fields = {
    'book':
        [('isbn', 's'), ('title', 's'), ('category', 's'),
         ('subtitle', 's'), ('persons', 'd'), ('publisher', 's'),
         ('published_year', 's'), ('edition', 's'), ('num_pages', 's'),
         ('series', 's'), ('description', 's'), # TODO picture, thumbnail
         ('references', 'd')],
    'person':
        [('id', 's'), ('first_name', 's'), ('last_name', 's')],
    'category':
        [('id', 's'), ('name', 's'), ('placement', 'l')] }
action_fields = {
    'new-book':
        { 'type': 'book',
          'required': ['isbn', 'title', 'category'] },
    'edit-book':
        { 'type': 'book',
          'required': ['isbn'] },
    'delete-book':
        { 'type': 'book',
          'required': ['isbn'] },
    'new-person':
        { 'type': 'person',
          'required': ['id', 'first_name', 'last_name'] },
    'edit-person':
        { 'type': 'person',
          'required': ['id'] },
    'delete-person':
        { 'type': 'person',
          'required': ['id'] },
    'new-category':
        { 'type': 'category',
          'required': ['id', 'name'] },
    'edit-category':
        { 'type': 'category',
          'required': ['id'] },
    'delete-category':
        { 'type': 'category',
          'required': ['id'] } }

def read_action(lines):
    d = {}
    lastfield = None
    for line in lines:
        if len(line) == 0:
            raise 'Empty line in action'
        if line[0] in [' ', '\t']: # continuation line
            if not lastfield:
                raise 'First line is continuation line'
            d[lastfield] = d[lastfield] + '\n' + line.strip()
        else:
            field, value = line.split(':', 1)
            # TODO skriv ferdig

def write_field_value_str(val):
    lines = ''
    value_lines = val.split('\n')
    for l in value_lines:
        lines += ' ' + l + '\n'
    return lines

def write_field_value_dict(val):
    lines = '\n'
    for (key,values) in val.items():
        for single_value in values:
            lines += ' ' + key + ' ' + single_value + '\n'
    return lines

def write_field_value_list(val):
    lines = ''
    for single_value in val:
        lines += ' ' + single_value
    return lines

def write_action(d):
    action = d['action']
    lines = 'action: ' + action + '\n'
    data_type = action_fields[action]['type']
    for field, ftype in fields[data_type]:
        if field in d:
            value_writer = {'s': write_field_value_str,
                            'd': write_field_value_dict,
                            'l': write_field_value_list}[ftype]
            lines += field + ':' + value_writer(d[field])
    return lines

def write_actionlist(actions):
    return '\n'.join(map(write_action, actions))

# test: print write_actionlist([{'action':'new-book','isbn':'434545'},{'action':'edit-book','isbn':'654654745','persons':{'author':['ab','foo'],'illustrator':['moo']}},{'action':'edit-category','id':'matematikk','name':'Matematikk','placement':['T10','T11']}])