export const MANAGED_BY_SELECTOR = {
  "app.kubernetes.io/managed-by": "kuber",
} as const;

export type LogTarget =
  | { kind: "managed-deployments" }
  | { kind: "service"; name: string };

export type KubernetesDeployment = {
  name: string;
  selector: Readonly<Record<string, string>>;
};

export type KubernetesService = {
  name: string;
  selector: Readonly<Record<string, string>>;
};

export type KubernetesPod = {
  name: string;
  uid: string;
  phase?: string;
  containers: readonly string[];
};

export type ContainerLogRequest = {
  namespace: string;
  pod: string;
  container: string;
  tailLines?: number;
  sinceSeconds?: number;
  sinceTime?: string;
  timestamps: boolean;
};

/** The only cluster operations the log service can perform. */
export interface KubernetesLogsBackend {
  listDeployments(
    namespace: string,
    labels: Readonly<Record<string, string>>,
    signal?: AbortSignal,
  ): Promise<readonly KubernetesDeployment[]>;
  getService(
    namespace: string,
    name: string,
    signal?: AbortSignal,
  ): Promise<KubernetesService | undefined>;
  listPods(
    namespace: string,
    selector: Readonly<Record<string, string>>,
    signal?: AbortSignal,
  ): Promise<readonly KubernetesPod[]>;
  readContainerLogs(
    request: ContainerLogRequest,
    signal?: AbortSignal,
  ): Promise<string>;
  streamContainerLogs(
    request: ContainerLogRequest,
    signal: AbortSignal,
  ): AsyncIterable<string | Uint8Array>;
}

export type LogOptions = {
  namespace: string;
  target: LogTarget;
  tailLines?: number;
  sinceSeconds?: number;
  sinceTime?: string | Date;
  timestamps?: boolean;
};

export type FollowLogOptions = LogOptions & {
  signal: AbortSignal;
  queueCapacity?: number;
  discoveryIntervalMs?: number;
  heartbeatIntervalMs?: number;
  retryIntervalMs?: number;
};

export type LogContainer = {
  namespace: string;
  targetKind: "deployment" | "service";
  targetName: string;
  pod: string;
  podUid: string;
  container: string;
};

export type LogLineEvent = LogContainer & {
  type: "log";
  timestamp: string;
  logTimestamp?: string;
  message: string;
};

export type LogHeartbeatEvent = {
  type: "heartbeat";
  timestamp: string;
};

export type LogErrorEvent = {
  type: "error";
  timestamp: string;
  message: string;
  retryable: boolean;
  retryAfterMs?: number;
  namespace: string;
  pod?: string;
  container?: string;
};

export type LogEvent = LogLineEvent | LogHeartbeatEvent | LogErrorEvent;

export class KubernetesLogError extends Error {
  constructor(
    message: string,
    readonly retryable: boolean,
  ) {
    super(message);
    this.name = "KubernetesLogError";
  }
}

type NormalizedOptions = Omit<LogOptions, "sinceTime" | "timestamps"> & {
  sinceTime?: string;
  timestamps: boolean;
};

type QueueWaiter<T> = (value: T | undefined) => void;

class BoundedAsyncQueue<T> {
  private readonly items: T[] = [];
  private readonly readers: QueueWaiter<T>[] = [];
  private readonly writers: Array<() => void> = [];
  private closed = false;

  constructor(private readonly capacity: number) {}

  async push(value: T): Promise<boolean> {
    while (!this.closed) {
      const reader = this.readers.shift();
      if (reader) {
        reader(value);
        return true;
      }
      if (this.items.length < this.capacity) {
        this.items.push(value);
        return true;
      }
      await new Promise<void>((resolve) => this.writers.push(resolve));
    }
    return false;
  }

  async shift(): Promise<T | undefined> {
    const item = this.items.shift();
    if (item !== undefined) {
      this.writers.shift()?.();
      return item;
    }
    if (this.closed) return;
    return new Promise<T | undefined>((resolve) => this.readers.push(resolve));
  }

