import { useEffect, useState } from "react";
import { get } from "../api";
import { getLang, useT } from "../i18n";

/**
 * Graphical editor for a 5-field cron expression (minute hour day month weekday,
 * server time zone): every N minutes, hourly, daily, on weekdays, monthly – or a
 * custom expression. Shows the next runs as computed by the server.
 */
type Mode = "minutes" | "hourly" | "daily" | "weekly" | "monthly" | "custom";

interface State {
  mode: Mode;
  every: number;
  minute: number;
  time: string; // HH:MM
  days: number[]; // cron weekdays, 0 = Sunday
  dom: number;
  custom: string;
}

const MINUTE_STEPS = [5, 10, 15, 20, 30];
/** Monday first; cron numbers (0 = Sunday). */
const WEEK = [1, 2, 3, 4, 5, 6, 0];

const pad = (n: number) => String(n).padStart(2, "0");
const hhmm = (h: string, m: string) => `${pad(Number(h))}:${pad(Number(m))}`;

function expandDays(field: string): number[] | null {
  const out = new Set<number>();
  for (const part of field.split(",")) {
    const m = part.match(/^(\d)(?:-(\d))?$/);
    if (!m) return null;
    const a = Number(m[1]);
    const b = m[2] ? Number(m[2]) : a;
    if (a > 7 || b > 7 || b < a) return null;
    for (let d = a; d <= b; d++) out.add(d % 7);
  }
  return [...out];
}

export function parseCron(expr: string): State {
  const base: State = { mode: "custom", every: 15, minute: 0, time: "03:00", days: [1, 2, 3, 4, 5], dom: 1, custom: expr.trim() };
  const f = expr.trim().split(/\s+/);
  if (f.length !== 5) return base;
  const [mi, h, dom, mon, dow] = f;
  const num = (s: string, max: number) => /^\d+$/.test(s) && Number(s) <= max;
  if (mon !== "*") return base;
  let m;
  if ((m = mi.match(/^\*\/(\d+)$/)) && h === "*" && dom === "*" && dow === "*" && MINUTE_STEPS.includes(Number(m[1]))) return { ...base, mode: "minutes", every: Number(m[1]) };
  if (num(mi, 59) && h === "*" && dom === "*" && dow === "*") return { ...base, mode: "hourly", minute: Number(mi) };
  if (!num(mi, 59) || !num(h, 23)) return base;
  const time = hhmm(h, mi);
  if (dom === "*" && dow === "*") return { ...base, mode: "daily", time };
  if (dom === "*") {
    const days = expandDays(dow);
    return days?.length ? { ...base, mode: "weekly", time, days } : base;
  }
  if (num(dom, 31) && Number(dom) >= 1 && dow === "*") return { ...base, mode: "monthly", time, dom: Number(dom) };
  return base;
}

export function buildCron(s: State): string {
  const [h, m] = s.time.split(":").map(Number);
  switch (s.mode) {
    case "minutes":
      return `*/${s.every} * * * *`;
    case "hourly":
      return `${s.minute} * * * *`;
    case "daily":
      return `${m} ${h} * * *`;
    case "weekly": {
      const days = [...s.days].sort((a, b) => a - b);
      return `${m} ${h} * * ${days.length ? days.join(",") : "*"}`;
    }
    case "monthly":
      return `${m} ${h} ${s.dom} * *`;
    default:
      return s.custom.trim();
  }
}

const dayName = (d: number, style: "short" | "long") => {
  // 2023-01-01 was a Sunday.
  return new Date(2023, 0, 1 + d).toLocaleDateString(getLang(), { weekday: style });
};

/** "2026-11-11T06:30" (server wall time) for display, without time zone conversion. */
const fmtWall = (s: string) => {
  const [d, hm] = s.split("T");
  const [y, mo, da] = d.split("-").map(Number);
  const date = new Date(y, mo - 1, da).toLocaleDateString(getLang(), { weekday: "short", day: "numeric", month: "short" });
  return `${date}, ${hm}`;
};

export function CronBuilder({ value, onChange }: { value: string; onChange: (cron: string) => void }) {
  const t = useT();
  const [s, setS] = useState<State>(() => parseCron(value));
  const [preview, setPreview] = useState<{ ok: boolean; next_local?: string[]; error?: string; tz?: string }>();

