roadamp/internal/resume/resume.go

// Package resume persists and restores the playback position across
// application restarts — a port of the Delphi setresume/getresume feature.
package resume

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

// State holds enough information to restore a playback session.
type State struct {
	PlaylistLength int    `json:"playlist_length"`
	PlaylistPos    int    `json:"playlist_pos"`
	OffsetSeconds  int    `json:"offset_seconds"`
	TrackTitle     string `json:"track_title"`
}

// Save persists the given state to a JSON file.
func Save(path string, s State) error {
	data, err := json.Marshal(s)
	if err != nil {
		return err
	}
	return os.WriteFile(path, data, 0644)
}

// Load reads the state from disk. Returns (nil, nil) if no file exists yet.
func Load(path string) (*State, error) {
	data, err := os.ReadFile(path)
	if errors.Is(err, os.ErrNotExist) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	var s State
	if err := json.Unmarshal(data, &s); err != nil {
		return nil, err
	}
	return &s, nil
}

// Delete removes the resume file (call after successful restore).
func Delete(path string) error {
	err := os.Remove(path)
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	return err
}