Create a dynamic provider features matrix (#201)

* adding simple provider feature matrix generator

* filling out matrix

* clean output

* dead code

* explanatory text

* explanatory text

* typo

* move stuff around

* clean

* editing

providers/capabilities.go

@@ -0,0 +1,97 @@
+package providers
+
+import (
+	"log"
+	"strings"
+)
+
+//Capability is a bitmasked set of "features" that a provider supports. Only use constants from this package.
+type Capability uint32
+
+const (
+	// CanUseAlias indicates the provider support ALIAS records (or flattened CNAMES). Up to the provider to translate them to the appropriate record type.
+	// If you add something to this list, you probably want to add it to pkg/normalize/validate.go checkProviderCapabilities() or somewhere near there.
+	CanUseAlias Capability = iota
+	// CanUsePTR indicates the provider can handle PTR records
+	CanUsePTR
+	// CanUseSRV indicates the provider can handle SRV records
+	CanUseSRV
+	// CanUseCAA indicates the provider can handle CAA records
+	CanUseCAA
+	// CantUseNOPURGE indicates NO_PURGE is broken for this provider. To make it
+	// work would require complex emulation of an incremental update mechanism,
+	// so it is easier to simply mark this feature as not working for this
+	// provider.
+	CantUseNOPURGE
+
+	// DocOfficiallySupported means it is actively used and maintained by stack exchange
+	DocOfficiallySupported
+	// DocDualHost means provider allows full management of apex NS records, so we can safely dual-host with anothe provider
+	DocDualHost
+	// DocCreateDomains means provider can add domains with the `dnscontrol create-domains` command
+	DocCreateDomains
+)
+
+var providerCapabilities = map[string]map[Capability]bool{}
+
+func ProviderHasCabability(pType string, cap Capability) bool {
+	if providerCapabilities[pType] == nil {
+		return false
+	}
+	return providerCapabilities[pType][cap]
+}
+
+// DocumentationNote is a way for providers to give more detail about what features they support.
+type DocumentationNote struct {
+	HasFeature bool
+	Comment    string
+}
+
+// DocumentationNotes is a full list of notes for a single provider
+type DocumentationNotes map[Capability]*DocumentationNote
+
+// ProviderMetadata is a common interface for DocumentationNotes and Capability to be used interchangably
+type ProviderMetadata interface{}
+
+// Notes is a collection of all documentation notes, keyed by provider type
+var Notes = map[string]DocumentationNotes{}
+
+func unwrapProviderCapabilities(pName string, meta []ProviderMetadata) {
+	for _, pm := range meta {
+		switch x := pm.(type) {
+		case Capability:
+			if providerCapabilities[pName] == nil {
+				providerCapabilities[pName] = map[Capability]bool{}
+			}
+			providerCapabilities[pName][x] = true
+		case DocumentationNotes:
+			if Notes[pName] == nil {
+				Notes[pName] = DocumentationNotes{}
+			}
+			for k, v := range x {
+				Notes[pName][k] = v
+			}
+		default:
+			log.Fatalf("Unrecognized ProviderMetadata type: %T", pm)
+		}
+
+	}
+}
+
+// Can is a small helper for concisely creating Documentation Notes
+// comments are variadic for easy ommission, so you generally should pass 0 or 1 only.
+func Can(comments ...string) *DocumentationNote {
+	return &DocumentationNote{
+		HasFeature: true,
+		Comment:    strings.Join(comments, " "),
+	}
+}
+
+// Cannot is a small helper for concisely creating Documentation Notes
+// comments are variadic for easy ommission, so you generally should pass 0 or 1 only.
+func Cannot(comments ...string) *DocumentationNote {
+	return &DocumentationNote{
+		HasFeature: false,
+		Comment:    strings.Join(comments, " "),
+	}
+}