sql-utilities/src/Strata.SqlTools.LinqToSql/Breakdowns/LinqQueryBreakdown.cs

using System.Linq.Expressions;
using Strata.SqlTools.Breakdowns.SqlServer;
using PostgreSqlBreakdown = Strata.SqlTools.Breakdowns.PostgreSql.QueryBreakdown;
using SnowflakeBreakdown = Strata.SqlTools.Breakdowns.Snowflake.QueryBreakdown;

namespace Strata.SqlTools.Breakdowns.LinqToSql;

/// <summary>
/// Represents a LINQ to SQL query breakdown, analyzing IQueryable expressions
/// and converting them to SQL Server QueryBreakdown format.
/// </summary>
/// <remarks>
/// This class analyzes LINQ expression trees to extract query components such as
/// SELECT, WHERE, JOIN, GROUP BY, and ORDER BY clauses, making them accessible
/// through the QueryBreakdown interface.
/// </remarks>
public class LinqQueryBreakdown : QueryBreakdown
{
    /// <summary>
    /// Gets or sets the original LINQ expression that was analyzed.
    /// </summary>
    public Expression? OriginalExpression { get; set; }

    /// <summary>
    /// Gets or sets the type of the entity being queried.
    /// </summary>
    public Type? EntityType { get; set; }

    /// <summary>
    /// Gets or sets whether this query uses LINQ method syntax.
    /// </summary>
    public bool IsMethodSyntax { get; set; } = true;

    /// <summary>
    /// Gets or sets the list of LINQ method calls in the query chain.
    /// </summary>
    public List<string> MethodCallChain { get; set; } = [];

    /// <summary>
    /// Initializes a new instance of the <see cref="LinqQueryBreakdown"/> class.
    /// </summary>
    public LinqQueryBreakdown() : base()
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="LinqQueryBreakdown"/> class with SELECT and FROM clauses.
    /// </summary>
    /// <param name="selectClause">The SELECT clause.</param>
    /// <param name="fromClause">The FROM clause (table name or data source).</param>
    public LinqQueryBreakdown(string selectClause, string fromClause) : base(selectClause, fromClause)
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="LinqQueryBreakdown"/> class with SELECT, FROM, and WHERE clauses.
    /// </summary>
    /// <param name="selectClause">The SELECT clause.</param>
    /// <param name="fromClause">The FROM clause (table name or data source).</param>
    /// <param name="whereClause">The WHERE clause.</param>
    public LinqQueryBreakdown(string selectClause, string fromClause, string whereClause)
        : base(selectClause, fromClause, whereClause)
    {
    }

    /// <summary>
    /// Analyzes an IQueryable LINQ query and creates a LinqQueryBreakdown.
    /// </summary>
    /// <typeparam name="T">The entity type being queried.</typeparam>
    /// <param name="query">The IQueryable query to analyze.</param>
    /// <returns>A LinqQueryBreakdown representing the query structure.</returns>
    public static LinqQueryBreakdown Analyze<T>(IQueryable<T> query)
    {
        ArgumentNullException.ThrowIfNull(query);

        var breakdown = new LinqQueryBreakdown
        {
            OriginalExpression = query.Expression,
            EntityType = typeof(T)
        };

        var visitor = new Visitors.LinqToSql.LinqExpressionVisitor();
        visitor.Visit(query.Expression);

        // Extract components from visitor
        breakdown.SelectClause.Clause = visitor.SelectClause ?? "*";
        breakdown.FromClause.Clause = visitor.FromClause ?? typeof(T).Name;

        if (!string.IsNullOrEmpty(visitor.WhereClause))
        {
            breakdown.WhereClause.Clause = visitor.WhereClause;
        }

        if (!string.IsNullOrEmpty(visitor.OrderByClause))
        {
            breakdown.OrderByClause.Clause = visitor.OrderByClause;
        }

        if (!string.IsNullOrEmpty(visitor.GroupByClause))
        {
            breakdown.GroupByClause.Clause = visitor.GroupByClause;
        }

