const SHEBANG_REGEXP = /^#!(.*)/
const SHELL_REGEXP = /bin[/](?:env )?(\w+)/

// Non exhaustive list of bash dialects that we potentially could support and try to analyze.
const BASH_DIALECTS = ['sh', 'bash', 'dash', 'ksh', 'zsh', 'csh', 'ash'] as const
type BashDialect = (typeof BASH_DIALECTS)[number]

const SHELL_DIRECTIVE_REGEXP = new RegExp(
  `^\\s*#\\s*shellcheck.*shell=(${BASH_DIALECTS.join('|')}).*$|^\\s*#.*$|^\\s*$`,
)

export function getShebang(fileContent: string): string | null {
  const match = SHEBANG_REGEXP.exec(fileContent)
  if (!match || !match[1]) {
    return null
  }

  return match[1].trim()
}

export function getShellDialect(shebang: string): BashDialect | null {
  const match = SHELL_REGEXP.exec(shebang)
  if (match && match[1]) {
    const bashDialect = match[1].trim() as any
    if (BASH_DIALECTS.includes(bashDialect)) {
      return bashDialect
    }
  }

  return null
}

export function getShellDialectFromShellDirective(
  fileContent: string,
): BashDialect | null {
  const contentLines = fileContent.split('\n')
  for (const line of contentLines) {
    const match = SHELL_DIRECTIVE_REGEXP.exec(line)
    if (match === null) {
      break
    }
    if (match[1]) {
      const bashDialect = match[1].trim() as any
      if (BASH_DIALECTS.includes(bashDialect)) {
        return bashDialect
      }
    }
  }
  return null
}

export function analyzeShebang(fileContent: string): {
  shellDialect: BashDialect | null
  shebang: string | null
} {
  const shebang = getShebang(fileContent)
  return {
    shebang,
    shellDialect:
      getShellDialectFromShellDirective(fileContent) ??
      (shebang ? getShellDialect(shebang) : null),
  }
}