const isDollarQuoteTagCharacter = (character: string): boolean => {
  return /^[A-Za-z0-9_]$/u.test(character)
}

const getDollarQuoteDelimiter = (sql: string, startIndex: number): string | undefined => {
  if (sql[startIndex] !== "$") {
    return undefined
  }

  const firstTagCharacter = sql[startIndex + 1]
  if (firstTagCharacter === "$") {
    return "$$"
  }
  if (firstTagCharacter === undefined || !/^[A-Za-z_]$/u.test(firstTagCharacter)) {
    return undefined
  }

  for (let endIndex = startIndex + 2; endIndex < sql.length; endIndex = endIndex + 1) {
    const character = sql[endIndex]!
    if (character === "$") {
      return sql.slice(startIndex, endIndex + 1)
    }
    if (!isDollarQuoteTagCharacter(character)) {
      return undefined
    }
  }

  return undefined
}

const hasExecutableSql = (sqlFragment: string): boolean => {
  let lineComment = false
  let blockCommentDepth = 0

  for (let i = 0; i < sqlFragment.length; i = i + 1) {
    const char = sqlFragment[i]!
    const next = sqlFragment[i + 1]

    if (lineComment) {
      if (char === "\n" || char === "\r") {
        lineComment = false
      }
      continue
    }

    if (blockCommentDepth > 0) {
      if (char === "/" && next === "*") {
        blockCommentDepth = blockCommentDepth + 1
        i = i + 1
        continue
      }
      if (char === "*" && next === "/") {
        blockCommentDepth = blockCommentDepth - 1
        i = i + 1
      }
      continue
    }

    if (char.trim() === "") {
      continue
    }

    if (char === "-" && next === "-") {
      lineComment = true
      i = i + 1
      continue
    }

    if (char === "/" && next === "*") {
      blockCommentDepth = 1
      i = i + 1
      continue
    }

    return true
  }

  return false
}

/**
 * @description 将包含多条 SQL 语句的字符串切分成单条 SQL 语句的数组。
 */
export const splitMultiStatementsSql = (multiStatementsSql: string): string[] => {
  const statements: string[] = []

  let current = ""
  let quote: "'" | '"' | "`" | null = null
  let dollarQuoteDelimiter: string | null = null
  let escapeNext = false
  let lineComment = false
  let blockCommentDepth = 0

  const appendToCurrent = (fragment: string): void => {
    current = `${current}${fragment}`
  }

  const pushStatement = (): void => {
    const trimmed = current.trim()
    if (trimmed.length !== 0 && hasExecutableSql(trimmed)) {
      statements.push(trimmed)
    }
    current = ""
  }

  for (let i = 0; i < multiStatementsSql.length; i = i + 1) {
    const char = multiStatementsSql[i]!
    const next = multiStatementsSql[i + 1]

    if (lineComment) {
      appendToCurrent(char)
      if (char === "\n" || char === "\r") {
        lineComment = false
      }
      continue
    }

    if (blockCommentDepth > 0) {
      if (char === "/" && next === "*") {
        blockCommentDepth = blockCommentDepth + 1
        appendToCurrent("/*")
        i = i + 1
        continue
      }
      if (char === "*" && next === "/") {
        blockCommentDepth = blockCommentDepth - 1
        appendToCurrent("*/")
        i = i + 1
        continue
      }
      appendToCurrent(char)
      continue
    }

    if (dollarQuoteDelimiter !== null) {
      const delimiter = dollarQuoteDelimiter
      if (multiStatementsSql.startsWith(delimiter, i)) {
        appendToCurrent(delimiter)
        i = i + delimiter.length - 1
        dollarQuoteDelimiter = null
        continue
      }
      appendToCurrent(char)
      continue
    }

    if (quote !== null) {
      appendToCurrent(char)
      if (escapeNext) {
        escapeNext = false
        continue
      }
      if (char === "\\") {
        escapeNext = true
        continue
      }
      if (char === quote) {
        if (next === quote) {
          appendToCurrent(quote)
          i = i + 1
          continue
        }
        quote = null
      }
      continue
    }

    if (char === "-" && next === "-") {
      lineComment = true
      appendToCurrent("--")
      i = i + 1
      continue
    }

    if (char === "/" && next === "*") {
      blockCommentDepth = 1
      appendToCurrent("/*")
      i = i + 1
      continue
    }

    const delimiter = getDollarQuoteDelimiter(multiStatementsSql, i)
    if (delimiter !== undefined) {
      dollarQuoteDelimiter = delimiter
      appendToCurrent(delimiter)
      i = i + delimiter.length - 1
      continue
    }

    if (char === "'" || char === '"' || char === "`") {
      quote = char
      escapeNext = false
      appendToCurrent(char)
      continue
    }

    if (char === ";") {
      pushStatement()
      continue
    }

    appendToCurrent(char)
  }

  pushStatement()

  return statements
}