package hal

import (
	"encoding/json"

	"github.com/raff/halgo"
)

// Resource is a simple HAL resource envelope that uses halgo.Link for links.
type Resource struct {
	Links    map[string]halgo.Link  `json:"_links,omitempty"`
	Embedded map[string]interface{} `json:"_embedded,omitempty"`
	// State holds arbitrary resource state merged at top-level when marshaled
	State map[string]interface{} `json:"-"`
}

// New creates a new HAL resource with a self link.
func New(selfHref string) *Resource {
	r := &Resource{
		Links:    map[string]halgo.Link{},
		Embedded: map[string]interface{}{},
		State:    map[string]interface{}{},
	}
	if selfHref != "" {
		r.AddLink("self", halgo.Link{Href: selfHref})
	}
	return r
}

// AddLink adds a link with the given rel.
func (r *Resource) AddLink(rel string, link halgo.Link) {
	if r.Links == nil {
		r.Links = map[string]halgo.Link{}
	}
	r.Links[rel] = link
}

// AddCurie adds a CURIE link for the sakila namespace.
// Note: HAL recommends an array for the "curies" rel. This implementation uses a single link
// due to the underlying link map being single-valued per rel. Most clients accept this form.
func (r *Resource) AddCurie() {
	r.AddLink("curies", halgo.Link{
		Href:      "/rels/{rel}",
		Templated: true,
		Name:      "sakila",
	})
}

// Embed sets an embedded payload under the rel.
func (r *Resource) Embed(rel string, v interface{}) {
	if r.Embedded == nil {
		r.Embedded = map[string]interface{}{}
	}
	r.Embedded[rel] = v
}

// SetState sets or merges state fields.
func (r *Resource) SetState(obj interface{}) {
	switch m := obj.(type) {
	case map[string]interface{}:
		for k, v := range m {
			r.State[k] = v
		}
	default:
		// marshal into map and merge
		b, _ := json.Marshal(obj)
		var mm map[string]interface{}
		_ = json.Unmarshal(b, &mm)
		for k, v := range mm {
			r.State[k] = v
		}
	}
}

// MarshalJSON merges State with _links and _embedded following HAL conventions.
func (r *Resource) MarshalJSON() ([]byte, error) {
	m := map[string]interface{}{}
	for k, v := range r.State {
		m[k] = v
	}
	if len(r.Links) > 0 {
		m["_links"] = r.Links
	}
	if len(r.Embedded) > 0 {
		m["_embedded"] = r.Embedded
	}
	return json.Marshal(m)
}