package phasea

import (
	"context"
	"crypto/rand"
	"database/sql"
	_ "embed"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"regexp"
	"strings"
	"time"

	"github.com/jackc/pgx/v5/pgconn"
	_ "github.com/jackc/pgx/v5/stdlib"
)

//go:embed migrations/001_phase_a.sql
var migration001 string

var (
	ErrConflict          = errors.New("resource conflicts with existing state")
	ErrInvalid           = errors.New("invalid phase A input")
	ErrNotFound          = errors.New("resource not found")
	idPattern            = regexp.MustCompile(`^[a-z0-9][a-z0-9-]{0,31}$`)
	refPattern           = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._/-]{0,127}$`)
	credentialKeyPattern = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]{0,63}/[A-Za-z0-9][A-Za-z0-9._/-]{0,126}$`)
)

type Store struct{ db *sql.DB }

type Account struct {
	ID                    string `json:"id"`
	CredentialReferenceID string `json:"credential_reference_id"`
	CredentialProvider    string `json:"credential_provider"`
	CredentialKey         string `json:"-"`
	ProfileID             string `json:"profile_id"`
}

type RuntimeBinding struct {
	ID         string    `json:"id"`
	AccountID  string    `json:"account_id"`
	RuntimeID  string    `json:"runtime_id"`
	LeaseUntil time.Time `json:"lease_until"`
}

type Draft struct {
	ID        string `json:"id"`
	AccountID string `json:"account_id"`
	Version   int64  `json:"version"`
	Content   string `json:"content"`
}

type Confirmation struct {
	ID             string `json:"id"`
	AccountID      string `json:"account_id"`
	AccountVersion int64  `json:"account_version"`
	DraftID        string `json:"draft_id"`
	DraftVersion   int64  `json:"draft_version"`
	Version        int64  `json:"version"`
}

type Task struct {
	ID                  string `json:"id"`
	IdempotencyKey      string `json:"idempotency_key"`
	AccountID           string `json:"account_id"`
	AccountVersion      int64  `json:"account_version"`
	DraftID             string `json:"draft_id"`
	DraftVersion        int64  `json:"draft_version"`
	ConfirmationID      string `json:"confirmation_id"`
	ConfirmationVersion int64  `json:"confirmation_version"`
	State               string `json:"state"`
}

type Execution struct {
	TaskID              string `json:"task_id"`
	AttemptID           string `json:"attempt_id"`
	AccountID           string `json:"account_id"`
	ConfirmationID      string `json:"confirmation_id"`
	ConfirmationVersion int64  `json:"confirmation_version"`
	State               string `json:"state"`
	WasClaimed          bool   `json:"was_claimed"`
}

type AuditEvent struct {
	ID                  int64           `json:"id"`
	EventType           string          `json:"event_type"`
	AccountID           string          `json:"account_id,omitempty"`
	ConfirmationID      string          `json:"confirmation_id,omitempty"`
	ConfirmationVersion int64           `json:"confirmation_version,omitempty"`
	AttemptID           string          `json:"attempt_id,omitempty"`
	TaskID              string          `json:"task_id,omitempty"`
	Details             json.RawMessage `json:"details"`
	CreatedAt           time.Time       `json:"created_at"`
}

func Open(ctx context.Context, databaseURL string) (*Store, error) {
	db, err := sql.Open("pgx", databaseURL)
	if err != nil {
		return nil, errors.New("open phase A database")
	}
	db.SetMaxOpenConns(10)
	db.SetMaxIdleConns(2)
	db.SetConnMaxIdleTime(5 * time.Minute)
	if err := db.PingContext(ctx); err != nil {
		db.Close()
		return nil, errors.New("connect to phase A database")
	}
	store := &Store{db: db}
	if err := store.migrate(ctx); err != nil {
		db.Close()
		return nil, err
	}
	return store, nil
}

