# Prometheus Charting — Delta (`grafana-metric-gateway`)

> Change: `grafana-metric-gateway` · Domain: `prometheus-charting` · Phase: **spec** (authored during `sdd-sync`).
>
> **This is the project's first non-additive canonical sync.** The `prometheus-charting` canonical
> domain (SC-101 … SC-127, created by `prometheus-direct-charting`) described the *direct* Prometheus
> transport. This change switches the `prometheus` service to a **Grafana gateway** transport
> (`POST {grafana_url}/api/ds/query`), renames the chart/gauge/mean widgets to neutral `Metric*`
> names, and validates the gateway path. Durable *behavior* requirements (multi-series chart, gauge
> threshold bands, windowed mean) are **preserved**; only the *transport* and a few naming/status
> statements are modified. The mapping of every change requirement (GM-101 … GM-116) to a canonical
> SC-xxx is recorded in the flat `spec.md` §"Canonical delta intent".
>
> This delta therefore contains **both** a `## MODIFIED Requirements` block (full replacement bodies
> for each superseded SC-xxx — matched by exact requirement ID) and an `## ADDED Requirements` block
> (genuinely new requirements assigned fresh canonical IDs SC-128 … SC-130). PRESERVED requirements
> (SC-106, SC-108, SC-110, SC-113, SC-117 … SC-120, SC-123, SC-124, SC-127) appear in **neither**
> section — they are unchanged in the canonical spec.

## MODIFIED Requirements

> Each block below replaces the full canonical requirement of the same ID (matched by the exact
> `### Requirement: SC-xxx — <name>` header). The requirement *intent* is preserved where the change
> only swaps the mechanism (direct Prom → Grafana gateway); the body text is updated to the gateway
> transport. No requirement IDs are renamed (RENAMED is unsupported by the native delta helper).

### Requirement: SC-101 — Prometheus range query returns the existing series shape

The `prometheus` service type's config MUST point at a Grafana gateway — declaring `grafana_url` (http(s)-schema-enforced), `datasource_uid` (default `"prometheus"`), and `timeout_seconds` — with a required, Fernet-encrypted `grafana_api_key` secret. The former direct-Prometheus `base_url` config field and the old optional `api_key` secret MUST be gone. When a `prometheus` widget of kind `chart` is fetched, the backend MUST issue `POST {grafana_url}/api/ds/query` (carrying `Authorization: Bearer {grafana_api_key}` and a `queries[0]` entry keyed by `datasource_uid`), MUST NOT issue any direct `GET /api/v1/query_range` against a Prometheus URL, and MUST return a payload of shape `{ "series": [{ "label": str, "points": [{ "t": int, "v": float|null }] }] }` — the exact shape the frontend chart renderer already consumes.

### Requirement: SC-102 — Series label normalization is shared and Prometheus-native

The metric-label → readable-label normalization MUST live in a single shared helper module that holds **both** normalizers — the retained Prom-matrix normalizer (`normalize_prometheus_matrix`) and the (re-)added Grafana-frames normalizer (`normalize_grafana_frames`) — and MUST deduplicate repeated labels via a `label (n)` suffix using **one shared dedup rule** (not duplicated across the two normalizers). Both normalizers produce the same `{label, points}` series shape, and the frames normalizer MUST apply the label fallback chain (displayName → sorted Prometheus labels excluding `__`-prefixed keys → `"value"`).

### Requirement: SC-103 — Range query errors degrade gracefully

A Grafana gateway timeout, connection error, HTTP 401/403 (auth), datasource-not-found, or non-2xx response MUST cause the widget data fetch to return `{ "error": str }` (not raise), so the frontend renders the standard per-widget error state and the rest of the dashboard remains functional. The error message MUST be specific enough to distinguish auth failure from unreachable-host from datasource-not-found where the Grafana response permits.

### Requirement: SC-104 — Step is derived from the window preset

Given a window preset (1h / 6h / 24h / 7d), the backend MUST reuse the existing `WINDOW_PRESETS` and `step_for_window` math to derive the gateway request's `intervalMs` (`step * 1000`), `maxDataPoints`, and `from`/`to` time bounds, landing the resulting point count in the same ~100–300 band as the pre-change direct-Prom path. Users do not configure `from`/`to`/`step`/`intervalMs` directly.

### Requirement: SC-105 — Chart widget moves from grafana to prometheus

Widget kinds `chart`, `gauge`, `mean`, and `metric` MUST remain bound to the `prometheus` service type — the kind strings are persisted in widget instance rows and MUST NOT change. The `grafana` service type MUST NOT be reintroduced and MUST NOT offer any widget kind. The backend adapter (internal class `MetricSource`, registry key still `"prometheus"`) and the frontend `SERVICE_REGISTRY` bind these kinds to the neutral `Metric*` components for `chart`/`gauge`/`mean` (and `PrometheusMetricWidget` for `metric`); all four kinds source their data via the Grafana gateway.

### Requirement: SC-107 — Chart supports multiple series

The `chart` widget MUST render all series returned by the gateway range query, each as its own line with a distinct color (via `normalize_grafana_frames`). There is no single-series restriction on `chart`.

