1package schema
2
3import (
4	"fmt"
5)
6
7// MultiLevelFieldReader reads from other field readers,
8// merging their results along the way in a specific order. You can specify
9// "levels" and name them in order to read only an exact level or up to
10// a specific level.
11//
12// This is useful for saying things such as "read the field from the state
13// and config and merge them" or "read the latest value of the field".
14type MultiLevelFieldReader struct {
15	Readers map[string]FieldReader
16	Levels  []string
17}
18
19func (r *MultiLevelFieldReader) ReadField(address []string) (FieldReadResult, error) {
20	return r.ReadFieldMerge(address, r.Levels[len(r.Levels)-1])
21}
22
23func (r *MultiLevelFieldReader) ReadFieldExact(
24	address []string, level string) (FieldReadResult, error) {
25	reader, ok := r.Readers[level]
26	if !ok {
27		return FieldReadResult{}, fmt.Errorf(
28			"Unknown reader level: %s", level)
29	}
30
31	result, err := reader.ReadField(address)
32	if err != nil {
33		return FieldReadResult{}, fmt.Errorf(
34			"Error reading level %s: %s", level, err)
35	}
36
37	return result, nil
38}
39
40func (r *MultiLevelFieldReader) ReadFieldMerge(
41	address []string, level string) (FieldReadResult, error) {
42	var result FieldReadResult
43	for _, l := range r.Levels {
44		if r, ok := r.Readers[l]; ok {
45			out, err := r.ReadField(address)
46			if err != nil {
47				return FieldReadResult{}, fmt.Errorf(
48					"Error reading level %s: %s", l, err)
49			}
50
51			// TODO: computed
52			if out.Exists {
53				result = out
54			}
55		}
56
57		if l == level {
58			break
59		}
60	}
61
62	return result, nil
63}
64