/**
 * The progress page's data: GET /api/stats from the SRS Worker, fetched in the
 * browser so `blume build` never depends on the API being up. API_BASE is the
 * deployed Worker — do not inline it anywhere else.
 *
 * Four islands read this (SolvedRing, SubmissionHeatmap, RecentSolves,
 * TopicBubbles). Each hydrates on its own, but they share this module, so the
 * one in-flight request is shared too: the page asks the Worker once.
 *
 * Invariants: a malformed body is an error state, never a throw; the first
 * frame is always the loading state, so server and client render identically.
 */
import { useEffect, useState } from "react";

const API_BASE = "https://srs-api.prdlk.workers.dev";

// ── /api/stats response shape (the fields these islands read) ────

export const DIFFICULTIES = ["easy", "medium", "hard"] as const;

export type Difficulty = (typeof DIFFICULTIES)[number];

export interface Stats {
  generated: string;
  /** Per difficulty, catalog size and how many entered the ladder. */
  difficulty: { difficulty: Difficulty; total: number; done: number }[];
  /** Problems whose most recent attempt failed — the sweep day's miss log. */
  attempting: number;
  topics: { issue: number; name: string; total: number; done: number; taught: boolean }[];
  /** The ten most recently solved, newest first, dated by first pass (ET). */
  recent: { lc: number; title: string; difficulty: Difficulty; date: string }[];
  /**
   * The 365 days ending today (ET), zeros included — always the current
   * calendar year to date. Per difficulty: every logged attempt, and every
   * first solve (the first-pass date `recent` uses).
   */
  year: Day[];
}

export interface Day {
  date: string;
  passes: number;
  attempts: Record<Difficulty, number>;
  solved: Record<Difficulty, number>;
}

function isStats(value: unknown): value is Stats {
  if (typeof value !== "object" || value === null) return false;
  const v = value as Record<string, unknown>;
  return (
    Array.isArray(v.difficulty) &&
    typeof v.attempting === "number" &&
    Array.isArray(v.topics) &&
    Array.isArray(v.recent) &&
    Array.isArray(v.year)
  );
}

// ── the shared request ───────────────────────────────────────────

export type Load = { phase: "loading" } | { phase: "error" } | { phase: "ready"; stats: Stats };

let request: Promise<Stats | null> | undefined;

/** The page's stats, fetched once however many islands ask. */
export function useStats(): Load {
  const [load, setLoad] = useState<Load>({ phase: "loading" });
  useEffect(() => {
    if (!request) {
      request = fetch(`${API_BASE}/api/stats`)
        .then((res) => (res.ok ? res.json() : null))
        .then((body: unknown) => (isStats(body) ? body : null))
        .catch(() => null);
    }
    let live = true;
    request.then((stats) => {
      if (live) setLoad(stats ? { phase: "ready", stats } : { phase: "error" });
    });
    return () => {
      live = false;
    };
  }, []);
  return load;
}

/** "YYYY-MM-DD" → a UTC-midnight Date, so calendar math never drifts with the reader's timezone. */
export function utcDate(iso: string): Date {
  const [y, m, d] = iso.split("-").map(Number);
  return new Date(Date.UTC(y!, m! - 1, d!));
}