Rename PidFileData to PidFile

- Rename struct and update all references throughout codebase
- Cleaner, more intuitive name that follows Rust conventions
- Update documentation comments
- No functional changes, purely cosmetic refactor

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

2 files changed, 275 insertions, 27 deletions

diff --git a/IMPROVEMENT_PLAN_V2.md b/IMPROVEMENT_PLAN_V2.md
new file mode 100644
index 0000000..abffa0e
--- /dev/null
+++ b/IMPROVEMENT_PLAN_V2.md
@@ -0,0 +1,248 @@
+# Demon CLI Improvement Plan v2
+
+## Overview
+This plan outlines four major improvements to enhance the demon CLI tool's usability, error handling, and documentation.
+
+## Task 1: Rename PidFileData to PidFile
+
+### Rationale
+- Shorter, cleaner name
+- More intuitive - it represents a PID file, not just data about one
+- Follows Rust naming conventions better
+
+### Implementation Steps
+1. Rename struct `PidFileData` to `PidFile`
+2. Update all references throughout the codebase
+3. Update comments and documentation
+4. Verify compilation and tests pass
+
+### Files to modify
+- `src/main.rs` - struct definition and all usages
+
+### Risk Assessment
+- **Low risk** - Simple rename refactor
+- No functional changes
+- All tests should continue to pass
+
+## Task 2: Implement PidFileReadError Enum
+
+### Rationale
+- Better error handling with specific error types
+- Eliminates redundant file existence checks
+- More idiomatic Rust error handling
+- Cleaner code in error handling paths
+
+### Design
+```rust
+#[derive(Debug)]
+pub enum PidFileReadError {
+    /// The PID file does not exist
+    FileNotFound,
+    /// The PID file exists but has invalid content
+    FileInvalid(String), // Include reason for invalidity
+    /// IO error occurred while reading
+    IoError(std::io::Error),
+}
+```
+
+### Implementation Steps
+1. Define `PidFileReadError` enum with appropriate variants
+2. Implement `Display` and `Error` traits for the enum
+3. Update `PidFile::read_from_file()` to return `Result<PidFile, PidFileReadError>`
+4. Update all call sites to handle the specific error types:
+   - `is_process_running()` - handle FileNotFound and FileInvalid as "not running"
+   - `stop_daemon()` - handle FileNotFound as "not running", FileInvalid as "cleanup needed"
+   - `list_daemons()` - handle FileInvalid as "INVALID" entry
+   - `status_daemon()` - handle FileNotFound as "NOT FOUND", FileInvalid as "ERROR"
+   - `clean_orphaned_files()` - handle FileInvalid as "needs cleanup"
+5. Remove redundant `Path::new().exists()` checks where the error type provides this info
+6. Test all error scenarios
+
+### Files to modify
+- `src/main.rs` - enum definition, read_from_file method, all usage sites
+
+### Risk Assessment
+- **Medium risk** - Changes error handling logic
+- Need thorough testing of error scenarios
+- Must ensure all edge cases are handled properly
+
+## Task 3: Make --id a Positional Argument
+
+### Analysis
+
+#### Current CLI Pattern
+```bash
+demon run --id web-server python -m http.server 8080
+demon stop --id web-server
+demon status --id web-server
+```
+
+#### Proposed CLI Pattern
+```bash
+demon run web-server python -m http.server 8080
+demon stop web-server
+demon status web-server
+```
+
+#### Pros
+- **Better UX**: More natural and concise
+- **Consistent with common tools**: Similar to git, docker, etc.
+- **Faster to type**: No --id flag needed
+- **More intuitive**: ID naturally comes first before the command
+
+#### Cons
+- **Breaking change**: Existing scripts/users need to update
+- **Potential ambiguity**: ID could be confused with command in some cases
+- **Parsing complexity**: Need careful handling of edge cases
+
+#### Design Decisions
+1. **Make ID positional for all commands that currently use --id**
+2. **Keep -- separator support** for complex commands
+3. **Update help text** to reflect new usage
+4. **Maintain backward compatibility** by supporting both patterns initially (with deprecation warning)
+
+#### Commands to Update
+- `run <id> <command...>` - ID becomes first positional arg
+- `stop <id>` - ID becomes positional arg, remove timeout flag positioning issues
+- `tail <id>` - ID becomes positional arg
+- `cat <id>` - ID becomes positional arg  
+- `status <id>` - ID becomes positional arg
+
+#### Implementation Strategy
+1. **Phase 1**: Support both patterns with deprecation warnings
+2. **Phase 2**: Remove old pattern support (future version)
+
+### Implementation Steps
+1. Define new argument structures with positional ID fields
+2. Update clap derive macros to make ID positional
+3. Update help text and documentation strings
+4. Add deprecation warnings for --id usage (optional)
+5. Update all internal function calls
+6. Update tests to use new CLI pattern
+7. Update LLM guide output
+
+### Files to modify
+- `src/main.rs` - argument structures, help text
+- `tests/cli.rs` - all test commands
+- LLM guide text
+
+### Risk Assessment
+- **High risk** - Breaking change for users
+- Need to update all tests
+- Must carefully verify argument parsing edge cases
+- Consider gradual migration strategy
+
+## Task 4: Write Comprehensive README.md
+
+### Target Audience
+- Developers who need background process management
+- LLM agents and their operators
+- DevOps engineers running long-term tasks
+- Anyone working with npm run dev, build processes, etc.
+
+### Content Structure
+```markdown
+# Demon - Background Process Manager
+
+## Overview
+Brief description focusing on core value proposition
+
+## Installation
+- `cargo install demon` (when published)
+- Building from source
+- System requirements
+
+## Quick Start
+- Basic examples
+- Common workflows
+
+## Use Cases
+- Development servers (npm run dev)
+- Background tasks and scripts
+- LLM agent process management
+- CI/CD pipeline tasks
+- Long-running computations
+
+## Command Reference
+- Complete command documentation
+- Examples for each command
+- Common flags and options
+
+## Integration with LLM Agents
+- How agents can use demon
+- Machine-readable output formats
+- Best practices for automation
+
+## Advanced Usage
+- File management
+- Process lifecycle
+- Troubleshooting
+- Performance considerations
+
+## Contributing
+- Development setup
+- Testing
+- Contribution guidelines
+```
+
+### Key Messages
+1. **Simplicity**: Easy background process management
+2. **Visibility**: Always know what's running and its status
+3. **Integration**: Built for automation and LLM agents
+4. **Reliability**: Robust process lifecycle management
+
+### Implementation Steps
+1. Research similar tools for README inspiration
+2. Write comprehensive content covering all sections
+3. Include practical examples and screenshots/command outputs
+4. Add badges for build status, crates.io, etc. (when applicable)
+5. Review and refine for clarity and completeness
+
+### Files to create
+- `README.md` - comprehensive documentation
+
+### Risk Assessment
+- **Low risk** - Documentation only
+- No functional changes
+- Easy to iterate and improve
+
+## Execution Order
+
+1. **Task 1**: Rename PidFileData to PidFile (Low risk, enables clean foundation)
+2. **Task 2**: Implement PidFileReadError enum (Medium risk, improves error handling)
+3. **Task 3**: Make --id positional (High risk, but significant UX improvement)
+4. **Task 4**: Write README.md (Low risk, improves project presentation)
+
+## Testing Strategy
+
+After each task:
+1. Run `cargo build` to ensure compilation
+2. Run `cargo test` to ensure all tests pass
+3. Manual testing of affected functionality
+4. Format code with `cargo fmt`
+5. Commit changes with descriptive message
+
+## Success Criteria
+
+- All tests pass after each change
+- No regressions in functionality
+- Improved error messages and handling
+- Better CLI usability
+- Comprehensive documentation
+- Clean, maintainable code
+
+## Rollback Plan
+
+Each task will be committed separately, allowing for easy rollback if issues arise:
+1. Git commit after each successful task
+2. If issues found, can revert specific commits
+3. Tests provide safety net for functionality
+
+## Timeline Estimate
+
+- Task 1: 15-20 minutes (straightforward refactor)
+- Task 2: 30-45 minutes (error handling logic)
+- Task 3: 45-60 minutes (CLI argument changes + tests)
+- Task 4: 30-45 minutes (documentation writing)
+
+Total: ~2-3 hours
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index c82208b..4ab1dd9 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,20 +11,20 @@ use std::time::Duration;
 
