import os from 'node:os';
import * as fs from 'node:fs/promises';
import type { IModelCatalogEntry } from '../interfaces/catalog.ts';
import type {
  IClusterConfig,
  IClusterDesiredDeployment,
  IClusterGpuTopologyGroup,
  IClusterModelLocation,
  IClusterNodeHeartbeat,
  IClusterNodeStatus,
  IClusterStatusResponse,
  TClusterNodeSchedulerState,
} from '../interfaces/cluster.ts';
import { CLUSTER, PATHS } from '../constants.ts';

export class ClusterManager {
  private config: IClusterConfig = {
    enabled: false,
    nodeName: os.hostname(),
    role: 'standalone',
    bindHost: CLUSTER.DEFAULT_BIND_HOST,
    gossipPort: CLUSTER.DEFAULT_GOSSIP_PORT,
    heartbeatIntervalMs: CLUSTER.DEFAULT_HEARTBEAT_INTERVAL_MS,
    seedNodes: [],
  };
  private localNode: IClusterNodeHeartbeat | null = null;
  private knownNodes = new Map<string, IClusterNodeHeartbeat>();
  private desiredDeployments = new Map<string, IClusterDesiredDeployment>();
  private nodeSchedulerStates = new Map<string, TClusterNodeSchedulerState>();
  private persistQueued = false;
  private controlPersistQueued = false;

  public async initialize(): Promise<void> {
    try {
      const stateContent = await fs.readFile(this.getStateFilePath(), 'utf-8');
      const data = JSON.parse(stateContent) as { nodes?: IClusterNodeHeartbeat[] };

      for (const node of data.nodes || []) {
        this.knownNodes.set(node.nodeName, node);
        if (node.nodeName === this.config.nodeName) {
          this.localNode = node;
        }
      }

      this.pruneStaleNodes();
    } catch {
      // No persisted cluster state yet.
    }

    try {
      const controlStateContent = await fs.readFile(this.getControlStateFilePath(), 'utf-8');
      const data = JSON.parse(controlStateContent) as {
        desiredDeployments?: IClusterDesiredDeployment[];
        nodeSchedulerStates?: Record<string, TClusterNodeSchedulerState>;
      };

      for (const deployment of data.desiredDeployments || []) {
        this.desiredDeployments.set(deployment.modelId, deployment);
      }

      for (const [nodeName, schedulerState] of Object.entries(data.nodeSchedulerStates || {})) {
        this.nodeSchedulerStates.set(nodeName, schedulerState);
      }
    } catch {
      // No persisted control state yet.
    }
  }

  public configure(config: IClusterConfig): void {
    this.config = {
      ...config,
      heartbeatIntervalMs: config.heartbeatIntervalMs || CLUSTER.DEFAULT_HEARTBEAT_INTERVAL_MS,
      seedNodes: config.seedNodes || [],
    };
  }

  public getConfig(): IClusterConfig {
    return this.config;
  }

  public isEnabled(): boolean {
    return this.config.enabled;
  }

  public isControlPlane(): boolean {
    return this.config.enabled && this.config.role === 'control-plane';
  }

  public isWorker(): boolean {
    return this.config.enabled && this.config.role === 'worker';
  }

  public getModeLabel(): string {
    if (!this.config.enabled) {
      return 'standalone';
    }

    return this.config.role;
  }

  public getHeartbeatIntervalMs(): number {
    return this.config.heartbeatIntervalMs || CLUSTER.DEFAULT_HEARTBEAT_INTERVAL_MS;
  }

  public getAdvertisedEndpoint(): string | undefined {
    return this.localNode?.endpoint || this.config.advertiseUrl;
  }

  public getControlPlaneUrl(): string | undefined {
    return this.config.controlPlaneUrl;
  }

  public getSharedSecret(): string | undefined {
    return this.config.sharedSecret || undefined;
  }

  public updateLocalNode(heartbeat: IClusterNodeHeartbeat): void {
    this.localNode = heartbeat;
    this.knownNodes.set(heartbeat.nodeName, heartbeat);
    this.schedulePersist();
  }

  public upsertNode(heartbeat: IClusterNodeHeartbeat): void {
    this.knownNodes.set(heartbeat.nodeName, heartbeat);
    this.schedulePersist();
  }

  public getLocalNodeStatus(): IClusterNodeStatus {
    return {
      nodeName: this.config.nodeName,
      role: this.config.role,
      endpoint: this.getAdvertisedEndpoint(),
      healthy: true,
      schedulerState: this.getNodeSchedulerState(this.config.nodeName),
    };
  }