  // A value from outside (another automation, reset) that the builder did not produce.
  useEffect(() => {
    if (value.trim() !== buildCron(s)) setS(parseCron(value));
    // eslint-disable-next-line react-hooks/exhaustive-deps
  }, [value]);

  useEffect(() => {
    const expr = value.trim();
    if (!expr) return setPreview(undefined);
    let alive = true;
    const h = setTimeout(() => {
      get<typeof preview>(`/jobs/schedule?expr=${encodeURIComponent(expr)}`)
        .then((p) => alive && setPreview(p))
        .catch(() => alive && setPreview(undefined));
    }, 250);
    return () => {
      alive = false;
      clearTimeout(h);
    };
  }, [value]);

  const set = (patch: Partial<State>) => {
    const next = { ...s, ...patch };
    // Switching to "custom" starts from the current expression.
    if (patch.mode === "custom" && s.mode !== "custom") next.custom = buildCron(s);
    setS(next);
    onChange(buildCron(next));
  };

  const modes: Mode[] = ["minutes", "hourly", "daily", "weekly", "monthly", "custom"];
  return (
    <div className="cron-builder">
      <div className="cron-modes" role="radiogroup" aria-label={t("cron.label")}>
        {modes.map((m) => (
          <button key={m} type="button" role="radio" aria-checked={s.mode === m} className={`chip-btn ${s.mode === m ? "active" : ""}`} onClick={() => set({ mode: m })}>
            {t(`cron.mode.${m}` as const)}
          </button>
        ))}
      </div>
      <div className="cron-fields">
        {s.mode === "minutes" && (
          <label>
            {t("cron.every")}
            <select value={s.every} onChange={(e) => set({ every: Number(e.target.value) })}>
              {MINUTE_STEPS.map((n) => (
                <option key={n} value={n}>
                  {n}
                </option>
              ))}
            </select>
            {t("cron.minutes")}
          </label>
        )}
        {s.mode === "hourly" && (
          <label>
            {t("cron.atMinute")}
            <input type="number" min={0} max={59} value={s.minute} onChange={(e) => set({ minute: Math.min(59, Math.max(0, Number(e.target.value) || 0)) })} />
          </label>
        )}
        {s.mode === "weekly" && (
          <div className="cron-days" role="group" aria-label={t("cron.days")}>
            {WEEK.map((d) => (
              <button
                key={d}
                type="button"
                aria-pressed={s.days.includes(d)}
                className={`chip-btn ${s.days.includes(d) ? "active" : ""}`}
                title={dayName(d, "long")}
                onClick={() => set({ days: s.days.includes(d) ? s.days.filter((x) => x !== d) : [...s.days, d] })}
              >
                {dayName(d, "short")}
              </button>
            ))}
            <button type="button" className="link-btn" onClick={() => set({ days: [1, 2, 3, 4, 5] })}>
              {t("cron.workdays")}
            </button>
          </div>
        )}
        {s.mode === "monthly" && (
          <label>
            {t("cron.onDay")}
            <select value={s.dom} onChange={(e) => set({ dom: Number(e.target.value) })}>
              {Array.from({ length: 31 }, (_, i) => i + 1).map((d) => (
                <option key={d} value={d}>
                  {d}.
                </option>
              ))}
            </select>
          </label>
        )}
        {(s.mode === "daily" || s.mode === "weekly" || s.mode === "monthly") && (
          <label>
            {t("cron.at")}
            <input type="time" value={s.time} onChange={(e) => e.target.value && set({ time: e.target.value })} />
          </label>
        )}
        {s.mode === "custom" && (
          <label className="cron-custom">
            <input className="mono" value={s.custom} placeholder="0 3 * * *" spellCheck={false} onChange={(e) => set({ custom: e.target.value })} />
            <small className="hint">{t("cron.customHint")}</small>
          </label>
        )}
      </div>
      <div className="cron-preview">
        <code>{value || "–"}</code>
        {preview?.ok === false && <span className="err">{preview.error}</span>}
        {preview?.ok && preview.next_local && preview.next_local.length > 0 && (
          <span>
            {t("cron.nextRuns")} {preview.next_local.slice(0, 3).map(fmtWall).join(" · ")}
          </span>
        )}
        {preview?.tz && s.mode !== "minutes" && <span className="hint">{t("cron.serverTz", { tz: preview.tz })}</span>}
        {s.mode === "monthly" && s.dom > 28 && <span className="hint">{t("cron.shortMonths")}</span>}
      </div>
    </div>
  );
}