/*
Copyright © 2025 filifa

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package markov

import (
	"errors"
	"strconv"

	"gonum.org/v1/gonum/graph"
	"gonum.org/v1/gonum/graph/encoding"
	"gonum.org/v1/gonum/graph/multi"
)

// Node is a DOT-aware graph.Node.
type Node struct {
	graph.Node
	dotID string
}

// SetDOTID sets the node's DOT ID. It enables storing the node name read from
// a DOT file.
func (n *Node) SetDOTID(id string) {
	n.dotID = id
}

// DOTID returns the node's DOT ID.
func (n *Node) DOTID() string {
	return n.dotID
}

// weightedEdge is a DOT-aware multi.WeightedLine. By being a
// multi.WeightedLine, it allows for self-loops, which are important for
// absorbing Markov chains.
// TODO: this is a little confusing, maybe just have checks in the code that
// there's only one line in each edge?
type weightedEdge struct {
	multi.WeightedLine
}

// ReversedEdge returns a new weightedEdge with the same weight, but the
// direction reversed. It exists mainly to satisfy the graph.Edge interface.
func (e *weightedEdge) ReversedEdge() graph.Edge {
	revLine := multi.WeightedLine{F: e.T, T: e.F, W: e.W}
	return &weightedEdge{WeightedLine: revLine}
}

// SetAttribute enables storing the weight read from a DOT file. It errors if
// an attribute is read that can't be stored in a weightedEdge.
func (e *weightedEdge) SetAttribute(attr encoding.Attribute) error {
	var err error

	switch attr.Key {
	case "weight":
		e.W, err = strconv.ParseFloat(attr.Value, 64)
	default:
		err = errors.New("unknown key:" + attr.Key)
	}

	return err
}