// Package gateway — 对外挂载点（R3 / Phase 6）
//
// 用户需求：插件与适配器可以注册**对外服务的端口**。
//
// 现状：插件已经能注册 HTTP 端点，但被固定在 /api/plugins/http/ 前缀下。
// 那条前缀限制是有理由的（可 grep、可整体撤销、插件无法影子内核路由），
// 但它也意味着插件无法提供"看起来像内核一部分"的接口——而对外服务恰恰
// 需要这个（例如给上游回调用的固定路径 /v1/plugins/<name>/callback）。
//
// 本文件放开这一点，同时把当初那条限制的**三个理由**逐条补回来：
//
//  1. 可 grep / 可整体撤销 → 每条自定义挂载都必须落在 /plugins/ 或
//     /v1/plugins/ 命名空间内（不接受任意前缀）
//  2. 不能影子内核路由 → 与内核保留路由表做前缀冲突检测，撞了直接拒绝
//  3. 鉴权默认关闭 → 沿用 HTTPHandler 的 roles/keys/public 语义
package gateway

import (
	"fmt"
	"net/http"
	"sort"
	"strings"

	"llmsproxy/internal/lua"
)

// allowedMountPrefixes are the only namespaces a plugin/adapters may claim.
//
// A free-form prefix would let a plugin register "/v1/chat/completions" and
// silently intercept every inference request on the gateway — the exact
// shadowing the narrow default prefix was protecting against. Constraining the
// namespace keeps the security property while still allowing a stable public
// path.
var allowedMountPrefixes = []string{"/plugins/", "/v1/plugins/"}

// kernelReservedPrefixes are prefixes the kernel owns. A custom mount that
// overlaps any of them is refused, so an operator's route table can never
// change meaning because a plugin was installed.
//
// This list is deliberately explicit rather than derived from the router's
// switch: the switch is code, and a future branch added there would silently
// become shadowable if this were inferred. The test
// TestKernelRoutesAreAllCoveredByReservedPrefixes keeps the two in sync.
var kernelReservedPrefixes = []string{
	"/v1/chat/completions",
	"/v1/messages",
	"/v1/images/generations",
	"/v1/models",
	"/api/",
	"/login",
	"/ui",
	"/",
}

// ValidateCustomMount checks that a plugin-declared mount point is allowed.
//
// Returns the normalized path (leading slash, no trailing slash) or an error
// naming the conflict. The error text is what an operator sees in the plugin's
// load-error field, so it says WHICH rule was hit.
func ValidateCustomMount(p string) (string, error) {
	p = strings.TrimSpace(p)
	if p == "" {
		return "", fmt.Errorf("empty mount path")
	}
	if !strings.HasPrefix(p, "/") {
		return "", fmt.Errorf("mount path %q must start with /", p)
	}
	if strings.Contains(p, "..") || strings.Contains(p, "//") {
		return "", fmt.Errorf("mount path %q contains an empty or escaping segment", p)
	}
	norm := strings.TrimRight(p, "/")
	if norm == "" {
		norm = "/"
	}

	// Rule 1: must live in one of the allowed namespaces.
	ok := false
	for _, pre := range allowedMountPrefixes {
		if strings.HasPrefix(norm+"/", pre) {
			ok = true
			break
		}
	}
	if !ok {
		return "", fmt.Errorf("mount path %q must be under %s",
			norm, strings.Join(allowedMountPrefixes, " or "))
	}

	// Rule 2: must not overlap a kernel route.
	for _, res := range kernelReservedPrefixes {
		if res == "/" {
			continue // the catch-all is handled by the namespace rule above
		}
		if norm == strings.TrimRight(res, "/") || strings.HasPrefix(norm, res) {
			return "", fmt.Errorf("mount path %q collides with the kernel route %q", norm, res)
		}
	}
	return norm, nil
}

// RouteOwner describes one occupied route, for conflict reporting.
type RouteOwner struct {
	Path  string
	Owner string // "kernel", "plugin:name", "adapter:name"
}

// BuildRouteTable assembles the set of paths a plugin/adapters must not take.
// It is used both to validate new mounts and to explain a conflict to an
// operator (a bare "conflict" is not actionable; "already served by plugin X" is).
func BuildRouteTable(pluginMounts, adapterMounts map[string]string) []RouteOwner {
	var out []RouteOwner
	for _, p := range kernelReservedPrefixes {
		if p == "/" {
			continue
		}
		out = append(out, RouteOwner{Path: strings.TrimRight(p, "/"), Owner: "kernel"})
	}
	for path, owner := range pluginMounts {
		out = append(out, RouteOwner{Path: path, Owner: "plugin:" + owner})
	}
	for path, owner := range adapterMounts {
		out = append(out, RouteOwner{Path: path, Owner: "adapter:" + owner})
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Path < out[j].Path })
	return out
}

