/* =====================================================================
   Importer — an existing exercise sheet → the document model.

   Lets you start from a finished sheet rather than a blank page, and
   doubles as the proof that the model covers everything the sheet uses:
   import → render → import again must reach a fixed point.

   Takes a DOM. In the browser that is DOMParser; the test harness feeds
   it an equivalent.
   ===================================================================== */

import { uid } from './model.js';
import { serialise } from './inline.js';

const text = (el) => serialise(el.innerHTML);

/** "BI122G · Long course name · Autumn 2026" back into its three fields. */
function splitEyebrow(line) {
  const bits = String(line).split('·').map((s) => s.trim()).filter(Boolean);
  if (bits.length >= 3) {
    return { courseCode: bits[0], courseName: bits.slice(1, -1).join(' · '), term: bits[bits.length - 1] };
  }
  return { courseCode: bits[0] || '', courseName: bits[1] || '', term: '' };
}

function slug(s, used) {
  let base = (s || 'part').toLowerCase().replace(/[^a-z0-9]+/g, '-')
    .replace(/^-|-$/g, '').split('-').slice(0, 3).join('-') || 'part';
  let out = base, n = 2;
  while (used.has(out)) out = `${base}-${n++}`;
  used.add(out);
  return out;
}

/* ---------- blocks ---------- */

function readBlock(el) {
  const cls = el.classList;

  if (el.tagName === 'P' && !cls.contains('said') && !cls.contains('standfirst')) {
    const variant = cls.contains('note') ? 'note' : null;
    return { id: uid('p'), kind: 'prose', text: text(el), variant };
  }
  if (cls.contains('cmd')) {
    return { id: uid('c'), kind: 'cmd', command: el.textContent.trim() };
  }
  if (cls.contains('term')) return readTerminal(el);
  if (cls.contains('protip')) return readProtip(el);
  if (cls.contains('tablewrap')) return readTable(el);
  if (cls.contains('note')) {
    return { id: uid('n'), kind: 'note', children: readChildren(el) };
  }
  if (cls.contains('callout')) {
    const h = el.querySelector('h3');
    return {
      id: uid('k'), kind: 'callout',
      heading: h ? text(h) : '',
      children: readChildren(el, (c) => c !== h),
    };
  }
  if (cls.contains('side-quest')) {
    const sum = el.querySelector('summary');
    return {
      id: uid('s'), kind: 'sidequest',
      summary: sum ? text(sum) : '',
      children: readChildren(el, (c) => c !== sum),
    };
  }
  if (el.tagName === 'UL' && cls.contains('plain')) {
    return {
      id: uid('u'), kind: 'list',
      items: [...el.querySelectorAll('li')].map(text),
    };
  }
  // a task list flattens into its steps: the <ol> is regenerated on render
  if (el.tagName === 'OL' && cls.contains('tasks')) {
    return [...el.querySelectorAll(':scope > li')].map((li) => ({
      id: uid('i'), kind: 'task', children: readChildren(li),
    }));
  }
  return null;                                   // decoration, skip
}

function readChildren(el, keep = () => true) {
  return [...el.children]
    .filter(keep)
    .flatMap((c) => readBlock(c) || [])   // a task list yields several nodes
    .filter(Boolean);
}

function readTerminal(el) {
  const capEl = el.querySelector('.cap');
  const caption = capEl ? capEl.textContent.trim() : '';

  // reading must never alter the document it reads, so the caption is
  // stripped from a copy of the markup rather than removed from the DOM
  const inner = el.innerHTML.replace(/<span class="cap">[\s\S]*?<\/span>/, '');

