glance/internal/glance/widget-custom-api.go

package glance

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"html/template"
	"io"
	"log/slog"
	"net/http"
	"time"

	"github.com/tidwall/gjson"
)

var customAPIWidgetTemplate = mustParseTemplate("custom-api.html", "widget-base.html")

type customAPIWidget struct {
	widgetBase       `yaml:",inline"`
	URL              string             `yaml:"url"`
	Template         string             `yaml:"template"`
	Frameless        bool               `yaml:"frameless"`
	Headers          map[string]string  `yaml:"headers"`
	APIRequest       *http.Request      `yaml:"-"`
	compiledTemplate *template.Template `yaml:"-"`
	CompiledHTML     template.HTML      `yaml:"-"`
}

func (widget *customAPIWidget) initialize() error {
	widget.withTitle("Custom API").withCacheDuration(1 * time.Hour)

	if widget.URL == "" {
		return errors.New("URL is required")
	}

	if widget.Template == "" {
		return errors.New("template is required")
	}

	compiledTemplate, err := template.New("").Funcs(customAPITemplateFuncs).Parse(widget.Template)
	if err != nil {
		return fmt.Errorf("parsing template: %w", err)
	}

	widget.compiledTemplate = compiledTemplate

	req, err := http.NewRequest(http.MethodGet, widget.URL, nil)
	if err != nil {
		return err
	}

	for key, value := range widget.Headers {
		req.Header.Add(key, value)
	}

	widget.APIRequest = req

	return nil
}

func (widget *customAPIWidget) update(ctx context.Context) {
	compiledHTML, err := fetchAndParseCustomAPI(widget.APIRequest, widget.compiledTemplate)
	if !widget.canContinueUpdateAfterHandlingErr(err) {
		return
	}

	widget.CompiledHTML = compiledHTML
}

func (widget *customAPIWidget) Render() template.HTML {
	return widget.renderTemplate(widget, customAPIWidgetTemplate)
}

func fetchAndParseCustomAPI(req *http.Request, tmpl *template.Template) (template.HTML, error) {
	emptyBody := template.HTML("")

	resp, err := defaultHTTPClient.Do(req)
	if err != nil {
		return emptyBody, err
	}
	defer resp.Body.Close()

	bodyBytes, err := io.ReadAll(resp.Body)
	if err != nil {
		return emptyBody, err
	}

	body := string(bodyBytes)

	if !gjson.Valid(body) {
		truncatedBody, isTruncated := limitStringLength(body, 100)
		if isTruncated {
			truncatedBody += "... <truncated>"
		}

		slog.Error("Invalid response JSON in custom API widget", "url", req.URL.String(), "body", truncatedBody)
		return emptyBody, errors.New("invalid response JSON")
	}

	var templateBuffer bytes.Buffer

	data := CustomAPITemplateData{
		JSON:     decoratedGJSONResult{gjson.Parse(body)},
		Response: resp,
	}

	err = tmpl.Execute(&templateBuffer, &data)
	if err != nil {
		return emptyBody, err
	}

	return template.HTML(templateBuffer.String()), nil
}

type decoratedGJSONResult struct {
	gjson.Result
}

type CustomAPITemplateData struct {
	JSON     decoratedGJSONResult
	Response *http.Response
}

func gJsonResultArrayToDecoratedResultArray(results []gjson.Result) []decoratedGJSONResult {
	decoratedResults := make([]decoratedGJSONResult, len(results))

	for i, result := range results {
		decoratedResults[i] = decoratedGJSONResult{result}
	}

	return decoratedResults
}

func (r *decoratedGJSONResult) Array(key string) []decoratedGJSONResult {
	if key == "" {
		return gJsonResultArrayToDecoratedResultArray(r.Result.Array())
	}

	return gJsonResultArrayToDecoratedResultArray(r.Get(key).Array())
}

func (r *decoratedGJSONResult) String(key string) string {
	if key == "" {
		return r.Result.String()
	}

	return r.Get(key).String()
}

func (r *decoratedGJSONResult) Int(key string) int64 {
	if key == "" {
		return r.Result.Int()
	}

	return r.Get(key).Int()
}

func (r *decoratedGJSONResult) Float(key string) float64 {
	if key == "" {
		return r.Result.Float()
	}

	return r.Get(key).Float()
}

func (r *decoratedGJSONResult) Bool(key string) bool {
	if key == "" {
		return r.Result.Bool()
	}

	return r.Get(key).Bool()
}

var customAPITemplateFuncs = func() template.FuncMap {
	funcs := template.FuncMap{
		"toFloat": func(a int64) float64 {
			return float64(a)
		},
		"toInt": func(a float64) int64 {
			return int64(a)
		},
		"mathexpr": func(left float64, op string, right float64) float64 {
			if right == 0 {
				return 0
			}

			switch op {
			case "+":
				return left + right
			case "-":
				return left - right
			case "*":
				return left * right
			case "/":
				return left / right
			default:
				return 0
			}
		},
	}

	for key, value := range globalTemplateFunctions {
		funcs[key] = value
	}

	return funcs
}()