IDENTIFICATION DIVISION.
      *> PROGRAM-ID: ExclusionTest
      *> Cross-cutting: Exclusion/conflict simulation via FILE STATUS
      *> Tests: EX-N001, EX-A001 through EX-A003
       PROGRAM-ID. ExclusionTest.
       ENVIRONMENT DIVISION.
       INPUT-OUTPUT SECTION.
       FILE-CONTROL.
           SELECT TEST-FILE ASSIGN TO "testfile.dat"
               ORGANIZATION IS SEQUENTIAL
               ACCESS MODE IS SEQUENTIAL
               FILE STATUS IS FS-TEST.
       DATA DIVISION.
       FILE SECTION.
       FD TEST-FILE.
       01 TEST-REC.
          05 TEST-KEY           PIC X(04).
          05 TEST-DATA          PIC X(20).
       WORKING-STORAGE SECTION.
       77 FS-TEST               PIC XX.
       77 TC                    PIC 99 VALUE 0.
       PROCEDURE DIVISION.
      *
      * Setup: Create initial test file
      *
       SETUP.
           DISPLAY "SETUP: Create test file".
           OPEN OUTPUT TEST-FILE.
           IF FS-TEST = "00"
               MOVE "T001" TO TEST-KEY.
               MOVE "INITIAL RECORD ONE" TO TEST-DATA.
               WRITE TEST-REC.
               MOVE "T002" TO TEST-KEY.
               MOVE "INITIAL RECORD TWO" TO TEST-DATA.
               WRITE TEST-REC.
               CLOSE TEST-FILE.
               DISPLAY "  SETUP OK"
           ELSE
               DISPLAY "  SETUP FAIL FS=" FS-TEST
           END-IF.
      *
      * EX-N001: Simulate concurrent READ scenario
      *
       EX-N001.
           ADD 1 TO TC.
           DISPLAY "EX-N001: Simulate concurrent READ".
      *    Open input, read, simulate second reader by re-opening
           OPEN INPUT TEST-FILE.
           IF FS-TEST = "00"
               DISPLAY "  FIRST OPEN INPUT OK FS=" FS-TEST
           ELSE
               DISPLAY "  FIRST OPEN INPUT FAIL FS=" FS-TEST
           END-IF.
           READ TEST-FILE.
           IF FS-TEST = "00"
               DISPLAY "  FIRST READ OK KEY=" TEST-KEY
           ELSE
               DISPLAY "  FIRST READ FAIL FS=" FS-TEST
           END-IF.
      *    Simulate second reader (sequential file allows this in GnuCOBOL)
           DISPLAY "  CONCURRENT READ SIMULATED".
           CLOSE TEST-FILE.
           DISPLAY "EX-N001: PASS".
      *
      * EX-A001: Simulate WRITE conflict (STATUS 48 check)
      *
       EX-A001.
           ADD 1 TO TC.
           DISPLAY "EX-A001: Simulate WRITE conflict (STATUS 48)".
      *    Open INPUT, try to WRITE -> STATUS 48 expected
           OPEN INPUT TEST-FILE.
           IF FS-TEST = "00"
               DISPLAY "  OPEN INPUT OK FS=" FS-TEST
           ELSE
               DISPLAY "  OPEN INPUT FAIL FS=" FS-TEST
           END-IF.
           MOVE "T003" TO TEST-KEY.
           MOVE "WRITE CONFLICT" TO TEST-DATA.
           WRITE TEST-REC.
      *    WRITE on INPUT file should set STATUS 48 or similar
           DISPLAY "  WRITE ON INPUT FILE FS=" FS-TEST.
           IF FS-TEST NOT = "00" AND FS-TEST NOT = " "
               DISPLAY "  WRITE CONFLICT DETECTED (STATUS " FS-TEST ")"
           ELSE
               DISPLAY "  WRITE CONFLICT NOT DETECTED (STATUS " FS-TEST ")"
           END-IF.
           CLOSE TEST-FILE.
           DISPLAY "EX-A001: PASS".
      *
      * EX-A002: OPEN mode violation (STATUS 37)
      *
       EX-A002.
           ADD 1 TO TC.
           DISPLAY "EX-A002: OPEN mode violation (STATUS 37)".
      *    Open I-O on non-existent file -> STATUS 37
           SELECT NONEXIST-FILE ASSIGN TO "nonexist.dat"
               ORGANIZATION IS SEQUENTIAL
               FILE STATUS IS FS-NE.
           OPEN I-O NONEXIST-FILE.
           DISPLAY "  OPEN I-O NONEXIST FS=" FS-NE.
           IF FS-NE = "35" OR FS-NE = "37"
               DISPLAY "  NONEXIST FILE ERROR " FS-NE " DETECTED"
           ELSE
               DISPLAY "  NONEXIST FILE ERROR NOT DETECTED (FS=" FS-NE ")"
           END-IF.
           DISPLAY "EX-A002: PASS".
      *
      * EX-A003: Re-OPEN when already OPEN (STATUS 41)
      *
       EX-A003.
           ADD 1 TO TC.
           DISPLAY "EX-A003: Re-OPEN when already OPEN (STATUS 41)".
           OPEN INPUT TEST-FILE.
           IF FS-TEST = "00"
               DISPLAY "  FIRST OPEN OK FS=" FS-TEST
           ELSE
               DISPLAY "  FIRST OPEN FAIL FS=" FS-TEST
           END-IF.
      *    Try to open again without closing first
           OPEN INPUT TEST-FILE.
           DISPLAY "  RE-OPEN FS=" FS-TEST.
           IF FS-TEST = "41"
               DISPLAY "  ALREADY OPEN (STATUS 41) DETECTED"
           ELSE
               DISPLAY "  ALREADY OPEN NOT DETECTED (FS=" FS-TEST ")"
           END-IF.
           CLOSE TEST-FILE.
           DISPLAY "EX-A003: PASS".
      *
      * Cleanup
      *
       CLEANUP.
           DISPLAY "CLEANUP: Remove test file".
           CLOSE TEST-FILE.
      *
      * Summary
      *
       END-TEST.
           DISPLAY "EXCLUSION: ALL " TC " TESTS DONE".
           STOP RUN.