Investigating HMS Internals

Purpose: Understand HEC-HMS internal implementation through decompiled Java classes to support hms-commander development and debugging.

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Quick Start

Check JythonHms Method

Q: "Does HMS support SetTimeWindow()?"
A: See hms_agents/hms_decompiler/knowledge/JYTHON_HMS_API.md

Check Version Compatibility

Q: "Does HMS 3.3 support Jython?"
A: See hms_agents/hms_decompiler/knowledge/HMS_3x_SUPPORT.md
→ YES! Discovered via decompilation

Decompile New Class

cd hms_agents/hms_decompiler/tools
decompile.bat "C:\...\hms.jar" "hms.model.ClassName" output

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Primary Sources

Production Agent

Location: hms_agents/hms_decompiler/

Quick access:

• QUICK_START.md - 5-minute guide
• AGENT.md - Comprehensive documentation
• knowledge/ - Curated API references
• reference/ - Key decompiled classes
• tools/ - Decompilation utilities (cfr.jar)
• examples/ - Usage workflows

This agent is self-contained with all necessary reference data and tools.

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When to Use This Skill

✅ Use When

1. Checking API Existence

   • "Does JythonHms have method X?"
   • "What parameters does SetLossRateValue accept?"
   • "Is there a method to set time window?"

2. Version Compatibility

   • "Does HMS 3.x support Jython?"
   • "What's different between HMS 3.x and 4.x?"
   • "Will this API work in HMS 3.5?"

3. Understanding Behavior

   • "Why does this HMS call fail?"
   • "What error codes does HMS use?"
   • "How does HMS execute scripts?"

4. Discovering Features

   • "Are there undocumented JythonHms methods?"
   • "What CLI flags does HMS support?"
   • "Does HMS have an RMI command server?"

5. Validating Automation

   • "Can I automate optimization via Jython?"
   • "How should I structure my script?"
   • "What's the correct method signature?"

❌ Don't Use When

1. Official Documentation Query

   • Use hms_doc_query agent instead
   • hms_doc_query searches User's Manual, Technical Reference

2. hms-commander API Questions

   • Read hms-commander docstrings
   • Check examples/ notebooks
   • See hms-commander documentation

3. Project File Parsing

   • Use parsing-basin-models skill
   • Use HmsBasin, HmsMet, HmsControl classes

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Knowledge Files

1. JYTHON_HMS_API.md

Location: hms_agents/hms_decompiler/knowledge/JYTHON_HMS_API.md

Contains:

• Complete JythonHms method reference (HMS 4.x)
• Method signatures, parameters, exceptions
• Examples and usage notes
• Internal implementation details
• Deprecated/removed methods

Example lookup:

Q: "What parameters does SetLossRateValue accept?"
A: SetLossRateValue(elementName, parameterName, value)
   - elementName (String): Subbasin name
   - parameterName (String): e.g., "Curve Number"
   - value (double): Parameter value

2. HMS_3x_SUPPORT.md

Location: hms_agents/hms_decompiler/knowledge/HMS_3x_SUPPORT.md

Contains:

• HMS 3.x Jython support discovery (✅ YES!)
• Python 2 vs 3 syntax differences
• API method availability (3.x vs 4.x)
• Example scripts for both versions
• Test results from hms-commander

Key finding:

HMS 3.3+ supports Jython scripting (undocumented)!
Requires Python 2 syntax: print "text" (not print("text"))
Use Compute() instead of ComputeRun()

3. HMS_CLI_OPTIONS.md

Location: hms_agents/hms_decompiler/knowledge/HMS_CLI_OPTIONS.md

Contains:

• Complete CLI arguments discovered via decompilation
• -script, -lite, -debug, -info, CommandServer
• Version compatibility (which flags in which HMS versions)
• Usage examples

Example:

Q: "How do I run HMS without GUI?"
A: HEC-HMS.cmd -lite -script path/to/script.py

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Reference Classes

Location: hms_agents/hms_decompiler/reference/

HMS 3.3

• HMS_3.3/hms/Hms.java - Entry point, CLI parsing
• HMS_3.3/hms/model/JythonHms.java - Scripting API (3.x)
• HMS_3.3/hec/map/hms/*.java - GIS support

HMS 4.13

• HMS_4.13/hms/Hms.java - Entry point, CLI parsing
• HMS_4.13/hms/model/JythonHms.java - Scripting API (4.x)
• HMS_4.13/hms/command/HmsCommandServerImpl.java - RMI server

Use: Review implementation details for specific methods

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Tools

CFR Decompiler

Location: hms_agents/hms_decompiler/tools/cfr.jar

Usage:

cd hms_agents/hms_decompiler/tools
java -jar cfr.jar "C:\Program Files\HEC\HEC-HMS\4.13\java\hms.jar" --classfilter "hms.model.ClassName" --outputdir output

Options:

• --classfilter <pattern> - Filter classes to decompile
• --outputdir <dir> - Output directory for decompiled classes

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Common Use Cases

Use Case 1: Query JythonHms API

Example: Check if SetTimeWindow() exists

Steps:

1. Open knowledge/JYTHON_HMS_API.md
2. Search for "SetTimeWindow"
3. Result: ✅ Found

See: examples/query_jython_api.md

Use Case 2: Check Version Compatibility

Example: Verify HMS 3.3 supports Jython

Steps:

1. Open knowledge/HMS_3x_SUPPORT.md
2. Review "Supported Versions"
3. Result: ✅ HMS 3.3+ supports Jython (Python 2 syntax required)

See: examples/version_compatibility.md

Use Case 3: Decompile New Class

Example: Investigate how optimization works

Steps:

1. Check if already in agent reference/
2. If not, use tools/cfr.jar to decompile
3. Review decompiled source
4. Document findings if high-value

See: examples/decompile_new_class.md

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Integration with hms-commander

How This Skill Supports Development

HmsJython.py implementation:

• Uses JythonHms API reference from JYTHON_HMS_API.md
• Implements python2_compatible flag based on HMS_3x_SUPPORT.md
• Method signatures validated against decompiled source

HmsCmdr.py execution:

• CLI options discovered from HMS_CLI_OPTIONS.md
• Version detection patterns from decompiled Hms.java
• Direct Java invocation (bypasses batch file bugs)

Error handling:

• Error codes from decompiled source
• Exception handling patterns from JythonHms.java

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On-Demand Decompilation

The agent provides tools for decompiling any HMS class as needed:

Included:

• CFR decompiler (tools/cfr.jar)
• Essential reference classes (reference/)
• Curated knowledge files (knowledge/)

For New Classes:

1. Use cfr.jar to decompile the class
2. Analyze the decompiled source
3. Add to agent reference/ if high-value
4. Document findings in knowledge/ if commonly needed

This agent contains all necessary tools for HMS internal investigation.

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Examples

Example 1: query_jython_api.md

Demonstrates: Checking if JythonHms method exists and understanding parameters

Workflow:

1. Open JYTHON_HMS_API.md
2. Search for method
3. Review signature and parameters
4. Check hms-commander integration status

Example 2: version_compatibility.md

Demonstrates: Understanding HMS 3.x vs 4.x differences

Key findings:

• HMS 3.x DOES support Jython (Python 2)
• API differences (Compute vs ComputeRun)
• Architecture (32-bit vs 64-bit)

Example 3: decompile_new_class.md

Demonstrates: Complete workflow from question to decompilation to documentation

Steps:

1. Identify target class
2. Check if already decompiled
3. Decompile using tools
4. Analyze findings
5. Document in library

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Skill Workflow

Standard Investigation Flow

User Question
    ↓
Check Agent Knowledge
    ├─ JYTHON_HMS_API.md → Found? → Answer
    ├─ HMS_3x_SUPPORT.md → Found? → Answer
    └─ HMS_CLI_OPTIONS.md → Found? → Answer
    ↓ (Not Found)
Check Library INDEX.md
    ├─ Class listed? → Read decompiled source → Answer
    └─ Not listed? → Decompile on-demand → Document → Answer

Adding New Knowledge

Decompile Class (tools/cfr.jar)
    ↓
Analyze Source
    ↓
High-Value Finding?
    ├─ YES → Add to agent reference/
    └─ NO → Keep in local output/
    ↓
Update AGENT.md if commonly needed
    ↓
Document in knowledge/ if API-relevant

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Limitations

What This Skill CAN Do

• ✅ Provide JythonHms API reference
• ✅ Show version differences (3.x vs 4.x)
• ✅ List CLI options
• ✅ Decompile any HMS class on-demand using included tools
• ✅ Explain HMS internal behavior

What This Skill CANNOT Do

• ❌ Replace official HMS documentation (use hms_doc_query)
• ❌ Modify HMS source code
• ❌ Guarantee 100% decompilation accuracy
• ❌ Explain "why" design decisions were made (only "how" implementation works)

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Related Skills & Agents

hms_doc_query Agent

Purpose: Search official HMS documentation

Complementary use:

• hms_doc_query → What's documented
• investigating-hms-internals → How it works internally

update_3_to_4 Agent

Purpose: Migrate HMS projects from 3.x to 4.x

Uses: HMS_3x_SUPPORT.md for version differences

managing-hms-versions Skill

Purpose: Detect and work with multiple HMS versions

Uses: Version detection patterns from decompilation

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Quality Checklist

Before answering user questions:

• Checked agent knowledge/ files first
• If not found, checked agent reference/ classes
• Decompiled on-demand using tools/cfr.jar if necessary
• Documented findings in agent if high-value
• Pointed to primary sources (not duplicated content)
• Clarified limitations of decompiled code

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Quick Reference

Common questions → Files:

Question	File
"What JythonHms methods exist?"	knowledge/JYTHON_HMS_API.md
"Does HMS 3.x support Jython?"	knowledge/HMS_3x_SUPPORT.md
"What CLI options are available?"	knowledge/HMS_CLI_OPTIONS.md
"How do I decompile a class?"	Use tools/cfr.jar directly
"What classes are available?"	reference/ directory + on-demand decompilation

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Status: Production skill Version: 1.0 Created: 2025-12-12 Agent: hms_decompiler