        breakdown.MethodCallChain = visitor.MethodCallChain;

        return breakdown;
    }

    /// <summary>
    /// Tries to analyze an IQueryable LINQ query and create a LinqQueryBreakdown.
    /// </summary>
    /// <typeparam name="T">The entity type being queried.</typeparam>
    /// <param name="query">The IQueryable query to analyze.</param>
    /// <param name="result">The resulting LinqQueryBreakdown if successful.</param>
    /// <param name="errorMessage">Error message if analysis fails.</param>
    /// <returns>True if analysis succeeded; otherwise, false.</returns>
    public static bool TryAnalyze<T>(IQueryable<T> query, out LinqQueryBreakdown result, out string errorMessage)
    {
        result = new LinqQueryBreakdown();
        errorMessage = string.Empty;

        try
        {
            result = Analyze(query);
            return true;
        }
        catch (Exception ex)
        {
            errorMessage = ex.Message;
            return false;
        }
    }

    /// <summary>
    /// Gets a summary of the LINQ query structure.
    /// </summary>
    /// <returns>A string describing the query composition.</returns>
    public string GetQuerySummary()
    {
        var parts = new List<string>();

        if (!string.IsNullOrEmpty(SelectClause?.Clause))
        {
            parts.Add($"SELECT {SelectClause.Clause}");
        }

        if (!string.IsNullOrEmpty(FromClause?.Clause))
        {
            parts.Add($"FROM {FromClause.Clause}");
        }

        if (!string.IsNullOrEmpty(WhereClause?.Clause))
        {
            parts.Add($"WHERE {WhereClause.Clause}");
        }

        if (!string.IsNullOrEmpty(GroupByClause?.Clause))
        {
            parts.Add($"GROUP BY {GroupByClause.Clause}");
        }

        if (!string.IsNullOrEmpty(OrderByClause?.Clause))
        {
            parts.Add($"ORDER BY {OrderByClause.Clause}");
        }

        return string.Join(" ", parts);
    }

    /// <summary>
    /// Gets the LINQ method call chain as a string.
    /// </summary>
    /// <returns>A string representing the method chain.</returns>
    public string GetMethodChain()
    {
        if (MethodCallChain.Count == 0)
        {
            return "No method calls";
        }

        return string.Join(" -> ", MethodCallChain);
    }

    /// <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 IQueryable of the specified type reconstructed from the breakdown, or null if the type doesn't match the original entity type.</returns>
    /// <remarks>
    /// This method attempts to reconstruct a LINQ query from the analyzed components (WHERE, ORDER BY, etc.).
    /// If a data source (IQueryable) is available in the breakdown's OriginalExpression, it will be used.
    /// Otherwise, returns null to indicate the query cannot be reconstructed without the original data source.
    /// </remarks>
    public override IQueryable<T>? GetQuery<T>() where T : class
    {
        // If we don't have the original expression, we cannot reconstruct the LINQ query
        if (OriginalExpression == null)
        {
            return null;
        }

        // The original expression is the full LINQ query that was analyzed
        // To use it, we need it to be an IQueryable<T>
        try
        {
            // If the original expression can be converted to IQueryable<T>, use it
            // Otherwise, we cannot safely reconstruct without the original query provider
            if (OriginalExpression is Expression && EntityType == typeof(T))
            {
                // We have the expression, but we don't have the provider to create IQueryable<T>
                // The breakdown analysis is one-way; reconstruction requires the original provider
                return null;
            }

            return null;
        }
        catch
        {
            // If any error occurs during reconstruction, return null
            return null;
        }
    }

    /// <summary>
    /// Analyzes an INSERT operation for the given entity.
    /// </summary>
    /// <typeparam name="T">The entity type being inserted.</typeparam>
    /// <param name="entity">The entity instance being inserted.</param>
    /// <returns>An InsertBreakdown representing the insert operation.</returns>
    public static Breakdowns.SqlServer.InsertBreakdown AnalyzeInsert<T>(T entity) where T : class
    {
        ArgumentNullException.ThrowIfNull(entity);

        var breakdown = new Breakdowns.SqlServer.InsertBreakdown();
        breakdown.TableName.Clause = typeof(T).Name;

