# Developer Guide

Architecture, data flow, extension points.

## Architecture

```
CLI (src/cli*.py)         GUI (src/gui/app.py + pages/)
     │                          │
     └──────────┐    ┌──────────┘
                ▼    ▼
            ┌────────────────┐
            │   src/core/    │
            └────────────────┘
```

**Core/UI rule**: business logic in `core/` only. CLI + GUI translate user input → core call → display result.

## Module map

| Module | Public surface |
|--------|----------------|
| `i18n` | `t(key, lang=None, **fmt)`, `current_language()`, `set_language()`, `render_language_selector()`, `LANGUAGES` |
| `core.dedup` | `deduplicate()`, `MatchStrategy`, `ColumnMatchStrategy`, `Algorithm`, `SurvivorRule`, `DeduplicationResult`, `MatchResult`, `build_default_strategies()` |
| `core.normalizers` | `normalize_email/phone/name/address/string`, `NormalizerType`, `get_normalizer()` |
| `core.io` | `read_file()`, `write_file()`, `list_sheets()`, `detect_encoding/delimiter/header_row`, `repair_bytes()` |
| `core.config` | `DeduplicationConfig.from_file/to_file/to_strategies/to_survivor_rule` |
| `core.analyze` | `analyze()`, `Finding`, `findings_by_tool()`, `_NULL_LIKE` |
| `core.fixes` | `@register("fix_id")` decorator, `get_fix()`, `available_actions()` |
| `core.normalize` | `auto_fix()`, `apply_decisions()`, `NormalizationResult`, `is_normalized()` |
| `core.text_clean` | `clean_dataframe()`, `CleanOptions`, `CleanResult`, `smart_title_case()` |
| `core.format_standardize` | `standardize_dataframe()`, `StandardizeOptions`, `StandardizeResult`, `FieldType`, per-cell `standardize_*()` |
| `core.errors` | `DataToolsError` hierarchy, `ensure_dataframe()`, `ensure_choice()`, `wrap_file_read/write()`, `format_for_user()` |
| `core._constants` | `US_STATE_NAMES`, `US_STATE_CODES`, `USPS_EXPANSIONS`, `USPS_COMPRESSIONS` |

## Data flow — Find Duplicates

```
read_file()                       # auto-detect encoding, delimiter, header
   ▼ DataFrame
build_default_strategies()        # if no explicit strategies
   ▼                              # strong keys (email, phone) → standalone OR
                                  # weak keys (name, address) → AND with strong
_apply_normalizations()           # add _norm_* shadow columns
   ▼
_find_match_groups()              # O(n²) pair compare, OR strategies, union-find
   ▼
[review_callback()]               # optional interactive review
   ▼
_select_survivor()                # per group: first/last/most-complete/most-recent
   ▼
[_merge_group()]                  # optional: fill blanks from losers
   ▼
DeduplicationResult               # deduplicated_df, removed_df, match_groups, log
```

## Extension recipes

### Add a normalizer

1. Add function to `core/normalizers.py`:
   ```python
   def normalize_company(value: Optional[str]) -> str:
       if not value or not isinstance(value, str): return ""
       name = value.strip().casefold()
       for sfx in ("inc", "llc", "corp", "ltd", "co"):
           name = re.sub(rf"\b{sfx}\.?\s*$", "", name).strip()
       return name
   ```
2. Register: add `COMPANY = "company"` to `NormalizerType` + entry in `_NORMALIZER_MAP`.
3. Auto-detect (optional): add a `_COLUMN_TYPE_PATTERNS` row in `core/dedup.py`.

### Add a fuzzy algorithm

1. Add value to `Algorithm` enum in `core/dedup.py`.
2. Add case in `_compute_similarity()`.
3. Document the value in CLI help text.

### Add a survivor rule

1. Add value to `SurvivorRule` enum.
2. Add branch in `_select_survivor()`.
3. Add CLI mapping.

### Add a fix + detector (analyzer/gate)

1. **Detector** in `core/analyze.py`: add `_detect_<thing>(df) -> list[Finding]`, hook into the main `analyze()` pipeline. Emit Finding with a unique `fix_action` id.
2. **Fix** in `core/fixes.py`:
   ```python
   @register("fix_id")
   def my_fix(df, payload=None) -> tuple[pd.DataFrame, int]:
       # ...
       return out_df, cells_changed
   ```
3. **Constant** in `core/analyze.py`: add `FIX_<NAME> = "fix_id"` so the detector and fix can reference it.

