Todo App

A complete command-line application: argument parsing with Os.args(), JSON persistence through the json library declared in dependencies:, match over subcommands, and rendering split into its own module.

Browse this example on GitHub

Run it

git clone https://github.com/lauriszz123/saule.git
cd saule/examples/todo-app
saule run -- add "write some Saule"
saule run -- list

saule.config

name: "todo-app"
version: "0.1.0"
entry: "src/main.sau"
src_dirs: ["src"]
dependencies: ["../json"]
min_saule_version: "26.1"

src/main.sau

src/main.sau

from storage import *
from render import *

class Main
  static fn help()
    println("TODO App Usage:")
    println("\ttodo list")
    println("\ttodo add [task] [optional-due-date YYYY-MM-DD]")
    println("\ttodo remove [number-of-task]")
    println("\ttodo done [number-of-task]")
    println("\ttodo due [number-of-task] [due-date YYYY-MM-DD]")
  end

  static fn main()
    local storage = Storage("todo.json")
    local args = Os.args()

    if not Os.exists("todo.json") then
      storage.save()
    elseif not storage.load() then
      println("error: todo.json is corrupt; refusing to overwrite")
      return
    end

    if #args == 0 then
      help()
      return
    end

    match args[1]
      case "list" then Renderer.print(storage.getAll())

      case "add" then
        local due: integer? = nil

        if args[3] != nil then
          due = Os.parsedate(args[3])
          if due == nil then
            println("invalid date: " .. args[3] .. " (expected YYYY-MM-DD)")
            return
          end
        end

        storage.add(args[2], dueDate: due)
        Renderer.print(storage.getAll())

      case "done" then
        local index: integer? = args[2] as integer
        if index == nil then
          println("error: invalid task number")
          return
        end

        storage.update(index, isDone: true)

      case "due" then
        local index: integer? = args[2] as integer

        if index == nil then
          println("error: invalid task number")
          return
        end

        if args[3] == nil then
          println("error: missing due date")
          return
        end

        local due: integer? = Os.parsedate(args[3])
        if due == nil then
          println("invalid date: " .. args[3] .. " (expected YYYY-MM-DD)")
          return
        end

        storage.update(index, dueDate: due)

      case "remove" then
        local index: integer? = args[2] as integer
        if index == nil then
          println("error: invalid task number")
          return
        end

        match storage.remove(index)
          case nil then printf("Task id %d does not exist\n", index)

          case task then printf("Removed task: %s\n", task)
        end

        Renderer.print(storage.getAll())

      case _ then help()
    end

    storage.save()
  end
end

src/storage.sau

src/storage.sau

from json import Json

export class Entry
  local todo: string
  local done: boolean
  local dueDate: integer?

  fn init(todo: string, dueDate: integer?)
    self.todo = todo
    self.done = false
    self.dueDate = dueDate
  end

  fn setTodo(todo: string)
    self.todo = todo
  end

  fn getTodo() -> string
    return self.todo
  end

  fn setDone(isDone: boolean)
    self.done = isDone
  end

  fn isDone() -> boolean
    return self.done
  end

  fn setDueDate(dueDate: integer)
    self.dueDate = dueDate
  end

  fn getDueDate() -> integer?
    return self.dueDate
  end

  fn isDue() -> boolean?
    if self.dueDate == nil then
      return
    end

    return Os.time() >= self.dueDate
  end
end

export class Storage
  local path: string
  local storage: table<Entry>

  fn init(path: string)
    self.path = path
    self.storage = {}
  end

  fn load() -> boolean
    if not Os.exists(self.path) then
      return false
    end

    local file = Io.open(self.path, IoMode.Read)!
    local source: string? = file.read()
    file.close()

    -- `read` is `string?`: an unreadable file is not a crash here, it is
    -- an empty todo list.
    if not source then
      return false
    end

    -- Decoded JSON is plain tables, not `Entry` instances — the rows
    -- below are validated field by field and fed through `Entry(...)`.
    local data = Json.decode(source!) as table<any>

    if not data then
      return false
    end

    if type(data) != "table" then
      return false
    end

    for _, entry in data do
      if type(entry) != "table" then
        return false
      end

      -- `as` is the checked cast out of `any`: it yields nil when the
      -- stored value has the wrong shape, so a nil here means the file
      -- is malformed.
      local todo = entry.todo as string
      if todo == nil then
        return false
      end

      local done = entry.done as boolean
      if done == nil then
        return false
      end

      local newEntry = Entry(todo, entry.dueDate as integer)
      newEntry.setDone(done)
      Table.insert(self.storage, newEntry)
    end

    return true
  end

  fn save()
    local data: table = {}

    for _, entry in self.storage do
      Table.insert(data, {todo: entry.getTodo(), done: entry.isDone(), dueDate: entry.getDueDate()})
    end

    local jsonData: string = Json.encode(data)
    local file = Io.open(self.path, IoMode.Write)
    file?.write(jsonData)
    file?.close()
  end

  fn add(item: string, dueDate: integer?)
    Table.insert(self.storage, Entry(item, dueDate))
  end

  fn remove(id: integer) -> string?
    return Table.remove(self.storage, id)?.getTodo()
  end

  fn update(id: integer, dueDate: integer?, isDone: boolean?)
    if self.storage[id] == nil then
      return
    end

    if dueDate != nil then
      self.storage[id].setDueDate(dueDate)
    end

    if isDone != nil then
      self.storage[id].setDone(isDone)
    end
  end

  fn getAll() -> table<Entry>
    return self.storage
  end
end

src/render.sau

src/render.sau

from storage import Entry

export class Renderer
  static fn print(tasks: table<Entry>)
    if #tasks == 0 then
      println("No tasks found.")
      return
    end

    for i, task in tasks do
      printf(
        "%s %d.%s %s\n",
        match task.isDone()
          case true then "[x]"

          case false then "[-]"
        end,
        i,
        match task.getDueDate()
          case nil then ""

          case dueDate then String.format(" (due %s)", Os.date("%Y-%m-%d", dueDate))
        end,
        task.getTodo()
      )
    end
  end
end