import { createHash, randomBytes } from "node:crypto";
import { spawn, type ChildProcessWithoutNullStreams } from "node:child_process";
import {
  closeSync,
  constants as fsConstants,
  fchmodSync,
  fstatSync,
  fsyncSync,
  lstatSync,
  mkdirSync,
  openSync,
  readFileSync,
  renameSync,
  unlinkSync,
  writeFileSync,
} from "node:fs";
import { dirname, join } from "node:path";

export type PreprocessingConflictCode = "preprocessing_conflict" | "preprocessing_resume_mismatch";

export class PreprocessingStateError extends Error {
  constructor(readonly code: PreprocessingConflictCode, message: string) {
    super(message);
    this.name = "PreprocessingStateError";
  }
}

export interface SessionInventoryRow {
  id: string;
  status: string;
  archived?: boolean;
  workspaceRevision?: string | null;
}

export interface WriterLockLease {
  holderPid: number;
  release(): Promise<void>;
}

export interface BeginPreprocessingJobOptions {
  operation: string;
  workspaceRevision: string;
  descriptorBlob: string;
  catalogBlob: string;
  configDigest: string;
  bindingDigest: string;
  embeddingId: string;
  embeddingDimensions: number;
  runId?: string;
}

export interface PreprocessingJobState {
  schemaVersion: 2;
  runId: string;
  operation: string;
  workspaceId: string;
  workspaceRevision: string;
  descriptorBlob: string;
  catalogBlob: string;
  configDigest: string;
  bindingDigest: string;
  embeddingId: string;
  embeddingDimensions: number;
  completedStages: string[];
  childRuns: Record<string, string>;
  status: "active" | "succeeded" | "blocked" | "failed";
  candidateDigest?: string;
  reviewDigest?: string;
}

export interface FkReviewRecord {
  reviewedCandidatesDigest: string;
  annotationsDigest: string;
  workspaceRevision: string;
  /** Curated Git blob id accepted at review time (P5); absent for legacy host-file reviews. */
  blobId?: string;
}

function sha256(value: string | Buffer): string {
  return `sha256:${createHash("sha256").update(value).digest("hex")}`;
}

function syncDirectory(directory: string): void {
  if (process.platform === "win32") return;
  const fd = openSync(directory, "r");
  try { fsyncSync(fd); } finally { closeSync(fd); }
}

function ensureDirectory(path: string): string {
  mkdirSync(path, { recursive: true, mode: 0o700 });
  const entry = lstatSync(path);
  if (!entry.isDirectory() || entry.isSymbolicLink()) {
    throw new Error("preprocessing state directory is unavailable");
  }
  return path;
}

function validateRunId(runId: string): string {
  if (!/^[0-9a-f]{32}$/.test(runId)) throw new Error("preprocessing run id is invalid");
  return runId;
}

function writeAtomicFile(path: string, contents: string, mode: number): void {
  ensureDirectory(join(path, ".."));
  const directory = path.slice(0, path.lastIndexOf("/"));
  ensureDirectory(directory);
  const staging = `${path}.tmp-${process.pid}-${Date.now()}-${randomBytes(6).toString("hex")}`;
  const fd = openSync(
    staging,
    fsConstants.O_WRONLY | fsConstants.O_CREAT | fsConstants.O_EXCL | fsConstants.O_NOFOLLOW,
    0o600,
  );
  let closed = false;
  try {
    writeFileSync(fd, contents, "utf8");
    fsyncSync(fd);
    fchmodSync(fd, mode);
    closeSync(fd);
    closed = true;
    renameSync(staging, path);
    syncDirectory(directory);
  } catch (error) {
    if (!closed) try { closeSync(fd); } catch { /* preserve original failure */ }
    try { unlinkSync(staging); } catch { /* best effort */ }
    throw error;
  }
}

function readTrustedFile(path: string): string {
  const entry = lstatSync(path);
  if (!entry.isFile() || entry.isSymbolicLink()) throw new Error("preprocessing state file is invalid");
  const fd = openSync(path, fsConstants.O_RDONLY | fsConstants.O_NOFOLLOW);
  try {
    const before = fstatSync(fd);
    if (!before.isFile() || before.nlink !== 1) throw new Error("preprocessing state file is invalid");
    const contents = readFileSync(fd, "utf8");
    const after = fstatSync(fd);
    if (
      before.dev !== after.dev || before.ino !== after.ino || before.size !== after.size || before.nlink !== after.nlink
    ) throw new Error("preprocessing state file changed while reading");
    return contents;
  } finally {
    closeSync(fd);
  }
}

