/*
This method evaluates the Field using the first and second value
and returns the result value. If the second operand type is a
missing return a missing value. If it is a string, and the
field is case insensitive, then convert the second operand to
lower case, range through the fields of the first and compare,
each field with the second. When equal, return the value. If
the field is case sensitive, use the Field method to directly
access the field and return it. For all other types, if the
first operand expression is missing, return missing, else return
null.
*/
func (this *Field) Apply(context Context, first, second value.Value) (value.Value, error) {
	switch second.Type() {
	case value.STRING:
		s := second.Actual().(string)
		v, ok := first.Field(s)

		if !ok && this.caseInsensitive {
			s = strings.ToLower(s)
			fields := first.Fields()
			for f, val := range fields {
				if s == strings.ToLower(f) {
					return value.NewValue(val), nil
				}
			}
		}

		return v, nil
	case value.MISSING:
		return value.MISSING_VALUE, nil
	default:
		if first.Type() == value.MISSING {
			return value.MISSING_VALUE, nil
		} else {
			return value.NULL_VALUE, nil
		}
	}
}

/*
Aggregate distinct intermediate results and return them.
If no partial result exists(its value is a null) return the
cumulative value. If the cumulative input value is null,
return the partial value. Get the input partial and cumulative
sets and add the smaller set to the bigger. Return this set.
*/
func cumulateSets(part, cumulative value.Value) (value.Value, error) {
	if part.Type() == value.NULL {
		return cumulative, nil
	} else if cumulative.Type() == value.NULL {
		return part, nil
	}

	pset, e := getSet(part)
	if e != nil {
		return nil, e
	}

	cset, e := getSet(cumulative)
	if e != nil {
		return nil, e
	}

	// Add smaller set to bigger
	var smaller, bigger *value.Set
	if pset.Len() <= cset.Len() {
		smaller, bigger = pset, cset
	} else {
		smaller, bigger = cset, pset
	}

	for _, v := range smaller.Values() {
		bigger.Add(v)
	}

	cumulative.(value.AnnotatedValue).SetAttachment("set", bigger)
	return cumulative, nil
}

/*
If the input argument type is greater than NULL, we return the complement
of its Truth() method's return type. If Null or missing return the argument
itself.
*/
func (this *Not) Apply(context Context, arg value.Value) (value.Value, error) {
	if arg.Type() > value.NULL {
		return value.NewValue(!arg.Truth()), nil
	} else {
		return arg, nil
	}
}

/*
This method returns an object value. The input of types
missing, null and object return themselves. For all other
values, return an _EMPTY_OBJECT value.
*/
func (this *ToObject) Apply(context Context, arg value.Value) (value.Value, error) {
	switch arg.Type() {
	case value.MISSING, value.NULL, value.OBJECT:
		return arg, nil
	}

	return _EMPTY_OBJECT, nil
}

/*
This method evaluates the less than equal to condition and
returns a value representing if the two operands satisfy the
condition or not. If either of the input operands are
missing, return missing value, and if they are null, then
return null value. For all other types call the Collate
method and check if it is less than equal to 0 for the
two values. If it is, then return true.
*/
func (this *LE) Apply(context Context, first, second value.Value) (value.Value, error) {
	if first.Type() == value.MISSING || second.Type() == value.MISSING {
		return value.MISSING_VALUE, nil
	} else if first.Type() == value.NULL || second.Type() == value.NULL {
		return value.NULL_VALUE, nil
	}

	return value.NewValue(first.Collate(second) <= 0), nil
}

/*
This method takes in an operand value and context and returns a value.
If the type of operand is missing then return it. Call MarshalJSON
to get the bytes, and then use Go's encoding/base64 package to
encode the bytes to string. Create a newValue using the string and
return it.
*/
func (this *Base64) Apply(context Context, operand value.Value) (value.Value, error) {
	if operand.Type() == value.MISSING {
		return operand, nil
	}

	bytes, _ := operand.MarshalJSON() // Ignore errors from BINARY values
	str := base64.StdEncoding.EncodeToString(bytes)
	return value.NewValue(str), nil
}

