Refactor current GAE abstraction library to be free of the SDK*

go/src/infra/gae/libs/gae/helper/datastore.go

Index: go/src/infra/gae/libs/gae/helper/datastore.go
diff --git a/go/src/infra/gae/libs/gae/helper/datastore.go b/go/src/infra/gae/libs/gae/helper/datastore.go
new file mode 100644
index 0000000000000000000000000000000000000000..32622b4c3910dd66d98d96e2d740092e27deef26
--- /dev/null
+++ b/go/src/infra/gae/libs/gae/helper/datastore.go
@@ -0,0 +1,77 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// HEAVILY adapted from github.com/golang/appengine/datastore
+
+package helper
+
+import (
+	"fmt"
+	"reflect"
+
+	"infra/gae/libs/gae"
+)
+
+// GetStructPLS resolves o into a gae.DSStructPLS. o must be a pointer to a
+// struct of some sort.
+func GetStructPLS(o interface{}) gae.DSStructPLS {
+	v := reflect.ValueOf(o)
+	if v.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct {
+		return &structPLS{c: &structCodec{problem: gae.ErrDSInvalidEntityType}}
+	}
+	v = v.Elem()
+	t := v.Type()
+
+	structCodecsMutex.RLock()
+	if c, ok := structCodecs[t]; ok {
+		structCodecsMutex.RUnlock()
+		return &structPLS{v, c}
+	}
+	structCodecsMutex.RUnlock()
+
+	structCodecsMutex.Lock()
+	defer structCodecsMutex.Unlock()
+	return &structPLS{v, getStructCodecLocked(t)}
+}
+
+// GetPLS resolves o into a gae.DSPropertyLoadSaver. If o implements the
+// gae.DSPropertyLoadSaver interface already, it's returned unchanged. Otherwise
+// this calls GetStructPLS and returns the result.
+func GetPLS(o interface{}) (gae.DSPropertyLoadSaver, error) {
+	if pls, ok := o.(gae.DSPropertyLoadSaver); ok {
+		return pls, nil
+	}
+	pls := GetStructPLS(o)
+	if err := pls.Problem(); err != nil {
+		return nil, err
+	}
+	return pls, nil
+}
+
+// MultiGetPLS resolves os to a []gae.DSPropertyLoadSaver. os must be a slice of
+// something. If os is already a []gae.DSPropertyLoadSaver, it's returned
+// unchanged. Otherwise this calls GetPLS on each item, and composes the
+// resulting slice that way.
+func MultiGetPLS(os interface{}) ([]gae.DSPropertyLoadSaver, error) {
+	if plss, ok := os.([]gae.DSPropertyLoadSaver); ok {
+		return plss, nil
+	}
+
+	v := reflect.ValueOf(os)
+	if v.Kind() != reflect.Slice {
+		return nil, fmt.Errorf("gae/helper: bad type in MultiObjToPLS: %T", os)
+	}
+
+	// TODO(riannucci): define a higher-level type DSMultiPropertyLoadSaver
+	// to avoid this slice?
+	ret := make([]gae.DSPropertyLoadSaver, v.Len())
+	for i := 0; i < v.Len(); i++ {
+		pls, err := GetPLS(v.Index(i).Interface())
+		if err != nil {
+			return nil, err
+		}
+		ret[i] = pls
+	}
+	return ret, nil
+}