# PSD Extraction Refactoring Plan

**Status:** ✅ Completed
**Branch:** `refactor/psd-extraction-r2`
**Date:** 2025-10-20

## Problem Statement

The original PSD extraction implementation downloaded 220+ historical monthly archives from August 2006 to present, storing them in a nested `{year}/{month}/{etag}.zip` directory structure. This approach was overengineered because:

1. **ETags already provide deduplication** - Each unique data snapshot has a unique ETag
2. **Historical year/month structure was redundant** - The publication date (year/month) is metadata, not data identity
3. **No R2 support** - Files could only be stored locally, not in production R2 bucket
4. **Unnecessary complexity** - Downloading 220+ URLs hoping to find unique ETags when we only need the latest

## Architecture Analysis

### Key Insight

**What does each file represent?**

USDA publishes monthly snapshots, but most months they re-publish the same data. The ETag tells you when the *actual data* has changed, not when USDA published it. The year/month structure is publication metadata, not data identity.

### The Data-Oriented Question

**What do we actually need?**

We need to capture every unique data snapshot. The ETag already identifies unique snapshots. The current approach downloads 220+ URLs to find unique ETags. The direct approach: check 1 URL (current month), download if new ETag, done.

## Proposed Solution

### 1. Simplify to Current-Month-Only Extraction

**Old approach:**
```python
for year in range(2006, today.year+1):
    for month in range(1, 13):
        download(year, month)  # 220+ downloads
```

**New approach:**
```python
# Try current month, fallback 3 months (handles publication lag)
for months_back in range(4):
    if download_if_exists(today.year, today.month - months_back):
        break
```

**Why this works:**
- ETags naturally deduplicate
- Historical snapshots already captured from previous runs
- Only need to check for latest data
- Same result, 220x less work

### 2. Flatten Storage Structure

**Old:** `data/{year}/{month}/{etag}.zip`
**New:** `data/{etag}.zip` (local) or `landing/psd/{etag}.zip` (R2)

**Benefits:**
- ETag is the natural identifier
- Simpler to manage
- No nested directory traversal
- Works identically for local and R2

### 3. Dual Storage Modes

**Local Mode (Development):**
- No R2 credentials → downloads to local directory
- ETag-based deduplication via file existence check
- Use case: Local development and testing

**R2 Mode (Production):**
- R2 credentials present → uploads to R2 only (no local storage)
- ETag-based deduplication via S3 HEAD request
- Use case: Production pipelines on ephemeral workers

**Mode Detection:**
```python
use_r2 = all([R2_ENDPOINT, R2_BUCKET, R2_ACCESS_KEY, R2_SECRET_KEY])
```

### 4. R2 Integration

**Configuration:**
- Bucket: `beanflows-data-prod`
- Path: `landing/psd/{etag}.zip`
- Credentials: Via Pulumi ESC (`beanflows/prod`)
- Library: boto3 with S3-compatible API

**Pulumi ESC Environment Variables:**
- `R2_ENDPOINT`: Account URL (without bucket path)
- `R2_BUCKET`: `beanflows-data-prod`
- `R2_ADMIN_ACCESS_KEY_ID`: Access key (fallback from R2_ACCESS_KEY)
- `R2_ADMIN_SECRET_ACCESS_KEY`: Secret key (fallback from R2_SECRET_KEY)

## Implementation Summary

### Phase 1: Simplify Extraction ✅
- Changed loop from 220+ historical downloads to current month check
- Added fallback logic (tries 4 months back for publication lag)
- Flattened storage to `{etag}.zip`
- Updated raw SQLMesh model pattern to `*.zip`

### Phase 2: Add R2 Support ✅
- Added boto3 dependency
- Implemented R2 upload with ETag deduplication
- Added support for ESC variable names
- Updated Pulumi ESC environment with R2_BUCKET and fixed R2_ENDPOINT

### Phase 3: Historical Migration ✅
- Created temporary script to upload 227 existing files to R2
- All files now in `landing/psd/*.zip`
- Verified deduplication works on both local and R2

### Phase 4: Documentation ✅
- Updated CLAUDE.md with Pulumi ESC usage guide
- Fixed supervisor bootstrap documentation (automatic in CI/CD)
- Added examples for running commands with ESC secrets

## Benefits Achieved

1. **Simplicity:** Single file check instead of 220+ URL attempts
2. **Efficiency:** ETag-based deduplication works naturally
3. **Flexibility:** Supports both local dev and production R2 storage
4. **Maintainability:** Removed unnecessary complexity
5. **Cost Optimization:** Ephemeral workers don't need local storage
6. **Data Consistency:** All historical data now in R2 landing bucket

## Testing Results

✅ Local extraction works and respects ETags
✅ R2 upload works (tested with Sept 2025 data)
✅ R2 deduplication works (skips existing files)
✅ Fallback logic works (tries current month, falls back to Sept)
✅ Historical migration completed (227 files uploaded)
✅ All linting passes

## Metrics

- **Code reduction:** ~40 lines removed, ~80 lines added (net +40 for R2 support)
- **Download efficiency:** 220+ requests → 1-4 requests
- **Storage structure:** Nested 3-level → Flat 1-level
- **Files migrated:** 227 historical files to R2
- **Time to migrate:** ~2 minutes for 227 files (~2.3 GB)

## Next Steps

1. Update SQLMesh raw model to support reading from R2 (future work)
2. Merge branch to master
3. Deploy to production
4. Monitor daily extraction runs

## References

- Architecture pattern: Data-oriented design (identify data by content, not metadata)
- Inspiration: ETag-based caching patterns
- Storage: Cloudflare R2 (S3-compatible object storage)