cleanOrderBy = Parser.ExtractSqlComments(orderByClause, out var orderByComments);
            OrderByClause.Clause = cleanOrderBy.Trim();
            OrderByClause.Comment = orderByComments.Count > 0 ? string.Join(" ", orderByComments) : null;
        }
    }

    #region Properties

    /// <summary>
    /// Gets the list of query parameters.
    /// </summary>
    public IEnumerable<IQueryParam> ParameterList => _parameterList;

    /// <summary>
    /// Gets the parameter dictionary containing parameter names and their values.
    /// Parameter values can be set/updated after parsing.
    /// </summary>
    public Dictionary<string, object> Parameters { get; } = [];

    /// <summary>
    /// Gets the WITH clauses (Common Table Expressions) as an ordered list.
    /// </summary>
    public IReadOnlyList<IWithClause> WithClauses => _withClauses.AsReadOnly();

    /// <summary>
    /// Gets or sets the WITH clause string for backward compatibility with parsing.
    /// </summary>
    protected internal string? WithClause { get; set; }

    /// <summary>
    /// Gets the WITH clause value (for derived classes to access).
    /// </summary>
    public string? GetWithClauseValue() => WithClause;

    /// <summary>
    /// Sets the WITH clause value (for derived classes to set).
    /// </summary>
    public void SetWithClauseValue(string? value) => WithClause = value;

    /// <summary>
    /// Gets a value indicating whether WITH clauses are being used.
    /// </summary>
    public bool IsUsingWithClause => _withClauses.Count > 0 || !string.IsNullOrEmpty(WithClause);

    /// <summary>
    /// Gets or sets the SELECT clause with optional comment.
    /// </summary>
    public ISqlExpressionClause SelectClause
    {
        get => _selectClause;
        set
        {
            _selectClause = value;
            InvalidateClausesCache();
        }
    }

    /// <summary>
    /// Gets a value indicating whether a FROM clause is being used.
    /// </summary>
    public bool IsUsingFromClause => !string.IsNullOrEmpty(FromClause.Clause);

    /// <summary>
    /// Gets or sets the FROM clause with optional comment.
    /// </summary>
    public ISqlClause FromClause
    {
        get => _fromClause;
        set
        {
            _fromClause = value;
            InvalidateClausesCache();
        }
    }

    /// <summary>
    /// Gets a value indicating whether a GROUP BY clause is being used.
    /// </summary>
    public bool IsUsingGroupByClause => !string.IsNullOrEmpty(GroupByClause.Clause);

    /// <summary>
    /// Gets or sets the GROUP BY clause with optional comment.
    /// </summary>
    public ISqlExpressionClause GroupByClause
    {
        get => _groupByClause;
        set
        {
            _groupByClause = value;
            InvalidateClausesCache();
        }
    }

    /// <summary>
    /// Gets a value indicating whether a WHERE clause is being used.
    /// </summary>
    public bool IsUsingWhereClause => !string.IsNullOrEmpty(WhereClause.Clause);

    /// <summary>
    /// Gets or sets the WHERE clause with optional comment.
    /// </summary>
    public ISqlExpressionClause WhereClause
    {
        get => _whereClause;
        set
        {
            _whereClause = value;
            InvalidateClausesCache();
        }
    }

    /// <summary>
    /// Gets or sets the ORDER BY clause with optional comment.
    /// </summary>
    public ISqlExpressionClause OrderByClause
    {
        get => _orderByClause;
        set
        {
            _orderByClause = value;
            InvalidateClausesCache();
        }
    }

    /// <summary>
    /// Gets a value indicating whether an ORDER BY clause is being used.
    /// </summary>
    public bool IsUsingOrderByClause => !string.IsNullOrEmpty(OrderByClause.Clause);

    /// <summary>
    /// Gets or sets the HAVING clause with optional comment.
    /// </summary>
    public ISqlExpressionClause HavingClause
    {
        get => _havingClause;
        set
        {
            _havingClause = value;
            InvalidateClausesCache();
        }
    }

    /// <summary>
    /// Gets a value indicating whether a HAVING clause is being used.
    /// </summary>
    public bool IsUsingHavingClause => !string.IsNullOrEmpty(HavingClause.Clause);

    #endregion

    #region Methods

    /// <summary>
    /// Adds a parameter to the query.
    /// </summary>
    /// <param name="parameterName">The parameter name.</param>
    /// <param name="value">The parameter value.</param>
    public void AddParameter(string parameterName, object value)
    {
        _parameterList.Add(new QueryParam(parameterName, value));
        // Also add/update in dictionary
        if (parameterName.StartsWith('@'))
        {
            Parameters[parameterName] = value;
        }
        else
        {
            Parameters[$"@{parameterName}"] = value;
        }
    }

    /// <summary>
    /// Adds multiple parameters to the query.
    /// </summary>
    /// <param name="queryParams">The query parameters to add.</param>
    public void AddParameter(IEnumerable<IQueryParam> queryParams)
    {
        _parameterList.AddRange(queryParams);
        // Also add/update in dictionary
        foreach (var param in queryParams)
        {
            var name = param.Name.StartsWith('@') ? param.Name : $"@{param.Name}";
            Parameters[name] = param.Value;
        }
    }

