starlark/runtime: basic implementation

Signed-off-by: Máximo Cuadros <mcuadros@gmail.com>

examples/encoding.star

@@ -0,0 +1,13 @@
+load("encoding/json", "json")
+load("encoding/base64", "base64")
+
+ignition = provider("ignition", "1.1.0")
+
+user = ignition.data.user()
+user.name = "foo"
+user.uid = 42
+user.groups = ["foo", "bar"]
+user.system = True
+
+print(json.dumps(user.__dict__))
+print(base64.encode("foo"))

main.go

@@ -6,12 +6,11 @@ import (
 	"log"
 	"os"
 
+	"github.com/ascode-dev/ascode/starlark/runtime"
 	"github.com/ascode-dev/ascode/starlark/types"
 	"github.com/ascode-dev/ascode/terraform"
 
 	"github.com/hashicorp/hcl2/hclwrite"
-	"go.starlark.net/repl"
-	"go.starlark.net/resolve"
 	"go.starlark.net/starlark"
 )
 
@@ -19,14 +18,9 @@ func main() {
 	log.SetOutput(ioutil.Discard)
 
 	pm := &terraform.PluginManager{".providers"}
-	resolve.AllowFloat = true
+	runtime := runtime.NewRuntime(pm)
 
-	thread := &starlark.Thread{Name: "thread", Load: repl.MakeLoad()}
-	predeclared := starlark.StringDict{
-		"provider": types.BuiltinProvider(pm),
-	}
-
-	out, err := starlark.ExecFile(thread, os.Args[1], nil, predeclared)
+	out, err := runtime.ExecFile(os.Args[1])
 	if err != nil {
 		fmt.Println(err)
 		if err, ok := err.(*starlark.EvalError); ok {

starlark/runtime/runtime.go

@@ -0,0 +1,54 @@
+package runtime
+
+import (
+	"os"
+
+	"github.com/ascode-dev/ascode/starlark/types"
+	"github.com/ascode-dev/ascode/terraform"
+	"github.com/qri-io/starlib/encoding/base64"
+	"github.com/qri-io/starlib/encoding/csv"
+	"github.com/qri-io/starlib/encoding/json"
+	"go.starlark.net/repl"
+	"go.starlark.net/resolve"
+	"go.starlark.net/starlark"
+)
+
+func init() {
+	resolve.AllowFloat = true
+}
+
+type LoadModuleFunc func() (starlark.StringDict, error)
+
+type Runtime struct {
+	predeclared  starlark.StringDict
+	modules      map[string]LoadModuleFunc
+	fallbackLoad func(t *starlark.Thread, module string) (starlark.StringDict, error)
+}
+
+func NewRuntime(pm *terraform.PluginManager) *Runtime {
+	return &Runtime{
+		fallbackLoad: repl.MakeLoad(),
+		modules: map[string]LoadModuleFunc{
+			"encoding/json":   json.LoadModule,
+			"encoding/base64": base64.LoadModule,
+			"encoding/csv":    csv.LoadModule,
+		},
+		predeclared: starlark.StringDict{
+			"provider": types.BuiltinProvider(pm),
+			"hcl":      types.BuiltinHCL(),
+		},
+	}
+}
+
+func (r *Runtime) ExecFile(filename string) (starlark.StringDict, error) {
+	thread := &starlark.Thread{Name: "thread", Load: r.load}
+	return starlark.ExecFile(thread, os.Args[1], nil, r.predeclared)
+}
+
+func (r *Runtime) load(t *starlark.Thread, module string) (starlark.StringDict, error) {
+	if m, ok := r.modules[module]; ok {
+		return m()
+	}
+
+	return nil, nil
+}