package repository

import (
	"context"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/jackc/pgx/v5/pgxpool"
	"go.uber.org/zap"
)

type Postgres struct {
	Pool   *pgxpool.Pool
	logger *zap.Logger
}

func NewPostgres(ctx context.Context, uri string, logger *zap.Logger) (*Postgres, error) {
	if uri == "" {
		return nil, fmt.Errorf("postgres URI is empty")
	}

	cfg, err := pgxpool.ParseConfig(uri)
	if err != nil {
		return nil, fmt.Errorf("postgres parse config: %w", err)
	}
	cfg.MaxConns = 20
	cfg.MinConns = 2
	cfg.MaxConnLifetime = 30 * time.Minute
	cfg.MaxConnIdleTime = 5 * time.Minute

	pingCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
	defer cancel()

	pool, err := pgxpool.NewWithConfig(pingCtx, cfg)
	if err != nil {
		return nil, fmt.Errorf("postgres connect: %w", err)
	}
	if err := pool.Ping(pingCtx); err != nil {
		pool.Close()
		return nil, fmt.Errorf("postgres ping: %w", err)
	}

	logger.Info("connected to Postgres")
	return &Postgres{Pool: pool, logger: logger}, nil
}

func (p *Postgres) Close() {
	if p == nil || p.Pool == nil {
		return
	}
	p.Pool.Close()
}

// RunMigrations applies any *.up.sql files in dir that haven't been recorded
// in schema_migrations yet, in lexical order. Tiny homegrown runner — no
// external dependency. Down-migrations are not executed automatically.
func (p *Postgres) RunMigrations(ctx context.Context, dir string) error {
	if _, err := p.Pool.Exec(ctx, `
		CREATE TABLE IF NOT EXISTS schema_migrations (
			version    BIGINT PRIMARY KEY,
			applied_at TIMESTAMPTZ NOT NULL DEFAULT now()
		)`); err != nil {
		return fmt.Errorf("create schema_migrations: %w", err)
	}

	files, err := filepath.Glob(filepath.Join(dir, "*.up.sql"))
	if err != nil {
		return fmt.Errorf("glob migrations: %w", err)
	}
	sort.Strings(files)

	for _, f := range files {
		version, err := parseMigrationVersion(f)
		if err != nil {
			p.logger.Warn("skipping unparseable migration filename", zap.String("file", f), zap.Error(err))
			continue
		}

		var exists bool
		if err := p.Pool.QueryRow(ctx,
			`SELECT EXISTS(SELECT 1 FROM schema_migrations WHERE version = $1)`, version,
		).Scan(&exists); err != nil {
			return fmt.Errorf("check migration %d: %w", version, err)
		}
		if exists {
			continue
		}

		sqlBytes, err := os.ReadFile(f)
		if err != nil {
			return fmt.Errorf("read %s: %w", f, err)
		}

		tx, err := p.Pool.Begin(ctx)
		if err != nil {
			return fmt.Errorf("begin tx for %s: %w", f, err)
		}
		if _, err := tx.Exec(ctx, string(sqlBytes)); err != nil {
			_ = tx.Rollback(ctx)
			return fmt.Errorf("apply %s: %w", f, err)
		}
		if _, err := tx.Exec(ctx, `INSERT INTO schema_migrations(version) VALUES ($1)`, version); err != nil {
			_ = tx.Rollback(ctx)
			return fmt.Errorf("record %s: %w", f, err)
		}
		if err := tx.Commit(ctx); err != nil {
			return fmt.Errorf("commit %s: %w", f, err)
		}

		p.logger.Info("applied migration", zap.String("file", filepath.Base(f)), zap.Int64("version", version))
	}
	return nil
}

func parseMigrationVersion(path string) (int64, error) {
	base := filepath.Base(path)
	idx := strings.Index(base, "_")
	if idx <= 0 {
		return 0, fmt.Errorf("filename %q must start with <version>_", base)
	}
	v, err := strconv.ParseInt(base[:idx], 10, 64)
	if err != nil {
		return 0, fmt.Errorf("version prefix not an integer: %w", err)
	}
	return v, nil
}