package runtime

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"regexp"
	"strings"
	"sync"
	"time"

	"fun.chick/msa-agent/internal/egress"
)

// NodeAuth holds the agent's own session against the local SimAdmin.
//
// This exists because the phone must never hold a node password: the agent logs in itself and the
// credential never traverses the relay in either direction. The login endpoints are therefore
// reachable by this code and permanently unreachable through the policy (authPaths.proxied=false
// plus the auth-pattern rejection in policy.Decision), so the only way to trigger a login attempt
// against the node is for the agent itself to need one.
//
// The semantics mirror server/core.js ensureAuthenticated in the console, including its failure
// modes: a stale password must not turn every command into a fresh login attempt, because some
// devices punish repeated failures with lockouts.
type NodeAuth struct {
	client   *http.Client
	origin   string
	password string
	cooldown time.Duration
	clock    func() time.Time

	mu     sync.Mutex
	state  authState
	cookie string
	// retryAt is the wall time after which a failed login may be attempted again.
	retryAt time.Time
}

type authState int

const (
	// authUnknown is the startup state: nothing has been probed yet.
	authUnknown authState = iota
	// authOpen means the node answers without a session (protection disabled, or the auth status
	// endpoint does not exist on an old build). Commands forward without a cookie.
	authOpen
	// authReady means cookie holds a live session.
	authReady
	// authFailed means a login was attempted and rejected; no command may trigger another until
	// retryAt passes. This is the cooldown that keeps a stale password from becoming a lockout.
	authFailed
	// authNoPassword means the node demands authentication but the agent was configured without a
	// password. Retrying cannot help; the operator has to fix the config.
	authNoPassword
)

var (
	// ErrAuthNoPassword is returned when a protected node was given an agent with no password.
	ErrAuthNoPassword = errors.New("runtime: node requires authentication but the agent has no password configured")
	// ErrAuthRejected is returned while a failed login is inside its cooldown.
	ErrAuthRejected = errors.New("runtime: node rejected the agent credential (in login cooldown)")
	// ErrAuthUnavailable is returned when the local SimAdmin could not be reached during a probe.
	ErrAuthUnavailable = errors.New("runtime: local SimAdmin unreachable during authentication")

	sessionCookieRe = regexp.MustCompile(`simadmin_session=([^;\s,]+)`)
)

// DefaultLoginCooldown matches the console's 60s auto-login cooldown. Two knobs in two languages
// would drift; this one lives next to the code that enforces it.
const DefaultLoginCooldown = 60 * time.Second

// AuthConfig configures NodeAuth. Password may be empty: an agent pointed at an unprotected node
// never logs in, and an agent pointed at a protected one fails with ErrAuthNoPassword rather than
// looping.
type AuthConfig struct {
	Password string
	Cooldown time.Duration
	Clock    func() time.Time
}

// NewNodeAuth builds the auth holder over the same loopback client the executor forwards with, so
// the login path cannot dial anywhere a command path could not.
func NewNodeAuth(client *http.Client, target egress.Target, cfg AuthConfig) (*NodeAuth, error) {
	if client == nil {
		return nil, errors.New("runtime: auth client is nil")
	}
	clock := cfg.Clock
	if clock == nil {
		clock = time.Now
	}
	cooldown := cfg.Cooldown
	if cooldown <= 0 {
		cooldown = DefaultLoginCooldown
	}
	return &NodeAuth{
		client:   client,
		origin:   target.Origin(),
		password: cfg.Password,
		cooldown: cooldown,
		clock:    clock,
	}, nil
}

// Cookie returns the current session cookie value, or "" when the node needs none. Callers on the
// forwarding path call Ensure first, which is what performs the probe and login.
func (a *NodeAuth) Cookie() string {
	a.mu.Lock()
	defer a.mu.Unlock()
	return a.cookie
}

// Ensure brings the agent to a usable authentication state, at most one probe/login per call.
//
// It is called before forwarding. A ready or open state returns without touching the network, so
// steady-state commands pay nothing; only an unknown or expired state triggers traffic.
func (a *NodeAuth) Ensure(ctx context.Context) error {
	a.mu.Lock()
	switch a.state {
	case authOpen, authReady:
		a.mu.Unlock()
		return nil
	case authNoPassword:
		a.mu.Unlock()
		return ErrAuthNoPassword
	case authFailed:
		if a.clock().Before(a.retryAt) {
			a.mu.Unlock()
			return ErrAuthRejected
		}
		// Cooldown elapsed: fall through to a fresh probe. A node whose password was fixed, or
		// whose lockout expired, recovers without a restart.
	}
	a.mu.Unlock()

	authenticated, loginRequired, err := a.probeStatus(ctx)
	if err != nil {
		return err
	}
	if authenticated || !loginRequired {
		a.mu.Lock()
		a.state = authOpen
		a.cookie = ""
		a.mu.Unlock()
		return nil
	}
	return a.login(ctx)
}

