Router/router.go

package router

import (
	"fmt"
)

// Handler processes HTTP requests with optional path parameters.
type Handler func(params []string)

// node represents a segment in the URL path and its handling logic.
type node struct {
	segment    string  // the path segment this node matches
	handler    Handler // handler for this path, if it's an endpoint
	children   []*node // child nodes for subsequent path segments
	isDynamic  bool    // true for param segments like [id]
	isWildcard bool    // true for catch-all segments like *filepath
	maxParams  uint8   // maximum number of parameters in paths under this node
}

// Router routes HTTP requests by method and path.
// It supports static paths, path parameters, and wildcards.
type Router struct {
	get    *node
	post   *node
	put    *node
	patch  *node
	delete *node
}

// New creates a new Router instance.
func New() *Router {
	return &Router{
		get:    &node{},
		post:   &node{},
		put:    &node{},
		patch:  &node{},
		delete: &node{},
	}
}

// HTTP method registration functions
// Routes can contain static segments (/users), parameters ([id]), and wildcards (*filepath)

// Get registers a handler for GET requests at the given path.
func (r *Router) Get(path string, handler Handler) error {
	return r.addRoute(r.get, path, handler)
}

// Post registers a handler for POST requests at the given path.
func (r *Router) Post(path string, handler Handler) error {
	return r.addRoute(r.post, path, handler)
}

// Put registers a handler for PUT requests at the given path.
func (r *Router) Put(path string, handler Handler) error {
	return r.addRoute(r.put, path, handler)
}

// Patch registers a handler for PATCH requests at the given path.
func (r *Router) Patch(path string, handler Handler) error {
	return r.addRoute(r.patch, path, handler)
}

// Delete registers a handler for DELETE requests at the given path.
func (r *Router) Delete(path string, handler Handler) error {
	return r.addRoute(r.delete, path, handler)
}

// readSegment extracts the next path segment starting at the given position.
// Returns the segment, the position after it, and whether there are more segments.
func readSegment(path string, start int) (segment string, end int, hasMore bool) {
	if start >= len(path) {
		return "", start, false
	}

	if path[start] == '/' {
		start++
	}

	if start >= len(path) {
		return "", start, false
	}

	end = start
	for end < len(path) && path[end] != '/' {
		end++
	}

	return path[start:end], end, end < len(path)
}

// addRoute adds a new route to the prefix tree.
// It validates wildcard positions and tracks parameter counts.
func (r *Router) addRoute(root *node, path string, handler Handler) error {
	if path == "/" {
		root.handler = handler
		return nil
	}

	current := root
	pos := 0
	var lastWildcard bool
	paramsCount := uint8(0)

	for {
		segment, newPos, hasMore := readSegment(path, pos)
		if segment == "" {
			break
		}

		isDynamic := len(segment) > 2 && segment[0] == '[' && segment[len(segment)-1] == ']'
		isWildcard := len(segment) > 0 && segment[0] == '*'

		if isWildcard {
			if lastWildcard {
				return fmt.Errorf("wildcard must be the last segment in the path")
			}
			if hasMore {
				return fmt.Errorf("wildcard must be the last segment in the path")
			}
			lastWildcard = true
		}

		if isDynamic || isWildcard {
			paramsCount++
		}

		var child *node
		for _, n := range current.children {
			if n.segment == segment {
				child = n
				break
			}
		}

		if child == nil {
			child = &node{
				segment:    segment,
				isDynamic:  isDynamic,
				isWildcard: isWildcard,
			}
			current.children = append(current.children, child)
		}

		if child.maxParams < paramsCount {
			child.maxParams = paramsCount
		}
		current = child
		pos = newPos
	}

	current.handler = handler
	return nil
}

// Lookup finds a handler matching the given method and path.
// Returns the handler, any captured parameters, and whether a match was found.
func (r *Router) Lookup(method, path string) (Handler, []string, bool) {
	var root *node
	switch method {
	case "GET":
		root = r.get
	case "POST":
		root = r.post
	case "PUT":
		root = r.put
	case "PATCH":
		root = r.patch
	case "DELETE":
		root = r.delete
	default:
		return nil, nil, false
	}

	if path == "/" {
		return root.handler, nil, root.handler != nil
	}

	params := make([]string, 0, root.maxParams)
	h, found := match(root, path, 0, &params)
	if !found {
		return nil, nil, false
	}
	return h, params, true
}

// match recursively traverses the prefix tree to find a matching handler.
// It populates params with any captured path parameters or wildcard matches.
func match(current *node, path string, start int, params *[]string) (Handler, bool) {
	// Check for wildcard children first
	for _, child := range current.children {
		if child.isWildcard {
			remaining := path[start:]
			if len(remaining) > 0 && remaining[0] == '/' {
				remaining = remaining[1:]
			}
			*params = append(*params, remaining)
			return child.handler, child.handler != nil
		}
	}

	// Read current segment
	segment, pos, hasMore := readSegment(path, start)
	if segment == "" {
		return current.handler, current.handler != nil
	}

	// Try to match children
	for _, child := range current.children {
		if child.segment == segment || child.isDynamic {
			if child.isDynamic {
				*params = append(*params, segment)
			}
			if !hasMore {
				return child.handler, child.handler != nil
			}
			if h, found := match(child, path, pos, params); found {
				return h, true
			}
		}
	}

	return nil, false
}