const TAGS = ['think', 'reasoning', 'thinking', 'thought', 'REASONING_SCRATCHPAD'] as const

export interface SplitReasoning {
  reasoning: string
  text: string
}

export function splitReasoning(input: string): SplitReasoning {
  let text = input
  const reasoning: string[] = []

  for (const tag of TAGS) {
    const paired = new RegExp(`<${tag}>([\\s\\S]*?)</${tag}>\\s*`, 'gi')
    text = text.replace(paired, (_m, inner: string) => {
      const trimmed = inner.trim()

      if (trimmed) {
        reasoning.push(trimmed)
      }

      return ''
    })

    // Anchor to start-of-input so a literal `<think>` mid-prose (model quoting
    // the word, code blocks containing the tag, etc.) doesn't eat every
    // paragraph after it. Real unclosed reasoning blocks always lead the
    // message — that's how reasoning models stream. See test
    // "does not strip trailing prose after a stray mid-text <think> mention".
    const unclosed = new RegExp(`^\\s*<${tag}>([\\s\\S]*)$`, 'i')
    text = text.replace(unclosed, (_m, inner: string) => {
      const trimmed = inner.trim()

      if (trimmed) {
        reasoning.push(trimmed)
      }

      return ''
    })
  }

  return {
    reasoning: reasoning.join('\n\n').trim(),
    text: text.trim()
  }
}

export const hasReasoningTag = (input: string) => {
  for (const tag of TAGS) {
    if (input.includes(`<${tag}>`)) {
      return true
    }
  }

  return false
}