# P4LF Session Log — 2026-07-29 (Session 6: Date-Stamped Filenames + MaxLogChunks Delete-Oldest)

## Session Goal

Implement three new requirements and update the README to reflect the actual Go implementation:

1. Add a date stamp to chunk filenames to prevent naming collisions after log rotation.
2. Change `MaxLogChunks` behavior from "pause when limit reached" to "delete oldest files to make room."
3. Update the README to remove outdated `p4 logtail` language.

## Prompts

User asked agent to review the `copilot-instructions.md` (AGENTS.md) and present a plan, then approved the plan.

## Key Decisions

### Filename format change
**Old:** `log.<offset1>.<offset2>.gz`
**New:** `log.<YYYY-MM-DD>.<offset1>.<offset2>.gz`

Using `time.Now()` at write time, formatted with Go's reference date `"2006-01-02"`. The date is embedded before the offsets for human readability and to prevent collisions when the same byte ranges appear in a freshly rotated log.

### MaxLogChunks: delete-oldest instead of pause-and-wait
The previous behavior paused chunk writes when `MaxLogChunks` was reached, waiting for the downstream consumer to delete files. The new behavior deletes the oldest files (by modification time) to make room before writing the new chunk. A `Warnf` is emitted for each enforcement action, making it clear in the p4lf log that data is being lost.

Rationale: It is more important to have current P4LOG data than to ensure continuity in the event the downstream consumer is not working.

The `WaitUntilGuardsPassed` method now only checks `MinLogSpace` (the disk-space guard), since `MaxLogChunks` no longer blocks writes.

### Default for MaxLogChunks changed from 0 to 5000
At 1 chunk/minute, 5000 files ≈ 3.5 days of buffering — a reasonable safety net before data loss begins. Operators can set to 0 to disable the limit.

### README rewrite
The README previously described a bash implementation using `p4 logtail` with offsets. The actual implementation is in Go, uses direct file reading with inode-based rotation detection, and never calls `p4 logtail`. The README was rewritten from scratch to accurately describe the Go implementation, the new filename format, and the updated `MaxLogChunks` semantics.

## Files Changed

| File | Change |
|---|---|
| `internal/chunker/chunker.go` | New filename format with date; `enforceMaxLogChunks()` replaces `checkGuards()`; `checkSpaceGuard()` split out; `chunkFilesSortedByAge()` helper added; updated package doc |
| `internal/chunker/chunker_test.go` | Updated `TestWrite_CreatesGzipFile` to use glob for date-stamped name; rewrote `TestWrite_MaxLogChunks` to verify delete-oldest behavior |
| `internal/config/config.go` | Default `MaxLogChunks` changed from `0` to `5000`; field doc updated |
| `internal/config/config_test.go` | Updated `TestLoad_Defaults` to expect `MaxLogChunks=5000` |
| `p4lf.cfg.example` | Updated `MaxLogChunks` comment to describe delete-oldest behavior, new default, and ~3.5 day buffer note |
| `README.md` | Full rewrite: removed `p4 logtail` language, described inode-based tailing, new filename format, updated config settings, accurate Basic Flow |

## make check Status

All tests passing on macOS after changes:
- `workshop.perforce.com/p4lf/internal/chunker` ✓
- `workshop.perforce.com/p4lf/internal/config` ✓
- `workshop.perforce.com/p4lf/internal/version` ✓

## Open Items / Next Steps

- Submit these changes to //p4lf/dev (pending user approval).
- Integration test on the customer sandbox: verify new filename format appears in LogChunksDir, verify MaxLogChunks deletion in action.
- Consider adding unit tests for tailer (rotation detection, state file resume) — noted as open in prior sessions.