package auth

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

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

// IdentitiesService implements Identities (and the routing.Resolver contract).
type IdentitiesService struct {
	*Core
}

var (
	_ Identities = (*IdentitiesService)(nil)
)

// Mint implements Identities.Mint (SPEC-004 §5).
//
// A user has at most one non-revoked identity at a time, so Mint refuses if one
// still exists — recovery goes through Rotate, which retires the old one first
// (D-007).
func (s *IdentitiesService) Mint(ctx context.Context, userID int64) (int64, string, error) {
	ok, err := s.userExists(userID)
	if err != nil {
		return 0, "", err
	}
	if !ok {
		return 0, "", fmt.Errorf("%w: user:%d", ErrUnknownUser, userID)
	}

	var live int
	if err := s.db.QueryRow(
		`SELECT count(*) FROM identities WHERE user_id = ? AND status <> 'revoked'`, userID,
	).Scan(&live); err != nil {
		return 0, "", fmt.Errorf("auth: count live identities: %w", err)
	}
	if live > 0 {
		return 0, "", fmt.Errorf("%w: user:%d", ErrIdentityExists, userID)
	}

	guid, err := newGUID(s.db)
	if err != nil {
		return 0, "", err
	}

	res, err := s.db.Exec(
		`INSERT INTO identities (user_id, guid, status, created_at)
		 VALUES (?, ?, ?, ?)`,
		userID, guid, string(StatusPendingEnrollment), store.FormatTime(s.clock()),
	)
	if err != nil {
		return 0, "", fmt.Errorf("auth: insert identity: %w", err)
	}
	id, err := res.LastInsertId()
	if err != nil {
		return 0, "", fmt.Errorf("auth: identity id: %w", err)
	}

	// The ACTOR is the creator/approver and comes from the audit.Meta on ctx
	// (ruling R-4); the affected user is the SUBJECT. The event leaves
	// ActorUserID unset so audit.Merge fills it from the context.
	s.record(ctx, audit.Event{
		Action:  "identity.mint",
		Subject: fmt.Sprintf("user:%d", userID),
		Detail:  fmt.Sprintf("identity:%d status=pending_enrollment", id),
	})
	return id, guid, nil
}

// Activate implements Identities.Activate: pending_enrollment -> active.
func (s *IdentitiesService) Activate(ctx context.Context, id int64) error {
	idn, err := s.identityByID(id)
	if err != nil {
		return err
	}
	if idn.Status != StatusPendingEnrollment {
		return fmt.Errorf("%w: identity:%d is %s", ErrIdentityNotPending, id, idn.Status)
	}

	now := store.FormatTime(s.clock())
	if _, err := s.db.Exec(
		`UPDATE identities SET status = ?, enrolled_at = ? WHERE identity_id = ?`,
		string(StatusActive), now, id,
	); err != nil {
		// The partial unique index rejects a second active identity (AC-1).
		return fmt.Errorf("auth: activate identity: %w", err)
	}

	// The actor is the context actor (R-4); the affected user is the subject.
	s.record(ctx, audit.Event{
		Action:  "identity.activate",
		Subject: fmt.Sprintf("user:%d", idn.UserID),
		Detail:  fmt.Sprintf("identity:%d status=active", id),
	})
	return nil
}

// Rotate implements Identities.Rotate (D-007, AC-5): revoke the current
// identity AND all its sessions, then mint a fresh pending identity with a NEW
// GUID. The old GUID is tombstoned forever.
func (s *IdentitiesService) Rotate(ctx context.Context, userID int64) (string, error) {
	ok, err := s.userExists(userID)
	if err != nil {
		return "", err
	}
	if !ok {
		return "", fmt.Errorf("%w: user:%d", ErrUnknownUser, userID)
	}

	now := store.FormatTime(s.clock())

	tx, err := s.db.Begin()
	if err != nil {
		return "", fmt.Errorf("auth: begin rotate: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	// Retire the current identity, if any.
	var oldID int64
	err = tx.QueryRow(
		`SELECT identity_id FROM identities
		  WHERE user_id = ? AND status <> 'revoked'
		  ORDER BY identity_id DESC LIMIT 1`, userID,
	).Scan(&oldID)
	switch {
	case errors.Is(err, sql.ErrNoRows):
		// nothing to revoke
	case err != nil:
		return "", fmt.Errorf("auth: find current identity: %w", err)
	default:
		if _, err := tx.Exec(
			`UPDATE identities SET status = ?, revoked_at = ? WHERE identity_id = ?`,
			string(StatusRevoked), now, oldID,
		); err != nil {
			return "", fmt.Errorf("auth: revoke old identity: %w", err)
		}
		if _, err := tx.Exec(
			`UPDATE sessions SET revoked_at = ? WHERE identity_id = ? AND revoked_at IS NULL`,
			now, oldID,
		); err != nil {
			return "", fmt.Errorf("auth: revoke old sessions: %w", err)
		}
	}

