export interface FileMentionRange {
  start: number
  end: number
  query: string
}

interface FindActiveFileMentionInput {
  text: string
  cursorIndex: number
}

interface ApplyFileMentionReplacementInput {
  text: string
  mention: FileMentionRange
  relativePath: string
}

const INVALID_MENTION_QUERY_CHARS = /[\s\n\r\t"']/

export function findActiveFileMention(input: FindActiveFileMentionInput): FileMentionRange | null {
  const clampedCursor = Math.max(0, Math.min(input.cursorIndex, input.text.length))
  const beforeCursor = input.text.slice(0, clampedCursor)

  for (
    let atIndex = beforeCursor.lastIndexOf('@');
    atIndex >= 0;
    atIndex = beforeCursor.lastIndexOf('@', atIndex - 1)
  ) {
    const query = beforeCursor.slice(atIndex + 1)
    if (INVALID_MENTION_QUERY_CHARS.test(query)) {
      continue
    }
    return {
      start: atIndex,
      end: clampedCursor,
      query,
    }
  }

  return null
}

export function applyFileMentionReplacement(input: ApplyFileMentionReplacementInput): string {
  const safePath = input.relativePath.replace(/"/g, '\\"')
  const before = input.text.slice(0, input.mention.start)
  const after = input.text.slice(input.mention.end)
  return `${before}"${safePath}"${after}`
}