framework.js

const errors = require("./errors");

const _fromRequest = f => async req => {
    const ctx = {};
    f.resolvers.forEach((resolver, i) => {
        if (!resolver) {
            throw new Error(`Incorrect resolver ${resolver} (index #${i} in resolvers array)`);
        }
        ctx[resolver.name] = resolver(req);
    });
    return f(ctx);
};

const _runHandler = (resolvers, func) => ctx => {
    const validatedCtx = ctx;
    return Promise.all(
        resolvers.map(async resolver => {
            try {
                validatedCtx[resolver.name] = resolver.validate(ctx[resolver.name]);
            } catch (err) {
                throw new errors.ValidationError(resolver.name, err);
            }
        }),
    ).then(() => func(validatedCtx));
};

const resolver = (name, resolve, validate) => {
    const f = req => {
        try {
            return resolve(req);
        } catch (err) {
            throw new errors.RequestContextError(resolver.name, err);
        }
    };
    Object.defineProperty(f, "name", { value: name });
    f.validate = validate || (identity => identity);
    return f;
};

const handler = (resolvers, func) => {
    let f = _runHandler(resolvers, func);
    Object.defineProperty(f, "name", { value: func.name });
    f.resolvers = resolvers;
    f.fromRequest = _fromRequest(f);
    return f;
};

module.exports = { handler, resolver };