'use strict'

const common = require('./common')
const YAMLException = require('./exception')
const DEFAULT_SCHEMA = require('./schema/default')

const _toString = Object.prototype.toString
const _hasOwnProperty = Object.prototype.hasOwnProperty

const CHAR_BOM = 0xFEFF
const CHAR_TAB = 0x09 /* Tab */
const CHAR_LINE_FEED = 0x0A /* LF */
const CHAR_CARRIAGE_RETURN = 0x0D /* CR */
const CHAR_SPACE = 0x20 /* Space */
const CHAR_EXCLAMATION = 0x21 /* ! */
const CHAR_DOUBLE_QUOTE = 0x22 /* " */
const CHAR_SHARP = 0x23 /* # */
const CHAR_PERCENT = 0x25 /* % */
const CHAR_AMPERSAND = 0x26 /* & */
const CHAR_SINGLE_QUOTE = 0x27 /* ' */
const CHAR_ASTERISK = 0x2A /* * */
const CHAR_COMMA = 0x2C /* , */
const CHAR_MINUS = 0x2D /* - */
const CHAR_COLON = 0x3A /* : */
const CHAR_EQUALS = 0x3D /* = */
const CHAR_GREATER_THAN = 0x3E /* > */
const CHAR_QUESTION = 0x3F /* ? */
const CHAR_COMMERCIAL_AT = 0x40 /* @ */
const CHAR_LEFT_SQUARE_BRACKET = 0x5B /* [ */
const CHAR_RIGHT_SQUARE_BRACKET = 0x5D /* ] */
const CHAR_GRAVE_ACCENT = 0x60 /* ` */
const CHAR_LEFT_CURLY_BRACKET = 0x7B /* { */
const CHAR_VERTICAL_LINE = 0x7C /* | */
const CHAR_RIGHT_CURLY_BRACKET = 0x7D /* } */

const ESCAPE_SEQUENCES = {}

ESCAPE_SEQUENCES[0x00] = '\\0'
ESCAPE_SEQUENCES[0x07] = '\\a'
ESCAPE_SEQUENCES[0x08] = '\\b'
ESCAPE_SEQUENCES[0x09] = '\\t'
ESCAPE_SEQUENCES[0x0A] = '\\n'
ESCAPE_SEQUENCES[0x0B] = '\\v'
ESCAPE_SEQUENCES[0x0C] = '\\f'
ESCAPE_SEQUENCES[0x0D] = '\\r'
ESCAPE_SEQUENCES[0x1B] = '\\e'
ESCAPE_SEQUENCES[0x22] = '\\"'
ESCAPE_SEQUENCES[0x5C] = '\\\\'
ESCAPE_SEQUENCES[0x85] = '\\N'
ESCAPE_SEQUENCES[0xA0] = '\\_'
ESCAPE_SEQUENCES[0x2028] = '\\L'
ESCAPE_SEQUENCES[0x2029] = '\\P'

const DEPRECATED_BOOLEANS_SYNTAX = [
  'y', 'Y', 'yes', 'Yes', 'YES', 'on', 'On', 'ON',
  'n', 'N', 'no', 'No', 'NO', 'off', 'Off', 'OFF'
]

const DEPRECATED_BASE60_SYNTAX = /^[-+]?[0-9_]+(?::[0-9_]+)+(?:\.[0-9_]*)?$/

function compileStyleMap (schema, map) {
  if (map === null) return {}

  const result = {}
  const keys = Object.keys(map)

  for (let index = 0, length = keys.length; index < length; index += 1) {
    let tag = keys[index]
    let style = String(map[tag])

    if (tag.slice(0, 2) === '!!') {
      tag = 'tag:yaml.org,2002:' + tag.slice(2)
    }
    const type = schema.compiledTypeMap['fallback'][tag]

    if (type && _hasOwnProperty.call(type.styleAliases, style)) {
      style = type.styleAliases[style]
    }

    result[tag] = style
  }

  return result
}

function encodeHex (character) {
  let handle
  let length

  const string = character.toString(16).toUpperCase()

  if (character <= 0xFF) {
    handle = 'x'
    length = 2
  } else if (character <= 0xFFFF) {
    handle = 'u'
    length = 4
  } else if (character <= 0xFFFFFFFF) {
    handle = 'U'
    length = 8
  } else {
    throw new YAMLException('code point within a string may not be greater than 0xFFFFFFFF')
  }