  close(discard = false): void {
    if (this.closed) return;
    this.closed = true;
    if (discard) this.items.length = 0;
    for (const reader of this.readers.splice(0)) reader(undefined);
    for (const writer of this.writers.splice(0)) writer();
  }
}

function positiveInteger(value: number | undefined, fallback: number): number {
  const result = value ?? fallback;
  if (!Number.isSafeInteger(result) || result <= 0)
    throw new Error(
      "Log service intervals and queue capacity must be positive integers",
    );
  return result;
}

function normalizeOptions(options: LogOptions): NormalizedOptions {
  if (!options.namespace.trim()) throw new Error("Namespace is required");
  if (options.target.kind === "service" && !options.target.name.trim())
    throw new Error("Service name is required");
  if (
    options.tailLines !== undefined &&
    (!Number.isSafeInteger(options.tailLines) || options.tailLines < 0)
  )
    throw new Error("tailLines must be a non-negative integer");
  if (
    options.sinceSeconds !== undefined &&
    (!Number.isSafeInteger(options.sinceSeconds) || options.sinceSeconds < 0)
  )
    throw new Error("sinceSeconds must be a non-negative integer");
  if (options.sinceSeconds !== undefined && options.sinceTime !== undefined)
    throw new Error("sinceSeconds and sinceTime are mutually exclusive");

  let sinceTime: string | undefined;
  if (options.sinceTime !== undefined) {
    const date =
      options.sinceTime instanceof Date
        ? options.sinceTime
        : new Date(options.sinceTime);
    if (Number.isNaN(date.getTime()))
      throw new Error("sinceTime must be valid");
    sinceTime = date.toISOString();
  }

  return { ...options, sinceTime, timestamps: options.timestamps ?? false };
}

function errorMessage(error: unknown): string {
  return error instanceof Error
    ? error.message
    : "Kubernetes log request failed";
}

function isAbort(signal: AbortSignal): boolean {
  return signal.aborted;
}

function isRetryable(error: unknown): boolean {
  if (
    error &&
    typeof error === "object" &&
    "code" in error &&
    typeof error.code === "string"
  )
    return false;
  return !(error instanceof KubernetesLogError) || error.retryable;
}

function requestFor(
  source: LogContainer,
  options: NormalizedOptions,
): ContainerLogRequest {
  return {
    namespace: source.namespace,
    pod: source.pod,
    container: source.container,
    tailLines: options.tailLines,
    sinceSeconds: options.sinceSeconds,
    sinceTime: options.sinceTime,
    timestamps: options.timestamps,
  };
}

function parseLine(
  line: string,
  source: LogContainer,
  timestamps: boolean,
  now: () => Date,
): LogLineEvent {
  let message = line.replace(/\r$/, "");
  let logTimestamp: string | undefined;
  if (timestamps) {
    const separator = message.indexOf(" ");
    if (separator > 0) {
      const candidate = message.slice(0, separator);
      if (!Number.isNaN(Date.parse(candidate))) {
        logTimestamp = candidate;
        message = message.slice(separator + 1);
      }
    }
  }
  return {
    type: "log",
    timestamp: now().toISOString(),
    ...(logTimestamp ? { logTimestamp } : {}),
    ...source,
    message,
  };
}

async function emitText(
  text: string,
  source: LogContainer,
  timestamps: boolean,
  now: () => Date,
  emit: (event: LogLineEvent) => void | Promise<unknown>,
): Promise<void> {
  if (!text) return;
  const lines = text.split(/\n/);
  if (text.endsWith("\n")) lines.pop();
  for (const line of lines)
    await emit(parseLine(line, source, timestamps, now));
}

