vorteil/direktiv

package engine

import (
    "bytes"
    "encoding/json"
    "errors"
    "fmt"

    "github.com/google/uuid"
)

const (
    instanceDescentInfoVersion1 = "v1"
)

var ErrInvalidInstanceDescentInfo = errors.New("invalid instance descent info")

// ParentInfo is part of the InstanceDescentInfo structure. It represents useful information about a single instance in the chain.
type ParentInfo struct {
    ID     uuid.UUID `json:"id"`
    State  string    `json:"state"`
    Step   int       `json:"step"`
    Branch int       `json:"branch"` // NOTE: renamed iterator to branch
}

// InstanceDescentInfo keeps a local copy of useful information about the entire chain of parent instances all the way to the root instance, excepting this instance.
type InstanceDescentInfo struct {
    Version string       // to let us identify and correct outdated versions of this struct
    Descent []ParentInfo // chain of callers from the root instance to the direct parent.
}

func (info *InstanceDescentInfo) MarshalJSON() ([]byte, error) {
    if info == nil {
        return json.Marshal(&InstanceDescentInfoV1{
            Version: instanceDescentInfoVersion1,
        })
    }

    return json.Marshal(&InstanceDescentInfoV1{
        Version: instanceDescentInfoVersion1,
        Descent: info.Descent,
    })
}

type InstanceDescentInfoV1 struct {
    Version string       `json:"version"`
    Descent []ParentInfo `json:"descent"`
}

func LoadInstanceDescentInfo(data []byte) (*InstanceDescentInfo, error) {
    m := make(map[string]interface{})

    err := json.Unmarshal(data, &m)
    if err != nil {
        return nil, err
    }

    version, defined := m["version"]
    if !defined {
        return nil, fmt.Errorf("failed to load instance descent info: %w: missing version", ErrInvalidInstanceDescentInfo)
    }

    var info *InstanceDescentInfo

    dec := json.NewDecoder(bytes.NewReader(data))
    dec.DisallowUnknownFields()

    switch version {
    case instanceDescentInfoVersion1:
        var v1 InstanceDescentInfoV1
        err = dec.Decode(&v1)
        if err != nil {
            return nil, fmt.Errorf("failed to load instance descent info: %w: %w", ErrInvalidInstanceDescentInfo, err)
        }

        info = &InstanceDescentInfo{
            Version: v1.Version,
            Descent: v1.Descent,
        }

    default:
        return nil, fmt.Errorf("failed to load instance descent info: %w: unknown version", ErrInvalidInstanceDescentInfo)
    }

    return info, nil
}