package chain

import "net/http"

type (
	Chain interface {
		Append(middleware ...Middleware) Chain
		Prepend(middleware ...Middleware) Chain
		Then(http.Handler) http.Handler
		ThenFunc(fn http.HandlerFunc) http.Handler
	}
	Middleware func(http.Handler) http.Handler
	chain      struct {
		middlewares []Middleware
	}
)

func New(middlewares ...Middleware) Chain {
	return chain{
		middlewares: append([]Middleware(nil), middlewares...),
	}
}

func (c chain) Append(middleware ...Middleware) Chain {
	return chain{
		middlewares: join(c.middlewares, middleware),
	}
}

func (c chain) Prepend(middleware ...Middleware) Chain {
	return chain{
		middlewares: join(middleware, c.middlewares),
	}
}

func (c chain) Then(h http.Handler) http.Handler {
	if h == nil {
		h = http.DefaultServeMux
	}
	for i := range c.middlewares {
		h = c.middlewares[len(c.middlewares)-i-1](h)
	}
	return h
}

func (c chain) ThenFunc(fn http.HandlerFunc) http.Handler {
	if fn == nil {
		return c.Then(nil)
	}
	return c.Then(fn)
}
func join(a, b []Middleware) []Middleware {
	mids := make([]Middleware, 0, len(a)+len(b))
	mids = append(mids, a...)
	mids = append(mids, b...)
	return mids
}