// Package store is the SQLite index over the statements. It is entirely
// rebuildable: delete index.db and re-import to get it back, except for the
// tags set by hand, which live only here.
package store

import (
	"database/sql"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	_ "modernc.org/sqlite"

	"git.petrovv.com/nikola/money/internal/model"
)

// DB wraps the SQLite handle.
type DB struct {
	sql *sql.DB
}

const schema = `
PRAGMA foreign_keys = ON;

CREATE TABLE IF NOT EXISTS accounts (
	id           INTEGER PRIMARY KEY AUTOINCREMENT,
	slug         TEXT NOT NULL UNIQUE,
	name         TEXT NOT NULL,
	currency     TEXT NOT NULL,
	minor_digits INTEGER NOT NULL DEFAULT 2
);

CREATE TABLE IF NOT EXISTS source_files (
	id          INTEGER PRIMARY KEY AUTOINCREMENT,
	account_id  INTEGER NOT NULL REFERENCES accounts(id),
	path        TEXT NOT NULL,
	sha256      TEXT NOT NULL,
	imported_at TEXT NOT NULL,
	UNIQUE(account_id, path)
);

CREATE TABLE IF NOT EXISTS transactions (
	id              INTEGER PRIMARY KEY AUTOINCREMENT,
	account_id      INTEGER NOT NULL REFERENCES accounts(id),
	source_file_id  INTEGER NOT NULL REFERENCES source_files(id),
	fingerprint     TEXT NOT NULL,
	date            TEXT NOT NULL,
	description     TEXT NOT NULL,
	amount_minor    INTEGER NOT NULL,
	type            TEXT NOT NULL DEFAULT '',
	balance_minor   INTEGER,
	rule_tag        TEXT,
	UNIQUE(account_id, fingerprint)
);

CREATE INDEX IF NOT EXISTS idx_txn_date ON transactions(date);
CREATE INDEX IF NOT EXISTS idx_txn_account ON transactions(account_id);
`

// migrations bring an index created by an older build up to date. SQLite
// errors on a duplicate column, which is how we detect "already applied".
var migrations = []string{
	`ALTER TABLE transactions ADD COLUMN type TEXT NOT NULL DEFAULT ''`,
	`ALTER TABLE transactions ADD COLUMN balance_minor INTEGER`,
}

// dropped are columns an older build created that this one no longer reads.
// Nothing indexes or constrains them, so they can simply go; leaving them
// would keep a NOT NULL column alive that no INSERT here ever names.
var dropped = []string{"counterparty", "rule_transfer", "manual_transfer", "manual_tag"}

// migrate brings an index created by an older build up to date, adding the
// columns it lacks and removing the ones it should no longer have.
func migrate(db *sql.DB) error {
	have, err := columns(db, "transactions")
	if err != nil {
		return err
	}
	for _, stmt := range migrations {
		name := addedColumn(stmt)
		if have[name] {
			continue
		}
		if _, err := db.Exec(stmt); err != nil {
			return fmt.Errorf("migrate (%s): %w", stmt, err)
		}
	}
	for _, name := range dropped {
		if !have[name] {
			continue
		}
		stmt := fmt.Sprintf(`ALTER TABLE transactions DROP COLUMN %s`, name)
		if _, err := db.Exec(stmt); err != nil {
			return fmt.Errorf("migrate (%s): %w", stmt, err)
		}
	}
	return nil
}

func columns(db *sql.DB, table string) (map[string]bool, error) {
	rows, err := db.Query(`SELECT name FROM pragma_table_info(?)`, table)
	if err != nil {
		return nil, fmt.Errorf("inspect %s: %w", table, err)
	}
	defer rows.Close()
	out := map[string]bool{}
	for rows.Next() {
		var name string
		if err := rows.Scan(&name); err != nil {
			return nil, err
		}
		out[name] = true
	}
	return out, rows.Err()
}

// addedColumn pulls the column name out of an ADD COLUMN statement.
func addedColumn(stmt string) string {
	_, rest, ok := strings.Cut(stmt, "ADD COLUMN ")
	if !ok {
		return ""
	}
	name, _, _ := strings.Cut(rest, " ")
	return name
}

