hermes-agent/ui-tui/packages/hermes-ink/src/utils/sliceAnsi.ts

import { type AnsiCode, ansiCodesToString, reduceAnsiCodes, tokenize, undoAnsiCodes } from '@alcalzone/ansi-tokenize'

import { stringWidth } from '../ink/stringWidth.js'

function isEndCode(code: AnsiCode): boolean {
  return code.code === code.endCode
}

function filterStartCodes(codes: AnsiCode[]): AnsiCode[] {
  return codes.filter(c => !isEndCode(c))
}

export default function sliceAnsi(str: string, start: number, end?: number): string {
  const tokens = tokenize(str)
  let activeCodes: AnsiCode[] = []
  let position = 0
  let result = ''
  let include = false

  for (const token of tokens) {
    const width = token.type === 'ansi' ? 0 : token.fullWidth ? 2 : stringWidth(token.value)

    if (end !== undefined && position >= end) {
      if (token.type === 'ansi' || width > 0 || !include) {
        break
      }
    }

    if (token.type === 'ansi') {
      activeCodes.push(token)

      if (include) {
        result += token.code
      }
    } else {
      if (!include && position >= start) {
        if (start > 0 && width === 0) {
          continue
        }

        include = true
        activeCodes = filterStartCodes(reduceAnsiCodes(activeCodes))
        result = ansiCodesToString(activeCodes)
      }

      if (include) {
        result += token.value
      }

      position += width
    }
  }

  const activeStartCodes = filterStartCodes(reduceAnsiCodes(activeCodes))
  result += ansiCodesToString(undoAnsiCodes(activeStartCodes))

  return result
}