Go CLI based Todo app

Install External Library used

go get github.com/aquasecurity/table

Directory structure

main.go

package main

func main() {
    todos := Todos{}

    storage := NewStorage[Todos]("todos.json")
    storage.Load(&todos)

    CmdFlags := NewCmdflags()
    CmdFlags.Execute(&todos)

    storage.Save(todos)
}

1. Creating a slice of of structure name Todos
2. Create a dynamic memory for the existing todos in the system locally in "todo.json" file that was earlier created with storage.Save
3. If not it will load as empty
4. Parse and validate the command flags provided by the user
5. Execute based on the flags provided

Functionality implementation

package main

import (
    "errors"
    "fmt"
    "os"
    "strconv"
    "time"

    "github.com/aquasecurity/table"
)

type Todo struct {
    Title     string
    Completed bool
    CreatedAt time.Time
    // this field here is a pointer reference because it can be null
    CompletedAt *time.Time
}

// a slice(array) of Todo
type Todos []Todo

// Passing Todo slice here as a reference
// declares a parameter named todos that is a pointer to a Todos slice.
// the function receives a copy of the slice under the name todos
func (todos *Todos) add(title string) {
    todo := Todo{
        Title:       title,
        Completed:   false,
        CompletedAt: nil,
        CreatedAt:   time.Now(),
    }
    *todos = append(*todos, todo)

}

func (todos *Todos) validateIndex(index int) error {
    if index < 0 || index >= len(*todos) {
        err := errors.New("invalid index")
        fmt.Println(err)
    }
    return nil
}

func (todos *Todos) delete(index int) error {
    t := *todos

    if err := t.validateIndex(index); err != nil {
        return err
    }

    *todos = append(t[:index], t[index+1:]...)

    return nil
}

func (todos *Todos) toggle(index int) error {
    t := *todos

    if err := t.validateIndex(index); err != nil {
        return err
    }

    isCompleted := t[index].Completed

    if !isCompleted {
        completionTime := time.Now()
        t[index].CompletedAt = &completionTime
    }

    t[index].Completed = !isCompleted

    return nil
}

func (todos *Todos) edit(index int, title string) error {
    t := *todos

    if err := t.validateIndex(index); err != nil {
        return err
    }

    t[index].Title = title

    return nil
}

func (todos *Todos) print() {
    table := table.New(os.Stdout)
    table.SetRowLines(false)
    table.SetHeaders("#", "Title", "Status", "Created", "Completed")

    for index, t := range *todos {
        mark := "❌"
        completedAt := ""

        if t.Completed {
            mark = "✅"
            if t.CompletedAt != nil {
                completedAt = t.CompletedAt.Format(time.RFC1123)
            }
        }
        table.AddRow(strconv.Itoa(index), t.Title, mark, t.CreatedAt.Format(time.RFC1123), completedAt)
    }

    table.Render()
}

Storage implementation

package main

import (
    "encoding/json"
    "os"
)

type Storage[T any] struct {
    FileName string
}

func NewStorage[T any](filename string) *Storage[T] {
    return &Storage[T]{FileName: filename}
}

func (s *Storage[T]) Save(data T) error {
    fileData, err := json.MarshalIndent(data, "", "\t")

    if err != nil {
        return err
    }

    return os.WriteFile(s.FileName, fileData, 0644)

}

func (s *Storage[T]) Load(data *T) error {
    fileData, err := os.ReadFile(s.FileName)

    if err != nil {
        return err
    }

    return json.Unmarshal(fileData, data)
}

Command Line Flags Validation and Execution

package main

import (
    "flag"
    "fmt"
    "os"
    "strconv"
    "strings"
)

type CmdFlags struct {
    Help   bool
    Add    string
    Del    int
    Edit   string
    Update int
    List   bool
}

func NewCmdflags() *CmdFlags {
    cf := CmdFlags{}

    flag.BoolVar(&cf.Help, "help", false, "List existing commands")
    flag.StringVar(&cf.Add, "add", "", "Add a new todo specify title")
    flag.StringVar(&cf.Edit, "edit", "", "Edit an existing todo, enter #index and specify a new title. \"id:new title\"")
    flag.IntVar(&cf.Del, "del", -1, "Specify a todo by #index to delete")
    flag.IntVar(&cf.Update, "update", -1, "Specify a todo #index to update")
    flag.BoolVar(&cf.List, "list", false, "List all todos")

    for _, arg := range os.Args[1:] {
        if strings.HasPrefix(arg, "-") && !isValidFlag(arg) {
            fmt.Printf("Unknown flag: %s\n", arg)
            fmt.Println("try --help to know more")

            os.Exit(0)
        }
    }

    flag.Parse()
    return &cf
}

func isValidFlag(flag string) bool {

    validFlags := []string{
        "-help", "--help",
        "-add", "--add",
        "-edit", "--edit",
        "-del", "--del",
        "-update", "--update",
        "-list", "--list",
    }

    if idx := strings.Index(flag, "="); idx != -1 {
        flag = flag[:idx]
    }

    for _, validFlag := range validFlags {
        if flag == validFlag {
            return true
        }
    }

    return false
}

func (cf *CmdFlags) Execute(todos *Todos) {
    switch {
    case cf.List:
        todos.print()

    case cf.Add != "":
        todos.add(cf.Add)

    case cf.Edit != "":
        parts := strings.SplitN(cf.Edit, ":", 2)
        if len(parts) != 2 {
            fmt.Printf("Error, invalid format for edit.\nCorrect Format: \"id:new title\" ")
            os.Exit(1)
        }

        index, err := strconv.Atoi(parts[0])

        if err != nil {
            fmt.Printf("Error, Invalid index for edit")
            os.Exit(1)
        }

        todos.edit(index, parts[1])

    case cf.Update != -1:
        todos.toggle(cf.Update)

    case cf.Del != -1:
        todos.delete(cf.Del)

    case cf.Help:
        fmt.Println("usage:")
        fmt.Println("--help\t\t| List existing commands")
        fmt.Println("--add\t\t| Add new task")
        fmt.Println("--del\t\t| Delete an existing task")
        fmt.Println("--update\t| Check/Uncheck existing task")
        fmt.Println("--edit\t\t| Edit an existing task")
    }
}

Github Repo: CLI Todo App

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