async function emitChunks(
  chunks: AsyncIterable<string | Uint8Array>,
  source: LogContainer,
  timestamps: boolean,
  now: () => Date,
  signal: AbortSignal,
  emit: (event: LogLineEvent) => Promise<unknown>,
): Promise<void> {
  const decoder = new TextDecoder();
  let buffer = "";
  for await (const chunk of chunks) {
    buffer +=
      typeof chunk === "string"
        ? chunk
        : decoder.decode(chunk, { stream: true });
    let newline = buffer.indexOf("\n");
    while (newline >= 0) {
      await emit(parseLine(buffer.slice(0, newline), source, timestamps, now));
      buffer = buffer.slice(newline + 1);
      newline = buffer.indexOf("\n");
    }
  }
  buffer += decoder.decode();
  if (buffer && !signal.aborted)
    await emit(parseLine(buffer, source, timestamps, now));
}

function wait(ms: number, signal: AbortSignal): Promise<void> {
  if (signal.aborted) return Promise.resolve();
  return new Promise((resolve) => {
    const timer = setTimeout(done, ms);
    function done() {
      clearTimeout(timer);
      signal.removeEventListener("abort", done);
      resolve();
    }
    signal.addEventListener("abort", done, { once: true });
  });
}

export function encodeLogEvent(event: LogEvent): string {
  return JSON.stringify(event);
}

export class LogService {
  constructor(
    private readonly backend: KubernetesLogsBackend,
    private readonly now: () => Date = () => new Date(),
  ) {}

  async listContainers(
    input: LogOptions,
    signal?: AbortSignal,
  ): Promise<LogContainer[]> {
    const options = normalizeOptions(input);
    const targets: Array<{
      kind: "deployment" | "service";
      name: string;
      selector: Readonly<Record<string, string>>;
    }> = [];
    if (options.target.kind === "managed-deployments") {
      const deployments = await this.backend.listDeployments(
        options.namespace,
        MANAGED_BY_SELECTOR,
        signal,
      );
      for (const deployment of deployments) {
        if (Object.keys(deployment.selector).length > 0)
          targets.push({ kind: "deployment", ...deployment });
      }
    } else {
      const service = await this.backend.getService(
        options.namespace,
        options.target.name,
        signal,
      );
      if (!service)
        throw new KubernetesLogError(
          `Service ${options.target.name} was not found`,
          false,
        );
      if (Object.keys(service.selector).length === 0)
        throw new KubernetesLogError(
          `Service ${options.target.name} has no pod selector`,
          false,
        );
      targets.push({ kind: "service", ...service });
    }

    const result = new Map<string, LogContainer>();
    for (const target of targets) {
      const pods = await this.backend.listPods(
        options.namespace,
        target.selector,
        signal,
      );
      for (const pod of pods) {
        if (!pod.name || !pod.uid) continue;
        for (const container of pod.containers) {
          if (!container) continue;
          const source: LogContainer = {
            namespace: options.namespace,
            targetKind: target.kind,
            targetName: target.name,
            pod: pod.name,
            podUid: pod.uid,
            container,
          };
          result.set(`${pod.uid}\0${container}`, source);
        }
      }
    }
    return [...result.values()];
  }

  async collect(input: LogOptions, signal?: AbortSignal): Promise<LogEvent[]> {
    const options = normalizeOptions(input);
    const sources = await this.listContainers(options, signal);
    const events: LogEvent[] = [];
    for (const source of sources) {
      try {
        const text = await this.backend.readContainerLogs(
          requestFor(source, options),
          signal,
        );
        await emitText(text, source, options.timestamps, this.now, (event) => {
          events.push(event);
        });
      } catch (error) {
        if (signal && isAbort(signal)) throw error;
        events.push({
          type: "error",
          timestamp: this.now().toISOString(),
          namespace: options.namespace,
          pod: source.pod,
          container: source.container,
          message: errorMessage(error),
          retryable: isRetryable(error),
        });
      }
    }
    return events;
  }