/*
Evaluates the Is Null comparison operation for expressions.
If the type of input argument is a null value, return true,
if missing return a missing value and by for all other types
return a false value.
*/
func (this *IsNull) Apply(context Context, arg value.Value) (value.Value, error) {
	switch arg.Type() {
	case value.NULL:
		return value.TRUE_VALUE, nil
	case value.MISSING:
		return value.MISSING_VALUE, nil
	default:
		return value.FALSE_VALUE, nil
	}
}

func (this *ParentScan) RunOnce(context *Context, parent value.Value) {
	this.once.Do(func() {
		defer context.Recover()       // Recover from any panic
		defer close(this.itemChannel) // Broadcast that I have stopped
		defer this.notify()           // Notify that I have stopped

		// Shallow copy of the parent includes
		// correlated and annotated aspects
		this.sendItem(parent.Copy().(value.AnnotatedValue))
	})
}

/*
Aggregate input partial values into cumulative result value.
If partial result is null return the current cumulative value,
and if the cumulative result is null, return the partial value.
For non null partial and cumulative values, call Collate and
return the smaller value depending on the N1QL collation order.
*/
func (this *Min) cumulatePart(part, cumulative value.Value, context Context) (value.Value, error) {
	if part == value.NULL_VALUE {
		return cumulative, nil
	} else if cumulative == value.NULL_VALUE {
		return part, nil
	} else if part.Collate(cumulative) < 0 {
		return part, nil
	} else {
		return cumulative, nil
	}
}

/*
Aggregates input data by evaluating operands. For missing
item values, return the input value itself. Call
cumulatePart to compute the intermediate aggregate value
and return it.
*/
func (this *ArrayAgg) CumulateInitial(item, cumulative value.Value, context Context) (value.Value, error) {
	item, e := this.Operand().Evaluate(item, context)
	if e != nil {
		return nil, e
	}

	if item.Type() <= value.MISSING {
		return cumulative, nil
	}

	return this.cumulatePart(value.NewValue([]interface{}{item}), cumulative, context)
}

func (this *Sum) CumulateInitial(item, cumulative value.Value, context Context) (value.Value, error) {
	item, e := this.Operand().Evaluate(item, context)
	if e != nil {
		return nil, e
	}

	if item.Type() != value.NUMBER {
		return cumulative, nil
	}

	return this.cumulatePart(item, cumulative, context)
}

/*
Aggregates input data by evaluating operands.For all
values other than Number, return the input value itself.
Call setAdd to compute the intermediate aggregate value
and return it.
*/
func (this *AvgDistinct) CumulateInitial(item, cumulative value.Value, context Context) (value.Value, error) {
	item, e := this.Operand().Evaluate(item, context)
	if e != nil {
		return nil, e
	}

	if item.Type() != value.NUMBER {
		return cumulative, nil
	}

	return setAdd(item, cumulative)
}

func (this *Order) Less(i, j int) bool {
	v1 := this.values[i]
	v2 := this.values[j]

	var ev1, ev2 value.Value
	var c int
	var e error

	for i, term := range this.plan.Terms() {
		s := strconv.Itoa(i)

		sv1 := v1.GetAttachment(s)
		switch sv1 := sv1.(type) {
		case value.Value:
			ev1 = sv1
		default:
			ev1, e = term.Expression().Evaluate(v1, this.context)
			if e != nil {
				this.context.Error(errors.NewError(e, "Error evaluating ORDER BY."))
				return false
			}

			v1.SetAttachment(s, ev1)
		}

		sv2 := v2.GetAttachment(s)
		switch sv2 := sv2.(type) {
		case value.Value:
			ev2 = sv2
		default:
			ev2, e = term.Expression().Evaluate(v2, this.context)
			if e != nil {
				this.context.Error(errors.NewError(e, "Error evaluating ORDER BY."))
				return false
			}

			v2.SetAttachment(s, ev2)
		}

		c = ev1.Collate(ev2)

		if c == 0 {
			continue
		} else if term.Descending() {
			return c > 0
		} else {
			return c < 0
		}
	}

	return false
}

/*
This method checks to see if the values of the two input
expressions are equal, and if true then returns a null
value. If not it returns the first input value. Use the
Equals method for the two values to determine equality.
*/
func (this *NullIf) Apply(context Context, first, second value.Value) (value.Value, error) {
	if first.Type() == value.MISSING || second.Type() == value.MISSING {
		return value.MISSING_VALUE, nil
	} else if first.Type() == value.NULL || second.Type() == value.NULL {
		return value.NULL_VALUE, nil
	}

	if first.Equals(second) {
		return value.NULL_VALUE, nil
	} else {
		return first, nil
	}
}

