import { useState } from 'react';
import { useApp } from '../context/AppContext.js';
import PageShell from '../components/study/PageShell.jsx';
import { bookOptions, makeId, parseBibleChapter } from '../utils/bibleUtils.jsx';
import { parseEpisodeListDocx, parseEpisodePassage } from '../utils/importParsers.js';

export default function ImportPage() {
  const { setCurrentPage, setProject } = useApp();
  const [importBookAbbrev, setImportBookAbbrev] = useState(bookOptions[0].abbrev);
  const importTranslation = 'BSB'; // studies use the Berean Standard Bible
  const [importTitle, setImportTitle] = useState('');
  const [importPreview, setImportPreview] = useState(null); // parsed episode specs, before fetching chapters
  const [importBusy, setImportBusy] = useState(false);
  const [importError, setImportError] = useState('');
  const [templateBusy, setTemplateBusy] = useState(false);

  // The template's Word library is only fetched when someone asks for it.
  const downloadTemplate = async () => {
    setTemplateBusy(true);
    try {
      const { downloadImportTemplate } = await import('../utils/importTemplate.js');
      await downloadImportTemplate();
    } catch {
      setImportError('Couldn’t build the template. Please try again.');
    } finally {
      setTemplateBusy(false);
    }
  };

  const handleImportFileChange = async (file) => {
    setImportPreview(null);
    setImportError('');
    if (!file) return;
    setImportBusy(true);
    try {
      const episodes = await parseEpisodeListDocx(file);
      if (episodes.length === 0) {
        throw new Error('No "Session # / Title / Passage" table found in that document.');
      }
      const specs = episodes.map((ep) => ({ ...ep, parsed: parseEpisodePassage(ep.passage) }));
      setImportPreview(specs);
    } catch (error) {
      setImportError(error.message || 'Failed to read that document.');
    } finally {
      setImportBusy(false);
    }
  };

  const runEpisodeImport = async () => {
    if (!importPreview || importPreview.length === 0) {
      setImportError('Choose a .docx file first.');
      return;
    }
    setImportBusy(true);
    setImportError('');
    try {
      const selectedBook = bookOptions.find((b) => b.abbrev === importBookAbbrev) ?? bookOptions[0];

      const chapterNumbersNeeded = new Set();
      importPreview.forEach((spec) => {
        if (spec.parsed && spec.parsed !== 'invalid') {
          chapterNumbersNeeded.add(spec.parsed.startChapter);
          chapterNumbersNeeded.add(spec.parsed.endChapter);
        }
      });
      const sortedChapters = Array.from(chapterNumbersNeeded).sort((a, b) => a - b);
      if (sortedChapters.length === 0) {
        throw new Error('No verse passages found to import.');
      }

      const versesByChapter = {};
      for (const chNum of sortedChapters) {
        const response = await fetch(
          `https://bible.helloao.org/api/${importTranslation}/${selectedBook.abbrev}/${chNum}.json`,
        );
        if (!response.ok) throw new Error(`Unable to load ${selectedBook.name} ${chNum}.`);
        const data = await response.json();
        const verses = parseBibleChapter(data);
        if (!verses.length) throw new Error(`No verses returned for ${selectedBook.name} ${chNum}.`);
        versesByChapter[chNum] = verses;
      }

      const chapterIndexByNum = new Map(sortedChapters.map((n, idx) => [n, idx]));
      const chapters = sortedChapters.map((chNum) => ({
        book: selectedBook.name,
        bookAbbrev: selectedBook.abbrev,
        chapter: chNum,
        verses: versesByChapter[chNum],
        chunks: [],
      }));

      // Markers (rows with no passage) attach to the nearest upcoming chapter with a
      // real passage, or fall back to the previous one for trailing markers.
      const anchorChapterFor = importPreview.map((spec, i) => {
        if (spec.parsed && spec.parsed !== 'invalid') return spec.parsed.startChapter;
        for (let j = i + 1; j < importPreview.length; j += 1) {
          const next = importPreview[j].parsed;
          if (next && next !== 'invalid') return next.startChapter;
        }
        for (let j = i - 1; j >= 0; j -= 1) {
          const prev = importPreview[j].parsed;
          if (prev && prev !== 'invalid') return prev.startChapter;
        }
        return sortedChapters[0];
      });

      importPreview.forEach((spec, i) => {
        if (spec.parsed === 'invalid') return; // skip unparseable rows entirely
        const chIdx = chapterIndexByNum.get(anchorChapterFor[i]);
        if (chIdx == null) return;
        const target = chapters[chIdx];

        const baseChunk = {
          id: makeId(),
          observation: '',
          interpretation: '',
          application: '',
          crossReferences: [],
          greekWords: [],
          generalNotes: '',
          episodeNumber: spec.episodeNumber,
          episodeTitle: spec.title,
          finalScript: '',
          tags: [],
        };

        if (!spec.parsed) {
          // No passage (e.g. a part intro/review) -> zero-length marker chunk.
          target.chunks.push({ ...baseChunk, startVerse: 0, endVerse: 0, spilloverEndVerse: null });
          return;
        }

        const { startChapter, startVerse, endChapter, endVerse } = spec.parsed;
        if (endChapter === startChapter) {
          target.chunks.push({ ...baseChunk, startVerse, endVerse, spilloverEndVerse: null });
        } else {
          const lastVerseOfStartChapter = versesByChapter[startChapter]?.at(-1)?.number ?? endVerse;
          target.chunks.push({
            ...baseChunk,
            startVerse,
            endVerse: lastVerseOfStartChapter,
            spilloverEndVerse: endVerse,
          });
        }
      });

