react-date-picker/src/DateFormatInput/parseFormat.js

A carefully crafted date picker for React

import assign from 'object-assign'
import FORMATS from './formats'

const SUGGESTIONS = {
  Y: ['YYYY', 'YY'],
  M: ['MM'],
  D: ['DD'],
  H: ['HH'],
  h: ['hh'],
  m: ['mm'],
  s: ['ss']
}

export default (format) => {
  let index = 0
  let positionIndex = 0

  let suggestions
  let suggestionMatch

  const positions = []
  const matches = []

  while (index < format.length) {
    const char = format[index]
    const match = FORMATS[char]
    let matchObject

    suggestionMatch = null
    suggestions = SUGGESTIONS[char]

    if (!match && !suggestions) {
      positions[positionIndex] = char
      matches.push(char)
    } else {
      if (suggestions && suggestions.length) {
        // it might be a longer match
        suggestionMatch = suggestions.filter(s => format.substr(index, s.length) == s)[0]
      }

      if (!suggestionMatch) {
        if (!FORMATS[char]) {
          console.warn(`Format ${char} is not supported yet!`)
          if (suggestions) {
            console.warn(`Use one of ["${suggestions.join(',')}"]`)
          }
          positions[positionIndex] = char
          matches.push(char)
        } else {
          // we found a match, with no other suggestion

          const currentFormat = FORMATS[char]
          let start = positionIndex
          const end = positionIndex + (currentFormat.length || 1) - 1

          matchObject = assign({}, currentFormat, { format: char, start, end })

          for (; start <= end; start++) {
            positions[positionIndex] = matchObject
            positionIndex++
          }
          index++
          matches.push(matchObject)
          continue; // to skip incrementing twice
        }
      } else {
        matchObject = assign({}, FORMATS[suggestionMatch], {
          format: suggestionMatch, start: positionIndex
        })
        matches.push(matchObject)

        const endIndex = positionIndex + suggestionMatch.length

        matchObject.end = endIndex - 1
        while (positionIndex < endIndex) {
          positions[positionIndex] = matchObject
          positionIndex++
          index++
        }
        continue; // to skip incrementing index once more
      }
    }

    positionIndex++
    index++
  }

  return { positions, matches }
}