  return '\\' + handle + common.repeat('0', length - string.length) + string
}

const QUOTING_TYPE_SINGLE = 1
const QUOTING_TYPE_DOUBLE = 2

function State (options) {
  this.schema = options['schema'] || DEFAULT_SCHEMA
  this.indent = Math.max(1, (options['indent'] || 2))
  this.noArrayIndent = options['noArrayIndent'] || false
  this.skipInvalid = options['skipInvalid'] || false
  this.flowLevel = (common.isNothing(options['flowLevel']) ? -1 : options['flowLevel'])
  this.styleMap = compileStyleMap(this.schema, options['styles'] || null)
  this.sortKeys = options['sortKeys'] || false
  this.lineWidth = options['lineWidth'] || 80
  this.noRefs = options['noRefs'] || false
  this.noCompatMode = options['noCompatMode'] || false
  this.condenseFlow = options['condenseFlow'] || false
  this.quotingType = options['quotingType'] === '"' ? QUOTING_TYPE_DOUBLE : QUOTING_TYPE_SINGLE
  this.forceQuotes = options['forceQuotes'] || false
  this.replacer = typeof options['replacer'] === 'function' ? options['replacer'] : null

  this.implicitTypes = this.schema.compiledImplicit
  this.explicitTypes = this.schema.compiledExplicit

  this.tag = null
  this.result = ''

  this.duplicates = []
  this.usedDuplicates = null
}

// Indents every line in a string. Empty lines (\n only) are not indented.
function indentString (string, spaces) {
  const ind = common.repeat(' ', spaces)
  let position = 0
  let result = ''
  const length = string.length

  while (position < length) {
    let line
    const next = string.indexOf('\n', position)
    if (next === -1) {
      line = string.slice(position)
      position = length
    } else {
      line = string.slice(position, next + 1)
      position = next + 1
    }

    if (line.length && line !== '\n') result += ind

    result += line
  }

  return result
}

function generateNextLine (state, level) {
  return '\n' + common.repeat(' ', state.indent * level)
}

function testImplicitResolving (state, str) {
  for (let index = 0, length = state.implicitTypes.length; index < length; index += 1) {
    const type = state.implicitTypes[index]

    if (type.resolve(str)) {
      return true
    }
  }

  return false
}

// [33] s-white ::= s-space | s-tab
function isWhitespace (c) {
  return c === CHAR_SPACE || c === CHAR_TAB
}

// Returns true if the character can be printed without escaping.
// From YAML 1.2: "any allowed characters known to be non-printable
// should also be escaped. [However,] This isn’t mandatory"
// Derived from nb-char - \t - #x85 - #xA0 - #x2028 - #x2029.
function isPrintable (c) {
  return (c >= 0x00020 && c <= 0x00007E) ||
    ((c >= 0x000A1 && c <= 0x00D7FF) && c !== 0x2028 && c !== 0x2029) ||
    ((c >= 0x0E000 && c <= 0x00FFFD) && c !== CHAR_BOM) ||
    (c >= 0x10000 && c <= 0x10FFFF)
}

// [34] ns-char ::= nb-char - s-white
// [27] nb-char ::= c-printable - b-char - c-byte-order-mark
// [26] b-char  ::= b-line-feed | b-carriage-return
// Including s-white (for some reason, examples doesn't match specs in this aspect)
// ns-char ::= c-printable - b-line-feed - b-carriage-return - c-byte-order-mark
function isNsCharOrWhitespace (c) {
  return isPrintable(c) &&
    c !== CHAR_BOM &&
    // - b-char
    c !== CHAR_CARRIAGE_RETURN &&
    c !== CHAR_LINE_FEED
}