    /// <summary>
    /// Sets the value of a parameter in the Parameters dictionary.
    /// If the parameter doesn't exist, it will be added.
    /// </summary>
    /// <param name="parameterName">The parameter name (with or without @).</param>
    /// <param name="value">The parameter value.</param>
    public void SetParameterValue(string parameterName, object value)
    {
        var name = parameterName.StartsWith('@') ? parameterName : $"@{parameterName}";
        Parameters[name] = value;

        // Update or add to parameter list
        var existingParam = _parameterList.FirstOrDefault(p => p.Name == name);
        if (existingParam != null)
        {
            _parameterList.Remove(existingParam);
        }
        _parameterList.Add(new QueryParam(name, value));
    }

    /// <summary>
    /// Gets the value of a parameter from the Parameters dictionary.
    /// </summary>
    /// <param name="parameterName">The parameter name (with or without @).</param>
    /// <returns>The parameter value, or null if not found.</returns>
    public object? GetParameterValue(string parameterName)
    {
        var name = parameterName.StartsWith('@') ? parameterName : $"@{parameterName}";
        return Parameters.TryGetValue(name, out var value) ? value : null;
    }

    /// <summary>
    /// Adds or updates a parameter with value validation.
    /// If the parameter exists with a non-null value and the new value is of a different type, throws an exception.
    /// If the parameter exists with a null value, sets the value.
    /// If the parameter exists with a non-null value of the same type, keeps the existing value.
    /// If the parameter doesn't exist, adds it.
    /// </summary>
    /// <param name="parameterName">The parameter name (with or without @ or :).</param>
    /// <param name="value">The parameter value.</param>
    /// <exception cref="InvalidOperationException">Thrown when trying to set a parameter to a different type than its existing value.</exception>
    protected void AddOrUpdateParameter(string parameterName, object? value)
    {
        // Normalize parameter name - keep : or @ prefix if present, otherwise add @
        string name;
        if (parameterName.StartsWith(':') || parameterName.StartsWith('@'))
        {
            name = parameterName;
        }
        else
        {
            name = $"@{parameterName}";
        }

        if (Parameters.TryGetValue(name, out var existingValue))
        {
            // Parameter already exists
            if (existingValue != null && value != null)
            {
                // Both existing and new values are non-null, check types
                var existingType = existingValue.GetType();
                var newType = value.GetType();

                if (existingType != newType)
                {
                    throw new InvalidOperationException(
                        $"Parameter '{name}' already exists with type '{existingType.Name}' but attempted to set it with type '{newType.Name}'.");
                }
                // Same type - keep existing value (don't update)
                // This is important for AddWhereClause behavior where extracted params are null
            }
            else if (existingValue == null && value != null)
            {
                // Existing value is null, new value is not null - set it
                Parameters[name] = value;
            }
            // If new value is null, keep existing value (don't overwrite)
        }
        else
        {
            // Parameter doesn't exist, add it
            Parameters[name] = value!;
        }
    }

    /// <summary>
    /// Extracts parameters from a SQL clause and adds them to the Parameters dictionary.
    /// </summary>
    /// <param name="sql">The SQL clause to extract parameters from.</param>
    protected void ExtractAndAddParameters(string sql)
    {
        if (string.IsNullOrWhiteSpace(sql))
        {
            return;
        }

        // Create a temporary dictionary to extract parameters
        var tempParams = new Dictionary<string, object>();
        Parser.ExtractParameters(tempParams, sql);

        // Add each parameter using the managed add method
        foreach (var kvp in tempParams)
        {
            AddOrUpdateParameter(kvp.Key, kvp.Value);
        }
    }

    /// <summary>
    /// Invalidates the GetClauses() cache, forcing a fresh SqlClauses object on the next call.
    /// Called automatically whenever any clause property is modified.
    /// </summary>
    private void InvalidateClausesCache()
    {
        _clausesCacheDirty = true;
        _cachedClauses = null;
    }

    /// <summary>
    /// Gets the SQL clauses from this query breakdown.
    /// </summary>
    /// <returns>A SqlClauses object containing the current clause properties.</returns>
    /// <remarks>
    /// This method uses caching to improve performance. The cached result is invalidated
    /// whenever any clause property is modified.
    /// </remarks>
    public virtual SqlClauses GetClauses()
    {
        if (_clausesCacheDirty || _cachedClauses == null)
        {
            _cachedClauses = new SqlClauses
            {
                SelectClause = SelectClause,
                FromClause = FromClause,
                WhereClause = WhereClause,
                GroupByClause = GroupByClause,
                HavingClause = HavingClause,
                OrderByClause = OrderByClause
            };
            _clausesCacheDirty = false;
        }

        return _cachedClauses;
    }

    /// <summary>
    /// Applies SQL clauses from a SqlClauses object to this query breakdown.
    /// Only non-null clauses are applied.
    /// </summary>
    /// <param name="clauses">The SQL clauses to apply.</param>
    public virtual void ApplyClauses(SqlClauses? clauses)
    {
        if (clauses == null)
        {
            return;
        }

        if (clauses.SelectClause != null)
        {
            SelectClause = clauses.SelectClause;
        }

        if (clauses.FromClause != null)
        {
            FromClause = clauses.FromClause;
        }

        if (clauses.WhereClause != null)
        {
            WhereClause = clauses.WhereClause;
        }

        if (clauses.GroupByClause != null)
        {
            GroupByClause = clauses.GroupByClause;
        }

        if (clauses.HavingClause != null)
        {
            HavingClause = clauses.HavingClause;
        }

        if (clauses.OrderByClause != null)
        {
            OrderByClause = clauses.OrderByClause;
        }
    }