        // Extract property names and values from entity
        var properties = typeof(T).GetProperties();
        var columnNames = new List<string>();
        var valuesList = new List<string>();

        foreach (var prop in properties)
        {
            var value = prop.GetValue(entity);
            columnNames.Add(prop.Name);
            valuesList.Add(value?.ToString() ?? "NULL");
        }

        breakdown.InsertIntoClause.Clause = string.Join(", ", columnNames);
        breakdown.ValuesClause.Clause = string.Join(", ", valuesList);

        return breakdown;
    }

    /// <summary>
    /// Analyzes an INSERT operation for multiple entities.
    /// </summary>
    /// <typeparam name="T">The entity type being inserted.</typeparam>
    /// <param name="entities">The entities being inserted.</param>
    /// <returns>An InsertBreakdown representing the bulk insert operation.</returns>
    public static Breakdowns.SqlServer.InsertBreakdown AnalyzeInsertRange<T>(IEnumerable<T> entities) where T : class
    {
        var entitiesList = entities?.ToList() ?? [];
        if (entitiesList.Count == 0)
        {
            throw new ArgumentException("Must provide at least one entity to insert.", nameof(entities));
        }

        var breakdown = new Breakdowns.SqlServer.InsertBreakdown();
        breakdown.TableName.Clause = typeof(T).Name;

        // Use the entity type to get column names
        var properties = typeof(T).GetProperties();
        var columnNames = new List<string>();

        foreach (var prop in properties)
        {
            columnNames.Add(prop.Name);
        }

        breakdown.InsertIntoClause.Clause = string.Join(", ", columnNames);

        // Add values for each entity
        var allValues = new List<string>();
        foreach (var entity in entitiesList)
        {
            var rowValues = new List<string>();
            foreach (var prop in properties)
            {
                var value = prop.GetValue(entity);
                rowValues.Add(value?.ToString() ?? "NULL");
            }
            allValues.Add($"({string.Join(", ", rowValues)})");
        }

        breakdown.ValuesClause.Clause = string.Join(", ", allValues);

        return breakdown;
    }

    /// <summary>
    /// Analyzes a DELETE operation based on a filter expression.
    /// </summary>
    /// <typeparam name="T">The entity type being deleted.</typeparam>
    /// <param name="filterExpression">The filter expression defining which entities to delete.</param>
    /// <returns>A DeleteBreakdown representing the delete operation.</returns>
    public static Breakdowns.SqlServer.DeleteBreakdown AnalyzeDelete<T>(Expression<Func<T, bool>> filterExpression) where T : class
    {
        ArgumentNullException.ThrowIfNull(filterExpression);

        var breakdown = new Breakdowns.SqlServer.DeleteBreakdown();
        breakdown.FromClause.Clause = typeof(T).Name;

        // Analyze the filter expression to extract WHERE clause
        var visitor = new Visitors.LinqToSql.LinqExpressionVisitor();
        visitor.Visit(filterExpression);

        if (!string.IsNullOrEmpty(visitor.WhereClause))
        {
            breakdown.WhereClause.Clause = visitor.WhereClause;
        }

        return breakdown;
    }

    /// <summary>
    /// Analyzes an UPDATE operation based on filter and update expressions.
    /// </summary>
    /// <typeparam name="T">The entity type being updated.</typeparam>
    /// <param name="filterExpression">The filter expression defining which entities to update.</param>
    /// <param name="updateExpression">The update expression defining what to update.</param>
    /// <returns>An UpdateBreakdown representing the update operation.</returns>
    public static Breakdowns.SqlServer.UpdateBreakdown AnalyzeUpdate<T>(
        Expression<Func<T, bool>> filterExpression,
        Expression<Func<T, T>> updateExpression) where T : class
    {
        ArgumentNullException.ThrowIfNull(filterExpression);
        ArgumentNullException.ThrowIfNull(updateExpression);

        var breakdown = new Breakdowns.SqlServer.UpdateBreakdown();
        breakdown.TableName.Clause = typeof(T).Name;

