JCL Job Step Sequencer for COBOL File Processing

Problem Context

In mainframe environments, Job Control Language (JCL) orchestrates the execution of batch programs. A common pattern involves running a COBOL program that reads from multiple input files and writes to an output file, with utility steps (like IEBGENER) for file preparation or copying.

You are given a simplified representation of JCL job steps as a list of step definitions. Each step has a name, a program it executes, and a list of DD (Data Definition) statements describing its input/output datasets. Your task is to validate and sequence the JCL job steps correctly, ensuring:

1. The COBOL program step has exactly two input DD statements (SYSUT1-style) and one output DD statement (SYSUT2-style).
2. An IEBGENER utility step precedes the COBOL step to prepare at least one input file.
3. Steps are returned in correct execution order with no dependency violations.

Input/Output Format

Input: A list of job step objects. Each step is represented as a string in the format:

STEPNAME,PROGRAM,DD1:TYPE,DD2:TYPE,...

Where TYPE is INPUT or OUTPUT.

Output: A list of valid step names in correct execution order, or "INVALID" if the job definition violates the rules.

Rules

• The COBOL step must have exactly 2 INPUT DDs and exactly 1 OUTPUT DD.
• At least one IEBGENER step must appear before the COBOL step.
• If multiple IEBGENER steps exist, they must all precede the COBOL step.
• If any step has 0 DDs, return "INVALID".
• Step names must be unique; duplicates return "INVALID".

Examples

Example 1

Input:

steps = [
  "STEP1,IEBGENER,SYSUT1:INPUT,SYSUT2:OUTPUT",
  "STEP2,COBPGM,INFILE1:INPUT,INFILE2:INPUT,OUTFILE:OUTPUT"
]

Output: ["STEP1", "STEP2"]

Explanation: STEP1 runs IEBGENER (1 input, 1 output — valid utility). STEP2 runs the COBOL program with 2 inputs and 1 output. Order is valid.

Example 2

Input:

steps = [
  "STEP1,COBPGM,INFILE1:INPUT,INFILE2:INPUT,OUTFILE:OUTPUT",
  "STEP2,IEBGENER,SYSUT1:INPUT,SYSUT2:OUTPUT"
]

Output: "INVALID"

Explanation: The IEBGENER step (STEP2) appears after the COBOL step (STEP1), violating the dependency rule.

Example 3

Input:

steps = [
  "STEP1,IEBGENER,SYSUT1:INPUT,SYSUT2:OUTPUT",
  "STEP2,COBPGM,INFILE1:INPUT,OUTFILE:OUTPUT"
]