// Open opens (creating if needed) the index at path.
func Open(path string) (*DB, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return nil, fmt.Errorf("create index dir: %w", err)
	}
	sqlDB, err := sql.Open("sqlite", path)
	if err != nil {
		return nil, fmt.Errorf("open index %s: %w", path, err)
	}
	if _, err := sqlDB.Exec(schema); err != nil {
		sqlDB.Close()
		return nil, fmt.Errorf("apply schema: %w", err)
	}
	if err := migrate(sqlDB); err != nil {
		sqlDB.Close()
		return nil, err
	}
	return &DB{sql: sqlDB}, nil
}

// Close releases the underlying handle.
func (d *DB) Close() error { return d.sql.Close() }

// UpsertAccount inserts or updates an account by slug and returns its id.
func (d *DB) UpsertAccount(a model.Account) (int64, error) {
	_, err := d.sql.Exec(`
		INSERT INTO accounts (slug, name, currency, minor_digits)
		VALUES (?, ?, ?, ?)
		ON CONFLICT(slug) DO UPDATE SET
			name = excluded.name,
			currency = excluded.currency,
			minor_digits = excluded.minor_digits`,
		a.Slug, a.Name, a.Currency, a.MinorDigits)
	if err != nil {
		return 0, fmt.Errorf("upsert account %s: %w", a.Slug, err)
	}
	var id int64
	if err := d.sql.QueryRow(`SELECT id FROM accounts WHERE slug = ?`, a.Slug).Scan(&id); err != nil {
		return 0, fmt.Errorf("read account id %s: %w", a.Slug, err)
	}
	return id, nil
}

// Accounts lists every known account, ordered by slug.
func (d *DB) Accounts() ([]model.Account, error) {
	rows, err := d.sql.Query(`SELECT id, slug, name, currency, minor_digits FROM accounts ORDER BY slug`)
	if err != nil {
		return nil, fmt.Errorf("list accounts: %w", err)
	}
	defer rows.Close()
	var out []model.Account
	for rows.Next() {
		var a model.Account
		if err := rows.Scan(&a.ID, &a.Slug, &a.Name, &a.Currency, &a.MinorDigits); err != nil {
			return nil, err
		}
		out = append(out, a)
	}
	return out, rows.Err()
}

// SourceFile records that a statement file was imported, returning its id.
func (d *DB) SourceFile(accountID int64, path, sha, importedAt string) (int64, error) {
	_, err := d.sql.Exec(`
		INSERT INTO source_files (account_id, path, sha256, imported_at)
		VALUES (?, ?, ?, ?)
		ON CONFLICT(account_id, path) DO UPDATE SET
			sha256 = excluded.sha256,
			imported_at = excluded.imported_at`,
		accountID, path, sha, importedAt)
	if err != nil {
		return 0, fmt.Errorf("record source file %s: %w", path, err)
	}
	var id int64
	if err := d.sql.QueryRow(
		`SELECT id FROM source_files WHERE account_id = ? AND path = ?`, accountID, path).Scan(&id); err != nil {
		return 0, fmt.Errorf("read source file id %s: %w", path, err)
	}
	return id, nil
}

// SourceFileSHA returns the recorded checksum for a statement file, and whether
// it has been imported before.
func (d *DB) SourceFileSHA(accountID int64, path string) (string, bool, error) {
	var sha string
	err := d.sql.QueryRow(
		`SELECT sha256 FROM source_files WHERE account_id = ? AND path = ?`, accountID, path).Scan(&sha)
	if err == sql.ErrNoRows {
		return "", false, nil
	}
	if err != nil {
		return "", false, err
	}
	return sha, true, nil
}

// InsertTransaction adds a transaction unless its fingerprint already exists
// for that account. It reports whether a new row was created.
//
// Existing rows are deliberately left untouched, so re-importing a statement
// that overlaps one already imported adds nothing rather than duplicating it.
func (d *DB) InsertTransaction(t model.Transaction) (bool, error) {
	var balance any
	if t.BalanceMinor != nil {
		balance = *t.BalanceMinor
	}
	res, err := d.sql.Exec(`
		INSERT INTO transactions
			(account_id, source_file_id, fingerprint, date, description, amount_minor,
			 type, balance_minor, rule_tag)
		VALUES (?, ?, ?, ?, ?, ?, ?, ?, NULLIF(?, ''))
		ON CONFLICT(account_id, fingerprint) DO NOTHING`,
		t.AccountID, t.SourceFileID, t.Fingerprint, t.Date, t.Description,
		t.AmountMinor, t.Type, balance, t.RuleTag)
	if err != nil {
		return false, fmt.Errorf("insert transaction: %w", err)
	}
	n, err := res.RowsAffected()
	if err != nil {
		return false, err
	}
	return n > 0, nil
}