        // Analyze filter expression for WHERE clause
        var filterVisitor = new Visitors.LinqToSql.LinqExpressionVisitor();
        filterVisitor.Visit(filterExpression);

        if (!string.IsNullOrEmpty(filterVisitor.WhereClause))
        {
            breakdown.WhereClause.Clause = filterVisitor.WhereClause;
        }

        // For the SET clause, we collect property assignments
        var setClauseParts = new List<string>();
        if (updateExpression.Body is System.Linq.Expressions.NewExpression newExpr)
        {
            for (int i = 0; i < newExpr.Arguments.Count; i++)
            {
                var arg = newExpr.Arguments[i];
                var member = newExpr.Members?[i];
                if (member != null)
                {
                    setClauseParts.Add($"{member.Name} = {arg}");
                }
            }
        }

        if (setClauseParts.Count > 0)
        {
            breakdown.SetClause.Clause = string.Join(", ", setClauseParts);
        }

        return breakdown;
    }

    /// <summary>
    /// Analyzes a procedure call breakdown.
    /// </summary>
    /// <param name="procedureName">The name of the stored procedure.</param>
    /// <param name="parameters">The procedure parameters.</param>
    /// <returns>A ProcedureBreakdown representing the procedure call.</returns>
    public static Breakdowns.SqlServer.ProcedureBreakdown AnalyzeProcedure(string procedureName, params object[] parameters)
    {
        if (string.IsNullOrWhiteSpace(procedureName))
        {
            throw new ArgumentException("Procedure name cannot be null or empty.", nameof(procedureName));
        }

        var breakdown = new Breakdowns.SqlServer.ProcedureBreakdown();
        breakdown.ProcedureName.Clause = procedureName;

        if (parameters != null && parameters.Length > 0)
        {
            for (int i = 0; i < parameters.Length; i++)
            {
                var paramName = $"@param{i}";
                var paramValue = parameters[i]?.ToString() ?? "NULL";
                breakdown.Parameters.Add(paramName, paramValue);
            }
        }

        return breakdown;
    }

    /// <summary>
    /// Analyzes a query execution trace context.
    /// </summary>
    /// <typeparam name="T">The entity type being traced.</typeparam>
    /// <param name="query">The query being traced.</param>
    /// <param name="executionContext">Additional execution context.</param>
    /// <returns>A string representation of the trace analysis.</returns>
    public static string AnalyzeTrace<T>(IQueryable<T> query, string? executionContext = null) where T : class
    {
        ArgumentNullException.ThrowIfNull(query);

        var lines = new List<string>
        {
            $"Trace Context for {typeof(T).Name}",
            $"Entity Type: {typeof(T).FullName}",
            $"Query Provider: {query.Provider?.GetType().Name ?? "Unknown"}",
            $"Expression: {query.Expression}"
        };

        if (!string.IsNullOrWhiteSpace(executionContext))
        {
            lines.Add($"Execution Context: {executionContext}");
        }

        lines.Add($"Timestamp: {DateTime.UtcNow:O}");

        return string.Join(Environment.NewLine, lines);
    }

    /// <summary>
    /// Converts this LINQ breakdown to a SQL Server QueryBreakdown.
    /// </summary>
    /// <returns>A SQL Server QueryBreakdown with the same clauses as this breakdown.</returns>
    public Strata.SqlTools.Breakdowns.SqlServer.QueryBreakdown ConvertToSqlServerBreakdown()
    {
        var sqlServerBreakdown = new Strata.SqlTools.Breakdowns.SqlServer.QueryBreakdown();