// Invalidate marks the session unusable after a forwarded request came back unauthenticated, so
// the next Ensure re-probes and (if needed) re-logs in. An agent that never invalidates turns every
// SimAdmin restart into permanent 401s until the agent restarts too.
func (a *NodeAuth) Invalidate() {
	a.mu.Lock()
	defer a.mu.Unlock()
	if a.state == authReady {
		a.state = authUnknown
		a.cookie = ""
	}
}

// probeStatus answers "does this request need a session, and does ours already work".
//
// The parse mirrors core.js: the payload nests under data on some builds and not others, the
// protection flag is snake_case on some and camelCase on others. The default when the shape is not
// recognised is *unprotected*, and that is deliberate in both directions. A legacy or odd build
// that answers 200 with something this parser cannot read is better served without a cookie, since
// the alternative is the agent demanding a password the node never asked for. Login is triggered
// only when the node explicitly says it wants authentication.
func (a *NodeAuth) probeStatus(ctx context.Context) (authenticated, loginRequired bool, err error) {
	request, err := http.NewRequestWithContext(ctx, http.MethodGet, a.origin+"/api/auth/status", nil)
	if err != nil {
		return false, false, err
	}
	if a.Cookie() != "" {
		request.Header.Set("cookie", a.Cookie())
	}
	response, err := a.client.Do(request)
	if err != nil {
		return false, false, fmt.Errorf("%w: %v", ErrAuthUnavailable, err)
	}
	defer drain(response)
	// 401/403 means the node is protected and our cookie (if any) did not authenticate it.
	if response.StatusCode == http.StatusUnauthorized || response.StatusCode == http.StatusForbidden {
		return false, true, nil
	}
	if response.StatusCode < 200 || response.StatusCode >= 300 {
		// 404 and friends: an old SimAdmin with no auth endpoints at all is an open node.
		return false, false, nil
	}
	payload, err := io.ReadAll(io.LimitReader(response.Body, 1<<20))
	if err != nil {
		return false, false, fmt.Errorf("%w: reading auth status: %v", ErrAuthUnavailable, err)
	}
	var doc map[string]any
	if err := json.Unmarshal(payload, &doc); err != nil {
		return false, false, nil
	}
	auth, _ := doc["data"].(map[string]any)
	if auth == nil {
		auth = doc
	}
	if v, ok := auth["authenticated"].(bool); ok {
		return v, !v, nil
	}
	if v, ok := auth["configured"].(bool); ok && !v {
		return false, false, nil
	}
	settings, _ := auth["settings"].(map[string]any)
	if settings != nil {
		if v, ok := settings["password_protection_enabled"].(bool); ok {
			return false, v, nil
		}
		if v, ok := settings["passwordProtectionEnabled"].(bool); ok {
			return false, v, nil
		}
	}
	return false, false, nil
}

// login performs POST /api/auth/login and stores the session cookie. Failures enter the cooldown;
// the cooldown is the reason a wrong password can be fixed in place rather than requiring a
// reinstall.
func (a *NodeAuth) login(ctx context.Context) error {
	if a.password == "" {
		a.mu.Lock()
		a.state = authNoPassword
		a.mu.Unlock()
		return ErrAuthNoPassword
	}
	body := strings.NewReader(`{"password":` + jsonQuote(a.password) + `}`)
	request, err := http.NewRequestWithContext(ctx, http.MethodPost, a.origin+"/api/auth/login", body)
	if err != nil {
		return err
	}
	request.Header.Set("content-type", "application/json")
	request.Header.Set("accept", "application/json")
	response, err := a.client.Do(request)
	if err != nil {
		return fmt.Errorf("%w: %v", ErrAuthUnavailable, err)
	}
	defer drain(response)
	if response.StatusCode < 200 || response.StatusCode >= 300 {
		a.mu.Lock()
		a.state = authFailed
		a.cookie = ""
		a.retryAt = a.clock().Add(a.cooldown)
		a.mu.Unlock()
		return fmt.Errorf("runtime: local SimAdmin rejected the agent password (status %d)", response.StatusCode)
	}
	match := sessionCookieRe.FindStringSubmatch(response.Header.Get("Set-Cookie"))
	if match == nil {
		// A 2xx without the session cookie is its own failure mode (a proxy that answered on the
		// node's behalf, say). Treat it as a rejection rather than forwarding cookie-less.
		a.mu.Lock()
		a.state = authFailed
		a.retryAt = a.clock().Add(a.cooldown)
		a.mu.Unlock()
		return errors.New("runtime: login succeeded but set no session cookie")
	}
	a.mu.Lock()
	a.state = authReady
	a.cookie = match[0]
	a.mu.Unlock()
	return nil
}

func drain(response *http.Response) {
	io.Copy(io.Discard, response.Body)
	response.Body.Close()
}

// jsonQuote encodes a string as a JSON string literal without pulling in an encoder for one field.
func jsonQuote(s string) string {
	b, _ := json.Marshal(s)
	return string(b)
}