//-----------------------------------------------------------------------------
//
// Copyright (C) Microsoft Corporation.  All Rights Reserved.
// Copyright by the contributors to the Dafny Project
// SPDX-License-Identifier: MIT
//
//-----------------------------------------------------------------------------

using System.Linq;
using Microsoft.Boogie;
using static Microsoft.Dafny.RewriterErrors;

namespace Microsoft.Dafny {

  public class PrecedenceLinter : IRewriter {
    private readonly CompilationData compilation;
    // Don't perform linting on doo files in general, since the source has already been processed.
    internal override void PreResolve(ModuleDefinition moduleDefinition) {
      if (moduleDefinition.tok.Uri != null && !moduleDefinition.ShouldVerify(compilation)) {
        return;
      }
      foreach (var topLevelDecl in moduleDefinition.TopLevelDecls.OfType<TopLevelDeclWithMembers>()) {
        foreach (var callable in topLevelDecl.Members.OfType<ICallable>()) {
          var visitor = new PrecedenceLinterVisitor(compilation, Reporter);
          visitor.Visit(callable, null);
        }
      }
    }

    public PrecedenceLinter(ErrorReporter reporter, CompilationData compilation) : base(reporter) {
      this.compilation = compilation;
    }
  }

  class LeftMargin {
    public int Column;

    public LeftMargin(int column) {
      Column = column;
    }
  }

  /// <summary>
  /// The PrecedenceLinterVisitor builds on Dafny's general TopDownVisitor. During the traversal, the overridable method VisitOneExpr
  /// performs some action on the given expression expr and parameter "st". The design of TopDownVisitor makes it possible for
  /// VisitOneExpr(expr, ...) to affect the traversal in the following ways:
  ///
  /// * It can request that no child of expr be visited. This is indicated by returning false.
  /// * It can request that the children of expr be visited using the same parameter value st. This is indicated by returning
  ///   true (and not assigning to st).
  /// * It can request that the children of expr be visited and provide a new parameter value st that will be passed to those
  ///   children. This is done by returning true and setting st to a different value.
  ///
  /// So, essentially, the traversal passes in one st value and gets a bool and an st back. This is encoded by making the bool
  /// be the method return value and making st a ref parameter.
  ///
  /// PrecedenceLinterVisitor.VisitOneExpr sometimes returns false, indicating that the main traversal should not go into the
  /// children of expr. Those children will therefore not be included in the stats gathered in st. Instead, PrecedenceLinterVisitor.VisitOneExpr
  /// will kick off a new visitation of its children, using a separate st object. This is how PrecedenceLinterVisitor can let the
  /// minimum-left-margin information be computed for just a part of the tree.
  ///
  /// The PrecedenceLinterVisitor also needs to be able to gather stats for all the nodes that are being visited. The design of
  /// TopDownVisitor does not use the ref parameter to accumulate values across the children; instead, it passes the same st to all
  /// children of expr. For this reason, PrecedenceLinterVisitor chooses the type of st to be a pointer to an integer.
  ///
  /// But PrecedenceLinterVisitor never uses the third case above. PrecedenceLinterVisitor would therefore be simpler if st were
  /// not a ref parameter in what is inherited from TopDownVisitor. Indeed, if we had another TopDownVisitor that streamlined this
  /// functionality, we could use it. Such a TopDownVisitor would then declare st (or, then more appropriately named "context") as
  /// an ordinary in-parameter to VisitOneExpr, since the method would only need to return a bool.
  /// </summary>
  class PrecedenceLinterVisitor : TopDownVisitor<LeftMargin> {
    private readonly CompilationData compilation;
    private readonly ErrorReporter reporter;

    public PrecedenceLinterVisitor(CompilationData compilation, ErrorReporter reporter) : base(false) {
      this.compilation = compilation;
      this.reporter = reporter;
    }

