import { createHash } from "node:crypto";
import { MongoServerError, ObjectId } from "mongodb";
import { collections } from "$lib/server/database";
import type {
	AgentConfigurationAction,
	AgentConfigurationKey,
	AgentConfigurationReceipt,
	Workspace,
} from "$lib/types/Workspace";

export type AgentConfigurationPayload =
	| { action: "set-model"; model: string }
	| { action: "set-thinking"; level: string }
	| { action: "set-policy"; policy: string };

export type AgentConfigurationReceiptState =
	| { status: "missing" }
	| { status: "pending"; receipt: AgentConfigurationReceipt }
	| { status: "completed"; receipt: AgentConfigurationReceipt }
	| { status: "conflict" }
	| { status: "stale" };

/** Canonical hash which binds one stable client id to one exact setting. */
export function fingerprintAgentConfiguration(payload: AgentConfigurationPayload): string {
	return createHash("sha256")
		.update(
			JSON.stringify({
				action: payload.action,
				value: configurationValue(payload),
			})
		)
		.digest("hex");
}

/** Read-only preflight lets completed retries succeed without opening the sandbox. */
export async function inspectAgentConfiguration(options: {
	workspaceId: Workspace["_id"];
	controlId: string;
	fingerprint: string;
}): Promise<AgentConfigurationReceiptState> {
	const receipt = await collections.agentConfigurationReceipts.findOne({
		workspaceId: options.workspaceId,
		controlId: options.controlId,
	});
	return classifyReceipt(receipt, options.fingerprint);
}

/**
 * Append a command to the durable per-workspace log and make it latest for its
 * setting kind. Receipts are separate documents, so stable ids are never
 * evicted and a hostile number of settings cannot grow the Workspace document.
 *
 * The placeholder's baseSequence closes both sides of the two-document crash
 * window: a missing head update can be resumed, while a later request which
 * advanced the same setting causes the older placeholder to be superseded.
 */
export async function registerAgentConfiguration(options: {
	workspace: Workspace;
	controlId: string;
	payload: AgentConfigurationPayload;
	now?: Date;
}): Promise<AgentConfigurationReceiptState> {
	const fingerprint = fingerprintAgentConfiguration(options.payload);
	const now = options.now ?? new Date();
	const key = configurationKey(options.payload.action);
	const sandbox = options.workspace.sandbox;
	if (!sandbox.id || !sandbox.generation || !sandbox.nonce) return { status: "stale" };

	await ensureLedger(options.workspace, now);
	for (;;) {
		const existing = await collections.agentConfigurationReceipts.findOne({
			workspaceId: options.workspace._id,
			controlId: options.controlId,
		});
		if (existing) {
			return resumeReceipt({
				workspace: options.workspace,
				receipt: existing,
				fingerprint,
				key,
				now,
			});
		}

		const ledger = await collections.agentConfigurationLedgers.findOne({
			_id: options.workspace._id,
		});
		if (!ledger) {
			await ensureLedger(options.workspace, now);
			continue;
		}
		const receipt: AgentConfigurationReceipt = {
			_id: new ObjectId(),
			workspaceId: options.workspace._id,
			conversationId: options.workspace.conversationId,
			controlId: options.controlId,
			fingerprint,
			action: options.payload.action,
			value: configurationValue(options.payload),
			baseSequence: ledger.nextSequence,
			status: "pending",
			requestedAt: now,
			sandboxId: sandbox.id,
			sandboxGeneration: sandbox.generation,
			sandboxNonce: sandbox.nonce,
			createdAt: now,
			updatedAt: now,
		};
		try {
			await collections.agentConfigurationReceipts.insertOne(receipt);
		} catch (cause) {
			if (cause instanceof MongoServerError && cause.code === 11000) continue;
			throw cause;
		}
		return resumeReceipt({
			workspace: options.workspace,
			receipt,
			fingerprint,
			key,
			now,
		});
	}
}

export async function completeAgentConfiguration(options: {
	workspaceId: Workspace["_id"];
	controlId: string;
	fingerprint: string;
	action: AgentConfigurationAction;
	now?: Date;
}): Promise<boolean> {
	const now = options.now ?? new Date();
	const receipt = await collections.agentConfigurationReceipts.findOne({
		workspaceId: options.workspaceId,
		controlId: options.controlId,
	});
	const classified = classifyReceipt(receipt, options.fingerprint);
	if (classified.status === "completed") return true;
	if (classified.status !== "pending" || classified.receipt.sequence === undefined) return false;

	const key = configurationKey(options.action);
	const ledger = await collections.agentConfigurationLedgers.findOne({
		_id: options.workspaceId,
	});
	const latest = ledger?.latest[key];
	if (
		!latest ||
		latest.controlId !== options.controlId ||
		latest.fingerprint !== options.fingerprint ||
		latest.sequence !== classified.receipt.sequence
	) {
		if (latest && latest.sequence > classified.receipt.sequence) {
			return markSuperseded(classified.receipt, options.fingerprint, now);
		}
		return false;
	}

	const completed = await collections.agentConfigurationReceipts.updateOne(
		{
			_id: classified.receipt._id,
			fingerprint: options.fingerprint,
			status: "pending",
			sequence: classified.receipt.sequence,
		},
		{
			$set: { status: "completed", completedAt: now, updatedAt: now },
		}
	);
	if (completed.matchedCount === 1) return true;
	const current = await inspectAgentConfiguration({
		workspaceId: options.workspaceId,
		controlId: options.controlId,
		fingerprint: options.fingerprint,
	});
	return current.status === "completed";
}

