# OpenSpec Change: enterprise-tides

- **Change ID**: enterprise-tides
- **Package**: `@suaveplan/tides`
- **Category**: universal
- **Target path**: `universal/geo/tides`
- **Status**: IN PROGRESS
- **Date**: 2026-04-24
- **Reference spec**: `/mnt/s/web/suaveplan/enterprise/tides.md`

---

## Summary

Deliver `@suaveplan/tides` on the genesis branch from scratch at enterprise quality. The package provides UK tidal prediction using offline TICON harmonic constituent data and ADMIRALTY-compatible algorithms: load harmonic data for any UK port, compute water height at any minute over any date range, find high/low-water times within a window, compute tidal range and mean water, generate 24-hour or multi-day tide tables, and a streaming prediction generator. Fully offline — no network calls. The main-branch version sat at 97.82% coverage. Genesis adds structured errors, Zod schemas, OTel instrumentation, injectable clock, and property-based tests to reach 100%.

---

## Current-state audit (genesis)

The package does not exist on genesis yet — this is a fresh build.

---

## Available workspace deps on genesis

| Package | Role |
|---|---|
| `@suaveplan/error` (`workspace:^`) | `TidesError`; `TIDES.*` error codes |
| `@suaveplan/types` (`workspace:^`) | `LoggerLike`, `Clock` |
| `@suaveplan/geo` (`workspace:^`) | `LatLng` type for port location |
| `zod` (`catalog:forms`) | Schema validation |
| `@opentelemetry/api` (`catalog:observability`) | Spans + counters |

Dev deps: `vitest`, `@vitest/coverage-istanbul`, `fast-check` (all `catalog:testing`).

---

## Public API surface

### Core types

```ts
interface TidalPort {
  id: string                    // ADMIRALTY port code e.g. '0113'
  name: string
  location: LatLng
  constituents: TidalConstituent[]
  timezone: string              // IANA timezone
  meanHighWaterSprings: number  // metres
  meanLowWaterSprings: number
  chartDatum: number            // LAT in metres
}

interface TidalConstituent {
  name: string      // e.g. 'M2', 'S2', 'N2'
  amplitude: number // metres
  phase: number     // degrees
  speed: number     // degrees/hour
}

interface TidePrediction {
  time: Date
  height: number    // metres above chart datum
  type?: 'high' | 'low'
}

interface TideTable {
  portId: string
  date: string      // ISO date
  predictions: TidePrediction[]
  highWaters: TidePrediction[]
  lowWaters: TidePrediction[]
  range: number
  meanLevel: number
}
```

### `TidePredictor`

```ts
class TidePredictor {
  constructor(options?: TidePredictorOptions)

  loadPort(port: TidalPort): void
  listPorts(): string[]

  predict(portId: string, time: Date): number     // metres at single instant
  predictRange(portId: string, from: Date, to: Date, intervalMinutes?: number): TidePrediction[]
  findExtrema(portId: string, from: Date, to: Date): TidePrediction[]
  generateTable(portId: string, date: Date): TideTable
  generateTables(portId: string, from: Date, to: Date): TideTable[]
  stream(portId: string, from: Date, to: Date, intervalMinutes?: number): AsyncGenerator<TidePrediction>
}

interface TidePredictorOptions {
  clock?: Clock
  logger?: LoggerLike
}
```

### Data loaders

```ts
function loadBuiltinPorts(): TidalPort[]    // bundled TICON data for UK ports
function parseTiconData(raw: string): TidalPort[]
function harmonicHeight(constituents: TidalConstituent[], time: Date): number
```

### Error codes

```ts
type TidesErrorCode =
  | 'TIDES_PORT_NOT_FOUND'
  | 'TIDES_INVALID_DATE_RANGE'
  | 'TIDES_INVALID_CONSTITUENT'
  | 'TIDES_PARSE_FAILED'
  | 'TIDES_PREDICTION_FAILED'
```

---

## Genesis additions

1. **`TidesError`** extends `SuaveplanError` with five stable codes.
2. **Zod schemas** for `TidalPort`, `TidalConstituent`, `TidePrediction`, `TideTable`.
3. **Streaming `stream()` method** — returns an `AsyncGenerator<TidePrediction>` for memory-efficient prediction over long date ranges.
4. **Injectable clock** — `TidePredictorOptions.clock` allows time-travel in tests; `predict()` without a `time` argument uses `clock.now()`.
5. **OTel instrumentation** — span `tides.predict_range` with attributes `tides.port_id`, `tides.interval_minutes`; counter `tides.table_generate_total`; histogram `tides.predict_duration_ms`.
6. **Property-based tests** — harmonic height at known published times (deterministic); extrema always come in alternating high/low order; prediction is a continuous function (no discontinuities > 0.5m per minute).

---

## File layout

```text
universal/geo/tides/
  package.json
  tsconfig.json
  vitest.config.ts
  src/
    index.ts
    error-codes.ts
    constants/
      index.ts              # DEGREES_PER_HOUR, G (gravitational const)
    types/
      common.ts
      common.md
    core/
      tide-predictor/
        tide-predictor.ts
        tide-predictor.md
        tide-predictor.types.ts
        tide-predictor.test.ts
        index.ts
      harmonic-engine/
        harmonic-engine.ts
        harmonic-engine.md
        harmonic-engine.test.ts
        index.ts
      extrema-finder/
        extrema-finder.ts
        extrema-finder.md
        extrema-finder.test.ts
        index.ts
    data/
      ticon-loader/
        ticon-loader.ts
        ticon-loader.md
        ticon-loader.test.ts
        index.ts
      builtin-ports.json    # bundled TICON data for UK ports
    __benchmarks__/
      tides.bench.ts
  tests/
    integration.test.ts
    property.test.ts
```

---

## Impact

**Downstream consumers**: `@suaveplan/ports` (tidal windows for port scheduling).

**Workspace dep prerequisites**: `@suaveplan/error`, `@suaveplan/types`, `@suaveplan/geo`.