identification division.
          program-id. "AoC 2021 Day 1".
          author. "Carl Svensson".

       environment division.
          configuration section.
            object-computer. GNU-COBOL-Compiler.

          input-output section.
            file-control.
              select fdat assign to "1.dat"
              organization is line sequential.

       data division.
          file section.
            fd fdat.
              01 rec_in.
                02 rec_depth pic 9(4).
            
          working-storage section.
            01 depths-table.
              02 depths pic 9(4) value 0
              occurs 2000 indexed by i.
            01 ans_a pic 9(4) value 0.
            01 ans_b pic 9(4) value 0.
            01 prev_depth pic 9(4) value 0.
            01 cur_depth pic 9(4) value 0.
            01 range1 pic 9(6) value 0.
            01 range2 pic 9(6) value 0.
            01 eof pic 9 value 0.
            01 idx pic 9(4) value 0.

       procedure division.
          move 1 to i.
          open input fdat.
          perform until eof = 1
            read fdat
              at end set eof to 1
              not at end perform store_line_and_solve_a
            end-read
          end-perform.
          close fdat.
          perform solve_b.
          display "Task A: "ans_a.
          display "Task B: "ans_b.
          stop run.

          store_line_and_solve_a.
      * Solve task A.
            unstring rec_depth into cur_depth
            if prev_depth > 0 and cur_depth > prev_depth
              add 1 to ans_a
            end-if.
            move cur_depth to prev_depth.

      * Store number in table for task B.
            unstring cur_depth into depths(i).
            add 1 to i.

          solve_b.
            perform with test before
            varying i from 1 by 1 until i=2000
              compute range1 = depths(i) +
                depths(i + 1) + depths(i + 2)
              compute range2 = depths(i + 1) +
                depths(i + 2) + depths(i + 3)

              if range2 > range1 then
                add 1 to ans_b
              end-if

            end-perform.