/**
 * update-eia-table.js
 *
 * Reusable function that fetches an average electricity retail price
 * (monthly) from the EIA Open Data API (v2) and updates the "Month/Year"
 * and "EIA Avg Rate" columns of a Finsweet-style table. The 3rd column
 * ("Average Rate") is never touched.
 *
 * USAGE
 *   <script src="update-eia-table.js"></script>
 *   <script>
 *     updateEIATable({
 *       apiKey: "YOUR_EIA_API_KEY",   // required — https://www.eia.gov/opendata/register.php
 *       stateId: "US",                // optional, default "US"
 *       sectorId: "ALL",              // optional, default "ALL" (RES, COM, IND, TRA, OTH, ALL)
 *       tableSelector: '[fs-table-instance="fs-table-2"]', // optional
 *       fetchMonths: 12,              // optional, how much EIA history to pull
 *     });
 *   </script>
 *
 *   Call it once the DOM is ready (e.g. inside a DOMContentLoaded listener,
 *   or place the <script> tags right before </body>). It returns a Promise
 *   if you want to know when the update finished:
 *
 *     updateEIATable({ apiKey: "..." }).then(() => console.log("done"));
 *
 * IMPORTANT — API key exposure
 *   This calls the EIA API directly from the browser, so the key is visible
 *   in network requests / page source. EIA keys are free and rate-limited,
 *   not billing-sensitive, so that's usually fine for a marketing page —
 *   but if you want to hide it, proxy this fetch through a small serverless
 *   function instead of calling api.eia.gov directly.
 */

function updateEIATable(config) {
  "use strict";

  const {
    apiKey = "z9FXNGL4TS39mFDjKpexEdib4gt3YSXxynTY0dzT",
    stateId = "US",
    sectorId = "ALL",
    tableSelector = '[data-table="electricity"]',
    fetchMonths = 12,
    endpoint = "https://api.eia.gov/v2/electricity/retail-sales/data/",
  } = config || {};

  if (!apiKey) {
    console.error("updateEIATable: an `apiKey` is required.");
    return Promise.reject(new Error("updateEIATable: missing apiKey"));
  }

  const MONTH_ABBR = [
    "Jan.", "Feb.", "Mar.", "Apr.", "May", "Jun.",
    "Jul.", "Aug.", "Sept.", "Oct.", "Nov.", "Dec.",
  ];

  // ---- Helpers -----------------------------------------------------------

  function periodKey(date) {
    const y = date.getFullYear();
    const m = String(date.getMonth() + 1).padStart(2, "0");
    return `${y}-${m}`;
  }

  function monthYearLabel(date) {
    return `${MONTH_ABBR[date.getMonth()]} ${date.getFullYear()}`;
  }

  function firstOfMonth(date) {
    return new Date(date.getFullYear(), date.getMonth(), 1);
  }

  function addMonths(date, delta) {
    return new Date(date.getFullYear(), date.getMonth() + delta, 1);
  }

  function formatRate(price, isEstimated) {
    const rounded = Number(price).toFixed(2).replace(/0$/, "").replace(/\.$/, "");
    return `${rounded}¢ / kWh${isEstimated ? "*" : ""}`;
  }

  function setCellText(row, cellIndex, text) {
    const cell = row.children[cellIndex];
    if (!cell) return;
    const textEl = cell.querySelector(".fs-table-2_text") || cell;
    textEl.textContent = text;
  }

  // ---- EIA fetch -----------------------------------------------------------

  async function fetchEIARates() {
    const url = new URL(endpoint);
    url.searchParams.set("api_key", apiKey);
    url.searchParams.set("frequency", "monthly");
    url.searchParams.append("data[0]", "price");
    url.searchParams.append("facets[stateid][]", stateId);
    url.searchParams.append("facets[sectorid][]", sectorId);
    url.searchParams.set("sort[0][column]", "period");
    url.searchParams.set("sort[0][direction]", "desc");
    url.searchParams.set("offset", "0");
    url.searchParams.set("length", String(fetchMonths));

    const res = await fetch(url.toString());
    if (!res.ok) {
      throw new Error(`EIA API request failed: ${res.status} ${res.statusText}`);
    }
    const json = await res.json();
    const rows = (json && json.response && json.response.data) || [];

    // Map of "YYYY-MM" -> price (as a number)
    const byPeriod = new Map();
    rows.forEach((row) => {
      byPeriod.set(row.period, parseFloat(row.price));
    });
    return byPeriod;
  }

  // ---- Main ----------------------------------------------------------------

  return (async () => {
    const wrapper = document.querySelector(tableSelector);
    if (!wrapper) {
      console.warn(`updateEIATable: no element matched "${tableSelector}"`);
      return;
    }
    const rows = Array.from(wrapper.querySelectorAll("tbody tr"));
    if (rows.length === 0) {
      console.warn("updateEIATable: no <tr> rows found inside the table body");
      return;
    }

    let ratesByPeriod;
    try {
      ratesByPeriod = await fetchEIARates();
    } catch (err) {
      console.error("updateEIATable: failed to fetch EIA data", err);
      throw err;
    }

    if (ratesByPeriod.size === 0) {
      console.warn("updateEIATable: EIA returned no data for the given facets");
      return;
    }

    // Most recent period EIA has actually published — used as a fallback
    // (marked estimated) for any newer table month that isn't published yet.
    const latestPeriod = Array.from(ratesByPeriod.keys()).sort().pop();
    const latestRate = ratesByPeriod.get(latestPeriod);

    const currentMonth = firstOfMonth(new Date());

    // rows[0] = newest month (this month), rows[rows.length - 1] = oldest.
    rows.forEach((row, i) => {
      const monthDate = addMonths(currentMonth, -i);
      const key = periodKey(monthDate);
      const label = monthYearLabel(monthDate);

      const published = ratesByPeriod.has(key);
      const rate = published ? ratesByPeriod.get(key) : latestRate;

      setCellText(row, 0, label);
      setCellText(row, 1, formatRate(rate, !published));
    });
  })();
}

// Expose globally so it can be called from an inline <script> tag or console.
if (typeof window !== "undefined") {
  window.updateEIATable = updateEIATable;
}

// Support `import { updateEIATable } from "./update-eia-table.js"` too.
if (typeof module !== "undefined" && module.exports) {
  module.exports = { updateEIATable };
}


window.addEventListener('DOMContentLoaded', e => {
  updateEIATable();
})