// What must be true of the content layer before a page is built from it.
//
// ## Why this exists
//
// `src/data/*.js` is prose in a data structure, and nothing checked it. A
// misspelt block type, a link to a route that does not exist, a section whose
// answer paragraph is missing, a missing `benefits` list that crashes the
// prerender with `Cannot read properties of undefined`: each was found by a
// person looking at a page, or not found at all.
//
// The long-form service pages made that worse in a specific way. Their copy is
// owner-approved and arrives as a markdown sheet that MIXES DIRECTIONS TO THE
// WEBSITE MANAGER INTO THE COPY: "Do not promise that every number is always
// portable", "Keep this factual:", "Place an official screenshot". Those lines
// look exactly like copy. Publishing one puts an internal instruction on a
// customer-facing page, and no build step would have noticed.
//
// So this refuses to build rather than publish. It runs inside prerender.js,
// before any page renders, which means every `npm run build` enforces it: the
// pre-commit hook, `npm run verify`, and the Docker image build.
//
// Exit codes for the runner: 0 clean, 1 findings, 2 nothing was checked.
import { existsSync } from 'fs'
import path from 'path'
import { fileURLToPath } from 'url'
import { ROUTES } from './routes.js'

const publicDir = path.join(path.dirname(fileURLToPath(import.meta.url)), '../../public')

// A block type, and the field it cannot be missing.
const BLOCK_FIELDS = {
  p: 'text',
  h3: 'text',
  ul: 'items',
  ol: 'items',
  callout: 'text',
  image: 'alt',
  links: 'items',
}

const ID_SHAPE = /^[a-z][a-z0-9]*(-[a-z0-9]+)*$/
// Ids already used by the layout. A section id that collides with one of these
// makes `#contact-form` scroll to the wrong element.
const RESERVED_IDS = new Set(['contact-form', 'mobile-nav-content', 'support-portal', 'root'])

// Directions to the website manager, which the sheets mix into their copy.
const SHEET_DIRECTIONS = [
  /website manager/i,
  /not for the (public )?webpage/i,
  /place an official/i,
  /do not add faq/i,
  /this section is (important|highly useful)/i,
  /\bQ\d+:/,
  /approved visual/i,
  /suggested (alt text|caption)/i,
  /before publication/i,
  /avoid (unsupported|promising|implying)/i,
  /link naturally to/i,
  /keep this factual/i,
  /factual differentiators/i,
  /reliability wording/i,
  /^direct[- ]answer/i,
]

// Markdown that would print literally on the page, and characters that must not
// reach it. React escapes text, so pasted markup shows up as itself.
const TEXT_FAULTS = [
  [/—/, 'an em dash (U+2014), which Null asked for nowhere in site copy'],
  [/�/, 'a U+FFFD replacement character, so the source was decoded with the wrong encoding'],
  [/\*\*/, 'markdown bold markers'],
  [/`/, 'a backtick'],
  [/\]\(/, 'a markdown link'],
  [/<\/?[a-z][^>]*>/i, 'an HTML tag'],
]

export const validateContent = ({ services, industries }) => {
  const errors = []
  const warnings = []
  let checked = 0

  const fail = (where, detail) => errors.push(`${where}: ${detail}`)

  // Every string that reaches a page, wherever it sits in the tree.
  const checkText = (where, value) => {
    if (typeof value !== 'string') return
    checked += 1
    for (const [pattern, detail] of TEXT_FAULTS) {
      if (pattern.test(value)) fail(where, `${detail} in ${JSON.stringify(value.slice(0, 60))}`)
    }
    for (const pattern of SHEET_DIRECTIONS) {
      if (pattern.test(value)) {
        fail(where, `reads as a direction to the website manager, not page copy: ${JSON.stringify(value.slice(0, 80))}`)
        break
      }
    }
  }

  const checkLink = (where, to, ownIds) => {
    checked += 1
    if (typeof to !== 'string' || !to) return fail(where, 'link has no destination')
    const [route, fragment] = to.split('#')
    if (route && !ROUTES.includes(route)) fail(where, `links to ${route}, which is not a route this site serves`)
    if (fragment && !route && !ownIds.has(fragment) && !RESERVED_IDS.has(fragment)) {
      fail(where, `links to #${fragment}, which is not a section on this page`)
    }
  }