// [127]  ns-plain-safe(c) ::= c = flow-out  ⇒ ns-plain-safe-out
//                             c = flow-in   ⇒ ns-plain-safe-in
//                             c = block-key ⇒ ns-plain-safe-out
//                             c = flow-key  ⇒ ns-plain-safe-in
// [128] ns-plain-safe-out ::= ns-char
// [129]  ns-plain-safe-in ::= ns-char - c-flow-indicator
// [130]  ns-plain-char(c) ::=  ( ns-plain-safe(c) - “:” - “#” )
//                            | ( /* An ns-char preceding */ “#” )
//                            | ( “:” /* Followed by an ns-plain-safe(c) */ )
function isPlainSafe (c, prev, inblock) {
  const cIsNsCharOrWhitespace = isNsCharOrWhitespace(c)
  const cIsNsChar = cIsNsCharOrWhitespace && !isWhitespace(c)
  return (
    (
      // ns-plain-safe
      inblock // c = flow-in
        ? cIsNsCharOrWhitespace
        : cIsNsCharOrWhitespace &&
          // - c-flow-indicator
          c !== CHAR_COMMA &&
          c !== CHAR_LEFT_SQUARE_BRACKET &&
          c !== CHAR_RIGHT_SQUARE_BRACKET &&
          c !== CHAR_LEFT_CURLY_BRACKET &&
          c !== CHAR_RIGHT_CURLY_BRACKET
    ) &&
    // ns-plain-char
    c !== CHAR_SHARP && // false on '#'
    !(prev === CHAR_COLON && !cIsNsChar)
  ) || // false on ': '
  (isNsCharOrWhitespace(prev) && !isWhitespace(prev) && c === CHAR_SHARP) || // change to true on '[^ ]#'
  (prev === CHAR_COLON && cIsNsChar) // change to true on ':[^ ]'
}

// Simplified test for values allowed as the first character in plain style.
function isPlainSafeFirst (c) {
  // Uses a subset of ns-char - c-indicator
  // where ns-char = nb-char - s-white.
  // No support of ( ( “?” | “:” | “-” ) /* Followed by an ns-plain-safe(c)) */ ) part
  return isPrintable(c) &&
    c !== CHAR_BOM &&
    !isWhitespace(c) && // - s-white
    // - (c-indicator ::=
    // “-” | “?” | “:” | “,” | “[” | “]” | “{” | “}”
    c !== CHAR_MINUS &&
    c !== CHAR_QUESTION &&
    c !== CHAR_COLON &&
    c !== CHAR_COMMA &&
    c !== CHAR_LEFT_SQUARE_BRACKET &&
    c !== CHAR_RIGHT_SQUARE_BRACKET &&
    c !== CHAR_LEFT_CURLY_BRACKET &&
    c !== CHAR_RIGHT_CURLY_BRACKET &&
    // | “#” | “&” | “*” | “!” | “|” | “=” | “>” | “'” | “"”
    c !== CHAR_SHARP &&
    c !== CHAR_AMPERSAND &&
    c !== CHAR_ASTERISK &&
    c !== CHAR_EXCLAMATION &&
    c !== CHAR_VERTICAL_LINE &&
    c !== CHAR_EQUALS &&
    c !== CHAR_GREATER_THAN &&
    c !== CHAR_SINGLE_QUOTE &&
    c !== CHAR_DOUBLE_QUOTE &&
    // | “%” | “@” | “`”)
    c !== CHAR_PERCENT &&
    c !== CHAR_COMMERCIAL_AT &&
    c !== CHAR_GRAVE_ACCENT
}

// Simplified test for values allowed as the last character in plain style.
function isPlainSafeLast (c) {
  // just not whitespace or colon, it will be checked to be plain character later
  return !isWhitespace(c) && c !== CHAR_COLON
}

// Same as 'string'.codePointAt(pos), but works in older browsers.
function codePointAt (string, pos) {
  const first = string.charCodeAt(pos)
  let second

  if (first >= 0xD800 && first <= 0xDBFF && pos + 1 < string.length) {
    second = string.charCodeAt(pos + 1)
    if (second >= 0xDC00 && second <= 0xDFFF) {
      // https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
      return (first - 0xD800) * 0x400 + second - 0xDC00 + 0x10000
    }
  }
  return first
}

// Determines whether block indentation indicator is required.
function needIndentIndicator (string) {
  const leadingSpaceRe = /^\n* /
  return leadingSpaceRe.test(string)
}

const STYLE_PLAIN = 1
const STYLE_SINGLE = 2
const STYLE_LITERAL = 3
const STYLE_FOLDED = 4
const STYLE_DOUBLE = 5

