package gus

import (
	"context"
	"crypto/tls"
	"net/url"
	"strings"

	"tildegit.org/tjp/gus/internal"
)

// Router stores a mapping of request path patterns to handlers.
//
// Pattern may begin with "/" and then contain slash-delimited segments.
//   - Segments beginning with colon (:) are wildcards and will match any path
//     segment at that location. It may optionally have a word after the colon,
//     which will be the parameter name the path segment is captured into.
//   - Segments beginning with asterisk (*) are remainder wildcards. This must
//     come last and will capture any remainder of the path. It may have a name
//     after the asterisk which will be the parameter name.
//   - Any other segment in the pattern must match a path segment exactly.
//
// These patterns do not match any path which shares a prefix, rather then
// full path must match a pattern. If you want to only match a prefix of the
// path you can end the pattern with a *remainder segment.
//
// The zero value is a usable Router which will fail to match any requst path.
type Router struct {
	tree internal.PathTree[Handler]
}

// Route adds a handler to the router under a path pattern.
func (r Router) Route(pattern string, handler Handler) {
	r.tree.Add(pattern, handler)
}

// Handler matches against the request path and dipatches to a route handler.
//
// If no route matches, it returns a nil response.
// Captured path parameters will be stored in the context passed into the handler
// and can be retrieved with RouteParams().
func (r Router) Handler(ctx context.Context, request *Request) *Response {
	handler, params := r.Match(request)
	if handler == nil {
		return nil
	}

	// as we may be a sub-router, check for existing stashed params
	// and combine with that map if found.
	priorParams := RouteParams(ctx)
	for k, v := range priorParams {
		if k == subrouterPathKey {
			continue
		}
		params[k] = v
	}

	return handler(context.WithValue(ctx, routeParamsKey, params), request)
}

// Match returns the matched handler and captured path parameters, or nils.
func (r Router) Match(request *Request) (Handler, map[string]string) {
	handler, params := r.tree.Match(request.Path)
	if handler == nil {
		return nil, nil
	}
	return *handler, params
}

// Mount attaches a sub-router to handle path suffixes after an initial prefix pattern.
//
// The prefix pattern may include segment :wildcards, but no *remainder segment. The
// mounted sub-router should have patterns which only include the portion of the path
// after whatever was matched by the prefix pattern.
func (r Router) Mount(prefix string, subrouter *Router) {
	prefix = strings.TrimSuffix(prefix, "/")
	r.Route(prefix+"/*"+subrouterPathKey, func(ctx context.Context, request *Request) *Response {
		r := cloneRequest(request)
		r.Path = "/" + RouteParams(ctx)[subrouterPathKey]
		return subrouter.Handler(ctx, r)
	})

	// TODO: better approach. the above works but it's a little hacky
	//   - add a method to PathTree that returns all the registered patterns
	//     and their associated handlers
	//   - have Mount pull those out of the subrouter, prepend the prefix to
	//     all its patterns, and re-add them to the parent router.
}

// RouteParams gathers captured path parameters from the request context.
//
// If the context doesn't contain a parameter map, it returns nil.
// If Router was used but no parameters were captured in the pattern, it
// returns a non-nil empty map.
func RouteParams(ctx context.Context) map[string]string {
	if m, ok := ctx.Value(routeParamsKey).(map[string]string); ok {
		return m
	}
	return nil
}

const subrouterPathKey = "subrouter_path"

type routeParamsKeyType struct{}

var routeParamsKey = routeParamsKeyType{}

func cloneRequest(start *Request) *Request {
	end := &Request{}
	*end = *start

	end.URL = &url.URL{}
	*end.URL = *start.URL

	if start.TLSState != nil {
		end.TLSState = &tls.ConnectionState{}
		*end.TLSState = *start.TLSState
	}

	return end
}