    /// <summary>
    /// Collects all parameters from the CTE hierarchy recursively.
    /// This method traverses all WITH clauses and their nested queries to collect parameters.
    /// </summary>
    /// <param name="allCollectedParams">Dictionary to collect parameters (passed recursively).</param>
    /// <remarks>
    /// Parameters from nested CTEs are collected using TryAdd, so existing parameters in the main query
    /// take precedence over CTE parameters with the same name.
    /// </remarks>
    protected virtual void CollectCteParameters(Dictionary<string, object> allCollectedParams)
    {
        // First add CTE parameters (so main query parameters can override them)
        foreach (var withClause in _withClauses)
        {
            if (withClause.Query == null)
            {
                continue;
            }

            CollectFromCteQuery(withClause.Query, allCollectedParams);

            // For recursive CTEs, also collect parameters from the recursive query
            if (withClause.IsRecursive)
            {
                CollectFromCteQuery(withClause.RecursiveQuery, allCollectedParams);
            }
        }
    }

    /// <summary>
    /// Recursively collects parameters from a single CTE query and its nested CTEs.
    /// Parameters are added with an '@' prefix via TryAdd, so existing entries take precedence.
    /// </summary>
    private static void CollectFromCteQuery(IQueryBreakdown? query, Dictionary<string, object> allCollectedParams)
    {
        if (query == null)
        {
            return;
        }

        // Recursively collect parameters from nested CTEs in this query
        if (query is QueryBreakdown nestedQueryBreakdown)
        {
            nestedQueryBreakdown.CollectCteParameters(allCollectedParams);
        }

        // Add the query's own parameters (TryAdd means existing params take precedence)
        foreach (var param in query.ParameterList)
        {
            var paramName = param.Name.StartsWith('@') ? param.Name : $"@{param.Name}";
            allCollectedParams.TryAdd(paramName, param.Value);
        }
    }

    /// <summary>
    /// Gets all parameters including those from the CTE hierarchy.
    /// The main query's parameters take precedence over CTE parameters with the same name.
    /// </summary>
    /// <returns>A dictionary containing all parameters merged from the CTE hierarchy and main query.</returns>
    public virtual Dictionary<string, object> GetMergedParameters()
    {
        var mergedParams = new Dictionary<string, object>();

        // First collect CTE parameters
        CollectCteParameters(mergedParams);

        // Then add/override with main query parameters
        foreach (var param in Parameters)
        {
            mergedParams[param.Key] = param.Value;
        }

        return mergedParams;
    }

#pragma warning disable S3776 // Cognitive Complexity of methods should not be too high
    /// <summary>
    /// Gets the SQL breakdown as a string (query-specific implementation).
    /// </summary>
    /// <returns>The SELECT SQL statement.</returns>
    protected override string GetSqlBreakdown()
#pragma warning restore S3776
    {
        var sb = new StringBuilder();

        if (IsUsingWithClause)
        {
            // Check if any CTE is recursive - if so, add RECURSIVE keyword
            bool hasRecursive = _withClauses.Any(wc => wc.IsRecursive);
            sb.Append("WITH ");
            if (hasRecursive)
            {
                sb.AppendLine("RECURSIVE");
            }
            else
            {
                sb.AppendLine();
            }

            for (int i = 0; i < _withClauses.Count; i++)
            {
                var withClause = _withClauses[i];
                var anchorSql = withClause.Query?.GetSql(includeSetupFinish: false).Trim() ?? string.Empty;

                if (i > 0)
                {
                    sb.Append(',');
                    sb.AppendLine();
                }

                // Include comment if present
                if (!string.IsNullOrWhiteSpace(withClause.Comment))
                {
                    sb.AppendLine($"     {withClause.Comment}");
                }

                // Write CTE name with optional column list
                var cteName = withClause.TableName;
                if (withClause.ColumnList != null && withClause.ColumnList.Count > 0)
                {
                    var columnList = string.Join(", ", withClause.ColumnList);
                    cteName = $"{withClause.TableName} ({columnList})";
                }
                sb.AppendLine($"     {cteName} AS (");

                if (withClause.IsRecursive && withClause.RecursiveQuery != null)
                {
                    // For recursive CTEs: anchor query UNION ALL recursive query
                    var recursiveSql = withClause.RecursiveQuery.GetSql(includeSetupFinish: false).Trim();
                    sb.AppendLine($"          {anchorSql}");
                    sb.AppendLine("          UNION ALL");
                    sb.AppendLine($"          {recursiveSql}");
                }
                else
                {
                    // For non-recursive CTEs: just the single query
                    sb.AppendLine($"          {anchorSql}");
                }

                sb.Append("     )");
            }
            sb.AppendLine();
        }

        sb.AppendLine("SELECT ");
        if (!string.IsNullOrEmpty(SelectClause.Comment))
        {
            sb.AppendLine($"     {SelectClause.Comment}");
        }
        sb.AppendLine($"     {SelectClause.Clause}");

        if (IsUsingFromClause)
        {
            sb.AppendLine("FROM ");
            if (!string.IsNullOrEmpty(FromClause.Comment))
            {
                sb.AppendLine($"     {FromClause.Comment}");
            }
            sb.AppendLine($"     {FromClause.Clause}");
        }

