diff --git a/android/sdk_version.go b/android/sdk_version.go
new file mode 100644
index 0000000..ce22b5f
--- /dev/null
+++ b/android/sdk_version.go
@@ -0,0 +1,311 @@
+// Copyright 2021 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package android
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type SdkContext interface {
+	// SdkVersion returns SdkSpec that corresponds to the sdk_version property of the current module
+	SdkVersion() SdkSpec
+	// SystemModules returns the system_modules property of the current module, or an empty string if it is not set.
+	SystemModules() string
+	// MinSdkVersion returns SdkSpec that corresponds to the min_sdk_version property of the current module,
+	// or from sdk_version if it is not set.
+	MinSdkVersion() SdkSpec
+	// TargetSdkVersion returns the SdkSpec that corresponds to the target_sdk_version property of the current module,
+	// or from sdk_version if it is not set.
+	TargetSdkVersion() SdkSpec
+}
+
+// SdkKind represents a particular category of an SDK spec like public, system, test, etc.
+type SdkKind int
+
+const (
+	SdkInvalid SdkKind = iota
+	SdkNone
+	SdkCore
+	SdkCorePlatform
+	SdkPublic
+	SdkSystem
+	SdkTest
+	SdkModule
+	SdkSystemServer
+	SdkPrivate
+)
+
+// String returns the string representation of this SdkKind
+func (k SdkKind) String() string {
+	switch k {
+	case SdkPrivate:
+		return "private"
+	case SdkNone:
+		return "none"
+	case SdkPublic:
+		return "public"
+	case SdkSystem:
+		return "system"
+	case SdkTest:
+		return "test"
+	case SdkCore:
+		return "core"
+	case SdkCorePlatform:
+		return "core_platform"
+	case SdkModule:
+		return "module-lib"
+	case SdkSystemServer:
+		return "system-server"
+	default:
+		return "invalid"
+	}
+}
+
+// SdkVersion represents a specific version number of an SDK spec of a particular kind
+type SdkVersion int
+
+const (
+	// special version number for a not-yet-frozen SDK
+	SdkVersionCurrent SdkVersion = SdkVersion(FutureApiLevelInt)
+	// special version number to be used for SDK specs where version number doesn't
+	// make sense, e.g. "none", "", etc.
+	SdkVersionNone SdkVersion = SdkVersion(0)
+)
+
+// IsCurrent checks if the SdkVersion refers to the not-yet-published version of an SdkKind
+func (v SdkVersion) IsCurrent() bool {
+	return v == SdkVersionCurrent
+}
+
+// IsNumbered checks if the SdkVersion refers to the published (a.k.a numbered) version of an SdkKind
+func (v SdkVersion) IsNumbered() bool {
+	return !v.IsCurrent() && v != SdkVersionNone
+}
+
+// String returns the string representation of this SdkVersion.
+func (v SdkVersion) String() string {
+	if v.IsCurrent() {
+		return "current"
+	} else if v.IsNumbered() {
+		return strconv.Itoa(int(v))
+	}
+	return "(no version)"
+}
+
+func (v SdkVersion) ApiLevel(ctx EarlyModuleContext) ApiLevel {
+	return ApiLevelOrPanic(ctx, v.String())
+}
+
+// AsNumberString directly converts the numeric value of this sdk version as a string.
+// When isNumbered() is true, this method is the same as String(). However, for SdkVersionCurrent
+// and SdkVersionNone, this returns 10000 and 0 while String() returns "current" and "(no version"),
+// respectively.
+func (v SdkVersion) AsNumberString() string {
+	return strconv.Itoa(int(v))
+}
+
+// SdkSpec represents the kind and the version of an SDK for a module to build against
+type SdkSpec struct {
+	Kind    SdkKind
+	Version SdkVersion
+	Raw     string
+}
+
+func (s SdkSpec) String() string {
+	return fmt.Sprintf("%s_%s", s.Kind, s.Version)
+}
+
+// Valid checks if this SdkSpec is well-formed. Note however that true doesn't mean that the
+// specified SDK actually exists.
+func (s SdkSpec) Valid() bool {
+	return s.Kind != SdkInvalid
+}
+
+// Specified checks if this SdkSpec is well-formed and is not "".
+func (s SdkSpec) Specified() bool {
+	return s.Valid() && s.Kind != SdkPrivate
+}
+
+// whether the API surface is managed and versioned, i.e. has .txt file that
+// get frozen on SDK freeze and changes get reviewed by API council.
+func (s SdkSpec) Stable() bool {
+	if !s.Specified() {
+		return false
+	}
+	switch s.Kind {
+	case SdkNone:
+		// there is nothing to manage and version in this case; de facto stable API.
+		return true
+	case SdkCore, SdkPublic, SdkSystem, SdkModule, SdkSystemServer:
+		return true
+	case SdkCorePlatform, SdkTest, SdkPrivate:
+		return false
+	default:
+		panic(fmt.Errorf("unknown SdkKind=%v", s.Kind))
+	}
+	return false
+}
+
+// PrebuiltSdkAvailableForUnbundledBuilt tells whether this SdkSpec can have a prebuilt SDK
+// that can be used for unbundled builds.
+func (s SdkSpec) PrebuiltSdkAvailableForUnbundledBuild() bool {
+	// "", "none", and "core_platform" are not available for unbundled build
+	// as we don't/can't have prebuilt stub for the versions
+	return s.Kind != SdkPrivate && s.Kind != SdkNone && s.Kind != SdkCorePlatform
+}
+
+func (s SdkSpec) ForVendorPartition(ctx EarlyModuleContext) SdkSpec {
+	// If BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES has a numeric value,
+	// use it instead of "current" for the vendor partition.
