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package firrtl

import firrtl.ir._

import java.nio.charset.StandardCharsets.UTF_8
import scala.annotation.tailrec

// Default implementations are for valid FIRRTL Strings
trait StringLitHandler {

  // Apply correct escaping for strings in a given language
  def escape(lit: StringLit): String = {
    @tailrec
    def escape(in: Array[Byte], str: String): String = {
      if (in.isEmpty) str
      else {
        val s = in.head match {
          case 0x5c => "\\\\"
          case 0x0a => "\\n"
          case 0x09 => "\\t"
          case 0x22 => "\\\""
          case c => 
            if (c >= 0x20 && c <= 0x7e) new String(Array(c), UTF_8)
            else throw new FIRRTLException(s"Unsupported byte in StringLit: $c")
        }
        escape(in.tail, str + s)
      }
    }
    escape(lit.array, "")
  }

  // Turn raw parsed strings into String Literals
  def unescape(raw: String): StringLit = {
    @tailrec
    def unescape(in: Array[Byte], out: Array[Byte]): Array[Byte] = {
      if (in.isEmpty) out
      else {
        val c = in.head
        if ((c < 0x20) || (c > 0x7e)) { // Range from ' ' to '~'
          val msg = "Unsupported unescaped UTF-8 Byte 0x%02x! ".format(c) + 
                    "Valid range [0x20-0x7e]"
          throw new InvalidStringLitException(msg)
        }
        // Handle escaped characters
        if (c == 0x5c) { // backslash
          val (n: Int, bytes: Array[Byte]) = in(1) match {
            case 0x5c => (2, Array[Byte](0x5c)) // backslash
            case 0x6e => (2, Array[Byte](0x0a)) // newline
            case 0x74 => (2, Array[Byte](0x09)) // tab
            case 0x27 => (2, Array[Byte](0x27)) // single quote
            case 0x22 => (2, Array[Byte](0x22)) // double quote
            // TODO Finalize supported escapes, implement hex2Bytes
            //case 0x78 => (4, hex2Bytes(in.slice(2, 3)))) // hex escape
            //case 0x75 => (6, hex2Bytes(in.slice(2, 5))) // unicode excape 
            case e => { // error
              val msg = s"Invalid escape character ${e.toChar}! " + 
                         "Valid characters [nt'\"\\]"
              throw new InvalidEscapeCharException(msg)
            }
          }
          unescape(in.drop(n), out ++ bytes) // consume n
        } else {
          unescape(in.tail, out :+ in.head)
        }
      }
    }

    val byteArray = raw.getBytes(java.nio.charset.StandardCharsets.UTF_8)
    StringLit(unescape(byteArray, Array()))
  }

  // Translate from FIRRTL formatting to the specific language's formatting
  def format(lit: StringLit): StringLit = ???
  // Translate from the specific language's formatting to FIRRTL formatting
  def unformat(lit: StringLit): StringLit = ???
}

object FIRRTLStringLitHandler extends StringLitHandler

object VerilogStringLitHandler extends StringLitHandler {
  // Change FIRRTL format string to Verilog format
  override def format(lit: StringLit): StringLit = {
    @tailrec
    def format(in: Array[Byte], out: Array[Byte], percent: Boolean): Array[Byte] = {
      if (in.isEmpty) out
      else {
        if (percent && in.head == 'x') format(in.tail, out :+ 'h'.toByte, false)
        else format(in.tail, out :+ in.head, in.head == '%' && !percent)
      }
    }
    StringLit(format(lit.array, Array(), false))
  }
}