package store

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

	"gitea.stevedudenhoeffer.com/steve/pansy/internal/domain"
)

// userColumns lists the users columns in the fixed order scanUser expects.
const userColumns = `id, email, display_name, password_hash, oidc_issuer, oidc_subject, is_admin, version, created_at, updated_at`

// scanner is satisfied by both *sql.Row and *sql.Rows, so scanUser works for
// single-row and multi-row queries alike.
type scanner interface {
	Scan(dest ...any) error
}

// scanUser reads one users row. is_admin is stored as INTEGER 0/1 (the driver
// returns it as int64, which does not convert straight to bool), so it is read
// into an int64 and mapped.
func scanUser(s scanner) (*domain.User, error) {
	var (
		u       domain.User
		isAdmin int64
	)
	if err := s.Scan(
		&u.ID, &u.Email, &u.DisplayName, &u.PasswordHash,
		&u.OIDCIssuer, &u.OIDCSubject, &isAdmin, &u.Version,
		&u.CreatedAt, &u.UpdatedAt,
	); err != nil {
		return nil, err
	}
	u.IsAdmin = isAdmin != 0
	return &u, nil
}

// CreateUser inserts a new user and returns the stored row (with generated id
// and timestamps). PasswordHash/OIDCIssuer/OIDCSubject may be nil.
//
// Two invariants are enforced inside the single INSERT statement so concurrent
// registrations can't violate them (SQLite serializes writers, and the COUNT
// subqueries see the latest committed state):
//   - is_admin is set iff this is the first user — no read-then-write window in
//     which two "first" registrations both become admin.
//   - the row is inserted only when the table is empty (bootstrap) or allowSignup
//     is true; otherwise zero rows are affected and ErrRegistrationClosed is
//     returned. This is the authoritative registration gate.
//
// A duplicate email trips the UNIQUE index and maps to ErrEmailTaken.
func (d *DB) CreateUser(ctx context.Context, u *domain.User, allowSignup bool) (*domain.User, error) {
	res, err := d.sql.ExecContext(ctx,
		`INSERT INTO users (email, display_name, password_hash, oidc_issuer, oidc_subject, is_admin)
		 SELECT ?, ?, ?, ?, ?, (SELECT count(*) FROM users) = 0
		 WHERE (SELECT count(*) FROM users) = 0 OR ?`,
		u.Email, u.DisplayName, u.PasswordHash, u.OIDCIssuer, u.OIDCSubject, boolToInt(allowSignup),
	)
	if err != nil {
		if isUniqueViolation(err) {
			return nil, domain.ErrEmailTaken
		}
		return nil, fmt.Errorf("store: insert user: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return nil, fmt.Errorf("store: user insert rows: %w", err)
	}
	if n == 0 {
		return nil, domain.ErrRegistrationClosed
	}
	id, err := res.LastInsertId()
	if err != nil {
		return nil, fmt.Errorf("store: user insert id: %w", err)
	}
	return d.GetUserByID(ctx, id)
}

// GetUserByID returns the user with the given id, or domain.ErrNotFound.
func (d *DB) GetUserByID(ctx context.Context, id int64) (*domain.User, error) {
	u, err := scanUser(d.sql.QueryRowContext(ctx,
		`SELECT `+userColumns+` FROM users WHERE id = ?`, id))
	if errors.Is(err, sql.ErrNoRows) {
		return nil, domain.ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("store: get user by id: %w", err)
	}
	return u, nil
}

// GetUserByEmail returns the user with the given email (case-insensitive via the
// column's NOCASE collation), or domain.ErrNotFound.
func (d *DB) GetUserByEmail(ctx context.Context, email string) (*domain.User, error) {
	u, err := scanUser(d.sql.QueryRowContext(ctx,
		`SELECT `+userColumns+` FROM users WHERE email = ?`, email))
	if errors.Is(err, sql.ErrNoRows) {
		return nil, domain.ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("store: get user by email: %w", err)
	}
	return u, nil
}

// GetUserByOIDC returns the user with the given (issuer, subject) identity pair,
// or domain.ErrNotFound. Both arguments must be non-empty.
func (d *DB) GetUserByOIDC(ctx context.Context, issuer, subject string) (*domain.User, error) {
	u, err := scanUser(d.sql.QueryRowContext(ctx,
		`SELECT `+userColumns+` FROM users WHERE oidc_issuer = ? AND oidc_subject = ?`, issuer, subject))
	if errors.Is(err, sql.ErrNoRows) {
		return nil, domain.ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("store: get user by oidc: %w", err)
	}
	return u, nil
}

// LinkOIDC stamps an OIDC identity onto an existing user (first OIDC login for a
// pre-existing local account) and returns the updated row.
//
// The UPDATE only matches when the account carries no identity yet, or already
// carries this exact one (idempotent) — it will NOT overwrite a different stored
// identity, which would let anyone asserting the same email at a second IdP
// hijack or lock out the account. A no-match (different identity, or the row is
// gone) and a UNIQUE (issuer, subject) collision with another account both
// surface as domain.ErrOIDCIdentityConflict. RETURNING folds the read-back into
// the same statement.
func (d *DB) LinkOIDC(ctx context.Context, userID int64, issuer, subject string) (*domain.User, error) {
	u, err := scanUser(d.sql.QueryRowContext(ctx,
		`UPDATE users
		    SET oidc_issuer = ?, oidc_subject = ?,
		        version = version + 1,
		        updated_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now')
		  WHERE id = ?
		    AND (oidc_subject IS NULL OR (oidc_issuer = ? AND oidc_subject = ?))
		  RETURNING `+userColumns,
		issuer, subject, userID, issuer, subject,
	))
	if errors.Is(err, sql.ErrNoRows) {
		// The account already has a different identity (or no longer exists).
		return nil, domain.ErrOIDCIdentityConflict
	}
	if err != nil {
		if isUniqueViolation(err) {
			return nil, domain.ErrOIDCIdentityConflict
		}
		return nil, fmt.Errorf("store: link oidc: %w", err)
	}
	return u, nil
}

// CountUsers returns the number of user rows. Used to decide first-user-is-admin
// and to allow bootstrap registration when signup is otherwise closed.
func (d *DB) CountUsers(ctx context.Context) (int, error) {
	var n int
	if err := d.sql.QueryRowContext(ctx, `SELECT count(*) FROM users`).Scan(&n); err != nil {
		return 0, fmt.Errorf("store: count users: %w", err)
	}
	return n, nil
}

// boolToInt maps a Go bool to the 0/1 SQLite stores for INTEGER "boolean" columns.
func boolToInt(b bool) int {
	if b {
		return 1
	}
	return 0
}

// isUniqueViolation reports whether err is a SQLite UNIQUE-constraint failure.
// modernc surfaces these in the error text; the message is stable across SQLite
// versions ("UNIQUE constraint failed: <table>.<column>").
func isUniqueViolation(err error) bool {
	return err != nil && strings.Contains(err.Error(), "UNIQUE constraint failed")
}