package behavior

import (
	"fmt"

	"gopkg.in/yaml.v3"
)

// DescVariant is one alternative description, optionally gated by a condition.
type DescVariant struct {
	Text      string     `yaml:"text"`
	Condition *Condition `yaml:"condition,omitempty"`
}

// DescList is an ordered list of description variants. The first variant whose
// condition matches is shown.
//
// Content may author the common single, unconditional description two ways:
// as a bare scalar (`description: "A dark room."`) or as a list of variants
// (`description: [{text: "A dark room."}]`). MarshalYAML collapses a single
// unconditional variant back to the scalar form so machine-written room files
// stay close to what a human would type.
type DescList []DescVariant

func (d *DescList) UnmarshalYAML(value *yaml.Node) error {
	switch value.Kind {
	case yaml.ScalarNode:
		var text string
		if err := value.Decode(&text); err != nil {
			return err
		}
		if text == "" {
			*d = nil
			return nil
		}
		*d = DescList{{Text: text}}
		return nil
	case yaml.SequenceNode:
		out := make(DescList, 0, len(value.Content))
		for _, item := range value.Content {
			// Accept a bare string element as shorthand for a variant.
			if item.Kind == yaml.ScalarNode {
				var text string
				if err := item.Decode(&text); err != nil {
					return err
				}
				out = append(out, DescVariant{Text: text})
				continue
			}
			var variant DescVariant
			if err := item.Decode(&variant); err != nil {
				return err
			}
			out = append(out, variant)
		}
		*d = out
		return nil
	case yaml.AliasNode:
		return d.UnmarshalYAML(value.Alias)
	case 0:
		// An omitted/zero node leaves the list empty.
		*d = nil
		return nil
	default:
		return fmt.Errorf("description must be a string or a list of variants")
	}
}

func (d DescList) MarshalYAML() (any, error) {
	if len(d) == 0 {
		return []DescVariant{}, nil
	}
	if len(d) == 1 && d[0].Condition == nil {
		return d[0].Text, nil
	}
	return []DescVariant(d), nil
}