tablespace.go

package main

import (
	"fmt"
	"os"
)

// schema
// {
//   "tbl1": [
//     {"col1": "val1", "col2": "val2", "col3": "val3"},
//     {"col1": "val4", "col2": "val5", "col3": "val6"},
//     {"col1": "val1", "col2": "val9", "col3": "val9"},
//   ],
//   "tbl2": [
//     {"col4": "val1", "col5": "val2", "col6": "val3"},
//     {"col4": "val4", "col5": "val5", "col6": "val6"},
//     {"col4": "val1", "col5": "val9", "col6": "val9"},
//   ]
// }
var datafile = "data/incdb.data"

func init() {
	// test mode
	if os.Getenv("INCDB_TEST") == "1" {
		datafile = "data/test.incdb.data"
	}

	// initialize file if empty
	f, err := os.OpenFile(datafile, os.O_RDWR|os.O_CREATE, 0755)
	if err != nil {
		fmt.Fprintf(os.Stderr, "could not read data file for initialization: %s\n", err)
		os.Exit(1)
	}
	defer f.Close()

	info, err := f.Stat()
	if err != nil {
		fmt.Fprintf(os.Stderr, "could not read data file stat for initialization: %s\n", err)
		os.Exit(1)
	}

	if info.Size() != 0 {
		return
	}

	if _, err := f.Write([]byte("{}")); err != nil {
		fmt.Fprintf(os.Stderr, "could not initialize empty data file: %s\n", err)
		os.Exit(1)
	}
}

func readData(tbl string) ([]*Record, error) {
	f, err := os.OpenFile(datafile, os.O_RDONLY|os.O_CREATE, 0755)
	if err != nil {
		return nil, fmt.Errorf("open tablespace file: %w", err)
	}
	defer f.Close()

	d := map[string][]map[string]string{}

	if err := readJsonFile(f, &d); err != nil {
		return nil, fmt.Errorf("read file: %w", err)
	}

	t, ok := d[tbl]
	if !ok {
		return nil, fmt.Errorf("table '%s' not found", tbl)
	}

	tDef, err := readCatalog(tbl)
	if err != nil {
		return nil, fmt.Errorf("read table '%s' definition from catalog: %w", tbl, err)
	}

	records := make([]*Record, len(t))
	for i := range t {
		r := &Record{
			Cols:  make([]string, len(tDef.Cols)),
			Types: make([]string, len(tDef.Cols)),
			Vals:  make([]string, len(tDef.Cols)),
		}
		for j := range tDef.Cols {
			r.Cols[j] = tDef.Cols[j].Name
			r.Types[j] = tDef.Cols[j].Type
			r.Vals[j] = t[i][tDef.Cols[j].Name]
		}
		records[i] = r
	}

	return records, nil
}

func save(tbl string, cols, vals []string) error {
	f, err := os.OpenFile(datafile, os.O_RDWR|os.O_CREATE, 0755)
	if err != nil {
		return fmt.Errorf("open tablespace file: %w", err)
	}
	defer f.Close()

	d := map[string][]map[string]string{}

	if err := readJsonFile(f, &d); err != nil {
		return fmt.Errorf("read file: %w", err)
	}

	if _, ok := d[tbl]; !ok {
		return fmt.Errorf("table '%s' not found", tbl)
	}

	tDef, err := readCatalog(tbl)
	if err != nil {
		return fmt.Errorf("read catalog: %w", err)
	}

	r := map[string]string{}

	if len(cols) != 0 {
		// in case at least one column is specified, data will be saved on the given columns
		for i := range cols {
			givenCol := cols[i]
			found := false
			for j := range tDef.Cols {
				colDef := tDef.Cols[j]
				// fill specified column value
				if colDef.Name == givenCol {
					r[colDef.Name] = vals[i]
					found = true
					break
				}
			}

			// Column not found in table definition
			// This means the column name is incorrect
			if !found {
				return fmt.Errorf("column '%s' is not found in table '%s'", givenCol, tbl)
			}
		}
	} else {
		// if column is not specified, all the data must be given
		if len(vals) != len(tDef.Cols) {
			return fmt.Errorf("%d values must be passed according to the table definition", len(tDef.Cols))
		}

		for i := range tDef.Cols {
			r[tDef.Cols[i].Name] = vals[i]
		}
	}

	d[tbl] = append(d[tbl], r)

	if err := updateJsonFile(f, &d); err != nil {
		return fmt.Errorf("update tablespace file: %w", err)
	}

	f.Sync()
	return nil
}

func createTable(tbl string) error {
	f, err := os.OpenFile(datafile, os.O_RDWR|os.O_CREATE, 0755)
	if err != nil {
		return fmt.Errorf("open tablespace file: %w", err)
	}
	defer f.Close()

	d := map[string][]map[string]string{}

	if err := readJsonFile(f, &d); err != nil {
		return fmt.Errorf("read tablespace file: %w", err)
	}

	if _, ok := d[tbl]; ok {
		return fmt.Errorf("table '%s' already exists", tbl)
	}

	d[tbl] = []map[string]string{}

	if err := updateJsonFile(f, &d); err != nil {
		return fmt.Errorf("update tablespace file: %w", err)
	}

	f.Sync()
	return nil
}