// Package db manages the SQLite database connection, schema migrations,
// and data access for server profiles and connection logs.
//
// It uses modernc.org/sqlite (a pure-Go driver) so the binary has no
// CGO dependency and cross-compiles trivially.
package db

import (
	"database/sql"
	"fmt"
	"net"
	"strings"

	"lmvpn/internal/paths"

	_ "modernc.org/sqlite"
)

// Store wraps the database handle and provides data access methods.
type Store struct {
	db *sql.DB
}

// Open creates or opens the SQLite database and runs migrations.
func Open() (*Store, error) {
	db, err := sql.Open("sqlite", paths.DBPath()+"?_pragma=journal_mode(WAL)&_pragma=busy_timeout(5000)")
	if err != nil {
		return nil, fmt.Errorf("open db: %w", err)
	}
	db.SetMaxOpenConns(1) // sqlite serialises writes
	s := &Store{db: db}
	if err := s.migrate(); err != nil {
		db.Close()
		return nil, fmt.Errorf("migrate: %w", err)
	}
	return s, nil
}

// Close closes the database connection.
func (s *Store) Close() error {
	return s.db.Close()
}

func (s *Store) migrate() error {
	_, err := s.db.Exec(schemaV2)
	if err != nil {
		return err
	}
	if err := s.migrateV2(); err != nil {
		return err
	}
	if err := s.migrateV3(); err != nil {
		return err
	}
	if err := s.migrateV4(); err != nil {
		return err
	}
	if err := s.migrateV5(); err != nil {
		return err
	}
	return s.migrateV6()
}

func (s *Store) migrateV2() error {
	// Detect if migration is needed by checking if old server_url column
	// still exists. If protocol column is present, v2 is already in place.
	_, err := s.db.Exec(`SELECT protocol, host, server_ips, port, path FROM server_profiles LIMIT 0`)
	if err == nil {
		return nil // already v2
	}

	// Check if old table exists.
	var count int
	err = s.db.QueryRow(`SELECT COUNT(*) FROM sqlite_master WHERE type='table' AND name='server_profiles' AND sql LIKE '%server_url%'`).Scan(&count)
	if err != nil || count == 0 {
		return nil // nothing to migrate
	}

	tx, err := s.db.Begin()
	if err != nil {
		return fmt.Errorf("migrate v2 begin: %w", err)
	}
	defer tx.Rollback()

	_, err = tx.Exec(`ALTER TABLE server_profiles RENAME TO server_profiles_old`)
	if err != nil {
		return fmt.Errorf("migrate v2 rename: %w", err)
	}

	_, err = tx.Exec(schemaV2)
	if err != nil {
		return fmt.Errorf("migrate v2 create new: %w", err)
	}

	rows, err := tx.Query(`SELECT id, name, server_url, username, auth_mode, routing_mode, custom_cidrs, mtu_override, auto_connect, created_at, last_connected_at FROM server_profiles_old`)
	if err != nil {
		return fmt.Errorf("migrate v2 read old: %w", err)
	}
	defer rows.Close()

	insert, err := tx.Prepare(`INSERT INTO server_profiles (id, name, protocol, host, server_ips, port, path, username, auth_mode, routing_mode, custom_cidrs, mtu_override, auto_connect, created_at, last_connected_at) VALUES (?,?,?,?,?,?,?,?,?,?,?,?,?,?,?)`)
	if err != nil {
		return fmt.Errorf("migrate v2 prepare insert: %w", err)
	}
	defer insert.Close()

	for rows.Next() {
		var id int64
		var name, serverURL, username, authMode, routingMode, customCIDRs string
		var mtuOverride int
		var autoConnect int
		var createdAt, lastConnectedAt sql.NullString
		if err := rows.Scan(&id, &name, &serverURL, &username, &authMode, &routingMode, &customCIDRs, &mtuOverride, &autoConnect, &createdAt, &lastConnectedAt); err != nil {
			return fmt.Errorf("migrate v2 scan: %w", err)
		}
		protocol, host, ips, port, path := parseOldURL(serverURL)
		_, err = insert.Exec(id, name, protocol, host, ips, port, path, username, authMode, routingMode, customCIDRs, mtuOverride, autoConnect, nullStr(createdAt), nullStr(lastConnectedAt))
		if err != nil {
			return fmt.Errorf("migrate v2 insert: %w", err)
		}
	}

	if err := rows.Err(); err != nil {
		return err
	}

	_, err = tx.Exec(`DROP TABLE server_profiles_old`)
	if err != nil {
		return fmt.Errorf("migrate v2 drop old: %w", err)
	}

	return tx.Commit()
}

func parseOldURL(raw string) (protocol, host, ips, path string, port int) {
	u := raw
	switch {
	case strings.HasPrefix(u, "wss://"):
		protocol = "wss"
		u = u[6:]
	case strings.HasPrefix(u, "ws://"):
		protocol = "ws"
		u = u[5:]
	default:
		protocol = "wss"
	}