 /// Represents the contents of a PID file
 #[derive(Debug, Clone)]
-struct PidFileData {
+struct PidFile {
     /// Process ID
     pid: u32,
     /// Command that was executed (program + arguments)
     command: Vec<String>,
 }
 
-impl PidFileData {
-    /// Create a new PidFileData instance
+impl PidFile {
+    /// Create a new PidFile instance
     fn new(pid: u32, command: Vec<String>) -> Self {
         Self { pid, command }
     }
 
-    /// Write PID file data to a file
+    /// Write PID file to a file
     fn write_to_file<P: AsRef<Path>>(&self, path: P) -> Result<()> {
         let mut file = File::create(path)?;
         writeln!(file, "{}", self.pid)?;
@@ -34,7 +34,7 @@ impl PidFileData {
         Ok(())
     }
 
-    /// Read PID file data from a file
+    /// Read PID file from a file
     fn read_from_file<P: AsRef<Path>>(path: P) -> Result<Self> {
         let contents = std::fs::read_to_string(path)?;
         let lines: Vec<&str> = contents.lines().collect();
@@ -244,8 +244,8 @@ fn run_daemon(id: &str, command: &[String]) -> Result<()> {
         .with_context(|| format!("Failed to start process '{}' with args {:?}", program, args))?;
 
