var assert = require("assert");
var types = require("./types");
var n = types.namedTypes;
var Node = n.Node;
var isArray = types.builtInTypes.array;
var isNumber = types.builtInTypes.number;
var util = require("./util.js");

function FastPath(value) {
  assert.ok(this instanceof FastPath);
  this.stack = [value];
}

var FPp = FastPath.prototype;
module.exports = FastPath;

// Static convenience function for coercing a value to a FastPath.
FastPath.from = function(obj) {
  if (obj instanceof FastPath) {
    // Return a defensive copy of any existing FastPath instances.
    return obj.copy();
  }

  if (obj instanceof types.NodePath) {
    // For backwards compatibility, unroll NodePath instances into
    // lightweight FastPath [..., name, value] stacks.
    var copy = Object.create(FastPath.prototype);
    var stack = [obj.value];
    for (var pp; (pp = obj.parentPath); obj = pp)
      stack.push(obj.name, pp.value);
    copy.stack = stack.reverse();
    return copy;
  }

  // Otherwise use obj as the value of the new FastPath instance.
  return new FastPath(obj);
};

FPp.copy = function copy() {
  var copy = Object.create(FastPath.prototype);
  copy.stack = this.stack.slice(0);
  return copy;
};

// The name of the current property is always the penultimate element of
// this.stack, and always a String.
FPp.getName = function getName() {
  var s = this.stack;
  var len = s.length;
  if (len > 1) {
    return s[len - 2];
  }
  // Since the name is always a string, null is a safe sentinel value to
  // return if we do not know the name of the (root) value.
  return null;
};

// The value of the current property is always the final element of
// this.stack.
FPp.getValue = function getValue() {
  var s = this.stack;
  return s[s.length - 1];
};

FPp.valueIsDuplicate = function () {
  var s = this.stack;
  var valueIndex = s.length - 1;
  return s.lastIndexOf(s[valueIndex], valueIndex - 1) >= 0;
};

function getNodeHelper(path, count) {
  var s = path.stack;

  for (var i = s.length - 1; i >= 0; i -= 2) {
    var value = s[i];
    if (n.Node.check(value) && --count < 0) {
      return value;
    }
  }

  return null;
}

FPp.getNode = function getNode(count) {
  return getNodeHelper(this, ~~count);
};

FPp.getParentNode = function getParentNode(count) {
  return getNodeHelper(this, ~~count + 1);
};

// The length of the stack can be either even or odd, depending on whether
// or not we have a name for the root value. The difference between the
// index of the root value and the index of the final value is always
// even, though, which allows us to return the root value in constant time
// (i.e. without iterating backwards through the stack).
FPp.getRootValue = function getRootValue() {
  var s = this.stack;
  if (s.length % 2 === 0) {
    return s[1];
  }
  return s[0];
};

// Temporarily push properties named by string arguments given after the
// callback function onto this.stack, then call the callback with a
// reference to this (modified) FastPath object. Note that the stack will
// be restored to its original state after the callback is finished, so it
// is probably a mistake to retain a reference to the path.
FPp.call = function call(callback/*, name1, name2, ... */) {
  var s = this.stack;
  var origLen = s.length;
  var value = s[origLen - 1];
  var argc = arguments.length;
  for (var i = 1; i < argc; ++i) {
    var name = arguments[i];
    value = value[name];
    s.push(name, value);
  }
  var result = callback(this);
  s.length = origLen;
  return result;
};

// Similar to FastPath.prototype.call, except that the value obtained by
// accessing this.getValue()[name1][name2]... should be array-like. The
// callback will be called with a reference to this path object for each
// element of the array.
FPp.each = function each(callback/*, name1, name2, ... */) {
  var s = this.stack;
  var origLen = s.length;
  var value = s[origLen - 1];
  var argc = arguments.length;

  for (var i = 1; i < argc; ++i) {
    var name = arguments[i];
    value = value[name];
    s.push(name, value);
  }

  for (var i = 0; i < value.length; ++i) {
    if (i in value) {
      s.push(i, value[i]);
      // If the callback needs to know the value of i, call
      // path.getName(), assuming path is the parameter name.
      callback(this);
      s.length -= 2;
    }
  }

  s.length = origLen;
};