async function ensureLedger(workspace: Workspace, now: Date): Promise<void> {
	await collections.agentConfigurationLedgers.updateOne(
		{ _id: workspace._id },
		{
			$setOnInsert: {
				conversationId: workspace.conversationId,
				nextSequence: 0,
				latest: {},
				createdAt: now,
				updatedAt: now,
			},
		},
		{ upsert: true }
	);
}

async function resumeReceipt(options: {
	workspace: Workspace;
	receipt: AgentConfigurationReceipt;
	fingerprint: string;
	key: AgentConfigurationKey;
	now: Date;
}): Promise<AgentConfigurationReceiptState> {
	let receipt = options.receipt;
	const classified = classifyReceipt(receipt, options.fingerprint);
	if (classified.status !== "pending") return classified;
	const sandbox = options.workspace.sandbox;
	if (
		receipt.sandboxId !== sandbox.id ||
		receipt.sandboxGeneration !== sandbox.generation ||
		receipt.sandboxNonce !== sandbox.nonce
	) {
		return { status: "stale" };
	}

	for (;;) {
		const ledger = await collections.agentConfigurationLedgers.findOne({
			_id: options.workspace._id,
		});
		if (!ledger) return { status: "stale" };
		const latest = ledger.latest[options.key];

		if (receipt.sequence !== undefined) {
			if (latest && latest.sequence > receipt.sequence) {
				await markSuperseded(receipt, options.fingerprint, options.now);
				return inspectAgentConfiguration({
					workspaceId: options.workspace._id,
					controlId: receipt.controlId,
					fingerprint: options.fingerprint,
				});
			}
			if (
				latest?.controlId === receipt.controlId &&
				latest.fingerprint === options.fingerprint &&
				latest.sequence === receipt.sequence
			) {
				return { status: "pending", receipt };
			}
			return { status: "stale" };
		}

		if (latest?.controlId === receipt.controlId && latest.fingerprint === options.fingerprint) {
			const restored = await collections.agentConfigurationReceipts.findOneAndUpdate(
				{ _id: receipt._id, fingerprint: options.fingerprint, sequence: { $exists: false } },
				{ $set: { sequence: latest.sequence, updatedAt: options.now } },
				{ returnDocument: "after", includeResultMetadata: false }
			);
			if (restored) return { status: "pending", receipt: restored };
			const current = await collections.agentConfigurationReceipts.findOne({ _id: receipt._id });
			if (!current) return { status: "stale" };
			receipt = current;
			continue;
		}

		if (latest && latest.sequence > receipt.baseSequence) {
			await markSuperseded(receipt, options.fingerprint, options.now);
			return inspectAgentConfiguration({
				workspaceId: options.workspace._id,
				controlId: receipt.controlId,
				fingerprint: options.fingerprint,
			});
		}

		const sequence = ledger.nextSequence + 1;
		const advanced = await collections.agentConfigurationLedgers.updateOne(
			{ _id: options.workspace._id, nextSequence: ledger.nextSequence },
			{
				$inc: { nextSequence: 1 },
				$set: {
					[`latest.${options.key}`]: {
						controlId: receipt.controlId,
						fingerprint: options.fingerprint,
						sequence,
					},
					updatedAt: options.now,
				},
			}
		);
		if (advanced.matchedCount !== 1) continue;

		const assigned = await collections.agentConfigurationReceipts.findOneAndUpdate(
			{ _id: receipt._id, fingerprint: options.fingerprint, sequence: { $exists: false } },
			{ $set: { sequence, updatedAt: options.now } },
			{ returnDocument: "after", includeResultMetadata: false }
		);
		if (assigned) return { status: "pending", receipt: assigned };
		const current = await collections.agentConfigurationReceipts.findOne({ _id: receipt._id });
		if (!current) return { status: "stale" };
		receipt = current;
	}
}

async function markSuperseded(
	receipt: AgentConfigurationReceipt,
	fingerprint: string,
	now: Date
): Promise<boolean> {
	const superseded = await collections.agentConfigurationReceipts.updateOne(
		{ _id: receipt._id, fingerprint, status: "pending" },
		{ $set: { status: "superseded", completedAt: now, updatedAt: now } }
	);
	if (superseded.matchedCount === 1) return true;
	const current = await collections.agentConfigurationReceipts.findOne({ _id: receipt._id });
	return current?.fingerprint === fingerprint && current.status !== "pending";
}

function classifyReceipt(
	receipt: AgentConfigurationReceipt | null | undefined,
	fingerprint: string
): AgentConfigurationReceiptState {
	if (!receipt) return { status: "missing" };
	if (receipt.fingerprint !== fingerprint) return { status: "conflict" };
	return receipt.status === "pending"
		? { status: "pending", receipt }
		: { status: "completed", receipt };
}

function configurationKey(action: AgentConfigurationAction): AgentConfigurationKey {
	switch (action) {
		case "set-model":
			return "model";
		case "set-thinking":
			return "thinking";
		case "set-policy":
			return "policy";
	}
}

function configurationValue(payload: AgentConfigurationPayload): string {
	switch (payload.action) {
		case "set-model":
			return payload.model;
		case "set-thinking":
			return payload.level;
		case "set-policy":
			return payload.policy;
	}
}