messageformat/lib/select-pattern.js

Intl.MessageFormat / Unicode MessageFormat 2 parser, runtime and polyfill

import { MessageResolutionError } from "./errors.js";
import { resolveVariableRef } from "./resolve/resolve-variable.js";
export function selectPattern(context, message) {
    if (message.type === 'message')
        return message.pattern;
    // message.type === 'select'
    const ctx = message.selectors.map(sel => {
        const selector = resolveVariableRef(context, sel);
        let selectKey;
        if (typeof selector.selectKey === 'function') {
            selectKey = selector.selectKey.bind(selector);
        }
        else {
            const msg = 'Selector does not support selection';
            context.onError(new MessageResolutionError('bad-selector', msg, selector.source));
            selectKey = () => null;
        }
        return {
            selectKey,
            source: selector.source,
            best: null,
            keys: null
        };
    });
    let candidates = message.variants;
    loop: for (let i = 0; i < ctx.length; ++i) {
        const sc = ctx[i];
        if (!sc.keys) {
            sc.keys = new Set();
            for (const { keys } of candidates) {
                const key = keys[i];
                if (!key)
                    break loop; // key-mismatch error
                if (key.type !== '*')
                    sc.keys.add(key.value);
            }
        }
        try {
            sc.best = sc.keys.size ? sc.selectKey(sc.keys) : null;
        }
        catch (error) {
            const msg = 'Selection failed';
            context.onError(new MessageResolutionError('bad-selector', msg, sc.source, error));
            sc.selectKey = () => null;
            sc.best = null;
        }
        // Leave out all candidate variants that aren't the best,
        // or only the catchall ones, if nothing else matches.
        candidates = candidates.filter(v => {
            const k = v.keys[i];
            if (k.type === '*')
                return sc.best == null;
            return sc.best === k.value;
        });
        // If we've run out of candidates,
        // drop the previous best key of the preceding selector,
        // reset all subsequent key sets,
        // and restart the loop.
        if (candidates.length === 0) {
            if (i === 0)
                break; // No match; should not happen
            const prev = ctx[i - 1];
            if (prev.best == null)
                prev.keys?.clear();
            else
                prev.keys?.delete(prev.best);
            for (let j = i; j < ctx.length; ++j)
                ctx[j].keys = null;
            candidates = message.variants;
            i = -1;
        }
    }
    const res = candidates[0];
    if (!res) {
        // This should not be possible with a valid message.
        const msg = 'No variant was selected!?';
        context.onError(new MessageResolutionError('no-match', msg, '.match'));
        return [];
    }
    return res.value;
}