FindAllHelper.groovy

import com.github.jknack.handlebars.Context
import com.github.jknack.handlebars.Helper
import com.github.jknack.handlebars.Options

/**
 * filters a list and adds a variable to the context
 *
 * options:
 * - assignTo: name of the variable to add to the context
 * - field: (optional) filter by "trueness" of the given property (this is default)
 *          may start with an '!' to indicate inversion of trueness
 *
 * {{#findAll list field="name" assignTo="filteredList"}}
 *   {{#each filteredList}}
 *      ...
 *   {{/each}}
 * {{/findAll}}
 *
 *
 * {{#findAll list field="!this" assignTo="filteredList"}}
 *   {{#each filteredList}}.
 *      ...
 *   {{/each}}
 * {{/findAll}}
 */
class FindAllHelper implements Helper<Collection<Object>> {

    public static final String id = "findAll"

    @Override
    public CharSequence apply(Collection<Object> context, Options options) throws IOException {
        def assignTo = (String) options.hash["assignTo"]
        if (!assignTo) {
            throw new IllegalArgumentException("assignTo not set")
        }

        def field = (String) options.hash("field", "this")
        def negate = field.startsWith("!")
        if (negate) {
            field = field.substring(1)
        }

        def filtered = (context ?: []).findAll { isTrue(it, field, negate) }

        return options.fn.apply(
            Context.newBuilder(options.context, [(assignTo): filtered]).build()
        )
    }

    private static boolean isTrue(Object value, String field, boolean negate) {
        if (field == "this") {
            field = null
        }

        def result = getField(value, field)

        if (negate) {
            return !result
        } else {
            return result
        }
    }

    protected static Object getField(Object value, String field) {
        if (field) {
            return ((Map) value)[field]
        } else {
            return value
        }
    }
}