No other call sites change. Gate auto-discovers it via the registry.

### Tool page header — `render_tool_header(tool_id)`

Every tool page renders its title block via `render_tool_header(tool_id)` in `src/gui/components/_legacy.py` — do not call `st.title()` + `st.caption()` directly. The helper renders:

- `tools.<id>.page_title` as the page title (left column).
- A **Help** popover button right of the title (icon `:material/help_outline:`, label from `help.button_label`). Clicking opens an `st.popover` containing the markdown body.
- `tools.<id>.page_caption` as the caption below.

All copy is i18n-driven; editors can tweak help text without touching Python. If a tool is missing its `help_md` key, the popover falls back to `help.missing_body`.

**`help_md` structure** (markdown, stored as a single string with `\n` line breaks in JSON):

```
**When to use**
- bullet 1
- bullet 2

**Steps**
1. numbered step
2. numbered step

**Examples**
- example 1
- example 2

**Tip** one-sentence pro tip.
```

Keep it short — the popover is intentionally compact. Mirror the structure across every tool so the muscle memory transfers.

### i18n — language packs

The GUI's user-facing strings live in `src/i18n/packs/<code>.json`, keyed by ISO-639-1 code. English (`en.json`) is canonical; missing keys in other packs fall back to English, and missing keys in English fall back to the literal dotted key so a typo is visible rather than silent.

**Look up a string in code:**
```python
from src.i18n import t
st.button(t("upload.run_button"))
st.warning(t("gate.warning", name=filename))   # {name} interpolated via str.format
```

`t()` reads the active language from `st.session_state["ui_lang"]`. Outside a Streamlit run (tests, scripts) it falls back to English.

**Add a new language:**
1. Copy `src/i18n/packs/en.json` to `src/i18n/packs/<code>.json` and translate values in place. Keep the key tree identical.
2. Add a one-line entry to `LANGUAGES` in `src/i18n/__init__.py`: `{"code": "fr", "label": "Français"}`. The sidebar picker auto-renders.
3. Run `pytest tests/test_lang_packs.py` — the parity test fails until every key from `en.json` exists in the new pack (and orphan keys not in English are also flagged).

**Add a new key:**
1. Add it to `en.json` first (canonical pack).
2. Add it to every other registered pack in the same commit. The parity test enforces this.
3. Use the dotted key at the call site: `t("section.subsection.key")` or `t("section.key", name=value)` for placeholder interpolation.

**Authoring rules:**
- Keys live under semantic sections (`home.*`, `upload.*`, `findings.*`, `help.*`, `tools.<id>.name`). Don't nest by language or by tool unless the string is genuinely tool-specific.
- Per-tool header copy lives under `tools.<id>.{page_title, page_caption, help_md}`. `page_caption` is the one-line subtitle under the title; `help_md` is the popover body (see *Tool page header* above). Top-level `help.button_label` / `help.missing_body` are shared across every tool.
- Use `{named}` placeholders (not positional `{0}`) so translators see what's being interpolated.
- Strings can contain Streamlit markdown (`**bold**`) — pass through `st.markdown` / `st.caption` as usual.
- Do **not** put strings inside the farewell-overlay JS payload without going through `_js_html_safe()` in `src/gui/components/_legacy.py`; the helper escapes both the JS string terminator and HTML special chars. The test `TestFarewellEscape` pins that contract.
- The sidebar picker is mounted by `hide_streamlit_chrome()`, so every page that calls that helper automatically gets the picker. Pages that don't call it (rare) can call `render_language_selector()` directly.

