// Package store is the SQLite index over the statements. It is entirely
// rebuildable: delete index.db and re-import to get it back. Nothing lives
// 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);

-- One row per matched movement between the user's own accounts, derived from
-- the [[transfer]] blocks in rules.toml. A leg belongs to at most one transfer,
-- which UNIQUE enforces rather than trusting the pairing to be well behaved.
CREATE TABLE IF NOT EXISTS transfers (
	id         INTEGER PRIMARY KEY AUTOINCREMENT,
	def_index  INTEGER NOT NULL,
	out_txn_id INTEGER NOT NULL UNIQUE REFERENCES transactions(id),
	in_txn_id  INTEGER NOT NULL UNIQUE REFERENCES transactions(id)
);
`

// Open opens (creating if needed) the index at path.
//
// There is no schema migration: the index caches what the statements and
// rules.toml already say, so a build that changes the schema is answered by
// deleting index.db and importing again, not by patching the old one in place.
// Until it is deleted, queries against it fail on the columns it lacks.
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)
	}
	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 selects the rows still waiting for a verdict: no tag, and not a
	// leg of a matched transfer. A paired leg has been accounted for by the
	// transfer that claimed it, so listing it as untagged would ask the user to
	// write a rule for something that is already spoken for and that the report
	// leaves out anyway.
	Untagged bool
	Month    string // YYYY-MM
	// From and To bound the dates inclusively, as YYYY-MM-DD, either side empty
	// for unbounded. Dates are stored ISO-8601, so a string comparison is a date
	// comparison; nothing has to be parsed to filter on a range.
	From   string
	To     string
	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, ''), x.id
		FROM transactions t
		JOIN accounts a ON a.id = t.account_id
		LEFT JOIN source_files s ON s.id = t.source_file_id
		LEFT JOIN transfers x ON x.out_txn_id = t.id OR x.in_txn_id = t.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 AND x.id IS NULL`
	}
	if f.Month != "" {
		q += ` AND substr(t.date, 1, 7) = ?`
		args = append(args, f.Month)
	}
	if f.From != "" {
		q += ` AND t.date >= ?`
		args = append(args, f.From)
	}
	if f.To != "" {
		q += ` AND t.date <= ?`
		args = append(args, f.To)
	}
	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
			transfer 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, &transfer); err != nil {
			return nil, err
		}
		if balance.Valid {
			v := balance.Int64
			t.BalanceMinor = &v
		}
		if transfer.Valid {
			v := transfer.Int64
			t.TransferID = &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()
}

// TransferLink is one matched pair, as decided by the transfer definitions.
type TransferLink struct {
	DefIndex int
	OutID    int64
	InID     int64
}

// ReplaceTransfers rewrites the whole pairing in one transaction. Like the
// tags, it is derived from a file the user edits, so it is replaced wholesale
// rather than patched: a definition removed from rules.toml must take its pairs
// with it.
func (d *DB) ReplaceTransfers(links []TransferLink) error {
	tx, err := d.sql.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	if _, err := tx.Exec(`DELETE FROM transfers`); err != nil {
		return fmt.Errorf("clear transfers: %w", err)
	}
	stmt, err := tx.Prepare(
		`INSERT INTO transfers (def_index, out_txn_id, in_txn_id) VALUES (?, ?, ?)`)
	if err != nil {
		return err
	}
	defer stmt.Close()

	for _, l := range links {
		if _, err := stmt.Exec(l.DefIndex, l.OutID, l.InID); err != nil {
			return fmt.Errorf("link transfer %d→%d: %w", l.OutID, l.InID, 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
}

// Months lists the distinct YYYY-MM the index holds, most recent first. It is
// asked of the whole index rather than of a filtered view on purpose: it is the
// time axis the report screen steps along, and an axis that grew and shrank as
// the account or search filter changed would move under the cursor.
func (d *DB) Months() ([]string, error) {
	rows, err := d.sql.Query(
		`SELECT DISTINCT substr(date, 1, 7) FROM transactions ORDER BY 1 DESC`)
	if err != nil {
		return nil, fmt.Errorf("list months: %w", 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()
}

// Tags lists every tag in use, for completion in the rule builder.
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()
}