const parser = require('postcss-selector-parser')
const parseSelector = parser()

function isObject(value) {
  return typeof value === 'object' && value !== null
}

function isPlainObject(value) {
  if (typeof value !== 'object' || value === null) {
    return false
  }

  if (Object.prototype.toString.call(value) !== '[object Object]') {
    return false
  }

  if (Object.getPrototypeOf(value) === null) {
    return true
  }

  let proto = value
  while (Object.getPrototypeOf(proto) !== null) {
    proto = Object.getPrototypeOf(proto)
  }

  return Object.getPrototypeOf(value) === proto
}

function merge(target, ...sources) {
  if (!sources.length) return target
  const source = sources.shift()

  if (isObject(target) && isObject(source)) {
    for (const key in source) {
      if (Array.isArray(source[key])) {
        if (!target[key]) target[key] = []
        source[key].forEach((item, index) => {
          if (isPlainObject(item) && isPlainObject(target[key][index])) {
            target[key][index] = merge(target[key][index], item)
          } else {
            target[key][index] = item
          }
        })
      } else if (isPlainObject(source[key])) {
        if (!target[key]) target[key] = {}
        merge(target[key], source[key])
      } else {
        target[key] = source[key]
      }
    }
  }

  return merge(target, ...sources)
}

function castArray(value) {
  return Array.isArray(value) ? value : [value]
}

module.exports = {
  isObject,
  isPlainObject,
  merge,
  castArray,
  isUsableColor(color, values) {
    return isPlainObject(values) && color !== 'gray' && values[600]
  },

  /**
   * @param {string} selector
   */
  commonTrailingPseudos(selector) {
    let ast = parseSelector.astSync(selector)

    /** @type {import('postcss-selector-parser').Pseudo[][]} */
    let matrix = []

    // Put the pseudo elements in reverse order in a sparse, column-major 2D array
    for (let [i, sel] of ast.nodes.entries()) {
      for (const [j, child] of [...sel.nodes].reverse().entries()) {
        // We only care about pseudo elements
        if (child.type !== 'pseudo' || !child.value.startsWith('::')) {
          break
        }

        matrix[j] = matrix[j] || []
        matrix[j][i] = child
      }
    }

    let trailingPseudos = parser.selector()

    // At this point the pseudo elements are in a column-major 2D array
    // This means each row contains one "column" of pseudo elements from each selector
    // We can compare all the pseudo elements in a row to see if they are the same
    for (const pseudos of matrix) {
      // It's a sparse 2D array so there are going to be holes in the rows
      // We skip those
      if (!pseudos) {
        continue
      }

      let values = new Set(pseudos.map((p) => p.value))

      // The pseudo elements are not the same
      if (values.size > 1) {
        break
      }

      pseudos.forEach((pseudo) => pseudo.remove())
      trailingPseudos.prepend(pseudos[0])
    }

    if (trailingPseudos.nodes.length) {
      return [trailingPseudos.toString(), ast.toString()]
    }

    return [null, selector]
  },
}