/*
Aggregates input data by evaluating operands. For all
values other than Number, return the input value itself. Call
cumulatePart to compute the intermediate aggregate value
and return it.
*/
func (this *Avg) CumulateInitial(item, cumulative value.Value, context Context) (value.Value, error) {
	item, e := this.Operand().Evaluate(item, context)
	if e != nil {
		return nil, e
	}

	if item.Type() != value.NUMBER {
		return cumulative, nil
	}

	part := value.NewValue(map[string]interface{}{"sum": item.Actual(), "count": 1})
	return this.cumulatePart(part, cumulative, context)
}

/*
Retrieve the set for annotated values. If the attachment type
is not a set, then throw an invalid distinct set error and
return.
*/
func getSet(item value.Value) (*value.Set, error) {
	switch item := item.(type) {
	case value.AnnotatedValue:
		ps := item.GetAttachment("set")
		switch ps := ps.(type) {
		case *value.Set:
			return ps, nil
		default:
			return nil, fmt.Errorf("Invalid DISTINCT set %v of type %T.", ps, ps)
		}
	default:
		return nil, fmt.Errorf("Invalid DISTINCT %v of type %T.", item, item)
	}
}

/*
Aggregates input data by evaluating operands. For missing and
null values return the input value itself. Call cumulatePart
to compute the intermediate aggregate value and return it.
*/
func (this *Count) CumulateInitial(item, cumulative value.Value, context Context) (value.Value, error) {
	if this.Operand() != nil {
		item, e := this.Operand().Evaluate(item, context)
		if e != nil {
			return nil, e
		}

		if item.Type() <= value.NULL {
			return cumulative, nil
		}
	}

	return this.cumulatePart(value.ONE_VALUE, cumulative, context)

}

/*
Aggregate input partial values into cumulative result number value.
If the partial and current cumulative result are both float64
numbers, add them and return.
*/
func (this *Count) cumulatePart(part, cumulative value.Value, context Context) (value.Value, error) {
	actual := part.Actual()
	switch actual := actual.(type) {
	case float64:
		count := cumulative.Actual()
		switch count := count.(type) {
		case float64:
			return value.NewValue(count + actual), nil
		default:
			return nil, fmt.Errorf("Invalid COUNT %v of type %T.", count, count)
		}
	default:
		return nil, fmt.Errorf("Invalid partial COUNT %v of type %T.", actual, actual)
	}
}

/*
Directly call the evaluate method for aggregate functions and
passe in the receiver, current item and current context, for
count with an input expression operand. For a count with no
operands (count (*)), get the count from the attachment and
then evaluate.
*/
func (this *Count) Evaluate(item value.Value, context expression.Context) (result value.Value, e error) {
	if this.Operand() != nil {
		return this.evaluate(this, item, context)
	}

	// Full keyspace count is short-circuited
	switch item := item.(type) {
	case value.AnnotatedValue:
		count := item.GetAttachment("count")
		if count != nil {
			return value.NewValue(count), nil
		}
	}

	return this.evaluate(this, item, context)
}

/*
IN evaluates to TRUE if the right-hand-side first value is an array
and directly contains the left-hand-side second value. If either
of the input operands are missing, return missing value, and
if the second is not an array return null. Range over the elements of the
array and check if any element is equal to the first value, return true.
For all other cases, return false.
*/
func (this *In) Apply(context Context, first, second value.Value) (value.Value, error) {
	if first.Type() == value.MISSING || second.Type() == value.MISSING {
		return value.MISSING_VALUE, nil
	} else if second.Type() != value.ARRAY {
		return value.NULL_VALUE, nil
	}

	sa := second.Actual().([]interface{})
	for _, s := range sa {
		if first.Equals(value.NewValue(s)) {
			return value.TRUE_VALUE, nil
		}
	}

	return value.FALSE_VALUE, nil
}