package main

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

	"github.com/julienschmidt/httprouter"
)

type envelope map[string]any

func (app *application) readJSON(w http.ResponseWriter, r *http.Request, dest any) error {
	maxBytes := 1_048_576
	r.Body = http.MaxBytesReader(w, r.Body, int64(maxBytes))

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

	err := decoder.Decode(dest)

	if err != nil {
		var syntaxError *json.SyntaxError
		var unmarshallError *json.UnmarshalTypeError
		var invalidUnmarshall *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, &unmarshallError):
			if unmarshallError.Field != "" {
				return fmt.Errorf("the body contains incorrect json type for field %q", unmarshallError.Field)
			}
			return fmt.Errorf("body contains incorrect JSON type (at character %d)", unmarshallError.Offset)

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

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

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

		case errors.As(err, &invalidUnmarshall):
			panic(err)

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

	return nil // no errors
}

func (app *application) readIDParam(r *http.Request) (int64, error) {
	params := httprouter.ParamsFromContext(r.Context())

	id, err := strconv.ParseInt(params.ByName("id"), 10, 64)
	if err != nil || id < 1 {
		return 0, errors.New("invalid id parameter")
	}

	return id, nil
}

func (app *application) writeJSON(w http.ResponseWriter, status int, data any, headers http.Header) error {
	js, err := json.Marshal(data)
	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)
	w.Write(js)

	return nil
}