Added expand function

Author: djthorpe

pkg/provider/expand.go

@@ -0,0 +1,19 @@
+package provider
+
+import "regexp"
+
+var (
+	reEval = regexp.MustCompile(`\$\{([^\}]+)\}|\$([a-zA-Z0-9_\.]+)`)
+)
+
+// Expand replaces ${var} or $var in the string based on the mapping function.
+// For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
+func Expand(s string, mapping func(string) string) string {
+	return reEval.ReplaceAllStringFunc(s, func(s string) string {
+		if s[1] == '{' {
+			return mapping(s[2 : len(s)-1])
+		} else {
+			return mapping(s[1:])
+		}
+	})
+}

pkg/provider/parser.go

@@ -46,7 +46,7 @@ func NewParser(plugins ...server.Plugin) (*Parser, error) {
 ////////////////////////////////////////////////////////////////////////////////
 // PUBLIC METHODS
 
-// Append an ast.Tree node
+// Append configurations from a JSON file
 func (p *Parser) ParseJSON(r io.Reader) error {
 	var result error
 
@@ -90,9 +90,23 @@ func (p *Parser) ParseJSON(r io.Reader) error {
 func (p *Parser) Bind() error {
 	var result error
 
-	// Set the evaluation function
+	// Evaluate each set instruction, creating a dependency graph
 	ctx := ast.NewContext(func(ctx *ast.Context, value any) (any, error) {
-		fmt.Printf("EVAL %s.%s => %q (%T)\n", ctx.Label(), ctx.Path(), value, value)
+		switch value := value.(type) {
+		case string:
+			var expanded bool
+			value = Expand(value, func(key string) string {
+				expanded = true
+				return "(ref:" + key + ")"
+			})
+			if expanded {
+				fmt.Printf("EVAL %s.%s => %q (%T)\n", ctx.Label(), ctx.Path(), value, value)
+			} else {
+				fmt.Printf("SET %s.%s => %q (%T)\n", ctx.Label(), ctx.Path(), value, value)
+			}
+		default:
+			fmt.Printf("SET %s.%s => %q (%T)\n", ctx.Label(), ctx.Path(), value, value)
+		}
 		return nil, nil
 	})