datatools-dev/docs/DEVELOPER.md

# Developer Guide

Architecture, data flow, and extension guide for the DataTools Deduplicator.

## Architecture

```
CLI (src/cli.py)                 GUI (src/gui/app.py)
     │                                │
     │  flags → strategies            │  widgets → strategies
     │  _interactive_review()         │  match_group_card()
     │  tqdm progress bar             │  st.progress()
     │                                │
     └──────────┐    ┌────────────────┘
                │    │
                ▼    ▼
          ┌─────────────────┐
          │   core.dedup     │
          │  deduplicate()   │
          └────────┬────────┘
                   │
      ┌────────────┼────────────┐
      ▼            ▼            ▼
 core.io      core.normalizers  core.config
 read/write   normalize_*()     save/load JSON
```

**Key principle:** All business logic lives in `src/core/`. The CLI and GUI are thin wrappers that translate user input into `deduplicate()` arguments and display the `DeduplicationResult`.

## File-by-File Reference

### src/core/dedup.py — Deduplication Engine

The central module. Contains:

- **Enums:** `Algorithm` (4 fuzzy algorithms), `SurvivorRule` (4 selection rules)
- **Data classes:** `ColumnMatchStrategy`, `MatchStrategy`, `MatchResult`, `DeduplicationResult`
- **`deduplicate()`** — main entry point. Takes a DataFrame + optional strategies/rules, returns a `DeduplicationResult` with deduplicated DataFrame, removed rows, match groups, and log entries.
- **`build_default_strategies()`** — scans column names with regex patterns to auto-detect email, phone, name, and address columns. Builds strong/weak key strategies with appropriate algorithms and normalizers.
- **`_UnionFind`** — disjoint-set data structure for transitive closure. If A matches B and B matches C, all three end up in one group.
- **`_find_match_groups()`** — O(n^2) pairwise comparison. For each pair, tries all strategies (OR semantics). Feeds matches into union-find. Returns match groups with confidence scores.
- **`_select_survivor()`** — picks the row to keep based on the survivor rule.
- **`_merge_group()`** — fills blank fields in the survivor from loser rows.

### src/core/normalizers.py — Text Normalization

Five normalizer functions, each `str → str`, idempotent, None-safe:

- **`normalize_email()`** — lowercase, strip Gmail dots, strip `+tag` suffixes
- **`normalize_phone()`** — parse with `phonenumbers` to E.164; fallback to digits-only
- **`normalize_name()`** — strip title prefixes (Dr., Mr.) and suffixes (Jr., PhD), case-fold
- **`normalize_address()`** — USPS abbreviations (Street→St, Avenue→Ave), case-fold
- **`normalize_string()`** — trim, collapse whitespace, case-fold

The `get_normalizer()` registry function maps `NormalizerType` enum values to functions.

### src/core/io.py — File I/O

Auto-detection stack:

1. **`detect_encoding()`** — checks BOM, then uses `charset-normalizer` heuristics
2. **`detect_delimiter()`** — uses `csv.Sniffer` on first 20 lines
3. **`detect_header_row()`** — finds first row where all cells look like column names

Main functions:
- **`read_file()`** — reads CSV/TSV/Excel with full auto-detection. Returns a DataFrame.
- **`write_file()`** — writes DataFrame to CSV or Excel. Uses `utf-8-sig` by default for Windows Excel compatibility.
- **`list_sheets()`** — returns sheet names from an Excel workbook.

### src/core/config.py — Configuration Profiles

Save/load deduplication settings as JSON:

- **`DeduplicationConfig`** — flat dataclass with all settings: strategies, survivor rule, merge flag, algorithm, threshold, normalizer map.
- **`.to_file()` / `.from_file()`** — JSON serialization
- **`.to_strategies()`** — converts config back to `MatchStrategy` objects for the engine
- **`.to_survivor_rule()`** — converts string to `SurvivorRule` enum

### src/cli.py — Command-Line Interface

Typer-based CLI with 17 options. Key responsibilities:

- Parse flags into strategies, survivor rule, and other config
- Set up logging (timestamped log files in `logs/`)
- Column name validation with fuzzy suggestions on typos
- `_interactive_review()` — side-by-side row display with y/n/s prompts
- Progress bar via `tqdm` for files > 10,000 rows
- Output formatting and file writing

### src/gui/app.py — Streamlit GUI

Single-page layout:
- File upload with instant preview
- Advanced options expander (column selection, fuzzy, normalizers, survivor rule, merge, config profiles)
- Find Duplicates button → runs `deduplicate()` with `progress_callback`
- Interactive review: expandable match group cards with merge/keep/skip buttons
- Download buttons for deduplicated CSV, removed rows, and match groups report

### src/gui/components.py — Reusable GUI Widgets

- **`match_group_card()`** — expandable card showing side-by-side row comparison with diff highlighting
- **`config_panel()`** — the advanced options expander, returns a `DeduplicationConfig`
- **`results_summary()`** — summary stats and download buttons

