--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmd/sievemgr/internal/config/parser.go	Tue Nov 03 23:44:45 2020 +0100
@@ -0,0 +1,148 @@
+// Copyright (C) 2020 Guido Berhoerster <guido+sievemgr@berhoerster.name>
+//
+// Permission is hereby granted, free of charge, to any person obtaining
+// a copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to
+// permit persons to whom the Software is furnished to do so, subject to
+// the following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+// SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+package config
+
+import (
+	"fmt"
+	"strconv"
+)
+
+type parser struct {
+	s *scanner
+}
+
+func (p *parser) scanType(expectedTok token) (string, error) {
+	tok, lit, err := p.s.scan()
+	if err != nil {
+		return lit, NewParserError(err.Error(), p.s.line)
+	} else if tok != expectedTok {
+		return lit, NewParserError(fmt.Sprintf("expected %s, got %s %q", expectedTok, tok, lit), p.s.line)
+	}
+	return lit, nil
+}
+
+func (p *parser) validateAccount(acct *Account) error {
+	if acct.Host == "" {
+		return NewParserError(fmt.Sprintf("no host specified for account %q",
+			acct.Name), 0)
+	} else if acct.User == "" {
+		return NewParserError(fmt.Sprintf("no user specified for account %q",
+			acct.Name), 0)
+	}
+	return nil
+}
+
+func (p *parser) parse(conf *Configuration) error {
+	var acct *Account
+	var isDefault bool
+	var tok token
+	var lit string
+	var err error
+parsing:
+	for {
+		tok, lit, err = p.s.scan()
+		if err != nil {
+			err = NewParserError(err.Error(), p.s.line)
+			break parsing
+		}
+		if tok == tokenIllegal {
+			err = NewParserError(fmt.Sprintf("illegal token %q", lit), p.s.line)
+			break parsing
+		} else if tok == tokenEOF {
+			break parsing
+		} else if tok != tokenIdent {
+			err = NewParserError(fmt.Sprintf("expected identifier, got %s %q", tok, lit), p.s.line)
+			break parsing
+		}
+		switch lit {
+		case "account":
+			if acct != nil {
+				if err = p.validateAccount(acct); err != nil {
+					break parsing
+				}
+				conf.Accounts = append(conf.Accounts, acct)
+				if isDefault {
+					conf.Default = acct
+					isDefault = false
+				}
+			}
+
+			// account name
+			if lit, err = p.scanType(tokenString); err != nil {
+				break parsing
+			}
+			acct = &Account{
+				Name: lit,
+				Port: "4190",
+			}
+		case "default":
+			isDefault = true
+		case "host":
+			if lit, err = p.scanType(tokenString); err != nil {
+				break parsing
+			}
+			acct.Host = lit
+		case "port":
+			if lit, err = p.scanType(tokenNumber); err != nil {
+				break parsing
+			}
+			var port int
+			if port, err = strconv.Atoi(lit); err != nil {
+				err = NewParserError(fmt.Sprintf("failed to parse port: %s", err), p.s.line)
+				break parsing
+			} else if port < 1 || port > 65535 {
+				err = NewParserError(fmt.Sprintf("invalid port number %d", port), p.s.line)
+				break parsing
+			}
+			acct.Port = lit
+		case "user":
+			if lit, err = p.scanType(tokenString); err != nil {
+				break parsing
+			}
+			acct.User = lit
+		case "pass":
+			if lit, err = p.scanType(tokenString); err != nil {
+				break parsing
+			}
+			acct.Password = lit
+		case "insecure":
+			acct.Insecure = true
+		default:
+			err = NewParserError(fmt.Sprintf("unknown %s: %q", tok, lit), p.s.line)
+			break parsing
+		}
+	}
+	if err != nil {
+		return err
+	}
+	if acct != nil {
+		if err = p.validateAccount(acct); err != nil {
+			return err
+		}
+		conf.Accounts = append(conf.Accounts, acct)
+		if isDefault {
+			conf.Default = acct
+		}
+	}
+
+	return nil
+}