  async *follow(input: FollowLogOptions): AsyncGenerator<LogEvent> {
    const options = normalizeOptions(input);
    const capacity = positiveInteger(input.queueCapacity, 128);
    const discoveryInterval = positiveInteger(input.discoveryIntervalMs, 2_000);
    const heartbeatInterval = positiveInteger(
      input.heartbeatIntervalMs,
      5_000,
    );
    const retryInterval = positiveInteger(input.retryIntervalMs, 1_000);
    const queue = new BoundedAsyncQueue<LogEvent>(capacity);
    const controller = new AbortController();
    const stop = () => {
      queue.close(true);
      controller.abort();
    };
    if (input.signal.aborted) controller.abort();
    else input.signal.addEventListener("abort", stop, { once: true });

    const active = new Map<string, AbortController>();
    const completed = new Set<string>();
    const retryNotBefore = new Map<string, number>();
    const streamTasks = new Set<Promise<void>>();
    const pushError = async (
      error: unknown,
      source?: LogContainer,
    ): Promise<void> => {
      await queue.push({
        type: "error",
        timestamp: this.now().toISOString(),
        namespace: options.namespace,
        pod: source?.pod,
        container: source?.container,
        message: errorMessage(error),
        retryable: isRetryable(error),
        ...(isRetryable(error) ? { retryAfterMs: retryInterval } : {}),
      });
    };

    const startStream = (source: LogContainer): void => {
      const key = `${source.podUid}\0${source.container}`;
      const local = new AbortController();
      active.set(key, local);
      const signal = AbortSignal.any([controller.signal, local.signal]);
      let task!: Promise<void>;
      task = (async () => {
        try {
          await emitChunks(
            this.backend.streamContainerLogs(
              requestFor(source, options),
              signal,
            ),
            source,
            options.timestamps,
            this.now,
            signal,
            (event) => queue.push(event),
          );
          if (!signal.aborted)
            throw new KubernetesLogError(
              "Kubernetes log stream ended unexpectedly",
              true,
            );
        } catch (error) {
          if (!isAbort(signal)) {
            await pushError(error, source);
            if (isRetryable(error))
              retryNotBefore.set(key, Date.now() + retryInterval);
            else completed.add(key);
          }
        } finally {
          active.delete(key);
          streamTasks.delete(task);
        }
      })();
      streamTasks.add(task);
    };

    const discover = async (): Promise<void> => {
      while (!controller.signal.aborted) {
        try {
          const sources = await this.listContainers(options, controller.signal);
          const desired = new Set(
            sources.map((source) => `${source.podUid}\0${source.container}`),
          );
          for (const key of completed) {
            if (!desired.has(key)) completed.delete(key);
          }
          for (const key of retryNotBefore.keys()) {
            if (!desired.has(key)) retryNotBefore.delete(key);
          }
          for (const [key, stream] of active) {
            if (!desired.has(key)) stream.abort();
          }
          for (const source of sources) {
            const key = `${source.podUid}\0${source.container}`;
            if (
              !active.has(key) &&
              !completed.has(key) &&
              (retryNotBefore.get(key) ?? 0) <= Date.now()
            ) {
              retryNotBefore.delete(key);
              startStream(source);
            }
          }
        } catch (error) {
          if (!isAbort(controller.signal)) {
            await pushError(error);
            if (!isRetryable(error)) controller.abort();
          }
        }
        await wait(discoveryInterval, controller.signal);
      }
    };

    const heartbeat = async (): Promise<void> => {
      while (!controller.signal.aborted) {
        await wait(heartbeatInterval, controller.signal);
        if (!controller.signal.aborted)
          await queue.push({
            type: "heartbeat",
            timestamp: this.now().toISOString(),
          });
      }
    };

    const runner = Promise.all([discover(), heartbeat()]).finally(async () => {
      for (const stream of active.values()) stream.abort();
      await Promise.allSettled([...streamTasks]);
      queue.close();
    });

    try {
      for (;;) {
        const event = await queue.shift();
        if (event === undefined) return;
        yield event;
      }
    } finally {
      input.signal.removeEventListener("abort", stop);
      controller.abort();
      queue.close(true);
      await runner;
    }
  }
}

export function createLogService(
  backend: KubernetesLogsBackend,
  now?: () => Date,
): LogService {
  return new LogService(backend, now);
}