sql-utilities/src/Strata.SqlTools.LinqToSql/Analyzers/QueryCollectionAnalyzer.cs

using Strata.SqlTools.Breakdowns.LinqToSql;
using Strata.SqlTools.Comparers.LinqToSql;

namespace Strata.SqlTools.Analyzers.LinqToSql;

/// <summary>
/// Statistics about a collection of analyzed queries.
/// </summary>
public record QueryCollectionStatistics(
    int TotalQueries,
    int UniqueQueries,
    List<LinqQueryBreakdown> DuplicateQueries,
    Dictionary<string, int> TableUsageFrequency,
    Dictionary<string, int> ColumnSelectionFrequency,
    int QueriesWithoutWhere,
    int QueriesWithoutOrderBy,
    int QueriesWithSelectAll,
    double AverageComplexity,
    int ComplexQueriesCount
)
{
    /// <summary>
    /// Gets the deduplication rate (unique queries / total queries).
    /// </summary>
    public double DeduplicationRate => TotalQueries == 0 ? 0.0 : (double)UniqueQueries / TotalQueries;

    /// <summary>
    /// Gets a formatted statistics report.
    /// </summary>
    public string GetReport()
    {
        var report = new System.Text.StringBuilder();
        report.AppendLine("Query Collection Analysis Report");
        report.AppendLine("================================");
        report.AppendLine($"Total Queries: {TotalQueries}");
        report.AppendLine($"Unique Queries: {UniqueQueries} ({DeduplicationRate * 100:F1}%)");
        report.AppendLine($"Duplicate Queries: {DuplicateQueries.Count}");
        report.AppendLine();

        report.AppendLine("Query Characteristics:");
        report.AppendLine($"  Queries without WHERE: {QueriesWithoutWhere}");
        report.AppendLine($"  Queries without ORDER BY: {QueriesWithoutOrderBy}");
        report.AppendLine($"  Queries with SELECT *: {QueriesWithSelectAll}");
        report.AppendLine();

        report.AppendLine("Complexity Analysis:");
        report.AppendLine($"  Average Complexity Level: {AverageComplexity:F2}");
        report.AppendLine($"  Complex Queries: {ComplexQueriesCount}");
        report.AppendLine();

        if (TableUsageFrequency.Count > 0)
        {
            report.AppendLine("Most Frequently Used Tables:");
            foreach (var kvp in TableUsageFrequency.OrderByDescending(x => x.Value).Take(5))
            {
                report.AppendLine($"  {kvp.Key}: {kvp.Value} times");
            }
            report.AppendLine();
        }

        if (ColumnSelectionFrequency.Count > 0)
        {
            report.AppendLine("Most Frequently Selected Columns:");
            foreach (var kvp in ColumnSelectionFrequency.OrderByDescending(x => x.Value).Take(5))
            {
                report.AppendLine($"  {kvp.Key}: {kvp.Value} times");
            }
        }

        return report.ToString();
    }
}

/// <summary>
/// Analyzes a collection of LinqQueryBreakdown queries for patterns, duplicates, and statistics.
/// </summary>
public class QueryCollectionAnalyzer
{
    private readonly List<LinqQueryBreakdown> _queries;

    /// <summary>
    /// Initializes a new instance of the <see cref="QueryCollectionAnalyzer"/> class.
    /// </summary>
    /// <param name="queries">The queries to analyze.</param>
    public QueryCollectionAnalyzer(IEnumerable<LinqQueryBreakdown> queries)
    {
        _queries = queries?.ToList() ?? throw new ArgumentNullException(nameof(queries));
    }

    /// <summary>
    /// Analyzes the query collection and returns comprehensive statistics.
    /// </summary>
    /// <returns>Statistics about the query collection.</returns>
    public QueryCollectionStatistics Analyze()
    {
        if (_queries.Count == 0)
        {
            return new QueryCollectionStatistics(
                0, 0, [],
                [],
                [],
                0, 0, 0, 0.0, 0);
        }

        var duplicates = FindDuplicates();
        var uniqueCount = _queries.Count - duplicates.Count;
        var tableUsage = AnalyzeTableUsage();
        var columnUsage = AnalyzeColumnUsage();
        var queriesWithoutWhere = _queries.Count(q => string.IsNullOrWhiteSpace(q.WhereClause?.Clause));
        var queriesWithoutOrderBy = _queries.Count(q => string.IsNullOrWhiteSpace(q.OrderByClause?.Clause));
        var queriesWithSelectAll = _queries.Count(q =>
            q.SelectClause?.Clause?.Trim() == "*");
        var complexityScores = _queries.Select(q => GetComplexityScore(q)).ToList();
        var avgComplexity = complexityScores.Average();
        var complexQueries = complexityScores.Count(c => c >= 7);

        return new QueryCollectionStatistics(
            _queries.Count,
            uniqueCount,
            duplicates,
            tableUsage,
            columnUsage,
            queriesWithoutWhere,
            queriesWithoutOrderBy,
            queriesWithSelectAll,
            avgComplexity,
            complexQueries);
    }

