#!/usr/bin/env swift

import Foundation

enum WireFormat: UInt8 {
  case varint = 0
  case fixed64 = 1
  case lengthDelimited = 2
  case startGroup = 3
  case endGroup = 4
  case fixed32 = 5
}

enum Matchers {
  case prefix(String, WireFormat)
  case suffix(String, WireFormat, WireFormat)
  case contains(String, WireFormat)
  case contains2(String, WireFormat, WireFormat)
  case containsAndPackable(String, WireFormat)
}

// The order of these matters since it is first match that is used.
let tests: [Matchers] = [
  .prefix("wkt", .lengthDelimited),
  .prefix("map", .lengthDelimited),
  .contains2("Group", .startGroup, .endGroup),
  .containsAndPackable("float", .fixed32),
  .containsAndPackable("double", .fixed64),
  .containsAndPackable("fixed64", .fixed64),
  .containsAndPackable("fixed", .fixed32),
  .containsAndPackable("int64", .varint),
  .containsAndPackable("int32", .varint),
  .containsAndPackable("bool", .varint),
  .containsAndPackable("enum", .varint),
  .contains("bytes", .lengthDelimited),
  .contains("string", .lengthDelimited),
  .contains("message", .lengthDelimited),
  // The single fields in the Groups.
  .contains("group_field", .varint),
]

func escapedVarint(_ x: Int) -> String {
  var escaped = String()
  var v = x
  while v > 127 {
    escaped.append(String(format: "\\x%02x", UInt8(v & 0x7f | 0x80)))
    v >>= 7
  }
  escaped.append(String(format: "\\x%02x", UInt8(v)))
  return escaped
}

func outputTag(_ fieldNum: Int, as wireformat: WireFormat) {
  let tag = UInt32(truncatingIfNeeded: fieldNum) << 3 | UInt32(wireformat.rawValue)
  print("\"\(escapedVarint(Int(tag)))\"")
}

if CommandLine.arguments.count != 2 {
  print("Expected only to get the proto file path as an argument")
  exit(1)
}

print("# Tags for all the fields")

let protoFile = try! String(contentsOfFile: CommandLine.arguments[1], encoding: .utf8)
let re = try NSRegularExpression(pattern: #"^ *.+ +(\w+) += (\d+)"#,
                                 options: [.anchorsMatchLines])
let range = NSRange(protoFile.startIndex..<protoFile.endIndex, in: protoFile)
re.enumerateMatches(in: protoFile, options: [], range: range) { (match, _, _) in
  guard let match = match else { return }
  guard match.numberOfRanges == 3 else { return }

  let fieldName = protoFile[Range(match.range(at: 1), in: protoFile)!]
  let fieldNum = Int(protoFile[Range(match.range(at: 2), in: protoFile)!])!
  
  // The regex matches enum cases, so skip those.
  guard fieldName.uppercased() != fieldName else { return }
  
  for test in tests {
    switch test {
      case .prefix(let s, let wf):
        if fieldName.hasPrefix(s) {
          outputTag(fieldNum, as: wf)
          return
        }
      case .suffix(let s, let wf1, let wf2):
        if fieldName.hasSuffix(s) {
          outputTag(fieldNum, as: wf1)
          outputTag(fieldNum, as: wf2)
          return
        }
      case .contains(let s, let wf):
        if fieldName.contains(s) {
          outputTag(fieldNum, as: wf)
          return
        }
      case .contains2(let s, let wf1, let wf2):
        if fieldName.contains(s) {
          outputTag(fieldNum, as: wf1)
          outputTag(fieldNum, as: wf2)
          return
        }
      case .containsAndPackable(let s, let wf):
        if fieldName.contains(s) {
          outputTag(fieldNum, as: wf)
          if fieldName.contains("repeated") {
            outputTag(fieldNum, as: .lengthDelimited)
          }
          return
        }
    }
  }
  print("Error: failed to match: \(fieldName)")
  exit(1)
}

print(#"""

# Include a few example values:
# varint:
"\#(escapedVarint(0))"
"\#(escapedVarint(5000))"
"\#(escapedVarint(50000))"
# fixed32:
"\x01\x02\x03\x04"
"\x05\x06\x07\x08"
# fixed64:
"\x01\x02\x03\x04\x05\x06\x07\x08"
"\x01\x02\x03\x04\x50\x60\x70\x80"
# length delimited:
"\#(escapedVarint(3))abc"
"\#(escapedVarint(7))1234567"
"\#(escapedVarint(26))abcdefghijklmnopqrstuvwxyz"
# start/end group just have tags/values after them, no tag specific payload; so
# nothing to provide as an example.
"""#)