Add get screen resolution code

shell.go

@@ -2,6 +2,8 @@ package adb
 
 import (
 	"context"
+	"regexp"
+	"strconv"
 	"time"
 
 	"github.com/google/shlex"
@@ -26,8 +28,26 @@ func (d Device) Shell(ctx context.Context, command string) (stdout string, stder
 
 // adb shell wm size
 // Physical size: 1440x3120
-func (d Device) GetScreenResolution(ctx context.Context) (width int, lenght int, err error) {
-	return 0, 0, nil
+func (d Device) GetScreenResolution(ctx context.Context) (width int, height int, err error) {
+	cmd := []string{"-s", string(d.SerialNo), "shell", "wm", "size"}
+	stdout, _, _, err := execute(ctx, cmd)
+	if err != nil {
+		return -1, -1, err
+	}
+	return parseScreenResolution(stdout)
+}
+
+// Parses input, example:
+// Physical size: 1440x3040
+func parseScreenResolution(in string) (int, int, error) {
+	r := regexp.MustCompile(`Physical size: ([0-9]+)x([0-9]+)`)
+	resStr := r.FindStringSubmatch(in)
+	if len(resStr) != 3 {
+		return -1, -1, ErrResolutionParseFail
+	}
+	w, _ := strconv.Atoi(resStr[1])
+	h, _ := strconv.Atoi(resStr[2])
+	return w, h, nil
 }
 
 func (d Device) Tap(ctx context.Context, X, Y int) error {