// Package recovery implements SPEC-007: the non-admin recovery path (manager
// escalation) and the config-gated admin recovery (D-033).
//
// The shape mirrors PROJECT_PLAN.md §6.4:
//
//	/access  -> enter the email on record        (ALWAYS a generic response)
//	   match -> recovery_request(pending) · notify the chain
//	approver (an ancestor in the chain — the manager upward — or the admin,
//	          never the requester) approves/denies
//	   approval -> revoke the OLD identity · mint a NEW GUID · email the link
//
// Email only INITIATES (D-009); a human in the chain authorises. Identity
// rotation (D-007) means a compromised inbox cannot take over alone.
//
// The package owns no routing: the door (SPEC-003/007) gates /access to the
// anonymous pre-session CSRF path and the approve/deny actions to a session.
//
// Spec: docs/specs/spec-007-roles-chain-recovery.md.
package recovery

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"strings"
	"time"

	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/audit"
	"git.lohmar.co.uk/cclohmar/NextMyDay/internal/core/store"
)

// Status is a recovery request's lifecycle state (SPEC-004 §4
// `recovery_requests`).
type Status string

const (
	StatusPending  Status = "pending"
	StatusApproved Status = "approved"
	StatusDenied   Status = "denied"
	StatusExpired  Status = "expired"
)

// Defaults (code defaults; settings live in config later, D-035).
const (
	// DefaultPendingTTL bounds how long a recovery request waits for a decision
	// before it may no longer be approved (~72h, SPEC-007 §4).
	DefaultPendingTTL = 72 * time.Hour
	// DefaultMaxPending caps the number of open requests one user may hold, so
	// the inbox and the chain cannot be flooded.
	DefaultMaxPending = 3
)

// Request is one recovery request (SPEC-004 §4 `recovery_requests`).
type Request struct {
	ID          int64
	UserID      int64
	Status      Status
	RequestedAt time.Time
	// DecidedBy is the approver/denier; nil while pending.
	DecidedBy *int64
	DecidedAt *time.Time
	ClientIP  string
}

// ExpiredAt reports the moment the request stops being approvable.
func (r Request) ExpiredAt(ttl time.Duration) time.Time { return r.RequestedAt.Add(ttl) }

// Sentinel errors.
var (
	// ErrNotFound is returned when no matching request exists.
	ErrNotFound = errors.New("recovery: request not found")
	// ErrTooManyPending is returned when a user is already at the cap.
	ErrTooManyPending = errors.New("recovery: too many pending recovery requests")
)

// Store is the SQLite-backed recovery-request service.
type Store struct {
	db    *sql.DB
	audit audit.Audit
	ttl   time.Duration
	cap   int
	now   func() time.Time
}

// Option configures a Store.
type Option func(*Store)

// WithTTL overrides the pending lifetime (default DefaultPendingTTL).
func WithTTL(d time.Duration) Option {
	return func(s *Store) {
		if d > 0 {
			s.ttl = d
		}
	}
}

// WithCap overrides the per-user pending cap (default DefaultMaxPending).
func WithCap(n int) Option {
	return func(s *Store) {
		if n > 0 {
			s.cap = n
		}
	}
}

// WithClock injects a clock (tests).
func WithClock(fn func() time.Time) Option {
	return func(s *Store) {
		if fn != nil {
			s.now = fn
		}
	}
}

// NewStore returns a recovery-request service over db. aud may be nil (tests).
func NewStore(db *sql.DB, aud audit.Audit, opts ...Option) *Store {
	s := &Store{
		db:    db,
		audit: aud,
		ttl:   DefaultPendingTTL,
		cap:   DefaultMaxPending,
		now:   time.Now,
	}
	for _, opt := range opts {
		opt(s)
	}
	return s
}

