github.com/dolthub/go-mysql-server@v0.18.0/sql/treeprinter.go (about)

     1  // Copyright 2020-2021 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package sql
    16  
    17  import (
    18  	"bufio"
    19  	"bytes"
    20  	"errors"
    21  	"fmt"
    22  	"io"
    23  	"strings"
    24  )
    25  
    26  // TreePrinter is a printer for tree nodes.
    27  type TreePrinter struct {
    28  	buf         bytes.Buffer
    29  	nodeWritten bool
    30  	written     bool
    31  }
    32  
    33  // NewTreePrinter creates a new tree printer.
    34  func NewTreePrinter() *TreePrinter {
    35  	return new(TreePrinter)
    36  }
    37  
    38  // WriteNode writes the main node.
    39  func (p *TreePrinter) WriteNode(format string, args ...interface{}) error {
    40  	if p.nodeWritten {
    41  		return ErrNodeAlreadyWritten
    42  	}
    43  
    44  	_, err := fmt.Fprintf(&p.buf, format, args...)
    45  	if err != nil {
    46  		return err
    47  	}
    48  	p.nodeWritten = true
    49  	p.buf.WriteRune('\n')
    50  	return nil
    51  }
    52  
    53  var (
    54  	// ErrNodeNotWritten is returned when the children are printed before the node.
    55  	ErrNodeNotWritten = errors.New("treeprinter: a child was written before the node")
    56  	// ErrNodeAlreadyWritten is returned when the node has already been written.
    57  	ErrNodeAlreadyWritten = errors.New("treeprinter: node already written")
    58  	// ErrChildrenAlreadyWritten is returned when the children have already been written.
    59  	ErrChildrenAlreadyWritten = errors.New("treeprinter: children already written")
    60  )
    61  
    62  // WriteChildren writes a children of the tree.
    63  func (p *TreePrinter) WriteChildren(children ...string) error {
    64  	if !p.nodeWritten {
    65  		return ErrNodeNotWritten
    66  	}
    67  
    68  	if p.written {
    69  		return ErrChildrenAlreadyWritten
    70  	}
    71  
    72  	p.written = true
    73  
    74  	for i, child := range children {
    75  		last := i+1 == len(children)
    76  		r := bufio.NewReader(strings.NewReader(child))
    77  
    78  		var first = true
    79  		for {
    80  			line, _, err := r.ReadLine()
    81  			if err == io.EOF {
    82  				break
    83  			}
    84  
    85  			if err != nil {
    86  				return err
    87  			}
    88  
    89  			if first && last {
    90  				p.buf.WriteString(" └─ ")
    91  			} else if first {
    92  				p.buf.WriteString(" ├─ ")
    93  			} else if !last {
    94  				p.buf.WriteString(" │  ")
    95  			} else {
    96  				p.buf.WriteString("    ")
    97  			}
    98  
    99  			p.buf.Write(line)
   100  			p.buf.WriteRune('\n')
   101  			first = false
   102  		}
   103  	}
   104  
   105  	return nil
   106  }
   107  
   108  // String returns the output of the printed tree.
   109  func (p *TreePrinter) String() string {
   110  	return p.buf.String()
   111  }