package storage

import (
	"fmt"
	"sort"
	"strings"
	"time"
)

// ReceiptRow is a display row for listings and duplicate warnings. It carries the
// resolved category/person labels (not ids) and omits the image blob.
type ReceiptRow struct {
	ID               string
	UploadedBy       string
	UploadedAt       time.Time
	ReceiptDate      time.Time
	AmountCents      int64
	Category         string
	Who              string // "" when unassigned
	OriginalFilename string
}

// recentColumns whitelists the sortable columns for ListRecent, so the column
// name can be interpolated into SQL safely (it is never user free-text).
var recentColumns = map[string]string{
	"uploaded_at":  "r.uploaded_at",
	"receipt_date": "r.receipt_date",
}

// ListRecent returns up to limit non-deleted receipts ordered by the given column
// (descending), skipping offset rows. orderBy must be "uploaded_at" or
// "receipt_date". One extra row is fetched so callers can tell if more exist.
func (s *Store) ListRecent(orderBy string, limit, offset int) (rows []ReceiptRow, hasMore bool, err error) {
	col, ok := recentColumns[orderBy]
	if !ok {
		return nil, false, fmt.Errorf("invalid sort column %q", orderBy)
	}
	q := `SELECT r.id, r.uploaded_by, r.uploaded_at, r.receipt_date, r.amount_cents,
	             c.label, COALESCE(p.label, ''), r.original_filename
	      FROM receipts r
	      JOIN categories c ON c.id = r.category_id
	      LEFT JOIN people p ON p.id = r.person_id
	      WHERE r.deleted_at IS NULL
	      ORDER BY ` + col + ` DESC, r.id DESC
	      LIMIT ? OFFSET ?`
	// Fetch one extra to detect "has more".
	res, err := s.db.Query(q, limit+1, offset)
	if err != nil {
		return nil, false, fmt.Errorf("list recent: %w", err)
	}
	defer res.Close()

	for res.Next() {
		row, err := scanReceiptRow(res)
		if err != nil {
			return nil, false, err
		}
		rows = append(rows, row)
	}
	if err := res.Err(); err != nil {
		return nil, false, err
	}
	if len(rows) > limit {
		return rows[:limit], true, nil
	}
	return rows, false, nil
}

// FindDuplicates returns non-deleted receipts with the same receipt date and
// amount — likely the same transaction already posted. Empty means no match.
func (s *Store) FindDuplicates(receiptDate time.Time, amountCents int64) ([]ReceiptRow, error) {
	q := `SELECT r.id, r.uploaded_by, r.uploaded_at, r.receipt_date, r.amount_cents,
	             c.label, COALESCE(p.label, ''), r.original_filename
	      FROM receipts r
	      JOIN categories c ON c.id = r.category_id
	      LEFT JOIN people p ON p.id = r.person_id
	      WHERE r.deleted_at IS NULL AND r.receipt_date = ? AND r.amount_cents = ?
	      ORDER BY r.uploaded_at DESC`
	res, err := s.db.Query(q, receiptDate.UTC().Format(rfc3339), amountCents)
	if err != nil {
		return nil, fmt.Errorf("find duplicates: %w", err)
	}
	defer res.Close()

	var rows []ReceiptRow
	for res.Next() {
		row, err := scanReceiptRow(res)
		if err != nil {
			return nil, err
		}
		rows = append(rows, row)
	}
	return rows, res.Err()
}

// rowScanner is satisfied by *sql.Rows.
type rowScanner interface {
	Scan(dest ...any) error
}

func scanReceiptRow(sc rowScanner) (ReceiptRow, error) {
	var row ReceiptRow
	var uploadedAt, receiptDate string
	if err := sc.Scan(&row.ID, &row.UploadedBy, &uploadedAt, &receiptDate,
		&row.AmountCents, &row.Category, &row.Who, &row.OriginalFilename); err != nil {
		return ReceiptRow{}, fmt.Errorf("scan receipt row: %w", err)
	}
	row.UploadedAt, _ = time.Parse(rfc3339, uploadedAt)
	row.ReceiptDate, _ = time.Parse(rfc3339, receiptDate)
	return row, nil
}

// TallyRow is one person's totals across years (cents).
type TallyRow struct {
	Person string
	ByYear map[int]int64
	Total  int64
}

// Tally is the person × year totals matrix with margins, for the Tally tab.
type Tally struct {
	Years      []int         // sorted ascending, only years that have data
	Rows       []TallyRow    // one per person ("Unassigned" sorts last)
	YearTotals map[int]int64 // grand total per year (all people)
	Grand      int64         // overall grand total
}