	// Mint the replacement.
	guid, err := newGUID(tx)
	if err != nil {
		return "", err
	}
	if _, err := tx.Exec(
		`INSERT INTO identities (user_id, guid, status, created_at)
		 VALUES (?, ?, ?, ?)`,
		userID, guid, string(StatusPendingEnrollment), now,
	); err != nil {
		return "", fmt.Errorf("auth: insert rotated identity: %w", err)
	}

	if err := tx.Commit(); err != nil {
		return "", fmt.Errorf("auth: commit rotate: %w", err)
	}

	s.record(ctx, audit.Event{
		Action:  "identity.rotate",
		Subject: fmt.Sprintf("user:%d", userID),
		Detail:  "old identity revoked; new GUID minted",
	})
	return guid, nil
}

// Revoke implements Identities.Revoke: revoke the identity and every session
// it minted.
func (s *IdentitiesService) Revoke(ctx context.Context, id int64) error {
	idn, err := s.identityByID(id)
	if err != nil {
		return err
	}
	if idn.Status == StatusRevoked {
		return nil // idempotent
	}

	now := store.FormatTime(s.clock())
	tx, err := s.db.Begin()
	if err != nil {
		return fmt.Errorf("auth: begin revoke: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	if _, err := tx.Exec(
		`UPDATE identities SET status = ?, revoked_at = ? WHERE identity_id = ?`,
		string(StatusRevoked), now, id,
	); err != nil {
		return fmt.Errorf("auth: revoke identity: %w", err)
	}
	if _, err := tx.Exec(
		`UPDATE sessions SET revoked_at = ? WHERE identity_id = ? AND revoked_at IS NULL`,
		now, id,
	); err != nil {
		return fmt.Errorf("auth: revoke sessions: %w", err)
	}
	if err := tx.Commit(); err != nil {
		return fmt.Errorf("auth: commit revoke: %w", err)
	}

	s.record(ctx, audit.Event{
		Action:  "identity.revoke",
		Subject: fmt.Sprintf("user:%d", idn.UserID),
		Detail:  fmt.Sprintf("identity:%d status=revoked", id),
	})
	return nil
}

// ByGUID implements Identities.ByGUID. Unlike a revoked GUID — which is
// tombstoned and looks like "not found" to the door — a revoked identity is
// still returned here so callers can distinguish and audit it.
//
// It takes a context for symmetry with the rest of the service contract
// (ruling R-1); the lookup itself is read-only.
func (s *IdentitiesService) ByGUID(ctx context.Context, guid string) (Identity, error) {
	return s.byGUID(guid)
}

// byGUID is the context-free read behind ByGUID and the routing.Resolver
// contract (which cannot take a context — it is part of the pure model,
// SPEC-002 §3.1).
func (s *IdentitiesService) byGUID(guid string) (Identity, error) {
	if guid == "" {
		return Identity{}, ErrIdentityNotFound
	}
	row := s.db.QueryRow(`
		SELECT identity_id, user_id, guid, status, created_at, enrolled_at, revoked_at
		  FROM identities WHERE guid = ?`, guid)
	return scanIdentity(row)
}

// ByUserID returns the user's current (non-revoked) identity — the newest row
// that is not a tombstone. It is the wizard's lookup (SPEC-005 §4): the step is
// derived from the admin's identity status. Revoked rows stay as tombstones
// (D-008) and are never selected.
func (s *IdentitiesService) ByUserID(ctx context.Context, userID int64) (Identity, error) {
	row := s.db.QueryRow(`
		SELECT identity_id, user_id, guid, status, created_at, enrolled_at, revoked_at
		  FROM identities
		 WHERE user_id = ? AND status <> 'revoked'
		 ORDER BY identity_id DESC LIMIT 1`, userID)
	return scanIdentity(row)
}

// GUID implements the routing.Resolver contract (SPEC-002 §3.1): it answers
// found/enrolled for the pure model. A revoked (tombstoned) GUID is reported as
// not found so the door returns 404 (SPEC-006 §3).
//
// It deliberately takes NO context: it is an implementation of the pure
// model's injected interface and never writes audit.
func (s *IdentitiesService) GUID(guid string) (found, enrolled bool) {
	idn, err := s.byGUID(guid)
	if err != nil {
		return false, false
	}
	switch idn.Status {
	case StatusActive:
		return true, true
	case StatusPendingEnrollment:
		return true, false
	default: // revoked
		return false, false
	}
}

// WithinEnrollmentWindow reports whether a pending identity is still inside its
// bounded invite window (SPEC-004 §4, A1). A non-pending identity is false.
func (s *IdentitiesService) WithinEnrollmentWindow(ctx context.Context, id int64) (bool, error) {
	idn, err := s.identityByID(id)
	if err != nil {
		return false, err
	}
	if idn.Status != StatusPendingEnrollment {
		return false, nil
	}
	return idn.CreatedAt.Add(s.enrollWindow).After(s.clock()), nil
}