@effect-ts/system/_src/Experimental/Stream/_internal/api/splitLines.ts

Effect-TS is a zero dependency set of libraries to write highly productive, purely functional TypeScript at scale.

// ets_tracing: off

import * as CK from "../../../../Collections/Immutable/Chunk/index.js"
import * as Tp from "../../../../Collections/Immutable/Tuple/index.js"
import { pipe } from "../../../../Function/index.js"
import * as O from "../../../../Option/index.js"
import * as CH from "../../Channel/index.js"
import * as C from "../core.js"

/**
 * Splits strings on newlines. Handles both Windows newlines (`\r\n`) and UNIX newlines (`\n`).
 */

export function splitLines<R, E, A>(
  self: C.Stream<R, E, string>
): C.Stream<R, E, string> {
  const next = (
    leftover: O.Option<string>,
    wasSplitCRLF: boolean
  ): CH.Channel<R, E, CK.Chunk<string>, unknown, E, CK.Chunk<string>, any> =>
    CH.readWithCause(
      (incomingChunk) => {
        const buffer = CK.builder<string>()
        let inCRLF = wasSplitCRLF
        let carry = O.getOrElse_(leftover, () => "")

        CK.forEach_(incomingChunk, (string) => {
          const concatenated = carry + string

          if (string.length > 0) {
            const continueFrom =
              inCRLF && carry.length > 0 ? carry.length - 1 : carry.length

            return pipe(
              CK.from(concatenated),
              CK.zipWithIndex,
              CK.drop(continueFrom),
              CK.reduce(
                Tp.tuple(0, false, inCRLF),
                (
                  { tuple: [sliceStart, skipNext, midCRLF] },
                  { tuple: [char, index] }
                ) => {
                  if (skipNext) {
                    return Tp.tuple(sliceStart, false, false)
                  } else {
                    switch (char) {
                      case "\n": {
                        buffer.append(concatenated.slice(sliceStart, index))
                        return Tp.tuple(index + 1, false, midCRLF)
                      }
                      case "\r": {
                        if (
                          index + 1 < concatenated.length &&
                          concatenated[index + 1] === "\n"
                        ) {
                          buffer.append(concatenated.slice(sliceStart, index))
                          return Tp.tuple(index + 2, true, false)
                        } else if (index === concatenated.length - 1) {
                          return Tp.tuple(sliceStart, false, true)
                        } else {
                          return Tp.tuple(index, false, false)
                        }
                      }
                      default: {
                        return Tp.tuple(sliceStart, false, midCRLF)
                      }
                    }
                  }
                }
              ),
              ({ tuple: [sliceStart, _, midCRLF] }) => {
                carry = concatenated.slice(sliceStart)
                inCRLF = midCRLF
              }
            )
          }
        })

        return CH.zipRight_(
          CH.write(buffer.build()),
          next(carry.length > 0 ? O.some(carry) : O.none, inCRLF)
        )
      },
      (halt) =>
        O.fold_(
          leftover,
          () => CH.failCause(halt),
          (value) => CH.zipRight_(CH.write(CK.single(value)), CH.failCause(halt))
        ),
      (done) =>
        O.fold_(
          leftover,
          () => CH.end(done),
          (value) => CH.zipRight_(CH.write(CK.single(value)), CH.end(done))
        )
    )

  return new C.Stream(self.channel[">>>"](next(O.none, false)))
}