Decouple Docker compiler from apt/npm providers

Establish phases within Docker compiler to allow providers (apt, npm,
etc.) to inject their own run/copy instructions into to the Dockerfile
compilation process while leaving the compiler agnostic to the providers
themselves.

The instructions and phases are also generalized to leave room for
alternative compilers should they be needed in the future (e.g.  aci
support via acbuild) but also as a general design constraint to leave
compiler implementation concerns out of providers.

2 files changed, 27 insertions, 0 deletions

diff --git a/build/instructions.go b/build/instructions.go
new file mode 100644
index 0000000..2676a75
--- /dev/null
+++ b/build/instructions.go
@@ -0,0 +1,13 @@
+package build
+
+type InstructionType int
+
+const (
+	Run InstructionType = iota
+	Copy
+)
+
+type Instruction struct {
+	Type InstructionType
+	Arguments []string
+}
diff --git a/build/phases.go b/build/phases.go
new file mode 100644
index 0000000..095263c
--- /dev/null
+++ b/build/phases.go
@@ -0,0 +1,14 @@
+package build
+
+type Phase int
+
+const (
+	PhasePrivileged Phase = iota
+	PhasePrivilegeDropped
+	PhasePreInstall
+	PhasePostInstall
+)
+
+type PhaseCompileable interface {
+	InstructionsForPhase(phase Phase) []Instruction
+}