        if (IsUsingWhereClause)
        {
            sb.AppendLine("WHERE ");
            if (!string.IsNullOrEmpty(WhereClause.Comment))
            {
                sb.AppendLine($"     {WhereClause.Comment}");
            }
            sb.AppendLine($"     {WhereClause.Clause}");
        }

        if (IsUsingGroupByClause)
        {
            sb.AppendLine("GROUP BY ");
            if (!string.IsNullOrEmpty(GroupByClause.Comment))
            {
                sb.AppendLine($"     {GroupByClause.Comment}");
            }
            sb.AppendLine($"     {GroupByClause.Clause}");
        }

        if (IsUsingHavingClause)
        {
            sb.AppendLine("HAVING ");
            if (!string.IsNullOrEmpty(HavingClause.Comment))
            {
                sb.AppendLine($"     {HavingClause.Comment}");
            }
            sb.AppendLine($"     {HavingClause.Clause}");
        }

        if (IsUsingOrderByClause)
        {
            sb.AppendLine("ORDER BY ");
            if (!string.IsNullOrEmpty(OrderByClause.Comment))
            {
                sb.AppendLine($"     {OrderByClause.Comment}");
            }
            sb.AppendLine($"     {OrderByClause.Clause}");
        }

        return sb.ToString();
    }

    /// <summary>
    /// Gets the complete SQL query including optional setup and finish clauses (for backward compatibility).
    /// </summary>
    /// <param name="includeSetupFinish">Whether to include setup and finish clauses.</param>
    /// <returns>The complete SQL query string.</returns>
    public new virtual string GetSql(bool includeSetupFinish = true)
    {
        return base.GetSql(includeSetupFinish);
    }

    /// <summary>
    /// Creates a deep clone of this query breakdown.
    /// </summary>
    /// <returns>A cloned instance.</returns>
    public new object Clone()
    {
        // Start with base clone (handles SetupClauses and FinishClauses)
        var clone = (QueryBreakdown)base.Clone();

        // Deep copy query-specific properties
        clone.SelectClause = new SqlExpressionClause(splitOnComma: true) { Clause = SelectClause.Clause, Comment = SelectClause.Comment };
        clone.FromClause = new SqlClause { Clause = FromClause.Clause, Comment = FromClause.Comment };
        clone.WhereClause = new SqlExpressionClause(splitOnComma: false) { Clause = WhereClause.Clause, Comment = WhereClause.Comment };
        clone.GroupByClause = new SqlExpressionClause(splitOnComma: true) { Clause = GroupByClause.Clause, Comment = GroupByClause.Comment };
        clone.HavingClause = new SqlExpressionClause(splitOnComma: false) { Clause = HavingClause.Clause, Comment = HavingClause.Comment };
        clone.OrderByClause = new SqlExpressionClause(splitOnComma: true) { Clause = OrderByClause.Clause, Comment = OrderByClause.Comment };
        clone.WithClause = WithClause;

        // Deep copy parameter list
        clone._parameterList = new List<IQueryParam>(_parameterList.Select(p => new QueryParam(p.Name, p.Value)));

        // Deep copy with clauses (recursive cloning for nested queries)
        clone._withClauses = new List<IWithClause>(
            _withClauses.Select(w =>
            {
                // Clone the query if it implements ICloneable, otherwise use the original reference
                var clonedQuery = w.Query is ICloneable cloneable
                    ? (IQueryBreakdown)cloneable.Clone()
                    : w.Query;
                return new WithClause(w.TableName, clonedQuery!) { Clause = w.Clause, Comment = w.Comment, Sql = w.Sql };
            }));

        // Deep copy parameters dictionary
        foreach (var kvp in Parameters)
        {
            clone.Parameters[kvp.Key] = kvp.Value;
        }

        return clone;
    }

    /// <summary>
    /// Gets a LINQ to SQL query of the specified type based on this breakdown.
    /// </summary>
    /// <typeparam name="T">The entity type for the query.</typeparam>
    /// <returns>An empty queryable by default, as QueryBreakdown operates on SQL. Override in derived classes to provide LINQ query reconstruction.</returns>
    /// <remarks>
    /// This base implementation returns an empty queryable since QueryBreakdown represents parsed SQL statements
    /// and has no built-in way to create LINQ queries.
    /// Derived classes (such as LinqQueryBreakdown) can override this method to reconstruct LINQ queries
    /// from the analyzed components.
    /// </remarks>
    public override IQueryable<T> GetQuery<T>() where T : class => Enumerable.Empty<T>().AsQueryable();

    /// <summary>
    /// Gets the complete SQL query string (interface implementation).
    /// </summary>
    /// <param name="includeSetupFinish">Whether to include setup and finish clauses.</param>
    /// <returns>The SQL query string.</returns>
    public string GetSQL(bool includeSetupFinish = true) => GetSql(includeSetupFinish);