// Similar to FastPath.prototype.each, except that the results of the
// callback function invocations are stored in an array and returned at
// the end of the iteration.
FPp.map = function map(callback/*, name1, name2, ... */) {
  var s = this.stack;
  var origLen = s.length;
  var value = s[origLen - 1];
  var argc = arguments.length;

  for (var i = 1; i < argc; ++i) {
    var name = arguments[i];
    value = value[name];
    s.push(name, value);
  }

  var result = new Array(value.length);

  for (var i = 0; i < value.length; ++i) {
    if (i in value) {
      s.push(i, value[i]);
      result[i] = callback(this, i);
      s.length -= 2;
    }
  }

  s.length = origLen;

  return result;
};

// Returns true if the node at the tip of the path is wrapped with
// parentheses, OR if the only reason the node needed parentheses was that
// it couldn't be the first expression in the enclosing statement (see
// FastPath#canBeFirstInStatement), and it has an opening `(` character.
// For example, the FunctionExpression in `(function(){}())` appears to
// need parentheses only because it's the first expression in the AST, but
// since it happens to be preceded by a `(` (which is not apparent from
// the AST but can be determined using FastPath#getPrevToken), there is no
// ambiguity about how to parse it, so it counts as having parentheses,
// even though it is not immediately followed by a `)`.
FPp.hasParens = function () {
  const node = this.getNode();

  const prevToken = this.getPrevToken(node);
  if (! prevToken) {
    return false;
  }

  const nextToken = this.getNextToken(node);
  if (! nextToken) {
    return false;
  }

  if (prevToken.value === "(") {
    if (nextToken.value === ")") {
      // If the node preceded by a `(` token and followed by a `)` token,
      // then of course it has parentheses.
      return true;
    }

    // If this is one of the few Expression types that can't come first in
    // the enclosing statement because of parsing ambiguities (namely,
    // FunctionExpression, ObjectExpression, and ClassExpression) and
    // this.firstInStatement() returns true, and the node would not need
    // parentheses in an expression context because this.needsParens(true)
    // returns false, then it just needs an opening parenthesis to resolve
    // the parsing ambiguity that made it appear to need parentheses.
    const justNeedsOpeningParen =
      ! this.canBeFirstInStatement() &&
      this.firstInStatement() &&
      ! this.needsParens(true);

    if (justNeedsOpeningParen) {
      return true;
    }
  }

  return false;
};

FPp.getPrevToken = function (node) {
  node = node || this.getNode();
  const loc = node && node.loc;
  const tokens = loc && loc.tokens;
  if (tokens && loc.start.token > 0) {
    const token = tokens[loc.start.token - 1];
    if (token) {
      // Do not return tokens that fall outside the root subtree.
      const rootLoc = this.getRootValue().loc;
      if (util.comparePos(rootLoc.start, token.loc.start) <= 0) {
        return token;
      }
    }
  }
  return null;
};

FPp.getNextToken = function (node) {
  node = node || this.getNode();
  const loc = node && node.loc;
  const tokens = loc && loc.tokens;
  if (tokens && loc.end.token < tokens.length) {
    const token = tokens[loc.end.token];
    if (token) {
      // Do not return tokens that fall outside the root subtree.
      const rootLoc = this.getRootValue().loc;
      if (util.comparePos(token.loc.end, rootLoc.end) <= 0) {
        return token;
      }
    }
  }
  return null;
};

// Inspired by require("ast-types").NodePath.prototype.needsParens, but
// more efficient because we're iterating backwards through a stack.
FPp.needsParens = function(assumeExpressionContext) {
  var node = this.getNode();

