/** Shared helpers for drive-resident /bin scripts (prepended before each command). */
function bareStdin(ctx) {
  return typeof ctx.shellStdin === 'string' ? ctx.shellStdin : ''
}

/**
 * Subset of POSIX/GNU grep behavior using JavaScript RegExp / string search.
 * Not bit-identical to GNU grep (no PCRE, different escaping, UTF-16 strings).
 */
async function run(ctx, argv) {
  const vfs = ctx.vfs
  const patterns = []
  const patternFiles = []
  let fixed = false
  let icase = false
  let invert = false
  let numbers = false
  let countOnly = false
  let listFiles = false
  let quiet = false
  let suppressErrors = false
  let forceFilename = false
  let noFilename = false

  const args = argv.slice(1)
  let i = 0

  function usage() {
    ctx.console.error(
      'usage: grep [-E|-F] [-i] [-v] [-n] [-c] [-l] [-q] [-s] [-H|-h] [-e pat] ... [-f file] ... [pattern] [file...]'
    )
    ctx.exitCode = 2
  }

  while (i < args.length) {
    const a = args[i]
    if (a === '--') {
      i++
      break
    }
    if (a === '-' || !a.startsWith('-')) break

    if (a.startsWith('--')) {
      ctx.console.error('grep: unknown option ' + a)
      ctx.exitCode = 2
      return
    }

    if (a === '-e') {
      if (i + 1 >= args.length) {
        usage()
        return
      }
      patterns.push(args[++i])
      i++
      continue
    }
    if (a.startsWith('-e') && a.length > 2) {
      patterns.push(a.slice(2))
      i++
      continue
    }
    if (a === '-f') {
      if (i + 1 >= args.length) {
        usage()
        return
      }
      patternFiles.push(args[++i])
      i++
      continue
    }
    if (a.startsWith('-f') && a.length > 2) {
      patternFiles.push(a.slice(2))
      i++
      continue
    }

    const rest = a.slice(1)
    for (let j = 0; j < rest.length; j++) {
      const c = rest[j]
      switch (c) {
        case 'E':
          /* Accepted for GNU compatibility; patterns use JS RegExp (ERE-like). */
          break
        case 'F':
          fixed = true
          break
        case 'i':
          icase = true
          break
        case 'v':
          invert = true
          break
        case 'n':
          numbers = true
          break
        case 'c':
          countOnly = true
          break
        case 'l':
          listFiles = true
          break
        case 'q':
          quiet = true
          break
        case 's':
          suppressErrors = true
          break
        case 'H':
          forceFilename = true
          break
        case 'h':
          noFilename = true
          break
        default:
          ctx.console.error('grep: invalid option -- ' + c)
          ctx.exitCode = 2
          return
      }
    }
    i++
  }

  for (const pf of patternFiles) {
    try {
      const buf = await vfs.readFile(pf)
      if (!buf) {
        if (!suppressErrors) ctx.console.error('grep: ' + pf + ': No such file')
        ctx.exitCode = 2
        return
      }
      const t = ctx.b4a.toString(buf)
      for (const line of t.split(/\r?\n/)) {
        const s = line.trimEnd()
        if (s === '' || s.startsWith('#')) continue
        patterns.push(s)
      }
    } catch (e) {
      if (!suppressErrors)
        ctx.console.error('grep: ' + pf + ': ' + (e.message || e))
      ctx.exitCode = 2
      return
    }
  }

  const rest = args.slice(i)
  if (patterns.length === 0) {
    if (rest.length === 0) {
      usage()
      return
    }
    patterns.push(rest.shift())
  }

  const fileArgs = rest
  const useStdin = fileArgs.length === 0
  const inputs = useStdin
    ? [{ label: null, path: null }]
    : fileArgs.map((p) => ({ label: p, path: p }))

  let matchers
  try {
    matchers = buildMatchers(patterns, { fixed, icase })
  } catch (e) {
    ctx.console.error('grep: ' + (e.message || e))
    ctx.exitCode = 2
    return
  }

  const multiFile = inputs.length > 1
  const showName =
    !noFilename && (multiFile || forceFilename || (useStdin && forceFilename))

  let anyMatch = false
  let fatal = false

  for (const { label, path } of inputs) {
    let text
    if (path == null) {
      text = bareStdin(ctx)
    } else {
      try {
        const buf = await vfs.readFile(path)
        if (!buf) {
          if (!suppressErrors)
            ctx.console.error('grep: ' + path + ': No such file')
          fatal = true
          continue
        }
        text = ctx.b4a.toString(buf)
      } catch (e) {
        if (!suppressErrors)
          ctx.console.error('grep: ' + path + ': ' + (e.message || e))
        fatal = true
        continue
      }
    }

    const lines = splitLines(text)
    let count = 0
    let fileMatched = false
    const out = []

    for (let li = 0; li < lines.length; li++) {
      const line = stripCr(lines[li])
      const lineNum = li + 1
      const matched = matchers.some((fn) => fn(line))
      const hit = invert ? !matched : matched
      if (hit) {
        fileMatched = true
        anyMatch = true
        count++
        if (!quiet && !countOnly && !listFiles) {
          let chunk = line
          if (numbers) chunk = lineNum + ':' + chunk
          if (showName && label != null) chunk = label + ':' + chunk
          else if (showName && label == null && useStdin)
            chunk = '(standard input):' + chunk
          out.push(chunk)
        }
      }
    }

    if (quiet) continue

    if (listFiles && countOnly) {
      if (fileMatched) {
        const prefix = namePrefixForCount(showName, label, useStdin, multiFile)
        ctx.console.log(prefix + count)
      }
    } else if (listFiles) {
      if (fileMatched) {
        if (label != null) ctx.console.log(label)
        else if (useStdin) ctx.console.log('(standard input)')
      }
    } else if (countOnly) {
      const prefix = namePrefixForCount(showName, label, useStdin, multiFile)
      ctx.console.log(prefix + count)
    } else {
      for (const o of out) ctx.console.log(o)
    }
  }

  if (fatal) ctx.exitCode = 2
  else ctx.exitCode = anyMatch ? 0 : 1
}

/**
 * @param {string[]} patterns
 * @param {{ fixed: boolean, icase: boolean }} o
 */
function buildMatchers(patterns, o) {
  if (patterns.length === 0) throw new Error('no pattern')
  if (o.fixed) {
    const pats = o.icase
      ? patterns.map((p) => p.toLowerCase())
      : patterns.slice()
    return pats.map(
      (p) => (line) =>
        o.icase ? line.toLowerCase().includes(p) : line.includes(p)
    )
  }
  const flags = o.icase ? 'i' : ''
  return patterns.map((p) => {
    try {
      const re = new RegExp(p, flags)
      return (line) => re.test(line)
    } catch (e) {
      throw new Error('invalid regex: ' + (e.message || e))
    }
  })
}

/** @param {string} text */
function splitLines(text) {
  if (text === '') return ['']
  return text.split(/\n/)
}

/** @param {string} line */
function stripCr(line) {
  return line.endsWith('\r') ? line.slice(0, -1) : line
}

/**
 * @param {boolean} showName
 * @param {string | null} label
 * @param {boolean} useStdin
 * @param {boolean} multiFile
 */
function namePrefixForCount(showName, label, useStdin, multiFile) {
  const need = multiFile || (showName && (label != null || useStdin))
  if (!need) return ''
  if (label != null) return label + ':'
  return '(standard input):'
}