build(snap): source metadata from repo (#380)

* build(snap): source metadata from external appstream file
* feat: source all metadata to allow icon caching

The metadata kept in snapcraft.yaml is obsolete
because it is being overridden on the store. 
This change will allow sourcing the central copy of metadata.

See canonical/edgex-snap-metadata#2

Signed-off-by: Mengyi Wang <mengyi.wang@canonical.com>

snap/snapcraft.yaml

@@ -1,33 +1,19 @@
 name: edgex-app-service-configurable
 base: core20
-adopt-info: app-service-config
 license: Apache-2.0
-summary:   The reference EdgeX App Service Configurable
-title: EdgeX App Service Configurable
-description: |
-  The reference EdgeX app-service-configurable is built using the App
-  Functions SDK. This service is provided as an easy way to get started
-  with processing data flowing through EdgeX. This service leverages the
-  App Functions SDK and provides a way for developers to use configuration
-  instead of having to compile standalone services to utilize built in
-  functions in the SDK.
-
-  Initially the daemon in the snap is disabled - this allows the configuration
-  to be modified and provided to app-service-config in
-  "$SNAP_DATA/config/app-service-configurable/res" before starting.
-
-# TODO: add armhf when the project supports this
+adopt-info: metadata
+
 architectures:
   - build-on: amd64
   - build-on: arm64
 
 grade: stable
 confinement: strict
 
-# edinburgh release is epoch 1
-# fuji release is epoch 2
-# geneva/hanoi releases were epoch 3
-# ireland is epoch 4
+# 1: edinburgh
+# 2: fuji
+# 3: geneva, hanoi
+# 4: ireland, jakarta
 epoch: 4
 
 slots:
@@ -61,6 +47,7 @@ plugs:
 
 parts:
   app-service-config:
+    after: [metadata]
     source: .
     plugin: make
     build-packages: [gcc, git, libzmq3-dev, pkg-config]
@@ -70,12 +57,8 @@ parts:
     override-build: |
       cd $SNAPCRAFT_PART_SRC
 
-      GIT_VERSION=$(git describe --tags --abbrev=0 | sed 's/v//')
-      if [ -z "$GIT_VERSION" ]; then
-        GIT_VERSION="0.0.0"
-      fi
-      snapcraftctl set-version ${GIT_VERSION}
-      echo $GIT_VERSION > ./VERSION
+      # the version is needed for the build
+      cat ./VERSION
 
       make tidy
       make build
@@ -100,10 +83,36 @@ parts:
       install -DT "./LICENSE" \
          "$SNAPCRAFT_PART_INSTALL/usr/share/doc/app-service-configurable/LICENSE"
 
-  config-common:
+  runtime-helpers:
     plugin: dump
     source: snap/local/runtime-helpers
 
+  metadata:
+    plugin: nil
+    source: https://github.com/canonical/edgex-snap-metadata.git
+    source-branch: appstream
+    source-depth: 1
+    override-build: |
+      # install the icon at the default internal path
+      install -DT edgex-snap-icon.png \
+        $SNAPCRAFT_PART_INSTALL/meta/gui/icon.png      
+
+      # change to this project's repo to get the version
+      cd $SNAPCRAFT_PROJECT_DIR
+
+      if git describe ; then
+        VERSION=$(git describe --tags --abbrev=0 | sed 's/v//')
+      else
+        VERSION="0.0.0"
+      fi
+      
+      # write version to file for the build
+      echo $VERSION > ./VERSION
+
+      # set the version of this snap
+      snapcraftctl set-version $VERSION
+    parse-info: [edgex-app-service-configurable.metainfo.xml]
+
   hooks:
     source: snap/local/hooks
     plugin: make