package router

import (
	"strings"

	"github.com/valyala/fasthttp"
)

func (n *node) matchChild(part string) *node {
	for _, child := range n.children {
		if child.part == part || child.isParam {
			return child
		}
	}
	return nil
}

func (n *node) matchChildren(part string) []*node {
	nodes := make([]*node, 0)
	for _, child := range n.children {
		if child.part == part || child.isParam {
			nodes = append(nodes, child)
		}
	}
	return nodes
}

func (n *node) insert(pattern string, parts []string, height int, handler HandlerFunc) {
	if len(parts) == height {
		n.pattern = pattern
		n.handler = handler
		return
	}
	part := parts[height]
	child := n.matchChild(part)
	if child == nil {
		child = &node{
			part:    part,
			isParam: len(part) > 0 && part[0] == ':',
		}
		n.children = append(n.children, child)
	}
	child.insert(pattern, parts, height+1, handler)
}

func (n *node) search(parts []string, height int, params map[string]string) *node {
	if len(parts) == height || n.part == "*" {
		if n.pattern == "" {
			return nil
		}
		return n
	}
	part := parts[height]
	children := n.matchChildren(part)

	for _, child := range children {
		if child.isParam {
			params[child.part[1:]] = part
		}
		res := child.search(parts, height+1, params)
		if res != nil {
			return res
		}
	}
	return nil
}

// 中间件条目
type middlewareEntry struct {
	handler       HandlerFunc
	excludePaths  map[string]struct{}
	excludePrefix []string
}

// 判断路径是否被排除
func (m *middlewareEntry) IsExcluded(path string) bool {
	path = strings.TrimSuffix(path, "/") // 去掉尾部斜杠
	if m.excludePaths != nil {
		if _, ok := m.excludePaths[path]; ok {
			return true
		}
	}
	for _, prefix := range m.excludePrefix {
		if strings.HasPrefix(path, prefix) {
			return true
		}
	}
	return false
}

// Router 主结构
type Router struct {
	roots      map[string]*node
	middleware []middlewareEntry
	basePath   string
}

// 创建 Router
func NewRouter(basePath ...string) *Router {
	path := "/"
	if len(basePath) > 0 && basePath[0] != "" {
		path = basePath[0]
	}
	return &Router{
		roots:    make(map[string]*node),
		basePath: path,
	}
}

// MiddlewareHandle 用于链式排除路径
type MiddlewareHandle struct {
	router   *Router
	entryIdx int
}

// Use 注册中间件
func (r *Router) Use(handler HandlerFunc) *MiddlewareHandle {
	entry := middlewareEntry{handler: handler}
	r.middleware = append(r.middleware, entry)
	return &MiddlewareHandle{
		router:   r,
		entryIdx: len(r.middleware) - 1,
	}
}

// ExcludePaths 支持 /** 前缀匹配
// ExcludePaths 支持 /** 前缀匹配，并自动带上 basePath
func (mh *MiddlewareHandle) ExcludePaths(paths ...string) *MiddlewareHandle {
	excludeMap := make(map[string]struct{})
	excludePrefix := make([]string, 0)

	basePath := strings.TrimSuffix(mh.router.basePath, "/") // 去掉尾部斜杠

	for _, p := range paths {
		fullPath := p
		if !strings.HasPrefix(p, "/") {
			fullPath = "/" + p
		}

		// 自动加上 basePath
		if basePath != "/" {
			fullPath = basePath + fullPath
		}

		if strings.HasSuffix(fullPath, "/**") {
			base := strings.TrimSuffix(fullPath, "/**")
			excludePrefix = append(excludePrefix, base)
		} else {
			excludeMap[fullPath] = struct{}{}
		}
	}

	mh.router.middleware[mh.entryIdx].excludePaths = excludeMap
	mh.router.middleware[mh.entryIdx].excludePrefix = excludePrefix

	return mh
}

// Group 创建子路由组
func (r *Router) Group(prefix string, m ...HandlerFunc) *Router {
	newMiddleware := make([]middlewareEntry, len(r.middleware))
	copy(newMiddleware, r.middleware)
	for _, handler := range m {
		entry := middlewareEntry{handler: handler}
		newMiddleware = append(newMiddleware, entry)
	}
	return &Router{
		roots:      r.roots,
		middleware: newMiddleware,
		basePath:   joinPaths(r.basePath, prefix),
	}
}

// GET/POST
func (r *Router) GET(path string, handler HandlerFunc) *Router {
	return r.handle("GET", path, handler)
}

func (r *Router) POST(path string, handler HandlerFunc) *Router {
	return r.handle("POST", path, handler)
}

func (r *Router) handle(method, path string, handler HandlerFunc) *Router {
	fullPath := joinPaths(r.basePath, path)
	parts := parsePattern(fullPath)
	if r.roots[method] == nil {
		r.roots[method] = &node{}
	}
	r.roots[method].insert(fullPath, parts, 0, handler)
	return r
}

// Handler 入口（fasthttp）
func (r *Router) Handler(ctx *fasthttp.RequestCtx) {
	method := string(ctx.Method())
	root := r.roots[method]

	if root == nil {
		ctx.Error("未找到该页面", fasthttp.StatusNotFound)
		return
	}

	searchParts := parsePattern(string(ctx.Path()))
	params := make(map[string]string)
	n := root.search(searchParts, 0, params)
	if n == nil || n.handler == nil {
		ctx.Error("404 Not Found", fasthttp.StatusNotFound)
		return
	}

	// 组装中间件链
	handlers := make([]HandlerFunc, 0)
	path := string(ctx.Path())
	for _, m := range r.middleware {
		if m.IsExcluded(path) {
			continue
		}
		handlers = append(handlers, m.handler)
	}
	handlers = append(handlers, n.handler) // 最终 handler

	c := &Context{
		RequestCtx: ctx,
		params:     params,
		index:      -1,
		handlers:   handlers,
	}

	_ = c.Next()
}

// 辅助函数
func parsePattern(pattern string) []string {
	vs := strings.Split(strings.Trim(pattern, "/"), "/")
	parts := make([]string, 0, len(vs))
	for _, item := range vs {
		if item != "" {
			parts = append(parts, item)
		}
	}
	return parts
}

func joinPaths(a, b string) string {
	if a == "" {
		if b == "" {
			return "/"
		}
		if !strings.HasPrefix(b, "/") {
			return "/" + b
		}
		return b
	}
	if b == "" {
		return a
	}
	aslash := strings.HasSuffix(a, "/")
	bslash := strings.HasPrefix(b, "/")
	switch {
	case aslash && bslash:
		return a + b[1:]
	case !aslash && !bslash:
		return a + "/" + b
	default:
		return a + b
	}
}