function decodeJob(value: unknown): PreprocessingJobState {
  if (!value || typeof value !== "object" || Array.isArray(value)) {
    throw new Error("preprocessing job state is invalid");
  }
  const record = value as Record<string, unknown>;
  if (
    record.schemaVersion !== 2
    || typeof record.runId !== "string"
    || typeof record.operation !== "string"
    || typeof record.workspaceId !== "string"
    || typeof record.workspaceRevision !== "string"
    || typeof record.descriptorBlob !== "string"
    || typeof record.catalogBlob !== "string"
    || typeof record.configDigest !== "string"
    || typeof record.bindingDigest !== "string"
    || typeof record.embeddingId !== "string"
    || typeof record.embeddingDimensions !== "number"
    || !Array.isArray(record.completedStages)
    || typeof record.childRuns !== "object" || record.childRuns === null || Array.isArray(record.childRuns)
    || !["active", "succeeded", "blocked", "failed"].includes(String(record.status))
  ) {
    throw new Error("preprocessing job state is invalid");
  }
  return record as unknown as PreprocessingJobState;
}

function decodeReview(value: unknown): FkReviewRecord {
  if (!value || typeof value !== "object" || Array.isArray(value)) {
    throw new Error("preprocessing review state is invalid");
  }
  const record = value as Record<string, unknown>;
  if (
    typeof record.reviewedCandidatesDigest !== "string"
    || typeof record.annotationsDigest !== "string"
    || typeof record.workspaceRevision !== "string"
    || (record.blobId !== undefined && typeof record.blobId !== "string")
  ) throw new Error("preprocessing review state is invalid");
  return record as unknown as FkReviewRecord;
}

export class PreprocessingStateStore {
  private readonly root: string;

  constructor(private readonly options: { dataRoot: string; workspaceId: string }) {
    if (!/^[a-z][a-z0-9-]{2,62}$/.test(options.workspaceId)) {
      throw new Error("workspace id is invalid");
    }
    this.root = join(options.dataRoot, "sessions", options.workspaceId, "preprocessing");
  }

  writerLockPath(): string { return join(this.root, "writer.lock"); }
  runtimeConfigDirectory(): string { return join(this.root, "runtime-config"); }
  runtimeConfigManifestDirectory(): string { return join(this.root, "runtime-config-manifests"); }
  jobsDirectory(): string { return join(this.root, "jobs"); }
  fkCandidatesDirectory(): string { return join(this.root, "fk-candidates"); }
  fkReviewsDirectory(): string { return join(this.root, "fk-reviews"); }
  jobPath(runId: string): string { return join(this.jobsDirectory(), `${validateRunId(runId)}.json`); }
  fkCandidatesPath(runId: string): string { return join(this.fkCandidatesDirectory(), `${validateRunId(runId)}.yaml`); }
  fkReviewPath(runId: string): string { return join(this.fkReviewsDirectory(), `${validateRunId(runId)}.json`); }

  private ensureLayout(): void {
    ensureDirectory(this.root);
    for (const directory of [
      this.runtimeConfigDirectory(),
      this.runtimeConfigManifestDirectory(),
      this.jobsDirectory(),
      this.fkCandidatesDirectory(),
      this.fkReviewsDirectory(),
    ]) ensureDirectory(directory);
  }

  async acquireWriterLock(): Promise<WriterLockLease> {
    this.ensureLayout();
    const lockPath = this.writerLockPath();
    try {
      const entry = lstatSync(lockPath);
      if (!entry.isFile() || entry.isSymbolicLink()) throw new Error("invalid writer lock path");
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
        throw new PreprocessingStateError("preprocessing_conflict", "Workspace preprocessing lock is unavailable");
      }
    }
    const holder = spawn("python3", ["-c", PreprocessingStateStore.HOLDER_PROGRAM, lockPath], {
      stdio: ["pipe", "pipe", "pipe"],
    });
    await new Promise<void>((resolve, reject) => {
      let output = "";
      const fail = (error: Error) => {
        holder.stdout.removeAllListeners("data");
        reject(error);
      };
      holder.once("error", () => fail(new PreprocessingStateError(
        "preprocessing_conflict",
        "Workspace preprocessing lock is unavailable",
      )));
      holder.once("exit", (code) => {
        fail(new PreprocessingStateError(
          "preprocessing_conflict",
          code === 73 ? "Workspace preprocessing is busy" : "Workspace preprocessing lock is unavailable",
        ));
      });
      holder.stdout.on("data", (chunk: Buffer) => {
        output += chunk.toString("utf8");
        if (output === "locked\n") {
          holder.stdout.removeAllListeners("data");
          resolve();
        }
      });
    });
    let released = false;
    return {
      holderPid: holder.pid ?? 0,
      release: async () => {
        if (released) return;
        released = true;
        if (!holder.stdin.destroyed) holder.stdin.end();
        await new Promise<void>((resolve) => holder.once("exit", () => resolve()));
      },
    };
  }