func (s *Store) Close() error { return s.db.Close() }

func (s *Store) migrate(ctx context.Context) error {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return errors.New("begin schema migration")
	}
	defer tx.Rollback()
	if _, err := tx.ExecContext(ctx, `SELECT pg_advisory_xact_lock(1542738011)`); err != nil {
		return errors.New("lock schema migration")
	}
	if _, err := tx.ExecContext(ctx, `CREATE TABLE IF NOT EXISTS schema_migration (version integer PRIMARY KEY, applied_at timestamptz NOT NULL DEFAULT now())`); err != nil {
		return errors.New("create schema migration table")
	}
	var applied bool
	if err := tx.QueryRowContext(ctx, `SELECT EXISTS (SELECT 1 FROM schema_migration WHERE version = 1)`).Scan(&applied); err != nil {
		return errors.New("read schema migration state")
	}
	if !applied {
		if _, err := tx.ExecContext(ctx, migration001); err != nil {
			return fmt.Errorf("apply schema migration 1: %w", err)
		}
		if _, err := tx.ExecContext(ctx, `INSERT INTO schema_migration (version) VALUES (1)`); err != nil {
			return errors.New("record schema migration 1")
		}
	}
	if err := tx.Commit(); err != nil {
		return errors.New("commit schema migration")
	}
	return nil
}

func (s *Store) CreateAccount(ctx context.Context, account Account) error {
	if !idPattern.MatchString(account.ID) || !refPattern.MatchString(account.CredentialReferenceID) ||
		!credentialKeyPattern.MatchString(account.CredentialKey) || !refPattern.MatchString(account.ProfileID) ||
		(account.CredentialProvider != "os_keyring" && account.CredentialProvider != "secret_manager") {
		return ErrInvalid
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return errors.New("begin account transaction")
	}
	defer tx.Rollback()
	if _, err := tx.ExecContext(ctx, `INSERT INTO credential_reference (id, provider, reference_key) VALUES ($1, $2, $3)`,
		account.CredentialReferenceID, account.CredentialProvider, account.CredentialKey); err != nil {
		return publicDatabaseError(err)
	}
	if _, err := tx.ExecContext(ctx, `INSERT INTO social_account (id, credential_reference_id, profile_id) VALUES ($1, $2, $3)`,
		account.ID, account.CredentialReferenceID, account.ProfileID); err != nil {
		return publicDatabaseError(err)
	}
	if err := appendAudit(ctx, tx, "account_created", account.ID, "", 0, "", "", map[string]string{"profile_id": account.ProfileID}); err != nil {
		return err
	}
	return commit(tx)
}

func (s *Store) BindRuntime(ctx context.Context, binding RuntimeBinding) error {
	if !refPattern.MatchString(binding.ID) || !idPattern.MatchString(binding.AccountID) ||
		!refPattern.MatchString(binding.RuntimeID) || !binding.LeaseUntil.After(time.Now()) {
		return ErrInvalid
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return errors.New("begin runtime transaction")
	}
	defer tx.Rollback()
	if _, err := tx.ExecContext(ctx, `UPDATE runtime_instance SET released_at = now() WHERE released_at IS NULL AND lease_until < now()`); err != nil {
		return errors.New("expire runtime bindings")
	}
	var accountID string
	if err := tx.QueryRowContext(ctx, `
		INSERT INTO runtime_instance (id, account_id, runtime_id, lease_until)
		SELECT $1, id, $3, $4 FROM social_account WHERE id = $2 AND status = 'active'
		RETURNING account_id`, binding.ID, binding.AccountID, binding.RuntimeID, binding.LeaseUntil).Scan(&accountID); err != nil {
		if errors.Is(err, sql.ErrNoRows) {
			return ErrConflict
		}
		return rowError(err)
	}
	if err := appendAudit(ctx, tx, "runtime_bound", accountID, "", 0, "", "", map[string]string{"runtime_id": binding.RuntimeID}); err != nil {
		return err
	}
	return commit(tx)
}

func (s *Store) ReleaseRuntime(ctx context.Context, id string) error {
	if !refPattern.MatchString(id) {
		return ErrInvalid
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return errors.New("begin runtime release")
	}
	defer tx.Rollback()
	var accountID string
	if err := tx.QueryRowContext(ctx, `UPDATE runtime_instance SET released_at = now() WHERE id = $1 AND released_at IS NULL RETURNING account_id`, id).Scan(&accountID); err != nil {
		return rowError(err)
	}
	if err := appendAudit(ctx, tx, "runtime_released", accountID, "", 0, "", "", map[string]string{"binding_id": id}); err != nil {
		return err
	}
	return commit(tx)
}