### Licensing

The license layer lives at ``src/license/``. The public API:

```python
from src.license import (
    get_manager, require_feature, current_state,
    FeatureFlag, Tier, License,
)

mgr = get_manager()
if not mgr.is_valid():
    raise RuntimeError("Not licensed")
require_feature(FeatureFlag.DEDUPLICATOR)
```

**Storage**: ``~/.datatools/license.json`` (override via
``DATATOOLS_LICENSE_PATH``). Signed with Ed25519 (asymmetric) — the
seller's private key signs; the buyer's binary verifies with the
embedded public key.

**Key material**:

| Variable | Who has it | Where it's used |
|---|---|---|
| ``DATATOOLS_LICENSE_PRIVKEY`` | Seller only | ``scripts/generate_license.py`` (mint a buyer's blob), ``scripts/generate_keypair.py`` writes a fresh one |
| ``DATATOOLS_LICENSE_PUBKEY`` | Every shipped binary | Verification at activation time; set at build time via PyInstaller env |

If neither env var is set, ``src.license.crypto`` falls back to the
deterministic dev keypair in ``src/license/_dev_keypair.py``. The
dev key is in source on purpose (so tests work without secrets),
but a frozen build that's still using it is a build-config bug —
:func:`assert_production_safe` refuses to start such a binary.

**First-time setup for shipped builds**:

1. ``python scripts/generate_keypair.py --output prod-keys.env`` —
   creates a fresh keypair.
2. Stash ``DATATOOLS_LICENSE_PRIVKEY`` somewhere safe (password
   manager / KMS). Lose it and you can't issue renewals without
   reshipping a new build with a new public key.
3. Configure the PyInstaller build env with
   ``DATATOOLS_LICENSE_PUBKEY=<hex>`` so the shipped binary
   verifies against the production key.
4. Mint buyer licenses with
   ``DATATOOLS_LICENSE_PRIVKEY=<hex> python scripts/generate_license.py ...``.

**Dev bypass**: ``DATATOOLS_DEV_MODE=1`` short-circuits every check.
The test suite's autouse fixture sets this so existing tests don't
need their own license fixtures. Tests that need the real check
explicitly use ``isolated_license_path`` /
``activated_license_manager`` / ``unactivated_license_manager``.

**Adding a feature flag**:

1. Add the enum value to ``FeatureFlag`` in ``src/license/schema.py``.
2. Add it to the relevant tier's set in
   ``FEATURES_BY_TIER`` in ``src/license/features.py``.
3. Gate at the call site: ``require_feature(FeatureFlag.YOUR_FLAG)``.

**Adding a new tier**:

1. Add the enum value to ``Tier``.
2. Add a row to ``FEATURES_BY_TIER`` listing the unlocked flags.
3. Add ``license.tier_<name>`` translation keys to every i18n pack.
4. The activation flow, sidebar status badge, feature gate, and home
   grid lock badge all pick up the new tier automatically.

**Worked example — the Lite tier**:

```python
# src/license/schema.py
class Tier(str, Enum):
    LITE = "lite"          # new
    CORE = "core"
    ...

# src/license/features.py
FEATURES_BY_TIER = {
    ...
    Tier.LITE: frozenset({
        FeatureFlag.DEDUPLICATOR,
        FeatureFlag.TEXT_CLEANER,
        FeatureFlag.FORMAT_STANDARDIZER,
    }),
    Tier.CORE: _all(),
    ...
}
```

Then in en.json/es.json add ``license.tier_lite``. That's it — the
existing ``require_feature_or_render_upgrade`` (GUI) and
``guard(feature=...)`` (CLI) calls in every tool page/CLI route a
Lite user into the upgrade prompt for any tool the tier doesn't
unlock. The home grid's lock badge fires off the same feature
lookup.

**Minting a license** (creator-only):

```bash
DATATOOLS_LICENSE_SECRET=<shipping-secret> \
    python scripts/generate_license.py \
        --name "Jane Doe" --email jane@example.com \
        --tier core --years 1
```

The script prints a ``DTLIC1:`` blob to stdout — deliver this in the
Gumroad / purchase email. The buyer pastes it into the activation
page or runs ``python -m src.license_cli activate <blob> --name ...``.

