av/cmd/vidforward/file.go

/*
DESCRIPTION
  files.go provides the functionality required for saving and loading
  broadcastManager state. This includes marshalling/unmarshalling overrides.

AUTHORS
  Saxon A. Nelson-Milton <saxon@ausocean.org>

LICENSE
  Copyright (C) 2022-2023 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License
  along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
*/

package main

import (
	"encoding/json"
	"fmt"
	"os"

	"bitbucket.org/ausocean/av/cmd/vidforward/global"
)

// inTest is used to indicate if we are within a test; some functionality is not
// employed in this case.
var inTest bool

// The file name for the broadcast manager state save.
const fileName = "state.json"

// BroadcastBasic is a crude version of the Broadcast used to simplify
// marshal/unmarshal overriding.
type BroadcastBasic struct {
	MAC
	URL    string
	Status string
}

// ManagerBasic is a crude version of the BroadcastManager struct use to simplify
// marshal/unmarshal overriding.
type ManagerBasic struct {
	Broadcasts       map[MAC]Broadcast
	SlateExitSignals []MAC
}

// MarshalJSON calls the default marshalling behaviour for the BroadcastBasic
// struct using the information from b.
func (b Broadcast) MarshalJSON() ([]byte, error) {
	return json.Marshal(BroadcastBasic{
		MAC:    b.mac,
		URL:    b.url,
		Status: b.status,
	})
}

// UnmarshalJSON unmarshals into a value of the BroadcastBasic struct and then
// populates a Broadcast value.
func (b *Broadcast) UnmarshalJSON(data []byte) error {
	var bm BroadcastBasic
	err := json.Unmarshal(data, &bm)
	if err != nil {
		return fmt.Errorf("could not unmarshal JSON: %w", err)
	}

	b.mac = bm.MAC
	b.url = bm.URL
	b.status = bm.Status

	b.rv, err = newRevid(global.GetLogger(), b.url)
	if err != nil {
		return fmt.Errorf("could not populate RV field: %w", err)
	}

	return nil
}

// MarshalJSON calls the default marshaller for a ManagerBasic value using data
// from a broadcastManager value.
func (m *broadcastManager) MarshalJSON() ([]byte, error) {
	var signals []MAC
	for k := range m.slateExitSignals {
		signals = append(signals, k)
	}
	return json.Marshal(ManagerBasic{
		Broadcasts:       m.broadcasts,
		SlateExitSignals: signals,
	})
}

// UnmarshalJSON populates a ManagerBasic value from the provided data and then
// populates the receiver broadcastManager to a usable state based on this data.
func (m *broadcastManager) UnmarshalJSON(data []byte) error {
	var mb ManagerBasic
	err := json.Unmarshal(data, &mb)
	if err != nil {
		return fmt.Errorf("could not unmarshal JSON: %w", err)
	}

	m.broadcasts = mb.Broadcasts
	m.slateExitSignals = make(map[MAC]chan struct{})
	m.log = global.GetLogger()

	notifier, err := newWatchdogNotifier(m.log, terminationCallback(m))
	if err != nil {
		return fmt.Errorf("could not create watchdog notifier: %w", err)
	}
	m.dogNotifier = notifier

	for _, mac := range mb.SlateExitSignals {
		sigCh := make(chan struct{})
		m.slateExitSignals[mac] = sigCh
		rv := m.getPipeline(mac)
		if rv == nil {
			panic("no pipeline for MAC")
		}
		if !inTest {
			err := writeSlateAndCheckErrors(rv, sigCh, m.log)
			if err != nil {
				return fmt.Errorf("couldn't write slate for MAC %v: %w", mac, err)
			}
		}
	}
	return nil
}

// save utilises marshalling functionality to save the broadcastManager state
// to a file.
func (m *broadcastManager) save() error {
	f, err := os.OpenFile(fileName, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0755)
	if err != nil {
		return fmt.Errorf("could not open file: %w", err)
	}
	defer f.Close()

	bytes, err := json.Marshal(m)
	if err != nil {
		return fmt.Errorf("could not marshal broadcast manager: %w", err)
	}

	_, err = f.Write(bytes)
	if err != nil {
		return fmt.Errorf("could not write bytes to file: %w", err)
	}

	return nil
}

// load populates a broadcastManager value based on the previously saved state.
func (m *broadcastManager) load() error {
	bytes, err := os.ReadFile(fileName)
	if err != nil {
		return fmt.Errorf("could not read state file: %w", err)
	}

	err = json.Unmarshal(bytes, &m)
	if err != nil {
		return fmt.Errorf("could not unmarshal state data: %w", err)
	}
	return nil
}