// TTL returns the configured pending lifetime.
func (s *Store) TTL() time.Duration { return s.ttl }

func (s *Store) clock() time.Time { return s.now().UTC().Truncate(time.Second) }

// Create opens a pending recovery request for userID. It expires stale rows
// first, then:
//
//   - reuses an existing live pending request (idempotent — created=false, so
//     the caller does NOT notify the chain a second time), and
//   - refuses once the per-user cap is reached (ErrTooManyPending).
//
// created reports whether a NEW row was inserted; only then should the caller
// send the notifications.
func (s *Store) Create(ctx context.Context, userID int64, clientIP string) (Request, bool, error) {
	now := s.clock()
	if _, err := s.Expire(ctx, now); err != nil {
		return Request{}, false, err
	}

	// The cap is a hard bound on a user's open requests (SPEC-007 §4); under
	// it, a live pending request is reused rather than duplicated.
	n, err := s.countPending(userID)
	if err != nil {
		return Request{}, false, err
	}
	if n >= s.cap {
		return Request{}, false, fmt.Errorf("%w: user:%d has %d pending", ErrTooManyPending, userID, n)
	}

	if existing, err := s.Pending(ctx, userID); err == nil {
		return existing, false, nil
	} else if !errors.Is(err, ErrNotFound) {
		return Request{}, false, err
	}

	res, err := s.db.Exec(
		`INSERT INTO recovery_requests (user_id, status, requested_at, client_ip)
		 VALUES (?, ?, ?, ?)`,
		userID, string(StatusPending), store.FormatTime(now), nullString(clientIP),
	)
	if err != nil {
		return Request{}, false, fmt.Errorf("recovery: insert request: %w", err)
	}
	id, err := res.LastInsertId()
	if err != nil {
		return Request{}, false, fmt.Errorf("recovery: request id: %w", err)
	}

	s.record(ctx, audit.Event{
		Action:   "recovery.request",
		Subject:  fmt.Sprintf("user:%d", userID),
		Detail:   fmt.Sprintf("request:%d status=pending", id),
		ClientIP: clientIP,
	})
	return Request{
		ID: id, UserID: userID, Status: StatusPending,
		RequestedAt: now, ClientIP: clientIP,
	}, true, nil
}

// Pending returns the user's live pending request (within the TTL). A stale or
// absent one yields ErrNotFound.
func (s *Store) Pending(ctx context.Context, userID int64) (Request, error) {
	row := s.db.QueryRow(`
		SELECT request_id, user_id, status, requested_at, decided_by, decided_at, client_ip
		  FROM recovery_requests
		 WHERE user_id = ? AND status = ?
		 ORDER BY request_id DESC LIMIT 1`, userID, string(StatusPending))
	req, err := scanRequest(row)
	if err != nil {
		return Request{}, err
	}
	if !req.ExpiredAt(s.ttl).After(s.clock()) {
		return Request{}, ErrNotFound // stale; Expire will tombstone it
	}
	return req, nil
}

// Get returns one request by id, whatever its status.
func (s *Store) Get(ctx context.Context, id int64) (Request, error) {
	row := s.db.QueryRow(`
		SELECT request_id, user_id, status, requested_at, decided_by, decided_at, client_ip
		  FROM recovery_requests WHERE request_id = ?`, id)
	return scanRequest(row)
}

// Decide moves a PENDING request to a terminal status, recording the deciding
// user (0 = the system, stored NULL) and the moment. It refuses a request that
// is no longer pending (ErrNotFound).
func (s *Store) Decide(ctx context.Context, id, decidedBy int64, status Status) error {
	switch status {
	case StatusApproved, StatusDenied, StatusExpired:
	default:
		return fmt.Errorf("recovery: cannot decide to %q", status)
	}

	now := store.FormatTime(s.clock())
	res, err := s.db.Exec(
		`UPDATE recovery_requests
		    SET status = ?, decided_by = ?, decided_at = ?
		  WHERE request_id = ? AND status = ?`,
		string(status), nullableID(decidedBy), now, id, string(StatusPending),
	)
	if err != nil {
		return fmt.Errorf("recovery: decide %d: %w", id, err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("recovery: decide rows: %w", err)
	}
	if n == 0 {
		return fmt.Errorf("%w: request:%d is not pending", ErrNotFound, id)
	}

	s.record(ctx, audit.Event{
		ActorUserID: decidedBy,
		Action:      decisionAction(status),
		Subject:     fmt.Sprintf("request:%d", id),
		Detail:      string(status),
	})
	return nil
}