### Add a format-standardizer field type

1. Add value to `FieldType` enum in `core/format_standardize.py`.
2. Add per-cell `standardize_<x>(value, *, …)` returning `(new_value, changed)`.
3. Add option fields to `StandardizeOptions` (with defaults that preserve existing behavior).
4. Wire into `_apply_field_type()` dispatcher (the `else` branch raises `AssertionError` — every enum value needs a branch).
5. Add validation entry in `StandardizeOptions.from_dict()` for any new enum-shaped option.

## Errors

Use `core/errors.py` instead of raw `ValueError` / `OSError`:

| Pattern | Use |
|---------|-----|
| Bad arg, wrong type, missing column | `InputValidationError` |
| Bad config / options file | `ConfigError` |
| File parses but isn't what we expected | `FileFormatError` |
| File I/O failure (perms, missing, disk full) | `FileAccessError` |
| Internal invariant broken (unreachable branch) | `AssertionError` |

Helpers:
- `ensure_dataframe(value, function="my_func")` at every public entry that takes a df.
- `ensure_choice(value, name="mode", choices=[...])` at every entry that takes a literal.
- `wrap_file_read(path, "operation", exc)` / `wrap_file_write(...)` when wrapping `OSError`.

GUI / CLI handlers: use `format_for_user(exc, context="...")` to render.

All `DataToolsError` subclasses extend stdlib `ValueError` or `OSError` so existing handlers still catch them.

## PDF Extractor — bundled Tesseract

Frozen builds (installer / AppImage) ship Tesseract OCR inside the bundle so scanned PDFs work without a separate system install. Source / `pip` developer environments still resolve Tesseract from `PATH`.

**Runtime layout (frozen bundles)**:

| Resource | Path |
|---|---|
| Tesseract binary | `Path(sys._MEIPASS) / "tesseract" / "tesseract"` (Linux/macOS), `…/tesseract/tesseract.exe` (Windows) |
| Tessdata directory | `Path(sys._MEIPASS) / "tesseract" / "tessdata"` |
| English model | `Path(sys._MEIPASS) / "tesseract" / "tessdata" / "eng.traineddata"` |

**Discovery order** (PDF Extractor runtime):

1. `DATATOOLS_TESSERACT_BIN` env var (override — explicit path to a `tesseract` binary).
2. Bundled path under `sys._MEIPASS` (frozen bundles only — falls through to step 3 otherwise).
3. `tesseract` on `PATH` (developer setups, source checkouts).
4. Windows well-known locations (`C:\Program Files\Tesseract-OCR\tesseract.exe`, etc.).

**Where the bytes come from**:

- **Tessdata** is vendored at `build/vendor/tessdata/eng.traineddata` — the "best" English model from [tessdata_best](https://github.com/tesseract-ocr/tessdata_best). PyInstaller's spec copies it into `tesseract/tessdata/` inside the bundle.
- **Tesseract binary** is fetched at build time by `build/tesseract.py` — per-platform download URLs are pinned in that module. The current pin is **Tesseract 5.5.0**. CI (`.github/workflows/build.yml`) imports `fetch_tessdata` + `fetch_tesseract_for_platform` and runs them before PyInstaller.

**To update Tesseract**:

1. Bump the version pin + the per-platform fetch URLs in `build/tesseract.py`.
2. If upstream changed the `eng.traineddata` schema, refresh `build/vendor/tessdata/eng.traineddata` from `tessdata_best` at the matching tag.
3. Push a `v*` tag so CI rebuilds all three platforms, then smoke-test a scanned-PDF run through the PDF Extractor before publishing the release.
4. Update `LICENSE_TESSERACT.txt` at the repo root if the upstream license terms change (Tesseract is Apache-2.0 today).

