Improvements to field generation (#137)

* Remove `no-embedded-types` flag

We don't use this.

* Use `fw-download.ubnt.com`

* Return firmware download URL from `latestUnifiVersion`

* Don't use version metadata

fields/fwupdate.go

@@ -0,0 +1,82 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/url"
+
+	"github.com/hashicorp/go-version"
+)
+
+var firmwareUpdateApi = "https://fw-update.ubnt.com/api/firmware-latest"
+
+const (
+	debianPlatform         = "debian"
+	releaseChannel         = "release"
+	unifiControllerProduct = "unifi-controller"
+)
+
+type firmwareUpdateApiResponse struct {
+	Embedded firmwareUpdateApiResponseEmbedded `json:"_embedded"`
+}
+
+type firmwareUpdateApiResponseEmbedded struct {
+	Firmware []firmwareUpdateApiResponseEmbeddedFirmware `json:"firmware"`
+}
+
+type firmwareUpdateApiResponseEmbeddedFirmware struct {
+	Channel  string                                         `json:"channel"`
+	Created  string                                         `json:"created"`
+	Id       string                                         `json:"id"`
+	Platform string                                         `json:"platform"`
+	Product  string                                         `json:"product"`
+	Version  *version.Version                               `json:"version"`
+	Links    firmwareUpdateApiResponseEmbeddedFirmwareLinks `json:"_links"`
+}
+
+type firmwareUpdateApiResponseEmbeddedFirmwareDataLink struct {
+	Href *url.URL `json:"href"`
+}
+
+func (l firmwareUpdateApiResponseEmbeddedFirmwareDataLink) MarshalJSON() ([]byte, error) {
+	var href string
+	if l.Href != nil {
+		href = l.Href.String()
+	}
+
+	aux := struct {
+		Href string `json:"href"`
+	}{
+		Href: href,
+	}
+
+	return json.Marshal(aux)
+}
+
+func (l *firmwareUpdateApiResponseEmbeddedFirmwareDataLink) UnmarshalJSON(j []byte) error {
+	var m map[string]interface{}
+
+	err := json.Unmarshal(j, &m)
+	if err != nil {
+		return err
+	}
+
+	if href := m["href"]; href != nil {
+		url, err := url.Parse(href.(string))
+		if err != nil {
+			return err
+		}
+
+		l.Href = url
+	}
+
+	return nil
+}
+
+type firmwareUpdateApiResponseEmbeddedFirmwareLinks struct {
+	Data firmwareUpdateApiResponseEmbeddedFirmwareDataLink `json:"data"`
+}
+
+func firmwareUpdateApiFilter(key, value string) string {
+	return fmt.Sprintf("%s~~%s~~%s", "eq", key, value)
+}