  // This needs to come before `if (!parent) { return false }` because
  // an object destructuring assignment requires parens for
  // correctness even when it's the topmost expression.
  if (node.type === "AssignmentExpression" && node.left.type === 'ObjectPattern') {
    return true;
  }

  var parent = this.getParentNode();
  if (!parent) {
    return false;
  }

  var name = this.getName();

  // If the value of this path is some child of a Node and not a Node
  // itself, then it doesn't need parentheses. Only Node objects (in fact,
  // only Expression nodes) need parentheses.
  if (this.getValue() !== node) {
    return false;
  }

  // Only statements don't need parentheses.
  if (n.Statement.check(node)) {
    return false;
  }

  // Identifiers never need parentheses.
  if (node.type === "Identifier") {
    return false;
  }

  if (parent.type === "ParenthesizedExpression") {
    return false;
  }

  switch (node.type) {
  case "UnaryExpression":
  case "SpreadElement":
  case "SpreadProperty":
    return parent.type === "MemberExpression"
      && name === "object"
      && parent.object === node;

  case "BinaryExpression":
  case "LogicalExpression":
    switch (parent.type) {
    case "CallExpression":
      return name === "callee"
        && parent.callee === node;

    case "UnaryExpression":
    case "SpreadElement":
    case "SpreadProperty":
      return true;

    case "MemberExpression":
      return name === "object"
        && parent.object === node;

    case "BinaryExpression":
    case "LogicalExpression":
      var po = parent.operator;
      var pp = PRECEDENCE[po];
      var no = node.operator;
      var np = PRECEDENCE[no];

      if (pp > np) {
        return true;
      }

      if (pp === np && name === "right") {
        assert.strictEqual(parent.right, node);
        return true;
      }

    default:
      return false;
    }

  case "SequenceExpression":
    switch (parent.type) {
    case "ReturnStatement":
      return false;

    case "ForStatement":
      // Although parentheses wouldn't hurt around sequence expressions in
      // the head of for loops, traditional style dictates that e.g. i++,
      // j++ should not be wrapped with parentheses.
      return false;

    case "ExpressionStatement":
      return name !== "expression";

    default:
      // Otherwise err on the side of overparenthesization, adding
      // explicit exceptions above if this proves overzealous.
      return true;
    }

  case "YieldExpression":
    switch (parent.type) {
    case "BinaryExpression":
    case "LogicalExpression":
    case "UnaryExpression":
    case "SpreadElement":
    case "SpreadProperty":
    case "CallExpression":
    case "MemberExpression":
    case "NewExpression":
    case "ConditionalExpression":
    case "YieldExpression":
      return true;

    default:
      return false;
    }

  case "IntersectionTypeAnnotation":
  case "UnionTypeAnnotation":
    return parent.type === "NullableTypeAnnotation";

  case "Literal":
    return parent.type === "MemberExpression"
      && isNumber.check(node.value)
      && name === "object"
      && parent.object === node;

  // Babel 6 Literal split
  case "NumericLiteral":
    return parent.type === "MemberExpression"
      && name === "object"
      && parent.object === node;

  case "AssignmentExpression":
  case "ConditionalExpression":
    switch (parent.type) {
    case "UnaryExpression":
    case "SpreadElement":
    case "SpreadProperty":
    case "BinaryExpression":
    case "LogicalExpression":
      return true;

    case "CallExpression":
    case "NewExpression":
      return name === "callee"
        && parent.callee === node;

    case "ConditionalExpression":
      return name === "test"
        && parent.test === node;

    case "MemberExpression":
      return name === "object"
        && parent.object === node;

    default:
      return false;
    }

  case "ArrowFunctionExpression":
    if (n.CallExpression.check(parent) &&
        name === 'callee') {
      return true;
    }

    if (n.MemberExpression.check(parent) &&
        name === 'object') {
      return true;
    }

    return isBinary(parent);

  case "ObjectExpression":
    if (parent.type === "ArrowFunctionExpression" &&
        name === "body") {
      return true;
    }

    break;

