# Developer Guide
This guide is for engineers who want to extend `tga`, integrate it with new data sources
or output formats, or understand the codebase well enough to contribute confidently.
---
## Table of Contents
1. [Architecture Overview](#1-architecture-overview)
2. [Module Responsibilities](#2-module-responsibilities)
3. [Classification Pipeline Deep-Dive](#3-classification-pipeline-deep-dive)
4. [How to Add a New PM Integration](#4-how-to-add-a-new-pm-integration)
5. [How to Add a New Output Format](#5-how-to-add-a-new-output-format)
6. [Database Migrations](#6-database-migrations)
7. [Coding Standards](#7-coding-standards)
8. [Testing](#8-testing)
---
## 1. Architecture Overview
`tga` is a single Rust crate that exposes both a library (`tga::*`) and a binary
(`tga`). All analytical logic lives in four library modules; the binary entry point
(`src/main.rs`) and its subcommand handlers (`src/commands/`) are binary-private.
### Three-stage pipeline
```
git repos external APIs
│ │
▼ ▼
┌─────────────────────────────┐
│ Stage 1: collect │ tga::collect
│ git2 revwalk + HTTP clients│
└──────────────┬──────────────┘
│ SQLite (tga.db)
▼
┌─────────────────────────────┐
│ Stage 2: classify │ tga::classify
│ Four-tier cascade │
└──────────────┬──────────────┘
│ SQLite (tga.db)
▼
┌─────────────────────────────┐
│ Stage 3: report │ tga::report
│ CSV / JSON / Markdown │
└──────────────┬──────────────┘
│
▼
./reports/
```
### Module dependency order
```
tga::core
│
├──► tga::collect ──────────────────────────────┐
│ │
├──► tga::classify ──────────────────────────────┤
│ │
└──► tga::report ──────────────────────────────► src/main.rs (binary)
src/commands/ (binary-private)
```
`tga::core` has no internal dependencies. All other library modules depend only on
`tga::core`. The binary depends on all four library modules. `src/commands/` is
compiled only as part of the binary and is not part of the public API.
### File layout
```
src/
├── main.rs # Binary entry point (#[tokio::main])
├── commands/ # Binary-private subcommand handlers
│ ├── analyze.rs
│ ├── collect.rs
│ ├── classify.rs
│ ├── report.rs
│ ├── pr_metrics.rs
│ ├── aliases.rs
│ ├── backfill.rs
│ ├── override_.rs
│ └── install.rs
├── core/ # tga::core
│ ├── config/ # serde_yaml config structs
│ ├── db/ # rusqlite wrapper + migration runner
│ │ └── sql/ # Embedded SQL migration files
│ ├── errors.rs # TgaError (thiserror)
│ └── models/ # Domain structs (Commit, Author, etc.)
├── collect/ # tga::collect
│ ├── git/ # git2 revwalk + diff extraction
│ ├── github/ # GitHub REST client (reqwest)
│ ├── bitbucket/ # Bitbucket REST client
│ ├── jira/ # JIRA REST client
│ ├── linear/ # Linear GraphQL client
│ ├── azdo/ # Azure DevOps REST client
│ ├── identity/ # IdentityResolver
│ ├── pm_adapter.rs # PmAdapter trait
│ ├── pr_provider.rs # PrProvider trait
│ └── collector.rs # CollectionPipeline
├── classify/ # tga::classify
│ ├── tiers/ # exact, regex, fuzzy, llm
│ ├── rules/ # Rule types, loader, default rules
│ ├── pipeline.rs # ClassificationPipeline
│ └── classifier.rs # ClassificationEngine
└── report/ # tga::report
├── formatters/ # csv, json, markdown writers
├── aggregator.rs # Data aggregation queries
├── models.rs # Report-level structs
└── pipeline.rs # ReportPipeline
```
---
## 2. Module Responsibilities
### tga::core
The foundation layer. No internal dependencies.
- **`config/`**: YAML deserialization via `serde_yaml`. The top-level struct is `Config`.
All fields use `#[serde(default)]` so unknown keys and missing optional fields never
cause parse errors. Path fields are `PathBuf`; callers apply `expand_path()` before I/O.
- **`db/`**: `Database` struct wraps a `rusqlite::Connection`. `Database::open()` applies
WAL mode, enables foreign keys, and runs all pending migrations. Each migration executes
inside a transaction.
- **`errors.rs`**: `TgaError` enum with `thiserror` derives. Used only within `tga::core`.
- **`models/`**: Domain structs shared across modules: `Commit`, `Author`,
`Classification`, `PullRequest`, `WorkItem`, etc. All use `serde` derives for
SQLite row mapping.
