package stdlib

import (
	"database/sql"
	"database/sql/driver"
	"errors"
	"fmt"
	"github.com/jackc/pgx"
	"io"
)

var openFromConnPoolCount int

func init() {
	d := &Driver{}
	sql.Register("pgx", d)
}

type Driver struct {
	Pool *pgx.ConnPool
}

func (d *Driver) Open(name string) (driver.Conn, error) {
	if d.Pool != nil {
		conn, err := d.Pool.Acquire()
		if err != nil {
			return nil, err
		}

		return &Conn{conn: conn, pool: d.Pool}, nil
	}

	connConfig, err := pgx.ParseURI(name)
	if err != nil {
		return nil, err
	}

	conn, err := pgx.Connect(connConfig)
	if err != nil {
		return nil, err
	}

	c := &Conn{conn: conn}
	return c, nil
}

// OpenFromConnPool takes the existing *pgx.ConnPool pool and returns a *sql.DB
// with pool as the backend. This enables full control over the connection
// process and configuration while maintaining compatibility with the
// database/sql interface. In addition, by calling Driver() on the returned
// *sql.DB and typecasting to *stdlib.Driver a reference to the pgx.ConnPool can
// be reaquired later. This allows fast paths targeting pgx to be used while
// still maintaining compatibility with other databases and drivers.
func OpenFromConnPool(pool *pgx.ConnPool) (*sql.DB, error) {
	d := &Driver{Pool: pool}
	name := fmt.Sprintf("pgx-%d", openFromConnPoolCount)
	openFromConnPoolCount++
	sql.Register(name, d)
	db, err := sql.Open(name, "")
	if err != nil {
		return nil, err
	}

	// Presumably OpenFromConnPool is being used because the user wants to use
	// database/sql most of the time, but fast path with pgx some of the time.
	// Allow database/sql to use all the connections, but release 2 idle ones.
	// Don't have database/sql immediately release all idle connections because
	// that would mean that prepared statements would be lost (which kills
	// performance if the prepared statements constantly have to be reprepared)
	db.SetMaxIdleConns(pool.MaxConnectionCount() - 2)
	db.SetMaxOpenConns(pool.MaxConnectionCount())

	return db, nil
}

type Conn struct {
	conn    *pgx.Conn
	pool    *pgx.ConnPool
	psCount int64 // Counter used for creating unique prepared statement names
}

func (c *Conn) Prepare(query string) (driver.Stmt, error) {
	if !c.conn.IsAlive() {
		return nil, driver.ErrBadConn
	}

	name := fmt.Sprintf("pgx_%d", c.psCount)
	c.psCount++

	ps, err := c.conn.Prepare(name, query)
	if err != nil {
		return nil, err
	}

	return &Stmt{ps: ps, conn: c}, nil
}

func (c *Conn) Close() error {
	if c.pool != nil {
		c.pool.Release(c.conn)
		return nil
	}

	return c.conn.Close()
}

func (c *Conn) Begin() (driver.Tx, error) {
	if !c.conn.IsAlive() {
		return nil, driver.ErrBadConn
	}

	_, err := c.conn.Exec("begin")
	if err != nil {
		return nil, err
	}

	return &Tx{conn: c.conn}, nil
}

func (c *Conn) Exec(query string, argsV []driver.Value) (driver.Result, error) {
	if !c.conn.IsAlive() {
		return nil, driver.ErrBadConn
	}

	args := valueToInterface(argsV)
	commandTag, err := c.conn.Exec(query, args...)
	return driver.RowsAffected(commandTag.RowsAffected()), err
}

func (c *Conn) Query(query string, argsV []driver.Value) (driver.Rows, error) {
	if !c.conn.IsAlive() {
		return nil, driver.ErrBadConn
	}

	args := valueToInterface(argsV)

	rows, err := c.conn.Query(query, args...)
	if err != nil {
		return nil, err
	}

	return &Rows{rows: rows}, nil
}

type Stmt struct {
	ps   *pgx.PreparedStatement
	conn *Conn
}

func (s *Stmt) Close() error {
	return s.conn.conn.Deallocate(s.ps.Name)
}

func (s *Stmt) NumInput() int {
	return len(s.ps.ParameterOids)
}

func (s *Stmt) Exec(argsV []driver.Value) (driver.Result, error) {
	return s.conn.Exec(s.ps.Name, argsV)
}

func (s *Stmt) Query(argsV []driver.Value) (driver.Rows, error) {
	return s.conn.Query(s.ps.Name, argsV)
}

// TODO - rename to avoid alloc
type Rows struct {
	rows *pgx.Rows
}

func (r *Rows) Columns() []string {
	fieldDescriptions := r.rows.FieldDescriptions()
	names := make([]string, 0, len(fieldDescriptions))
	for _, fd := range fieldDescriptions {
		names = append(names, fd.Name)
	}
	return names
}

func (r *Rows) Close() error {
	r.rows.Close()
	return nil
}

func (r *Rows) Next(dest []driver.Value) error {
	more := r.rows.Next()
	if !more {
		if r.rows.Err() == nil {
			return io.EOF
		} else {
			return r.rows.Err()
		}
	}

	values, err := r.rows.Values()
	if err != nil {
		return err
	}

	if len(dest) < len(values) {
		fmt.Printf("%d: %#v\n", len(dest), dest)
		fmt.Printf("%d: %#v\n", len(values), values)
		return errors.New("expected more values than were received")
	}

	for i, v := range values {
		dest[i] = driver.Value(v)
	}

	return nil
}

func valueToInterface(argsV []driver.Value) []interface{} {
	args := make([]interface{}, 0, len(argsV))
	for _, v := range argsV {
		args = append(args, v.(interface{}))
	}
	return args
}

type Tx struct {
	conn *pgx.Conn
}

func (t *Tx) Commit() error {
	_, err := t.conn.Exec("commit")
	return err
}

func (t *Tx) Rollback() error {
	_, err := t.conn.Exec("rollback")
	return err
}