function playCompletionChime() {
    try {
        const AudioContext = window.AudioContext || window.webkitAudioContext;
        if (!AudioContext) return;
        const context = new AudioContext();
        const oscillator = context.createOscillator();
        const gain = context.createGain();
        oscillator.type = "sine";
        oscillator.frequency.setValueAtTime(523.25, context.currentTime);
        oscillator.frequency.setValueAtTime(659.25, context.currentTime + 0.12);
        gain.gain.setValueAtTime(0.0001, context.currentTime);
        gain.gain.exponentialRampToValueAtTime(0.12, context.currentTime + 0.02);
        gain.gain.exponentialRampToValueAtTime(0.0001, context.currentTime + 0.35);
        oscillator.connect(gain);
        gain.connect(context.destination);
        oscillator.start();
        oscillator.stop(context.currentTime + 0.36);
        oscillator.addEventListener("ended", () => context.close());
    } catch (_error) {
        // Audio feedback is optional; browser policy must never block completion.
    }
}

function initializeTimer(timer) {
    const duration = Number(timer.dataset.duration);
    const taskId = timer.dataset.taskId;
    const storageKey = `steady.timer.${taskId}`;
    const display = timer.querySelector(".timer__display");
    const progress = timer.querySelector(".timer__progress span");
    const announcement = timer.querySelector(".timer__announcement");
    let intervalId;

    function readState() {
        try {
            const stored = JSON.parse(localStorage.getItem(storageKey));
            if (stored && Number.isFinite(stored.remaining)) return stored;
        } catch (_error) {
            // A corrupt or unavailable local store simply starts a fresh timer.
        }
        return { remaining: duration, running: false, updatedAt: Date.now() };
    }

    let state = readState();

    function currentRemaining() {
        if (!state.running) return state.remaining;
        const elapsed = Math.floor((Date.now() - state.updatedAt) / 1000);
        return Math.max(0, state.remaining - elapsed);
    }

    function saveState() {
        try {
            localStorage.setItem(storageKey, JSON.stringify(state));
        } catch (_error) {
            // The countdown still works for this page when storage is unavailable.
        }
    }

    function render() {
        const remaining = currentRemaining();
        const minutes = Math.floor(remaining / 60);
        const seconds = remaining % 60;
        display.textContent = `${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}`;
        progress.style.width = `${Math.max(0, Math.min(100, (remaining / duration) * 100))}%`;

        if (remaining === 0 && state.running) {
            state = { remaining: 0, running: false, updatedAt: Date.now() };
            saveState();
            clearInterval(intervalId);
            timer.classList.add("timer--complete");
            announcement.textContent = "Focus block complete. Take a breath.";
            if (timer.dataset.chime === "true") playCompletionChime();
        }
    }

    timer.querySelector("[data-timer-start]").addEventListener("click", () => {
        const remaining = currentRemaining() || duration;
        state = { remaining, running: true, updatedAt: Date.now() };
        timer.classList.remove("timer--complete");
        saveState();
        clearInterval(intervalId);
        intervalId = window.setInterval(render, 250);
        render();
    });

    timer.querySelector("[data-timer-pause]").addEventListener("click", () => {
        state = {
            remaining: currentRemaining(),
            running: false,
            updatedAt: Date.now(),
        };
        saveState();
        clearInterval(intervalId);
        render();
    });

    timer.querySelector("[data-timer-reset]").addEventListener("click", () => {
        state = { remaining: duration, running: false, updatedAt: Date.now() };
        saveState();
        clearInterval(intervalId);
        timer.classList.remove("timer--complete");
        announcement.textContent = "Timer reset.";
        render();
    });

    if (state.running) intervalId = window.setInterval(render, 250);
    render();
}

document.querySelectorAll("[data-focus-timer]").forEach(initializeTimer);

const celebration = document.querySelector('[data-celebrate="true"]');
if (celebration && celebration.dataset.chime === "true") {
    playCompletionChime();
}