// Copyright 2020-2021 Dolthub, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package mvdata

import (
	"fmt"
	"io"

	"github.com/dolthub/go-mysql-server/sql"
)

// ChannelRowSource is a sql.Node that wraps a channel as a sql.RowIter.
type ChannelRowSource struct {
	schema     sql.Schema
	rowChannel chan sql.Row
}

var _ sql.ExecSourceRel = (*ChannelRowSource)(nil)

// NewChannelRowSource returns a ChannelRowSource object.
func NewChannelRowSource(schema sql.Schema, rowChannel chan sql.Row) *ChannelRowSource {
	return &ChannelRowSource{schema: schema, rowChannel: rowChannel}
}

var _ sql.Node = (*ChannelRowSource)(nil)

// Resolved implements the sql.Node interface.
func (c *ChannelRowSource) Resolved() bool {
	return true
}

// String implements the sql.Node interface.
func (c *ChannelRowSource) String() string {
	return fmt.Sprintf("ChannelRowSource()")
}

// Schema implements the sql.Node interface.
func (c *ChannelRowSource) Schema() sql.Schema {
	return c.schema
}

// Children implements the sql.Node interface.
func (c *ChannelRowSource) Children() []sql.Node {
	return nil
}

// RowIter implements the sql.Node interface.
func (c *ChannelRowSource) RowIter(ctx *sql.Context, row sql.Row) (sql.RowIter, error) {
	return &channelRowIter{
		rowChannel: c.rowChannel,
	}, nil
}

// WithChildren implements the sql.Node interface.
func (c *ChannelRowSource) WithChildren(children ...sql.Node) (sql.Node, error) {
	if len(children) != 0 {
		return nil, sql.ErrInvalidChildrenNumber.New(c, len(children), 0)
	}

	return c, nil
}

// CheckPrivileges implements the sql.Node interface.
func (c *ChannelRowSource) CheckPrivileges(ctx *sql.Context, opChecker sql.PrivilegedOperationChecker) bool {
	return true
}

// channelRowIter wraps the channel under the sql.RowIter interface
type channelRowIter struct {
	rowChannel chan sql.Row
}

var _ sql.RowIter = (*channelRowIter)(nil)

// Next implements the sql.RowIter interface.
func (c *channelRowIter) Next(ctx *sql.Context) (sql.Row, error) {
	for r := range c.rowChannel {
		select {
		case <-ctx.Done():
			return nil, io.EOF
		default:
			return r, nil
		}
	}
	return nil, io.EOF
}

// Close implements the sql.RowIter interface.
func (c *channelRowIter) Close(context *sql.Context) error {
	return nil
}