### tga::collect
Stage 1 pipeline.
- **`git/`**: Uses `git2` to walk the commit graph between a `since` and `until`
boundary. Extracts commit metadata, diff stats, and author information. Does not
fork the `git` subprocess.
- **`identity/`**: `IdentityResolver` maps raw `(author_name, author_email)` pairs to
canonical identities using exact alias lookup followed by Jaro-Winkler fuzzy matching
(`strsim`).
- **`github/`**, **`bitbucket/`**, **`jira/`**, **`linear/`**, **`azdo/`**: HTTP clients
using `reqwest` + `tokio`. Each implements either `PrProvider` (for PR metadata) or
`PmAdapter` (for ticket data), or both.
- **`collector.rs`**: `CollectionPipeline::run()` orchestrates per-repo git extraction,
identity resolution, PR and ticket fetching, and upserts into `tga.db`.
### tga::classify
Stage 2 pipeline.
- **`rules/`**: `Rule` struct (keyword list, regex patterns, category, priority,
confidence). `RuleLoader` reads a YAML rules file and merges with (or replaces) the
80+ built-in default rules.
- **`tiers/`**: Four independent matchers — see
[Classification Pipeline Deep-Dive](#3-classification-pipeline-deep-dive).
- **`classifier.rs`**: `ClassificationEngine` holds all four tiers. `classify_batch()`
runs tiers 0–2 in parallel via `rayon`. `classify().await` is async and adds the LLM
fallback (Tier 3).
- **`pipeline.rs`**: `ClassificationPipeline::run()` loads unclassified commits from
`tga.db`, runs `classify_batch()` via Rayon, then calls the async `classify()` for any
remaining unclassified commits when LLM is enabled.
### tga::report
Stage 3 pipeline.
- **`aggregator.rs`**: SQL queries that join `commits`, `classifications`, `authors`, and
`pull_requests` into report-ready result sets.
- **`formatters/csv`**: Writes 9 CSV files using the `csv` crate.
- **`formatters/json`**: Writes 4 JSON files using `serde_json`.
- **`formatters/markdown`**: Renders `report.md` using `tera` templates (Jinja2-compatible).
- **`pipeline.rs`**: `ReportPipeline::run()` calls the aggregator then fans out to each
registered formatter.
---
## 3. Classification Pipeline Deep-Dive
The cascade runs four tiers in order. The first tier to produce a result above
`confidence_threshold` wins. Commits not matched by any tier receive the label
`uncategorized` with confidence 0.0.
### Tier 0 — Overrides table
Before any rule is consulted, `ClassificationEngine` queries the `classification_overrides`
table for the commit SHA. If a row exists, its `work_type` and `change_type` are returned
with confidence 1.0 and method `manual`. No further tiers are evaluated.
Overrides are managed via `tga override add|list|remove`. They survive
re-classification — `tga classify` always respects Tier 0 entries.
### Tier 1 — Exact keyword matching (Aho-Corasick)
`ExactMatcher` feeds all `keywords` fields from all loaded rules into a single
Aho-Corasick automaton at construction time. Classification is one O(n) scan of the
commit message, where n is the message length regardless of the number of keywords.
Rules are sorted by `priority` (highest first) before automaton construction. When a
keyword fires, the associated rule's category, subcategory, and confidence are returned.
The `aho-corasick` crate implements the multi-pattern search.
### Tier 2 — Regex matching
`RegexMatcher` compiles each `pattern` field from each rule into a `regex::Regex` at
construction. Classification iterates rules in priority order and applies each compiled
regex. The first match returns the rule's classification.
`RegexMatcher::extract_ticket_id()` is a standalone helper that applies the configured
`ticket_regex` (or the default JIRA pattern `\b[A-Z][A-Z0-9]+-\d+\b`) to extract ticket
references. Both Tier 1 and Tier 2 call this helper to populate `ticket_id` on their
results.
### Tier 2.5 — Fuzzy / structural heuristics
`FuzzyClassifier` applies structural rules that require no pattern data:
- If the commit has `is_merge: true`: return category `merge`, confidence 0.8.
- If the message starts with `"Merge pull request"` or `"Merge branch"` (case-insensitive):
return category `merge`, confidence 0.8.
- If the message starts with `"Revert "` (case-insensitive): return category `revert`,
confidence 0.8.
All fuzzy results use `ClassificationMethod::FuzzyMatch`.
The `strsim` crate provides Jaro-Winkler similarity for identity resolution (not used
in commit classification tiers).
### Tier 3 — LLM fallback (async)
`LlmClassifier` is only invoked when `use_llm: true` is set in config and an API key
is available. It formats the commit message into a prompt requesting a JSON object
`{"category": "...", "confidence": 0.0}` and sends it to the configured provider
(OpenRouter, OpenAI, or Bedrock).