func (s *Store) CreateDraft(ctx context.Context, draft Draft) error {
	if !refPattern.MatchString(draft.ID) || !idPattern.MatchString(draft.AccountID) || draft.Version < 1 || strings.TrimSpace(draft.Content) == "" {
		return ErrInvalid
	}
	_, err := s.db.ExecContext(ctx, `INSERT INTO content_draft (id, account_id, version, content) VALUES ($1, $2, $3, $4)`,
		draft.ID, draft.AccountID, draft.Version, draft.Content)
	return publicDatabaseError(err)
}

func (s *Store) Confirm(ctx context.Context, confirmation Confirmation) error {
	if !refPattern.MatchString(confirmation.ID) || !idPattern.MatchString(confirmation.AccountID) ||
		!refPattern.MatchString(confirmation.DraftID) || confirmation.AccountVersion < 1 || confirmation.DraftVersion < 1 || confirmation.Version < 1 {
		return ErrInvalid
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return errors.New("begin confirmation transaction")
	}
	defer tx.Rollback()
	var valid bool
	if err := tx.QueryRowContext(ctx, `
		SELECT EXISTS (
			SELECT 1 FROM social_account a JOIN content_draft d ON d.account_id = a.id
			WHERE a.id = $1 AND a.version = $2 AND d.id = $3 AND d.version = $4
		)`, confirmation.AccountID, confirmation.AccountVersion, confirmation.DraftID, confirmation.DraftVersion).Scan(&valid); err != nil {
		return errors.New("validate confirmation versions")
	}
	if !valid {
		return ErrConflict
	}
	if _, err := tx.ExecContext(ctx, `
		INSERT INTO confirmation (id, account_id, account_version, draft_id, draft_version, version)
		VALUES ($1, $2, $3, $4, $5, $6)`, confirmation.ID, confirmation.AccountID, confirmation.AccountVersion,
		confirmation.DraftID, confirmation.DraftVersion, confirmation.Version); err != nil {
		return publicDatabaseError(err)
	}
	if err := appendAudit(ctx, tx, "draft_confirmed", confirmation.AccountID, confirmation.ID, confirmation.Version, "", "", map[string]any{
		"account_version": confirmation.AccountVersion, "draft_id": confirmation.DraftID, "draft_version": confirmation.DraftVersion,
	}); err != nil {
		return err
	}
	return commit(tx)
}

func (s *Store) Enqueue(ctx context.Context, task Task) (Task, bool, error) {
	if !refPattern.MatchString(task.ID) || !refPattern.MatchString(task.IdempotencyKey) || !idPattern.MatchString(task.AccountID) ||
		!refPattern.MatchString(task.DraftID) || task.AccountVersion < 1 || task.DraftVersion < 1 ||
		((task.ConfirmationID == "") != (task.ConfirmationVersion == 0)) ||
		(task.ConfirmationID != "" && (!refPattern.MatchString(task.ConfirmationID) || task.ConfirmationVersion < 1)) {
		return Task{}, false, ErrInvalid
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return Task{}, false, errors.New("begin task transaction")
	}
	defer tx.Rollback()
	var insertedID string
	err = tx.QueryRowContext(ctx, `
		INSERT INTO operation_task (id, idempotency_key, account_id, account_version, draft_id, draft_version, confirmation_id, confirmation_version)
		VALUES ($1, $2, $3, $4, $5, $6, NULLIF($7, ''), NULLIF($8, 0))
		ON CONFLICT (idempotency_key) DO NOTHING RETURNING id`, task.ID, task.IdempotencyKey, task.AccountID, task.AccountVersion,
		task.DraftID, task.DraftVersion, task.ConfirmationID, task.ConfirmationVersion).Scan(&insertedID)
	if err != nil && !errors.Is(err, sql.ErrNoRows) {
		return Task{}, false, publicDatabaseError(err)
	}
	if insertedID != "" {
		task.State = "queued"
		if err := appendAudit(ctx, tx, "task_queued", task.AccountID, task.ConfirmationID, task.ConfirmationVersion, "", task.ID, nil); err != nil {
			return Task{}, false, err
		}
		if err := commit(tx); err != nil {
			return Task{}, false, err
		}
		return task, true, nil
	}

