// Package authz contains the single authorization policy used by all control
// surfaces. Clients identify a surface; the bus decides what it may emit.
package authz

import (
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/hex"
	"fmt"
	"net/http"
	"strings"
	"sync"
	"time"
)

type Surface string

const (
	Telegram Surface = "telegram"
	Ntfy     Surface = "ntfy"
	TUI      Surface = "tui"
	Web      Surface = "web"
	MCP      Surface = "mcp"
	Maven    Surface = "maven"
	// System identifies the plane itself — the router, coordinator, provider
	// adapters, and lease-expiry reclaim. Per invariant 2 ("the plane emits
	// events, not the agent"), these are the only non-surface emitters and are
	// always full control. Every event must carry an explicit Surface; there
	// is no unauthenticated default, so an emitter that forgets to declare one
	// is rejected at the bus rather than silently treated as trusted.
	System Surface = "system"
)

type Capability int

const (
	Observe Capability = iota
	NotifyOnly
	GatedWrite
	FullControl
)

func ParseSurface(v string) Surface { return Surface(strings.ToLower(strings.TrimSpace(v))) }
func CapabilityFor(s Surface) Capability {
	switch s {
	case Telegram, Ntfy:
		return NotifyOnly
	case TUI, Web, System:
		return FullControl
	case MCP, Maven:
		return GatedWrite
	default:
		return Observe
	}
}
func (s Surface) CanRead() bool { return CapabilityFor(s) >= Observe }
func (s Surface) CanEmit(typ string) bool {
	if CapabilityFor(s) == FullControl {
		return true
	}
	return typ == "ApprovalRequested" && CapabilityFor(s) == GatedWrite
}
func (s Surface) RequiresApproval(typ string) bool {
	return CapabilityFor(s) == GatedWrite && typ != "ApprovalRequested"
}

func AuthorizeEvent(s Surface, typ string) error {
	if !s.CanEmit(typ) {
		return fmt.Errorf("surface %q cannot emit %s", s, typ)
	}
	return nil
}

// SessionCookie carries a browser's proof of the Web-surface token. A
// top-level document load cannot set an Authorization header, so a
// bearer-only gate forces operators to run the UI with no token at all
// (AUDIT.md B18). The cookie is the browser-presentable equivalent; it is
// never a second credential, only a receipt for the same token.
const SessionCookie = "orchestra_session"

// SessionPath is the one Web-surface endpoint exempt from the token gate,
// because it *is* the token check: it verifies the Web token itself and
// exchanges it for a cookie. Gating it would make login unreachable.
const SessionPath = "/v1/ui/session"

// Sessions issues and validates those receipts. Values are random and stored
// hashed, so a leaked snapshot of this map does not yield a usable cookie.
type Sessions struct {
	mu  sync.Mutex
	TTL time.Duration
	ids map[string]time.Time
}

func (s *Sessions) ttl() time.Duration {
	if s.TTL > 0 {
		return s.TTL
	}
	return 12 * time.Hour
}

// Issue mints a session value. The caller must have already verified the
// Web-surface token; Issue does not check credentials itself.
func (s *Sessions) Issue() (string, error) {
	b := make([]byte, 32)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	v := hex.EncodeToString(b)
	sum := sha256.Sum256([]byte(v))
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.ids == nil {
		s.ids = map[string]time.Time{}
	}
	now := time.Now()
	for k, exp := range s.ids {
		if now.After(exp) {
			delete(s.ids, k)
		}
	}
	s.ids[hex.EncodeToString(sum[:])] = now.Add(s.ttl())
	return v, nil
}

func (s *Sessions) Valid(v string) bool {
	if v == "" {
		return false
	}
	sum := sha256.Sum256([]byte(v))
	s.mu.Lock()
	defer s.mu.Unlock()
	exp, ok := s.ids[hex.EncodeToString(sum[:])]
	if !ok {
		return false
	}
	if time.Now().After(exp) {
		delete(s.ids, hex.EncodeToString(sum[:]))
		return false
	}
	return true
}

// HTTP enforces the same policy at the bus boundary. Authentication is
// optional for local development; when a token is supplied, control surfaces
// must present it as a Bearer token.
func HTTP(tokens map[Surface]string, next http.Handler) http.Handler {
	return HTTPWithSessions(tokens, nil, next)
}

// HTTPWithSessions additionally accepts a valid session cookie in place of a
// Bearer token, but only for the Web surface — every non-browser surface
// still has to present the token directly.
func HTTPWithSessions(tokens map[Surface]string, sessions *Sessions, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		s := ParseSurface(r.Header.Get("X-Orchestra-Surface"))
		if s == "" {
			s = Web
		}
		// System means "the plane itself, in-process" (router, coordinator,
		// adapters, lease-expiry reclaim) and is always FullControl with no
		// token gate — it must never be reachable by declaring it over HTTP.
		// Without this, tokens[System] being unset (as it is by default: no
		// caller ever needs a System token) makes the check at line ~78 a
		// no-op, and any LAN request with this header gets unauthenticated
		// full control over every task.
		if s == System {
			s = Web
		}
		if expected := tokens[s]; expected != "" && subtle.ConstantTimeCompare([]byte(r.Header.Get("Authorization")), []byte("Bearer "+expected)) != 1 {
			ok := false
			if s == Web && sessions != nil {
				if c, err := r.Cookie(SessionCookie); err == nil {
					ok = sessions.Valid(c.Value)
				}
				// The login endpoint authenticates itself, and the SPA shell
				// must load before a browser can present anything. Static
				// assets are not secrets; every /v1/ control path stays gated.
				if r.URL.Path == SessionPath {
					ok = true
				}
				if !strings.HasPrefix(r.URL.Path, "/v1/") && (r.Method == http.MethodGet || r.Method == http.MethodHead) {
					ok = true
				}
			}
			if !ok {
				http.Error(w, "unauthorized surface", http.StatusUnauthorized)
				return
			}
		}
		if (s == Telegram || s == Ntfy) && r.Method != http.MethodGet && r.Method != http.MethodHead {
			http.Error(w, "notify-only surface", http.StatusForbidden)
			return
		}
		if (s == MCP || s == Maven) && r.Method != http.MethodGet && r.Method != http.MethodHead && r.URL.Path != "/v1/events" {
			// Gated clients may submit only approval requests; ordinary control
			// endpoints must never become an accidental write path.
			if !strings.HasSuffix(r.URL.Path, "/approval") {
				http.Error(w, "approval required", http.StatusForbidden)
				return
			}
		}
		next.ServeHTTP(w, r)
	})
}