#13 Added WAIT_ELEMENT function

pkg/stdlib/html/driver/browser/document.go

@@ -2,11 +2,14 @@ package browser
 
 import (
 	"context"
+	"fmt"
 	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
 	"github.com/mafredri/cdp"
 	"github.com/mafredri/cdp/protocol/dom"
 	"github.com/mafredri/cdp/rpcc"
 	"strings"
+	"time"
 )
 
 type HtmlDocument struct {
@@ -108,3 +111,23 @@ func (doc *HtmlDocument) Compare(other core.Value) int {
 		return 1
 	}
 }
+
+func (doc *HtmlDocument) WaitForSelector(selector values.String, timeout values.Int) error {
+	task := NewWaitTask(
+		doc.client,
+		fmt.Sprintf(`
+			el = document.querySelector("%s");
+
+			if (el != null) {
+				return true;
+			}
+
+			return null;
+		`, selector),
+		time.Millisecond*time.Duration(timeout),
+	)
+
+	_, err := task.Run()
+
+	return err
+}

pkg/stdlib/html/driver/browser/wait.go

@@ -0,0 +1,96 @@
+package browser
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
+	"github.com/MontFerret/ferret/pkg/runtime/values"
+	"github.com/mafredri/cdp"
+	"github.com/mafredri/cdp/protocol/runtime"
+	"time"
+)
+
+type WaitTask struct {
+	client    *cdp.Client
+	predicate string
+	timeout   time.Duration
+}
+
+func NewWaitTask(
+	client *cdp.Client,
+	predicate string,
+	timeout time.Duration,
+) *WaitTask {
+	return &WaitTask{
+		client,
+		fmt.Sprintf("((function () {%s})())", predicate),
+		timeout,
+	}
+}
+
+func (task *WaitTask) Run() (core.Value, error) {
+	var result core.Value = values.None
+	var err error
+	var done bool
+	timer := time.NewTimer(task.timeout)
+
+	for !done {
+		select {
+		case <-timer.C:
+			err = core.ErrTimeout
+			done = true
+		default:
+			out, e := task.exec()
+
+			if e != nil {
+				done = true
+				timer.Stop()
+				err = e
+
+				break
+			}
+
+			if out != values.None {
+				timer.Stop()
+
+				result = out
+				done = true
+				break
+			}
+		}
+	}
+
+	return result, err
+}
+
+func (task *WaitTask) exec() (core.Value, error) {
+	args := runtime.NewEvaluateArgs(task.predicate).SetReturnByValue(true)
+	out, err := task.client.Runtime.Evaluate(context.Background(), args)
+
+	if err != nil {
+		return values.None, err
+	}
+
+	if out.ExceptionDetails != nil {
+		ex := out.ExceptionDetails
+		return values.None, core.Error(
+			core.ErrUnexpected,
+			fmt.Sprintf("%s %s", ex.Text, *ex.Exception.Description),
+		)
+	}
+
+	if out.Result.Type != "undefined" {
+		var o interface{}
+
+		err := json.Unmarshal(out.Result.Value, &o)
+
+		if err != nil {
+			return values.None, core.Error(core.ErrUnexpected, err.Error())
+		}
+
+		return values.Parse(o), nil
+	}
+
+	return values.None, nil
+}

pkg/stdlib/html/driver/driver.go

@@ -2,6 +2,8 @@ package driver
 
 import (
 	"context"
+	"fmt"
+	"github.com/MontFerret/ferret/pkg/runtime/core"
 	"github.com/MontFerret/ferret/pkg/runtime/values"
 	"github.com/MontFerret/ferret/pkg/stdlib/html/driver/browser"
 	"github.com/MontFerret/ferret/pkg/stdlib/html/driver/http"
@@ -19,16 +21,16 @@ func ToContext(ctx context.Context, name string, drv Driver) context.Context {
 	return context.WithValue(ctx, name, drv)
 }
 
-func FromContext(ctx context.Context, name string) Driver {
+func FromContext(ctx context.Context, name string) (Driver, error) {
 	val := ctx.Value(name)
 
 	drv, ok := val.(Driver)
 
 	if ok {
-		return drv
+		return drv, nil
 	}
 
-	return nil
+	return nil, core.Error(core.ErrNotFound, fmt.Sprintf("%s driver", name))
 }
 
 func WithCdpDriver(ctx context.Context, addr string) context.Context {