sql-utilities/src/Strata.SqlTools.Markdown/LinqToSql/SqlStatementGenerator.cs

using Strata.SqlTools.SqlBreakdown.Interfaces;
using Strata.SqlTools.SqlBreakdown.Interfaces.QueryEngine;

namespace Strata.SqlTools.Markdown.LinqToSql;

/// <summary>
/// Generates Mermaid diagrams for LINQ to SQL statements, including sequence diagrams
/// for statement execution flow and entity-relationship diagrams.
/// </summary>
public class SqlStatementGenerator
{
    private readonly SqlServer.SqlStatementGenerator _baseGenerator;

    /// <summary>
    /// Initializes a new instance of the SqlStatementGenerator class.
    /// </summary>
    public SqlStatementGenerator()
    {
        _baseGenerator = new SqlServer.SqlStatementGenerator();
    }

    /// <summary>
    /// Generates a Mermaid sequence diagram showing LINQ to SQL statement execution flow.
    /// </summary>
    /// <param name="sqlBreakdown">The LINQ to SQL breakdown object.</param>
    /// <param name="title">Optional title for the diagram.</param>
    /// <returns>A string containing the Mermaid sequence diagram markdown.</returns>
    public string GenerateSequenceDiagram(ISqlBreakdown sqlBreakdown, string? title = null)
    {
        return _baseGenerator.GenerateSequenceDiagram(sqlBreakdown, title);
    }

    /// <summary>
    /// Generates a Mermaid entity-relationship diagram from a SQL breakdown.
    /// </summary>
    /// <param name="sqlBreakdown">The SQL breakdown containing query information.</param>
    /// <param name="title">Optional title for the diagram.</param>
    /// <returns>A string containing the Mermaid ER diagram markdown.</returns>
    public string GenerateEntityRelationshipDiagram(ISqlBreakdown sqlBreakdown, string? title = null)
    {
        //Extract table names from breakdown - just use FROM clause for now
        var queryBreakdown = sqlBreakdown as IQueryBreakdown;
        var tableNames = new List<string>();

        var fromClauseText = queryBreakdown?.FromClause?.ToString();
        if (!string.IsNullOrWhiteSpace(fromClauseText))
        {
            tableNames.Add(fromClauseText);
        }

        return _baseGenerator.GenerateEntityRelationshipDiagram(tableNames, title);
    }

    /// <summary>
    /// Generates a diagram showing LINQ execution pipeline from a SQL breakdown.
    /// </summary>
    /// <param name="queryBreakdown">The query breakdown containing query information.</param>
    /// <param name="title">Optional title for the diagram.</param>
    /// <returns>A string containing the Mermaid diagram markdown.</returns>
    public static string GenerateLinqPipelineDiagram(IQueryBreakdown queryBreakdown, string? title = null)
    {
        var sb = new System.Text.StringBuilder();

        if (!string.IsNullOrWhiteSpace(title))
        {
            sb.AppendLine($"### {title}");
            sb.AppendLine();
        }

        sb.AppendLine("```mermaid");
        sb.AppendLine("sequenceDiagram");
        sb.AppendLine("    participant Client as Client Application");
        sb.AppendLine("    participant LINQ as LINQ Provider");
        sb.AppendLine("    participant ET as Expression Tree");
        sb.AppendLine("    participant SQL as SQL Generator");
        sb.AppendLine("    participant DB as Database");
        sb.AppendLine();
        sb.AppendLine("    Client->>LINQ: LINQ Query");
        sb.AppendLine("    activate LINQ");

        // Check if there's a WHERE clause
        var whereClause = queryBreakdown.WhereClause?.Clause;
        if (!string.IsNullOrWhiteSpace(whereClause))
        {
            sb.AppendLine("    LINQ->>ET: Where Predicate");
            sb.AppendLine("    activate ET");
        }

        // Check if there's a custom SELECT
        var selectClause = queryBreakdown.SelectClause?.Clause;
        if (!string.IsNullOrWhiteSpace(selectClause) && selectClause.Trim() != "*")
        {
            sb.AppendLine("    LINQ->>ET: Select Projection");
            if (string.IsNullOrWhiteSpace(whereClause))
            {
                sb.AppendLine("    activate ET");
            }
        }

        sb.AppendLine("    ET->>SQL: Expression Tree");
        sb.AppendLine("    deactivate ET");
        sb.AppendLine("    SQL->>DB: Generate SQL");
        sb.AppendLine("    activate DB");
        sb.AppendLine("    DB-->>SQL: Result Set");
        sb.AppendLine("    deactivate DB");
        sb.AppendLine("    SQL-->>LINQ: Mapped Objects");
        sb.AppendLine("    LINQ-->>Client: IEnumerable Result");
        sb.AppendLine("    deactivate LINQ");
        sb.AppendLine("```");
        sb.AppendLine();

        return sb.ToString();
    }
}