middleware/paginate/paginate.go

package paginate

import (
	"context"
	"errors"
	"net/http"
	"strconv"

	"go.pkg.cx/middleware"
)

// Errors
var (
	ErrPaginationDefaults = errors.New("pagination defaults are nil")
)

// Context keys
var (
	PaginationCtxKey = &middleware.CtxKey{Pkg: "go.pkg.cx/middleware/paginate", Name: "Pagination"}
)

// DefaultOptions represents default paginate middleware options
var DefaultOptions = Options(
	WithFindPaginationFn(PaginationFromQuery("page", "pageSize")),
	SetPaginationDefaults(1, 50),
	SetValidatePaginationFn(allowAll),
	SetResponseHandler(RespondWithBadRequest),
)

// Pagination represents pagination info
type Pagination struct {
	Page     int
	PageSize int
}

// Options turns a list of option instances into an option
func Options(opts ...Option) Option {
	return func(p *paginate) {
		for _, opt := range opts {
			opt(p)
		}
	}
}

// Option configures paginate middleware
type Option func(p *paginate)

// WithFindPaginationFn adds pagination find function to the list
func WithFindPaginationFn(fn func(r *http.Request, p *Pagination) *Pagination) Option {
	return func(p *paginate) {
		p.findPaginationFns = append(p.findPaginationFns, fn)
	}
}

// SetFindPaginationFns sets pagination find functions list
func SetFindPaginationFns(fns ...func(r *http.Request, p *Pagination) *Pagination) Option {
	return func(p *paginate) {
		p.findPaginationFns = fns
	}
}

// SetPaginationDefaults sets pagination defaults function
func SetPaginationDefaults(page int, pageSize int) Option {
	return func(p *paginate) {
		p.paginationDefaultsFn = func() *Pagination {
			return &Pagination{Page: page, PageSize: pageSize}
		}
	}
}

// SetValidatePaginationFn sets pagination validation function
func SetValidatePaginationFn(fn func(p *Pagination) error) Option {
	return func(p *paginate) {
		p.validatePaginationFn = fn
	}
}

// SetResponseHandler sets response handler
func SetResponseHandler(fn middleware.ResponseHandle) Option {
	return func(p *paginate) {
		p.responseHandler = fn
	}
}

type paginate struct {
	findPaginationFns    []func(r *http.Request, p *Pagination) *Pagination
	paginationDefaultsFn func() *Pagination
	validatePaginationFn func(p *Pagination) error
	responseHandler      middleware.ResponseHandle
}

// Middleware returns paginate middleware
func Middleware(opts ...Option) func(next http.Handler) http.Handler {
	p := &paginate{}
	opts = append([]Option{DefaultOptions}, opts...)

	for _, opt := range opts {
		opt(p)
	}

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			pagination := p.paginationDefaultsFn()
			if pagination == nil {
				p.responseHandler(w, r, ErrPaginationDefaults)
				return
			}

			for _, fn := range p.findPaginationFns {
				if nextPagination := fn(r, pagination); nextPagination != nil {
					pagination = nextPagination
				}
			}

			if err := p.validatePaginationFn(pagination); err != nil {
				p.responseHandler(w, r, err)
				return
			}

			ctx := r.Context()
			ctx = context.WithValue(ctx, PaginationCtxKey, pagination)

			next.ServeHTTP(w, r.WithContext(ctx))
		})
	}
}

// PaginationFromContext returns pagination from context
func PaginationFromContext(ctx context.Context) *Pagination {
	if pagination, ok := ctx.Value(PaginationCtxKey).(*Pagination); ok {
		return pagination
	}

	return nil
}

// PaginationFromQuery returns pagination from query params
func PaginationFromQuery(pageParam string, pageSizeParam string) func(r *http.Request, p *Pagination) *Pagination {
	return func(r *http.Request, p *Pagination) *Pagination {
		if page, err := strconv.Atoi(r.URL.Query().Get(pageParam)); err == nil {
			p.Page = page
		}

		if pageSize, err := strconv.Atoi(r.URL.Query().Get(pageSizeParam)); err == nil {
			p.PageSize = pageSize
		}

		return p
	}
}

// RespondWithBadRequest is a default response handler
func RespondWithBadRequest(w http.ResponseWriter, _ *http.Request, _ error) {
	http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
}

func allowAll(_ *Pagination) error {
	return nil
}