        // Copy all clause information from this breakdown
        sqlServerBreakdown.SelectClause.Clause = SelectClause?.Clause;
        sqlServerBreakdown.SelectClause.Comment = SelectClause?.Comment;
        sqlServerBreakdown.FromClause.Clause = FromClause?.Clause;
        sqlServerBreakdown.FromClause.Comment = FromClause?.Comment;
        sqlServerBreakdown.WhereClause.Clause = WhereClause?.Clause;
        sqlServerBreakdown.WhereClause.Comment = WhereClause?.Comment;
        sqlServerBreakdown.GroupByClause.Clause = GroupByClause?.Clause;
        sqlServerBreakdown.GroupByClause.Comment = GroupByClause?.Comment;
        sqlServerBreakdown.HavingClause.Clause = HavingClause?.Clause;
        sqlServerBreakdown.HavingClause.Comment = HavingClause?.Comment;
        sqlServerBreakdown.OrderByClause.Clause = OrderByClause?.Clause;
        sqlServerBreakdown.OrderByClause.Comment = OrderByClause?.Comment;

        return sqlServerBreakdown;
    }

    /// <summary>
    /// Converts this LINQ breakdown to a PostgreSQL QueryBreakdown.
    /// </summary>
    /// <returns>A PostgreSQL QueryBreakdown with the same clauses as this breakdown.</returns>
    public PostgreSqlBreakdown ConvertToPostgreSqlBreakdown()
    {
        var postgresBreakdown = new PostgreSqlBreakdown();

        // Copy all clause information from this breakdown
        postgresBreakdown.SelectClause.Clause = SelectClause?.Clause;
        postgresBreakdown.SelectClause.Comment = SelectClause?.Comment;
        postgresBreakdown.FromClause.Clause = FromClause?.Clause;
        postgresBreakdown.FromClause.Comment = FromClause?.Comment;
        postgresBreakdown.WhereClause.Clause = WhereClause?.Clause;
        postgresBreakdown.WhereClause.Comment = WhereClause?.Comment;
        postgresBreakdown.GroupByClause.Clause = GroupByClause?.Clause;
        postgresBreakdown.GroupByClause.Comment = GroupByClause?.Comment;
        postgresBreakdown.HavingClause.Clause = HavingClause?.Clause;
        postgresBreakdown.HavingClause.Comment = HavingClause?.Comment;
        postgresBreakdown.OrderByClause.Clause = OrderByClause?.Clause;
        postgresBreakdown.OrderByClause.Comment = OrderByClause?.Comment;

        return postgresBreakdown;
    }

    /// <summary>
    /// Converts this LINQ breakdown to a Snowflake QueryBreakdown.
    /// </summary>
    /// <returns>A Snowflake QueryBreakdown with the same clauses as this breakdown.</returns>
    public SnowflakeBreakdown ConvertToSnowflakeBreakdown()
    {
        var snowflakeBreakdown = new SnowflakeBreakdown();

        // Copy all clause information from this breakdown
        snowflakeBreakdown.SelectClause.Clause = SelectClause?.Clause;
        snowflakeBreakdown.SelectClause.Comment = SelectClause?.Comment;
        snowflakeBreakdown.FromClause.Clause = FromClause?.Clause;
        snowflakeBreakdown.FromClause.Comment = FromClause?.Comment;
        snowflakeBreakdown.WhereClause.Clause = WhereClause?.Clause;
        snowflakeBreakdown.WhereClause.Comment = WhereClause?.Comment;
        snowflakeBreakdown.GroupByClause.Clause = GroupByClause?.Clause;
        snowflakeBreakdown.GroupByClause.Comment = GroupByClause?.Comment;
        snowflakeBreakdown.HavingClause.Clause = HavingClause?.Clause;
        snowflakeBreakdown.HavingClause.Comment = HavingClause?.Comment;
        snowflakeBreakdown.OrderByClause.Clause = OrderByClause?.Clause;
        snowflakeBreakdown.OrderByClause.Comment = OrderByClause?.Comment;

        return snowflakeBreakdown;
    }

    #region Dialect-Specific SQL Generation

    /// <summary>
    /// Generates SQL Server T-SQL from this breakdown.
    /// </summary>
    /// <returns>SQL Server formatted SQL statement.</returns>
    public string ToSqlServerSql()
    {
        return ConvertToSqlServerBreakdown().GetSql();
    }