### Requirement: SC-109 — Gauge renders an instant scalar

A widget kind named `gauge` MUST be bound to the `prometheus` service. Its data fetch MUST run an instant PromQL query through the Grafana gateway (a gateway query with a minimal window / single data point) and return the scalar result for rendering as a gauge.

### Requirement: SC-111 — Gauge is scalar-only

The `gauge` widget MUST render exactly one scalar value. If the gateway query returns multiple series, the adapter MUST return `{ "error": str }` (not silently pick one), directing the user to refine the PromQL.

### Requirement: SC-112 — Mean computes client-side over a window

A widget kind named `mean` MUST be bound to the `prometheus` service. Its data fetch MUST run a range query through the Grafana gateway over the configured window preset and return the arithmetic mean of all non-null point values of the single series as a single scalar.

### Requirement: SC-114 — Mean is scalar-only

The `mean` widget MUST render exactly one scalar value. If the gateway range query returns multiple series, the adapter MUST return `{ "error": str }` (not silently aggregate across series).

### Requirement: SC-115 — No grafana references in backend source

Grafana is the sanctioned **transport** for the `prometheus` service, so backend source legitimately contains Grafana transport references (e.g. `grafana_url`, `grafana_api_key`, `normalize_grafana_frames`, `POST …/api/ds/query`). After the change, those references are transport-only: there MUST be no `grafana` **service type**, no `grafana` service definition, and no `grafana` entry in the backend `SERVICE_DEFINITIONS` / `SERVICE_ADAPTERS` registries. The `integrations/grafana.py` service-type module stays deleted.

### Requirement: SC-116 — No grafana references in frontend source

Grafana transport is allowed in the frontend — the `prometheus` service config form renders Grafana gateway fields (`grafana_url`, `datasource_uid`) from the backend-provided schema. No frontend code MUST reintroduce a `grafana` **service type**, a Grafana deep-link / dashboard widget, `LinksTab`, or any Grafana-status UI surface. (Test fixtures where "Grafana" appears as a user-authored dashboard *shortcut label* unrelated to a service type remain excluded.)

### Requirement: SC-121 — config.yaml matches implementation

`openspec/config.yaml` MUST reflect that metric queries for the `prometheus` service are routed through a Grafana gateway (`POST /api/ds/query`) and that in-app charting via `recharts` is the sanctioned renderer. It MUST NOT carry the stale claims "Do NOT re-implement charting in-app", "No recharts/d3 is in use", or "Prometheus is queried directly (no Grafana middleman)".

### Requirement: SC-122 — CHANGELOG documents the migration

`CHANGELOG.md` `[Unreleased]` MUST include a **BREAKING** entry stating that existing `prometheus` service instances must be reconfigured: replace the old `base_url` with `grafana_url`, add the `grafana_api_key` secret, and optionally set `datasource_uid`, because metric queries now route through Grafana's `POST /api/ds/query`.

### Requirement: SC-125 — New widget kinds have tests

The renamed widgets `MetricChartWidget`, `MetricGaugeWidget`, and `MetricMeanWidget` MUST each have a frontend test covering at least: loading state, error state, and a rendered data case. (The `metric`-kind widget `PrometheusMetricWidget` is not renamed but remains tested.)

### Requirement: SC-126 — No silent data migration

The change MUST NOT auto-migrate persisted `prometheus` service instances from the old `base_url` config shape to the new `grafana_url` gateway shape (URLs and credentials differ; a safe automated rewrite is not possible). Migration is operator-driven per the CHANGELOG note; old-shape instances are flagged on startup (see SC-129) and degrade at runtime to a gateway error until reconfigured.

## ADDED Requirements

> Genuinely new requirements with fresh canonical IDs continuing the SC- sequence. The `GM-` change
> prefixes are intentionally not reused in the canonical store.

### Requirement: SC-128 — get_prometheus_status validates the full gateway path

`get_prometheus_status` MUST validate the full metric path by running a trivial query (e.g. `up`) through the Grafana gateway (`POST {grafana_url}/api/ds/query`). Success MUST return `{ "up": true, "version": <str>, … }` — a sentinel such as `"ok"` is acceptable when Grafana's `/api/ds/query` response carries no Prometheus build-info. Failure MUST return `{ "up": false, "error": <specific str> }` distinguishing auth failure (HTTP 401/403), unreachable host, and datasource/gateway error where the response permits.

### Requirement: SC-129 — Startup logs old-shape prometheus config without crashing

When the backend starts and a persisted `prometheus` service instance carries the old `base_url` config key without `grafana_url`, startup MUST log a clear migration message naming the service and instructing reconfiguration, and MUST complete without crashing (it MUST NOT delete, disable, or otherwise mutate the instance). The instance's widget fetches degrade to a gateway error until the operator reconfigures it.

### Requirement: SC-130 — Grafana is the sanctioned transport for the prometheus service

The `prometheus` service type is the sole metric surface in Manage. Its metric queries (`chart`, `gauge`, `mean`, `metric`) are sanctioned to route through a Grafana gateway — `POST {grafana_url}/api/ds/query` with a `grafana_api_key` and a Prometheus `datasource_uid`. Grafana is the transport, not a first-class service type; a direct-Prometheus HTTP path is not supported.