// decisionAction names the audit event for a terminal decision, following the
// SPEC-004 §5 vocabulary (recovery request/approve/deny).
func decisionAction(status Status) string {
	switch status {
	case StatusApproved:
		return "recovery.approve"
	case StatusDenied:
		return "recovery.deny"
	default:
		return "recovery.expire"
	}
}

// Expire tombstones every pending request older than the TTL and returns how
// many it retired.
func (s *Store) Expire(ctx context.Context, now time.Time) (int, error) {
	cutoff := store.FormatTime(now.UTC().Add(-s.ttl))
	res, err := s.db.Exec(
		`UPDATE recovery_requests
		    SET status = ?, decided_at = ?
		  WHERE status = ? AND requested_at <= ?`,
		string(StatusExpired), store.FormatTime(now.UTC()), string(StatusPending), cutoff,
	)
	if err != nil {
		return 0, fmt.Errorf("recovery: expire: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return 0, fmt.Errorf("recovery: expire rows: %w", err)
	}
	if n > 0 {
		s.record(ctx, audit.Event{
			Action: "recovery.expire",
			Detail: fmt.Sprintf("expired=%d", n),
		})
	}
	return int(n), nil
}

// countPending counts a user's live pending requests.
func (s *Store) countPending(userID int64) (int, error) {
	var n int
	if err := s.db.QueryRow(
		`SELECT count(*) FROM recovery_requests WHERE user_id = ? AND status = ?`,
		userID, string(StatusPending),
	).Scan(&n); err != nil {
		return 0, fmt.Errorf("recovery: count pending: %w", err)
	}
	return n, nil
}

// scanRequest reads one recovery_requests row.
func scanRequest(row rowScanner) (Request, error) {
	var (
		req       Request
		status    string
		requested string
		decidedBy sql.NullInt64
		decidedAt sql.NullString
		clientIP  sql.NullString
	)
	err := row.Scan(&req.ID, &req.UserID, &status, &requested, &decidedBy, &decidedAt, &clientIP)
	if errors.Is(err, sql.ErrNoRows) {
		return Request{}, ErrNotFound
	}
	if err != nil {
		return Request{}, fmt.Errorf("recovery: scan request: %w", err)
	}
	req.Status = Status(status)
	if req.RequestedAt, err = store.ParseTime(requested); err != nil {
		return Request{}, fmt.Errorf("recovery: parse requested_at: %w", err)
	}
	if decidedBy.Valid {
		v := decidedBy.Int64
		req.DecidedBy = &v
	}
	if decidedAt.Valid && decidedAt.String != "" {
		t, err := store.ParseTime(decidedAt.String)
		if err != nil {
			return Request{}, fmt.Errorf("recovery: parse decided_at: %w", err)
		}
		req.DecidedAt = &t
	}
	req.ClientIP = clientIP.String
	return req, nil
}

// rowScanner is satisfied by *sql.Row and *sql.Rows.
type rowScanner interface {
	Scan(dest ...any) error
}

func nullableID(id int64) any {
	if id == 0 {
		return nil
	}
	return id
}

// nullString maps "" to NULL so the trail distinguishes "absent" from "empty".
func nullString(s string) any {
	if strings.TrimSpace(s) == "" {
		return nil
	}
	return s
}

func (s *Store) record(ctx context.Context, e audit.Event) {
	if s.audit != nil {
		s.audit.Record(ctx, e)
	}
}