var diff = require('fast-diff');
var is = require('./is');
var op = require('./op');


var NULL_CHARACTER = String.fromCharCode(0);  // Placeholder char for embed in diff()


var Delta = function (ops) {
  // Assume we are given a well formed ops
  if (is.array(ops)) {
    this.ops = ops;
  } else if (is.object(ops) && is.array(ops.ops)) {
    this.ops = ops.ops;
  } else {
    this.ops = [];
  }
};


Delta.prototype.insert = function (text, attributes) {
  var newOp = {};
  if (is.string(text)) {
    if (text.length === 0) return this;
    newOp.insert = text;
  } else if (is.number(text)) {
    newOp.insert = text;
  }
  if (is.object(attributes) && Object.keys(attributes).length > 0) newOp.attributes = attributes;
  return this.push(newOp);
};

Delta.prototype['delete'] = function (length) {
  if (length <= 0) return this;
  return this.push({ 'delete': length });
};

Delta.prototype.retain = function (length, attributes) {
  if (length <= 0) return this;
  var newOp = { retain: length };
  if (is.object(attributes) && Object.keys(attributes).length > 0) newOp.attributes = attributes;
  return this.push(newOp);
};

Delta.prototype.push = function (newOp) {
  var index = this.ops.length;
  var lastOp = this.ops[index - 1];
  newOp = op.clone(newOp);
  if (is.object(lastOp)) {
    if (is.number(newOp['delete']) && is.number(lastOp['delete'])) {
      this.ops[index - 1] = { 'delete': lastOp['delete'] + newOp['delete'] };
      return this;
    }
    // Since it does not matter if we insert before or after deleting at the same index,
    // always prefer to insert first
    if (is.number(lastOp['delete']) && (is.string(newOp.insert) || is.number(newOp.insert))) {
      index -= 1;
      lastOp = this.ops[index - 1];
      if (!is.object(lastOp)) {
        this.ops.unshift(newOp);
        return this;
      }
    }
    if (is.equal(newOp.attributes, lastOp.attributes)) {
      if (is.string(newOp.insert) && is.string(lastOp.insert)) {
        this.ops[index - 1] = { insert: lastOp.insert + newOp.insert };
        if (is.object(newOp.attributes)) this.ops[index - 1].attributes = newOp.attributes
        return this;
      } else if (is.number(newOp.retain) && is.number(lastOp.retain)) {
        this.ops[index - 1] = { retain: lastOp.retain + newOp.retain };
        if (is.object(newOp.attributes)) this.ops[index - 1].attributes = newOp.attributes
        return this;
      }
    }
  }
  this.ops.splice(index, 0, newOp);
  return this;
};

Delta.prototype.chop = function () {
  var lastOp = this.ops[this.ops.length - 1];
  if (lastOp && lastOp.retain && !lastOp.attributes) {
    this.ops.pop();
  }
  return this;
};

Delta.prototype.length = function () {
  return this.ops.reduce(function (length, elem) {
    return length + op.length(elem);
  }, 0);
};

Delta.prototype.slice = function (start, end) {
  start = start || 0;
  if (!is.number(end)) end = Infinity;
  var delta = new Delta();
  var iter = op.iterator(this.ops);
  var index = 0;
  while (index < end && iter.hasNext()) {
    var nextOp;
    if (index < start) {
      nextOp = iter.next(start - index);
    } else {
      nextOp = iter.next(end - index);
      delta.push(nextOp);
    }
    index += op.length(nextOp);
  }
  return delta;
};


