Adding basic pretty print support- breaking on parenthesis expression…

…s and binary expressions (#12)

Co-authored-by: James Luck <[email protected]>

src/PromQL.Parser/Printer.cs

@@ -1,21 +1,38 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Text;
 using PromQL.Parser.Ast;
 
 namespace PromQL.Parser
 {
-    // TODO fix bug around "and"
-    // TODO pretty print support
+    /// <summary>
+    /// Converts PromQL Abstract Syntax Tress (AST's) into a string representation.
+    /// </summary>
+    /// <remarks>
+    /// Instances of this class are <i>not</i> thread safe and so should not be shared between threads.
+    /// </remarks>
     public class Printer : IVisitor
     {
-        private StringBuilder _sb = new ();
+        private readonly PrinterOptions _options;
+        private readonly IndentedStringBuilder _sb;
+
+        /// <summary>
+        /// Initializes a new printer instance.
+        /// </summary>
+        /// <param name="options">Allows customization of the output generated by the printer. Defaults to <see cref="PrinterOptions.PrettyDefault"/>.</param>
+        public Printer(PrinterOptions? options = null)
+        {
+            _options = options ?? PrinterOptions.PrettyDefault;
+            _sb = new IndentedStringBuilder(_options.IndentChar, _options.IndentCount);
+        }
 
         public virtual void Visit(StringLiteral s)
         {
             // Raw strings are denoted by ` and should not have their values escaped
             if (s.Quote == '`')
             {
-                _sb.Append($"{s.Quote}{s.Value}{s.Quote}");
+                Write($"{s.Quote}{s.Value}{s.Quote}");
                 return;
             }
 
@@ -31,61 +48,61 @@ public virtual void Visit(StringLiteral s)
                 .Replace("\t", "\\t")
                 .Replace("\v", "\\v");
 
-            _sb.Append($"{s.Quote}{escaped}{s.Quote}");
+            Write($"{s.Quote}{escaped}{s.Quote}");
         }
 
         public virtual void Visit(SubqueryExpr sq)
         {
             sq.Expr.Accept(this);
-            _sb.Append("[");
+            Write("[");
             sq.Range.Accept(this);
-            _sb.Append(":");
+            Write(":");
             sq.Step?.Accept(this);
-            _sb.Append("]");
+            Write("]");
         }
 
         public virtual void Visit(Duration d)
         {
             if (d.Value.Days > 0)
-                _sb.Append($"{d.Value.Days}d");
+                Write($"{d.Value.Days}d");
             if (d.Value.Hours > 0)
-                _sb.Append($"{d.Value.Hours}h");
+                Write($"{d.Value.Hours}h");
             if (d.Value.Minutes > 0)
-                _sb.Append($"{d.Value.Minutes}m");
+                Write($"{d.Value.Minutes}m");
             if (d.Value.Seconds > 0)
-                _sb.Append($"{d.Value.Seconds}s");
+                Write($"{d.Value.Seconds}s");
             if (d.Value.Milliseconds > 0)
-                _sb.Append($"{d.Value.Milliseconds}ms");
+                Write($"{d.Value.Milliseconds}ms");
         }
 
-        public virtual void Visit(NumberLiteral n) => _sb.Append(n.Value switch
+        public virtual void Visit(NumberLiteral n) => Write(n.Value switch
         {
             double.PositiveInfinity => "Inf",
             double.NegativeInfinity => "-Inf",
             _ => n.Value.ToString()
         });
 
-        public virtual void Visit(MetricIdentifier mi) => _sb.Append(mi.Value);
+        public virtual void Visit(MetricIdentifier mi) => Write(mi.Value);
 
         public virtual void Visit(LabelMatcher lm)
         {
-            _sb.Append($"{lm.LabelName}{lm.Operator.ToPromQl()}");
+            Write($"{lm.LabelName}{lm.Operator.ToPromQl()}");
             lm.Value.Accept(this);
         }
 
         public virtual void Visit(LabelMatchers lms)
         {
             bool first = true;
-            _sb.Append("{");
+            Write("{");
             foreach (var lm in lms.Matchers)
             {
                 if (!first)
-                    _sb.Append(", ");
+                    Write(", ");
 