	path = "/ws"
	if i := strings.IndexByte(u, '/'); i >= 0 {
		path = u[i:]
		u = u[:i]
	}

	port = 443
	if i := strings.LastIndexByte(u, ':'); i >= 0 {
		if p, err := stringToInt(u[i+1:]); err == nil {
			port = p
			u = u[:i]
		}
	}

	host = u
	return
}

func stringToInt(s string) (int, error) {
	var n int
	for _, c := range s {
		if c < '0' || c > '9' {
			return 0, fmt.Errorf("not a number: %s", s)
		}
		n = n*10 + int(c-'0')
	}
	return n, nil
}

func nullStr(s sql.NullString) sql.NullString {
	return s
}

// migrateV3 adds the assigned_ip6 column to connection_logs for IPv6
// dual-stack support. Idempotent: skips if the column already exists.
func (s *Store) migrateV3() error {
	if columnExists(s.db, "connection_logs", "assigned_ip6") {
		return nil
	}
	_, err := s.db.Exec(`ALTER TABLE connection_logs ADD COLUMN assigned_ip6 TEXT NOT NULL DEFAULT ''`)
	if err != nil {
		return fmt.Errorf("migrate v3 add assigned_ip6: %w", err)
	}
	return nil
}

// migrateV4 adds TLS certificate verification columns to
// server_profiles for custom CA, insecure mode, and cert pinning.
// Idempotent: skips columns that already exist.
func (s *Store) migrateV4() error {
	cols := []struct {
		name string
		sql  string
	}{
		{"tls_ca_cert", "ALTER TABLE server_profiles ADD COLUMN tls_ca_cert TEXT NOT NULL DEFAULT ''"},
		{"tls_ca_path", "ALTER TABLE server_profiles ADD COLUMN tls_ca_path TEXT NOT NULL DEFAULT ''"},
		{"tls_insecure", "ALTER TABLE server_profiles ADD COLUMN tls_insecure INTEGER NOT NULL DEFAULT 0"},
		{"tls_pinned_hash", "ALTER TABLE server_profiles ADD COLUMN tls_pinned_hash TEXT NOT NULL DEFAULT ''"},
	}
	for _, c := range cols {
		if !columnExists(s.db, "server_profiles", c.name) {
			if _, err := s.db.Exec(c.sql); err != nil {
				return fmt.Errorf("migrate v4 add %s: %w", c.name, err)
			}
		}
	}
	return nil
}

// migrateV5 replaces the single custom_cidrs column with separate
// cidr_v4, cidr_v6, cidr_v4_urls, cidr_v6_urls columns. It migrates
// existing routing modes: 'custom' -> 'proxy', 'split' -> 'full'.
// Existing custom_cidrs are split into v4/v6 based on address family.
// Idempotent: skips columns that already exist.
func (s *Store) migrateV5() error {
	cols := []struct {
		name string
		sql  string
	}{
		{"cidr_v4", "ALTER TABLE server_profiles ADD COLUMN cidr_v4 TEXT NOT NULL DEFAULT ''"},
		{"cidr_v6", "ALTER TABLE server_profiles ADD COLUMN cidr_v6 TEXT NOT NULL DEFAULT ''"},
		{"cidr_v4_urls", "ALTER TABLE server_profiles ADD COLUMN cidr_v4_urls TEXT NOT NULL DEFAULT ''"},
		{"cidr_v6_urls", "ALTER TABLE server_profiles ADD COLUMN cidr_v6_urls TEXT NOT NULL DEFAULT ''"},
	}
	needMigration := false
	for _, c := range cols {
		if !columnExists(s.db, "server_profiles", c.name) {
			needMigration = true
			break
		}
	}
	if !needMigration {
		return nil
	}

	for _, c := range cols {
		if !columnExists(s.db, "server_profiles", c.name) {
			if _, err := s.db.Exec(c.sql); err != nil {
				return fmt.Errorf("migrate v5 add %s: %w", c.name, err)
			}
		}
	}

	// Migrate existing custom_cidrs into cidr_v4 / cidr_v6 and update
	// routing mode codes. Only process rows that still have a non-empty
	// custom_cidrs or an old routing mode.
	rows, err := s.db.Query(`SELECT id, routing_mode, custom_cidrs FROM server_profiles`)
	if err != nil {
		return fmt.Errorf("migrate v5 read rows: %w", err)
	}
	type row struct {
		id          int64
		routingMode string
		customCIDRs string
	}
	var toUpdate []row
	for rows.Next() {
		var r row
		if err := rows.Scan(&r.id, &r.routingMode, &r.customCIDRs); err != nil {
			rows.Close()
			return fmt.Errorf("migrate v5 scan: %w", err)
		}
		toUpdate = append(toUpdate, r)
	}
	rows.Close()

	for _, r := range toUpdate {
		newMode := r.routingMode
		switch newMode {
		case "custom":
			newMode = "proxy"
		case "split":
			newMode = "full"
		}

		v4CIDRs, v6CIDRs := splitCIDRsByFamily(r.customCIDRs)