// Determines which scalar styles are possible and returns the preferred style.
// lineWidth = -1 => no limit.
// Pre-conditions: str.length > 0.
// Post-conditions:
//    STYLE_PLAIN or STYLE_SINGLE => no \n are in the string.
//    STYLE_LITERAL => no lines are suitable for folding (or lineWidth is -1).
//    STYLE_FOLDED => a line > lineWidth and can be folded (and lineWidth != -1).
function chooseScalarStyle (string, singleLineOnly, indentPerLevel, lineWidth,
  testAmbiguousType, quotingType, forceQuotes, inblock) {
  let i
  let char = 0
  let prevChar = null
  let hasLineBreak = false
  let hasFoldableLine = false // only checked if shouldTrackWidth
  const shouldTrackWidth = lineWidth !== -1
  let previousLineBreak = -1 // count the first line correctly
  let plain = isPlainSafeFirst(codePointAt(string, 0)) &&
    isPlainSafeLast(codePointAt(string, string.length - 1))

  if (singleLineOnly || forceQuotes) {
    // Case: no block styles.
    // Check for disallowed characters to rule out plain and single.
    for (i = 0; i < string.length; char >= 0x10000 ? i += 2 : i++) {
      char = codePointAt(string, i)
      if (!isPrintable(char)) {
        return STYLE_DOUBLE
      }
      plain = plain && isPlainSafe(char, prevChar, inblock)
      prevChar = char
    }
  } else {
    // Case: block styles permitted.
    for (i = 0; i < string.length; char >= 0x10000 ? i += 2 : i++) {
      char = codePointAt(string, i)
      if (char === CHAR_LINE_FEED) {
        hasLineBreak = true
        // Check if any line can be folded.
        if (shouldTrackWidth) {
          hasFoldableLine = hasFoldableLine ||
            // Foldable line = too long, and not more-indented.
            (i - previousLineBreak - 1 > lineWidth &&
             string[previousLineBreak + 1] !== ' ')
          previousLineBreak = i
        }
      } else if (!isPrintable(char)) {
        return STYLE_DOUBLE
      }
      plain = plain && isPlainSafe(char, prevChar, inblock)
      prevChar = char
    }
    // in case the end is missing a \n
    hasFoldableLine = hasFoldableLine || (shouldTrackWidth &&
      (i - previousLineBreak - 1 > lineWidth &&
       string[previousLineBreak + 1] !== ' '))
  }
  // Although every style can represent \n without escaping, prefer block styles
  // for multiline, since they're more readable and they don't add empty lines.
  // Also prefer folding a super-long line.
  if (!hasLineBreak && !hasFoldableLine) {
    // Strings interpretable as another type have to be quoted;
    // e.g. the string 'true' vs. the boolean true.
    if (plain && !forceQuotes && !testAmbiguousType(string)) {
      return STYLE_PLAIN
    }
    return quotingType === QUOTING_TYPE_DOUBLE ? STYLE_DOUBLE : STYLE_SINGLE
  }
  // Edge case: block indentation indicator can only have one digit.
  if (indentPerLevel > 9 && needIndentIndicator(string)) {
    return STYLE_DOUBLE
  }
  // At this point we know block styles are valid.
  // Prefer literal style unless we want to fold.
  if (!forceQuotes) {
    return hasFoldableLine ? STYLE_FOLDED : STYLE_LITERAL
  }
  return quotingType === QUOTING_TYPE_DOUBLE ? STYLE_DOUBLE : STYLE_SINGLE
}

// Note: line breaking/folding is implemented for only the folded style.
// NB. We drop the last trailing newline (if any) of a returned block scalar
//  since the dumper adds its own newline. This always works:
//    • No ending newline => unaffected; already using strip "-" chomping.
//    • Ending newline    => removed then restored.
//  Importantly, this keeps the "+" chomp indicator from gaining an extra line.
function writeScalar (state, string, level, iskey, inblock) {
  state.dump = (function () {
    if (string.length === 0) {
      return state.quotingType === QUOTING_TYPE_DOUBLE ? '""' : "''"
    }
    if (!state.noCompatMode) {
      if (DEPRECATED_BOOLEANS_SYNTAX.indexOf(string) !== -1 || DEPRECATED_BASE60_SYNTAX.test(string)) {
        return state.quotingType === QUOTING_TYPE_DOUBLE ? ('"' + string + '"') : ("'" + string + "'")
      }
    }

    const indent = state.indent * Math.max(1, level) // no 0-indent scalars
    // As indentation gets deeper, let the width decrease monotonically
    // to the lower bound min(state.lineWidth, 40).
    // Note that this implies
    //  state.lineWidth ≤ 40 + state.indent: width is fixed at the lower bound.
    //  state.lineWidth > 40 + state.indent: width decreases until the lower bound.
    // This behaves better than a constant minimum width which disallows narrower options,
    // or an indent threshold which causes the width to suddenly increase.
    const lineWidth = (state.lineWidth === -1)
      ? -1
      : Math.max(Math.min(state.lineWidth, 40), state.lineWidth - indent)

