// Copyright (c) 2018, Compiler Explorer Authors
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
//     * Redistributions of source code must retain the above copyright notice,
//       this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above copyright
//       notice, this list of conditions and the following disclaimer in the
//       documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

const BaseCache = require('./base.js');

// A write-through multiple cache.
// Writes get pushed to all caches, but reads are serviced from the first cache that returns
// a hit.
class MultiCache extends BaseCache {
    constructor(...upstream) {
        super("Multi");
        this.upstream = upstream;
    }

    statString() {
        return `${super.statString()}. ${this.upstream.map(c => `${c.name}: ${c.statString()}`).join(". ")}`;
    }

    getInternal(key) {
        let promiseChain = Promise.resolve({hit: false});
        for (let cache of this.upstream) {
            promiseChain = promiseChain.then(upstream => {
                if (upstream.hit) {
                    // TODO: could propagate hits to lower-level caches. But that's a lot of work and it's not
                    // clear to me it is better than just serving from the lowest-level cache.
                    return upstream;
                }
                return cache.get(key);
            });
        }
        return promiseChain;
    }

    putInternal(object, value, creator) {
        return Promise.all(this.upstream.map(cache => {
            return cache.put(object, value, creator);
        }));
    }
}

module.exports = MultiCache;