// Tally sums non-deleted receipt amounts grouped by person and by the year of the
// receipt date. Receipts with no "who" are grouped under "Unassigned".
func (s *Store) Tally() (Tally, error) {
	q := `SELECT COALESCE(p.label, 'Unassigned'),
	             CAST(strftime('%Y', r.receipt_date) AS INTEGER),
	             SUM(r.amount_cents)
	      FROM receipts r
	      LEFT JOIN people p ON p.id = r.person_id
	      WHERE r.deleted_at IS NULL
	      GROUP BY COALESCE(p.label, 'Unassigned'), strftime('%Y', r.receipt_date)`
	res, err := s.db.Query(q)
	if err != nil {
		return Tally{}, fmt.Errorf("tally: %w", err)
	}
	defer res.Close()

	byPerson := map[string]map[int]int64{}
	yearSet := map[int]bool{}
	t := Tally{YearTotals: map[int]int64{}}
	for res.Next() {
		var person string
		var year int
		var sum int64
		if err := res.Scan(&person, &year, &sum); err != nil {
			return Tally{}, fmt.Errorf("scan tally: %w", err)
		}
		if byPerson[person] == nil {
			byPerson[person] = map[int]int64{}
		}
		byPerson[person][year] += sum
		yearSet[year] = true
		t.YearTotals[year] += sum
		t.Grand += sum
	}
	if err := res.Err(); err != nil {
		return Tally{}, err
	}

	for y := range yearSet {
		t.Years = append(t.Years, y)
	}
	sort.Ints(t.Years)

	names := make([]string, 0, len(byPerson))
	for name := range byPerson {
		names = append(names, name)
	}
	// Alphabetical, but "Unassigned" always last.
	sort.Slice(names, func(i, j int) bool {
		if (names[i] == "Unassigned") != (names[j] == "Unassigned") {
			return names[j] == "Unassigned"
		}
		return strings.ToLower(names[i]) < strings.ToLower(names[j])
	})
	for _, name := range names {
		row := TallyRow{Person: name, ByYear: byPerson[name]}
		for _, v := range byPerson[name] {
			row.Total += v
		}
		t.Rows = append(t.Rows, row)
	}
	return t, nil
}

// ReconcilePeople merges stray partial-name person rows into the canonical
// config-seeded labels: e.g. a leftover "Jude" is merged into "Jude Tremblay".
// For each existing person that is NOT itself a canonical label, if its label
// matches the first name of exactly one canonical label (case-insensitive), its
// receipts are reassigned to that canonical person and the stray row is deleted.
// Ambiguous or unmatched strays are left untouched. Returns the number merged.
//
// This is conservative on purpose — it only collapses an unambiguous first-name
// duplicate, so genuinely custom people added via the manage page survive.
func (s *Store) ReconcilePeople(canonical []string) (int, error) {
	// Map first-name -> canonical label, dropping ambiguous first names.
	firstToCanon := map[string]string{}
	ambiguous := map[string]bool{}
	canonSet := map[string]bool{}
	for _, label := range canonical {
		label = strings.TrimSpace(label)
		if label == "" {
			continue
		}
		canonSet[strings.ToLower(label)] = true
		first := strings.ToLower(strings.Fields(label)[0])
		if _, seen := firstToCanon[first]; seen {
			ambiguous[first] = true
		}
		firstToCanon[first] = label
	}

	people, err := s.ListPeople()
	if err != nil {
		return 0, err
	}

	merged := 0
	for _, p := range people {
		lower := strings.ToLower(strings.TrimSpace(p.Label))
		if canonSet[lower] {
			continue // already a canonical full name
		}
		canon, ok := firstToCanon[lower]
		if !ok || ambiguous[lower] {
			continue // no unambiguous canonical match — leave it alone
		}
		if err := s.mergePerson(p.ID, canon); err != nil {
			return merged, err
		}
		merged++
	}
	return merged, nil
}

// mergePerson reassigns every receipt pointing at stray personID to the canonical
// person (looked up / created by label), then deletes the stray row. Done in a
// transaction so a receipt never loses its "who".
func (s *Store) mergePerson(strayID int64, canonLabel string) error {
	tx, err := s.db.Begin()
	if err != nil {
		return fmt.Errorf("begin merge: %w", err)
	}
	defer tx.Rollback()

	var canonID int64
	if err := tx.QueryRow(`SELECT id FROM people WHERE label = ?`, canonLabel).Scan(&canonID); err != nil {
		return fmt.Errorf("find canonical %q: %w", canonLabel, err)
	}
	if _, err := tx.Exec(`UPDATE receipts SET person_id = ? WHERE person_id = ?`, canonID, strayID); err != nil {
		return fmt.Errorf("reassign receipts: %w", err)
	}
	if _, err := tx.Exec(`DELETE FROM people WHERE id = ?`, strayID); err != nil {
		return fmt.Errorf("delete stray person: %w", err)
	}
	return tx.Commit()
}