package debconf

import (
	"bufio"
	"fmt"
	"io"
	"strings"
)

const (
	DefaultConfigDat    = `/var/cache/debconf/config.dat`
	DefaultPasswordsDat = `/var/cache/debconf/passwords.dat`
	DefaultTemplatesDat = `/var/cache/debconf/templates.dat`
)

type Entry struct {
	Name       string
	Properties [][2]string
}

type Database struct {
	Entries        []Entry
	AllColumnNames []string
}

func Parse(r io.Reader) (*Database, error) {
	sc := bufio.NewScanner(r)

	var entries []Entry
	var wip Entry
	var linenum int = 0

	knownColumnNames := map[string]struct{}{
		"Name": struct{}{},
	}
	var discoveredColumns []string

	for sc.Scan() {
		linenum++
		line := sc.Text()

		if line == "" {
			if wip.Name != "" {
				entries = append(entries, wip)
				wip = Entry{}
			}
			continue
		}

		if line[0] == ' ' {
			// continuation of last text entry
			if len(wip.Properties) == 0 {
				return nil, fmt.Errorf("Continuation of nonexistent entry on line %d", linenum)
			}

			wip.Properties[len(wip.Properties)-1][1] += line[1:]

		} else {
			// New pair on current element
			key, rest, ok := strings.Cut(line, `:`)
			if !ok {
				return nil, fmt.Errorf("Missing : on line %d", linenum)
			}

			if _, ok := knownColumnNames[key]; !ok {
				knownColumnNames[key] = struct{}{}
				discoveredColumns = append(discoveredColumns, key)
			}

			if key == `Name` {
				wip.Name = rest
			} else {
				wip.Properties = append(wip.Properties, [2]string{key, rest})
			}

		}

	}

	if sc.Err() != nil {
		return nil, sc.Err()
	}

	if wip.Name != "" {
		entries = append(entries, wip)
	}

	return &Database{
		Entries:        entries,
		AllColumnNames: discoveredColumns,
	}, nil
}