// 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"
	// Agent identifies a coding session running inside a harness pane. It may
	// perform work and *request* lifecycle changes; it may never perform one.
	// Everything Orchestra owns — phase, review, submission, completion, lease
	// state — is denied to it by GatedWrite, at the endpoint and at the bus.
	Agent Surface = "agent"
	// 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, Agent:
		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"
}

// RequireCredentials refuses to serve a full-control surface that has no token.
// An unset token means the middleware performs no check for that surface, so an
// unconfigured FullControl surface is an unauthenticated control plane, not a
// closed one. Found live during burn-in: with ORCHESTRA_TUI_TOKEN unset, any
// LAN caller could lease, release, complete or block any task by declaring one
// header. Web is exempt because Sessions makes its login mandatory and it
// carries its own credentials.
func RequireCredentials(tokens map[Surface]string) error {
	for _, s := range []Surface{TUI} {
		if CapabilityFor(s) == FullControl && strings.TrimSpace(tokens[s]) == "" {
			return fmt.Errorf("surface %q is full control and has no token: set its credential or leave the surface unused", s)
		}
	}
	return nil
}

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 a successful Web login. A
// top-level document load cannot set an Authorization header, so browser
// credentials are exchanged once for this HttpOnly receipt.
const SessionCookie = "orchestra_session"

// HarnessTurnPath authenticates its own bearer token inside the handler, the
// way federation endpoints do. It needs an exemption from the surface gate
// below for the same reason they do: an unlabelled request defaults to the Web
// surface, which is session-gated, so a harness could never reach it.
const HarnessTurnPath = "/v1/harness/turn"

// GatedWritePaths are the only mutating paths a GatedWrite surface may reach.
// Each one records a request — an approval, a bounded question, a deferred
// finding — and none of them moves the lifecycle. Handlers re-check with
// AuthorizeEvent, so widening this list alone cannot grant authority.
func GatedWritePath(p string) bool {
	return strings.HasSuffix(p, "/approval") ||
		strings.HasSuffix(p, "/decision-request") ||
		strings.HasSuffix(p, "/deferred")
}

// SessionPath is the one Web-surface endpoint exempt from the session gate,
// because it verifies login credentials and exchanges them for a cookie.
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 browserSession struct {
	Username string
	Expires  time.Time
}

type Sessions struct {
	mu  sync.Mutex
	TTL time.Duration
	ids map[string]browserSession
}

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

// Duration exposes the configured session lifetime for the cookie Max-Age.
func (s *Sessions) Duration() time.Duration { return s.ttl() }

// 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) {
	return s.IssueFor("")
}

// IssueFor mints a session bound to one database-backed operator identity.
func (s *Sessions) IssueFor(username string) (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]browserSession{}
	}
	now := time.Now()
	for k, session := range s.ids {
		if now.After(session.Expires) {
			delete(s.ids, k)
		}
	}
	s.ids[hex.EncodeToString(sum[:])] = browserSession{Username: username, Expires: now.Add(s.ttl())}
	return v, nil
}

func (s *Sessions) Valid(v string) bool {
	_, ok := s.Username(v)
	return ok
}

// Username validates a receipt and returns the operator it belongs to.
func (s *Sessions) Username(v string) (string, bool) {
	if v == "" {
		return "", false
	}
	sum := sha256.Sum256([]byte(v))
	key := hex.EncodeToString(sum[:])
	s.mu.Lock()
	defer s.mu.Unlock()
	session, ok := s.ids[key]
	if !ok {
		return "", false
	}
	if time.Now().After(session.Expires) {
		delete(s.ids, key)
		return "", false
	}
	return session.Username, true
}

// Revoke removes one browser session. It is deliberately idempotent so a
// logout request remains safe after expiry or after a cookie was cleared by
// the browser.
func (s *Sessions) Revoke(v string) {
	if v == "" {
		return
	}
	sum := sha256.Sum256([]byte(v))
	s.mu.Lock()
	defer s.mu.Unlock()
	delete(s.ids, hex.EncodeToString(sum[:]))
}

// RevokeUser ends every browser session for an identity after its username or
// password changes.
func (s *Sessions) RevokeUser(username string) {
	s.mu.Lock()
	defer s.mu.Unlock()
	for key, session := range s.ids {
		if strings.EqualFold(session.Username, username) {
			delete(s.ids, key)
		}
	}
}

// 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 accepts a valid browser session cookie only for the Web
// surface. Supplying Sessions makes Web authentication mandatory even when
// the legacy Web bearer-token slot is empty.
func HTTPWithSessions(tokens map[Surface]string, sessions *Sessions, next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Federation has per-worker credentials, not one shared surface token.
		// Let only its registration request and requests that name a worker
		// reach their handlers; those handlers authenticate the admission token
		// or worker token respectively. Without this exception, an authenticated
		// worker is incorrectly treated as the default Web surface.
		worker := r.Header.Get("X-Orchestra-Worker") != ""
		federationRegistration := r.Method == http.MethodPost && r.URL.Path == "/v1/federation/workers"
		workerPath := strings.HasPrefix(r.URL.Path, "/v1/federation/") ||
			(r.Method == http.MethodGet && r.URL.Path == "/v1/tasks") ||
			(r.Method == http.MethodPost && r.URL.Path == "/v1/artifacts") ||
			(r.Method == http.MethodGet && strings.HasPrefix(r.URL.Path, "/v1/artifacts/")) ||
			// A federated worker renders its own launch instruction from the
			// reduced intent, so this read is as necessary to it as the task
			// list. Found live on the first burn-in task: the endpoint was
			// added for workers, the exemption was not, and every federated
			// launch failed with "effective intent: federation: 401
			// Unauthorized: unauthorized surface".
			(r.Method == http.MethodGet && strings.HasPrefix(r.URL.Path, "/v1/tasks/") && strings.HasSuffix(r.URL.Path, "/intent"))
		if federationRegistration || r.URL.Path == HarnessTurnPath || (worker && workerPath) {
			next.ServeHTTP(w, r)
			return
		}
		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 s == Web && sessions != nil {
			ok := false
			if c, err := r.Cookie(SessionCookie); err == nil {
				ok = sessions.Valid(c.Value)
			}
			// The session endpoint authenticates login and session lookup itself,
			// and the SPA shell must
			// load before a browser can present a session. Static assets are not
			// secrets; every other /v1/ control path remains session-gated.
			if r.URL.Path == SessionPath || (!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
			}
		} else if expected := tokens[s]; expected != "" && subtle.ConstantTimeCompare([]byte(r.Header.Get("Authorization")), []byte("Bearer "+expected)) != 1 {
			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 CapabilityFor(s) == GatedWrite && r.Method != http.MethodGet && r.Method != http.MethodHead && r.URL.Path != "/v1/events" {
			// Gated clients may only ask; ordinary control endpoints must never
			// become an accidental write path.
			if !GatedWritePath(r.URL.Path) {
				http.Error(w, "approval required", http.StatusForbidden)
				return
			}
		}
		next.ServeHTTP(w, r)
	})
}