// Package projectindex implements the project-index hierarchy from
// DevDocs/design/03-记忆.md §3 ("项目记忆"作用域): a project is indexed as an
// entry plus description, and its content is split into chapters that can be
// searched line by line. The three-layer depth is 项目索引 → 项目描述 → 章节内容.
//
// The two tables model that depth: the project row is the index entry (layer 1)
// carrying its description (layer 2), and project_chapter holds the chapter
// content (layer 3). Project memory is readable and writable by every persona
// (design §3 "人人可读可写", "项目索引各角色可查"), so the store carries no
// persona/role column and never filters by identity here.
//
// This package is deliberately separate from the vector index
// (internal/runtime/memory/vector): it does text-based hierarchical indexing of
// project entries, descriptions, and chapters. Semantic/vector search belongs to
// the vector package.
//
// The store owns its schema: New creates the project and project_chapter tables
// and the chapter index idempotently. All SQL is parameterized (?), column lists
// are explicit (no SELECT *), reads take a context.Cancel, and every error is
// wrapped with %w so callers can use errors.Is against the package sentinels.
package projectindex

import (
	"context"
	"database/sql"
	"errors"
	"fmt"
	"io"
	"log/slog"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
)

// Sentinels distinguishing projectindex failures. Each is wrapped with %w at the
// call site so callers can use errors.Is.
var (
	// ErrProjectNotFound is returned when a project id is blank or does not exist.
	ErrProjectNotFound = errors.New("projectindex: project not found")

	// ErrChapterNotFound is returned when a required chapter reference is invalid.
	ErrChapterNotFound = errors.New("projectindex: chapter not found")

	// ErrNilDB is returned when New receives a nil *sql.DB.
	ErrNilDB = errors.New("projectindex: nil db")

	// ErrMissingProject is returned when a required project id is blank.
	ErrMissingProject = errors.New("projectindex: project_id is required")

	// ErrMissingTitle is returned when a project or chapter title is blank.
	ErrMissingTitle = errors.New("projectindex: title is required")

	// ErrMissingContent is returned when a chapter has no content.
	ErrMissingContent = errors.New("projectindex: content is required")

	// ErrMissingKeyword is returned when Search receives a blank keyword.
	ErrMissingKeyword = errors.New("projectindex: keyword is required")
)

// Store is a project-index store backed by a *sql.DB.
//
// It owns its schema: New creates the project / project_chapter tables and the
// chapter index idempotently. Concurrency is delegated to *sql.DB, which is safe
// for concurrent use by contract, so Store holds no further lock. Every query is
// parameterized and reads take a context.Cancel.
type Store struct {
	db  *sql.DB
	log *slog.Logger
}

// rowScanner is satisfied by both *sql.Row and *sql.Rows so a single scanProject
// or scanChapter helper serves both the Get and List paths.
type rowScanner interface {
	Scan(dest ...any) error
}

// New builds a Store on db, ensuring the schema exists.
//
// db must be a live connection (the migration framework is owned by
// internal/db). A nil db returns ErrNilDB. log may be nil, in which case a
// discard logger is used; the active logger is tagged with source
// "memory/projectindex" so every record is traceable. ctx controls schema
// creation and must be honored by the caller.
func New(ctx context.Context, db *sql.DB, log *slog.Logger) (*Store, error) {
	if db == nil {
		return nil, ErrNilDB
	}
	log = logger.WithSource(discardLogger(log), "memory/projectindex")
	for _, ddl := range []string{
		createProjectTable,
		createProjectChapterTable,
		createProjectChapterIndex,
	} {
		if _, err := db.ExecContext(ctx, ddl); err != nil {
			return nil, fmt.Errorf("projectindex: apply schema: %w", err)
		}
	}
	return &Store{db: db, log: log}, nil
}

// discardLogger returns log if non-nil, otherwise a logger that writes nowhere.
func discardLogger(log *slog.Logger) *slog.Logger {
	if log != nil {
		return log
	}
	return slog.New(slog.NewTextHandler(io.Discard, nil))
}

// ListProjects returns every project index entry in insertion order (created_at
// ASC, id ASC). An empty (non-nil) slice is returned when there are none, so
// callers can range over it unconditionally. A read error is wrapped with %w so
// callers can use errors.Is against the package sentinels.
func (s *Store) ListProjects(ctx context.Context) ([]Project, error) {
	rows, err := s.db.QueryContext(ctx, `SELECT id, title, desc, created_at, updated_at
		FROM project ORDER BY created_at ASC, id ASC`)
	if err != nil {
		return nil, fmt.Errorf("projectindex: list projects: %w", err)
	}
	defer func() { _ = rows.Close() }()

	projects := make([]Project, 0)
	for rows.Next() {
		p, err := scanProject(rows)
		if err != nil {
			return nil, fmt.Errorf("projectindex: scan project: %w", err)
		}
		projects = append(projects, *p)
	}
	if err := rows.Err(); err != nil {
		return nil, fmt.Errorf("projectindex: iterate projects: %w", err)
	}
	return projects, nil
}

// Schema DDL, applied idempotently by New. The two tables model the three-layer
// hierarchy: the project row is the index entry (layer 1) plus its description
// (layer 2), and project_chapter holds the chapter content (layer 3).
const createProjectTable = `
CREATE TABLE IF NOT EXISTS project (
    id         TEXT PRIMARY KEY,
    title      TEXT NOT NULL,
    desc       TEXT NOT NULL DEFAULT '',
    created_at TEXT NOT NULL,
    updated_at TEXT NOT NULL
)`

const createProjectChapterTable = `
CREATE TABLE IF NOT EXISTS project_chapter (
    id         TEXT PRIMARY KEY,
    project_id TEXT NOT NULL,
    title      TEXT NOT NULL,
    content    TEXT NOT NULL,
    created_at TEXT NOT NULL,
    updated_at TEXT NOT NULL
)`

const createProjectChapterIndex = `
CREATE INDEX IF NOT EXISTS idx_project_chapter_project_id
    ON project_chapter (project_id)`