package research

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"regexp"
	"strconv"
	"strings"
)

// The fixed Paper Atlas migration a3b677b preserves business columns as TEXT
// and BIGINT and creates the English title/abstract GIN expression below.
// No schema creation, indexing or other writes belong to this repository.
type PostgresRepository struct {
	db     *sql.DB
	prefix string
}

var schemaName = regexp.MustCompile(`^[a-z][a-z0-9_]{0,35}$`)

func NewPostgresRepository(db *sql.DB, schema string) (*PostgresRepository, error) {
	if db == nil || !schemaName.MatchString(schema) {
		return nil, errors.New("invalid research database configuration")
	}
	return &PostgresRepository{db: db, prefix: `"` + schema + `".`}, nil
}

func (r *PostgresRepository) query(value string) string {
	return strings.ReplaceAll(value, "{schema}", r.prefix)
}

func (r *PostgresRepository) begin(ctx context.Context) (*sql.Tx, error) {
	tx, err := r.db.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelRepeatableRead, ReadOnly: true})
	if err != nil {
		return nil, err
	}
	_, err = tx.ExecContext(ctx, `SELECT set_config('statement_timeout','8000',true),
		set_config('lock_timeout','1000',true), set_config('work_mem','2MB',true),
		set_config('max_parallel_workers_per_gather','0',true)`)
	if err != nil {
		_ = tx.Rollback()
		return nil, err
	}
	return tx, nil
}

// Check resolves required columns and SELECT permissions without scanning the
// corpus. The migration publishes the complete schema atomically.
func (r *PostgresRepository) Check(ctx context.Context) error {
	tx, err := r.begin(ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback()
	rows, err := tx.QueryContext(ctx, r.query(`SELECT p.id,p.title,p.abstract,p.authors_json,p.first_published,p.title_key,
		r.external_id,r.url,r.metadata_json,so.name,i.scheme,i.value,t.namespace,t.value,
		s.id,e.year,e.track,v.acronym,d.status,d.evidence_url,d.observed_at,d.decision_date
		FROM {schema}papers p LEFT JOIN {schema}source_records r ON r.paper_id=p.id
		LEFT JOIN {schema}sources so ON so.id=r.source_id LEFT JOIN {schema}identifiers i ON i.paper_id=p.id
		LEFT JOIN {schema}paper_tags pt ON pt.paper_id=p.id LEFT JOIN {schema}tags t ON t.id=pt.tag_id
		LEFT JOIN {schema}submissions s ON s.paper_id=p.id LEFT JOIN {schema}editions e ON e.id=s.edition_id
		LEFT JOIN {schema}venues v ON v.id=e.venue_id LEFT JOIN {schema}decisions d ON d.submission_id=s.id WHERE false`))
	if err != nil {
		return err
	}
	if err = rows.Close(); err != nil {
		return err
	}
	return tx.Commit()
}

func whereClause(filters Filters) (string, []any) {
	clauses, values := []string{}, []any{}
	if filters.Query != "" {
		values = append(values, filters.Query)
		if filters.SearchIn == "author" {
			// JSON stores author strings or [family,given,suffix] tuples. Plain
			// full-text terms search names regardless of tuple display order.
			clauses = append(clauses, `to_tsvector('simple'::regconfig,p.authors_json) @@ plainto_tsquery('simple'::regconfig,$1)`)
		} else {
			clauses = append(clauses, `to_tsvector('english'::regconfig,coalesce(p.title,'') || ' ' || coalesce(p.abstract,'')) @@ plainto_tsquery('english'::regconfig,$1)`)
		}
	}
	if filters.Topic != "" {
		values = append(values, filters.Topic)
		clauses = append(clauses, fmt.Sprintf(`EXISTS(SELECT 1 FROM {schema}paper_tags pt
			JOIN {schema}tags t ON t.id=pt.tag_id
			WHERE pt.paper_id=p.id AND t.namespace='arxiv:category' AND t.value=$%d)`, len(values)))
	}
	if len(clauses) == 0 {
		return "", values
	}
	return " WHERE " + strings.Join(clauses, " AND "), values
}

