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expression.go
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expression.go
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package steps
import (
"bytes"
"fmt"
"math"
"time"
"github.com/Knetic/govaluate"
"github.com/bitflow-stream/go-bitflow/bitflow"
)
type Expression struct {
expr *govaluate.EvaluableExpression
vars map[string]bool
varIndices map[int]string
sample *bitflow.Sample
header *bitflow.Header
num int
}
func NewExpression(expressionString string) (*Expression, error) {
expr := &Expression{
vars: make(map[string]bool),
}
compiled, err := govaluate.NewEvaluableExpressionWithFunctions(expressionString, expr.makeFunctions())
if err != nil {
return nil, err
}
expr.expr = compiled
for _, variable := range compiled.Vars() {
expr.vars[variable] = true
}
return expr, nil
}
func (p *Expression) UpdateHeader(header *bitflow.Header) error {
resolvedVariables := make(map[string]bool)
p.varIndices = make(map[int]string)
for i, field := range header.Fields {
if p.vars[field] {
p.varIndices[i] = field
resolvedVariables[field] = true
}
}
for variable := range p.vars {
if !resolvedVariables[variable] {
return fmt.Errorf("%v: Variable %v cannot be resolved in header", p.expr, variable)
}
}
return nil
}
func (p *Expression) Evaluate(sample *bitflow.Sample, header *bitflow.Header) (interface{}, error) {
parameters := p.makeParameters(sample)
p.sample = sample // Set the sample/header so that the functions in makeFunctions() can access its values
p.header = header
defer func() {
p.sample = nil
p.header = nil
}()
res, err := p.expr.Evaluate(parameters)
p.num++
return res, err
}
func (p *Expression) EvaluateBool(sample *bitflow.Sample, header *bitflow.Header) (bool, error) {
result, err := p.Evaluate(sample, header)
if err != nil {
return false, err
}
if boolResult, ok := result.(bool); ok {
return boolResult, nil
} else {
return false, fmt.Errorf("%v: Non-boolean result returned: %v (%T)", p.expr, result, result)
}
}
func (p *Expression) makeParameters(sample *bitflow.Sample) map[string]interface{} {
parameters := make(map[string]interface{})
for index, variable := range p.varIndices {
parameters[variable] = float64(sample.Values[index])
}
return parameters
}
func (p *Expression) makeFunctions() map[string]govaluate.ExpressionFunction {
return map[string]govaluate.ExpressionFunction{
"tag": p.makeStringFunction("tag", 1, func(sample *bitflow.Sample, args ...string) (interface{}, error) {
return sample.Tag(args[0]), nil
}),
"has_tag": p.makeStringFunction("has_tag", 1, func(sample *bitflow.Sample, args ...string) (interface{}, error) {
return sample.HasTag(args[0]), nil
}),
"set_tag": p.makeStringFunction("set_tag", 2, func(sample *bitflow.Sample, args ...string) (interface{}, error) {
sample.SetTag(args[0], args[1])
return args[1], nil
}),
"timestamp": p.makeStringFunction("timestamp", 0, func(sample *bitflow.Sample, args ...string) (interface{}, error) {
return float64(sample.Time.Unix()), nil
}),
// Dates are parsed automatically by the govaluate library if a date/time formatted string is encountered. The Unix() value is used.
// If alternative date formats are required, this function can be added.
// "date": p.makeStringFunction("date", 1, func(sample *bitflow.Sample, args ...string) (interface{}, error) {
// date, err := time.Parse(bitflow.TextMarshallerDateFormat, args[0])
// return float64(date.Unix()), fmt.Errorf("Cannot parse date (format: %v): %v", bitflow.TextMarshallerDateFormat, err)
// }),
"now": p.makeStringFunction("now", 0, func(sample *bitflow.Sample, args ...string) (interface{}, error) {
return float64(time.Now().Unix()), nil
}),
"num": p.makeStringFunction("num", 0, func(sample *bitflow.Sample, args ...string) (interface{}, error) {
return p.num, nil
}),
"str": func(arguments ...interface{}) (interface{}, error) {
if len(arguments) == 1 {
return fmt.Sprintf("%v", arguments[0]), nil
}
return nil, fmt.Errorf("str() needs 1 parameter, but received: %v", printParamStrings(arguments))
},
"date_str": func(arguments ...interface{}) (interface{}, error) {
if len(arguments) == 1 {
if numArg, ok := arguments[0].(float64); ok {
return time.Unix(int64(numArg), 0).Format(bitflow.TextMarshallerDateFormat), nil
}
}
return nil, fmt.Errorf("date_str() needs 1 float64 parameter, but received: %v", printParamStrings(arguments))
},
"set_timestamp": func(arguments ...interface{}) (interface{}, error) {
if len(arguments) == 1 {
if numArg, ok := arguments[0].(float64); ok {
p.currentSample().Time = time.Unix(int64(numArg), 0)
return arguments[0], nil
}
}
return nil, fmt.Errorf("set_timestamp() needs 1 float64 parameter, but received: %v", printParamStrings(arguments))
},
"floor": func(arguments ...interface{}) (interface{}, error) {
if len(arguments) == 1 {
if numArg, ok := arguments[0].(float64); ok {
return math.Floor(numArg), nil
}
}
return nil, fmt.Errorf("floor() needs 1 float64 parameter, but received: %v", printParamStrings(arguments))
},
}
}
func (p *Expression) makeStringFunction(funcName string, numArgs int, f func(sample *bitflow.Sample, args ...string) (interface{}, error)) govaluate.ExpressionFunction {
return func(args ...interface{}) (interface{}, error) {
sample := p.currentSample()
if len(args) == numArgs {
strArgs := make([]string, 0, numArgs)
for _, arg := range args {
if strArg, ok := arg.(string); ok {
strArgs = append(strArgs, strArg)
} else {
break
}
}
if len(strArgs) == numArgs {
return f(sample, strArgs...)
}
}
return nil, fmt.Errorf("%v() needs %v string parameter(s), but received: %v", funcName, numArgs, printParamStrings(args))
}
}
func (p *Expression) currentSample() *bitflow.Sample {
sample := p.sample
if sample == nil {
panic("An expression function was called outside of Expression.Evaluate()")
}
return sample
}
func (p *Expression) currentHeader() *bitflow.Header {
header := p.header
if header == nil {
panic("An expression function was called outside of Expression.Evaluate()")
}
return header
}
func printParamStrings(values []interface{}) string {
var buf bytes.Buffer
for _, val := range values {
if buf.Len() > 0 {
buf.WriteString(", ")
}
fmt.Fprintf(&buf, "%v (%T)", val, val)
}
return buf.String()
}