    /// <summary>
    /// Merges another query breakdown into this one.
    /// </summary>
    /// <param name="query">The query to merge.</param>
#pragma warning disable S3776 // Cognitive Complexity of methods should not be too high
    public void MergeWith(IQueryBreakdown query)
#pragma warning restore S3776
    {
        FromClause.Clause = $"{FromClause.Clause} {query.FromClause.Clause}";

        if (query.IsUsingWhereClause)
        {
            // Ensure join clause is present
            if (!string.IsNullOrEmpty(WhereClause.Clause) && !string.IsNullOrEmpty(query.WhereClause.Clause))
            {
                string trimmedWhere = query.WhereClause.Clause.Trim().ToUpperInvariant();
                if (!trimmedWhere.Equals("AND") && !trimmedWhere.Equals("OR") &&
                    !trimmedWhere.StartsWith("AND ") && !trimmedWhere.StartsWith("OR "))
                {
                    string currentWhereTrimmed = WhereClause.Clause.Trim().ToUpperInvariant();
                    if (!currentWhereTrimmed.EndsWith(" AND") && !currentWhereTrimmed.EndsWith(" OR"))
                    {
                        WhereClause.Clause += " AND ";
                    }
                }
            }

            WhereClause.Clause = $"{WhereClause.Clause} {query.WhereClause.Clause}";
        }

        if (query.IsUsingSetupClause)
        {
            SetupClauses.AddRange(query.SetupClauses);
        }

        if (query.IsUsingFinishClause)
        {
            FinishClauses.AddRange(query.FinishClauses);
        }

        foreach (var param in query.ParameterList)
        {
            AddParameter(param.Name, param.Value);
        }
    }

    /// <summary>
    /// Adds a WHERE clause condition.
    /// </summary>
    /// <param name="sql">The SQL condition to add.</param>
    public void AddWhereClause(string sql)
    {
        if (string.IsNullOrWhiteSpace(sql))
        {
            return;
        }
        AddWhereClause(sql, "and");
    }

    /// <summary>
    /// Adds a WHERE clause condition with a specific logical operation.
    /// Extracts and preserves any SQL comments in the clause.
    /// Automatically extracts parameters from the WHERE clause and adds them to the Parameters dictionary.
    /// </summary>
    /// <param name="sql">The SQL condition to add.</param>
    /// <param name="operation">The logical operation ("and" or "or").</param>
    public virtual void AddWhereClause(string sql, string operation)
    {
        if (string.IsNullOrWhiteSpace(sql))
        {
            return;
        }

        // Extract comments from the incoming SQL
        var cleanSql = Parser.ExtractSqlComments(sql, out var comments);
        var commentText = comments.Count > 0 ? string.Join(" ", comments) : null;

        AppendToClause(WhereClause, cleanSql.Trim(), operation, commentText);

        // Extract and add parameters from the WHERE clause
        ExtractAndAddParameters(cleanSql);
    }

    /// <summary>
    /// Adds an expression to the SELECT clause.
    /// </summary>
    /// <param name="expression">The expression to add.</param>
    /// <param name="comment">Optional comment to add with the expression.</param>
    public void AddSelectExpression(Expression expression, string? comment = null)
    {
        if (expression is null)
        {
            throw new ArgumentNullException(nameof(expression), ExpressionNullErrorMessage);
        }

        var visitor = new CommandVisitor();
        var sql = expression.Accept(visitor);

        if (string.IsNullOrWhiteSpace(SelectClause.Clause))
        {
            SelectClause.Clause = sql;
        }
        else
        {
            SelectClause.Clause = $"{SelectClause.Clause}, {sql}";
        }

        if (!string.IsNullOrWhiteSpace(comment))
        {
            if (string.IsNullOrWhiteSpace(SelectClause.Comment))
            {
                SelectClause.Comment = comment;
            }
            else
            {
                SelectClause.Comment = $"{SelectClause.Comment} {comment}";
            }
        }
    }

    /// <summary>
    /// Adds an expression to the WHERE clause.
    /// </summary>
    /// <param name="expression">The expression to add.</param>
    /// <param name="comment">Optional comment to add with the expression.</param>
    /// <param name="operation">The logical operation ("and" or "or"). Defaults to "and".</param>
    public void AddWhereExpression(Expression expression, string? comment = null, string operation = "and")
    {
        if (expression is null)
        {
            throw new ArgumentNullException(nameof(expression), ExpressionNullErrorMessage);
        }

        var visitor = new CommandVisitor();
        AppendToClause(WhereClause, expression.Accept(visitor), operation, comment);
    }

    /// <summary>
    /// Adds an expression to the GROUP BY clause.
    /// </summary>
    /// <param name="expression">The expression to add.</param>
    /// <param name="comment">Optional comment to add with the expression.</param>
    public virtual void AddGroupByExpression(Expression expression, string? comment = null)
    {
        if (expression is null)
        {
            throw new ArgumentNullException(nameof(expression), ExpressionNullErrorMessage);
        }

        var visitor = new CommandVisitor();
        var sql = expression.Accept(visitor);

        if (string.IsNullOrWhiteSpace(GroupByClause.Clause))
        {
            GroupByClause.Clause = sql;
        }
        else
        {
            GroupByClause.Clause = $"{GroupByClause.Clause}, {sql}";
        }

        if (!string.IsNullOrWhiteSpace(comment))
        {
            if (string.IsNullOrWhiteSpace(GroupByClause.Comment))
            {
                GroupByClause.Comment = comment;
            }
            else
            {
                GroupByClause.Comment = $"{GroupByClause.Comment} {comment}";
            }
        }
    }

