// SPDX-License-Identifier: Apache-2.0

// Macro transforms that statically (at compile time) parse range specifiers and emit the raw
// (non-human-friendly) range constructor calls.

package chisel3.internal

import scala.language.experimental.macros
import scala.reflect.macros.blackbox
import scala.util.matching.Regex

// Workaround for https://github.com/sbt/sbt/issues/3966
object RangeTransform {
  val UnspecifiedNumber: Regex = """(\?).*""".r
  val IntegerNumber: Regex = """(-?\d+).*""".r
  val DecimalNumber: Regex = """(-?\d+\.\d+).*""".r
}

/** Convert the string to IntervalRange, with unknown, open or closed endpoints and a binary point
  * ranges looks like
  * range"[0,4].1" range starts at 0 inclusive ends at 4.inclusively with a binary point of 1
  * range"(0,4).1" range starts at 0 exclusive ends at 4.exclusively with a binary point of 1
  *
  * the min and max of the range are the actually min and max values, thus the binary point
  * becomes a sort of multiplier for the number of bits.
  * E.g. range"[0,3].2" will require at least 4 bits two provide the two decimal places
  *
  * @param c contains the string context to be parsed
  */
class RangeTransform(val c: blackbox.Context) {
  import c.universe._
  def apply(args: c.Tree*): c.Tree = {
    val stringTrees = c.prefix.tree match {
      case q"$_(scala.StringContext.apply(..$strings))" => strings
      case _ =>
        c.abort(
          c.enclosingPosition,
          s"Range macro unable to parse StringContext, got: ${showCode(c.prefix.tree)}"
        )
    }
    val strings = stringTrees.map {
      case Literal(Constant(string: String)) => string
      case tree =>
        c.abort(
          c.enclosingPosition,
          s"Range macro unable to parse StringContext element, got: ${showRaw(tree)}"
        )
    }

    var nextStringIndex: Int = 1
    var nextArgIndex: Int = 0
    var currString: String = strings.head

    /** Mutably gets the next numeric value in the range specifier.
      */
    def computeNextValue(): c.Tree = {
      currString = currString.dropWhile(_ == ' ') // allow whitespace
      if (currString.isEmpty) {
        if (nextArgIndex >= args.length) {
          c.abort(c.enclosingPosition, s"Incomplete range specifier")
        }
        val nextArg = args(nextArgIndex)
        nextArgIndex += 1

        if (nextStringIndex >= strings.length) {
          c.abort(c.enclosingPosition, s"Incomplete range specifier")
        }
        currString = strings(nextStringIndex)
        nextStringIndex += 1

        nextArg
      } else {
        val nextStringVal = currString match {
          case RangeTransform.DecimalNumber(numberString) => numberString
          case RangeTransform.IntegerNumber(numberString) => numberString
          case RangeTransform.UnspecifiedNumber(_)        => "?"
          case _ =>
            c.abort(
              c.enclosingPosition,
              s"Bad number or unspecified bound $currString"
            )
        }
        currString = currString.substring(nextStringVal.length)

        if (nextStringVal == "?") {
          Literal(Constant("?"))
        } else {
          c.parse(nextStringVal)
        }
      }
    }

    // Currently, not allowed to have the end stops (inclusive / exclusive) be interpolated.
    currString = currString.dropWhile(_ == ' ')
    val startInclusive = currString.headOption match {
      case Some('[') => true
      case Some('(') => false
      case Some('?') =>
        c.abort(
          c.enclosingPosition,
          s"start of range as unknown s must be '[?' or '(?' not '?'"
        )
      case Some(other) =>
        c.abort(
          c.enclosingPosition,
          s"Unknown start inclusive/exclusive specifier, got: '$other'"
        )
      case None =>
        c.abort(
          c.enclosingPosition,
          s"No initial inclusive/exclusive specifier"
        )
    }

    currString = currString.substring(1) // eat the inclusive/exclusive specifier
    val minArg = computeNextValue()
    currString = currString.dropWhile(_ == ' ')
    if (currString(0) != ',') {
      c.abort(c.enclosingPosition, s"Incomplete range specifier, expected ','")
    }
    if (currString.head != ',') {
      c.abort(
        c.enclosingPosition,
        s"Incomplete range specifier, expected ',', got $currString"
      )
    }

    currString = currString.substring(1) // eat the comma

    val maxArg = computeNextValue()
    currString = currString.dropWhile(_ == ' ')

    val endInclusive = currString.headOption match {
      case Some(']') => true
      case Some(')') => false
      case Some('?') =>
        c.abort(
          c.enclosingPosition,
          s"start of range as unknown s must be '[?' or '(?' not '?'"
        )
      case Some(other) =>
        c.abort(
          c.enclosingPosition,
          s"Unknown end inclusive/exclusive specifier, got: '$other' expecting ')' or ']'"
        )
      case None =>
        c.abort(
          c.enclosingPosition,
          s"Incomplete range specifier, missing end inclusive/exclusive specifier"
        )
    }
    currString = currString.substring(1) // eat the inclusive/exclusive specifier
    currString = currString.dropWhile(_ == ' ')

    val binaryPointString = currString.headOption match {
      case Some('.') =>
        currString = currString.substring(1)
        computeNextValue()
      case Some(other) =>
        c.abort(
          c.enclosingPosition,
          s"Unknown end binary point prefix, got: '$other' was expecting '.'"
        )
      case None =>
        Literal(Constant(0))
    }

    if (nextArgIndex < args.length) {
      val unused = args.mkString("")
      c.abort(
        c.enclosingPosition,
        s"Unused interpolated values in range specifier: '$unused'"
      )
    }
    if (!currString.isEmpty || nextStringIndex < strings.length) {
      val unused = currString + strings
        .slice(nextStringIndex, strings.length)
        .mkString(", ")
      c.abort(
        c.enclosingPosition,
        s"Unused characters in range specifier: '$unused'"
      )
    }

    val startBound =
      q"_root_.chisel3.internal.firrtl.IntervalRange.getBound($startInclusive, $minArg)"

    val endBound =
      q"_root_.chisel3.internal.firrtl.IntervalRange.getBound($endInclusive, $maxArg)"

    val binaryPoint =
      q"_root_.chisel3.internal.firrtl.IntervalRange.getBinaryPoint($binaryPointString)"

    q"_root_.chisel3.internal.firrtl.IntervalRange($startBound, $endBound, $binaryPoint)"
  }
}