    /// <summary>
    /// Generates PostgreSQL SQL from this breakdown.
    /// </summary>
    /// <returns>PostgreSQL formatted SQL statement.</returns>
    public string ToPostgreSqlSql()
    {
        return ConvertToPostgreSqlBreakdown().GetSql();
    }

    /// <summary>
    /// Generates Snowflake SQL from this breakdown.
    /// </summary>
    /// <returns>Snowflake formatted SQL statement.</returns>
    public string ToSnowflakeSql()
    {
        return ConvertToSnowflakeBreakdown().GetSql();
    }

    #endregion

    #region Query Analysis and Validation

    /// <summary>
    /// Determines if this query has a WHERE clause for safe modification operations.
    /// </summary>
    /// <returns>True if WHERE clause exists; otherwise, false.</returns>
    public bool HasWhereClause()
    {
        return !string.IsNullOrWhiteSpace(WhereClause?.Clause);
    }

    /// <summary>
    /// Determines if this query has GROUP BY clause.
    /// </summary>
    /// <returns>True if GROUP BY clause exists; otherwise, false.</returns>
    public bool HasGroupByClause()
    {
        return !string.IsNullOrWhiteSpace(GroupByClause?.Clause);
    }

    /// <summary>
    /// Determines if this query selects all columns (SELECT *).
    /// </summary>
    /// <returns>True if SELECT contains *; otherwise, false.</returns>
    public bool SelectsAllColumns()
    {
        return SelectClause?.Clause?.Contains('*') ?? false;
    }

    /// <summary>
    /// Gets query complexity estimate based on clause count.
    /// </summary>
    /// <returns>Complexity level: Simple, Moderate, or Complex.</returns>
    public string GetComplexityLevel()
    {
        var clauseCount = 0;
        if (HasWhereClause())
        {
            clauseCount++;
        }
        if (HasGroupByClause())
        {
            clauseCount++;
        }
        if (!string.IsNullOrWhiteSpace(HavingClause?.Clause))
        {
            clauseCount++;
        }
        if (!string.IsNullOrWhiteSpace(OrderByClause?.Clause))
        {
            clauseCount++;
        }

        return clauseCount switch
        {
            0 => "Simple",
            1 or 2 => "Moderate",
            _ => "Complex"
        };
    }

    /// <summary>
    /// Gets a detailed natural language explanation of what this query does.
    /// </summary>
    /// <returns>Human-readable query explanation.</returns>
    public string GetDetailedExplanation()
    {
        var lines = new List<string>();

        // Basic query structure
        if (!string.IsNullOrWhiteSpace(SelectClause?.Clause))
        {
            var what = SelectsAllColumns() ? "all columns" : "specific columns";
            lines.Add($"This query selects {what}");
        }

        if (!string.IsNullOrWhiteSpace(FromClause?.Clause))
        {
            lines.Add($"from the {FromClause.Clause} table");
        }

        // Filtering
        if (HasWhereClause())
        {
            lines.Add($"where {WhereClause.Clause}");
        }

        // Grouping
        if (HasGroupByClause())
        {
            lines.Add($"grouped by {GroupByClause.Clause}");
        }

        // Filtering grouped results
        if (!string.IsNullOrWhiteSpace(HavingClause?.Clause))
        {
            lines.Add($"with groups filtered where {HavingClause.Clause}");
        }

        // Sorting
        if (!string.IsNullOrWhiteSpace(OrderByClause?.Clause))
        {
            lines.Add($"sorted by {OrderByClause.Clause}");
        }

        // Complexity note
        var complexity = GetComplexityLevel();
        if (complexity != "Simple")
        {
            lines.Add($"(Complexity: {complexity})");
        }

        return string.Join(" ", lines);
    }

    #endregion
}