    /// <summary>
    /// Adds an expression to the ORDER BY clause.
    /// </summary>
    /// <param name="expression">The expression to add.</param>
    /// <param name="comment">Optional comment to add with the expression.</param>
    public virtual void AddOrderByExpression(Expression expression, string? comment = null)
    {
        if (expression is null)
        {
            throw new ArgumentNullException(nameof(expression), ExpressionNullErrorMessage);
        }

        var visitor = new CommandVisitor();
        var sql = expression.Accept(visitor);

        if (string.IsNullOrWhiteSpace(OrderByClause.Clause))
        {
            OrderByClause.Clause = sql;
        }
        else
        {
            OrderByClause.Clause = $"{OrderByClause.Clause}, {sql}";
        }

        if (!string.IsNullOrWhiteSpace(comment))
        {
            if (string.IsNullOrWhiteSpace(OrderByClause.Comment))
            {
                OrderByClause.Comment = comment;
            }
            else
            {
                OrderByClause.Comment = $"{OrderByClause.Comment} {comment}";
            }
        }
    }

    /// <summary>
    /// Adds an expression to the HAVING clause.
    /// </summary>
    /// <param name="expression">The expression to add.</param>
    /// <param name="comment">Optional comment to add with the expression.</param>
    /// <param name="operation">The logical operation ("and" or "or"). Defaults to "and".</param>
    public virtual void AddHavingExpression(Expression expression, string? comment = null, string operation = "and")
    {
        if (expression is null)
        {
            throw new ArgumentNullException(nameof(expression), ExpressionNullErrorMessage);
        }

        var visitor = new CommandVisitor();
        AppendToClause(HavingClause, expression.Accept(visitor), operation, comment);
    }

    /// <summary>
    /// Adds a Common Table Expression (CTE) to the WITH clause.
    /// </summary>
    /// <param name="withTableName">The table name for the WITH clause.</param>
    /// <param name="withTableQuery">The query breakdown representing the WITH table.</param>
    /// <exception cref="CteValidationException">Thrown when CTE validation fails.</exception>
    /// <remarks>
    /// <para>
    /// CTEs inherit parameters from their parent query. When the same parameter name exists in both the CTE
    /// and the main query, the main query's parameter value takes precedence. This allows CTEs to reference
    /// parameters from the outer scope while permitting the main query to override them.
    /// </para>
    /// <para>
    /// Duplicate CTE names (case-insensitive) are not allowed within the same query.
    /// </para>
    /// </remarks>
    /// <example>
    /// <code>
    /// var cteQuery = new QueryBreakdown()
    ///     .Select("id, name")
    ///     .From("users")
    ///     .Where("active = 1");
    /// mainQuery.AddWithClause("active_users", cteQuery);
    /// </code>
    /// </example>
    public void AddWithClause(string withTableName, IQueryBreakdown withTableQuery)
    {
        // Validate table name
        if (string.IsNullOrWhiteSpace(withTableName))
        {
            throw new CteValidationException(
                "CTE table name cannot be null, empty, or whitespace.",
                withTableName,
                "TableNameRequired");
        }

        // Validate query
        if (withTableQuery == null)
        {
            throw new CteValidationException(
                "CTE query cannot be null. Provide a valid IQueryBreakdown instance.",
                withTableName,
                "QueryRequired");
        }

        // Check for duplicate CTE names
        if (_withClauses.Any(c => c.TableName.Equals(withTableName, StringComparison.OrdinalIgnoreCase)))
        {
            throw new CteValidationException(
                $"A CTE with the name '{withTableName}' already exists in this query. Each CTE name must be unique.",
                withTableName,
                "DuplicateCteName");
        }

        // Create and add a WithClause object
        var withClause = new WithClause(withTableName, withTableQuery);
        _withClauses.Add(withClause);
    }

    /// <summary>
    /// Adds a Common Table Expression (CTE) with full WithClause configuration to the WITH clause.
    /// This overload allows setting IsRecursive, RecursiveQuery, and ColumnList properties.
    /// </summary>
    /// <param name="withClause">The WithClause object containing the CTE configuration.</param>
    /// <exception cref="CteValidationException">Thrown when CTE validation fails.</exception>
    /// <remarks>
    /// <para>
    /// Use this overload when you need advanced CTE features:
    /// <list type="bullet">
    /// <item><description>Recursive CTEs (set IsRecursive = true and provide RecursiveQuery)</description></item>
    /// <item><description>Explicit column lists (set ColumnList to define output column names)</description></item>
    /// <item><description>Complex CTE configurations requiring fine-grained control</description></item>
    /// </list>
    /// </para>
    /// <para>
    /// Parameter inheritance follows the same rules as other AddWithClause overloads: main query parameters
    /// take precedence over CTE parameters with the same name.
    /// </para>
    /// </remarks>
    /// <example>
    /// <code>
    /// var withClause = new WithClause("active_users", cteQuery)
    /// {
    ///     ColumnList = new List&lt;string&gt; { "id", "name", "email" },
    ///     IsRecursive = false
    /// };
    /// mainQuery.AddWithClause(withClause);
    /// </code>
    /// </example>
    public void AddWithClause(IWithClause withClause)
    {
        if (withClause == null)
        {
            throw new CteValidationException(
                "WithClause cannot be null. Provide a valid IWithClause instance.",
                null,
                "QueryRequired");
        }

        if (string.IsNullOrWhiteSpace(withClause.TableName))
        {
            throw new CteValidationException(
                "CTE table name cannot be null, empty, or whitespace.",
                withClause.TableName,
                "TableNameRequired");
        }

