// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

import {readFile} from 'fs';
import {Backend, env, InferenceSession, SessionHandler} from 'onnxruntime-common';
import {cpus} from 'os';
import {promisify} from 'util';

import {OnnxruntimeWebAssemblySessionHandler} from './wasm/session-handler';
import {initializeWebAssembly} from './wasm/wasm-factory';

/**
 * This function initializes all flags for WebAssembly.
 *
 * Those flags are accessible from `ort.env.wasm`. Users are allow to set those flags before the first inference session
 * being created, to override default value.
 */
export const initializeFlags = (): void => {
  if (typeof env.wasm.initTimeout !== 'number' || env.wasm.initTimeout < 0) {
    env.wasm.initTimeout = 0;
  }

  if (typeof env.wasm.numThreads !== 'number' || !Number.isInteger(env.wasm.numThreads) || env.wasm.numThreads < 0) {
    const numCpuLogicalCores = typeof navigator === 'undefined' ? cpus().length : navigator.hardwareConcurrency;
    env.wasm.numThreads = Math.ceil((numCpuLogicalCores || 1) / 2);
  }
  env.wasm.numThreads = Math.min(4, env.wasm.numThreads);

  if (typeof env.wasm.loggingLevel !== 'string' ||
      ['verbose', 'info', 'warning', 'error', 'fatal'].indexOf(env.wasm.loggingLevel) === -1) {
    env.wasm.loggingLevel = 'warning';
  }
};

class OnnxruntimeWebAssemblyBackend implements Backend {
  async init(): Promise<void> {
    // populate wasm flags
    initializeFlags();

    // init wasm
    await initializeWebAssembly();
  }
  createSessionHandler(path: string, options?: InferenceSession.SessionOptions): Promise<SessionHandler>;
  createSessionHandler(buffer: Uint8Array, options?: InferenceSession.SessionOptions): Promise<SessionHandler>;
  async createSessionHandler(pathOrBuffer: string|Uint8Array, options?: InferenceSession.SessionOptions):
      Promise<SessionHandler> {
    let buffer: Uint8Array;
    if (typeof pathOrBuffer === 'string') {
      if (typeof fetch === 'undefined') {
        // node
        buffer = await promisify(readFile)(pathOrBuffer);
      } else {
        // browser
        const response = await fetch(pathOrBuffer);
        const arrayBuffer = await response.arrayBuffer();
        buffer = new Uint8Array(arrayBuffer);
      }
    } else {
      buffer = pathOrBuffer;
    }

    const handler = new OnnxruntimeWebAssemblySessionHandler();
    handler.loadModel(buffer, options);
    return Promise.resolve(handler);
  }
}

export const wasmBackend = new OnnxruntimeWebAssemblyBackend();