package database

import (
	"context"
	"fmt"
	"runtime"

	"zombiezen.com/go/sqlite"
	"zombiezen.com/go/sqlite/sqlitex"
)

const DefaultPath = "dk.db"

// Global singleton instance
var pool *sqlitex.Pool

// Init initializes the global database connection pool
func Init(path string) error {
	if path == "" {
		path = DefaultPath
	}

	poolSize := max(runtime.GOMAXPROCS(0), 2)

	var err error
	pool, err = sqlitex.NewPool(path, sqlitex.PoolOptions{
		PoolSize: poolSize,
		Flags:    sqlite.OpenCreate | sqlite.OpenReadWrite | sqlite.OpenWAL,
	})
	if err != nil {
		return fmt.Errorf("failed to open database pool: %w", err)
	}

	conn, err := pool.Take(context.Background())
	if err != nil {
		pool.Close()
		return fmt.Errorf("failed to get connection from pool: %w", err)
	}
	defer pool.Put(conn)

	if err := sqlitex.ExecuteTransient(conn, "PRAGMA journal_mode = WAL", nil); err != nil {
		pool.Close()
		return fmt.Errorf("failed to set WAL mode: %w", err)
	}

	if err := sqlitex.ExecuteTransient(conn, "PRAGMA synchronous = NORMAL", nil); err != nil {
		pool.Close()
		return fmt.Errorf("failed to set synchronous mode: %w", err)
	}

	return nil
}

// Close closes the global database connection pool
func Close() error {
	if pool == nil {
		return nil
	}
	return pool.Close()
}

// GetConn gets a connection from the pool - caller must call PutConn when done
func GetConn(ctx context.Context) (*sqlite.Conn, error) {
	if pool == nil {
		return nil, fmt.Errorf("database not initialized")
	}
	return pool.Take(ctx)
}

// PutConn returns a connection to the pool
func PutConn(conn *sqlite.Conn) {
	if pool != nil {
		pool.Put(conn)
	}
}

// Exec executes a SQL statement without returning results
func Exec(query string, args ...any) error {
	if pool == nil {
		return fmt.Errorf("database not initialized")
	}

	conn, err := pool.Take(context.Background())
	if err != nil {
		return fmt.Errorf("failed to get connection from pool: %w", err)
	}
	defer pool.Put(conn)

	if len(args) == 0 {
		return sqlitex.ExecuteTransient(conn, query, nil)
	}

	return sqlitex.ExecuteTransient(conn, query, &sqlitex.ExecOptions{
		Args: args,
	})
}

// Query executes a SQL query and calls fn for each row
func Query(query string, fn func(*sqlite.Stmt) error, args ...any) error {
	if pool == nil {
		return fmt.Errorf("database not initialized")
	}

	conn, err := pool.Take(context.Background())
	if err != nil {
		return fmt.Errorf("failed to get connection from pool: %w", err)
	}
	defer pool.Put(conn)

	if len(args) == 0 {
		return sqlitex.ExecuteTransient(conn, query, &sqlitex.ExecOptions{
			ResultFunc: fn,
		})
	}

	return sqlitex.ExecuteTransient(conn, query, &sqlitex.ExecOptions{
		Args:       args,
		ResultFunc: fn,
	})
}

// Begin starts a new transaction
func Begin() (*Tx, error) {
	if pool == nil {
		return nil, fmt.Errorf("database not initialized")
	}

	conn, err := pool.Take(context.Background())
	if err != nil {
		return nil, fmt.Errorf("failed to get connection from pool: %w", err)
	}

	if err := sqlitex.ExecuteTransient(conn, "BEGIN", nil); err != nil {
		pool.Put(conn)
		return nil, fmt.Errorf("failed to begin transaction: %w", err)
	}

	return &Tx{conn: conn, pool: pool}, nil
}

// Transaction runs a function within a transaction
func Transaction(fn func(*Tx) error) error {
	if pool == nil {
		return fmt.Errorf("database not initialized")
	}

	tx, err := Begin()
	if err != nil {
		return err
	}

	if err := fn(tx); err != nil {
		tx.Rollback()
		return err
	}

	return tx.Commit()
}

// Tx represents a database transaction
type Tx struct {
	conn *sqlite.Conn
	pool *sqlitex.Pool
}

// Exec executes a SQL statement within the transaction
func (tx *Tx) Exec(query string, args ...any) error {
	if len(args) == 0 {
		return sqlitex.ExecuteTransient(tx.conn, query, nil)
	}

	return sqlitex.ExecuteTransient(tx.conn, query, &sqlitex.ExecOptions{
		Args: args,
	})
}

// Query executes a SQL query within the transaction
func (tx *Tx) Query(query string, fn func(*sqlite.Stmt) error, args ...any) error {
	if len(args) == 0 {
		return sqlitex.ExecuteTransient(tx.conn, query, &sqlitex.ExecOptions{
			ResultFunc: fn,
		})
	}

	return sqlitex.ExecuteTransient(tx.conn, query, &sqlitex.ExecOptions{
		Args:       args,
		ResultFunc: fn,
	})
}

// Commit commits the transaction
func (tx *Tx) Commit() error {
	defer tx.pool.Put(tx.conn)
	return sqlitex.ExecuteTransient(tx.conn, "COMMIT", nil)
}

// Rollback rolls back the transaction
func (tx *Tx) Rollback() error {
	defer tx.pool.Put(tx.conn)
	return sqlitex.ExecuteTransient(tx.conn, "ROLLBACK", nil)
}