mediocre-go-lib/mcfg/source.go
2019-04-04 16:25:02 -04:00

62 lines
2.0 KiB
Go

package mcfg
import (
"context"
"encoding/json"
)
// ParamValue describes a value for a parameter which has been parsed by a
// Source.
type ParamValue struct {
Name string
Path []string
Value json.RawMessage
}
// Source parses ParamValues out of a particular configuration source, given the
// Context which the Params were added to (via WithInt, WithString, etc...).
// CollectParams can be used to retrieve these Params.
//
// It's possible for Parsing to affect the Context itself, for example in the
// case of sub-commands. For this reason Parse can return a Context, which will
// get used for subsequent Parse commands inside Populate.
//
// Source should not return ParamValues which were not explicitly set to a value
// by the configuration source.
//
// The returned []ParamValue may contain duplicates of the same Param's value.
// in which case the later value takes precedence. It may also contain
// ParamValues which do not correspond to any of the passed in Params. These
// will be ignored in Populate.
type Source interface {
Parse(context.Context) (context.Context, []ParamValue, error)
}
// ParamValues is simply a slice of ParamValue elements, which implements Parse
// by always returning itself as-is.
type ParamValues []ParamValue
// Parse implements the method for the Source interface.
func (pvs ParamValues) Parse(ctx context.Context) (context.Context, []ParamValue, error) {
return ctx, pvs, nil
}
// Sources combines together multiple Source instances into one. It will call
// Parse on each element individually. Values from later Sources take precedence
// over previous ones.
type Sources []Source
// Parse implements the method for the Source interface.
func (ss Sources) Parse(ctx context.Context) (context.Context, []ParamValue, error) {
var pvs []ParamValue
for _, s := range ss {
var innerPVs []ParamValue
var err error
if ctx, innerPVs, err = s.Parse(ctx); err != nil {
return nil, nil, err
}
pvs = append(pvs, innerPVs...)
}
return ctx, pvs, nil
}