Introduce APKs suggestions

Suggested APK must be compatible with a particular device. This is
always one of the set of suggested APKs. This set contains APKs with the
same version string but different version codes (flavours of the same
version, e.g. targeting different hardware architectures).

index.go

@@ -9,6 +9,8 @@ import (
 	"io"
 	"sort"
 	"strings"
+
+	"github.com/mvdan/adb"
 )
 
 type Index struct {
@@ -209,6 +211,29 @@ func (a *Apk) SrcURL() string {
 	return fmt.Sprintf("%s/%s", a.Repo.URL, a.SrcName)
 }
 
+func (apk *Apk) IsCompatibleABI(ABIs []string) bool {
+	if len(apk.ABIs) == 0 {
+		return true // APK does not contain native code
+	}
+	for i := range apk.ABIs {
+		for j := range ABIs {
+			if apk.ABIs[i] == ABIs[j] {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func (apk *Apk) IsCompatibleAPILevel(sdk int) bool {
+	return sdk >= apk.MinSdk && (apk.MaxSdk == 0 || sdk <= apk.MaxSdk)
+}
+
+func (apk *Apk) IsCompatible(device *adb.Device) bool {
+	return apk.IsCompatibleABI(device.ABIs) &&
+		apk.IsCompatibleAPILevel(device.APILevel)
+}
+
 type AppList []App
 
 func (al AppList) Len() int           { return len(al) }
@@ -254,3 +279,57 @@ func (a *App) CurApk() *Apk {
 	}
 	return nil
 }
+
+func (a *App) ApksByVName(vname string) []Apk {
+	var apks []Apk
+	for i := range a.Apks {
+		if vname == a.Apks[i].VName {
+			apks = append(apks, a.Apks[i])
+		}
+	}
+	return apks
+}
+
+func (a *App) SuggestedVName() string {
+	for i := range a.Apks {
+		apk := &a.Apks[i]
+		if a.CVCode >= apk.VCode {
+			return apk.VName
+		}
+	}
+	return ""
+}
+
+func (a *App) SuggestedApks() []Apk {
+	// No APKs => nothing to suggest
+	if len(a.Apks) == 0 {
+		return nil
+	}
+
+	// First, try to follow CV
+	apks := a.ApksByVName(a.SuggestedVName())
+	if len(apks) > 0 {
+		return apks
+	}
+
+	// When CV is missing current version code or it's invalid (no APKs
+	// match it), use heuristic: find all APKs having the same version
+	// string as the APK with the greatest version code
+	return a.ApksByVName(a.Apks[0].VName)
+}
+
+func (a *App) SuggestedApk(device *adb.Device) *Apk {
+	for i := range a.Apks {
+		apk := &a.Apks[i]
+		if a.CVCode >= apk.VCode && apk.IsCompatible(device) {
+			return apk
+		}
+	}
+	for i := range a.Apks {
+		apk := &a.Apks[i]
+		if apk.IsCompatible(device) {
+			return apk
+		}
+	}
+	return nil
+}