                 lm.Accept(this);
                 first = false;
             }
-            _sb.Append("}");
+            Write("}");
         }
 
         public virtual void Visit(VectorSelector vs)
@@ -96,132 +113,145 @@ public virtual void Visit(VectorSelector vs)
 
         public virtual void Visit(UnaryExpr unary)
         {
-            _sb.Append(unary.Operator.ToPromQl());
+            Write(unary.Operator.ToPromQl());
             unary.Expr.Accept(this);
         }
 
         public virtual void Visit(MatrixSelector ms)
         {
             ms.Vector.Accept(this);
-            _sb.Append("[");
+            Write("[");
             ms.Duration.Accept(this);
-            _sb.Append("]");
+            Write("]");
         }
 
         public virtual void Visit(OffsetExpr offset)
         {
             offset.Expr.Accept(this);
-            _sb.Append(" offset ");
+            Write(" offset ");
 
             Duration d = offset.Duration;
 
             if (d.Value < TimeSpan.Zero)
             {
                 // Negative durations cannot be printed by the duration visitor. Convert to positive and emit sign here.
                 d = d with { Value = new TimeSpan(Math.Abs(d.Value.Ticks))};
-                _sb.Append("-");
+                Write("-");
             }
 
             d.Accept(this);
         }
 
         public virtual void Visit(ParenExpression paren)
         {
-            _sb.Append("(");
-            paren.Expr.Accept(this);
-            _sb.Append(")");
+            Write("(");
+
+            using (_options.BreakOnParenExpr ? _sb.IncreaseIndent() : null)
+                paren.Expr.Accept(this);
+
+            Write(")");
         }
 
         public virtual void Visit(FunctionCall fnCall)
         {
-            _sb.Append($"{fnCall.Function.Name}(");
+            Write($"{fnCall.Function.Name}(");
 
             bool isFirst = true;
             foreach (var arg in fnCall.Args)
             {
                 if (!isFirst)
-                    _sb.Append(", ");
+                    Write(", ");
 
                 arg.Accept(this);
                 isFirst = false;
             }
 
-            _sb.Append(")");
+            Write(")");
         }
 
         public virtual void Visit(VectorMatching vm)
         {
             if (vm.ReturnBool)
-                _sb.Append("bool");
+            {
+                Write("bool");
+            }
 
             if (vm.On || vm.MatchingLabels.Length > 0)
             {
-                if (_sb.Length > 0)
-                    _sb.Append(" ");
+                if (vm.ReturnBool)
+                    Write(" ");
 
-                _sb.Append(vm.On ? "on" : "ignoring");
-                _sb.Append(" (");
-                _sb.Append(string.Join(", ", vm.MatchingLabels));
-                _sb.Append(")");
+                Write(vm.On ? "on" : "ignoring");
+                Write(" (");
+                Write(string.Join(", ", vm.MatchingLabels));
+                Write(")");
             }
 
             if (vm.MatchCardinality != VectorMatching.DefaultMatchCardinality)
             {
                 if (_sb.Length > 0)
-                    _sb.Append(" ");
+                    Write(" ");
 
-                _sb.Append(vm.MatchCardinality.ToPromQl());
+                Write(vm.MatchCardinality.ToPromQl()!);
             }
 
             if (vm.Include.Length > 0 || vm.MatchCardinality != VectorMatching.DefaultMatchCardinality)
             {
                 if (_sb.Length > 0)
-                    _sb.Append(" ");
+                    Write(" ");
 
-                _sb.Append("(");
-                _sb.Append(string.Join(", ", vm.Include));
-                _sb.Append(")");
+                Write("(");
+                Write(string.Join(", ", vm.Include));
+                Write(")");
             }
         }
 
         public virtual void Visit(BinaryExpr expr)
         {
             expr.LeftHandSide.Accept(this);
 
