package mysql

import (
	"context"
	"database/sql"
	"strconv"
	"time"

	_ "github.com/go-sql-driver/mysql"

	"bugs.watch/agent/internal/aggregate"
)

// Collector queries MySQL global status each sample interval.
// All queries run under a 3-second timeout; any failure is silently skipped.
type Collector struct {
	db              *sql.DB
	prevSlowQueries uint64
	hasPrev         bool
}

func New(dsn string) (*Collector, error) {
	db, err := sql.Open("mysql", dsn)
	if err != nil {
		return nil, err
	}
	db.SetMaxOpenConns(2)
	db.SetMaxIdleConns(1)
	db.SetConnMaxLifetime(5 * time.Minute)
	return &Collector{db: db}, nil
}

func (c *Collector) Name() string { return "mysql" }

func (c *Collector) Close() { c.db.Close() }

func (c *Collector) Collect(window *aggregate.Window) {
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()

	rows, err := c.db.QueryContext(ctx,
		"SHOW GLOBAL STATUS WHERE Variable_name IN ('Threads_connected','Threads_running','Slow_queries')",
	)
	if err != nil {
		return
	}
	defer rows.Close()

	vars := make(map[string]uint64, 3)
	for rows.Next() {
		var name, raw string
		if err := rows.Scan(&name, &raw); err != nil {
			continue
		}
		if v, err := strconv.ParseUint(raw, 10, 64); err == nil {
			vars[name] = v
		}
	}
	if err := rows.Err(); err != nil {
		return
	}

	var maxConn uint64
	if err := c.db.QueryRowContext(ctx, "SELECT @@max_connections").Scan(&maxConn); err != nil || maxConn == 0 {
		maxConn = 1
	}

	connPct := float64(vars["Threads_connected"]) / float64(maxConn) * 100
	window.AddDBConnPct(connPct)
	window.AddDBThreadsRunning(float64(vars["Threads_running"]))

	slow := vars["Slow_queries"]
	if c.hasPrev {
		var delta uint64
		if slow >= c.prevSlowQueries {
			delta = slow - c.prevSlowQueries
		}
		window.AddDBSlowQueriesDelta(delta)
	}
	c.prevSlowQueries = slow
	c.hasPrev = true

	var sizeBytes uint64
	err = c.db.QueryRowContext(ctx,
		"SELECT COALESCE(SUM(data_length + index_length), 0)"+
			" FROM information_schema.tables"+
			" WHERE table_schema NOT IN ('information_schema','performance_schema','mysql','sys')",
	).Scan(&sizeBytes)
	if err == nil {
		window.SetDBSizeBytes(sizeBytes)
	}
}