		_, err := s.db.Exec(
			`UPDATE server_profiles SET routing_mode = ?, cidr_v4 = ?, cidr_v6 = ? WHERE id = ?`,
			newMode, v4CIDRs, v6CIDRs, r.id)
		if err != nil {
			return fmt.Errorf("migrate v5 update row %d: %w", r.id, err)
		}
	}

	return nil
}

// migrateV6 adds the ip_preference column to server_profiles for
// controlling IPv4/IPv6 address selection when connecting by hostname.
// Idempotent: skips if the column already exists.
func (s *Store) migrateV6() error {
	if columnExists(s.db, "server_profiles", "ip_preference") {
		return nil
	}
	_, err := s.db.Exec(`ALTER TABLE server_profiles ADD COLUMN ip_preference TEXT NOT NULL DEFAULT 'auto'`)
	if err != nil {
		return fmt.Errorf("migrate v6 add ip_preference: %w", err)
	}
	return nil
}

// splitCIDRsByFamily splits a comma-separated CIDR string into IPv4 and
// IPv6 parts. Used for migration from the old custom_cidrs column.
func splitCIDRsByFamily(customCIDRs string) (v4, v6 string) {
	if customCIDRs == "" {
		return "", ""
	}
	var v4Parts, v6Parts []string
	for _, part := range strings.Split(customCIDRs, ",") {
		c := strings.TrimSpace(part)
		if c == "" {
			continue
		}
		if _, ipNet, err := net.ParseCIDR(c); err == nil {
			if ipNet.IP.To4() != nil {
				v4Parts = append(v4Parts, c)
			} else {
				v6Parts = append(v6Parts, c)
			}
		}
	}
	return strings.Join(v4Parts, ", "), strings.Join(v6Parts, ", ")
}

// columnExists reports whether a column exists on a table.
func columnExists(db *sql.DB, table, column string) bool {
	rows, err := db.Query(fmt.Sprintf("PRAGMA table_info(%s)", table))
	if err != nil {
		return false
	}
	defer rows.Close()
	for rows.Next() {
		var cid int
		var name, ctype string
		var notnull, pk int
		var dflt sql.NullString
		if err := rows.Scan(&cid, &name, &ctype, &notnull, &dflt, &pk); err != nil {
			return false
		}
		if name == column {
			return true
		}
	}
	return false
}

const schemaV2 = `
CREATE TABLE IF NOT EXISTS server_profiles (
	id              INTEGER PRIMARY KEY AUTOINCREMENT,
	name            TEXT    NOT NULL,
	protocol        TEXT    NOT NULL DEFAULT 'wss',
	host            TEXT    NOT NULL,
	server_ips      TEXT    NOT NULL DEFAULT '',
	port            INTEGER NOT NULL DEFAULT 443,
	path            TEXT    NOT NULL DEFAULT '/ws',
	username        TEXT    NOT NULL,
	auth_mode       TEXT    NOT NULL DEFAULT 'both',
	routing_mode    TEXT    NOT NULL DEFAULT 'full',
	custom_cidrs    TEXT    NOT NULL DEFAULT '',
	cidr_v4         TEXT    NOT NULL DEFAULT '',
	cidr_v6         TEXT    NOT NULL DEFAULT '',
	cidr_v4_urls    TEXT    NOT NULL DEFAULT '',
	cidr_v6_urls    TEXT    NOT NULL DEFAULT '',
	mtu_override    INTEGER NOT NULL DEFAULT 0,
	auto_connect    INTEGER NOT NULL DEFAULT 0,
	ip_preference   TEXT    NOT NULL DEFAULT 'auto',
	created_at      DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
	last_connected_at DATETIME
);

CREATE TABLE IF NOT EXISTS connection_logs (
	id           INTEGER PRIMARY KEY AUTOINCREMENT,
	profile_id   INTEGER NOT NULL,
	started_at   DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
	ended_at     DATETIME,
	assigned_ip  TEXT    NOT NULL DEFAULT '',
	assigned_ip6 TEXT    NOT NULL DEFAULT '',
	rx_bytes     INTEGER NOT NULL DEFAULT 0,
	tx_bytes     INTEGER NOT NULL DEFAULT 0,
	status       TEXT    NOT NULL DEFAULT 'connected',
	error_msg    TEXT    NOT NULL DEFAULT '',
	FOREIGN KEY (profile_id) REFERENCES server_profiles(id) ON DELETE CASCADE
);

CREATE INDEX IF NOT EXISTS idx_logs_profile ON connection_logs(profile_id);
`