Project: a to-do list

//! A to-do list that lives in a JSON file.
//!
//!     todo add "buy rope"      todo list      todo done 1      todo clear
//!
//! With no arguments it runs a demonstration session against a temporary
//! file. `--file PATH` chooses the file (default: todo.json in the temp dir).

import std.args
import std.fs
import std.json

struct Item { text: String, done: bool }

/// The items in the file, or none when there is no file yet.
fn load(path: []u8) -> !List(Item) {
    var items = List(Item).new()
    if !fs.exists(path) { return items }
    let doc = try json.parse((try fs.read(path))[..])
    for i in 0..json.len(&doc) {
        let entry = json.at(&doc, i) orelse continue
        let text = json.as_str(json.get(entry, "text") orelse continue) orelse continue
        let done = json.as_bool(json.get(entry, "done") orelse continue) orelse false
        items.append(Item{ .text = String.from(text), .done = done })
    }
    return items
}

fn save(path: []u8, items: *List(Item)) -> !void {
    var doc = json.array()
    for it in items.* {
        var entry = json.object()
        json.set(&mut entry, "text", json.string(it.text[..]))
        json.set(&mut entry, "done", json.boolean(it.done))
        json.push(&mut doc, entry)
    }
    try fs.write(path, json.pretty(&doc, 2)[..])
}

fn show(items: *List(Item)) {
    if items.len == 0 { println("nothing to do", .{}); return }
    for it, i in items.* {
        println("{>2}. [{}] {}", .{i + 1, if it.done { "x" } else { " " }, it.text})
    }
}

/// One command against the file; the exit code.
fn run(path: []u8, command: []u8, rest: [][]u8) -> !i32 {
    var items = try load(path)
    if command == "list" {
        show(&items)
    } else if command == "add" {
        if rest.len == 0 { eprintln("add what?", .{}); return 2 }
        var text = String.new()
        for w, i in rest { if i > 0 { text.append(" ") }; text.append(w) }
        items.append(Item{ .text = text, .done = false })
        try save(path, &items)
        println("added #{}", .{items.len})
    } else if command == "done" {
        if rest.len == 0 { eprintln("done which?", .{}); return 2 }
        let n = rest[0].parse_int(usize) catch { eprintln("not a number: {}", .{rest[0]}); return 2 }
        if n == 0 or n > items.len { eprintln("no item #{}", .{n}); return 1 }
        items[n - 1].done = true
        try save(path, &items)
        println("done: {}", .{items[n - 1].text})
    } else if command == "clear" {
        fs.remove(path) catch { }
        println("cleared", .{})
    } else {
        eprintln("usage: todo [--file PATH] add TEXT | list | done N | clear", .{})
        return 2
    }
    return 0
}

fn main() -> !u8 {
    var p = args.Parser.new(os.args())
    let given = p.option("--file", "-f")
    let path = if let f = given { String.from(f) } else { fs.join(fs.temp_dir()[..], "todo.json") }
    let rest = p.rest()
    if rest.len > 0 {
        return (try run(path[..], rest[0], rest[1..])) as u8
    }
    // no command: a demonstration against a fresh file
    fs.remove(path[..]) catch { }
    let session = ["add buy rope", "add sharpen crampons", "add pack the tent", "list", "done 2", "list", "done 9", "clear", "list"]
    for line in session {
        println("$ todo {}", .{line})
        var words = List([]u8).new()
        for w in line.split(" ") { words.append(w) }
        _ = try run(path[..], words[0], words[1..])
    }
    return 0
}

$ todo add buy rope
added #1
$ todo add sharpen crampons
added #2
$ todo add pack the tent
added #3
$ todo list
 1. [ ] buy rope
 2. [ ] sharpen crampons
 3. [ ] pack the tent
$ todo done 2
done: sharpen crampons
$ todo list
 1. [ ] buy rope
 2. [x] sharpen crampons
 3. [ ] pack the tent
$ todo done 9
$ todo clear
cleared
$ todo list
nothing to do
no item #9