    // Without knowing if keys are implicit/explicit, assume implicit for safety.
    const singleLineOnly = iskey ||
      // No block styles in flow mode.
      (state.flowLevel > -1 && level >= state.flowLevel)
    function testAmbiguity (string) {
      return testImplicitResolving(state, string)
    }

    switch (chooseScalarStyle(string, singleLineOnly, state.indent, lineWidth,
      testAmbiguity, state.quotingType, state.forceQuotes && !iskey, inblock)) {
      case STYLE_PLAIN:
        return string
      case STYLE_SINGLE:
        return "'" + string.replace(/'/g, "''") + "'"
      case STYLE_LITERAL:
        return '|' + blockHeader(string, state.indent) +
          dropEndingNewline(indentString(string, indent))
      case STYLE_FOLDED:
        return '>' + blockHeader(string, state.indent) +
          dropEndingNewline(indentString(foldString(string, lineWidth), indent))
      case STYLE_DOUBLE:
        return '"' + escapeString(string, lineWidth) + '"'
      default:
        throw new YAMLException('impossible error: invalid scalar style')
    }
  }())
}

// Pre-conditions: string is valid for a block scalar, 1 <= indentPerLevel <= 9.
function blockHeader (string, indentPerLevel) {
  const indentIndicator = needIndentIndicator(string) ? String(indentPerLevel) : ''

  // note the special case: the string '\n' counts as a "trailing" empty line.
  const clip = string[string.length - 1] === '\n'
  const keep = clip && (string[string.length - 2] === '\n' || string === '\n')
  const chomp = keep ? '+' : (clip ? '' : '-')

  return indentIndicator + chomp + '\n'
}

// (See the note for writeScalar.)
function dropEndingNewline (string) {
  return string[string.length - 1] === '\n' ? string.slice(0, -1) : string
}

// Note: a long line without a suitable break point will exceed the width limit.
// Pre-conditions: every char in str isPrintable, str.length > 0, width > 0.
function foldString (string, width) {
  // In folded style, $k$ consecutive newlines output as $k+1$ newlines—
  // unless they're before or after a more-indented line, or at the very
  // beginning or end, in which case $k$ maps to $k$.
  // Therefore, parse each chunk as newline(s) followed by a content line.
  const lineRe = /(\n+)([^\n]*)/g

  // first line (possibly an empty line)
  let result = (function () {
    let nextLF = string.indexOf('\n')
    nextLF = nextLF !== -1 ? nextLF : string.length
    lineRe.lastIndex = nextLF
    return foldLine(string.slice(0, nextLF), width)
  }())
  // If we haven't reached the first content line yet, don't add an extra \n.
  let prevMoreIndented = string[0] === '\n' || string[0] === ' '
  let moreIndented

  // rest of the lines
  let match
  while ((match = lineRe.exec(string))) {
    const prefix = match[1]
    const line = match[2]

    moreIndented = (line[0] === ' ')
    result += prefix +
      ((!prevMoreIndented && !moreIndented && line !== '') ? '\n' : '') +
      foldLine(line, width)
    prevMoreIndented = moreIndented
  }

  return result
}

// Greedy line breaking.
// Picks the longest line under the limit each time,
// otherwise settles for the shortest line over the limit.
// NB. More-indented lines *cannot* be folded, as that would add an extra \n.
function foldLine (line, width) {
  if (line === '' || line[0] === ' ') return line

  // Since a more-indented line adds a \n, breaks can't be followed by a space.
  const breakRe = / [^ ]/g // note: the match index will always be <= length-2.
  let match
  // start is an inclusive index. end, curr, and next are exclusive.
  let start = 0
  let end
  let curr = 0
  let next = 0
  let result = ''

