/**
 * Fast-upload interceptor for the chunked-shell file transfer protocol used by
 * `@paperclipai/adapter-utils`'s `command-managed-runtime.writeFile()`.
 *
 * The default protocol uploads a binary file by:
 *   1. INIT:     mkdir -p '<DIR>' && rm -f '<B64>' && : > '<B64>'
 *   2. CHUNKS:   printf '%s' '<base64-chunk>' >> '<B64>'   (repeated N times)
 *   3. FINALIZE: base64 -d < '<B64>' > '<TARGET>' && rm -f '<B64>'
 *
 * Where `<B64>` is `<TARGET>.paperclip-upload.b64`. Over k8s exec each call costs
 * ~50-100ms (new WebSocket + container exec), so N chunks = N round trips. For
 * a 1MB payload split into 64KB base64 chunks that's ~250 round trips.
 *
 * This interceptor short-circuits the protocol entirely:
 *   - INIT: capture `<B64>`, start a buffer, RESPOND success without exec.
 *   - CHUNK: append the literal base64 chunk to the buffer, RESPOND success.
 *   - FINALIZE: decode the buffered base64 → bytes → one exec `cat > '<TARGET>'`
 *               with stdin = bytes. Drop intermediate `.b64` entirely.
 *
 * If any step doesn't match the protocol exactly, we abandon the buffer and let
 * the caller go through the slow path (passthrough). This keeps the optimization
 * **transparent and safe**: pattern drift → graceful fallback.
 *
 * Reference: see packages/adapter-utils/src/command-managed-runtime.ts.
 */
import { posix as pathPosix } from "node:path";

const INIT_RE =
  /^mkdir -p '([^']+)' && rm -f '([^']+)\.paperclip-upload\.b64' && : > '\2\.paperclip-upload\.b64'$/;
const CHUNK_RE =
  /^printf '%s' '([A-Za-z0-9+/=]+)' >> '([^']+)\.paperclip-upload\.b64'$/;
const FINALIZE_RE =
  /^base64 -d < '([^']+)\.paperclip-upload\.b64' > '\1' && rm -f '\1\.paperclip-upload\.b64'$/;

const MAX_BUFFER_BYTES = 100 * 1024 * 1024; // 100MB safety cap

export interface InterceptStateFlush {
  /** Final target path on the remote (decoded payload goes here). */
  targetPath: string;
  /** Decoded payload bytes. */
  payload: Buffer;
}

export type InterceptDecision =
  /** Pattern recognized; respond with success without running the command. */
  | { action: "ack"; reason: string }
  /** Pattern recognized; flush via single exec. Caller does the exec. */
  | { action: "flush"; flush: InterceptStateFlush }
  /** Pattern not recognized; pass through to the normal exec path. */
  | { action: "passthrough"; reason: string };

interface BufferState {
  targetPath: string;
  chunks: string[];
  totalChars: number;
}

/**
 * Stateful interceptor. Keyed by the base64 temp path (`<TARGET>.paperclip-upload.b64`).
 * One instance per plugin worker is fine — concurrent uploads to different paths
 * don't interfere.
 */
export class FastUploadInterceptor {
  private buffers = new Map<string, BufferState>();

  /**
   * Inspect a single shell command (the literal argument to `sh -c <cmd>`).
   * Returns the action the plugin should take.
   */
  decide(command: string): InterceptDecision {
    // 1. INIT
    const initMatch = INIT_RE.exec(command);
    if (initMatch) {
      const dir = initMatch[1];
      const targetPath = initMatch[2];
      const b64Path = `${targetPath}.paperclip-upload.b64`;
      // Sanity: dir should be the parent of target. If not, fall through.
      if (pathPosix.dirname(targetPath) !== dir) {
        return { action: "passthrough", reason: "init dir/target mismatch" };
      }
      this.buffers.set(b64Path, { targetPath, chunks: [], totalChars: 0 });
      return { action: "ack", reason: `init upload to ${targetPath}` };
    }

    // 2. CHUNK
    const chunkMatch = CHUNK_RE.exec(command);
    if (chunkMatch) {
      const base64 = chunkMatch[1];
      const targetPath = chunkMatch[2];
      const b64Path = `${targetPath}.paperclip-upload.b64`;
      const state = this.buffers.get(b64Path);
      if (!state) {
        // Chunk arrived without init — must passthrough (the upload was started
        // some other way, perhaps before we started tracking).
        return { action: "passthrough", reason: "chunk without prior init" };
      }
      if (state.totalChars + base64.length > MAX_BUFFER_BYTES * 4 / 3) {
        // base64 is ~4/3 of binary size; cap memory.
        this.buffers.delete(b64Path);
        return { action: "passthrough", reason: "buffer cap exceeded" };
      }
      state.chunks.push(base64);
      state.totalChars += base64.length;
      return { action: "ack", reason: `buffered ${base64.length} b64 chars` };
    }

    // 3. FINALIZE
    const finalizeMatch = FINALIZE_RE.exec(command);
    if (finalizeMatch) {
      const targetPath = finalizeMatch[1];
      const b64Path = `${targetPath}.paperclip-upload.b64`;
      const state = this.buffers.get(b64Path);
      if (!state) {
        return { action: "passthrough", reason: "finalize without buffered state" };
      }
      this.buffers.delete(b64Path);
      // Decode in one go. base64.decode handles concatenated base64 strings
      // because each chunk was emitted from the encoder in fixed-size pieces.
      const joined = state.chunks.join("");
      const payload = Buffer.from(joined, "base64");
      return {
        action: "flush",
        flush: {
          targetPath: state.targetPath,
          payload,
        },
      };
    }

    return { action: "passthrough", reason: "no upload pattern" };
  }

  /**
   * Drop all buffered state. Called on releaseLease so a new lease doesn't
   * inherit stale buffers (lease IDs are unique so target paths shouldn't
   * collide, but cleanup is hygiene).
   */
  reset(): void {
    this.buffers.clear();
  }

  /** Number of in-flight uploads being tracked. Mostly for tests / diagnostics. */
  get pendingCount(): number {
    return this.buffers.size;
  }
}