  case "CallExpression":
    if (name === "declaration" &&
        n.ExportDefaultDeclaration.check(parent) &&
        n.FunctionExpression.check(node.callee)) {
      return true;
    }
  }

  if (parent.type === "NewExpression" &&
      name === "callee" &&
      parent.callee === node) {
    return containsCallExpression(node);
  }

  if (assumeExpressionContext !== true &&
      !this.canBeFirstInStatement() &&
      this.firstInStatement()) {
    return true;
  }

  return false;
};

function isBinary(node) {
  return n.BinaryExpression.check(node)
    || n.LogicalExpression.check(node);
}

function isUnaryLike(node) {
  return n.UnaryExpression.check(node)
  // I considered making SpreadElement and SpreadProperty subtypes of
  // UnaryExpression, but they're not really Expression nodes.
    || (n.SpreadElement && n.SpreadElement.check(node))
    || (n.SpreadProperty && n.SpreadProperty.check(node));
}

var PRECEDENCE = {};
[["||"],
 ["&&"],
 ["|"],
 ["^"],
 ["&"],
 ["==", "===", "!=", "!=="],
 ["<", ">", "<=", ">=", "in", "instanceof"],
 [">>", "<<", ">>>"],
 ["+", "-"],
 ["*", "/", "%", "**"]
].forEach(function(tier, i) {
  tier.forEach(function(op) {
    PRECEDENCE[op] = i;
  });
});

function containsCallExpression(node) {
  if (n.CallExpression.check(node)) {
    return true;
  }

  if (isArray.check(node)) {
    return node.some(containsCallExpression);
  }

  if (n.Node.check(node)) {
    return types.someField(node, function(name, child) {
      return containsCallExpression(child);
    });
  }

  return false;
}

FPp.canBeFirstInStatement = function() {
  var node = this.getNode();

  if (n.FunctionExpression.check(node)) {
    return false;
  }

  if (n.ObjectExpression.check(node)) {
    return false;
  }

  if (n.ClassExpression.check(node)) {
    return false;
  }

  return true;
};

FPp.firstInStatement = function() {
  var s = this.stack;
  var parentName, parent;
  var childName, child;

  for (var i = s.length - 1; i >= 0; i -= 2) {
    if (n.Node.check(s[i])) {
      childName = parentName;
      child = parent;
      parentName = s[i - 1];
      parent = s[i];
    }

    if (!parent || !child) {
      continue;
    }

    if (n.BlockStatement.check(parent) &&
        parentName === "body" &&
        childName === 0) {
      assert.strictEqual(parent.body[0], child);
      return true;
    }

    if (n.ExpressionStatement.check(parent) &&
        childName === "expression") {
      assert.strictEqual(parent.expression, child);
      return true;
    }

    if (n.AssignmentExpression.check(parent) &&
        childName === "left") {
      assert.strictEqual(parent.left, child);
      return true;
    }

    if (n.ArrowFunctionExpression.check(parent) &&
        childName === "body") {
      assert.strictEqual(parent.body, child);
      return true;
    }

    if (n.SequenceExpression.check(parent) &&
        parentName === "expressions" &&
        childName === 0) {
      assert.strictEqual(parent.expressions[0], child);
      continue;
    }

    if (n.CallExpression.check(parent) &&
        childName === "callee") {
      assert.strictEqual(parent.callee, child);
      continue;
    }

    if (n.MemberExpression.check(parent) &&
        childName === "object") {
      assert.strictEqual(parent.object, child);
      continue;
    }

    if (n.ConditionalExpression.check(parent) &&
        childName === "test") {
      assert.strictEqual(parent.test, child);
      continue;
    }

    if (isBinary(parent) &&
        childName === "left") {
      assert.strictEqual(parent.left, child);
      continue;
    }

    if (n.UnaryExpression.check(parent) &&
        !parent.prefix &&
        childName === "argument") {
      assert.strictEqual(parent.argument, child);
      continue;
    }

    return false;
  }

  return true;
};
