var hasExcape = /~/
var escapeMatcher = /~[01]/g
function escapeReplacer (m) {
 switch (m) {
 case '~1': return '/'
 case '~0': return '~'
 }
 throw new Error('Invalid tilde escape: ' + m)
}

function untilde (str) {
 if (!hasExcape.test(str)) return str
 return str.replace(escapeMatcher, escapeReplacer)
}

function setter (obj, pointer, value) {
 var part
 var hasNextPart

 for (var p = 1, len = pointer.length; p < len;) {
 part = untilde(pointer[p++])
 hasNextPart = len > p

 if (typeof obj[part] === 'undefined') {
 // support setting of /-
 if (Array.isArray(obj) && part === '-') {
 part = obj.length
 }

 // support nested objects/array when setting values
 if (hasNextPart) {
 if ((pointer[p] !== '' && pointer[p] < Infinity) || pointer[p] === '-') obj[part] = []
 else obj[part] = {}
 }
 }

 if (!hasNextPart) break
 obj = obj[part]
 }

 var oldValue = obj[part]
 if (value === undefined) delete obj[part]
 else obj[part] = value
 return oldValue
}

function compilePointer (pointer) {
 if (typeof pointer === 'string') {
 pointer = pointer.split('/')
 if (pointer[0] === '') return pointer
 throw new Error('Invalid JSON pointer.')
 } else if (Array.isArray(pointer)) {
 return pointer
 }

 throw new Error('Invalid JSON pointer.')
}

function get (obj, pointer) {
 if (typeof obj !== 'object') throw new Error('Invalid input object.')
 pointer = compilePointer(pointer)
 var len = pointer.length
 if (len === 1) return obj

 for (var p = 1; p < len;) {
 obj = obj[untilde(pointer[p++])]
 if (len === p) return obj
 if (typeof obj !== 'object') return undefined
 }
}

function set (obj, pointer, value) {
 if (typeof obj !== 'object') throw new Error('Invalid input object.')
 pointer = compilePointer(pointer)
 if (pointer.length === 0) throw new Error('Invalid JSON pointer for set.')
 return setter(obj, pointer, value)
}

function compile (pointer) {
 var compiled = compilePointer(pointer)
 return {
 get: function (object) {
 return get(object, compiled)
 },
 set: function (object, value) {
 return set(object, compiled, value)
 }
 }
}

exports.get = get
exports.set = set
exports.compile = compile