      const newProject = {
        id: makeId(),
        title: importTitle.trim() || `${selectedBook.name} Sessions`,
        translation: importTranslation,
        lastEdited: Date.now(),
        selectedChunkId: null,
        chapters,
      };
      setProject(newProject);
      setCurrentPage('setup');
    } catch (error) {
      setImportError(error.message || 'Import failed.');
    } finally {
      setImportBusy(false);
    }
  };

  const field = 'mt-1 w-full rounded-xl border border-[var(--r-line)] bg-[var(--r-bg)] px-3 py-2 text-sm text-[var(--r-text)] focus:outline-none focus:ring-2 focus:ring-[var(--r-line)]';

  return (
    <PageShell title="Import Session List" active="studies" onBack={() => setCurrentPage('home')} maxWidth="max-w-3xl">
      <main className="mx-auto max-w-3xl space-y-6 px-4 py-8">
        <section className="space-y-5 rounded-2xl border border-[var(--r-line)] bg-[var(--r-bar)] p-6">
          <div className="space-y-2 rounded-xl bg-[var(--r-bg)] p-4 text-sm text-[var(--r-sub)]">
            <p className="font-medium text-[var(--r-text)]">How this works</p>
            <p>
              This is a shortcut for setting up a multi-part study — a teaching series, sermon series, class
              curriculum, or podcast — all at once, instead of building each chapter and chunk by hand.
            </p>
            <p>
              Upload a .docx containing a table with three columns: session number, title, and passage
              (e.g. <span className="font-mono text-xs">1:1–2</span>). Each row becomes one chunk, grouped
              automatically by chapter. If you don't have a document like this, just use{' '}
              <span className="font-medium text-[var(--r-text)]">+ New Project</span> on the home page instead — this import
              step is entirely optional.
            </p>
            <div className="pt-1">
              <button type="button" onClick={downloadTemplate} disabled={templateBusy}
                className="rounded-full border border-[var(--r-line)] px-4 py-1.5 text-sm font-medium text-[var(--r-text)] transition hover:bg-black/5 disabled:opacity-50">
                {templateBusy ? 'Building…' : 'Download template (.docx)'}
              </button>
              <span className="ml-3 text-xs">A blank session list with example rows to fill in.</span>
            </div>
          </div>

          <div className="grid gap-4 sm:grid-cols-2">
            <label className="block text-sm">Book
              <select value={importBookAbbrev} onChange={(e) => setImportBookAbbrev(e.target.value)} className={field}>
                {bookOptions.map((b) => <option key={b.abbrev} value={b.abbrev}>{b.name}</option>)}
              </select>
            </label>
            <label className="block text-sm">Project title
              <input type="text" value={importTitle} onChange={(e) => setImportTitle(e.target.value)}
                placeholder={`${bookOptions.find((b) => b.abbrev === importBookAbbrev)?.name ?? ''} Sessions`} className={field} />
            </label>
          </div>
          <p className="text-xs text-[var(--r-sub)]">Text: Berean Standard Bible (BSB).</p>

          <label className="block text-sm">Session list (.docx)
            <input type="file" accept=".docx" onChange={(e) => handleImportFileChange(e.target.files?.[0] ?? null)}
              className="mt-1 block w-full text-sm text-[var(--r-sub)] file:mr-4 file:rounded-lg file:border-0 file:bg-[var(--r-text)] file:px-4 file:py-2 file:text-sm file:text-[var(--r-bg)]" />
          </label>

          {importBusy && <p className="text-sm text-[var(--r-sub)]">Working…</p>}
          {importError && <p className="text-sm text-[var(--r-danger,#b42318)]">{importError}</p>}

          {importPreview && !importBusy && (
            <div className="space-y-3">
              <p className="text-sm font-medium">
                {importPreview.length} session{importPreview.length === 1 ? '' : 's'} found
                {' · '}
                {importPreview.filter((s) => s.parsed && s.parsed !== 'invalid').length} with passages
              </p>
              <div className="max-h-80 overflow-y-auto rounded-xl border border-[var(--r-line)]">
                <table className="w-full text-sm">
                  <tbody>
                    {importPreview.map((spec) => (
                      <tr key={spec.episodeNumber} className="border-b border-[var(--r-line)] last:border-0">
                        <td className="px-3 py-1.5 text-[var(--r-sub)]">#{spec.episodeNumber}</td>
                        <td className="px-3 py-1.5">{spec.title}</td>
                        <td className="px-3 py-1.5 text-right text-[var(--r-sub)]">
                          {spec.parsed === 'invalid'
                            ? <span className="text-[var(--r-danger,#b42318)]">unrecognized — skipped</span>
                            : spec.parsed ? spec.passage : <span>marker (no passage)</span>}
                        </td>
                      </tr>
                    ))}
                  </tbody>
                </table>
              </div>
              <button type="button" onClick={runEpisodeImport} disabled={importBusy}
                className="rounded-full bg-[var(--r-accent)] px-6 py-2.5 text-sm font-medium text-[var(--r-on)] hover:opacity-90 disabled:opacity-50">Create Project from Import</button>
            </div>
          )}
        </section>
      </main>
    </PageShell>
  );
}