package exql

import (
	"errors"
	"reflect"
	"strings"

	"git.hexq.cn/tiglog/mydb/internal/cache"
)

var errUnknownTemplateType = errors.New("Unknown template type")

// represents different kinds of SQL statements.
type Statement struct {
	Type
	Table        Fragment
	Database     Fragment
	Columns      Fragment
	Values       Fragment
	Distinct     bool
	ColumnValues Fragment
	OrderBy      Fragment
	GroupBy      Fragment
	Joins        Fragment
	Where        Fragment
	Returning    Fragment

	Limit
	Offset

	SQL string

	amendFn func(string) string
}

func (layout *Template) doCompile(c Fragment) (string, error) {
	if c != nil && !reflect.ValueOf(c).IsNil() {
		return c.Compile(layout)
	}
	return "", nil
}

// Hash returns a unique identifier for the struct.
func (s *Statement) Hash() uint64 {
	if s == nil {
		return cache.NewHash(FragmentType_Statement, nil)
	}
	return cache.NewHash(
		FragmentType_Statement,
		s.Type,
		s.Table,
		s.Database,
		s.Columns,
		s.Values,
		s.Distinct,
		s.ColumnValues,
		s.OrderBy,
		s.GroupBy,
		s.Joins,
		s.Where,
		s.Returning,
		s.Limit,
		s.Offset,
		s.SQL,
	)
}

func (s *Statement) SetAmendment(amendFn func(string) string) {
	s.amendFn = amendFn
}

func (s *Statement) Amend(in string) string {
	if s.amendFn == nil {
		return in
	}
	return s.amendFn(in)
}

func (s *Statement) template(layout *Template) (string, error) {
	switch s.Type {
	case Truncate:
		return layout.TruncateLayout, nil
	case DropTable:
		return layout.DropTableLayout, nil
	case DropDatabase:
		return layout.DropDatabaseLayout, nil
	case Count:
		return layout.CountLayout, nil
	case Select:
		return layout.SelectLayout, nil
	case Delete:
		return layout.DeleteLayout, nil
	case Update:
		return layout.UpdateLayout, nil
	case Insert:
		return layout.InsertLayout, nil
	default:
		return "", errUnknownTemplateType
	}
}

// Compile transforms the Statement into an equivalent SQL query.
func (s *Statement) Compile(layout *Template) (compiled string, err error) {
	if s.Type == SQL {
		// No need to hit the cache.
		return s.SQL, nil
	}

	if z, ok := layout.Read(s); ok {
		return s.Amend(z), nil
	}

	tpl, err := s.template(layout)
	if err != nil {
		return "", err
	}

	compiled = layout.MustCompile(tpl, s)

	compiled = strings.TrimSpace(compiled)
	layout.Write(s, compiled)

	return s.Amend(compiled), nil
}

// RawSQL represents a raw SQL statement.
func RawSQL(s string) *Statement {
	return &Statement{
		Type: SQL,
		SQL:  s,
	}
}