package rule

import (
	"go/ast"
	"go/token"

	"github.com/mgechev/revive/lint"
)

// BoolLiteralRule warns when logic expressions contains Boolean literals.
type BoolLiteralRule struct{}

// Apply applies the rule to given file.
func (*BoolLiteralRule) Apply(file *lint.File, _ lint.Arguments) []lint.Failure {
	var failures []lint.Failure

	onFailure := func(failure lint.Failure) {
		failures = append(failures, failure)
	}

	astFile := file.AST
	w := &lintBoolLiteral{astFile, onFailure}
	ast.Walk(w, astFile)

	return failures
}

// Name returns the rule name.
func (*BoolLiteralRule) Name() string {
	return "bool-literal-in-expr"
}

type lintBoolLiteral struct {
	file      *ast.File
	onFailure func(lint.Failure)
}

func (w *lintBoolLiteral) Visit(node ast.Node) ast.Visitor {
	switch n := node.(type) {
	case *ast.BinaryExpr:
		if !isBoolOp(n.Op) {
			return w
		}

		lexeme, ok := isExprABooleanLit(n.X)
		if !ok {
			lexeme, ok = isExprABooleanLit(n.Y)
			if !ok {
				return w
			}
		}

		isConstant := (n.Op == token.LAND && lexeme == "false") || (n.Op == token.LOR && lexeme == "true")

		if isConstant {
			w.addFailure(n, "Boolean expression seems to always evaluate to "+lexeme, lint.FailureCategoryLogic)
		} else {
			w.addFailure(n, "omit Boolean literal in expression", lint.FailureCategoryStyle)
		}
	}

	return w
}

func (w lintBoolLiteral) addFailure(node ast.Node, msg string, cat lint.FailureCategory) {
	w.onFailure(lint.Failure{
		Confidence: 1,
		Node:       node,
		Category:   cat,
		Failure:    msg,
	})
}

// isBoolOp returns true if the given token corresponds to a bool operator.
func isBoolOp(t token.Token) bool {
	switch t {
	case token.LAND, token.LOR, token.EQL, token.NEQ:
		return true
	}

	return false
}

func isExprABooleanLit(n ast.Node) (lexeme string, ok bool) {
	oper, ok := n.(*ast.Ident)

	if !ok {
		return "", false
	}

	return oper.Name, oper.Name == "true" || oper.Name == "false"
}
