package storage

import (
	"context"
	"database/sql"
	"embed"
	"fmt"
	"time"

	"github.com/bergabruh/stats-gateway/internal/probes"
	_ "github.com/mattn/go-sqlite3"
)

//go:embed migrations/*.sql
var migrations embed.FS

// tsLayout is RFC3339 with fixed 9-digit nanosecond fraction. Lexical
// ordering of formatted strings preserves chronological order — unlike
// time.RFC3339Nano which strips trailing zeros (".1Z" lex-sorts after
// ".100000001Z" because 'Z' > '0'). SQLite TEXT columns are compared
// lexically, so this matters for QueryRange boundaries.
const tsLayout = "2006-01-02T15:04:05.000000000Z07:00"

// Store wraps a SQLite database for probe sample persistence.
type Store struct {
	db *sql.DB
}

// Open opens (or creates) the SQLite database at path and runs migrations.
func Open(path string) (*Store, error) {
	db, err := sql.Open("sqlite3", path+"?_journal_mode=WAL&_busy_timeout=5000")
	if err != nil {
		return nil, err
	}
	s := &Store{db: db}
	if err := s.migrate(); err != nil {
		return nil, fmt.Errorf("migrate: %w", err)
	}
	return s, nil
}

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

func (s *Store) migrate() error {
	body, err := migrations.ReadFile("migrations/001_init.sql")
	if err != nil {
		return err
	}
	_, err = s.db.Exec(string(body))
	return err
}

// InsertSample stores a probe result for the given node.
func (s *Store) InsertSample(ctx context.Context, node string, r *probes.Result) error {
	_, err := s.db.ExecContext(ctx, `
		INSERT INTO samples (node, ts, http_latency_ms, tcp_rtt_ms, dns_resolve_ms, tls_handshake_ms, throughput_kbps)
		VALUES (?, ?, ?, ?, ?, ?, ?)
	`, node, r.Timestamp.Format(tsLayout),
		r.HTTPLatencyMs, r.TCPRttMs, r.DNSResolveMs, r.TLSHandshakeMs, r.ThroughputKbps)
	return err
}

// QueryRecent returns up to limit samples for node ordered by ts DESC.
// If since is zero, no lower bound is applied. If node is empty, all nodes are returned.
func (s *Store) QueryRecent(ctx context.Context, node string, limit int, since time.Time) ([]probes.Result, error) {
	q := `SELECT node, ts, http_latency_ms, tcp_rtt_ms, dns_resolve_ms, tls_handshake_ms, throughput_kbps
	      FROM samples WHERE 1=1`
	args := []any{}
	if node != "" {
		q += ` AND node = ?`
		args = append(args, node)
	}
	if !since.IsZero() {
		q += ` AND ts >= ?`
		args = append(args, since.Format(tsLayout))
	}
	q += ` ORDER BY ts DESC LIMIT ?`
	args = append(args, limit)

	return s.scanSamples(ctx, q, args...)
}

// QueryRange returns samples for [since, until). Used by Aggregate (Task 5).
func (s *Store) QueryRange(ctx context.Context, node string, since, until time.Time) ([]probes.Result, error) {
	q := `SELECT node, ts, http_latency_ms, tcp_rtt_ms, dns_resolve_ms, tls_handshake_ms, throughput_kbps
	      FROM samples WHERE ts >= ? AND ts < ?`
	args := []any{since.Format(tsLayout), until.Format(tsLayout)}
	if node != "" {
		q += ` AND node = ?`
		args = append(args, node)
	}
	q += ` ORDER BY ts ASC`
	return s.scanSamples(ctx, q, args...)
}

func (s *Store) scanSamples(ctx context.Context, q string, args ...any) ([]probes.Result, error) {
	rows, err := s.db.QueryContext(ctx, q, args...)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	var out []probes.Result
	for rows.Next() {
		var ts string
		var r probes.Result
		if err := rows.Scan(&r.Node, &ts, &r.HTTPLatencyMs, &r.TCPRttMs, &r.DNSResolveMs, &r.TLSHandshakeMs, &r.ThroughputKbps); err != nil {
			return nil, err
		}
		r.Timestamp, _ = time.Parse(tsLayout, ts)
		out = append(out, r)
	}
	return out, rows.Err()
}