components/media/media-autosave.ts

Functions

Imports

It imports no other module of this repo. Imported by components/media/media-inspector.ts, components/media/media.ts.

Source

1// The media inspector's autosave.
2
3// ---------------------------------------------------------------------------------------
4// Autosave, pure. It waits until typing stops, saves, and says where it is. A change that
5// arrives while a save runs is saved after it. Nothing here touches the fields, so what was
6// typed is never lost: a failure only changes the state.
7
8export type SaveState = "idle" | "dirty" | "saving" | "saved" | "failed";
9
10export interface AutosaveOptions {
11  // Milliseconds of quiet before a save: 800.
12  delay?: number;
13  // Reads the fields and sends them. Called synchronously when a save starts, so what it reads is
14  // what the person had typed at that moment. Reject with an Error that says why.
15  save: () => Promise<void>;
16  onState?: (state: SaveState, error?: string) => void;
17}
18
19export interface Autosave {
20  // A change was made: save when typing stops.
21  schedule(): void;
22  // Save now, if there is anything unsaved (a field lost focus).
23  flush(): Promise<void>;
24  // Try again after a failure.
25  retry(): Promise<void>;
26  state(): SaveState;
27  // Forget the timer (the inspector moved to another file).
28  cancel(): void;
29}
30
31export const AUTOSAVE_MS = 800;
32
33export function createAutosave(opts: AutosaveOptions): Autosave {
34  const delay = opts.delay ?? AUTOSAVE_MS;
35  let state: SaveState = "idle";
36  let timer: ReturnType<typeof setTimeout> | null = null;
37  let running: Promise<void> | null = null;
38  let again = false;
39  const set = (s: SaveState, error?: string) => {
40    state = s;
41    opts.onState?.(s, error);
42  };
43  const stop = () => {
44    if (timer !== null) clearTimeout(timer);
45    timer = null;
46  };
47  const run = (): Promise<void> => {
48    stop();
49    if (running) {
50      again = true;
51      return running;
52    }
53    set("saving");
54    let pending: Promise<void>;
55    try {
56      pending = opts.save();
57    } catch (err) {
58      pending = Promise.reject(err);
59    }
60    running = pending
61      .then(
62        () => {
63          running = null;
64          if (again) {
65            again = false;
66            return run();
67          }
68          set("saved");
69          return undefined;
70        },
71        (err: unknown) => {
72          running = null;
73          again = false;
74          set("failed", err instanceof Error && err.message ? err.message : "Nothing says why.");
75        },
76      )
77      .then(() => undefined);
78    return running;
79  };
80  return {
81    schedule() {
82      if (running) again = true;
83      else set("dirty");
84      stop();
85      timer = setTimeout(() => void run(), delay);
86    },
87    flush() {
88      if (running) {
89        again = again || state === "dirty";
90        return running;
91      }
92      if (state === "dirty") return run();
93      return Promise.resolve();
94    },
95    retry() {
96      return run();
97    },
98    state: () => state,
99    cancel: stop,
100  };
101}
102