// Copyright 2020 CUE Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package adt

// Default returns the default value or itself if there is no default.
func Default(v Value) Value {
	switch x := v.(type) {
	case *Vertex:
		return x.Default()
	case *Disjunction:
		return x.Default()
	default:
		return v
	}
}

func (d *Disjunction) Default() Value {
	switch d.NumDefaults {
	case 0:
		return d
	case 1:
		return d.Values[0]
	default:
		return &Disjunction{
			Src:         d.Src,
			Values:      d.Values[:d.NumDefaults],
			NumDefaults: 0,
		}
	}
}

// Default returns the default value or itself if there is no default.
func (v *Vertex) Default() *Vertex {
	d, ok := v.Value.(*Disjunction)
	if !ok {
		return v
	}

	var w *Vertex

	switch d.NumDefaults {
	case 0:
		return v
	case 1:
		w = d.Values[0]
	default:
		x := *v
		x.Value = &Disjunction{
			Src:         d.Src,
			Values:      d.Values[:d.NumDefaults],
			NumDefaults: 0,
		}
		w = &x
	}

	w.Conjuncts = nil
	for _, c := range v.Conjuncts {
		// TODO: preserve field information.
		expr, _ := stripNonDefaults(c.Expr())
		w.AddConjunct(MakeConjunct(c.Env, expr))
	}
	return w
}

// TODO: this should go: record preexpanded disjunctions in Vertex.
func stripNonDefaults(expr Expr) (r Expr, stripped bool) {
	switch x := expr.(type) {
	case *DisjunctionExpr:
		if !x.HasDefaults {
			return x, false
		}
		d := *x
		d.Values = []Disjunct{}
		for _, v := range x.Values {
			if v.Default {
				d.Values = append(d.Values, v)
			}
		}
		if len(d.Values) == 1 {
			return d.Values[0].Val, true
		}
		return &d, true

	case *BinaryExpr:
		if x.Op != AndOp {
			return x, false
		}
		a, sa := stripNonDefaults(x.X)
		b, sb := stripNonDefaults(x.Y)
		if sa || sb {
			bin := *x
			bin.X = a
			bin.Y = b
			return &bin, true
		}
		return x, false

	default:
		return x, false
	}
}