# sframe — CLAUDE.md

## Project

sframe (Simple Frame) is a lightweight command-line tool written in C
following the suckless philosophy. It extracts unique frames from video
files for research purposes, using perceptual hashing to eliminate
duplicates and embedding timestamps in filenames.

## Coding Standards — Suckless C Style

All code in this project MUST follow the suckless.org coding style:

### Language
- C99 (ISO/IEC 9899:1999), no extensions
- POSIX.1-2008 (`_POSIX_C_SOURCE 200809L`)

### Indentation & Whitespace
- Tabs for indentation (1 tab = 1 level)
- Spaces for alignment only, never for indentation
- No tabs except at the beginning of a line
- Maximum line length: 79 characters

### Comments
- Use `/* */` only, never `//`
- Comment fallthrough cases in switch statements

### Variables
- All declarations at the top of the block
- Pointer `*` adjacent to variable name: `char *p`, not `char* p`
- No C99 `bool`; use `int` (0/1)
- Global/static variables not used outside TU must be `static`

### Functions
- Return type on its own line
- Function name at column 0 on next line (enables `grep ^funcname`)
- Opening `{` on its own line for functions
- Functions not used outside their file: `static`

```c
static void
usage(void)
{
	fprintf(stderr, "usage: sframe [-t thresh] [-f fmt] video\n");
	exit(1);
}
```

### Braces
- Opening `{` on same line for control flow (if, for, while, switch)
- Closing `}` on its own line unless continuing (else, do-while)
- Use braces even for single statements when sibling branches use them

### Naming
- lowercase_with_underscores for functions and variables
- UPPERCASE for macros and constants
- CamelCase for typedef'd struct types
- No `_t` suffix (reserved by POSIX)
- Prefix module functions: `dec_open()`, `diff_hash()`, `util_die()`

### Control Flow
- Space after `if`, `for`, `while`, `switch`
- No space after `(` or before `)`
- Use `goto` for cleanup/unwind, not nested ifs
- Return/exit early on failure
- Test against 0, not -1: `if (func() < 0)`

### Error Handling
- All allocation checked; goto cleanup on failure
- `die()` for fatal errors (prints message, exits)
- `warn()` for recoverable errors (prints, continues)

### File Organization Order
1. License header
2. System includes (alphabetical)
3. Local includes
4. Macros
5. Type definitions
6. Function declarations
7. Global variables
8. Function definitions (same order as declarations)

### Headers
- System headers first, alphabetical
- Local headers after blank line
- No cyclic dependencies
- Include only what is needed

## Architecture Rules

- **No global mutable state.** Pass context structs explicitly.
- **No `system()` calls.** Use `fork()/execvp()` or `popen()`.
- **No hardcoded paths** except sensible defaults (`~/frames`).
- **Separate compilation.** Every .c file compiles independently.

## Module Prefixes

| Module | Prefix | File |
|--------|--------|------|
| Main/CLI | — | main.c |
| Decode | `dec_` | decode.c |
| Diff | `diff_` | diff.c |
| Utilities | `die()`, `warn()`, `ecalloc()` | util.c |

## Build

```sh
make        # build sframe binary
make clean  # remove build artifacts
make install PREFIX=/usr/local  # install
```

## Dependencies

- FFmpeg libraries: libavformat, libavcodec, libavutil, libswscale

## Git Conventions

- No `Co-Authored-By: Claude` lines
- Commit messages: imperative, <72 chars, no period
- One logical change per commit

## CRITICAL: No Building on Moirai

NEVER run `make`, `sudo make install`, or any build command unless
Kris explicitly says "build" in his message.