## Tests

```bash
# All (core + CLI + GUI)
pytest -q
# Quick loop — skip the GUI layer
pytest -q -m 'not gui'
# Only the GUI tests
pytest -q -m gui
# By module
pytest tests/test_dedup.py
# Include slow / integration
pytest -m slow
# Single test
pytest tests/test_dedup.py::TestExactMatch::test_basic
```

Test layout:
```
tests/
├── conftest.py                        # core/CLI fixtures
├── test_dedup.py · test_normalizers.py · test_io.py · test_config.py
├── test_analyze.py · test_normalize.py · test_text_clean.py
├── test_format_standardize.py
├── test_format_standardize_corpus.py  # 199-row buyer corpus
├── test_pipeline.py                   # pipeline engine: adapters, run, validate, serialize
├── test_cli_pipeline.py               # pipeline CLI: recommend/apply/strict/audit
├── test_audit_fixes.py · test_errors.py · test_fixes_unit.py
├── test_corpus.py · test_encodings_corpus.py · test_fixtures_sweep.py
├── test_cli.py · test_cli_*.py · test_e2e.py · test_install.py
├── test_perf_regressions.py           # shape pins for the perf wins
└── gui/                               # Streamlit AppTest-driven tests
    ├── conftest.py                    # AppTest fixtures + helpers
    ├── _findings_panel_harness.py     # isolated component test page
    ├── test_smoke.py                  # every page renders in EN + ES
    ├── test_chrome.py                 # language selector, hide_chrome
    ├── test_gate.py                   # require_normalization_gate
    ├── test_workflows.py              # happy path per Ready tool
    ├── test_dedup_review.py           # match-group card interactions
    ├── test_advanced_panels.py        # config_panel widgets
    ├── test_pipeline_builder.py       # module-card builder: cards, reorder, JSON, run
    ├── test_pipeline_phrasing.py      # step_phrase/step_status + name bridge (pure fns)
    ├── test_errors.py                 # malformed-upload error paths
    └── test_findings_panel.py         # analyzer findings rendering
```

### Pipeline (Automated Workflows) coverage

The pipeline feature is pinned end to end across four files (~115 tests):
`test_pipeline.py` (core engine — every adapter's summary numbers, step
data-flow, error stop/continue, empty/single-column/all-disabled edges,
dict + file serialization round-trips, `recommended_pipeline(include=…)`,
soft-dependency validation), `test_cli_pipeline.py` (CLI — `--recommend`,
dry-run-by-default, `--apply` output + audit JSON, `--steps`, `--strict`,
`--continue-on-error`, arg validation, save→load round-trip),
`test_pipeline_builder.py` (the visual builder via AppTest — card seeding,
toggle, reorder ▲/▼, add/remove, restore-recommended, Advanced JSON
import/export, per-tool Configure panels emitting the right option dicts),
and `test_pipeline_phrasing.py` (the plain-English `step_phrase`/`step_status`
helpers and the adapter-key→friendly-name bridge as pure functions).

### GUI test layer

GUI tests drive pages with `streamlit.testing.v1.AppTest` —
in-process, no browser, no display. They pre-populate
`st.session_state` with stashed-upload bytes (via the
`stash_upload()` helper in `tests/gui/conftest.py`) and either click
buttons via `app.button[i].click().run()` or assert on the
`session_state` after the run.

Marker registered in `pytest.ini`. Default `pytest` runs everything;
`pytest -m 'not gui'` skips them for a faster core-only loop.
Coming-Soon stubs are pinned by the smoke tests so a regression
("import error", "missing widget") shows up immediately.

Fixture corpora: `test-cases/text-cleaner-corpus/` (21 files) · `test-cases/encodings-corpus/` (31 files) · `test-cases/format-cleaner-corpus/` (7 files + spec).

## Known limitations

- **Dedup pair-compare is O(n²)** for fuzzy strategies. Exact-only
  strategies (every column uses `Algorithm.EXACT` at threshold 100)
  now route through an O(n) groupby fast path automatically — no API
  change. Fuzzy strategies can opt into prefix blocking via
  `deduplicate(..., blocking_columns=[...], blocking_prefix_len=1)`
  to partition pairs by a cheap key (trades recall for speed).
- **Threading is opt-in for format_standardize** —
  `StandardizeOptions.parallel_columns > 1` uses a thread pool.
  On CPython 3.12 the GIL caps the win at roughly neutral; the
  scaffolding is in place for free-threaded Python 3.13+.
- **Memory-bound** — entire file loaded into pandas. Streaming reads
  exist but not integrated with the dedup engine.
- **No multi-sheet dedup** — each Excel sheet processed independently.
- **Phonenumbers minimum-length** — international numbers without
  country codes fall back to digits-only.