type scanner interface{ Scan(...any) error }

func scanPaper(row scanner) (Paper, error) {
	p := Paper{Authors: []string{}, Topics: []string{}, Sources: []Source{}}
	var id int64
	var abstract, published sql.NullString
	var authors string
	if err := row.Scan(&id, &p.Title, &abstract, &authors, &published); err != nil {
		return p, err
	}
	p.ID = strconv.FormatInt(id, 10)
	if abstract.Valid {
		p.Abstract = &abstract.String
	}
	if published.Valid {
		p.PublishedAt = &published.String
	}
	var err error
	p.Authors, err = decodeAuthors(authors)
	return p, err
}

func decodeAuthors(raw string) ([]string, error) {
	var entries []json.RawMessage
	if err := json.Unmarshal([]byte(raw), &entries); err != nil {
		return nil, errors.New("invalid stored authors")
	}
	names := []string{}
	for _, entry := range entries {
		var name string
		if json.Unmarshal(entry, &name) == nil {
			if name = strings.TrimSpace(name); name != "" {
				names = append(names, name)
			}
			continue
		}
		var tuple []string
		if json.Unmarshal(entry, &tuple) != nil || len(tuple) == 0 || len(tuple) > 3 {
			return nil, errors.New("unsupported stored author")
		}
		if len(tuple) >= 2 {
			tuple[0], tuple[1] = tuple[1], tuple[0]
		}
		parts := []string{}
		for _, part := range tuple {
			if part = strings.TrimSpace(part); part != "" {
				parts = append(parts, part)
			}
		}
		if name = strings.Join(parts, " "); name != "" {
			names = append(names, name)
		}
	}
	return names, nil
}

func (r *PostgresRepository) List(ctx context.Context, filters Filters) (Page, error) {
	result := Page{Items: []Paper{}, Topics: []string{}, Page: filters.Page, PageSize: filters.PageSize}
	tx, err := r.begin(ctx)
	if err != nil {
		return result, err
	}
	defer tx.Rollback()
	where, args := whereClause(filters)
	if err = tx.QueryRowContext(ctx, r.query(`SELECT count(*) FROM {schema}papers p`+where), args...).Scan(&result.Total); err != nil {
		return result, err
	}
	order := "p.id DESC"
	if filters.Sort == "title" {
		order = "p.title_key,p.id"
	}
	args = append(args, filters.PageSize, (filters.Page-1)*filters.PageSize)
	query := fmt.Sprintf(`SELECT p.id,p.title,p.abstract,p.authors_json,p.first_published
		FROM {schema}papers p%s ORDER BY %s LIMIT $%d OFFSET $%d`, where, order, len(args)-1, len(args))
	rows, err := tx.QueryContext(ctx, r.query(query), args...)
	if err != nil {
		return result, err
	}
	for rows.Next() {
		p, err := scanPaper(rows)
		if err != nil {
			_ = rows.Close()
			return result, err
		}
		result.Items = append(result.Items, p)
	}
	err = rows.Err()
	_ = rows.Close()
	if err != nil {
		return result, err
	}
	if err = r.enrich(ctx, tx, result.Items); err != nil {
		return result, err
	}
	rows, err = tx.QueryContext(ctx, r.query(`SELECT value FROM {schema}tags WHERE namespace='arxiv:category' ORDER BY value`))
	if err != nil {
		return result, err
	}
	for rows.Next() {
		var topic string
		if err = rows.Scan(&topic); err != nil {
			_ = rows.Close()
			return result, err
		}
		result.Topics = append(result.Topics, topic)
	}
	err = rows.Err()
	_ = rows.Close()
	if err != nil {
		return result, err
	}
	return result, tx.Commit()
}

func (r *PostgresRepository) Get(ctx context.Context, id int64) (Paper, error) {
	tx, err := r.begin(ctx)
	if err != nil {
		return Paper{}, err
	}
	defer tx.Rollback()
	p, err := scanPaper(tx.QueryRowContext(ctx, r.query(`SELECT id,title,abstract,authors_json,first_published FROM {schema}papers WHERE id=$1`), id))
	if err != nil {
		return p, err
	}
	papers := []Paper{p}
	if err = r.enrich(ctx, tx, papers); err != nil {
		return p, err
	}
	return papers[0], tx.Commit()
}