        // Check for duplicate CTE names
        if (_withClauses.Any(c => c.TableName.Equals(withClause.TableName, StringComparison.OrdinalIgnoreCase)))
        {
            throw new CteValidationException(
                $"A CTE with the name '{withClause.TableName}' already exists in this query. Each CTE name must be unique.",
                withClause.TableName,
                "DuplicateCteName");
        }

        // Validate that either Query or Sql is set
        if (withClause.Query == null && withClause.Sql == null)
        {
            throw new CteValidationException(
                $"CTE '{withClause.TableName}' must have either a Query or Sql property set.",
                withClause.TableName,
                "QueryRequired");
        }

        // Add the provided WithClause object directly
        _withClauses.Add((WithClause)withClause);
    }

    /// <summary>
    /// Adds a Common Table Expression (CTE) to the WITH clause using a raw SQL string.
    /// The SQL will be parsed into a QueryBreakdown object.
    /// </summary>
    /// <param name="withTableName">The table name for the WITH clause.</param>
    /// <param name="withTableSql">The SQL query for the WITH table.</param>
    /// <param name="isMicrosoftSql">If true, uses Microsoft T-SQL parsing rules. Defaults to true.</param>
    /// <exception cref="CteValidationException">Thrown when CTE validation fails.</exception>
    /// <exception cref="SqlParseException">Thrown when SQL parsing fails.</exception>
    /// <remarks>
    /// <para>
    /// This is a convenience overload for adding CTEs when you have a SQL string. The SQL is parsed
    /// automatically using <see cref="Parse(string)"/>. If parsing fails, a <see cref="SqlParseException"/>
    /// is thrown with position information and context to help diagnose the issue.
    /// </para>
    /// <para>
    /// Parameter inheritance: Parameters defined in the CTE SQL can be referenced by the main query.
    /// If the same parameter exists in both the CTE and main query, the main query's value takes precedence.
    /// </para>
    /// </remarks>
    /// <example>
    /// <code>
    /// mainQuery.AddWithClause("active_users", "SELECT id, name FROM users WHERE active = 1");
    /// </code>
    /// </example>
    public virtual void AddWithClause(string withTableName, string withTableSql, bool isMicrosoftSql = true)
    {
        // Validate table name
        if (string.IsNullOrWhiteSpace(withTableName))
        {
            throw new CteValidationException(
                "CTE table name cannot be null, empty, or whitespace.",
                withTableName,
                "TableNameRequired");
        }

        // Validate SQL
        if (string.IsNullOrWhiteSpace(withTableSql))
        {
            throw new CteValidationException(
                $"CTE '{withTableName}' SQL cannot be null, empty, or whitespace.",
                withTableName,
                "QueryRequired");
        }

        // Check for duplicate CTE names
        if (_withClauses.Any(c => c.TableName.Equals(withTableName, StringComparison.OrdinalIgnoreCase)))
        {
            throw new CteValidationException(
                $"A CTE with the name '{withTableName}' already exists in this query. Each CTE name must be unique.",
                withTableName,
                "DuplicateCteName");
        }

        // Parse the SQL string into a QueryBreakdown object
        QueryBreakdown parsedQuery;
        try
        {
            parsedQuery = QueryBreakdown.Parse(withTableSql);
        }
        catch (Exception ex)
        {
            throw new SqlParseException(
                $"Failed to parse SQL for CTE '{withTableName}'.",
                withTableSql,
                0,
                ex);
        }

        // Create and add the WithClause
        var withClause = new WithClause(withTableName, parsedQuery);
        _withClauses.Add(withClause);
    }

    /// <summary>
    /// Parses the SELECT clause into a collection of Expression objects.
    /// Each column/expression in the SELECT list is parsed separately.
    /// </summary>
    /// <returns>An enumerable collection of parsed Expression objects from the SELECT clause.</returns>
    /// <exception cref="FormatException">Thrown when the SELECT clause cannot be parsed.</exception>
    public virtual IEnumerable<Expression> GetSelectExpressions()
        => SelectClause.GetExpressions(CreateExpressionParser());

    /// <summary>
    /// Parses the WHERE clause into an Expression object.
    /// </summary>
    /// <returns>A parsed Expression object from the WHERE clause, or null if WHERE clause is empty.</returns>
    /// <exception cref="FormatException">Thrown when the WHERE clause cannot be parsed.</exception>
    public virtual Expression? GetWhereExpression()
        => WhereClause.GetExpressions(CreateExpressionParser()).FirstOrDefault();

    /// <summary>
    /// Parses the HAVING clause into an Expression object.
    /// </summary>
    /// <returns>A parsed Expression object from the HAVING clause, or null if HAVING clause is empty.</returns>
    /// <exception cref="FormatException">Thrown when the HAVING clause cannot be parsed.</exception>
    public virtual Expression? GetHavingExpression()
        => HavingClause.GetExpressions(CreateExpressionParser()).FirstOrDefault();

    /// <summary>
    /// Creates the appropriate statement expression parser for this query type.
    /// Override in derived classes to provide dialect-specific parsers.
    /// </summary>
    /// <returns>An IStatementExpressionParser instance.</returns>
    protected virtual IStatementExpressionParser CreateExpressionParser()
        => new StatementExpressionParser();