Responses below `confidence_threshold` are discarded. Malformed JSON causes the tier
to return `None` (not a hard error), and the commit falls through to `uncategorized`.
LLM requests are sent concurrently up to `llm_fallback_concurrency` (default: 8).
The LLM tier is async (`tokio`). It is never called from `classify_batch()`. The
`ClassificationPipeline` runs the Rayon batch first, collects commits still without a
result, then calls the async LLM path sequentially (from within the `tokio` runtime).
### Confidence threshold and progression
Each tier's result includes a `confidence` field. If a tier's confidence is below
`confidence_threshold`, the result is discarded and the next tier is tried. This means
a well-matched Tier 1 exact rule with confidence 0.95 does not trigger the LLM even when
`use_llm: true`.
The `llm_fallback_threshold` setting provides a coarser gate: any commit whose
best rule-based confidence exceeds this value skips the LLM entirely (even if below
`confidence_threshold`). Setting `llm_fallback_threshold: 0.5` prevents API calls for
commits that are "good enough."
### Backfill complexity
`tga classify --backfill-complexity` runs a second pass that queries commits with
a classification but no complexity score, then assigns a score from 1 (trivial) to 5
(high complexity) using a heuristic based on lines changed, file count, and the
classification tier used. It does not re-run the full classification cascade.
---
## 4. How to Add a New PM Integration
To add a new project management source (e.g. ClickUp, Shortcut):
### 4.1 Add the config struct
In `src/core/config/`, create a new struct (e.g. `ClickUpConfig`) with `serde::Deserialize`
and add it as an optional field to the top-level `Config` struct:
```rust
// src/core/config/clickup.rs
#[derive(Debug, Default, Deserialize)]
#[serde(default)]
pub struct ClickUpConfig {
pub api_token: String,
pub workspace_id: String,
pub fetch_on_reference: bool,
pub ticket_regex: Option<String>,
}
```
```rust
// src/core/config/mod.rs
pub struct Config {
// ... existing fields ...
pub clickup: Option<ClickUpConfig>,
}
```
### 4.2 Implement the traits
In `src/collect/`, create a new module (e.g. `src/collect/clickup/`). Implement
the relevant trait(s):
- **`PmAdapter`**: for fetching work items/tickets. Required method:
`fetch_work_items(&self, refs: &[&str]) -> Result<Vec<WorkItem>>`.
- **`PrProvider`**: for fetching pull requests. Required method:
`fetch_prs(&self, since: DateTime, until: DateTime) -> Result<Vec<PullRequest>>`.
Use `reqwest` + `tokio` for HTTP. Follow the pattern established in
`src/collect/azdo/` (which implements `PmAdapter`) or `src/collect/github/`
(which implements `PrProvider`).
### 4.3 Register in build_adapters()
In `src/collect/collector.rs`, add your new adapter to `build_adapters()`:
```rust
fn build_adapters(config: &Config) -> Vec<Box<dyn PmAdapter>> {
let mut adapters: Vec<Box<dyn PmAdapter>> = vec![];
// ... existing adapters ...
if let Some(clickup_cfg) = &config.clickup {
adapters.push(Box::new(ClickUpAdapter::new(clickup_cfg)));
}
adapters
}
```
### 4.4 Add a database migration if needed
If your integration stores additional data (e.g. a `clickup_issues` table), add a new
SQL migration file — see [Database Migrations](#6-database-migrations).
---
## 5. How to Add a New Output Format
To add a new report format (e.g. Excel, HTML):
### 5.1 Implement the formatter
Create a new file in `src/report/formatters/` (e.g. `excel.rs`). Implement the
`ReportFormatter` trait:
```rust
pub trait ReportFormatter {
fn write(&self, data: &ReportData, output_dir: &Path) -> Result<()>;
fn format_name(&self) -> &'static str;
}
```
`ReportData` (defined in `src/report/models.rs`) contains all pre-aggregated result
sets from the database.
### 5.2 Register in ReportPipeline
In `src/report/pipeline.rs`, add your formatter to the pipeline builder:
```rust
pub fn build_formatters(formats: &[String]) -> Vec<Box<dyn ReportFormatter>> {
formats.iter().filter_map(|f| match f.as_str() {
"csv" => Some(Box::new(CsvFormatter::new()) as Box<dyn ReportFormatter>),
"json" => Some(Box::new(JsonFormatter::new()) as Box<dyn ReportFormatter>),
"markdown" => Some(Box::new(MarkdownFormatter::new()) as Box<dyn ReportFormatter>),
"excel" => Some(Box::new(ExcelFormatter::new()) as Box<dyn ReportFormatter>),
other => { warn!("unknown format: {other}"); None }
}).collect()
}
```
Users can then enable it via `output.formats: [csv, excel]` in config or
`tga report --formats excel`.
