package projectindex

import (
	"context"
	"crypto/rand"
	"database/sql"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
	"time"
)

// Project is a project index entry (design §3): the project marker that links
// its chapters, together with the project's description. It is layer 1 (index
// entry) and layer 2 (description) of the hierarchy. The zero value is not a
// valid project: ID and Title are required.
type Project struct {
	ID        string
	Title     string
	Desc      string
	CreatedAt time.Time
	UpdatedAt time.Time
}

// PutProject upserts p by id. On an existing id it updates title, desc, and
// updated_at while preserving the original created_at; on a new id it assigns
// missing timestamps and inserts. A blank id or title returns ErrMissingProject
// or ErrMissingTitle.
func (s *Store) PutProject(ctx context.Context, p Project) error {
	if strings.TrimSpace(p.ID) == "" {
		return ErrMissingProject
	}
	if strings.TrimSpace(p.Title) == "" {
		return ErrMissingTitle
	}
	now := time.Now().UTC()
	if p.CreatedAt.IsZero() {
		p.CreatedAt = now
	}
	if p.UpdatedAt.IsZero() {
		p.UpdatedAt = now
	}
	_, err := s.db.ExecContext(ctx, `INSERT INTO project (id, title, desc, created_at, updated_at)
		VALUES (?, ?, ?, ?, ?)
		ON CONFLICT(id) DO UPDATE SET
			title = excluded.title,
			desc = excluded.desc,
			updated_at = excluded.updated_at`,
		p.ID, p.Title, p.Desc, formatTime(p.CreatedAt), formatTime(p.UpdatedAt))
	if err != nil {
		return fmt.Errorf("projectindex: upsert project: %w", err)
	}
	s.log.Debug("project upserted", "id", p.ID)
	return nil
}

// GetProject returns the project with the given id. It returns ErrProjectNotFound
// when the id is blank or does not exist.
func (s *Store) GetProject(ctx context.Context, id string) (*Project, error) {
	if strings.TrimSpace(id) == "" {
		return nil, ErrProjectNotFound
	}
	row := s.db.QueryRowContext(ctx, `SELECT id, title, desc, created_at, updated_at
		FROM project WHERE id = ?`, id)
	p, err := scanProject(row)
	if errors.Is(err, sql.ErrNoRows) {
		return nil, ErrProjectNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("projectindex: get project: %w", err)
	}
	return p, nil
}

// DeleteProject removes the project by id and, as a cascade, every chapter that
// references it. It returns ErrProjectNotFound when the id is blank or no
// project row was removed. The project removal and the chapter removal happen in
// one transaction so a failure never leaves an orphaned project or chapter.
func (s *Store) DeleteProject(ctx context.Context, id string) error {
	if strings.TrimSpace(id) == "" {
		return ErrProjectNotFound
	}
	tx, err := s.db.BeginTx(ctx, nil)
	if err != nil {
		return fmt.Errorf("projectindex: begin delete tx: %w", err)
	}
	defer func() { _ = tx.Rollback() }()

	res, err := tx.ExecContext(ctx, `DELETE FROM project_chapter WHERE project_id = ?`, id)
	if err != nil {
		return fmt.Errorf("projectindex: delete chapters: %w", err)
	}
	if _, err := res.RowsAffected(); err != nil {
		return fmt.Errorf("projectindex: delete chapters row count: %w", err)
	}

	res, err = tx.ExecContext(ctx, `DELETE FROM project WHERE id = ?`, id)
	if err != nil {
		return fmt.Errorf("projectindex: delete project: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return fmt.Errorf("projectindex: delete row count: %w", err)
	}
	if n == 0 {
		return ErrProjectNotFound
	}
	if err := tx.Commit(); err != nil {
		return fmt.Errorf("projectindex: commit delete tx: %w", err)
	}
	s.log.Debug("project deleted", "id", id)
	return nil
}

// scanProject reads one project row.
func scanProject(sc rowScanner) (*Project, error) {
	var (
		p                   Project
		createdAt, updatedAt string
	)
	if err := sc.Scan(&p.ID, &p.Title, &p.Desc, &createdAt, &updatedAt); err != nil {
		return nil, err
	}
	var err error
	if p.CreatedAt, err = parseTime(createdAt); err != nil {
		return nil, err
	}
	if p.UpdatedAt, err = parseTime(updatedAt); err != nil {
		return nil, err
	}
	return &p, nil
}

// newID returns a 128-bit cryptographically random id, hex-encoded. It avoids a
// UUID dependency so the package stays self-contained. rand.Read fails only if
// the platform entropy source is broken, so the error is propagated.
func newID() (string, error) {
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return "", fmt.Errorf("projectindex: generate id: %w", err)
	}
	return hex.EncodeToString(b), nil
}

// formatTime encodes t in UTC as an RFC3339Nano string so ordering and
// round-trips are stable across processes.
func formatTime(t time.Time) string {
	return t.UTC().Format(time.RFC3339Nano)
}

// parseTime decodes a stored RFC3339 string; blank input yields a zero time.
func parseTime(s string) (time.Time, error) {
	if strings.TrimSpace(s) == "" {
		return time.Time{}, nil
	}
	t, err := time.Parse(time.RFC3339Nano, s)
	if err != nil {
		return time.Time{}, fmt.Errorf("projectindex: parse time %q: %w", s, err)
	}
	return t, nil
}