    #endregion

    #region Parsing Methods

    /// <summary>
    /// Parses a T-SQL SELECT statement into a QueryBreakdown object.
    /// </summary>
    /// <param name="sql">The T-SQL SELECT statement to parse.</param>
    /// <returns>A QueryBreakdown object representing the parsed query.</returns>
    /// <exception cref="ArgumentNullException">Thrown when sql is null or empty.</exception>
    /// <exception cref="SqlParseException">Thrown when the SQL statement cannot be parsed.</exception>
    /// <example>
    /// <code>
    /// var query = QueryBreakdown.Parse("SELECT id, name FROM users WHERE active = 1");
    /// Console.WriteLine(query.GetSql());
    /// </code>
    /// </example>
    public static QueryBreakdown Parse(string sql)
    {
        if (string.IsNullOrWhiteSpace(sql))
        {
            throw new ArgumentNullException(nameof(sql), "SQL statement cannot be null, empty, or whitespace.");
        }

        if (!TryParse(sql, out var result, out var error))
        {
            // Try to find approximate error position (if available in error message)
            var position = 0;
            // Look for common parse error patterns that might contain position info
            if (error.Contains("position", StringComparison.OrdinalIgnoreCase))
            {
                // Try to extract position from error message
                var match = System.Text.RegularExpressions.Regex.Match(error, @"position[:\s]+(\d+)",
                    System.Text.RegularExpressions.RegexOptions.IgnoreCase, Strata.SqlTools.SqlBreakdown.Utilities.RegexDefaults.MatchTimeout);
                if (match.Success && int.TryParse(match.Groups[1].Value, out var parsedPos))
                {
                    position = parsedPos;
                }
            }

            throw new SqlParseException(
                $"Failed to parse SQL statement: {error}",
                sql,
                position);
        }

        return result;
    }

    /// <summary>
    /// Attempts to parse a T-SQL SELECT statement into a QueryBreakdown object.
    /// </summary>
    /// <param name="sql">The T-SQL SELECT statement to parse.</param>
    /// <param name="result">When this method returns, contains the parsed QueryBreakdown if successful, or null if parsing failed.</param>
    /// <returns>true if the SQL was successfully parsed; otherwise, false.</returns>
    public static bool TryParse(string sql, out QueryBreakdown result)
        => TryParse(sql, out result, out _);

    /// <summary>
    /// Attempts to parse a T-SQL SELECT statement into a QueryBreakdown object.
    /// </summary>
    /// <param name="sql">The T-SQL SELECT statement to parse.</param>
    /// <param name="result">When this method returns, contains the parsed QueryBreakdown if successful, or null if parsing failed.</param>
    /// <param name="errorMessage">When this method returns false, contains a message describing why parsing failed.</param>
    /// <returns>true if the SQL was successfully parsed; otherwise, false.</returns>
    public static bool TryParse(string sql, out QueryBreakdown result, out string errorMessage)
    {
        result = null!;
        errorMessage = null!;

        try
        {
            if (string.IsNullOrWhiteSpace(sql))
            {
                errorMessage = "SQL statement cannot be null or empty.";
                return false;
            }

            // Create parser instance
            var parser = new StatementParser();

            // Normalize whitespace while preserving comments
            sql = parser.NormalizeSqlPreservingComments(sql);

            // Extract setup clauses (everything before the main SELECT that's not part of it)
            var setupClauses = new List<string>();
            sql = parser.ExtractSetupClauses(sql, setupClauses);

            // Extract finish clauses (cleanup statements after the main query)
            var finishClauses = new ArrayList();
            sql = parser.ExtractFinishClauses(sql, finishClauses);

            // Parse WITH clause separately if present (before parsing SELECT)
            string? withClause = null;
            if (parser.TryParseWithClause(sql, out withClause, out var mainQuery))
            {
                sql = mainQuery; // Continue with the main query after WITH
            }

            // Parse the main SELECT statement - now with comments preserved
            if (!parser.TryParseSelectStatement(sql, out var clauses, out errorMessage))
            {
                return false;
            }

            // Create the QueryBreakdown object
            result = new QueryBreakdown
            {
                WithClause = withClause?.Trim(),
                SelectClause = clauses!.SelectClause ?? new SqlExpressionClause(splitOnComma: true),
                FromClause = clauses.FromClause ?? new SqlClause(),
                WhereClause = clauses.WhereClause ?? new SqlExpressionClause(splitOnComma: false),
                GroupByClause = clauses.GroupByClause ?? new SqlExpressionClause(splitOnComma: true),
                HavingClause = clauses.HavingClause ?? new SqlExpressionClause(splitOnComma: false),
                OrderByClause = clauses.OrderByClause ?? new SqlExpressionClause(splitOnComma: true),
                SetupClauses = setupClauses,
                FinishClauses = finishClauses
            };

            // Extract parameters from all clauses (use comment-free version for this)
            var sqlWithoutComments = parser.RemoveSqlComments(sql);
            parser.ExtractParameters(result.Parameters, sqlWithoutComments);

            return true;
        }
        catch (Exception ex)
        {
            errorMessage = $"Unexpected error during parsing: {ex.Message}";
            return false;
        }
    }

    #endregion
}
#pragma warning restore S2325