feat: .NET appsettings files in repos (#88)

Co-authored-by: Karl-Einar Bergstrøm <karl-einarb@outlook.com>

internal/provider/repo/dotnet.go

@@ -0,0 +1,74 @@
+package repo
+
+import (
+	"fmt"
+	"path"
+	"regexp"
+	"strings"
+
+	"go.yaml.in/yaml/v3"
+)
+
+// .NET config files: appsettings.json and appsettings.<Environment>.json.
+// Keys are named as .NET's configuration names them, sections joined by
+// colons: ConnectionStrings:Default, Servers:0:Name.
+
+var dotnetType = configType{
+	name: "dotnet", is: IsDotnet, format: func(string) string { return "json" }, parse: parseDotnet,
+	placeholder: dotnetPlaceholder,
+}
+
+var dotnetName = regexp.MustCompile(`^appsettings(\.[^/]+)?\.json$`)
+
+// IsDotnet reports whether f is named like a .NET appsettings file.
+func IsDotnet(f string) bool {
+	return dotnetName.MatchString(strings.ToLower(path.Base(f)))
+}
+
+// dotnetPlaceholder reads an App Service Key Vault reference,
+// @Microsoft.KeyVault(SecretUri=…): the secret is in the vault.
+func dotnetPlaceholder(v string) (name, def string, hasDef, ok bool) {
+	if strings.HasPrefix(v, "@Microsoft.KeyVault(") && strings.HasSuffix(v, ")") {
+		return v, "", false, true
+	}
+	return "", "", false, false
+}
+
+func parseDotnet(_ string, b []byte) ([]configKey, error) {
+	var doc yaml.Node // JSON is YAML, and the YAML parser says where each key is
+	if err := yaml.Unmarshal(b, &doc); err != nil {
+		return nil, err
+	}
+	var out []configKey
+	if len(doc.Content) > 0 {
+		dotnetWalk(doc.Content[0], "", &out)
+	}
+	for i := range out {
+		out[i].name = out[i].key
+		out[i].ref = reference(dotnetPlaceholder, out[i].value)
+	}
+	return out, nil
+}
+
+func dotnetWalk(n *yaml.Node, name string, out *[]configKey) {
+	join := func(child string) string {
+		if name == "" {
+			return child
+		}
+		return name + ":" + child
+	}
+	switch n.Kind {
+	case yaml.MappingNode:
+		for i := 0; i+1 < len(n.Content); i += 2 {
+			dotnetWalk(n.Content[i+1], join(n.Content[i].Value), out)
+		}
+	case yaml.SequenceNode:
+		for i, c := range n.Content {
+			dotnetWalk(c, join(fmt.Sprint(i)), out)
+		}
+	case yaml.ScalarNode:
+		if name != "" {
+			*out = append(*out, configKey{key: name, value: n.Value, line: n.Line})
+		}
+	}
+}