package main

import "fmt"

// renderExpr centralizes expression lowering; callers supply parameter, owned
// field, or getter references. No expression decisions are left to templates.
func renderExpr(n *Node, ref func(string) string, m *Module) (string, error) {
	if n == nil {
		return "", nil
	}
	switch n.Kind {
	case "value":
		return n.Text, nil
	case "fieldref":
		return ref(n.Text), nil
	case "enumref":
		e, owner := findEnum(m, n.Attr["ref"])
		if e == nil {
			return "", n.fail("unknown enum %s", n.Attr["ref"])
		}
		return "int(" + qualified(m, owner, e.Name+goName(n.Text)) + ")", nil
	case "op", "unop", "popcount":
		var parts []string
		for _, c := range n.Children {
			s, err := renderExpr(c, ref, m)
			if err != nil {
				return "", err
			}
			parts = append(parts, s)
		}
		if n.Kind == "popcount" {
			return "bits.OnesCount(uint(" + parts[0] + "))", nil
		}
		if n.Kind == "unop" {
			return "(^" + parts[0] + ")", nil
		}
		if len(parts) != 2 {
			return "", n.fail("invalid binary expression")
		}
		return "(" + parts[0] + " " + n.Attr["op"] + " " + parts[1] + ")", nil
	}
	return "", fmt.Errorf("%s:%d: unsupported expression %s", n.File, n.Line, n.Kind)
}