  const checkBlocks = (where, section, ownIds) => {
    const blocks = section.blocks
    if (!Array.isArray(blocks) || blocks.length === 0) return fail(where, 'has no blocks')

    blocks.forEach((block, index) => {
      const at = `${where} blocks[${index}]`
      const field = BLOCK_FIELDS[block?.type]
      if (!field) {
        return fail(at, `unknown block type ${JSON.stringify(block?.type)}. Known types: ${Object.keys(BLOCK_FIELDS).join(', ')}`)
      }
      if (block[field] == null) return fail(at, `a ${block.type} block has no ${field}`)
      checked += 1

      if (block.type === 'p') {
        if (Array.isArray(block.text)) {
          block.text.forEach((part, i) => {
            if (typeof part === 'string') checkText(`${at}.text[${i}]`, part)
            else {
              checkText(`${at}.text[${i}].text`, part?.text)
              checkLink(`${at}.text[${i}]`, part?.to, ownIds)
            }
          })
        } else checkText(`${at}.text`, block.text)
      } else if (block.type === 'ul' || block.type === 'ol') {
        if (!Array.isArray(block.items) || !block.items.length) fail(at, 'a list with no items')
        block.items?.forEach((item, i) => {
          if (typeof item === 'string') checkText(`${at}.items[${i}]`, item)
          else {
            checkText(`${at}.items[${i}].text`, item?.text)
            checkText(`${at}.items[${i}].detail`, item?.detail)
            if (item?.text == null) fail(`${at}.items[${i}]`, 'a step with no text')
          }
        })
      } else if (block.type === 'links') {
        block.items?.forEach((item, i) => {
          checkText(`${at}.items[${i}].label`, item?.label)
          checkLink(`${at}.items[${i}]`, item?.to, ownIds)
        })
      } else if (block.type === 'image') {
        checkText(`${at}.alt`, block.alt)
        checkText(`${at}.caption`, block.caption)
        if (!block.alt) fail(at, 'an image with no alt text')
        // A slot waiting for a file the owner has to supply carries src: null and
        // renders nothing. A src that IS set must point at a file that exists,
        // or the page ships a broken image nobody sees until a visitor does.
        if (block.src) {
          if (!block.src.startsWith('/') || block.src.includes('..')) {
            fail(at, `image src ${JSON.stringify(block.src)} must be a site-absolute path under public/`)
          } else if (!existsSync(path.join(publicDir, block.src.replace(/^\//, '')))) {
            fail(at, `image src ${JSON.stringify(block.src)} does not exist under public/`)
          }
          if (!block.width || !block.height) fail(at, 'an image with a src needs width and height, or the page shifts as it loads')
        }
      } else {
        checkText(`${at}.text`, block.text)
      }
    })

    // The opening block decides whether an answer engine can quote the section.
    const first = blocks[0]?.type
    if (section.kind === 'faq') {
      blocks.forEach((block, index) => {
        if (block.type !== 'h3') return
        if (blocks[index + 1]?.type !== 'p') fail(`${where} blocks[${index}]`, 'a FAQ question with no answer paragraph after it')
      })
      if (first !== 'h3') fail(where, 'a FAQ section must open with its first question')
    } else if (section.kind === 'list') {
      if (first !== 'ul' && first !== 'ol') fail(where, "kind 'list' says the section opens with a list, and it does not")
    } else if (first !== 'p') {
      fail(where, `opens with a ${first} block. A section opens with its direct answer, which is what a search result or an AI answer quotes. Use kind 'list' when the approved copy genuinely has no answer paragraph.`)
    }
  }

  const checkPage = (where, page) => {
    const ownIds = new Set((page.sections || []).map((section) => section.id))

    if (!page.seo?.title) fail(`${where}.page.seo`, 'no title')
    if (!page.seo?.description) fail(`${where}.page.seo`, 'no description')
    checkText(`${where}.page.seo.title`, page.seo?.title)
    checkText(`${where}.page.seo.description`, page.seo?.description)
    if (page.seo?.description && page.seo.description.length > 160) {
      warnings.push(
        `${where}.page.seo.description is ${page.seo.description.length} characters. Search results show about 155 to 160, so the tail may not be seen. Owner-approved copy is published as written.`,
      )
    }

