---
phase: 01-capture-and-classification
plan: 03
subsystem: aggregation
tags: [go, channels, goroutines, time-windows, io-writer, stderr-output]

# Dependency graph
requires:
  - phase: 01-capture-and-classification
    provides: classify.ClassifiedPacket and classify.WindowSnapshot types from classify/types.go (Plan 01)

provides:
  - Ticker-driven Aggregate function reading ClassifiedPackets, emitting WindowSnapshots per time window
  - PrintSummary for final per-protocol packet counts with percentages to io.Writer
  - PrintWindowLine for verbose per-window activity output
  - AccumulateTotals for merging snapshot counts into cumulative totals

affects: [02-audio-synthesis, audio-engine-phase]

# Tech tracking
tech-stack:
  added: []
  patterns:
    - "Aggregate pattern: done+events+ticker select loop with flush-on-done"
    - "io.Writer injection for testable output (bytes.Buffer in tests, os.Stderr in main)"
    - "Sorted output via sort.Strings on map keys for deterministic stderr display"

key-files:
  created:
    - aggregate/window.go
    - aggregate/window_test.go
    - aggregate/summary.go
    - aggregate/summary_test.go
  modified: []

key-decisions:
  - "DefaultWindowMs=500: 500ms windows balance temporal resolution against snapshot frequency"
  - "onSnapshot callback in Aggregate for optional verbose mode, nil-safe (no overhead when not verbose)"
  - "io.Writer injection in PrintSummary/PrintWindowLine enables unit-test capture via bytes.Buffer and production use via os.Stderr"

patterns-established:
  - "Pattern: aggregate package bridges classify output to Phase 2 audio synthesis via WindowSnapshot channel"
  - "Pattern: AccumulateTotals + PrintSummary separation keeps formatting logic independent of accumulation"

requirements-completed: [CLAS-03, CLAS-04]

# Metrics
duration: 8min
completed: 2026-03-25
---

# Phase 01 Plan 03: Aggregation and Stats Reporting Summary

**Ticker-driven window aggregator with per-class packet counting, verbose per-window stdout lines, and sorted exit protocol summary — bridging packet classification to Phase 2 audio synthesis**

## Performance

- **Duration:** ~8 min
- **Started:** 2026-03-25T11:15:42Z
- **Completed:** 2026-03-25T11:23:00Z
- **Tasks:** 2
- **Files modified:** 4

## Accomplishments

- Aggregate goroutine accumulates ClassifiedPackets into time windows using done+events+ticker select loop, emitting WindowSnapshot per tick and flushing partial window on done
- PrintSummary renders per-protocol packet counts with percentages and TOTAL line to any io.Writer, sorted alphabetically for deterministic output
- PrintWindowLine renders per-window verbose activity line in "[window N] CLASS:count (total: N)" format
- AccumulateTotals merges snapshot counts into cumulative totals for use with PrintSummary on exit
- 11 unit tests total passing across both files (no race detector — CGO_ENABLED=0 environment)

## Task Commits

Each task was committed atomically:

1. **Task 1: Ticker-driven window aggregator** - `2a8fd7d` (feat)
2. **Task 2: Exit summary and verbose window output** - `f2bebaf` (feat)

**Plan metadata:** TBD (docs: complete plan)

_Note: TDD tasks had test → feat commit pattern per task._

## Files Created/Modified

- `aggregate/window.go` - Aggregate function with done/events/ticker select loop and DefaultWindowMs constant
- `aggregate/window_test.go` - 5 tests: EmitsSnapshot, MultipleClasses, DoneFlushesPartial, EmptyWindow, WindowIndex
- `aggregate/summary.go` - PrintSummary, PrintWindowLine, AccumulateTotals functions
- `aggregate/summary_test.go` - 6 tests: PrintSummary, PrintSummaryEmpty, PrintSummarySorted, PrintWindowLine, PrintWindowLineEmpty, AccumulateTotals

## Decisions Made

- DefaultWindowMs set to 500ms (0.5 seconds) — matches typical human perception granularity for network bursts without overwhelming snapshot channel
- onSnapshot callback passed as nil-safe function pointer into Aggregate; main.go will set this to PrintWindowLine when --verbose flag is active, zero overhead otherwise
- io.Writer interface chosen over os.Stderr hardcoding — allows test capture with bytes.Buffer while production code passes os.Stderr

## Deviations from Plan

None — plan executed exactly as written.

One note: `-race` flag requires CGO_ENABLED=1, which is not available in this build environment. Tests were run without the race detector (`go test -v -count=1 ./aggregate/...`) and passed. The race-detector requirement from the plan verification section cannot be satisfied without CGO. This is a pre-existing environment constraint, not a code issue.

## Issues Encountered

- `go test -race` requires CGO_ENABLED=1 (LAME's CGo requirement). Environment has CGO_ENABLED=0. Tests ran and passed without -race flag.

## User Setup Required

None — no external service configuration required.

## Next Phase Readiness

- aggregate package ready for Phase 2 audio synthesis wiring
- Aggregate output channel (WindowSnapshot) is the contract Phase 2 audio engine consumes
- Main CLI (cmd/) will wire: capture → classify → Aggregate → audio synthesis, passing os.Stderr and --verbose flag to PrintWindowLine

## Self-Check: PASSED

All claimed files exist and both task commits are present in git history.

---
*Phase: 01-capture-and-classification*
*Completed: 2026-03-25*