// FindMountConflict reports whether candidate overlaps an occupied route and, if
// so, who holds it.
//
// Overlap is checked in BOTH directions: a new mount that CONTAINS an existing
// one shadows it just as effectively as one nested inside it, and only checking
// the prefix direction would let "/plugins/x/sub" be registered before
// "/plugins/x" and then silently swallow it.
func FindMountConflict(candidate string, table []RouteOwner) (RouteOwner, bool) {
	c := strings.TrimRight(candidate, "/")
	for _, r := range table {
		rp := strings.TrimRight(r.Path, "/")
		if rp == "" {
			continue
		}
		if c == rp || strings.HasPrefix(c, rp+"/") || strings.HasPrefix(rp, c+"/") {
			return r, true
		}
	}
	return RouteOwner{}, false
}

// handleCustomMount dispatches a request to a plugin that claimed a custom mount
// path (/plugins/<name>/… or /v1/plugins/<name>/…).
//
// It deliberately REUSES handlePluginHTTP rather than reimplementing dispatch:
// that function already does longest-match resolution, per-endpoint
// roles/keys/public authorization and the Lua call protocol. Duplicating it here
// would create two dispatch paths that must be kept in agreement — and a
// security rule that is enforced on only one of them is worse than none.
//
// The rewrite below maps a claimed mount onto the handler table's canonical
// form: handler paths are declared as "<name>/<rest>", so the request path is
// reduced to exactly that. Anything that does not reduce cleanly (a missing
// name, a name with no registered handler) is a 404, not a fallthrough — a
// custom namespace that silently answered from the default prefix would make
// the mount validation meaningless.
func (g *Gateway) handleCustomMount(w http.ResponseWriter, r *http.Request) {
	owner, rest, ok := parseMountRef(r.URL.Path)
	if !ok || owner == "" {
		writeError(w, http.StatusNotFound, "not_found", "malformed plugin mount path")
		return
	}
	ps := g.core.Plugins()
	if ps == nil {
		writeError(w, http.StatusNotFound, "not_found", "no plugins loaded")
		return
	}
	// Resolve which handler owns this mount, so an unclaimed namespace is a 404.
	handlers := ps.HTTPHandlers()
	candidate := owner
	if rest != "" {
		candidate = owner + "/" + rest
	}
	if !mountClaimed(handlers, candidate) {
		writeError(w, http.StatusNotFound, "not_found",
			"no plugin serves "+r.URL.Path)
		return
	}
	// Reuse the default dispatcher by presenting the path in its own shape.
	r2 := r.Clone(r.Context())
	r2.URL.Path = pluginHTTPPrefix + candidate
	g.handlePluginHTTP(w, r2)
}

// mountClaimed reports whether any registered handler's path is a prefix of the
// candidate (longest-match semantics: /plugins/auth/token is served by a
// handler declared as "auth").
func mountClaimed(handlers []lua.HTTPHandler, candidate string) bool {
	for i := range handlers {
		h := strings.Trim(handlers[i].Path, "/")
		if h == "" {
			continue
		}
		if candidate == h || strings.HasPrefix(candidate, h+"/") {
			return true
		}
	}
	return false
}

// parseMountRef splits "/plugins/<name>/<rest>" or "/v1/plugins/<name>/<rest>"
// into its owner name and remaining path.
//
// The "/v1/plugins/" form is checked first because it has the longer prefix:
// testing "/plugins/" first would match nothing for a /v1/ path, but keeping the
// ordering explicit avoids a future prefix being added that nests inside
// another.
func parseMountRef(p string) (owner, rest string, ok bool) {
	prefixes := []string{"/v1/plugins/", "/plugins/"}
	for _, prefix := range prefixes {
		if !strings.HasPrefix(p, prefix) {
			continue
		}
		trimmed := strings.TrimPrefix(p, prefix)
		if trimmed == "" {
			return "", "", false
		}
		if i := strings.Index(trimmed, "/"); i >= 0 {
			return trimmed[:i], trimmed[i+1:], true
		}
		return trimmed, "", true
	}
	return "", "", false
}