module xml

import strings

pub const default_entities = {
    'lt':   '<'
    'gt':   '>'
    'amp':  '&'
    'apos': "'"
    'quot': '"'
}

pub const default_entities_reverse = {
    '<': 'lt'
    '>': 'gt'
    '&': 'amp'
    "'": 'apos'
    '"': 'quot'
}

@[params]
pub struct EscapeConfig {
pub:
    reverse_entities map[string]string = default_entities_reverse
}

// escape_text replaces all entities in the given string with their respective
// XML entity strings. See default_entities, which can be overridden.
pub fn escape_text(content string, config EscapeConfig) string {
    mut flattened_entities := []string{cap: 2 * config.reverse_entities.len}

    for target, replacement in config.reverse_entities {
        flattened_entities << target
        flattened_entities << '&' + replacement + ';'
    }

    return content.replace_each(flattened_entities)
}

@[params]
pub struct UnescapeConfig {
pub:
    entities map[string]string = default_entities
}

// unescape_text replaces all entities in the given string with their respective
// original characters or strings. See default_entities_reverse, which can be overridden.
pub fn unescape_text(content string, config UnescapeConfig) !string {
    mut buffer := strings.new_builder(content.len)
    mut index := 0
    runes := content.runes()
    for index < runes.len {
        match runes[index] {
            `&` {
                mut offset := 1
                mut entity_buf := strings.new_builder(8)
                for index + offset < runes.len && runes[index + offset] != `;` {
                    entity_buf.write_rune(runes[index + offset])
                    offset++
                }
                // Did we reach the end of the string?
                if index + offset == runes.len {
                    return error('Unexpected end of string while parsing entity.')
                }
                // Did we find a valid entity?
                entity := entity_buf.str()
                if entity in config.entities {
                    buffer.write_string(config.entities[entity])
                    index += offset
                } else {
                    return error('Unknown entity: ' + entity)
                }
            }
            else {
                buffer.write_rune(runes[index])
            }
        }

        index++
    }
    return buffer.str()
}