# 2bc4be78ebca7d2bec41e37989e84ba7e7a411d8adf202dff046771d9084709a Elan 2.0.0-alpha valid

# Exercise: implement a function to search for an item in a sorted list, 
# using the 'binary search' algorithm
# The code below defines the signature for the 'binarySearch' function,
# with just enough code to compile, but it fails multiple tests.
# Your task is to implement binarySearch sufficient to get all the tests passing.
# You can then run the main program, which applies the function.
# 
# Hints:
# - Use a recursive implementation, but as with any recursive function think first
#   about the 'termination' condition
# - Find the mid-point of ths list using integer division ('div')
# - To compare strings alphabetically use the .isBefore or .isAfter dot-methods 
# - To extract the lists before and after the mid-point use the range indexes:
#    'li.subList(0, mid)' and 'li.subList(mid+1, li.length())'
# - You can implement the whole algorithm just by adding a new 'if' statement between the
#   first and last lines, containing 'elif/else' clauses as needed. Each clause should
#   set the result.
# - Use 'let' statements to calculate any sub-expression that will be used more than once
#   in your logic and/or to improve readability.
function binarySearch(li as List<of String>, item as String) returns Boolean
  variable result set to false
  return result
end function

main
  variable fruit set to ["apple", "avocado", "banana", "blueberry", "cherry", "fig", "grape", "kiwi", "lemon", "lychee", "mango", "orange", "papaya", "peach", "pear", "pineapple", "plum", "raspberry", "strawberry", "watermelon"]
  variable exit set to false
  while exit is false
    variable wanted set to input("What type of fruit do you want ("x" to exit)? ")
    if wanted isnt "x" then
      variable result set to binarySearch(fruit, wanted)
      if result then
        call print($"We can supply a {wanted}")
      else
        call print($"Sorry, we cannot supply a {wanted}")
      end if
    else
      set exit to true
    end if
  end while
end main

test test_binarySearch
  variable li1 set to ["lemon", "lime", "orange"]
  assert binarySearch(li1, "lemon") is true
  assert binarySearch(li1, "lime") is true
  assert binarySearch(li1, "orange") is true
  assert binarySearch(li1, "pear") is false
  variable li2 set to ["lemon", "orange"]
  assert binarySearch(li2, "lemon") is true
  assert binarySearch(li2, "orange") is true
  assert binarySearch(li2, "pear") is false
  variable li3 set to ["lemon"]
  assert binarySearch(li3, "lemon") is true
  assert binarySearch(li3, "lime") is false
  variable li4 set to new List<of String>()
  assert binarySearch(li4, "pear") is false
end test