	var existing Task
	var confirmationID sql.NullString
	var confirmationVersion sql.NullInt64
	err = tx.QueryRowContext(ctx, `
		SELECT id, idempotency_key, account_id, account_version, draft_id, draft_version, confirmation_id, confirmation_version, state
		FROM operation_task WHERE idempotency_key = $1`, task.IdempotencyKey).Scan(&existing.ID, &existing.IdempotencyKey,
		&existing.AccountID, &existing.AccountVersion, &existing.DraftID, &existing.DraftVersion, &confirmationID, &confirmationVersion, &existing.State)
	if err != nil {
		return Task{}, false, rowError(err)
	}
	existing.ConfirmationID = confirmationID.String
	existing.ConfirmationVersion = confirmationVersion.Int64
	if existing.AccountID != task.AccountID || existing.AccountVersion != task.AccountVersion || existing.DraftID != task.DraftID ||
		existing.DraftVersion != task.DraftVersion || existing.ConfirmationID != task.ConfirmationID || existing.ConfirmationVersion != task.ConfirmationVersion {
		return Task{}, false, ErrConflict
	}
	if err := commit(tx); err != nil {
		return Task{}, false, err
	}
	return existing, false, nil
}

func (s *Store) PauseAccount(ctx context.Context, accountID string) error {
	if !idPattern.MatchString(accountID) {
		return ErrInvalid
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return errors.New("begin pause transaction")
	}
	defer tx.Rollback()
	var version int64
	var status string
	if err := tx.QueryRowContext(ctx, `SELECT version, status FROM social_account WHERE id = $1 FOR UPDATE`, accountID).Scan(&version, &status); err != nil {
		return rowError(err)
	}
	if status == "paused" {
		return commit(tx)
	}
	if err := tx.QueryRowContext(ctx, `
		UPDATE social_account SET status = 'paused', paused_at = now(), version = version + 1, updated_at = now()
		WHERE id = $1 RETURNING version`, accountID).Scan(&version); err != nil {
		return errors.New("pause account")
	}
	result, err := tx.ExecContext(ctx, `
		UPDATE operation_task SET state = 'policy_hold', updated_at = now()
		WHERE account_id = $1 AND state = 'queued'`, accountID)
	if err != nil {
		return errors.New("hold queued account tasks")
	}
	held, _ := result.RowsAffected()
	if err := appendAudit(ctx, tx, "account_paused", accountID, "", 0, "", "", map[string]any{"account_version": version, "tasks_held": held}); err != nil {
		return err
	}
	return commit(tx)
}

func (s *Store) CancelTask(ctx context.Context, taskID string) error {
	if !refPattern.MatchString(taskID) {
		return ErrInvalid
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return errors.New("begin cancel transaction")
	}
	defer tx.Rollback()
	var accountID, state string
	var attemptID sql.NullString
	var confirmationID sql.NullString
	var confirmationVersion sql.NullInt64
	err = tx.QueryRowContext(ctx, `
		UPDATE operation_task SET state = CASE WHEN state = 'executing' THEN 'needs_confirmation' ELSE 'cancelled' END,
			lease_owner = NULL, lease_until = NULL, updated_at = now()
		WHERE id = $1 AND state IN ('queued', 'executing', 'needs_confirmation', 'policy_hold')
		RETURNING account_id, state, current_attempt_id, confirmation_id, confirmation_version`, taskID).Scan(
		&accountID, &state, &attemptID, &confirmationID, &confirmationVersion)
	if err != nil {
		return rowError(err)
	}
	if attemptID.Valid {
		if _, err := tx.ExecContext(ctx, `
			UPDATE execution_attempt SET finished_at = now(), outcome = 'uncertain'
			WHERE id = $1 AND finished_at IS NULL`, attemptID.String); err != nil {
			return errors.New("mark cancelled attempt uncertain")
		}
	}
	if err := appendAudit(ctx, tx, "task_cancel_requested", accountID, confirmationID.String, confirmationVersion.Int64, attemptID.String, taskID, map[string]string{"state": state}); err != nil {
		return err
	}
	return commit(tx)
}