+	currentSdkVersion := ctx.DeviceConfig().CurrentApiLevelForVendorModules()
+	if currentSdkVersion == "current" {
+		return s
+	}
+
+	if s.Kind == SdkPublic || s.Kind == SdkSystem {
+		if s.Version.IsCurrent() {
+			if i, err := strconv.Atoi(currentSdkVersion); err == nil {
+				version := SdkVersion(i)
+				return SdkSpec{s.Kind, version, s.Raw}
+			}
+			panic(fmt.Errorf("BOARD_CURRENT_API_LEVEL_FOR_VENDOR_MODULES must be either \"current\" or a number, but was %q", currentSdkVersion))
+		}
+	}
+	return s
+}
+
+// UsePrebuilt determines whether prebuilt SDK should be used for this SdkSpec with the given context.
+func (s SdkSpec) UsePrebuilt(ctx EarlyModuleContext) bool {
+	if s.Version.IsCurrent() {
+		// "current" can be built from source and be from prebuilt SDK
+		return ctx.Config().AlwaysUsePrebuiltSdks()
+	} else if s.Version.IsNumbered() {
+		// validation check
+		if s.Kind != SdkPublic && s.Kind != SdkSystem && s.Kind != SdkTest && s.Kind != SdkModule {
+			panic(fmt.Errorf("prebuilt SDK is not not available for SdkKind=%q", s.Kind))
+			return false
+		}
+		// numbered SDKs are always from prebuilt
+		return true
+	}
+	// "", "none", "core_platform" fall here
+	return false
+}
+
+// EffectiveVersion converts an SdkSpec into the concrete SdkVersion that the module
+// should use. For modules targeting an unreleased SDK (meaning it does not yet have a number)
+// it returns FutureApiLevel(10000).
+func (s SdkSpec) EffectiveVersion(ctx EarlyModuleContext) (SdkVersion, error) {
+	if !s.Valid() {
+		return s.Version, fmt.Errorf("invalid sdk version %q", s.Raw)
+	}
+
+	if ctx.DeviceSpecific() || ctx.SocSpecific() {
+		s = s.ForVendorPartition(ctx)
+	}
+	if s.Version.IsNumbered() {
+		return s.Version, nil
+	}
+	return SdkVersion(ctx.Config().DefaultAppTargetSdk(ctx).FinalOrFutureInt()), nil
+}
+
+// EffectiveVersionString converts an SdkSpec into the concrete version string that the module
+// should use. For modules targeting an unreleased SDK (meaning it does not yet have a number)
+// it returns the codename (P, Q, R, etc.)
+func (s SdkSpec) EffectiveVersionString(ctx EarlyModuleContext) (string, error) {
+	ver, err := s.EffectiveVersion(ctx)
+	if err == nil && int(ver) == ctx.Config().DefaultAppTargetSdk(ctx).FinalOrFutureInt() {
+		return ctx.Config().DefaultAppTargetSdk(ctx).String(), nil
+	}
+	return ver.String(), err
+}
+
+func SdkSpecFrom(str string) SdkSpec {
+	switch str {
+	// special cases first
+	case "":
+		return SdkSpec{SdkPrivate, SdkVersionNone, str}
+	case "none":
+		return SdkSpec{SdkNone, SdkVersionNone, str}
+	case "core_platform":
+		return SdkSpec{SdkCorePlatform, SdkVersionNone, str}
+	default:
+		// the syntax is [kind_]version
+		sep := strings.LastIndex(str, "_")
+
+		var kindString string
+		if sep == 0 {
+			return SdkSpec{SdkInvalid, SdkVersionNone, str}
+		} else if sep == -1 {
+			kindString = ""
+		} else {
+			kindString = str[0:sep]
+		}
+		versionString := str[sep+1 : len(str)]
+
+		var kind SdkKind
+		switch kindString {
+		case "":
+			kind = SdkPublic
+		case "core":
+			kind = SdkCore
+		case "system":
+			kind = SdkSystem
+		case "test":
+			kind = SdkTest
+		case "module":
+			kind = SdkModule
+		case "system_server":
+			kind = SdkSystemServer
+		default:
+			return SdkSpec{SdkInvalid, SdkVersionNone, str}
+		}
+
+		var version SdkVersion
+		if versionString == "current" {
+			version = SdkVersionCurrent
+		} else if i, err := strconv.Atoi(versionString); err == nil {
+			version = SdkVersion(i)
+		} else {
+			return SdkSpec{SdkInvalid, SdkVersionNone, str}
+		}
+
+		return SdkSpec{kind, version, str}
+	}
+}
+
+func (s SdkSpec) ValidateSystemSdk(ctx EarlyModuleContext) bool {
+	// Ensures that the specified system SDK version is one of BOARD_SYSTEMSDK_VERSIONS (for vendor/product Java module)
+	// Assuming that BOARD_SYSTEMSDK_VERSIONS := 28 29,
+	// sdk_version of the modules in vendor/product that use system sdk must be either system_28, system_29 or system_current
+	if s.Kind != SdkSystem || !s.Version.IsNumbered() {
+		return true
+	}
+	allowedVersions := ctx.DeviceConfig().PlatformSystemSdkVersions()
+	if ctx.DeviceSpecific() || ctx.SocSpecific() || (ctx.ProductSpecific() && ctx.Config().EnforceProductPartitionInterface()) {
+		systemSdkVersions := ctx.DeviceConfig().SystemSdkVersions()
+		if len(systemSdkVersions) > 0 {
+			allowedVersions = systemSdkVersions
+		}
+	}
+	if len(allowedVersions) > 0 && !InList(s.Version.String(), allowedVersions) {
+		ctx.PropertyErrorf("sdk_version", "incompatible sdk version %q. System SDK version should be one of %q",
+			s.Raw, allowedVersions)
+		return false
+	}
+	return true
+}