// Package redirect is middleware for redirecting certain requests
// to other locations.
package redirect

import (
	"net/http"
	"strings"

	"github.com/mholt/caddy/middleware"
)

// New instantiates a new Redirect middleware.
func New(c middleware.Controller) (middleware.Middleware, error) {
	rules, err := parse(c)
	if err != nil {
		return nil, err
	}

	return func(next middleware.Handler) middleware.Handler {
		return Redirect{Next: next, Rules: rules}
	}, nil
}

// Redirect is middleware to respond with HTTP redirects
type Redirect struct {
	Next  middleware.Handler
	Rules []Rule
}

// ServeHTTP implements the middleware.Handler interface.
func (rd Redirect) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
	for _, rule := range rd.Rules {
		if rule.From == "/" {
			// Catchall redirect preserves path (TODO: Standardize/formalize this behavior)
			http.Redirect(w, r, strings.TrimSuffix(rule.To, "/")+r.URL.Path, rule.Code)
			return 0, nil
		}
		if r.URL.Path == rule.From {
			http.Redirect(w, r, rule.To, rule.Code)
			return 0, nil
		}
	}
	return rd.Next.ServeHTTP(w, r)
}

func parse(c middleware.Controller) ([]Rule, error) {
	var redirects []Rule

	for c.Next() {
		var rule Rule
		args := c.RemainingArgs()

		switch len(args) {
		case 1:
			// To specified
			rule.From = "/"
			rule.To = args[0]
			rule.Code = http.StatusMovedPermanently
		case 2:
			// To and Code specified
			rule.From = "/"
			rule.To = args[0]
			if code, ok := httpRedirs[args[1]]; !ok {
				return redirects, c.Err("Invalid redirect code '" + args[1] + "'")
			} else {
				rule.Code = code
			}
		case 3:
			// From, To, and Code specified
			rule.From = args[0]
			rule.To = args[1]
			if code, ok := httpRedirs[args[2]]; !ok {
				return redirects, c.Err("Invalid redirect code '" + args[2] + "'")
			} else {
				rule.Code = code
			}
		default:
			return redirects, c.ArgErr()
		}

		if rule.From == rule.To {
			return redirects, c.Err("Redirect rule cannot allow From and To arguments to be the same.")
		}

		redirects = append(redirects, rule)
	}

	return redirects, nil
}

// Rule describes an HTTP redirect rule.
type Rule struct {
	From, To string
	Code     int
}

// httpRedirs is a list of supported HTTP redirect codes.
var httpRedirs = map[string]int{
	"300": 300,
	"301": 301,
	"302": 302,
	"303": 303,
	"304": 304,
	"305": 305,
	"307": 307,
	"308": 308,
}