(function () {
  if (window.__fc_addsource_injected) return;
  window.__fc_addsource_injected = true;

  // Cached probe result for the current URL so click-handlers know which
  // action to dispatch without round-tripping again.
  let currentProbe = null;

  evaluate();

  const reEval = () => evaluate();
  window.addEventListener('popstate', reEval);
  const origPush = history.pushState;
  history.pushState = function () { origPush.apply(this, arguments); reEval(); };

  async function evaluate() {
    const url = window.location.href;
    const platform = getPlatformFromUrl(url);
    const onArtist = platform && isArtistPage(url, platform);
    const btn = document.getElementById('fc-add-source-btn');
    if (!onArtist) {
      if (btn) btn.remove();
      currentProbe = null;
      return;
    }
    // On artist pages, ask the backend what state the URL is in BEFORE
    // injecting the button — so the chip can render the right state on
    // first paint instead of flashing the generic "Add" copy and
    // updating afterwards.
    let probe;
    try {
      probe = await browser.runtime.sendMessage({ type: 'PROBE_SOURCE', url });
    } catch (e) {
      probe = { error: e?.message || 'probe failed' };
    }
    currentProbe = probe;
    if (probe?.state === 'unknown_platform') {
      if (btn) btn.remove();
      return;
    }
    renderButton(probe);
  }

  function renderButton(probe) {
    let btn = document.getElementById('fc-add-source-btn');
    if (!btn) {
      btn = document.createElement('button');
      btn.id = 'fc-add-source-btn';
      btn.addEventListener('click', onClick);
      document.body.appendChild(btn);
    }
    // Reset state classes so re-renders (SPA navigation) don't stack.
    btn.className = 'fc-add-source-btn';
    btn.classList.add(`fc-add-source-btn--${stateModifier(probe)}`);
    btn.textContent = labelFor(probe);
    btn.disabled = false;
  }

  function stateModifier(probe) {
    if (!probe || probe.error) return 'new';
    return ({
      source_match: 'source-match',
      artist_match: 'artist-match',
      new: 'new',
    })[probe.state] || 'new';
  }

  function labelFor(probe) {
    if (!probe || probe.error) return '+ Add to FabledCurator';
    const platformName = platformDisplayName(probe.platform);
    const artistName = probe.artist?.name;
    switch (probe.state) {
      case 'source_match':
        return `✓ In FabledCurator · ${platformName}`;
      case 'artist_match':
        return `+ Add ${platformName} source to ${artistName || 'artist'}`;
      case 'new':
      default:
        return '+ Add to FabledCurator';
    }
  }

  function platformDisplayName(key) {
    return PLATFORMS[key]?.name || key || '';
  }

  async function onClick() {
    const btn = document.getElementById('fc-add-source-btn');
    if (!btn) return;
    btn.disabled = true;
    const original = btn.textContent;
    const probe = currentProbe;

    if (probe?.state === 'source_match') {
      btn.textContent = 'Opening…';
      try {
        const r = await browser.runtime.sendMessage({
          type: 'OPEN_ARTIST_PAGE',
          slug: probe.artist?.slug,
        });
        if (r?.error) showToast(`Error: ${r.error}`, 'error');
      } catch (e) {
        showToast(`Error: ${e.message}`, 'error');
      } finally {
        btn.disabled = false;
        btn.textContent = original;
      }
      return;
    }

    btn.textContent = 'Adding…';
    try {
      const r = await browser.runtime.sendMessage({
        type: 'ADD_AS_SOURCE',
        url: window.location.href,
      });
      if (r?.error) {
        showToast(`Error: ${r.error}`, 'error');
      } else {
        const verb = r.created_source ? 'Added' : 'Already a source for';
        showToast(`${verb} ${r.artist?.name || 'artist'} (${r.source?.platform || ''})`, 'success');
        // Re-probe so the chip flips green without waiting for the next
        // navigation.
        evaluate();
        return;
      }
    } catch (e) {
      showToast(`Error: ${e.message}`, 'error');
    } finally {
      btn.disabled = false;
      btn.textContent = original;
    }
  }

  function showToast(text, kind) {
    const t = document.createElement('div');
    t.className = `fc-toast fc-toast--${kind}`;
    t.textContent = text;
    document.body.appendChild(t);
    setTimeout(() => t.remove(), 4000);
  }
})();