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package schema
import (
"fmt"
)
// MultiLevelFieldReader reads from other field readers,
// merging their results along the way in a specific order. You can specify
// "levels" and name them in order to read only an exact level or up to
// a specific level.
//
// This is useful for saying things such as "read the field from the state
// and config and merge them" or "read the latest value of the field".
type MultiLevelFieldReader struct {
Readers map[string]FieldReader
Levels []string
}
func (r *MultiLevelFieldReader) ReadField(address []string) (FieldReadResult, error) {
return r.ReadFieldMerge(address, r.Levels[len(r.Levels)-1])
}
func (r *MultiLevelFieldReader) ReadFieldExact(
address []string, level string) (FieldReadResult, error) {
reader, ok := r.Readers[level]
if !ok {
return FieldReadResult{}, fmt.Errorf(
"Unknown reader level: %s", level)
}
result, err := reader.ReadField(address)
if err != nil {
return FieldReadResult{}, fmt.Errorf(
"Error reading level %s: %s", level, err)
}
return result, nil
}
func (r *MultiLevelFieldReader) ReadFieldMerge(
address []string, level string) (FieldReadResult, error) {
var result FieldReadResult
for _, l := range r.Levels {
if r, ok := r.Readers[l]; ok {
out, err := r.ReadField(address)
if err != nil {
return FieldReadResult{}, fmt.Errorf(
"Error reading level %s: %s", l, err)
}
// TODO: computed
if out.Exists {
result = out
}
}
if l == level {
break
}
}
return result, nil
}
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