  public getLocalNode(): IClusterNodeHeartbeat | null {
    return this.localNode;
  }

  public getNode(nodeName: string): IClusterNodeHeartbeat | null {
    const node = this.knownNodes.get(nodeName);
    if (!node) {
      return null;
    }

    return this.decorateNode(node);
  }

  public pruneStaleNodes(): void {
    const now = Date.now();
    for (const [nodeName, node] of this.knownNodes) {
      if (nodeName === this.config.nodeName) {
        continue;
      }

      if (now - node.lastSeenAt > CLUSTER.NODE_STALE_AFTER_MS) {
        this.knownNodes.delete(nodeName);
        this.schedulePersist();
      }
    }
  }

  public getAllNodes(): IClusterNodeHeartbeat[] {
    this.pruneStaleNodes();
    return Array.from(this.knownNodes.values()).map((node) => this.decorateNode(node)).sort(
      (left, right) => {
        if (left.nodeName === this.config.nodeName) {
          return -1;
        }
        if (right.nodeName === this.config.nodeName) {
          return 1;
        }
        return left.nodeName.localeCompare(right.nodeName);
      },
    );
  }

  public getHealthyNodes(): IClusterNodeHeartbeat[] {
    return this.getAllNodes().filter((node) => node.healthy);
  }

  public getNodeSchedulerState(nodeName: string): TClusterNodeSchedulerState {
    return this.nodeSchedulerStates.get(nodeName) || 'active';
  }

  public setNodeSchedulerState(
    nodeName: string,
    schedulerState: TClusterNodeSchedulerState,
  ): TClusterNodeSchedulerState {
    this.nodeSchedulerStates.set(nodeName, schedulerState);
    this.scheduleControlPersist();
    return schedulerState;
  }

  public getDesiredDeployments(): IClusterDesiredDeployment[] {
    return Array.from(this.desiredDeployments.values()).sort((left, right) =>
      left.modelId.localeCompare(right.modelId)
    );
  }

  public getDesiredDeployment(modelId: string): IClusterDesiredDeployment | null {
    return this.desiredDeployments.get(modelId) || null;
  }

  public upsertDesiredDeployment(
    modelId: string,
    desiredReplicas: number,
  ): IClusterDesiredDeployment {
    const deployment: IClusterDesiredDeployment = {
      modelId,
      desiredReplicas,
      updatedAt: Date.now(),
    };
    this.desiredDeployments.set(modelId, deployment);
    this.scheduleControlPersist();
    return deployment;
  }

  public removeDesiredDeployment(modelId: string): boolean {
    const removed = this.desiredDeployments.delete(modelId);
    if (removed) {
      this.scheduleControlPersist();
    }
    return removed;
  }

  public getModelLocations(modelId: string): IClusterModelLocation[] {
    const locations: IClusterModelLocation[] = [];

    for (const node of this.getHealthyNodes()) {
      for (const deployment of node.deployments) {
        if (deployment.modelId !== modelId || !deployment.healthy) {
          continue;
        }

        locations.push({
          modelId,
          nodeName: node.nodeName,
          endpoint: deployment.endpoint,
          healthy: deployment.healthy,
          engine: deployment.engine,
          containerId: deployment.containerId,
        });
      }
    }

    return locations;
  }

  public getActiveModelLocations(modelId: string): IClusterModelLocation[] {
    return this.getModelLocations(modelId).filter((location) =>
      this.getNodeSchedulerState(location.nodeName) === 'active'
    );
  }

  public resolveModel(modelId: string): IClusterModelLocation | null {
    const locations = this.getModelLocations(modelId);
    if (locations.length === 0) {
      return null;
    }

    locations.sort((left, right) => {
      const schedulerPreference = this.compareSchedulerState(
        this.getNodeSchedulerState(left.nodeName),
        this.getNodeSchedulerState(right.nodeName),
      );
      if (schedulerPreference !== 0) {
        return schedulerPreference;
      }

      if (left.nodeName === this.config.nodeName) {
        return -1;
      }
      if (right.nodeName === this.config.nodeName) {
        return 1;
      }
      return left.nodeName.localeCompare(right.nodeName);
    });

    return locations[0];
  }

  public pickNodeForModel(
    model: IModelCatalogEntry,
    excludedNodeNames: string[] = [],
  ): IClusterNodeHeartbeat | null {
    const requiredVram = model.requirements.minVramGb;
    const minGpuCount = model.requirements.minGpuCount || 1;
    const preferredTensorParallel = model.launchDefaults?.tensorParallelSize || minGpuCount;