  async beginJob(options: BeginPreprocessingJobOptions): Promise<PreprocessingJobState> {
    this.ensureLayout();
    if (!/^[0-9a-f]{40}$/.test(options.workspaceRevision)) {
      throw new Error("workspace revision is invalid");
    }
    const runId = options.runId ?? randomBytes(16).toString("hex");
    const path = this.jobPath(runId);
    try {
      const existing = this.readJob(runId);
      if (
        existing.operation !== options.operation
        || existing.workspaceRevision !== options.workspaceRevision
        || existing.descriptorBlob !== options.descriptorBlob
        || existing.catalogBlob !== options.catalogBlob
        || existing.configDigest !== options.configDigest
        || existing.bindingDigest !== options.bindingDigest
        || existing.embeddingId !== options.embeddingId
        || existing.embeddingDimensions !== options.embeddingDimensions
      ) {
        throw new PreprocessingStateError(
          "preprocessing_resume_mismatch",
          "Workspace preprocessing resume no longer matches the pinned revision",
        );
      }
      return existing;
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
        if (error instanceof PreprocessingStateError) throw error;
        throw error;
      }
      if (options.runId) {
        throw new PreprocessingStateError(
          "preprocessing_resume_mismatch",
          "Workspace preprocessing run is unavailable",
        );
      }
    }
    const job: PreprocessingJobState = {
      schemaVersion: 2,
      runId,
      operation: options.operation,
      workspaceId: this.options.workspaceId,
      workspaceRevision: options.workspaceRevision,
      descriptorBlob: options.descriptorBlob,
      catalogBlob: options.catalogBlob,
      configDigest: options.configDigest,
      bindingDigest: options.bindingDigest,
      embeddingId: options.embeddingId,
      embeddingDimensions: options.embeddingDimensions,
      completedStages: [],
      childRuns: {},
      status: "active",
    };
    writeAtomicFile(path, `${JSON.stringify(job)}
`, 0o600);
    return job;
  }

  readJob(runId: string): PreprocessingJobState {
    return decodeJob(JSON.parse(readTrustedFile(this.jobPath(runId))));
  }

  writeJob(job: PreprocessingJobState): PreprocessingJobState {
    this.ensureLayout();
    writeAtomicFile(this.jobPath(job.runId), `${JSON.stringify(job)}
`, 0o600);
    return job;
  }

  writeFkCandidates(runId: string, yaml: string): { path: string; digest: string } {
    this.ensureLayout();
    const path = this.fkCandidatesPath(runId);
    writeAtomicFile(path, yaml, 0o600);
    return { path, digest: sha256(yaml) };
  }

  readFkCandidates(runId: string): { path: string; yaml: string; digest: string } | undefined {
    const path = this.fkCandidatesPath(runId);
    try {
      const yaml = readTrustedFile(path);
      return { path, yaml, digest: sha256(yaml) };
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code === "ENOENT") return undefined;
      throw error;
    }
  }

  writeFkReview(runId: string, review: FkReviewRecord): { path: string; digest: string } {
    this.ensureLayout();
    const path = this.fkReviewPath(runId);
    const json = `${JSON.stringify(review)}
`;
    writeAtomicFile(path, json, 0o600);
    return { path, digest: sha256(json) };
  }

  readFkReview(runId: string): FkReviewRecord | undefined {
    try {
      return decodeReview(JSON.parse(readTrustedFile(this.fkReviewPath(runId))));
    } catch (error) {
      if ((error as NodeJS.ErrnoException).code === "ENOENT") return undefined;
      throw error;
    }
  }

  async assertSessionInventoryCompatible(
    workspaceRevision: string,
    sessions: readonly SessionInventoryRow[],
  ): Promise<void> {
    const conflicting = sessions.find((session) => (
      session.workspaceRevision
      && session.workspaceRevision !== workspaceRevision
      && session.status !== "finalized"
      && !session.archived
    ));
    if (conflicting) {
      throw new PreprocessingStateError(
        "preprocessing_conflict",
        "A resumable session is pinned to a different workspace revision",
      );
    }
  }

  private static readonly HOLDER_PROGRAM = [
    "import fcntl, os, sys",
    "fd = os.open(sys.argv[1], os.O_RDWR | os.O_CREAT | getattr(os, 'O_NOFOLLOW', 0), 0o600)",
    "try:",
    "    fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)",
    "except BlockingIOError:",
    "    sys.exit(73)",
    "sys.stdout.write('locked\\n')",
    "sys.stdout.flush()",
    "sys.stdin.buffer.read()",
  ].join("\n");
}