    for (const field of ['h1', 'subheading']) {
      if (!page.hero?.[field]) fail(`${where}.page.hero`, `no ${field}`)
      checkText(`${where}.page.hero.${field}`, page.hero?.[field])
    }
    if (!Array.isArray(page.hero?.intro) || !page.hero.intro.length) fail(`${where}.page.hero`, 'no intro copy')
    page.hero?.intro?.forEach((text, i) => checkText(`${where}.page.hero.intro[${i}]`, text))

    for (const cta of ['primaryCta', 'secondaryCta']) {
      const value = page.hero?.[cta]
      if (!value) {
        if (cta === 'primaryCta') fail(`${where}.page.hero`, 'no primaryCta')
        continue
      }
      checkText(`${where}.page.hero.${cta}.label`, value.label)
      checkLink(`${where}.page.hero.${cta}`, value.to, ownIds)
    }

    if (!Array.isArray(page.sections) || !page.sections.length) return fail(`${where}.page`, 'no sections')

    const seen = new Set()
    page.sections.forEach((section, index) => {
      const at = `${where}.page.sections[${index}]${section?.id ? ` (${section.id})` : ''}`
      if (!ID_SHAPE.test(section?.id || '')) {
        fail(at, `id ${JSON.stringify(section?.id)} must be lowercase, start with a letter and join words with single hyphens. An id starting with a digit cannot be used as a CSS selector`)
      }
      if (RESERVED_IDS.has(section?.id)) fail(at, `id ${JSON.stringify(section.id)} is already used by the page layout`)
      if (seen.has(section?.id)) fail(at, `id ${JSON.stringify(section.id)} appears twice on this page`)
      seen.add(section?.id)
      if (!section?.title) fail(at, 'no title')
      checkText(`${at}.title`, section?.title)
      checkBlocks(at, section, ownIds)
    })

    page.related?.forEach((link, i) => {
      checkText(`${where}.page.related[${i}].label`, link?.label)
      checkLink(`${where}.page.related[${i}]`, link?.to, ownIds)
    })
  }

  for (const service of services || []) {
    const where = `services/${service?.id}`
    for (const field of ['id', 'name', 'shortDesc', 'homeDesc', 'icon']) {
      if (!service?.[field]) fail(where, `no ${field}`)
    }
    checkText(`${where}.shortDesc`, service.shortDesc)
    checkText(`${where}.homeDesc`, service.homeDesc)

    if (service.page) checkPage(where, service.page)
    else {
      // The layout used by every service without long-form copy maps these with
      // no guard, so a missing one is a build crash with no useful message.
      if (!service.fullDesc) fail(where, 'no fullDesc, and no page copy either')
      for (const field of ['benefits', 'idealFor']) {
        if (!Array.isArray(service[field]) || !service[field].length) fail(where, `no ${field}, which the service layout maps without checking`)
      }
      checkText(`${where}.fullDesc`, service.fullDesc)
    }
    // Every service is a card on the Services index, which shows idealFor[0].
    if (!Array.isArray(service.idealFor) || !service.idealFor.length) {
      fail(where, 'no idealFor. The Services index prints idealFor[0] as "Best fit"')
    }
    service.related?.forEach((link, i) => {
      checkText(`${where}.related[${i}].label`, link?.label)
      checkLink(`${where}.related[${i}]`, link?.to, new Set())
    })
  }

  for (const industry of industries || []) {
    const where = `industries/${industry?.id}`
    for (const field of ['id', 'name', 'shortDesc', 'fullDesc', 'icon']) {
      if (!industry?.[field]) fail(where, `no ${field}`)
    }
    for (const field of ['painPoints', 'solutions']) {
      if (!Array.isArray(industry?.[field]) || !industry[field].length) fail(where, `no ${field}, which the industry layout maps without checking`)
    }
    checkText(`${where}.shortDesc`, industry?.shortDesc)
    checkText(`${where}.fullDesc`, industry?.fullDesc)
    industry?.related?.forEach((link, i) => {
      checkText(`${where}.related[${i}].label`, link?.label)
      checkLink(`${where}.related[${i}]`, link?.to, new Set())
    })
  }

  return { errors, warnings, checked }
}