/**
 * Proofing: the mistakes that matter in a PROCEDURE, not a document.
 *
 * A spellchecker catches "teh". None of these are spelling, and every one has
 * been seen for real:
 *
 *   - a smart quote in a command, so the command does not run
 *   - a checklist item with no text, so a step is silently missing
 *   - a heading with nothing under it, left when a draft was reorganised
 *   - an image with no alt text, invisible to anyone who cannot see it
 *   - a TODO that was never finished, published anyway
 *
 * Warnings, not blocks. A person publishing a guide at 14:40 with one empty
 * bullet should be told, not stopped - the tool does not know that the bullet is
 * deliberate, and a procedure that exists imperfectly beats one nobody wrote.
 */

// Characters an editor or a word processor substitutes silently. In prose they
// are harmless; in a command they are the difference between working and a
// syntax error nobody can explain.
const SMARTCHARS = [
  // Written as escapes, not literals: the repo's style gate forbids non-ASCII in
  // source, and a file whose job is detecting smart quotes cannot contain any.
  // The escapes are also unambiguous in a diff, where a curly quote and a
  // straight one look identical.
  ['\u2018', "'"], ['\u2019', "'"],   // single quotes
  ['\u201C', '"'], ['\u201D', '"'],   // double quotes
  ['\u2013', '-'], ['\u2014', '-'],   // en dash, em dash
  ['\u00A0', ' '],                   // non-breaking space
]

const UNFINISHED = /\b(TODO|TBD|FIXME|XXX|\?\?\?)\b/i

function issue (level, blockid, message, fix) {
  return { level, blockid, message, fix: fix || null }
}

export function proof (guide, blocks) {
  const issues = []

  if (!guide.title || !guide.title.trim()) {
    issues.push(issue('error', null, 'This guide has no title'))
  }
  if (!guide.summary || !guide.summary.trim()) {
    issues.push(issue('warn', null,
      'No summary. It is what people read in the list and in search results.'))
  }
  if (!guide.tags || !guide.tags.trim()) {
    issues.push(issue('warn', null, 'No tags, so this will be hard to find'))
  }
  if (!blocks.length) {
    issues.push(issue('error', null, 'This guide is empty'))
    return issues
  }

  blocks.forEach((block, index) => {
    const where = 'block ' + (index + 1) + ' (' + block.type + ')'

    if (block.type === 'code') {
      // The important one. An autocorrected quote in a command looks right and
      // does not run.
      //
      // Reported ONCE per block, however many offending characters it has: a
      // command with an opening and a closing smart quote is one problem with
      // one fix, and listing it twice makes the panel look like it is nagging.
      const found = SMARTCHARS.filter(([bad]) => (block.text || '').includes(bad))
      if (found.length) {
        issues.push(issue('error', block.id,
          where + ': contains ' + found.map(([, good]) => 'a curly or long ' +
            (good === "'" ? 'quote' : good === '"' ? 'double quote' :
             good === '-' ? 'dash' : 'space')).filter(
              (v, i, a) => a.indexOf(v) === i).join(' and ') +
          ' where a command needs the plain character. Autocorrect does this, ' +
          'and the command will not run.',
          { type: 'replaceAll', pairs: found }))
      }
      if (!(block.text || '').trim()) {
        issues.push(issue('error', block.id, where + ' is empty'))
      }
    } else if (['heading', 'paragraph', 'callout'].includes(block.type)) {
      if (!(block.text || '').trim() && !(block.title || '').trim()) {
        issues.push(issue('warn', block.id, where + ' is empty'))
      }
    }

    if (block.type === 'step' && !(block.title || '').trim()
        && !(block.text || '').trim()) {
      issues.push(issue('warn', block.id, where + ' has no title and no text'))
    }

    if (['checklist', 'bullets', 'numbers'].includes(block.type)) {
      const empties = (block.items || []).filter(
        item => !String(typeof item === 'string' ? item : item.text || '').trim())
      if (empties.length) {
        issues.push(issue('warn', block.id,
          where + ': ' + empties.length + ' empty item' +
          (empties.length > 1 ? 's' : '') +
          '. An empty step reads as a step somebody forgot to write.'))
      }
    }

    if (block.type === 'image' && !(block.alt || '').trim()) {
      issues.push(issue('warn', block.id,
        where + ': no alt text. Anyone who cannot see the image gets nothing.'))
    }

    if (block.type === 'table' && !(block.rows || []).length) {
      issues.push(issue('warn', block.id, where + ' has a header but no rows'))
    }

    const text = [block.text, block.title].filter(Boolean).join(' ')
    if (UNFINISHED.test(text)) {
      issues.push(issue('warn', block.id,
        where + ': still contains ' + text.match(UNFINISHED)[0]))
    }
  })

  // A heading immediately followed by another heading usually means the section
  // under the first one was moved or never written.
  blocks.forEach((block, index) => {
    if (block.type !== 'heading') return
    const next = blocks[index + 1]
    if (!next || next.type === 'heading') {
      issues.push(issue('warn', block.id,
        'Heading "' + (block.text || '').slice(0, 40) + '" has nothing under it'))
    }
  })

  return issues
}

/** Apply a suggested fix in place, for the ones where the answer is obvious. */
export function applyFix (block, fix) {
  if (!fix) return false
  const before = block.text || ''
  let after = before
  if (fix.type === 'replaceAll') {
    for (const [bad, good] of fix.pairs) after = after.split(bad).join(good)
  } else if (fix.type === 'replace') {
    after = after.split(fix.from).join(fix.to)
  }
  if (after === before) return false
  block.text = after
  return true
}