  // Invariants: 0 <= start <= length-1.
  //   0 <= curr <= next <= max(0, length-2). curr - start <= width.
  // Inside the loop:
  //   A match implies length >= 2, so curr and next are <= length-2.
  while ((match = breakRe.exec(line))) {
    next = match.index
    // maintain invariant: curr - start <= width
    if (next - start > width) {
      end = (curr > start) ? curr : next // derive end <= length-2
      result += '\n' + line.slice(start, end)
      // skip the space that was output as \n
      start = end + 1                    // derive start <= length-1
    }
    curr = next
  }

  // By the invariants, start <= length-1, so there is something left over.
  // It is either the whole string or a part starting from non-whitespace.
  result += '\n'
  // Insert a break if the remainder is too long and there is a break available.
  if (line.length - start > width && curr > start) {
    result += line.slice(start, curr) + '\n' + line.slice(curr + 1)
  } else {
    result += line.slice(start)
  }

  return result.slice(1) // drop extra \n joiner
}

// Escapes a double-quoted string.
function escapeString (string) {
  let result = ''
  let char = 0

  for (let i = 0; i < string.length; char >= 0x10000 ? i += 2 : i++) {
    char = codePointAt(string, i)
    const escapeSeq = ESCAPE_SEQUENCES[char]

    if (!escapeSeq && isPrintable(char)) {
      result += string[i]
      if (char >= 0x10000) result += string[i + 1]
    } else {
      result += escapeSeq || encodeHex(char)
    }
  }

  return result
}

function writeFlowSequence (state, level, object) {
  let _result = ''
  const _tag = state.tag

  for (let index = 0, length = object.length; index < length; index += 1) {
    let value = object[index]

    if (state.replacer) {
      value = state.replacer.call(object, String(index), value)
    }

    // Write only valid elements, put null instead of invalid elements.
    if (writeNode(state, level, value, false, false) ||
        (typeof value === 'undefined' &&
         writeNode(state, level, null, false, false))) {
      if (_result !== '') _result += ',' + (!state.condenseFlow ? ' ' : '')
      _result += state.dump
    }
  }

  state.tag = _tag
  state.dump = '[' + _result + ']'
}

function writeBlockSequence (state, level, object, compact) {
  let _result = ''
  const _tag = state.tag

  for (let index = 0, length = object.length; index < length; index += 1) {
    let value = object[index]

    if (state.replacer) {
      value = state.replacer.call(object, String(index), value)
    }

    // Write only valid elements, put null instead of invalid elements.
    if (writeNode(state, level + 1, value, true, true, false, true) ||
        (typeof value === 'undefined' &&
         writeNode(state, level + 1, null, true, true, false, true))) {
      if (!compact || _result !== '') {
        _result += generateNextLine(state, level)
      }

      if (state.dump && CHAR_LINE_FEED === state.dump.charCodeAt(0)) {
        _result += '-'
      } else {
        _result += '- '
      }

      _result += state.dump
    }
  }

  state.tag = _tag
  state.dump = _result || '[]' // Empty sequence if no valid values.
}

function writeFlowMapping (state, level, object) {
  let _result = ''
  const _tag = state.tag
  const objectKeyList = Object.keys(object)

  for (let index = 0, length = objectKeyList.length; index < length; index += 1) {
    let pairBuffer = ''
    if (_result !== '') pairBuffer += ', '

    if (state.condenseFlow) pairBuffer += '"'

    const objectKey = objectKeyList[index]
    let objectValue = object[objectKey]

    if (state.replacer) {
      objectValue = state.replacer.call(object, objectKey, objectValue)
    }

    if (!writeNode(state, level, objectKey, false, false)) {
      continue // Skip this pair because of invalid key;
    }

    if (state.dump.length > 1024) pairBuffer += '? '

    pairBuffer += state.dump + (state.condenseFlow ? '"' : '') + ':' + (state.condenseFlow ? '' : ' ')

    if (!writeNode(state, level, objectValue, false, false)) {
      continue // Skip this pair because of invalid value.
    }

    pairBuffer += state.dump

    // Both key and value are valid.
    _result += pairBuffer
  }

  state.tag = _tag
  state.dump = '{' + _result + '}'
}

function writeBlockMapping (state, level, object, compact) {
  let _result = ''
  const _tag = state.tag
  const objectKeyList = Object.keys(object)

