// Copyright 2021 Harness Inc. All rights reserved.
// Use of this source code is governed by the Polyform Free Trial License
// that can be found in the LICENSE.md file for this repository.

package render

import (
	"fmt"
	"net/http"
	"strconv"
)

// format string for the link header value.
var linkf = `<%s>; rel="%s"`

// Pagination writes the pagination and link headers
// to the http.Response.
func Pagination(r *http.Request, w http.ResponseWriter, page, size, total int) {
	var (
		last = pagelen(size, total)
		next = min(page+1, last)
		prev = max(page-1, 1)
	)

	uri := *r.URL

	// parse the existing query parameters and
	// sanize parameter list.
	params := uri.Query()
	params.Del("access_token")
	params.Del("token")
	params.Set("page", strconv.Itoa(page))
	params.Set("per_page", strconv.Itoa(size))

	w.Header().Set("x-page", strconv.Itoa(page))
	w.Header().Set("x-per-page", strconv.Itoa(size))

	if page != last {
		// update the page query parameter and re-encode
		params.Set("page", strconv.Itoa(next))
		uri.RawQuery = params.Encode()

		// write the next page to the header.
		w.Header().Set("x-next-page", strconv.Itoa(next))
		w.Header().Add("Link", fmt.Sprintf(linkf, uri.String(), "next"))
	}

	if page > 1 {
		// update the page query parameter and re-encode.
		params.Set("page", strconv.Itoa(prev))
		uri.RawQuery = params.Encode()

		// write the previous page to the header.
		w.Header().Set("x-prev-page", strconv.Itoa(prev))
		w.Header().Add("Link", fmt.Sprintf(linkf, uri.String(), "prev"))
	}

	{
		// update the page query parameter and re-encode
		params.Set("page", strconv.Itoa(last))
		uri.RawQuery = params.Encode()

		// write the page total to the header.
		w.Header().Set("x-total", strconv.Itoa(total))
		w.Header().Set("x-total-pages", strconv.Itoa(last))
		w.Header().Add("Link", fmt.Sprintf(linkf, uri.String(), "last"))
	}
}