index.js

const exec = require("child_process").exec
const log = console.debug

function recognize(filename, config = {}) {
  const options = getOptions(config)
  const binary = config.binary || "tesseract"

  const command = [binary, filename, "stdout", ...options].join(" ")
  if (config.debug) log("command", command)

  return new Promise((resolve, reject) => {
    exec(command, {encoding: 'buffer', maxBuffer: 134217728}, (error, stdout, stderr) => {
      if (config.debug) log(stderr)
      if (error) reject(error)
      resolve(stdout)
    })
  })
}

function getOptions(config) {
  const ocrOptions = ["tessdata-dir", "user-words", "user-patterns", "psm", "oem", "dpi"]

  return Object.entries(config)
    .map(([key, value]) => {
      if (["debug", "presets", "binary"].includes(key)) return
      if (key === "lang") return `-l ${value}`
      if (ocrOptions.includes(key)) return `--${key} ${value}`

      return `-c ${key}=${value}`
    })
    .concat(config.presets)
    .filter(Boolean)
}

module.exports = {
  recognize,
}