package web

// Sessions and the pending authorisations in flight (novox/hq ADR 0440 §3, issue 1263): both kept in memory
// only, never on disk — a restart signs everyone out, accepted (design 59 milestone 1's prepare step).

import (
	"crypto/rand"
	"encoding/base64"
	"sync"
	"time"
)

// SessionCookie is the cookie's own name.
const SessionCookie = "mesh_mail_web_session"

// SessionLifetime is how long a session lasts after it is made (novox/hq ADR 0440 §3, issue 1263/AC2, AC5).
const SessionLifetime = 12 * time.Hour

// PendingLifetime is how long a sign-in may take between the redirect to the issuer and its callback, before
// the state is no longer honoured.
const PendingLifetime = 10 * time.Minute

func randomID() (string, error) {
	var b [32]byte
	if _, err := rand.Read(b[:]); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(b[:]), nil
}

// Session is one signed-in operator's own session: its identity, when it was made (SessionLifetime decides
// when it ends), and the per-session token issue 1284 binds every changing form to.
type Session struct {
	Operator string
	Made     time.Time
	Token    string
}

// Sessions keeps every session in memory, by its cookie's own id.
type Sessions struct {
	mu   sync.Mutex
	now  func() time.Time
	byID map[string]Session
}

// NewSessions is an empty Sessions; now is time.Now unless a test gives its own.
func NewSessions(now func() time.Time) *Sessions {
	if now == nil {
		now = time.Now
	}
	return &Sessions{now: now, byID: map[string]Session{}}
}

// Create starts a new session for operator, answering its id (the cookie's own value) and its own per-session
// token (issue 1284).
func (s *Sessions) Create(operator string) (id string, err error) {
	id, err = randomID()
	if err != nil {
		return "", err
	}
	token, err := randomID()
	if err != nil {
		return "", err
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	s.byID[id] = Session{Operator: operator, Made: s.now(), Token: token}
	return id, nil
}

// Get is the session at id, or false when there is none or it ended SessionLifetime ago (1263/AC5): an expired
// session reads as no session at all, dropped on the same look (no background sweep is needed: every read
// already checks the time).
func (s *Sessions) Get(id string) (Session, bool) {
	if id == "" {
		return Session{}, false
	}
	s.mu.Lock()
	defer s.mu.Unlock()
	sess, ok := s.byID[id]
	if !ok {
		return Session{}, false
	}
	if s.now().Sub(sess.Made) > SessionLifetime {
		delete(s.byID, id)
		return Session{}, false
	}
	return sess, true
}

// PendingAuth is one sign-in asked of the issuer, remembered between the redirect and its callback: the PKCE
// verifier the challenge was made from, and the page the browser first asked for.
type PendingAuth struct {
	Verifier string
	Return   string
	Created  time.Time
}

// PendingAuths keeps every sign-in in flight, by its own state, in memory only.
type PendingAuths struct {
	mu      sync.Mutex
	now     func() time.Time
	byState map[string]PendingAuth
}

// NewPendingAuths is an empty PendingAuths; now is time.Now unless a test gives its own.
func NewPendingAuths(now func() time.Time) *PendingAuths {
	if now == nil {
		now = time.Now
	}
	return &PendingAuths{now: now, byState: map[string]PendingAuth{}}
}

// Create remembers one sign-in in flight, answering the state it is kept under.
func (p *PendingAuths) Create(verifier, returnTo string) (state string, err error) {
	state, err = randomID()
	if err != nil {
		return "", err
	}
	p.mu.Lock()
	defer p.mu.Unlock()
	p.byState[state] = PendingAuth{Verifier: verifier, Return: returnTo, Created: p.now()}
	return state, nil
}

// Take reads back and removes the sign-in kept under state — once; a state never issued, already taken, or
// older than PendingLifetime answers false (1263/AC4's "a state it did not issue").
func (p *PendingAuths) Take(state string) (PendingAuth, bool) {
	if state == "" {
		return PendingAuth{}, false
	}
	p.mu.Lock()
	defer p.mu.Unlock()
	pa, ok := p.byState[state]
	if !ok {
		return PendingAuth{}, false
	}
	delete(p.byState, state)
	if p.now().Sub(pa.Created) > PendingLifetime {
		return PendingAuth{}, false
	}
	return pa, true
}