     // Write PID and command to file
-    let pid_data = PidFileData::new(child.id(), command.to_vec());
-    pid_data.write_to_file(&pid_file)?;
+    let pid_file_data = PidFile::new(child.id(), command.to_vec());
+    pid_file_data.write_to_file(&pid_file)?;
 
     // Don't wait for the child - let it run detached
     std::mem::forget(child);
@@ -261,14 +261,14 @@ fn is_process_running(pid_file: &str) -> Result<bool> {
         return Ok(false); // No PID file means no running process
     }
 
-    let pid_data = match PidFileData::read_from_file(pid_file) {
+    let pid_file_data = match PidFile::read_from_file(pid_file) {
         Ok(data) => data,
         Err(_) => return Ok(false), // Invalid PID file
     };
 
     // Check if process is still running using kill -0
     let output = Command::new("kill")
-        .args(&["-0", &pid_data.pid.to_string()])
+        .args(&["-0", &pid_file_data.pid.to_string()])
         .output()?;
 
     Ok(output.status.success())
@@ -278,7 +278,7 @@ fn stop_daemon(id: &str, timeout: u64) -> Result<()> {
     let pid_file = format!("{}.pid", id);
 
     // Check if PID file exists and read PID data
-    let pid_data = match PidFileData::read_from_file(&pid_file) {
+    let pid_file_data = match PidFile::read_from_file(&pid_file) {
         Ok(data) => data,
         Err(_) => {
             if Path::new(&pid_file).exists() {
@@ -291,7 +291,7 @@ fn stop_daemon(id: &str, timeout: u64) -> Result<()> {
         }
     };
 
-    let pid = pid_data.pid;
+    let pid = pid_file_data.pid;
 
     tracing::info!(
         "Stopping daemon '{}' (PID: {}) with timeout {}s",
@@ -599,19 +599,19 @@ fn list_daemons(quiet: bool) -> Result<()> {
         let id = path_str.strip_suffix(".pid").unwrap_or(&path_str);
 
         // Read PID data from file
-        match PidFileData::read_from_file(&path) {
-            Ok(pid_data) => {
-                let status = if is_process_running_by_pid(pid_data.pid) {
+        match PidFile::read_from_file(&path) {
+            Ok(pid_file_data) => {
+                let status = if is_process_running_by_pid(pid_file_data.pid) {
                     "RUNNING"
                 } else {
                     "DEAD"
                 };
 
                 if quiet {
-                    println!("{}:{}:{}", id, pid_data.pid, status);
+                    println!("{}:{}:{}", id, pid_file_data.pid, status);
                 } else {
-                    let command = pid_data.command_string();
-                    println!("{:<20} {:<8} {:<10} {}", id, pid_data.pid, status, command);
+                    let command = pid_file_data.command_string();
+                    println!("{:<20} {:<8} {:<10} {}", id, pid_file_data.pid, status, command);
                 }
             }
             Err(_) => {
@@ -649,12 +649,12 @@ fn status_daemon(id: &str) -> Result<()> {
     }
 
     // Read PID data from file
-    match PidFileData::read_from_file(&pid_file) {
-        Ok(pid_data) => {
-            println!("PID: {}", pid_data.pid);
-            println!("Command: {}", pid_data.command_string());
+    match PidFile::read_from_file(&pid_file) {
+        Ok(pid_file_data) => {
+            println!("PID: {}", pid_file_data.pid);
+            println!("Command: {}", pid_file_data.command_string());
 
-            if is_process_running_by_pid(pid_data.pid) {
+            if is_process_running_by_pid(pid_file_data.pid) {
                 println!("Status: RUNNING");
 
                 // Show file information
@@ -696,13 +696,13 @@ fn clean_orphaned_files() -> Result<()> {
         let id = path_str.strip_suffix(".pid").unwrap_or(&path_str);
 
         // Read PID data from file
-        match PidFileData::read_from_file(&path) {
-            Ok(pid_data) => {
+        match PidFile::read_from_file(&path) {
+            Ok(pid_file_data) => {
                 // Check if process is still running
-                if !is_process_running_by_pid(pid_data.pid) {
+                if !is_process_running_by_pid(pid_file_data.pid) {
                     println!(
                         "Cleaning up orphaned files for '{}' (PID: {})",
-                        id, pid_data.pid
+                        id, pid_file_data.pid
                     );
 
                     // Remove PID file
@@ -737,7 +737,7 @@ fn clean_orphaned_files() -> Result<()> {
                     tracing::info!(
                         "Skipping '{}' (PID: {}) - process is still running",
                         id,
-                        pid_data.pid
+                        pid_file_data.pid
                     );
                 }
             }