    const eligible = this.getHealthyNodes().filter((node) => {
      if (excludedNodeNames.includes(node.nodeName)) {
        return false;
      }

      if (node.role === 'standalone' && node.nodeName !== this.config.nodeName) {
        return false;
      }

      if (node.schedulerState && node.schedulerState !== 'active') {
        return false;
      }

      return node.resources.availableVramGb >= requiredVram &&
        this.hasEligibleTopologyGroup(node.resources.topologyGroups, requiredVram, minGpuCount);
    });

    if (eligible.length === 0) {
      return null;
    }

    eligible.sort((left, right) => {
      if (left.nodeName === this.config.nodeName) {
        return -1;
      }
      if (right.nodeName === this.config.nodeName) {
        return 1;
      }

      if (right.resources.availableVramGb !== left.resources.availableVramGb) {
        return right.resources.availableVramGb - left.resources.availableVramGb;
      }

      const leftTopologyDelta = Math.abs(
        left.resources.largestGpuGroupCount - preferredTensorParallel,
      );
      const rightTopologyDelta = Math.abs(
        right.resources.largestGpuGroupCount - preferredTensorParallel,
      );
      if (leftTopologyDelta !== rightTopologyDelta) {
        return leftTopologyDelta - rightTopologyDelta;
      }

      return left.resources.deploymentCount - right.resources.deploymentCount;
    });

    return eligible[0];
  }

  public getStatus(): IClusterStatusResponse {
    const models: Record<string, IClusterModelLocation[]> = {};
    for (const node of this.getHealthyNodes()) {
      for (const deployment of node.deployments) {
        if (!models[deployment.modelId]) {
          models[deployment.modelId] = [];
        }

        models[deployment.modelId].push({
          modelId: deployment.modelId,
          nodeName: node.nodeName,
          endpoint: deployment.endpoint,
          healthy: deployment.healthy,
          engine: deployment.engine,
          containerId: deployment.containerId,
        });
      }
    }

    return {
      localNode: this.localNode ? this.decorateNode(this.localNode) : null,
      nodes: this.getAllNodes(),
      models,
      desiredDeployments: this.getDesiredDeployments(),
    };
  }

  private hasEligibleTopologyGroup(
    groups: IClusterGpuTopologyGroup[],
    requiredVramGb: number,
    minGpuCount: number,
  ): boolean {
    return groups.some((group) =>
      group.gpuCount >= minGpuCount && group.totalVramGb >= requiredVramGb
    );
  }

  private getStateFilePath(): string {
    return `${PATHS.DATA_DIR}/cluster-state.json`;
  }

  private getControlStateFilePath(): string {
    return `${PATHS.DATA_DIR}/cluster-control-state.json`;
  }

  private schedulePersist(): void {
    if (this.persistQueued) {
      return;
    }

    this.persistQueued = true;
    queueMicrotask(() => {
      this.persistQueued = false;
      void this.persistState();
    });
  }

  private scheduleControlPersist(): void {
    if (this.controlPersistQueued) {
      return;
    }

    this.controlPersistQueued = true;
    queueMicrotask(() => {
      this.controlPersistQueued = false;
      void this.persistControlState();
    });
  }

  private async persistState(): Promise<void> {
    try {
      await fs.mkdir(PATHS.DATA_DIR, { recursive: true });
      await fs.writeFile(
        this.getStateFilePath(),
        JSON.stringify({ nodes: Array.from(this.knownNodes.values()) }, null, 2),
      );
    } catch {
      // Persistence failure should not break the control plane.
    }
  }

  private async persistControlState(): Promise<void> {
    try {
      await fs.mkdir(PATHS.DATA_DIR, { recursive: true });
      await fs.writeFile(
        this.getControlStateFilePath(),
        JSON.stringify(
          {
            desiredDeployments: this.getDesiredDeployments(),
            nodeSchedulerStates: Object.fromEntries(this.nodeSchedulerStates.entries()),
          },
          null,
          2,
        ),
      );
    } catch {
      // Persistence failure should not break the control plane.
    }
  }

  private decorateNode(node: IClusterNodeHeartbeat): IClusterNodeHeartbeat {
    return {
      ...node,
      schedulerState: this.getNodeSchedulerState(node.nodeName),
    };
  }

  private compareSchedulerState(
    left: TClusterNodeSchedulerState,
    right: TClusterNodeSchedulerState,
  ): number {
    const order: TClusterNodeSchedulerState[] = ['active', 'cordoned', 'draining'];
    return order.indexOf(left) - order.indexOf(right);
  }
}