package main

import (
	"errors"
	"github.com/julienschmidt/httprouter"
	"net/http"
	"strconv"
)

/*
Note: The readIDParam() method doesn't use any dependencies from our
application struct so it could just be a regular function, rather than a method on
application. But in general, I suggest setting up all your application-specific handlers
and helpers so that they are methods on application. It helps maintain consistency in
your code structure, and also future-proofs your code for when those handlers and
helpers change later and they do need access to dependency.

Retrieve the "id" URL parameter from the current request context, then convert it to
an integer and return it. If the operation isn't successful, return 0 and an error.
*/
func (app *application) readIDParam(r *http.Request) (int64, error) {
	/*
		When httprouter is parsing a request, any interpolated URL parameters will be
		stored in the request context. We can use the ParamsFromContext() function to
		retrieve a slice containing these parameter names and values.
	*/
	params := httprouter.ParamsFromContext(r.Context())

	/*
		We can then use the ByName() method to get the value of the "id" parameter from
		the slice. In our project all movies will have a unique positive integer ID, but
		the value returned by ByName() is always a string. So we try to convert it to a
		base 10 integer (with a bit size of 64). If the parameter couldn't be converted,
		or is less than 1, we know the ID is invalid so we use the http.NotFound()
		func to return a 404 Not Found Response.
	*/
	id, err := strconv.ParseInt(params.ByName("id"), 10, 64)
	if err != nil || id < 1 {
		return 0, errors.New("invalid id parameter")
	}

	return id, nil
}