node_evaluator.go

package stateful

import (
	"errors"
	"fmt"
	"regexp"
	"time"

	"github.com/influxdata/kapacitor/tick/ast"
)

// ErrTypeGuardFailed is returned when a speicifc value type is requested thorugh NodeEvaluator (for example: "Float64Value")
// when the node doesn't support the given type, for example "Float64Value" is called on BoolNode
type ErrTypeGuardFailed struct {
	RequestedType ast.ValueType
	ActualType    ast.ValueType
}

func (e ErrTypeGuardFailed) Error() string {
	return fmt.Sprintf("TypeGuard: expression returned unexpected type %s, expected %s", e.ActualType, e.RequestedType)
}

type ReadOnlyScope interface {
	Get(name string) (interface{}, error)
	References() []string
	DynamicFunc(name string) *DynamicFunc
}

// NodeEvaluator provides a generic way for trying to fetch
// node value, if a speicifc type is requested (so Value isn't called, the *Value is called) ErrTypeGuardFailed must be returned
type NodeEvaluator interface {
	EvalFloat(scope *Scope, executionState ExecutionState) (float64, error)
	EvalInt(scope *Scope, executionState ExecutionState) (int64, error)
	EvalString(scope *Scope, executionState ExecutionState) (string, error)
	EvalBool(scope *Scope, executionState ExecutionState) (bool, error)
	EvalRegex(scope *Scope, executionState ExecutionState) (*regexp.Regexp, error)
	EvalTime(scope *Scope, executionState ExecutionState) (time.Time, error)
	EvalDuration(scope *Scope, executionState ExecutionState) (time.Duration, error)
	EvalMissing(scope *Scope, executionState ExecutionState) (*ast.Missing, error)

	// Type returns the type of ast.ValueType
	Type(scope ReadOnlyScope) (ast.ValueType, error)
	// Whether the type returned by the node can change.
	IsDynamic() bool
}

func createNodeEvaluator(n ast.Node) (NodeEvaluator, error) {
	switch node := n.(type) {

	case *ast.BoolNode:
		return &EvalBoolNode{Node: node}, nil

	case *ast.NumberNode:
		switch {
		case node.IsFloat:
			return &EvalFloatNode{Float64: node.Float64}, nil

		case node.IsInt:
			return &EvalIntNode{Int64: node.Int64}, nil

		default:
			// We wouldn't reach ever, unless there is bug in tick parsing ;)
			return nil, errors.New("Invalid NumberNode: Not float or int")
		}

	case *ast.DurationNode:
		return &EvalDurationNode{Duration: node.Dur}, nil
	case *ast.StringNode:
		return &EvalStringNode{Node: node}, nil

	case *ast.RegexNode:
		return &EvalRegexNode{Node: node}, nil

	case *ast.BinaryNode:
		return NewEvalBinaryNode(node)

	case *ast.ReferenceNode:
		return &EvalReferenceNode{Node: node}, nil

	case *ast.FunctionNode:
		return NewEvalFunctionNode(node)

	case *ast.UnaryNode:
		return NewEvalUnaryNode(node)

	case *ast.LambdaNode:
		return NewEvalLambdaNode(node)
	}

	return nil, fmt.Errorf("Given node type is not valid evaluation node: %T", n)
}

// getCostantNodeType - Given a ast.Node we want to know it's return type
// this method does exactly this, few examples:
// *) StringNode -> ast.TString
// *) UnaryNode -> we base the type by the node type
func getConstantNodeType(n ast.Node) ast.ValueType {
	switch node := n.(type) {
	case *ast.NumberNode:
		if node.IsInt {
			return ast.TInt
		}

		if node.IsFloat {
			return ast.TFloat
		}
	case *ast.DurationNode:
		return ast.TDuration
	case *ast.StringNode:
		return ast.TString
	case *ast.BoolNode:
		return ast.TBool
	case *ast.RegexNode:
		return ast.TRegex

	case *ast.UnaryNode:
		// If this is comparison operator we know for sure the output must be boolean
		if node.Operator == ast.TokenNot {
			return ast.TBool
		}

		// Could be float int or duration
		if node.Operator == ast.TokenMinus {
			return getConstantNodeType(node.Node)
		}

	case *ast.BinaryNode:
		// Check first using only the operator
		if ast.IsCompOperator(node.Operator) || ast.IsLogicalOperator(node.Operator) {
			return ast.TBool
		}
		leftType := getConstantNodeType(node.Left)
		rightType := getConstantNodeType(node.Right)
		// Check known constant types
		return binaryConstantTypes[operationKey{operator: node.Operator, leftType: leftType, rightType: rightType}]
	case *ast.LambdaNode:
		return getConstantNodeType(node.Expression)
	}

	return ast.InvalidType
}