// Filter narrows a transaction query.
type Filter struct {
	AccountSlug string
	Untagged    bool   // only rows with no effective tag
	Month       string // YYYY-MM
	Search      string // case-insensitive substring of the description
	Limit       int
}

// Transactions returns rows matching f, newest first.
func (d *DB) Transactions(f Filter) ([]model.Transaction, error) {
	q := `
		SELECT t.id, t.account_id, a.slug, a.currency, a.minor_digits,
		       t.fingerprint, t.date, t.description, t.amount_minor,
		       COALESCE(s.path, ''), t.type, t.balance_minor,
		       COALESCE(t.rule_tag, '')
		FROM transactions t
		JOIN accounts a ON a.id = t.account_id
		LEFT JOIN source_files s ON s.id = t.source_file_id
		WHERE 1 = 1`
	var args []any
	if f.AccountSlug != "" {
		q += ` AND a.slug = ?`
		args = append(args, f.AccountSlug)
	}
	if f.Untagged {
		q += ` AND NULLIF(t.rule_tag, '') IS NULL`
	}
	if f.Month != "" {
		q += ` AND substr(t.date, 1, 7) = ?`
		args = append(args, f.Month)
	}
	q += ` ORDER BY t.date DESC, t.id DESC`
	// Search and Limit are applied in Go: SQLite's upper()/LIKE fold ASCII
	// only, which would silently fail on Cyrillic statement descriptions.

	rows, err := d.sql.Query(q, args...)
	if err != nil {
		return nil, fmt.Errorf("query transactions: %w", err)
	}
	defer rows.Close()

	needle := model.NormalizeDescription(f.Search)
	var out []model.Transaction
	for rows.Next() {
		var (
			t       model.Transaction
			balance sql.NullInt64
		)
		if err := rows.Scan(&t.ID, &t.AccountID, &t.AccountSlug, &t.Currency, &t.MinorDigits,
			&t.Fingerprint, &t.Date, &t.Description, &t.AmountMinor, &t.SourcePath,
			&t.Type, &balance, &t.RuleTag); err != nil {
			return nil, err
		}
		if balance.Valid {
			v := balance.Int64
			t.BalanceMinor = &v
		}
		if needle != "" && !strings.Contains(model.NormalizeDescription(t.Description), needle) {
			continue
		}
		out = append(out, t)
		if f.Limit > 0 && len(out) >= f.Limit {
			break
		}
	}
	return out, rows.Err()
}

// RuleAssignment is one row's recomputed rule verdict.
type RuleAssignment struct {
	ID  int64
	Tag string
}

// ApplyRuleResults rewrites rule_tag for every listed row in a single
// transaction. The manual column is never touched.
func (d *DB) ApplyRuleResults(rs []RuleAssignment) error {
	tx, err := d.sql.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	stmt, err := tx.Prepare(
		`UPDATE transactions SET rule_tag = NULLIF(?, '') WHERE id = ?`)
	if err != nil {
		return err
	}
	defer stmt.Close()

	for _, r := range rs {
		if _, err := stmt.Exec(r.Tag, r.ID); err != nil {
			return fmt.Errorf("apply rules to txn %d: %w", r.ID, err)
		}
	}
	return tx.Commit()
}

// Balance sums every transaction in an account.
func (d *DB) Balance(accountID int64) (int64, error) {
	var v sql.NullInt64
	err := d.sql.QueryRow(
		`SELECT SUM(amount_minor) FROM transactions WHERE account_id = ?`, accountID).Scan(&v)
	if err != nil {
		return 0, err
	}
	return v.Int64, nil
}

// Count returns the number of transactions in an account.
func (d *DB) Count(accountID int64) (int, error) {
	var n int
	err := d.sql.QueryRow(
		`SELECT COUNT(*) FROM transactions WHERE account_id = ?`, accountID).Scan(&n)
	return n, err
}

// Tags lists every tag in use, for completion in the TUI.
func (d *DB) Tags() ([]string, error) {
	rows, err := d.sql.Query(`
		SELECT DISTINCT rule_tag FROM transactions
		WHERE rule_tag IS NOT NULL AND rule_tag != '' ORDER BY rule_tag`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []string
	for rows.Next() {
		var s string
		if err := rows.Scan(&s); err != nil {
			return nil, err
		}
		out = append(out, s)
	}
	return out, rows.Err()
}