func (s *Store) ExecuteMock(ctx context.Context, workerID, outcome string) (Execution, error) {
	if !refPattern.MatchString(workerID) || (outcome != "succeeded" && outcome != "failed" && outcome != "uncertain" && outcome != "policy_hold") {
		return Execution{}, ErrInvalid
	}
	execution, err := s.claim(ctx, workerID)
	if err != nil || !execution.WasClaimed {
		return execution, err
	}
	return s.complete(ctx, workerID, execution, outcome)
}

func (s *Store) claim(ctx context.Context, workerID string) (Execution, error) {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return Execution{}, errors.New("begin claim transaction")
	}
	defer tx.Rollback()
	if err := quarantineExpired(ctx, tx); err != nil {
		return Execution{}, err
	}
	if err := quarantineInvalid(ctx, tx); err != nil {
		return Execution{}, err
	}
	var execution Execution
	err = tx.QueryRowContext(ctx, `
		WITH candidate AS (
			SELECT t.id
			FROM operation_task t
			JOIN social_account a ON a.id = t.account_id
			JOIN content_draft d ON d.id = t.draft_id
			JOIN confirmation c ON c.id = t.confirmation_id
			WHERE t.state = 'queued' AND a.status = 'active'
			  AND a.version = t.account_version
			  AND d.account_id = t.account_id AND d.version = t.draft_version
			  AND c.account_id = t.account_id AND c.account_version = t.account_version
			  AND c.draft_id = t.draft_id AND c.draft_version = t.draft_version
			  AND c.version = t.confirmation_version
			ORDER BY t.created_at, t.id
			FOR UPDATE OF t SKIP LOCKED LIMIT 1
		)
		UPDATE operation_task t SET state = 'executing', lease_owner = $1,
			lease_until = now() + interval '1 minute', updated_at = now()
		FROM candidate WHERE t.id = candidate.id
		RETURNING t.id, t.account_id, t.confirmation_id, t.confirmation_version`, workerID).Scan(
		&execution.TaskID, &execution.AccountID, &execution.ConfirmationID, &execution.ConfirmationVersion)
	if errors.Is(err, sql.ErrNoRows) {
		if err := commit(tx); err != nil {
			return Execution{}, err
		}
		return Execution{}, nil
	}
	if err != nil {
		return Execution{}, errors.New("claim task")
	}
	execution.AttemptID = newID()
	execution.State = "executing"
	execution.WasClaimed = true
	if _, err := tx.ExecContext(ctx, `INSERT INTO execution_attempt (id, task_id) VALUES ($1, $2)`, execution.AttemptID, execution.TaskID); err != nil {
		return Execution{}, publicDatabaseError(err)
	}
	if _, err := tx.ExecContext(ctx, `UPDATE operation_task SET current_attempt_id = $1 WHERE id = $2`, execution.AttemptID, execution.TaskID); err != nil {
		return Execution{}, errors.New("attach execution attempt")
	}
	if err := appendAudit(ctx, tx, "task_claimed", execution.AccountID, execution.ConfirmationID, execution.ConfirmationVersion, execution.AttemptID, execution.TaskID, map[string]string{"worker_id": workerID}); err != nil {
		return Execution{}, err
	}
	if err := commit(tx); err != nil {
		return Execution{}, err
	}
	return execution, nil
}