  // split into lines, then each line into typed segments plus the plain
  // text between them — transcripts mix roles freely on a single line
  const lines = inner.split('\n').map((raw) => {
    const segments = [];
    const re = /<span class="([pceo])">(.*?)<\/span>/gs;
    let at = 0, m;
    while ((m = re.exec(raw)) !== null) {
      if (m.index > at) {
        const between = decode(raw.slice(at, m.index));
        if (between) segments.push({ role: null, text: between });
      }
      segments.push({ role: m[1], text: decode(m[2]) });
      at = m.index + m[0].length;
    }
    if (at < raw.length) {
      const tail = decode(raw.slice(at));
      if (tail) segments.push({ role: null, text: tail });
    }
    return segments;
  }).filter((segs) => segs.length);

  return { id: uid('m'), kind: 'terminal', caption, lines };
}

function decode(s) {
  return s.replace(/<[^>]+>/g, '')
    .replace(/&(amp|lt|gt|quot|#39);/g,
      (m) => ({ '&amp;': '&', '&lt;': '<', '&gt;': '>', '&quot;': '"', '&#39;': "'" }[m]));
}

function readProtip(el) {
  const said = el.querySelector('.said');
  const b = said && said.querySelector('b');
  const label = b ? b.textContent.trim() : 'Protip';
  const body = said ? said.innerHTML.replace(/^\s*<b>[\s\S]*?<\/b>\s*/, '') : '';
  return {
    id: uid('r'), kind: 'protip',
    keys: [...el.querySelectorAll('.keys kbd')].map((k) => k.textContent.trim()),
    label,
    text: serialise(body),
    emphasis: el.classList.contains('headline'),
  };
}

function readTable(el) {
  const head = [...el.querySelectorAll('thead th')].map(text);
  const rows = [...el.querySelectorAll('tbody tr')]
    .map((tr) => [...tr.children].map(text));
  return {
    id: uid('b'), kind: 'table',
    columns: head.length ? head : new Array(rows[0] ? rows[0].length : 2).fill(''),
    rows,
  };
}

/* ---------- whole document ---------- */

export function importSheet(doc) {
  const sheet = doc.querySelector('.sheet');
  if (!sheet) throw new Error('no .sheet in that file');

  const grab = (sel, fn, fallback = '') => {
    const el = sheet.querySelector(sel);
    return el ? fn(el) : fallback;
  };

  const h1 = sheet.querySelector('h1');
  const [exercise, title] = h1
    ? h1.innerHTML.split(/<br\s*\/?>/).map((s) => serialise(s))
    : ['Exercise', 'Untitled'];

  const out = {
    meta: {
      ...splitEyebrow(grab('.eyebrow', (e) => e.textContent.trim())),
      exercise, title,
      standfirst: grab('.standfirst', text),
      logo: grab('.logo', (e) => e.getAttribute('src')),
      legendText: {},
    },
    intro: [],
    parts: [],
    closing: [],
  };

  const legendEl = sheet.querySelector('.legend');
  if (legendEl) {
    const card = (c) => {
      const el = legendEl.querySelector('.' + c);
      if (!el) return '';
      return el.innerHTML
        .replace(/^\s*<b>[\s\S]*?<\/b>\s*/, '')
        .trim()
        .replace(/\s+/g, ' ');
    };
    out.meta.legendText = { core: card('l-core'), side: card('l-side'), protip: card('l-protip') };
  }

  // everything between the masthead and the first part is the intro
  for (const el of [...sheet.children]) {
    if (el.tagName === 'HEADER') continue;
    if (el.classList.contains('legend')) { out.intro.push({ id: uid('l'), kind: 'legend' }); continue; }
    if (el.classList.contains('part')) break;
    const b = readBlock(el);
    if (b) out.intro.push(b);
  }

  const used = new Set();
  sheet.querySelectorAll(':scope > .part').forEach((el) => {
    const h2 = el.querySelector('.body > h2');
    const heading = h2 ? text(h2) : '';
    out.parts.push({
      id: slug(heading, used),
      kind: 'part',
      track: el.classList.contains('is-side') ? 'side' : 'core',
      title: heading,
      children: readChildren(el.querySelector('.body'), (c) => c !== h2),
    });
  });

  const closing = sheet.querySelector('.closing');
  if (closing) {
    [...closing.children].forEach((el) => {
      if (el.classList.contains('colophon')) return;
      if (el.tagName === 'H2') {
        out.closing.push({ id: uid('h'), kind: 'heading', text: text(el) });
        return;
      }
      const b = readBlock(el);
      if (b) out.closing.push(b);
    });
  }

  return out;
}