// Self-contained dev smoke for FunctionCall empty-args
// Goal: echo() -> empty line, itoa() -> 0

static box MiniVm {
  // simple substring find from position
  index_of_from(hay, needle, pos) {
    if pos < 0 { pos = 0 }
    if pos >= hay.length() { return -1 }
    local tail = hay.substring(pos, hay.length())
    local rel = tail.indexOf(needle)
    if rel < 0 { return -1 } else { return pos + rel }
  }

  // collect only FunctionCall with empty arguments [] for echo/itoa
  collect_prints(json) {
    local out = new ArrayBox()
    local pos = 0
    local guard = 0
    loop (true) {
      guard = guard + 1
      if guard > 16 { break }
      local k_fc = "\"kind\":\"FunctionCall\""
      local p = index_of_from(json, k_fc, pos)
      if p < 0 { break }
      // name
      local k_n = "\"name\":\""
      local np = index_of_from(json, k_n, p)
      if np < 0 { break }
      local ni = np + k_n.length()
      local nj = index_of_from(json, "\"", ni)
      if nj < 0 { break }
      local fname = json.substring(ni, nj)
      // args [] detection
      local k_a = "\"arguments\":["  
      local ap = index_of_from(json, k_a, nj)
      if ap < 0 { break }
      local rb = index_of_from(json, "]", ap)
      if rb < 0 { break }
      // no content between '[' and ']'
      if rb == ap + k_a.length() {
        if fname == "echo" { out.push("") }
        if fname == "itoa" { out.push("0") }
      }
      pos = rb + 1
    }
    return out
  }
}

static box Main {
  main(args) {
    local json = "{\"kind\":\"Program\",\"statements\":[{\"kind\":\"Print\",\"expression\":{\"kind\":\"FunctionCall\",\"name\":\"echo\",\"arguments\":[]}},{\"kind\":\"Print\",\"expression\":{\"kind\":\"FunctionCall\",\"name\":\"itoa\",\"arguments\":[]}}]}"

    local arr = new MiniVm().collect_prints(json)
    local i = 0
    loop (i < arr.size()) { print(arr.get(i))  i = i + 1 }
    return 0
  }
}