-            _sb.Append($" {expr.Operator.ToPromQl()} ");
+            if (_options.BreakOnBinaryOperators)
+                _sb.AppendLine();
+            else
+                Write(" ");
+
+            Write($"{expr.Operator.ToPromQl()} ");
 
             var preLen = _sb.Length;
             expr.VectorMatching?.Accept(this);
 
             if (_sb.Length > preLen)
-                _sb.Append(" ");
+                Write(" ");
 
             expr.RightHandSide.Accept(this);
         }
 
         public virtual void Visit(AggregateExpr expr)
         {
-            _sb.Append($"{expr.Operator.Name}");
+            Write($"{expr.Operator.Name}");
 
             if (expr.GroupingLabels.Length > 0)
             {
-                _sb.Append(" ");
-                _sb.Append(expr.Without ? "without" : "by");
-                _sb.Append($" ({string.Join(", ", expr.GroupingLabels)}) ");
+                Write(" ");
+                Write(expr.Without ? "without" : "by");
+                Write($" ({string.Join(", ", expr.GroupingLabels)}) ");
             }
 
-            _sb.Append("(");
+            Write("(");
             if (expr.Param != null)
             {
                 expr.Param.Accept(this);
-                _sb.Append(", ");
+                Write(", ");
             }
 
             expr.Expr.Accept(this);
-            _sb.Append(")");
+            Write(")");
         }
 
-        protected void Write(string s) => _sb.Append(s);
+        protected void Write(string s)
+        {
+           _sb.Append(s);
+        }
 
         public string ToPromQl(IPromQlNode node)
         {
@@ -231,7 +261,92 @@ public string ToPromQl(IPromQlNode node)
             _sb.Clear();
             node.Accept(this);
 
-            return _sb.ToString();
+            return _sb.ToString()!;
+        }
+    }
+
+    internal class IndentedStringBuilder
+    {
+        private int _indentLevel = 0;
+        private readonly string[] _indents;
+        private const int MaxIndent = 20;
+        private StringBuilder _sb = new StringBuilder();
+
+        public IndentedStringBuilder(char indentChar, int indentCount)
+        {
+            _indents = Enumerable.Range(0, MaxIndent)
+                .Select(n => new string(Enumerable.Repeat(indentChar, indentCount * n).ToArray()))
+                .ToArray();
+        }
+
+        public void Append(string? s) => _sb.Append(s);
+
+        public int Length => _sb.Length;
+
+        public void Clear() => _sb.Clear();
+
+        public void AppendLine()
+        {
+            _sb.AppendLine();
+            _sb.Append(_indents[_indentLevel]);
         }
+
+        public override string ToString() => _sb.ToString();
+
+        public IDisposable IncreaseIndent()
+        {
+            _indentLevel++;
+            if (_indentLevel == MaxIndent)
+                throw new InvalidOperationException($"Cannot increase indent beyond {MaxIndent}");
+
+            AppendLine();
+            return new DisposableIndent(this);
+        }
+
+        public void DecreaseIndent()
+        {
+            _indentLevel--;
+            AppendLine();
+        }
+
+        internal class DisposableIndent : IDisposable
+        {
+            private readonly IndentedStringBuilder _isb;
+            private bool _disposed;
+
+            public DisposableIndent(IndentedStringBuilder isb)
+            {
+                _isb = isb;
+                _disposed = false;
+            }
+
+            public void Dispose()
+            {
+                if (_disposed)
+                    return;
+
+                _isb.DecreaseIndent();
+                _disposed = true;
+            }
+        }
+    }
+
+    public record PrinterOptions(
+        int IndentCount,
+        char IndentChar,
+        bool BreakOnParenExpr,
+        bool BreakOnBinaryOperators
+    )
+    {
+        /// <summary>
+        /// Formats the printed output of PromQL expressions into a more human-readable format,
+        /// by inserting line breaks and indentation. 
+        /// </summary>
+        public static PrinterOptions PrettyDefault = new(2, ' ', true, true);
+
+        /// <summary>
+        /// Doesn't format the printed output of PromQL expressions.
+        /// </summary>
+        public static PrinterOptions NoFormatting = new(0, ' ', false, false);
     }
 }