package database

import (
	"context"
	"crypto/sha256"
	"embed"
	"fmt"
	"sort"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"
	"veyra/services/api/internal/platform/config"
)

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

func Open(ctx context.Context, c config.Config) (*pgxpool.Pool, error) {
	if err := c.ValidateDatabase(); err != nil {
		return nil, err
	}
	p, err := pgxpool.New(ctx, c.DatabaseURL(c.PGDatabase))
	if err != nil {
		return nil, fmt.Errorf("configure PostgreSQL pool")
	}
	if err := p.Ping(ctx); err != nil {
		p.Close()
		return nil, fmt.Errorf("PostgreSQL connection unavailable")
	}
	return p, nil
}

// Create creates only the configured database and never drops or resets data.
func Create(ctx context.Context, c config.Config) (bool, error) {
	if err := c.ValidateDatabase(); err != nil {
		return false, err
	}
	conn, err := pgx.Connect(ctx, c.DatabaseURL(c.PGAdminDatabase))
	if err != nil {
		return false, fmt.Errorf("administrative PostgreSQL connection unavailable")
	}
	defer conn.Close(context.Background())
	if _, err := conn.Exec(ctx, "SELECT pg_advisory_lock(hashtext($1)::bigint)", "veyra:create:"+c.PGDatabase); err != nil {
		return false, fmt.Errorf("lock database creation: %w", err)
	}
	var exists bool
	if err := conn.QueryRow(ctx, "SELECT EXISTS(SELECT 1 FROM pg_database WHERE datname = $1)", c.PGDatabase).Scan(&exists); err != nil {
		return false, fmt.Errorf("inspect database: %w", err)
	}
	if exists {
		return false, nil
	}
	if _, err := conn.Exec(ctx, "CREATE DATABASE "+pgx.Identifier{c.PGDatabase}.Sanitize()); err != nil {
		return false, fmt.Errorf("create database failed; verify role CREATEDB permission")
	}
	return true, nil
}

// Migrate serializes concurrent runners and atomically records each migration.
// Even the migration ledger follows the veyra_ prefix and string UUID ID rules.
func Migrate(ctx context.Context, pool *pgxpool.Pool) error {
	conn, err := pool.Acquire(ctx)
	if err != nil {
		return err
	}
	defer conn.Release()
	tx, err := conn.Begin(ctx)
	if err != nil {
		return err
	}
	defer tx.Rollback(context.Background())
	if _, err := tx.Exec(ctx, "SELECT pg_advisory_xact_lock(727198321)"); err != nil {
		return err
	}
	if _, err := tx.Exec(ctx, `CREATE TABLE IF NOT EXISTS veyra_schema_migration (
id varchar(36) PRIMARY KEY CHECK (id ~ '^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$'),
version varchar(120) NOT NULL UNIQUE, checksum varchar(64) NOT NULL, applied_at timestamptz NOT NULL DEFAULT now())`); err != nil {
		return fmt.Errorf("create migration ledger: %w", err)
	}
	entries, err := migrations.ReadDir("migrations")
	if err != nil {
		return err
	}
	sort.Slice(entries, func(i, j int) bool { return entries[i].Name() < entries[j].Name() })
	for _, entry := range entries {
		sql, err := migrations.ReadFile("migrations/" + entry.Name())
		if err != nil {
			return err
		}
		checksum := fmt.Sprintf("%x", sha256.Sum256(sql))
		var stored string
		err = tx.QueryRow(ctx, "SELECT checksum FROM veyra_schema_migration WHERE version=$1", entry.Name()).Scan(&stored)
		if err == nil {
			if stored != checksum {
				return fmt.Errorf("migration %s checksum mismatch", entry.Name())
			}
			continue
		}
		if err != pgx.ErrNoRows {
			return err
		}
		if _, err := tx.Exec(ctx, string(sql)); err != nil {
			return fmt.Errorf("apply %s: %w", entry.Name(), err)
		}
		if _, err := tx.Exec(ctx, "INSERT INTO veyra_schema_migration(id,version,checksum) VALUES($1,$2,$3)", uuid.NewString(), entry.Name(), checksum); err != nil {
			return err
		}
	}
	return tx.Commit(ctx)
}