import { type Counter, type Histogram, metrics } from "@opentelemetry/api";

/**
 * Bundle of OpenTelemetry instruments emitted by the vault plugin.
 *
 * - `itemsCreatedTotal{outcome}` — incremented on every `POST /vault/items`.
 * - `itemsReadTotal{outcome}` — incremented on every `GET /vault/items/:id` or
 *   `GET /vault/items` listing.
 * - `itemsUpdatedTotal{outcome}` — incremented on every `PATCH /vault/items/:id`.
 * - `itemsDeletedTotal{outcome}` — incremented on every `DELETE /vault/items/:id`.
 * - `itemSizeBytes` — histogram of item body byte size, sampled on
 *   successful create + update.
 *
 * `outcome ∈ "success" | "failure"`.
 */
export interface VaultPluginInstruments {
    readonly itemsCreatedTotal: Counter;
    readonly itemsReadTotal: Counter;
    readonly itemsUpdatedTotal: Counter;
    readonly itemsDeletedTotal: Counter;
    readonly itemSizeBytes: Histogram;
}

let cached: VaultPluginInstruments | undefined;

/**
 * Lazily build (and cache) the vault-plugin instruments bundle against
 * the current global `MeterProvider`. Call `resetVaultPluginInstruments()`
 * in test setup to force a re-bind against a freshly-installed provider.
 */
export function getVaultPluginInstruments(): VaultPluginInstruments {
    if (cached !== undefined) return cached;
    const meter = metrics.getMeter("@suaveplan/api-plugin-vault");
    cached = {
        itemsCreatedTotal: meter.createCounter("vault.items.created_total", {
            description:
                "Total vault-item create attempts, partitioned by outcome label",
        }),
        itemsReadTotal: meter.createCounter("vault.items.read_total", {
            description:
                "Total vault-item read attempts, partitioned by outcome label",
        }),
        itemsUpdatedTotal: meter.createCounter("vault.items.updated_total", {
            description:
                "Total vault-item update attempts, partitioned by outcome label",
        }),
        itemsDeletedTotal: meter.createCounter("vault.items.deleted_total", {
            description:
                "Total vault-item delete attempts, partitioned by outcome label",
        }),
        itemSizeBytes: meter.createHistogram("vault.item.size_bytes", {
            description:
                "Distribution of vault-item body sizes in bytes (create + update)",
            unit: "By",
        }),
    };
    return cached;
}

/**
 * Drop the cached instrument bundle so the next
 * `getVaultPluginInstruments()` call binds against whichever
 * `MeterProvider` is globally registered at that moment. Tests call
 * this after installing a fresh provider.
 */
export function resetVaultPluginInstruments(): void {
    cached = undefined;
}