schema2go

schema2go.go

// Copyright 2018 Google LLC
//
// 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
//
//     https://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.

// schema2go converts a sequence of SQL files into a Go source file of constants.
package main

import (
	"bytes"
	"errors"
	"flag"
	"fmt"
	"go/format"
	"io/ioutil"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
)

func main() {
	pkg := flag.String("pkg", "main", "package name")
	prefix := flag.String("prefix", "", "name prefix")
	sortFiles := flag.Bool("sort", true, "sort files")
	flag.Parse()
	args := append([]string(nil), flag.Args()...)
	if *sortFiles {
		sort.Slice(args, func(i, j int) bool {
			return filepath.Base(args[i]) < filepath.Base(args[j])
		})
	}
	src, err := run(*pkg, *prefix, args)
	if err != nil {
		fmt.Fprintln(os.Stderr, "schema2go:", err)
		os.Exit(1)
	}
	_, err = os.Stdout.Write(src)
	if err != nil {
		fmt.Fprintln(os.Stderr, "schema2go:", err)
		os.Exit(1)
	}
}

func run(pkg, prefix string, files []string) ([]byte, error) {
	if len(files) == 0 {
		return nil, errors.New("no schemas")
	}
	var schemas [][]byte
	for _, path := range files {
		sql, err := ioutil.ReadFile(path)
		if err != nil {
			return nil, err
		}
		schemas = append(schemas, minifySQL(sql))
	}
	buf := new(bytes.Buffer)
	fmt.Fprint(buf, "// Code generated by schema2go. DO NOT EDIT.\n\n")
	fmt.Fprintf(buf, "package %s\n\n", pkg)

	fmt.Fprintf(buf, "// %sFull is the in-order concatenation of all the schemas.\n", prefix)
	fmt.Fprintf(buf, "const %sFull = ", prefix)
	for first, s := true, joinSchemas(schemas); len(s) > 0; {
		if first {
			first = false
		} else {
			buf.WriteString(" +\n\t")
		}
		end := strings.IndexByte(s, '\n')
		if end == -1 {
			end = len(s)
		}
		buf.WriteString(strconv.Quote(s[:end+1]))
		s = s[end+1:]
	}
	fmt.Fprint(buf, "\n\n")

	fmt.Fprintf(buf, "// %sMigrations has the set of SQL to apply at each version to get to the latest schema.\n", prefix)
	fmt.Fprintf(buf, "var %sMigrations = [...]string{\n", prefix)
	for i, idx := 0, 0; i < len(schemas); i++ {
		fmt.Fprintf(buf, "\t// %s", filepath.Base(files[i]))
		if i < len(schemas)-1 {
			fmt.Fprint(buf, " + ...")
		}
		fmt.Fprintf(buf, "\n\t%d: %sFull[%d:],\n", i, prefix, idx)
		idx += len(schemas[i])
	}
	fmt.Fprintln(buf, "\t// Last entry empty: all migrated.")
	fmt.Fprintf(buf, "\t%d: \"\",\n", len(schemas))
	fmt.Fprint(buf, "}\n\n")

	fmt.Fprintf(buf, "// %sLatest is the highest known schema version.\n", prefix)
	fmt.Fprintf(buf, "const %sLatest = %d\n", prefix, len(schemas))

	return format.Source(buf.Bytes())
}

func minifySQL(sql []byte) []byte {
	min := sql[:0]
	for len(sql) > 0 {
		var line []byte
		if i := bytes.IndexByte(sql, '\n'); i != -1 {
			line, sql = sql[:i+1], sql[i+1:]
		} else {
			line, sql = sql, nil
		}
		if isCommentLine(line) {
			continue
		}
		min = append(min, bytes.TrimLeft(line, " \t")...)
	}
	return min
}

func isCommentLine(line []byte) bool {
	for ; len(line) > 0; line = line[1:] {
		if line[0] == '-' {
			return len(line) >= 2 && line[1] == '-'
		}
		if !isSpace(line[0]) {
			return false
		}
	}
	return true
}

func isSpace(b byte) bool {
	return b == ' ' || b == '\t' || b == '\r' || b == '\n'
}

func joinSchemas(schemas [][]byte) string {
	var b strings.Builder
	for _, sql := range schemas {
		b.Write(sql)
	}
	return b.String()
}