MECapture.swift

//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2021-2022 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//

@_implementationOnly import _RegexParser

/*

 TODO: Specialized data structure for all captures:

 - We want to be able to refer to COW prefixes for which
   simple appends do not invalidate
 - We want a compact save-point representation

 TODO: Conjectures:

 - We should be able to remove the entire capture history,
   lazily recomputing it on-request from the initial stored
   save point
 - We should be able to keep these flat and simple, lazily
   constructing structured types on-request

 */


extension Processor {
  struct _StoredCapture {
    var range: Range<Position>? = nil

    var value: Any? = nil

    // An in-progress capture start
    var currentCaptureBegin: Position? = nil

    fileprivate func _invariantCheck() {
      if range == nil {
        assert(value == nil)
      }
    }

    // MARK: - IPI

    var deconstructed: (range: Range<Position>, value: Any?)? {
      guard let r = range else { return nil }
      return (r, value)
    }

    /// Start a new capture. If the previously started one was un-ended,
    /// will clear it and restart.
    mutating func startCapture(
      _ idx: Position
    ) {
      _invariantCheck()
      defer { _invariantCheck() }

      currentCaptureBegin = idx
    }

    mutating func endCapture(_ idx: Position) {
      _invariantCheck()
      defer { _invariantCheck() }

      guard let low = currentCaptureBegin else {
        fatalError("Invariant violated: ending unstarted capture")
      }

      range = low..<idx
      value = nil // TODO: cleaner IPI around this...
      currentCaptureBegin = nil
    }

    mutating func registerValue(_ value: Any) {
      _invariantCheck()
      defer { _invariantCheck() }

      self.value = value
    }
  }
}

struct MECaptureList {
  var values: Array<Processor._StoredCapture>
  var referencedCaptureOffsets: [ReferenceID: Int]

  func latestUntyped(from input: String) -> Array<Substring?> {
    values.map {
      guard let range = $0.range else {
        return nil
      }
      return input[range]
    }
  }
}