export const LOC_BLOCK_START = '<!-- orca-pr-loc -->'
export const LOC_BLOCK_END = '<!-- /orca-pr-loc -->'
export const LOC_HANDS_OFF_COMMENT =
  '<!-- Generated by the "PR test LoC" GitHub Action and rewritten on every push. Humans and AI agents: do not edit, move, or remove this block when updating the PR body. -->'

// __-wrapped segments unambiguously mark test data; bare fixtures/ could be production, and this classifier bills every PR.
const TEST_DIR_SEGMENT = /(?:^|\/)(?:__tests__|__fixtures__|__snapshots__|e2e|tests)(?:\/|$)/i
const TEST_FILENAME = /\.(?:test|spec|e2e)\.[^/]+$/i

export function isTestPath(path) {
  const normalized = path.replaceAll('\\', '/')
  return TEST_DIR_SEGMENT.test(normalized) || TEST_FILENAME.test(normalized)
}

export function emptyLocTotals() {
  return {
    test: { files: 0, added: 0, deleted: 0 },
    nonTest: { files: 0, added: 0, deleted: 0 }
  }
}

export function sumChangedFiles(files) {
  const totals = emptyLocTotals()
  for (const file of files) {
    const path = file.filename
    if (path == null) {
      continue
    }
    const bucket = isTestPath(path) ? totals.test : totals.nonTest
    bucket.files += 1
    bucket.added += Number(file.additions ?? 0)
    bucket.deleted += Number(file.deletions ?? 0)
  }
  return totals
}

const COLOR_ADDED = '#1a7f37'
const COLOR_DELETED = '#cf222e'

function diffCell(count) {
  if (count === 0) {
    return '0'
  }
  if (count > 0) {
    return `$\\color{${COLOR_ADDED}}{\\Huge{\\mathbf{+}}}$\u200b${count}`
  }
  return `$\\color{${COLOR_DELETED}}{\\Huge{\\mathbf{−}}}$\u200b${Math.abs(count)}`
}

function locTableRow(label, bucket) {
  const added = bucket.added ?? 0
  const deleted = bucket.deleted ?? 0
  return `| ${label} | ${bucket.files ?? 0} | ${diffCell(added)} | ${diffCell(-deleted)} | ${diffCell(added - deleted)} |`
}

export function formatLocTable({ test, nonTest }) {
  return [
    '| | Files | Added | Deleted | Net |',
    '| :--- | ---: | ---: | ---: | ---: |',
    locTableRow('Test', test),
    locTableRow('Prod', nonTest)
  ].join('\n')
}

export function renderLocBlock(totals) {
  return [
    LOC_BLOCK_START,
    LOC_HANDS_OFF_COMMENT,
    '',
    formatLocTable(totals),
    '',
    LOC_BLOCK_END
  ].join('\n')
}

function stripLocBlock(body) {
  const start = body.indexOf(LOC_BLOCK_START)
  const end = body.indexOf(LOC_BLOCK_END)
  if (start === -1 || end === -1 || end < start) {
    return body
  }
  const before = body.slice(0, start).trimEnd()
  const after = body.slice(end + LOC_BLOCK_END.length).trimStart()
  return before.length > 0 && after.length > 0 ? `${before}\n\n${after}` : before || after
}

const ELI5_HEADING = /^(#{1,6})[ \t]*ELI5\b.*$/im

// Index of the heading that ends the ELI5 section, or -1 when absent or it runs to the end.
function eli5SectionEnd(body) {
  const heading = ELI5_HEADING.exec(body)
  if (heading == null) {
    return -1
  }
  const level = heading[1].length
  const sectionStart = heading.index + heading[0].length
  const nextHeading = new RegExp(`^#{1,${level}}[ \\t]`, 'm').exec(body.slice(sectionStart))
  return nextHeading == null ? -1 : sectionStart + nextHeading.index
}

// Slack/GitHub link unfurls show the start of the body, so the table goes after ELI5 (or at the end), never first.
export function mergeLocBlock(body, totals) {
  const block = renderLocBlock(totals)
  const rest = stripLocBlock(body ?? '')

  if (rest.trim().length === 0) {
    return `${block}\n`
  }

  const insertAt = eli5SectionEnd(rest)
  if (insertAt === -1) {
    return `${rest.trimEnd()}\n\n${block}\n`
  }
  return `${rest.slice(0, insertAt).trimEnd()}\n\n${block}\n\n${rest.slice(insertAt)}`
}