import type { ReactNode } from "react";
import {
	createCorrelationId,
	fail,
	type HousekeepingResult,
} from "../../../foundation/contracts";
import { HousekeepingPageShell } from "../../../foundation/page/housekeeping-page-shell";
import { HousekeepingPageState } from "../../../foundation/page/housekeeping-page-state";
import type { HousekeepingPageInput } from "../../../route-handlers";
import {
	type SystemObservabilityQueryData,
	type SystemObservabilityQueryInput,
	systemObservabilityQuery,
} from "../queries/observability";

interface SystemObservabilityPageProps {
	readonly result?: HousekeepingResult<SystemObservabilityQueryData>;
}

function pageState(
	kind: "loading" | "empty" | "error",
	title: string,
	description: string,
) {
	return (
		<div data-housekeeping-state={kind}>
			<HousekeepingPageState
				state={kind}
				title={title}
				description={description}
			/>
		</div>
	);
}

function forbiddenState() {
	return (
		<section
			role="alert"
			data-housekeeping-state="forbidden"
			className="rounded-lg border border-[var(--admin-error)] bg-[var(--admin-surface)] p-4"
		>
			<h2 className="font-medium text-[var(--admin-text)]">Access denied</h2>
			<p className="mt-1 text-sm text-[var(--admin-text-muted)]">
				Your account cannot view this observability source.
			</p>
		</section>
	);
}

function observabilityContent(data: SystemObservabilityQueryData) {
	if (data.kind === "devops") {
		return (
			<div className="grid gap-4 lg:grid-cols-2">
				<section className="rounded-lg border border-[var(--admin-border)] bg-[var(--admin-surface)] p-4">
					<h2 className="font-medium text-[var(--admin-text)]">
						Service health
					</h2>
					{data.health ? (
						<dl className="mt-3 grid grid-cols-2 gap-2 text-sm text-[var(--admin-text-muted)]">
							<dt>Database</dt>
							<dd>{data.health.dbOk ? "Available" : "Unavailable"}</dd>
							<dt>Redis</dt>
							<dd>
								{data.health.redisOk === null
									? "Not configured"
									: data.health.redisOk
										? "Available"
										: "Unavailable"}
							</dd>
							<dt>Emulator</dt>
							<dd>{data.health.emulatorOk ? "Available" : "Unavailable"}</dd>
							<dt>Online users</dt>
							<dd>{data.health.onlineUsers}</dd>
						</dl>
					) : (
						<p className="mt-3 text-sm text-[var(--admin-text-muted)]">
							Health data is unavailable.
						</p>
					)}
				</section>
				{observationRows("Recent emulator errors", data.errors)}
			</div>
		);
	}
	if (data.kind === "devops-errors") {
		return observationRows("Emulator errors", data.errors);
	}
	return (
		<div className="space-y-4">
			<div className="grid gap-3 sm:grid-cols-2 xl:grid-cols-4">
				{data.metrics.map((metric) => (
					<section
						key={metric.label}
						className="rounded-lg border border-[var(--admin-border)] bg-[var(--admin-surface)] p-4"
					>
						<p className="text-xs text-[var(--admin-text-muted)]">
							{metric.label}
						</p>
						<p className="mt-1 text-xl font-semibold text-[var(--admin-text)]">
							{metric.value}
						</p>
					</section>
				))}
			</div>
			{observationRows(
				data.kind === "logs" ? "Recent entries" : "Details",
				data.rows,
			)}
		</div>
	);
}

function observationRows(
	title: string,
	rows: readonly { id: string; primary: string; secondary?: string }[],
) {
	return (
		<section className="rounded-lg border border-[var(--admin-border)] bg-[var(--admin-surface)] p-4">
			<h2 className="font-medium text-[var(--admin-text)]">{title}</h2>
			<ul className="mt-3 divide-y divide-[var(--admin-border)]">
				{rows.map((row) => (
					<li key={row.id} className="py-2 text-sm">
						<p className="font-medium text-[var(--admin-text)]">
							{row.primary}
						</p>
						{row.secondary ? (
							<p className="break-words text-[var(--admin-text-muted)]">
								{row.secondary}
							</p>
						) : null}
					</li>
				))}
			</ul>
		</section>
	);
}

function isEmpty(data: SystemObservabilityQueryData): boolean {
	if (data.kind === "devops")
		return data.health === null && data.errors.length === 0;
	if (data.kind === "devops-errors") return data.errors.length === 0;
	return data.metrics.length === 0 && data.rows.length === 0;
}

export function SystemObservabilityPage({
	result,
}: SystemObservabilityPageProps) {
	let body: ReactNode;
	if (!result) {
		body = pageState(
			"loading",
			"Loading observability data",
			"Reading metrics and operational logs.",
		);
	} else if (!result.ok) {
		body =
			result.error.code === "FORBIDDEN"
				? forbiddenState()
				: pageState(
						"error",
						"Observability data unavailable",
						`Request ${result.correlationId} could not be completed.`,
					);
	} else if (
		isEmpty(result.data) &&
		result.data.partialDependencies.length === 0
	) {
		body = pageState(
			"empty",
			"No observations",
			"The selected source returned no records.",
		);
	} else {
		body = (
			<div
				data-housekeeping-state={
					result.data.partialDependencies.length > 0 ? "partial" : "ready"
				}
				className="space-y-4"
			>
				{result.data.partialDependencies.length > 0 ? (
					<HousekeepingPageState
						state="partial"
						partialLabel="Partial data"
						title="Some observability data is unavailable"
						description={`Unavailable: ${result.data.partialDependencies.join(", ")}`}
					/>
				) : null}
				{observabilityContent(result.data)}
			</div>
		);
	}

	return (
		<HousekeepingPageShell
			title="System observability"
			description="Review metrics, service health, and operational records."
		>
			{body}
		</HousekeepingPageShell>
	);
}

export async function renderSystemObservabilityPage(
	input: HousekeepingPageInput,
) {
	const routeId = input.match
		.routeId as SystemObservabilityQueryInput["routeId"];
	const supported = routeId.startsWith("system.observability.");
	const result = supported
		? await systemObservabilityQuery.run(input.context, { routeId })
		: fail("NOT_FOUND", "errors.housekeeping.notFound", createCorrelationId());
	return <SystemObservabilityPage result={result} />;
}