package web

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

const defaultCollectionPageSize = 20

type paginationData struct {
	Page        int
	TotalPages  int
	PreviousURL string
	NextURL     string
}

func paginateCollection[T any](r *http.Request, values []T) ([]T, *paginationData) {
	pageSize := collectionPageSize(r)
	totalPages := (len(values) + pageSize - 1) / pageSize
	if totalPages <= 1 {
		return values, nil
	}

	page, _ := strconv.Atoi(r.URL.Query().Get("page"))
	if page < 1 {
		page = 1
	}
	if page > totalPages {
		page = totalPages
	}
	start := (page - 1) * pageSize
	end := min(start+pageSize, len(values))
	pagination := &paginationData{Page: page, TotalPages: totalPages}
	if page > 1 {
		pagination.PreviousURL = collectionPageURL(r.URL, page-1)
	}
	if page < totalPages {
		pagination.NextURL = collectionPageURL(r.URL, page+1)
	}
	return values[start:end], pagination
}

func collectionPageSize(r *http.Request) int {
	userSuffix := ""
	if user, ok := userFromContext(r.Context()); ok {
		userSuffix = "." + strconv.Itoa(user.ID)
	}
	for _, cookieName := range []string{"gardomatic.entries-per-page" + userSuffix, "gardomatic.tasks-per-page" + userSuffix} {
		cookie, err := r.Cookie(cookieName)
		if err != nil {
			continue
		}
		pageSize, err := strconv.Atoi(cookie.Value)
		if err == nil && validCollectionPageSize(pageSize) {
			return pageSize
		}
	}
	return defaultCollectionPageSize
}

func validCollectionPageSize(pageSize int) bool {
	switch pageSize {
	case 10, 20, 50, 100:
		return true
	default:
		return false
	}
}

func collectionPageURL(current *url.URL, page int) string {
	query := current.Query()
	query.Set("page", strconv.Itoa(page))
	path := current.Path
	if path == "" {
		path = "?"
	} else {
		path += "?"
	}
	return path + query.Encode()
}