import invariant from 'invariant'

function escapeRegExp(string) {
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')
}

function _compilePattern(pattern) {
  let regexpSource = ''
  const paramNames = []
  const tokens = []

  let match, lastIndex = 0, matcher = /:([a-zA-Z_$][a-zA-Z0-9_$]*)|\*\*|\*|\(|\)/g
  while ((match = matcher.exec(pattern))) {
    if (match.index !== lastIndex) {
      tokens.push(pattern.slice(lastIndex, match.index))
      regexpSource += escapeRegExp(pattern.slice(lastIndex, match.index))
    }

    if (match[1]) {
      regexpSource += '([^/]+)'
      paramNames.push(match[1])
    } else if (match[0] === '**') {
      regexpSource += '(.*)'
      paramNames.push('splat')
    } else if (match[0] === '*') {
      regexpSource += '(.*?)'
      paramNames.push('splat')
    } else if (match[0] === '(') {
      regexpSource += '(?:'
    } else if (match[0] === ')') {
      regexpSource += ')?'
    }

    tokens.push(match[0])

    lastIndex = matcher.lastIndex
  }

  if (lastIndex !== pattern.length) {
    tokens.push(pattern.slice(lastIndex, pattern.length))
    regexpSource += escapeRegExp(pattern.slice(lastIndex, pattern.length))
  }

  return {
    pattern,
    regexpSource,
    paramNames,
    tokens
  }
}

const CompiledPatternsCache = {}

export function compilePattern(pattern) {
  if (!(pattern in CompiledPatternsCache))
    CompiledPatternsCache[pattern] = _compilePattern(pattern)

  return CompiledPatternsCache[pattern]
}

/**
 * Attempts to match a pattern on the given pathname. Patterns may use
 * the following special characters:
 *
 * - :paramName     Matches a URL segment up to the next /, ?, or #. The
 *                  captured string is considered a "param"
 * - ()             Wraps a segment of the URL that is optional
 * - *              Consumes (non-greedy) all characters up to the next
 *                  character in the pattern, or to the end of the URL if
 *                  there is none
 * - **             Consumes (greedy) all characters up to the next character
 *                  in the pattern, or to the end of the URL if there is none
 *
 * The return value is an object with the following properties:
 *
 * - remainingPathname
 * - paramNames
 * - paramValues
 */
export function matchPattern(pattern, pathname) {
  // Ensure pattern starts with leading slash for consistency with pathname.
  if (pattern.charAt(0) !== '/') {
    pattern = `/${pattern}`
  }
  let { regexpSource, paramNames, tokens } = compilePattern(pattern)

  if (pattern.charAt(pattern.length - 1) !== '/') {
    regexpSource += '/?' // Allow optional path separator at end.
  }

  // Special-case patterns like '*' for catch-all routes.
  if (tokens[tokens.length - 1] === '*') {
    regexpSource += '$'
  }

  const match = pathname.match(new RegExp(`^${regexpSource}`, 'i'))

  let remainingPathname, paramValues
  if (match != null) {
    const matchedPath = match[0]
    remainingPathname = pathname.substr(matchedPath.length)

    if (remainingPathname) {
      // Require that the match ends at a path separator, if we didn't match
      // the full path, so any remaining pathname is a new path segment.
      if (matchedPath.charAt(matchedPath.length - 1) !== '/') {
        return {
          remainingPathname: null,
          paramNames,
          paramValues: null
        }
      }

      // If there is a remaining pathname, treat the path separator as part of
      // the remaining pathname for properly continuing the match.
      remainingPathname = `/${remainingPathname}`
    }

    paramValues = match.slice(1).map(v => v && decodeURIComponent(v))
  } else {
    remainingPathname = paramValues = null
  }

  return {
    remainingPathname,
    paramNames,
    paramValues
  }
}

export function getParamNames(pattern) {
  return compilePattern(pattern).paramNames
}

export function getParams(pattern, pathname) {
  const { paramNames, paramValues } = matchPattern(pattern, pathname)

  if (paramValues != null) {
    return paramNames.reduce(function (memo, paramName, index) {
      memo[paramName] = paramValues[index]
      return memo
    }, {})
  }

  return null
}

/**
 * Returns a version of the given pattern with params interpolated. Throws
 * if there is a dynamic segment of the pattern for which there is no param.
 */
export function formatPattern(pattern, params) {
  params = params || {}

  const { tokens } = compilePattern(pattern)
  let parenCount = 0, pathname = '', splatIndex = 0

  let token, paramName, paramValue
  for (let i = 0, len = tokens.length; i < len; ++i) {
    token = tokens[i]

    if (token === '*' || token === '**') {
      paramValue = Array.isArray(params.splat) ? params.splat[splatIndex++] : params.splat

      invariant(
        paramValue != null || parenCount > 0,
        'Missing splat #%s for path "%s"',
        splatIndex, pattern
      )

      if (paramValue != null)
        pathname += encodeURI(paramValue)
    } else if (token === '(') {
      parenCount += 1
    } else if (token === ')') {
      parenCount -= 1
    } else if (token.charAt(0) === ':') {
      paramName = token.substring(1)
      paramValue = params[paramName]

      invariant(
        paramValue != null || parenCount > 0,
        'Missing "%s" parameter for path "%s"',
        paramName, pattern
      )

      if (paramValue != null)
        pathname += encodeURIComponent(paramValue)
    } else {
      pathname += token
    }
  }

  return pathname.replace(/\/+/g, '/')
}