func (s *Store) complete(ctx context.Context, workerID string, execution Execution, outcome string) (Execution, error) {
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return Execution{}, errors.New("begin completion transaction")
	}
	defer tx.Rollback()
	var leaseUntil time.Time
	err = tx.QueryRowContext(ctx, `
		SELECT lease_until FROM operation_task
		WHERE id = $1 AND state = 'executing' AND lease_owner = $2 AND current_attempt_id = $3
		FOR UPDATE`, execution.TaskID, workerID, execution.AttemptID).Scan(&leaseUntil)
	if err != nil {
		return Execution{}, rowError(err)
	}
	state := map[string]string{"succeeded": "succeeded", "failed": "failed", "uncertain": "needs_confirmation", "policy_hold": "policy_hold"}[outcome]
	if leaseUntil.Before(time.Now()) {
		outcome, state = "uncertain", "needs_confirmation"
	}
	result, _ := json.Marshal(map[string]string{"mock_outcome": outcome})
	if _, err := tx.ExecContext(ctx, `UPDATE execution_attempt SET finished_at = now(), outcome = $1, result = $2 WHERE id = $3`, outcome, result, execution.AttemptID); err != nil {
		return Execution{}, errors.New("finish execution attempt")
	}
	if _, err := tx.ExecContext(ctx, `
		UPDATE operation_task SET state = $1, lease_owner = NULL, lease_until = NULL, updated_at = now() WHERE id = $2`, state, execution.TaskID); err != nil {
		return Execution{}, errors.New("finish task")
	}
	if err := appendAudit(ctx, tx, "task_finished", execution.AccountID, execution.ConfirmationID, execution.ConfirmationVersion, execution.AttemptID, execution.TaskID, map[string]string{"state": state}); err != nil {
		return Execution{}, err
	}
	if err := commit(tx); err != nil {
		return Execution{}, err
	}
	execution.State = state
	return execution, nil
}

func quarantineExpired(ctx context.Context, tx *sql.Tx) error {
	rows, err := tx.QueryContext(ctx, `
		UPDATE operation_task SET state = 'needs_confirmation', lease_owner = NULL, lease_until = NULL, updated_at = now()
		WHERE state = 'executing' AND lease_until < now()
		RETURNING id, account_id, current_attempt_id, confirmation_id, confirmation_version`)
	if err != nil {
		return errors.New("quarantine expired tasks")
	}
	type expiredTask struct {
		taskID, accountID, attemptID, confirmationID string
		confirmationVersion                          int64
	}
	var expired []expiredTask
	for rows.Next() {
		var taskID, accountID string
		var attemptID sql.NullString
		var confirmationID sql.NullString
		var confirmationVersion sql.NullInt64
		if err := rows.Scan(&taskID, &accountID, &attemptID, &confirmationID, &confirmationVersion); err != nil {
			rows.Close()
			return errors.New("read expired task")
		}
		expired = append(expired, expiredTask{taskID, accountID, attemptID.String, confirmationID.String, confirmationVersion.Int64})
	}
	if err := rows.Close(); err != nil {
		return errors.New("close expired task rows")
	}
	for _, task := range expired {
		if task.attemptID != "" {
			if _, err := tx.ExecContext(ctx, `UPDATE execution_attempt SET finished_at = now(), outcome = 'uncertain' WHERE id = $1 AND finished_at IS NULL`, task.attemptID); err != nil {
				return errors.New("mark expired attempt uncertain")
			}
		}
		if err := appendAudit(ctx, tx, "task_lease_expired", task.accountID, task.confirmationID, task.confirmationVersion, task.attemptID, task.taskID, nil); err != nil {
			return err
		}
	}
	return nil
}