  // Allow sorting keys so that the output file is deterministic
  if (state.sortKeys === true) {
    // Default sorting
    objectKeyList.sort()
  } else if (typeof state.sortKeys === 'function') {
    // Custom sort function
    objectKeyList.sort(state.sortKeys)
  } else if (state.sortKeys) {
    // Something is wrong
    throw new YAMLException('sortKeys must be a boolean or a function')
  }

  for (let index = 0, length = objectKeyList.length; index < length; index += 1) {
    let pairBuffer = ''

    if (!compact || _result !== '') {
      pairBuffer += generateNextLine(state, level)
    }

    const objectKey = objectKeyList[index]
    let objectValue = object[objectKey]

    if (state.replacer) {
      objectValue = state.replacer.call(object, objectKey, objectValue)
    }

    if (!writeNode(state, level + 1, objectKey, true, true, true)) {
      continue // Skip this pair because of invalid key.
    }

    const explicitPair = (state.tag !== null && state.tag !== '?') ||
                   (state.dump && state.dump.length > 1024)

    if (explicitPair) {
      if (state.dump && CHAR_LINE_FEED === state.dump.charCodeAt(0)) {
        pairBuffer += '?'
      } else {
        pairBuffer += '? '
      }
    }

    pairBuffer += state.dump

    if (explicitPair) {
      pairBuffer += generateNextLine(state, level)
    }

    if (!writeNode(state, level + 1, objectValue, true, explicitPair)) {
      continue // Skip this pair because of invalid value.
    }

    if (state.dump && CHAR_LINE_FEED === state.dump.charCodeAt(0)) {
      pairBuffer += ':'
    } else {
      pairBuffer += ': '
    }

    pairBuffer += state.dump

    // Both key and value are valid.
    _result += pairBuffer
  }

  state.tag = _tag
  state.dump = _result || '{}' // Empty mapping if no valid pairs.
}

function detectType (state, object, explicit) {
  const typeList = explicit ? state.explicitTypes : state.implicitTypes

  for (let index = 0, length = typeList.length; index < length; index += 1) {
    const type = typeList[index]

    if ((type.instanceOf || type.predicate) &&
        (!type.instanceOf || ((typeof object === 'object') && (object instanceof type.instanceOf))) &&
        (!type.predicate || type.predicate(object))) {
      if (explicit) {
        if (type.multi && type.representName) {
          state.tag = type.representName(object)
        } else {
          state.tag = type.tag
        }
      } else {
        state.tag = '?'
      }

      if (type.represent) {
        const style = state.styleMap[type.tag] || type.defaultStyle

        let _result
        if (_toString.call(type.represent) === '[object Function]') {
          _result = type.represent(object, style)
        } else if (_hasOwnProperty.call(type.represent, style)) {
          _result = type.represent[style](object, style)
        } else {
          throw new YAMLException('!<' + type.tag + '> tag resolver accepts not "' + style + '" style')
        }

        state.dump = _result
      }

      return true
    }
  }

  return false
}

// Serializes `object` and writes it to global `result`.
// Returns true on success, or false on invalid object.
//
function writeNode (state, level, object, block, compact, iskey, isblockseq) {
  state.tag = null
  state.dump = object

  if (!detectType(state, object, false)) {
    detectType(state, object, true)
  }

  const type = _toString.call(state.dump)
  const inblock = block

  if (block) {
    block = (state.flowLevel < 0 || state.flowLevel > level)
  }

  const objectOrArray = type === '[object Object]' || type === '[object Array]'
  let duplicateIndex
  let duplicate

  if (objectOrArray) {
    duplicateIndex = state.duplicates.indexOf(object)
    duplicate = duplicateIndex !== -1
  }

  if ((state.tag !== null && state.tag !== '?') || duplicate || (state.indent !== 2 && level > 0)) {
    compact = false
  }