// Batch metadata queries avoid per-paper round trips and share the count/page
// snapshot. User values are bound; only the validated schema is interpolated.
func (r *PostgresRepository) enrich(ctx context.Context, tx *sql.Tx, papers []Paper) error {
	if len(papers) == 0 {
		return nil
	}
	ids := make([]int64, len(papers))
	byID := map[int64]*Paper{}
	for i := range papers {
		id, err := strconv.ParseInt(papers[i].ID, 10, 64)
		if err != nil {
			return err
		}
		ids[i] = id
		byID[id] = &papers[i]
	}
	rows, err := tx.QueryContext(ctx, r.query(`SELECT DISTINCT pt.paper_id,t.value
		FROM {schema}paper_tags pt JOIN {schema}tags t ON t.id=pt.tag_id
		WHERE pt.paper_id=ANY($1) AND t.namespace='arxiv:category' ORDER BY pt.paper_id,t.value`), ids)
	if err != nil {
		return err
	}
	for rows.Next() {
		var id int64
		var topic string
		if err = rows.Scan(&id, &topic); err != nil {
			_ = rows.Close()
			return err
		}
		byID[id].Topics = append(byID[id].Topics, topic)
	}
	err = rows.Err()
	_ = rows.Close()
	if err != nil {
		return err
	}
	rows, err = tx.QueryContext(ctx, r.query(`SELECT r.paper_id,s.name,r.external_id,r.url,r.metadata_json
		FROM {schema}source_records r JOIN {schema}sources s ON s.id=r.source_id
		WHERE r.paper_id=ANY($1) ORDER BY r.paper_id,r.id`), ids)
	if err != nil {
		return err
	}
	for rows.Next() {
		var id int64
		var source Source
		var metadata string
		if err = rows.Scan(&id, &source.Label, &source.ExternalID, &source.URL, &metadata); err != nil {
			_ = rows.Close()
			return err
		}
		p := byID[id]
		switch source.Label {
		case "arxiv":
			source.Label = "arXiv"
		case "openreview":
			source.Label = "OpenReview"
		case "pmlr":
			source.Label = "PMLR"
		}
		p.Sources = append(p.Sources, source)
		var fields map[string]json.RawMessage
		if json.Unmarshal([]byte(metadata), &fields) == nil {
			for key, target := range map[string]**string{"doi": &p.DOI, "journal-ref": &p.Journal, "comments": &p.Comments} {
				var value string
				if *target == nil && json.Unmarshal(fields[key], &value) == nil && strings.TrimSpace(value) != "" {
					*target = &value
				}
			}
		}
	}
	err = rows.Err()
	_ = rows.Close()
	if err != nil {
		return err
	}
	rows, err = tx.QueryContext(ctx, r.query(`SELECT paper_id,value FROM {schema}identifiers WHERE paper_id=ANY($1) AND scheme='doi' ORDER BY paper_id,value`), ids)
	if err != nil {
		return err
	}
	for rows.Next() {
		var id int64
		var value string
		if err = rows.Scan(&id, &value); err != nil {
			_ = rows.Close()
			return err
		}
		if byID[id].DOI == nil && strings.TrimSpace(value) != "" {
			byID[id].DOI = &value
		}
	}
	err = rows.Err()
	_ = rows.Close()
	if err != nil {
		return err
	}
	rows, err = tx.QueryContext(ctx, r.query(`SELECT s.paper_id,v.acronym,e.year,e.track,coalesce(d.status,'unknown'),coalesce(d.evidence_url,'')
		FROM {schema}submissions s JOIN {schema}editions e ON e.id=s.edition_id JOIN {schema}venues v ON v.id=e.venue_id
		LEFT JOIN LATERAL (SELECT status,evidence_url FROM {schema}decisions WHERE submission_id=s.id
			ORDER BY observed_at DESC,coalesce(decision_date,observed_at) DESC,id DESC LIMIT 1) d ON true
		WHERE s.paper_id=ANY($1) ORDER BY s.paper_id,e.year DESC,v.acronym,e.track,s.id`), ids)
	if err != nil {
		return err
	}
	for rows.Next() {
		var id int64
		var publication Publication
		if err = rows.Scan(&id, &publication.Venue, &publication.Year, &publication.Track, &publication.Status, &publication.EvidenceURL); err != nil {
			_ = rows.Close()
			return err
		}
		byID[id].Publications = append(byID[id].Publications, publication)
	}
	err = rows.Err()
	_ = rows.Close()
	return err
}