    /// <summary>
    /// Regarding the "st" parameter, see the comment above the class.
    /// </summary>
    protected override bool VisitOneExpr(Expression expr, ref LeftMargin st) {
      if (AutoGeneratedToken.Is(expr.tok) || expr is DefaultValueExpression || expr.RangeToken == null) {
        return false; // don't traverse further
      }

      if (st != null) {
        int column;
        if (expr is DatatypeUpdateExpr or SeqSelectExpr or SeqUpdateExpr or MultiSelectExpr or TernaryExpr) {
          // These expressions are handled below as being all-independent components, which means the
          // formatting of their internal structure is not relevant to the enclosing context. Yet, the .tok of
          // these expressions sits someone inside that internal structure (for example, the .tok of
          // a SeqSelectExpr is the open-bracket). To avoid looking at that internal structure, we instead
          // use the .StartToken for these expressions.
          column = expr.StartToken.col;
        } else {
          column = expr.tok.col;
        }
        if (column < st.Column) {
          st.Column = column;
        }
      }

      // Our aim is to try to detect if some expressions are longer than the user intended.
      // This can happen if the user accidentally left off parentheses around a lower-precedence
      // operator (e.g., ==>). As a guide, we look at how the user formatted the code,
      // that is, we inspect line and column information.

      if (expr is ApplySuffix applySuffix) {
        Visit(applySuffix.Lhs, st);
        foreach (var argument in applySuffix.Bindings.ArgumentBindings.Select(b => b.Actual)) {
          VisitIndependentComponent(argument);
        }

        return false;
      }

      if (expr is BinaryExpr bin && (bin.Op == BinaryExpr.Opcode.Imp || bin.Op == BinaryExpr.Opcode.Exp || bin.Op == BinaryExpr.Opcode.Iff)) {
        // For
        //   a)  LHS ==> RHS
        //   b)  LHS ==>
        //         RHS-somewhere-on-this-line
        // use LHS.StartToken as the left margin.
        // For
        //   c)  LHS0 &&
        //       LHS1 ==> RHS
        // use expr.tok (that is, the location of ==>) as the left margin. This is bound to generate a warning.
        // For
        //   d)  LHS0 &&
        //       LHS1 ==>
        //         RHS-somewhere-on-this-line
        //   e)  LHS0 &&
        //       LHS1
        //       ==>
        //         RHS-somewhere-on-this-line
        // use LHS.StartToken as the left margin.
        VisitLhsComponent(expr.tok, bin.E0,
          bin.E0.StartToken.line == expr.tok.line ? bin.E0.StartToken.col :
          bin.E1.StartToken.line == expr.tok.line ? expr.tok.col :
          bin.E0.StartToken.col,
          "left-hand operand of " + BinaryExpr.OpcodeString(bin.Op));
        VisitRhsComponent(expr.tok, bin.E1, "right-hand operand of " + BinaryExpr.OpcodeString(bin.Op));
        return false; // indicate that we've already processed expr's subexpressions

      } else if (expr is ITEExpr ifThenElse) {
        VisitIndependentComponent(ifThenElse.Test);
        VisitIndependentComponent(ifThenElse.Thn);
        VisitRhsComponent(expr.tok, ifThenElse.Els, "else branch of if-then-else");
        return false; // indicate that we've already processed expr's subexpressions

      } else if (expr is QuantifierExpr quantifierExpr) {
        Attributes.SubExpressions(quantifierExpr.Attributes).ForEach(VisitIndependentComponent);
        if (quantifierExpr.Range != null) {
          VisitIndependentComponent(quantifierExpr.Range);
        }
        VisitRhsComponent(expr.tok, quantifierExpr.Term,
          expr.tok.line == quantifierExpr.Term.StartToken.line ? expr.tok.col + 1 : quantifierExpr.Term.StartToken.col,
          "body of " + (expr is ForallExpr ? "forall" : "exists"));
        return false; // indicate that we've already processed expr's subexpressions

      } else if (expr is LetExpr letExpr) {
        Attributes.SubExpressions(letExpr.Attributes).ForEach(VisitIndependentComponent);
        letExpr.RHSs.ForEach(VisitIndependentComponent);
        VisitRhsComponent(expr.tok, letExpr.Body, "body of let-expression");
        return false; // indicate that we've already processed expr's subexpressions

