Adding logic example

examples/logic/.gitignore

@@ -0,0 +1,2 @@
+logic
+logic.exe

examples/logic/main.go

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+// examples/logic/main.go
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"strings"
+	"time"
+
+	cdp "github.com/knq/chromedp"
+	cdptypes "github.com/knq/chromedp/cdp"
+)
+
+func main() {
+	var err error
+
+	// create context
+	ctxt, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// create chrome instance
+	c, err := cdp.New(ctxt, cdp.WithLog(log.Printf))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// list awesome go projects for the "Selenium and browser control tools."
+	res, err := listAwesomeGoProjects(ctxt, c, "Selenium and browser control tools.")
+	if err != nil {
+		log.Fatalf("could not list awesome go projects: %v", err)
+	}
+
+	// shutdown chrome
+	err = c.Shutdown(ctxt)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// wait for chrome to finish
+	err = c.Wait()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// output the values
+	for k, v := range res {
+		log.Printf("project %s (%s): '%s'", k, v.URL, v.Description)
+	}
+}
+
+// ud contains a url, description for a project.
+type ud struct {
+	URL, Description string
+}
+
+// listAwesomeGoProjects is the highest level logic for browsing to the
+// awesome-go page, finding the specified section sect, and retrieving the
+// associated projects from the page.
+func listAwesomeGoProjects(ctxt context.Context, c *cdp.CDP, sect string) (map[string]ud, error) {
+	// force max timeout of 15 seconds for retrieving and processing the data
+	var cancel func()
+	ctxt, cancel = context.WithTimeout(ctxt, 25*time.Second)
+	defer cancel()
+
+	sel := fmt.Sprintf(`//p[text()[contains(., '%s')]]`, sect)
+
+	// navigate
+	if err := c.Run(ctxt, cdp.Navigate(`https://github.com/avelino/awesome-go`)); err != nil {
+		return nil, fmt.Errorf("could not navigate to github: %v", err)
+	}
+
+	// wait visible
+	if err := c.Run(ctxt, cdp.WaitVisible(sel)); err != nil {
+		return nil, fmt.Errorf("could not get section: %v", err)
+	}
+
+	sib := sel + `/following-sibling::ul/li`
+
+	// get project link text
+	var projects []*cdptypes.Node
+	if err := c.Run(ctxt, cdp.Nodes(sib+`/child::a/text()`, &projects)); err != nil {
+		return nil, fmt.Errorf("could not get projects: %v", err)
+	}
+
+	// get links and description text
+	var linksAndDescriptions []*cdptypes.Node
+	if err := c.Run(ctxt, cdp.Nodes(sib+`/child::node()`, &linksAndDescriptions)); err != nil {
+		return nil, fmt.Errorf("could not get links and descriptions: %v", err)
+	}
+
+	// check length
+	if 2*len(projects) != len(linksAndDescriptions) {
+		return nil, fmt.Errorf("projects and links and descriptions lengths do not match (2*%d != %d)", len(projects), len(linksAndDescriptions))
+	}
+
+	// process data
+	res := make(map[string]ud)
+	for i := 0; i < len(projects); i++ {
+		res[projects[i].NodeValue] = ud{
+			URL:         linksAndDescriptions[2*i].AttributeValue("href"),
+			Description: strings.TrimPrefix(strings.TrimSpace(linksAndDescriptions[2*i+1].NodeValue), "- "),
+		}
+	}
+
+	return res, nil
+}