import { createContext, useContext, useEffect, useRef, useState, type ReactNode } from "react";

const STORAGE_KEY = "counsel.timer.v1";

interface PersistedTimer {
  clientId: string | null;
  caseId: string | null;
  description: string;
  // Total accumulated milliseconds while running, excluding current segment
  accumulatedMs: number;
  // Timestamp (ms) when the current running segment started, or null if paused
  runningSince: number | null;
  startedAt: string | null;
}

interface TimerState {
  timer: PersistedTimer;
  elapsedMs: number;
  isRunning: boolean;
  hasStarted: boolean;
  setClient: (clientId: string | null) => void;
  setCase: (caseId: string | null) => void;
  setDescription: (description: string) => void;
  start: () => void;
  pause: () => void;
  resume: () => void;
  reset: () => void;
  consume: () => { hours: number };
}

const empty: PersistedTimer = {
  clientId: null,
  caseId: null,
  description: "",
  accumulatedMs: 0,
  runningSince: null,
  startedAt: null,
};

const TimerContext = createContext<TimerState | undefined>(undefined);

function read(): PersistedTimer {
  if (typeof window === "undefined") return empty;
  try {
    const raw = localStorage.getItem(STORAGE_KEY);
    if (!raw) return empty;
    return { ...empty, ...(JSON.parse(raw) as PersistedTimer) };
  } catch {
    return empty;
  }
}

function write(t: PersistedTimer) {
  if (typeof window === "undefined") return;
  if (t.accumulatedMs === 0 && !t.runningSince && !t.clientId && !t.caseId && !t.description) {
    localStorage.removeItem(STORAGE_KEY);
  } else {
    localStorage.setItem(STORAGE_KEY, JSON.stringify(t));
  }
}

function computeElapsed(t: PersistedTimer): number {
  return t.accumulatedMs + (t.runningSince ? Date.now() - t.runningSince : 0);
}

export function TimerProvider({ children }: { children: ReactNode }) {
  const [timer, setTimer] = useState<PersistedTimer>(empty);
  const [elapsedMs, setElapsedMs] = useState(0);
  const intervalRef = useRef<number | null>(null);

  useEffect(() => {
    const t = read();
    setTimer(t);
    setElapsedMs(computeElapsed(t));
  }, []);

  useEffect(() => {
    if (intervalRef.current) {
      clearInterval(intervalRef.current);
      intervalRef.current = null;
    }
    if (timer.runningSince) {
      intervalRef.current = window.setInterval(() => {
        setElapsedMs(computeElapsed(timer));
      }, 1000);
    }
    return () => {
      if (intervalRef.current) clearInterval(intervalRef.current);
    };
  }, [timer]);

  useEffect(() => {
    const onStorage = (e: StorageEvent) => {
      if (e.key !== STORAGE_KEY) return;
      const t = read();
      setTimer(t);
      setElapsedMs(computeElapsed(t));
    };
    window.addEventListener("storage", onStorage);
    return () => window.removeEventListener("storage", onStorage);
  }, []);

  const persist = (t: PersistedTimer) => {
    write(t);
    setTimer(t);
    setElapsedMs(computeElapsed(t));
  };

  const setClient = (clientId: string | null) =>
    persist({ ...timer, clientId, caseId: clientId === timer.clientId ? timer.caseId : null });
  const setCase = (caseId: string | null) => persist({ ...timer, caseId });
  const setDescription = (description: string) => persist({ ...timer, description });

  const start = () => {
    if (timer.runningSince) return;
    persist({
      ...timer,
      runningSince: Date.now(),
      startedAt: timer.startedAt ?? new Date().toISOString(),
    });
  };

  const pause = () => {
    if (!timer.runningSince) return;
    const accumulatedMs = timer.accumulatedMs + (Date.now() - timer.runningSince);
    persist({ ...timer, accumulatedMs, runningSince: null });
  };

  const resume = () => {
    if (timer.runningSince) return;
    persist({ ...timer, runningSince: Date.now() });
  };

  const reset = () => persist(empty);

  const consume = () => {
    const ms = computeElapsed(timer);
    // Round UP to the nearest 0.1 hour (6 minute / 360,000 ms increments).
    const increment = 6 * 60 * 1000;
    const rounded = Math.max(increment, Math.ceil(ms / increment) * increment);
    const hours = Math.round((rounded / 3600000) * 10) / 10;
    persist(empty);
    return { hours };
  };

  return (
    <TimerContext.Provider
      value={{
        timer,
        elapsedMs,
        isRunning: !!timer.runningSince,
        hasStarted: timer.accumulatedMs > 0 || !!timer.runningSince,
        setClient,
        setCase,
        setDescription,
        start,
        pause,
        resume,
        reset,
        consume,
      }}
    >
      {children}
    </TimerContext.Provider>
  );
}

export function useTimer() {
  const ctx = useContext(TimerContext);
  if (!ctx) throw new Error("useTimer must be used within TimerProvider");
  return ctx;
}

export function formatHMS(ms: number): string {
  const total = Math.floor(ms / 1000);
  const h = Math.floor(total / 3600);
  const m = Math.floor((total % 3600) / 60);
  const s = total % 60;
  return `${String(h).padStart(2, "0")}:${String(m).padStart(2, "0")}:${String(s).padStart(2, "0")}`;
}

/** Round hours UP to the nearest 0.1 (6-minute) increment, with 0.1 minimum. */
export function roundToTenth(hours: number): number {
  if (!hours || hours <= 0) return 0;
  return Math.max(0.1, Math.round(Math.ceil(hours * 10)) / 10);
}

/** Round hours UP to the nearest 1/6 hour (10-minute) increment, with 1/6 minimum. */
export function roundToSixth(hours: number): number {
  if (!hours || hours <= 0) return 0;
  const sixths = Math.max(1, Math.ceil(hours * 6));
  return Math.round((sixths / 6) * 1000) / 1000;
}