# Design: enterprise-form-builder

> Non-normative. Architecture, file layout, and integration narrative for
> `@suaveplan/form-builder`. The normative contract is `./specs/form-builder/spec.md`.

## Tier & dependencies

Universal-tier (runs in Bun, Node, browser without polyfills). Direct deps:

- `@suaveplan/error` (`workspace:^`) — `SuaveplanError`, `defineCodes`.
- `@suaveplan/events` (`workspace:^`) — `EventBus<FormEventMap>` for state-change emission.
- `@suaveplan/types` (`workspace:^`) — `Clock`, `IdGenerator` for injectable time / id.
- `@opentelemetry/api` (`catalog:observability`) — counters + histograms.
- `tslib` (`catalog:build`).
- `zod` (`catalog:forms`) — boundary validation + Zod schema generator.

`devDependencies`: `@suaveplan/testing`, `@vitest/coverage-istanbul`, `vite`, `vite-plugin-dts`,
`vitest`, `typescript`, `@types/node`.

## File layout

```text
packages/ui/forms/form-builder/
  package.json
  tsconfig.lib.json
  vite.config.ts
  vitest.config.ts
  README.md
  tests/setup/polyfills.ts
  src/
    index.ts                                      # root barrel (named re-exports only)
    types/form.types.ts                           # shared structural types (no .md)
    constants/index.ts                            # FIELD_TYPES, OPERATORS, defaults
    schema/schema/
      schema.ts                                   # Zod schemas + parse/validate
      schema.test.ts
      schema.md
      index.ts
    fields/field-registry/
      field-registry.ts                           # FieldRegistry + 17 built-ins
      field-registry.test.ts
      field-registry.md
      index.ts
    validation/validation/
      validation.ts                               # runRule, runField, runForm (sync + async)
      validation.test.ts
      validation.md
      index.ts
    validation/validators/
      validators.ts                               # 11 built-in rule runners
      validators.test.ts
      validators.md
      index.ts
    conditional/conditional/
      conditional.ts                              # operator + boolean evaluator
      conditional.test.ts
      conditional.md
      index.ts
    conditional/dependency-graph/
      dependency-graph.ts                         # topo sort + cycle detect
      dependency-graph.test.ts
      dependency-graph.md
      index.ts
    state/form-state/
      form-state.ts                               # FormState machine
      form-state.test.ts
      form-state.md
      index.ts
    state/undo-redo/
      undo-redo.ts                                # bounded history stack
      undo-redo.test.ts
      undo-redo.md
      index.ts
    builder/form-builder/
      form-builder.ts                             # FormBuilder class (entry-point)
      form-builder.test.ts
      form-builder.md
      index.ts
    submission/submission/
      submission.ts                               # submit pipeline
      submission.test.ts
      submission.md
      index.ts
    serialise/serialise/
      serialise.ts                                # JSON round-trip
      serialise.test.ts
      serialise.md
      index.ts
    zod-schema/zod-schema/
      zod-schema.ts                               # FormSchema → ZodObject
      zod-schema.test.ts
      zod-schema.md
      index.ts
    errors/form-error/
      form-error.ts                               # defineCodes + FormError
      form-error.test.ts
      form-error.md
      index.ts
    otel/instruments/
      instruments.ts                              # lazy-init counters + histograms
      instruments.test.ts
      instruments.md
      index.ts
```

## Error codes — `FORM_BUILDER.*`

| Code | When |
|---|---|
| `FORM_BUILDER.FIELD_NOT_FOUND` | `getField`, `removeField`, `updateField` on missing id |
| `FORM_BUILDER.SECTION_NOT_FOUND` | `getSectionById`, `removeSection` on missing id |
| `FORM_BUILDER.DUPLICATE_ID` | `addField` / `addSection` with already-registered id |
| `FORM_BUILDER.CONFIG_INVALID` | Zod parse failure on `FormSchema` or empty `id`/`name` |
| `FORM_BUILDER.VALIDATION_FAILED` | `submit` aborted because validation produced errors |
| `FORM_BUILDER.CYCLIC_DEPENDENCY` | `DependencyGraph.topoSort` detects a cycle |

## Conditional logic

`ConditionalRule` is a discriminated union:

```ts
type ConditionalRule =
  | { kind: "leaf"; field: string; operator: LeafOperator; value: unknown }
  | { kind: "and"; rules: readonly ConditionalRule[] }
  | { kind: "or"; rules: readonly ConditionalRule[] }
  | { kind: "not"; rule: ConditionalRule };
```

Leaf operators: `eq`, `neq`, `in`, `notIn`, `gt`, `lt`, `gte`, `lte`, `contains`.

A `FieldDefinition.conditional` may be a single rule (backwards-compatible with the upstream
`{ field, operator, value }` shape; the deserialiser auto-wraps in a `leaf`).

## Dependency graph

`DependencyGraph` extracts every referenced field id from a `ConditionalRule` (and from
`equalsField` validators), forms a DAG keyed by field id, runs Kahn's topo sort, and emits
`CYCLIC_DEPENDENCY` if a cycle is found. The builder evaluates conditional visibility in topo
order so chains (`a → b → c`) settle in one pass.

## Undo / redo

Schema-mutation operations (`addField`, `removeField`, `updateField`, `addSection`,
`removeSection`) push a reverse-op onto a bounded `UndoRedoStack` (default capacity 100). `undo()`
applies the inverse and pushes the forward-op onto the redo stack; any new mutation clears the redo
stack. The stack is opt-in: `FormBuilder` exposes `enableHistory(capacity?)`.

## Zod schema generator

`toZodSchema(form)` walks `form.fields` and emits a `z.ZodObject` whose shape mirrors the field
types and validation rules. Conditional `required` is folded into the schema via
`z.unknown().superRefine` so consumers using `react-hook-form` or `@hookform/resolvers/zod` get
identical behaviour to the schema engine's `validateForm`.

## OTel instruments

Lazily initialised via `metrics.getMeter("@suaveplan/form-builder")`:

| Instrument | Kind | Attributes |
|---|---|---|
| `form_builder.field.mutated_total` | counter | `op: add\|remove\|update` |
| `form_builder.validation.run_total` | counter | `scope: field\|form`, `result: ok\|errors` |
| `form_builder.submission.total` | counter | `result: ok\|invalid\|failed` |
| `form_builder.validation.duration_ms` | histogram | `scope: field\|form` |
| `form_builder.submission.duration_ms` | histogram | `result: ok\|invalid\|failed` |

## Determinism

No `Date.now()` or `Math.random()` at module scope. The builder takes an optional `Clock` and
`IdGenerator` in its constructor; defaults derive from `@suaveplan/types`. Timestamps on
`FormSchema.createdAt` / `updatedAt` come from the injected clock.