  if (duplicate && state.usedDuplicates[duplicateIndex]) {
    state.dump = '*ref_' + duplicateIndex
  } else {
    if (objectOrArray && duplicate && !state.usedDuplicates[duplicateIndex]) {
      state.usedDuplicates[duplicateIndex] = true
    }
    if (type === '[object Object]') {
      if (block && (Object.keys(state.dump).length !== 0)) {
        writeBlockMapping(state, level, state.dump, compact)
        if (duplicate) {
          state.dump = '&ref_' + duplicateIndex + state.dump
        }
      } else {
        writeFlowMapping(state, level, state.dump)
        if (duplicate) {
          state.dump = '&ref_' + duplicateIndex + ' ' + state.dump
        }
      }
    } else if (type === '[object Array]') {
      if (block && (state.dump.length !== 0)) {
        if (state.noArrayIndent && !isblockseq && level > 0) {
          writeBlockSequence(state, level - 1, state.dump, compact)
        } else {
          writeBlockSequence(state, level, state.dump, compact)
        }
        if (duplicate) {
          state.dump = '&ref_' + duplicateIndex + state.dump
        }
      } else {
        writeFlowSequence(state, level, state.dump)
        if (duplicate) {
          state.dump = '&ref_' + duplicateIndex + ' ' + state.dump
        }
      }
    } else if (type === '[object String]') {
      if (state.tag !== '?') {
        writeScalar(state, state.dump, level, iskey, inblock)
      }
    } else if (type === '[object Undefined]') {
      return false
    } else {
      if (state.skipInvalid) return false
      throw new YAMLException('unacceptable kind of an object to dump ' + type)
    }

    if (state.tag !== null && state.tag !== '?') {
      // Need to encode all characters except those allowed by the spec:
      //
      // [35] ns-dec-digit    ::=  [#x30-#x39] /* 0-9 */
      // [36] ns-hex-digit    ::=  ns-dec-digit
      //                         | [#x41-#x46] /* A-F */ | [#x61-#x66] /* a-f */
      // [37] ns-ascii-letter ::=  [#x41-#x5A] /* A-Z */ | [#x61-#x7A] /* a-z */
      // [38] ns-word-char    ::=  ns-dec-digit | ns-ascii-letter | “-”
      // [39] ns-uri-char     ::=  “%” ns-hex-digit ns-hex-digit | ns-word-char | “#”
      //                         | “;” | “/” | “?” | “:” | “@” | “&” | “=” | “+” | “$” | “,”
      //                         | “_” | “.” | “!” | “~” | “*” | “'” | “(” | “)” | “[” | “]”
      //
      // Also need to encode '!' because it has special meaning (end of tag prefix).
      //
      let tagStr = encodeURI(
        state.tag[0] === '!' ? state.tag.slice(1) : state.tag
      ).replace(/!/g, '%21')

      if (state.tag[0] === '!') {
        tagStr = '!' + tagStr
      } else if (tagStr.slice(0, 18) === 'tag:yaml.org,2002:') {
        tagStr = '!!' + tagStr.slice(18)
      } else {
        tagStr = '!<' + tagStr + '>'
      }

      state.dump = tagStr + ' ' + state.dump
    }
  }

  return true
}

function getDuplicateReferences (object, state) {
  const objects = []
  const duplicatesIndexes = []

  inspectNode(object, objects, duplicatesIndexes)

  const length = duplicatesIndexes.length
  for (let index = 0; index < length; index += 1) {
    state.duplicates.push(objects[duplicatesIndexes[index]])
  }
  state.usedDuplicates = new Array(length)
}

function inspectNode (object, objects, duplicatesIndexes) {
  if (object !== null && typeof object === 'object') {
    const index = objects.indexOf(object)
    if (index !== -1) {
      if (duplicatesIndexes.indexOf(index) === -1) {
        duplicatesIndexes.push(index)
      }
    } else {
      objects.push(object)

      if (Array.isArray(object)) {
        for (let i = 0, length = object.length; i < length; i += 1) {
          inspectNode(object[i], objects, duplicatesIndexes)
        }
      } else {
        const objectKeyList = Object.keys(object)

        for (let i = 0, length = objectKeyList.length; i < length; i += 1) {
          inspectNode(object[objectKeyList[i]], objects, duplicatesIndexes)
        }
      }
    }
  }
}

function dump (input, options) {
  options = options || {}

  const state = new State(options)

  if (!state.noRefs) getDuplicateReferences(input, state)

  let value = input

  if (state.replacer) {
    value = state.replacer.call({ '': value }, '', value)
  }

  if (writeNode(state, 0, value, true, true)) return state.dump + '\n'

  return ''
}

module.exports.dump = dump