---
## 6. Database Migrations
`tga` uses a migration runner that applies numbered SQL files in order on every
`Database::open()`.
### Location
SQL files live in `src/core/db/sql/`. They are embedded at compile time via
`include_str!()` and referenced by the `MIGRATIONS` constant in
`src/core/db/migrations.rs`.
### Adding a migration
1. Create a new file: `src/core/db/sql/NNNN_description.sql` where `NNNN` is the
next sequential integer.
2. Write idempotent SQL (safe to call on a database that already has the schema).
Use `CREATE TABLE IF NOT EXISTS` and `ALTER TABLE ... ADD COLUMN IF NOT EXISTS`.
3. Register the migration in `migrations.rs`:
```rust
Migration {
version: NNNN,
name: "description",
sql: include_str!("sql/NNNN_description.sql"),
},
```
The migration runner applies any migrations with `version > current_version` inside a
transaction that also inserts the version record. Partial application is impossible.
### Never modify existing migrations
If a migration has been applied to a production database, changing it will cause a
version mismatch. Always add a new migration instead of editing an existing one.
### Current migration count
`tga` has 13 migrations (files `0001` through `0013`). Future migrations continue the
sequence from `0014`.
---
## 7. Coding Standards
These rules are enforced in CI. PRs that violate them will not be merged.
### Error handling
- Use `anyhow::Result` in `src/main.rs` and all files in `src/commands/`.
- Use `thiserror` error enums in all library modules (`src/core/`, `src/collect/`,
`src/classify/`, `src/report/`).
- Do not mix the two: library modules must not import `anyhow`. The binary lets `?`
convert library errors via `std::error::Error`.
- No `unwrap()` or `expect()` in library code. Propagate errors with `?`.
- `expect()` is acceptable in test code, with a descriptive message.
### Logging
Use `tracing::{info, warn, error, debug, trace}`. Never use `println!` or `eprintln!`
in library code or command handlers. Log levels:
- `error`: unrecoverable failures (after which the process exits or the operation is
skipped with a hard warning).
- `warn`: degraded operation (e.g. fetch failed, continuing with local refs).
- `info`: significant milestones (pipeline start/end, commit counts, file writes).
- `debug`: per-item decisions (individual commit classification results).
- `trace`: raw HTTP request/response bodies.
### Concurrency
- Use `rayon::par_iter()` for CPU-bound batch operations (commit classification tiers
0–2, diff stat aggregation).
- Use `tokio` for all async I/O (HTTP clients, LLM calls). Do not mix runtimes.
- `git2` repository handles are not `Send`. Open and drop them within a single
per-repo processing block; never share across threads.
### Public API documentation
All `pub` items in library modules must have doc comments (`///`). Binary-private
items in `src/commands/` do not require doc comments.
### CI gates
All PRs must pass:
```bash
cargo clippy --workspace --all-targets -- -D warnings
cargo fmt --check
cargo test --workspace
```
Run these locally before pushing:
```bash
cargo clippy -- -D warnings
cargo fmt
cargo test
```
---
## 8. Testing
### Running tests
```bash
cargo test
```
This runs all unit tests (located inline in modules using `#[cfg(test)]` blocks) and
doc tests.
### Integration test
One integration test is gated behind an environment variable to prevent it from running
in CI without a real repository:
```bash
INTEGRATION_REPO_PATH=/path/to/some/git/repo cargo test --test integration
```
The integration test runs a full collect → classify → report pipeline against the
specified repository and asserts that output files are produced with non-zero content.
### HTTP mocking
Tests that exercise HTTP clients use `wiremock` (listed in `[dev-dependencies]`) to
run a mock HTTP server. Tests set up stub responses and assert that the correct requests
were made. No real network calls are made in the test suite.
```rust
#[tokio::test]
async fn github_fetch_prs_handles_pagination() {
let mock_server = MockServer::start().await;
Mock::given(method("GET"))
.and(path("/repos/acme/api/pulls"))
.respond_with(ResponseTemplate::new(200).set_body_json(&pr_page_1()))
.mount(&mock_server)
.await;
// ...
}
```
### Adding tests
- Unit tests live in the same file as the code they test, in a `#[cfg(test)]` module.
- Integration tests live in `tests/`.
- Property-based tests may use the `proptest` crate (add to `[dev-dependencies]` if needed).
- New features require accompanying tests. The PR template will ask you to confirm
coverage.