    /// <summary>
    /// Finds duplicate queries in the collection.
    /// </summary>
    /// <returns>List of queries that are identical to another query in the collection.</returns>
    public List<LinqQueryBreakdown> FindDuplicates()
    {
        var duplicates = new List<LinqQueryBreakdown>();

        for (int i = 0; i < _queries.Count; i++)
        {
            for (int j = i + 1; j < _queries.Count; j++)
            {
                if (QueryComparator.AreQueriesIdentical(_queries[i], _queries[j]) && !duplicates.Contains(_queries[j]))
                {
                    duplicates.Add(_queries[j]);
                }
            }
        }

        return duplicates;
    }

    /// <summary>
    /// Finds similar queries that are not identical but have high similarity.
    /// </summary>
    /// <param name="minimumSimilarity">Minimum similarity score (0.0-1.0).</param>
    /// <returns>Pairs of similar queries and their similarity scores.</returns>
    public List<(LinqQueryBreakdown Query1, LinqQueryBreakdown Query2, double Similarity)> FindSimilarQueries(double minimumSimilarity = 0.75)
    {
        var similarPairs = new List<(LinqQueryBreakdown, LinqQueryBreakdown, double)>();

        for (int i = 0; i < _queries.Count; i++)
        {
            for (int j = i + 1; j < _queries.Count; j++)
            {
                var similarity = QueryComparator.GetSimilarity(_queries[i], _queries[j]);
                if (similarity >= minimumSimilarity && similarity < 1.0)
                {
                    similarPairs.Add((_queries[i], _queries[j], similarity));
                }
            }
        }

        return similarPairs.OrderByDescending(x => x.Item3).ToList();
    }

    /// <summary>
    /// Analyzes table usage frequency across all queries.
    /// </summary>
    /// <returns>Dictionary of table names and their usage counts.</returns>
    private Dictionary<string, int> AnalyzeTableUsage()
    {
        var tableUsage = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);

        foreach (var query in _queries)
        {
            var table = query.FromClause?.Clause?.Trim();
            if (!string.IsNullOrWhiteSpace(table))
            {
                if (tableUsage.TryGetValue(table, out int value))
                {
                    tableUsage[table] = ++value;
                }
                else
                {
                    tableUsage[table] = 1;
                }
            }
        }

        return tableUsage;
    }

    /// <summary>
    /// Analyzes column selection frequency across all queries.
    /// </summary>
    /// <returns>Dictionary of column names and their selection frequency.</returns>
    private Dictionary<string, int> AnalyzeColumnUsage()
    {
        var columnUsage = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);

        foreach (var query in _queries)
        {
            var selectClause = query.SelectClause?.Clause;
            if (string.IsNullOrWhiteSpace(selectClause) || selectClause.Trim() == "*")
            {
                continue;
            }

            // Split columns and count them
            var columns = selectClause.Split(',');
            foreach (var col in columns)
            {
                var columnName = col.Trim();
                if (columnUsage.TryGetValue(columnName, out int value))
                {
                    columnUsage[columnName] = ++value;
                }
                else
                {
                    columnUsage[columnName] = 1;
                }
            }
        }

        return columnUsage;
    }

    /// <summary>
    /// Calculates a complexity score for a query (0-10).
    /// </summary>
    private static int GetComplexityScore(LinqQueryBreakdown query)
    {
        int score = 1; // Base score for having a query

        if (!string.IsNullOrWhiteSpace(query.WhereClause?.Clause))
        { score += 2; }
        if (!string.IsNullOrWhiteSpace(query.GroupByClause?.Clause))
        { score += 2; }
        if (!string.IsNullOrWhiteSpace(query.HavingClause?.Clause))
        { score += 2; }
        if (!string.IsNullOrWhiteSpace(query.OrderByClause?.Clause))
        { score += 1; }

        // Bonus points for complex WHERE conditions
        var whereClause = query.WhereClause?.Clause ?? string.Empty;
        var complexityIndicators = new[] { " AND ", " OR ", "IN (", "BETWEEN", "LIKE" };
        var complexParts = complexityIndicators.Count(ind => whereClause.Contains(ind, StringComparison.OrdinalIgnoreCase));
        score += Math.Min(complexParts, 2); // Cap at +2

        return Math.Min(score, 10); // Cap at 10
    }

    /// <summary>
    /// Creates a new analyzer for the given queries.
    /// </summary>
    /// <param name="queries">The queries to analyze.</param>
    /// <returns>A new QueryCollectionAnalyzer instance.</returns>
    public static QueryCollectionAnalyzer Analyze(IEnumerable<LinqQueryBreakdown> queries)
    {
        return new QueryCollectionAnalyzer(queries);
    }

    /// <summary>
    /// Gets a summary report for the query collection.
    /// </summary>
    /// <returns>A formatted analysis report.</returns>
    public string GetReport()
    {
        return Analyze().GetReport();
    }
}