package models

import (
	"encoding/json"
	"errors"
	"time"
)

// A Change is a change in the timeline.
type Change struct {
	ID      string         `json:"id"`
	Model   string         `json:"model"`
	Op      string         `json:"op"`
	Author  string         `json:"author"`
	Date    time.Time      `json:"date"`
	Keys    []ChangeKey    `json:"keys"`
	Objects []ChangeObject `json:"objects"`
}

// A ChangeKey describes a model directly or indirectly affected by the change.
type ChangeKey struct {
	Model string `json:"model"`
	ID    string `json:"id"`
}

// A ChangeObject is an object affected by the change.
type ChangeObject struct {
	Data     json.RawMessage `json:"-"`
	TypeName string          `json:"-"`
}

type changeObjectHeader struct {
	TypeName string `json:"__typename"`
}

// Channel parses the ChangeObject as a channel.
func (co *ChangeObject) Channel() (Channel, error) {
	if co.TypeName != "Channel" {
		return Channel{}, errors.New("Incorrect Type Name")
	}

	channel := Channel{}
	err := json.Unmarshal(co.Data, &channel)

	return channel, err
}

// UnmarshalJSON implements json.Unmarshaller
func (co *ChangeObject) UnmarshalJSON(b []byte) error {
	data := make([]byte, len(b))
	copy(data, b)

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

	co.Data = data
	co.TypeName = header.TypeName

	return nil
}