      } else if (expr is OldExpr or FreshExpr or UnchangedExpr or DisplayExpression or MapDisplayExpr) {
        // In these expressions, all subexpressions are contained in parentheses, so there's no risk of precedence confusion
        expr.SubExpressions.ForEach(VisitIndependentComponent);
        return false; // indicate that we've already processed expr's subexpressions

      } else if (expr is DatatypeUpdateExpr datatypeUpdateExpr) {
        return VisitComponentsAsIndependentExceptOne(expr, datatypeUpdateExpr.Root, st);
      } else if (expr is SeqSelectExpr selectExpr) {
        return VisitComponentsAsIndependentExceptOne(expr, selectExpr.Seq, st);
      } else if (expr is SeqUpdateExpr seqUpdateExpr) {
        return VisitComponentsAsIndependentExceptOne(expr, seqUpdateExpr.Seq, st);
      } else if (expr is MultiSelectExpr multiSelectExpr) {
        return VisitComponentsAsIndependentExceptOne(expr, multiSelectExpr.Array, st);

      } else if (expr is TernaryExpr ternaryExpr) {
        VisitIndependentComponent(ternaryExpr.E0);
        Visit(ternaryExpr.E1, st);
        Visit(ternaryExpr.E2, st);
        return false; // indicate that we've already processed expr's subexpressions

      } else if (expr is NestedMatchExpr nestedMatchExpr) {
        // Handle each case like the "else" of an if-then-else
        Attributes.SubExpressions(nestedMatchExpr.Attributes).ForEach(VisitIndependentComponent);
        VisitIndependentComponent(nestedMatchExpr.Source);
        var n = nestedMatchExpr.Cases.Count;
        for (var i = 0; i < n; i++) {
          var body = nestedMatchExpr.Cases[i].Body;
          if (i == n - 1 && !nestedMatchExpr.UsesOptionalBraces) {
            VisitRhsComponent(body.StartToken, body, "case expression");
          } else {
            VisitIndependentComponent(body);
          }
        }

        return false; // indicate that we've already processed expr's subexpressions
      }

      return base.VisitOneExpr(expr, ref st);
    }

    /// <summary>
    /// For each subexpression of "expr", call "VisitIndependentComponent" unless the subexpression
    /// is "exception", in which case call "Visit(exception, st)".
    /// For convenience to the caller, this method always returns "false".
    /// </summary>
    bool VisitComponentsAsIndependentExceptOne(Expression expr, Expression exception, LeftMargin st) {
      foreach (var e in expr.SubExpressions) {
        if (e == exception) {
          Visit(e, st);
        } else {
          VisitIndependentComponent(e);
        }
      }
      return false;
    }

    void VisitIndependentComponent(Expression expr) {
      Visit(expr, null);
    }

    void VisitLhsComponent(IToken errorToken, Expression expr, int leftMargin, string what) {
      if (expr is ParensExpression || expr.StartToken.line == errorToken.line) {
        VisitIndependentComponent(expr);
      } else {
        var st = new LeftMargin(leftMargin);
        Visit(expr, st);
        if (st.Column < leftMargin) {
          reporter.Warning(MessageSource.Rewriter, ErrorId.rw_unusual_indentation_start, errorToken,
            $"unusual indentation in {what} (which starts at {LineCol(expr.StartToken)}); do you perhaps need parentheses?");
        }
      }
    }

    void VisitRhsComponent(IToken errorToken, Expression expr, string what) {
      VisitRhsComponent(errorToken, expr, expr.StartToken.col, what);
    }

    void VisitRhsComponent(IToken errorToken, Expression expr, int rightMargin, string what) {
      if (expr is ParensExpression || errorToken.FromIncludeDirective(compilation)) {
        VisitIndependentComponent(expr);
      } else {
        var st = new LeftMargin(rightMargin);
        Visit(expr, st);
        if (st.Column < rightMargin) {
          reporter.Warning(MessageSource.Rewriter, ErrorId.rw_unusual_indentation_end, errorToken,
            $"unusual indentation in {what} (which ends at {LineCol(expr.RangeToken.EndToken)}); do you perhaps need parentheses?");
        }
      }
    }

    static string LineCol(IToken tok) {
      return $"line {tok.line}, column {tok.col}";
    }
  }
}