Delta.prototype.compose = function (other) {
  var thisIter = op.iterator(this.ops);
  var otherIter = op.iterator(other.ops);
  this.ops = [];
  while (thisIter.hasNext() || otherIter.hasNext()) {
    if (otherIter.peekType() === 'insert') {
      this.push(otherIter.next());
    } else if (thisIter.peekType() === 'delete') {
      this.push(thisIter.next());
    } else {
      var length = Math.min(thisIter.peekLength(), otherIter.peekLength());
      var thisOp = thisIter.next(length);
      var otherOp = otherIter.next(length);
      if (is.number(otherOp.retain)) {
        var newOp = {};
        if (is.number(thisOp.retain)) {
          newOp.retain = length;
        } else {
          newOp.insert = thisOp.insert;
        }
        // Preserve null when composing with a retain, otherwise remove it for inserts
        var attributes = op.attributes.compose(thisOp.attributes, otherOp.attributes, is.number(thisOp.retain));
        if (attributes) newOp.attributes = attributes;
        this.push(newOp);
      // Other op should be delete, we could be an insert or retain
      // Insert + delete cancels out
      } else if (is.number(otherOp['delete']) && is.number(thisOp.retain)) {
        this.push(otherOp);
      }
    }
  }
  return this.chop();
};

Delta.prototype.diff = function (other) {
  var strings = [this.ops, other.ops].map(function (ops) {
    return ops.map(function (op) {
      if (is.string(op.insert)) return op.insert;
      if (is.number(op.insert)) return NULL_CHARACTER;
      var prep = ops === other.ops ? 'on' : 'with';
      throw new Error('diff() called ' + prep + ' non-document');
    }).join('');
  });
  var diffResult = diff(strings[0], strings[1]);
  var thisIter = op.iterator(this.ops);
  var otherIter = op.iterator(other.ops);
  var delta = new Delta();
  diffResult.forEach(function (component) {
    var length = component[1].length;
    while (length > 0) {
      var opLength = 0;
      switch (component[0]) {
        case diff.INSERT:
          opLength = Math.min(otherIter.peekLength(), length);
          delta.push(otherIter.next(opLength));
          break;
        case diff.DELETE:
          opLength = Math.min(length, thisIter.peekLength());
          thisIter.next(opLength);
          delta['delete'](opLength);
          break;
        case diff.EQUAL:
          opLength = Math.min(thisIter.peekLength(), otherIter.peekLength(), length);
          var thisOp = thisIter.next(opLength);
          var otherOp = otherIter.next(opLength);
          if (thisOp.insert === otherOp.insert) {
            delta.retain(opLength, op.attributes.diff(thisOp.attributes, otherOp.attributes));
          } else {
            delta.push(otherOp)['delete'](opLength);
          }
          break;
      }
      length -= opLength;
    }
  });
  return delta.chop();
};

Delta.prototype.transform = function (other, priority) {
  priority = !!priority;
  if (is.number(other)) {
    return this.transformPosition(other, priority);
  }
  var thisIter = op.iterator(this.ops);
  var otherIter = op.iterator(other.ops);
  var delta = new Delta();
  while (thisIter.hasNext() || otherIter.hasNext()) {
    if (thisIter.peekType() === 'insert' && (priority || otherIter.peekType() !== 'insert')) {
      delta.retain(op.length(thisIter.next()));
    } else if (otherIter.peekType() === 'insert') {
      delta.push(otherIter.next());
    } else {
      var length = Math.min(thisIter.peekLength(), otherIter.peekLength());
      var thisOp = thisIter.next(length);
      var otherOp = otherIter.next(length);
      if (thisOp['delete']) {
        // Our delete either makes their delete redundant or removes their retain
        continue;
      } else if (otherOp['delete']) {
        delta.push(otherOp);
      } else {
        // We retain either their retain or insert
        delta.retain(length, op.attributes.transform(thisOp.attributes, otherOp.attributes, priority));
      }
    }
  }
  return delta.chop();
};

Delta.prototype.transformPosition = function (index, priority) {
  priority = !!priority;
  var thisIter = op.iterator(this.ops);
  var offset = 0;
  while (thisIter.hasNext() && offset <= index) {
    var length = thisIter.peekLength();
    var nextType = thisIter.peekType();
    thisIter.next();
    if (nextType === 'delete') {
      index -= Math.min(length, index - offset);
      continue;
    } else if (nextType === 'insert' && (offset < index || !priority)) {
      index += length;
    }
    offset += length;
  }
  return index;
};


module.exports = Delta;