package store

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

	"github.com/urpi/go-bananas/internal/domain"
)

// Preferences returns what the subject has chosen for their own interface.
//
// A subject with no row, which is everybody until they save a preference once,
// reads as empty rather than as an error: the zero value is the documented "no
// choice made" state and every caller renders a default for it.
//
// A stored theme that has since been deleted or archived is reported as no
// choice, for the same reason. Resolving the name against the themes table on
// read keeps a stale preference from pinning the UI to something that no longer
// exists, and it means an unpublish is reflected without a migration.
func (s *Store) Preferences(ctx context.Context, subject string) (domain.UserPreferences, error) {
	if subject == "" {
		return domain.UserPreferences{}, fmt.Errorf("%w: subject must not be empty", domain.ErrInvalid)
	}

	var stored domain.UserPreferences
	err := s.db.QueryRowContext(ctx, `
		SELECT selected_theme, selected_appearance
		FROM user_preferences
		WHERE subject = ?`, subject).
		Scan(&stored.SelectedTheme, &stored.SelectedAppearance)
	if errors.Is(err, sql.ErrNoRows) {
		return domain.UserPreferences{}, nil
	}
	if err != nil {
		return domain.UserPreferences{}, translateError(err)
	}

	if stored.SelectedTheme != "" {
		usable, err := s.themeUsable(ctx, stored.SelectedTheme)
		if err != nil {
			return domain.UserPreferences{}, err
		}
		if !usable {
			return domain.UserPreferences{}, nil
		}
	}
	if stored.SelectedAppearance != "" && !stored.SelectedAppearance.Valid() {
		// A build that no longer knows an appearance must not hand it to a
		// client, which would set an attribute nothing styles.
		return domain.UserPreferences{}, nil
	}
	return stored, nil
}

// SetPreferences records the subject's choice and returns what was stored.
//
// The theme must already exist and be published or archived. Drafts are rejected
// because they are invisible to runtime consumers, so a preference pointing at one
// would leave the UI rendering a theme it cannot load.
func (s *Store) SetPreferences(ctx context.Context, subject string, prefs domain.UserPreferences) (domain.UserPreferences, error) {
	if subject == "" {
		return domain.UserPreferences{}, fmt.Errorf("%w: subject must not be empty", domain.ErrInvalid)
	}
	if err := prefs.Validate(); err != nil {
		return domain.UserPreferences{}, err
	}

	if prefs.SelectedTheme != "" {
		usable, err := s.themeUsable(ctx, prefs.SelectedTheme)
		if err != nil {
			return domain.UserPreferences{}, err
		}
		if !usable {
			return domain.UserPreferences{}, fmt.Errorf(
				"%w: selectedTheme %q is not a published theme", domain.ErrInvalid, prefs.SelectedTheme)
		}
	} else {
		// An appearance without a theme has nothing to select a scheme from, so it
		// is dropped rather than stored. Clearing a choice by sending an empty
		// theme therefore works even if the client leaves the appearance set.
		prefs.SelectedAppearance = ""
	}

	_, err := s.db.ExecContext(ctx, `
		INSERT INTO user_preferences (subject, selected_theme, selected_appearance, updated_at)
		VALUES (?, ?, ?, ?)
		ON CONFLICT(subject) DO UPDATE SET
			selected_theme      = excluded.selected_theme,
			selected_appearance = excluded.selected_appearance,
			updated_at          = excluded.updated_at`,
		subject, prefs.SelectedTheme, string(prefs.SelectedAppearance), s.timestamp())
	if err != nil {
		return domain.UserPreferences{}, translateError(err)
	}
	return prefs, nil
}

// ClearPreferences forgets the subject's choice, which is how the UI returns to
// its own default. It reports whether a row was removed.
func (s *Store) ClearPreferences(ctx context.Context, subject string) (bool, error) {
	if subject == "" {
		return false, fmt.Errorf("%w: subject must not be empty", domain.ErrInvalid)
	}
	result, err := s.db.ExecContext(ctx, `DELETE FROM user_preferences WHERE subject = ?`, subject)
	if err != nil {
		return false, translateError(err)
	}
	affected, err := result.RowsAffected()
	if err != nil {
		// Drivers that cannot report this are not a reason to fail the request:
		// the row is gone either way, which is all the caller asked for.
		return true, nil //nolint:nilerr // see comment above
	}
	return affected > 0, nil
}

// ThemePreferenceCount reports how many subjects have chosen a theme, which the
// admin UI shows so an editor can see who a change would affect before making it.
func (s *Store) ThemePreferenceCount(ctx context.Context, slug string) (int, error) {
	if err := domain.ValidateSlug(slug); err != nil {
		return 0, fmt.Errorf("%w: %s", domain.ErrInvalid, err.Error())
	}
	var count int
	err := s.db.QueryRowContext(ctx, `
		SELECT count(*) FROM user_preferences WHERE selected_theme = ?`, slug).Scan(&count)
	if err != nil {
		return 0, translateError(err)
	}
	return count, nil
}

// themeUsable reports whether a slug names a theme a runtime consumer may load.
// Archived themes qualify because the last published revision of an archived theme
// stays resolvable for consumers pinned to it.
func (s *Store) themeUsable(ctx context.Context, slug string) (bool, error) {
	var status string
	err := s.db.QueryRowContext(ctx, `SELECT status FROM themes WHERE slug = ?`, slug).Scan(&status)
	if errors.Is(err, sql.ErrNoRows) {
		return false, nil
	}
	if err != nil {
		return false, translateError(err)
	}
	switch domain.ThemeStatus(status) {
	case domain.StatusPublished, domain.StatusArchived:
		return true, nil
	default:
		return false, nil
	}
}