package api

import (
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"strings"
)

type Envelope[D any, M any] struct {
	Data     D `json:"data"`
	Metadata M `json:"metadata,omitempty"`
}

type None *struct{}

func (app *App) WriteJSON(w http.ResponseWriter, status int, data any, headers http.Header) error {

	js, err := json.MarshalIndent(data, "", "\t")

	if err != nil {
		return err
	}

	js = append(js, '\n')

	for key, value := range headers {
		w.Header()[key] = value
	}

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_, err = w.Write(js)

	if err != nil {
		return err
	}

	return nil
}

func (app *App) ReadJSON(w http.ResponseWriter, r *http.Request, dst any) error {

	maxBytes := 1_048_576
	r.Body = http.MaxBytesReader(w, r.Body, int64(maxBytes))

	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()

	err := dec.Decode(dst)

	if err != nil {
		var syntaxError *json.SyntaxError
		var unmarshalTypeError *json.UnmarshalTypeError
		var invalidUnmarshalError *json.InvalidUnmarshalError
		var maxBytesError *http.MaxBytesError

		switch {
		case errors.As(err, &syntaxError):
			return fmt.Errorf("body contains badly-formed JSON (at character %d)", syntaxError.Offset)

		case errors.Is(err, io.ErrUnexpectedEOF):
			return errors.New("body contains badly-formed JSON")

		case errors.As(err, &unmarshalTypeError):
			if unmarshalTypeError.Field != "" {
				return fmt.Errorf("body contains incorrect JSON type for field %q", unmarshalTypeError.Field)
			}
			return fmt.Errorf("body contains incorrect JSON type (at character %d)", unmarshalTypeError.Offset)

		case errors.Is(err, io.EOF):
			return errors.New("body must not be empty")

		case errors.As(err, &maxBytesError):
			return fmt.Errorf("body must not be larger than %d bytes", maxBytesError.Limit)

		case strings.HasPrefix(err.Error(), "json: unknown field "):
			fieldName := strings.TrimPrefix(err.Error(), "json: unknown field ")
			return fmt.Errorf("body contains unknown key %s", fieldName)

		case errors.As(err, &invalidUnmarshalError):
			panic(err)
		default:
			return err
		}
	}

	err = dec.Decode(&struct{}{})
	if !errors.Is(err, io.EOF) {
		return errors.New("body must only contain a single JSON value")
	}

	return nil
}

func ParseURLTemplate(tmpl string, params map[string]string) string {
	args := make([]string, len(params)*2)

	for k, v := range params {
		args = append(args, ":"+k, v)
	}

	r := strings.NewReplacer(args...)

	return r.Replace(tmpl)
}