## Data Flow

```
Input File
    │
    ▼
read_file()          ← auto-detect encoding, delimiter, header
    │
    ▼
DataFrame
    │
    ▼
build_default_strategies()   ← (if no explicit strategies)
    │                            scan column names → regex patterns
    │                            strong keys: email, phone (standalone OR)
    │                            weak keys: name, address (AND with strong)
    ▼
_apply_normalizations()      ← add _norm_* shadow columns
    │                            normalize_email(), normalize_phone(), etc.
    ▼
_find_match_groups()         ← O(n²) pairwise comparison
    │                            for each pair: try all strategies (OR)
    │                            _compute_similarity() per column
    │                            union-find for transitive closure
    ▼
[review_callback()]          ← optional: interactive review per group
    │                            True=accept, False=reject, None=skip
    ▼
_select_survivor()           ← per group: first/last/most-complete/most-recent
    │
    ▼
[_merge_group()]             ← optional: fill blanks from losers
    │
    ▼
DeduplicationResult
    ├── deduplicated_df      ← cleaned DataFrame (shadow cols dropped)
    ├── removed_df           ← rows that were removed
    ├── match_groups         ← list of MatchResult with confidence, columns
    └── log_entries          ← human-readable audit log
```

## How to Add a Normalizer

1. **Add the function** in `src/core/normalizers.py`:

```python
def normalize_company(value: Optional[str]) -> str:
    """Strip legal suffixes (Inc, LLC, Corp), case-fold."""
    if not value or not isinstance(value, str):
        return ""
    name = value.strip().casefold()
    # Strip common suffixes
    for suffix in ("inc", "llc", "corp", "ltd", "co"):
        name = re.sub(rf"\b{suffix}\.?\s*$", "", name).strip()
    return name
```

2. **Register it** in the same file:

```python
class NormalizerType(str, Enum):
    # ... existing types ...
    COMPANY = "company"      # ← add enum value

_NORMALIZER_MAP: dict[NormalizerType, Callable[[str], str]] = {
    # ... existing entries ...
    NormalizerType.COMPANY: normalize_company,   # ← add mapping
}
```

3. **Add auto-detection pattern** in `src/core/dedup.py` (optional):

```python
_COLUMN_TYPE_PATTERNS = [
    # ... existing patterns ...
    (re.compile(r"company|organization|org_name", re.I),
     NormalizerType.COMPANY, Algorithm.TOKEN_SET_RATIO, 85.0, False),
]
```

## How to Add a Matching Algorithm

1. **Add the enum value** in `src/core/dedup.py`:

```python
class Algorithm(str, Enum):
    # ... existing values ...
    SOUNDEX = "soundex"
```

2. **Add the computation** in `_compute_similarity()`:

```python
def _compute_similarity(val_a: str, val_b: str, algorithm: Algorithm) -> float:
    # ... existing cases ...
    if algorithm == Algorithm.SOUNDEX:
        return 100.0 if _soundex(val_a) == _soundex(val_b) else 0.0
```

3. **Add the CLI flag value** in `src/cli.py` help text for `--algorithm`.

## How to Add a Survivor Strategy

1. **Add the enum value** in `src/core/dedup.py`:

```python
class SurvivorRule(str, Enum):
    # ... existing values ...
    KEEP_LONGEST = "longest"
```

2. **Add the logic** in `_select_survivor()`:

```python
if rule == SurvivorRule.KEEP_LONGEST:
    return max(indices, key=lambda i: len(str(df.iloc[i].to_dict())))
```

3. **Add to the CLI** survivor map in `src/cli.py`.

## Testing

### Run Tests

```bash
# All tests
pytest tests/ -q

# Specific module
pytest tests/test_dedup.py -q
pytest tests/test_normalizers.py -q
pytest tests/test_io.py -q
pytest tests/test_config.py -q
pytest tests/test_cli.py -q

# Verbose with output
pytest tests/ -v

# Stop on first failure
pytest tests/ -x
```

### Test Structure

```
tests/
├── conftest.py          # Shared fixtures
│   ├── sample_csv_path  # Path to samples/messy_sales.csv
│   ├── sample_df        # Loaded sample CSV as DataFrame
│   ├── simple_df        # Small 5-row DataFrame with obvious duplicates
│   ├── merge_df         # DataFrame with partial records
│   └── tmp_csv          # Temporary CSV from simple_df
├── test_dedup.py        # Engine tests: similarity, union-find, pairs, integration
├── test_normalizers.py  # Normalizer tests: all 5 types with edge cases
├── test_io.py           # I/O tests: encoding, delimiter, header, read/write
├── test_config.py       # Config tests: serialization round-trip
└── test_cli.py          # CLI tests: argument parsing, file handling
```

### Writing Tests

Follow existing patterns. Tests use pytest fixtures from `conftest.py`:

```python
def test_my_feature(simple_df):
    """Test description."""
    result = deduplicate(simple_df, ...)
    assert len(result.match_groups) == expected
    assert result.deduplicated_df.shape[0] == expected_rows
```

## Known Limitations

- **O(n^2) pairwise comparison** — no blocking or indexing. Works well up to ~50,000 rows. Beyond that, performance degrades quadratically. Future optimization: add blocking (partition by first letter, zip code prefix, etc.) to reduce comparison space.
- **No multi-sheet dedup** — each Excel sheet is processed independently. Cross-sheet deduplication is not supported.
- **Phone normalization requires valid-length numbers** — the `phonenumbers` library rejects numbers that are too short or too long for the detected region. Fallback is digits-only, which may produce false negatives for international numbers without country codes.
- **Single-threaded** — no parallel comparison. Could benefit from `multiprocessing` for large files.
- **Memory-bound** — entire file is loaded into a pandas DataFrame. Files larger than available RAM will fail. Chunked reading exists but is not integrated with the dedup engine.