func quarantineInvalid(ctx context.Context, tx *sql.Tx) error {
	rows, err := tx.QueryContext(ctx, `
		UPDATE operation_task t SET
			state = CASE WHEN EXISTS (
				SELECT 1 FROM social_account paused WHERE paused.id = t.account_id AND paused.status = 'paused'
			) THEN 'policy_hold' ELSE 'needs_confirmation' END,
			updated_at = now()
		WHERE t.state = 'queued' AND NOT EXISTS (
			SELECT 1
			FROM social_account a
			JOIN content_draft d ON d.id = t.draft_id
			JOIN confirmation c ON c.id = t.confirmation_id
			WHERE a.id = t.account_id AND a.status = 'active' AND a.version = t.account_version
			  AND d.account_id = t.account_id AND d.version = t.draft_version
			  AND c.account_id = t.account_id AND c.account_version = t.account_version
			  AND c.draft_id = t.draft_id AND c.draft_version = t.draft_version
			  AND c.version = t.confirmation_version
		)
		RETURNING t.id, t.account_id, t.confirmation_id, t.confirmation_version, t.state`)
	if err != nil {
		return errors.New("quarantine invalid tasks")
	}
	type invalidTask struct {
		taskID, accountID, confirmationID, state string
		confirmationVersion                      int64
	}
	var invalid []invalidTask
	for rows.Next() {
		var taskID, accountID, state string
		var confirmationID sql.NullString
		var confirmationVersion sql.NullInt64
		if err := rows.Scan(&taskID, &accountID, &confirmationID, &confirmationVersion, &state); err != nil {
			rows.Close()
			return errors.New("read quarantined task")
		}
		invalid = append(invalid, invalidTask{taskID, accountID, confirmationID.String, state, confirmationVersion.Int64})
	}
	if err := rows.Close(); err != nil {
		return errors.New("close quarantined task rows")
	}
	for _, task := range invalid {
		if err := appendAudit(ctx, tx, "task_quarantined", task.accountID, task.confirmationID, task.confirmationVersion, "", task.taskID, map[string]string{"state": task.state}); err != nil {
			return err
		}
	}
	return nil
}

func (s *Store) Audit(ctx context.Context) ([]AuditEvent, error) {
	rows, err := s.db.QueryContext(ctx, `
		SELECT id, event_type, account_id, confirmation_id, confirmation_version, attempt_id, task_id, details, created_at
		FROM audit_event ORDER BY id`)
	if err != nil {
		return nil, errors.New("read audit events")
	}
	defer rows.Close()
	var events []AuditEvent
	for rows.Next() {
		var event AuditEvent
		var accountID, confirmationID, attemptID, taskID sql.NullString
		var confirmationVersion sql.NullInt64
		if err := rows.Scan(&event.ID, &event.EventType, &accountID, &confirmationID, &confirmationVersion, &attemptID, &taskID, &event.Details, &event.CreatedAt); err != nil {
			return nil, errors.New("decode audit event")
		}
		event.AccountID, event.ConfirmationID, event.ConfirmationVersion = accountID.String, confirmationID.String, confirmationVersion.Int64
		event.AttemptID, event.TaskID = attemptID.String, taskID.String
		events = append(events, event)
	}
	return events, rows.Err()
}

func appendAudit(ctx context.Context, tx *sql.Tx, eventType, accountID, confirmationID string, confirmationVersion int64, attemptID, taskID string, details any) error {
	if details == nil {
		details = map[string]any{}
	}
	encoded, err := json.Marshal(details)
	if err != nil {
		return errors.New("encode audit details")
	}
	_, err = tx.ExecContext(ctx, `
		INSERT INTO audit_event (event_type, account_id, confirmation_id, confirmation_version, attempt_id, task_id, details)
		VALUES ($1, NULLIF($2, ''), NULLIF($3, ''), NULLIF($4, 0), NULLIF($5, ''), NULLIF($6, ''), $7)`,
		eventType, accountID, confirmationID, confirmationVersion, attemptID, taskID, encoded)
	if err != nil {
		return errors.New("append audit event")
	}
	return nil
}

func newID() string {
	var value [16]byte
	_, _ = rand.Read(value[:])
	return hex.EncodeToString(value[:])
}

func commit(tx *sql.Tx) error {
	if err := tx.Commit(); err != nil {
		return errors.New("commit transaction")
	}
	return nil
}

func rowError(err error) error {
	if errors.Is(err, sql.ErrNoRows) {
		return ErrNotFound
	}
	return publicDatabaseError(err)
}

func publicDatabaseError(err error) error {
	if err == nil {
		return nil
	}
	var postgresError *pgconn.PgError
	if errors.As(err, &postgresError) && (postgresError.Code == "23505" || postgresError.Code == "23503" || postgresError.Code == "23514") {
		return ErrConflict
	}
	return errors.New("phase A persistence operation failed")
}