/*

 * Copyright (c) 2016 Justin Zhu

 *

 * Permission is hereby granted, free of charge, to any person obtaining a copy

 * of this software and associated documentation files (the "Software"), to

 * deal in the Software without restriction, including without limitation the

 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or

 * sell copies of the Software, and to permit persons to whom the Software is

 * furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS

 * IN THE SOFTWARE.

 */

#include <stdlib.h>

#include "h2o.h"

typedef struct st_throttle_resp_t {

    h2o_ostream_t super;

    h2o_timer_t timeout_entry;

    struct {

        uint64_t at;

        ssize_t bytes_left;

    } window;

    h2o_req_t *req;

    size_t bytes_per_sec;

    struct {

        H2O_VECTOR(h2o_sendvec_t) bufs;

        h2o_send_state_t stream_state;

    } state;

} throttle_resp_t;

/**

 * Given current deficit (`bytes_left` which would be negative) and bytes_per_sec, returns when the deficit would become

 * non-negative.

 */

static uint64_t calc_delay(ssize_t bytes_left, size_t bytes_per_sec)

{

    return (-bytes_left * (uint64_t)1000 + bytes_per_sec - 1) / bytes_per_sec;

}

static void real_send(throttle_resp_t *self)

{

    uint64_t now = h2o_now(self->req->conn->ctx->loop);

    /* if time has changed since previous invocation, update window */

    if (self->window.at < now) {

        /* burst rate (after upstream remains silent) is limited to 1-second worth of data */

        uint64_t addition = (self->bytes_per_sec * (now - self->window.at)) / 1000;

        if (addition > self->bytes_per_sec)

            addition = self->bytes_per_sec;

        self->window.bytes_left += addition;

        self->window.at = now;

    }

    /* schedule the timer for delayed invocation, if window is negative at this moment */

    if (self->window.bytes_left < 0) {

        uint64_t delay = calc_delay(self->window.bytes_left, self->bytes_per_sec);

        assert(delay > 0);

        h2o_timer_link(self->req->conn->ctx->loop, delay, &self->timeout_entry);

        return;

    }

    /* adjust window and send */

    for (size_t i = 0; i < self->state.bufs.size; i++)

        self->window.bytes_left -= self->state.bufs.entries[i].len;

    h2o_ostream_send_next(&self->super, self->req, self->state.bufs.entries, self->state.bufs.size, self->state.stream_state);

}

static void on_timer(h2o_timer_t *entry)

{

    throttle_resp_t *self = H2O_STRUCT_FROM_MEMBER(throttle_resp_t, timeout_entry, entry);

    real_send(self);

}

static void on_send(h2o_ostream_t *_self, h2o_req_t *req, h2o_sendvec_t *inbufs, size_t inbufcnt, h2o_send_state_t state)

{

    throttle_resp_t *self = (void *)_self;

    assert(!h2o_timer_is_linked(&self->timeout_entry));

    /* save state */

    h2o_vector_reserve(&req->pool, &self->state.bufs, inbufcnt);

    for (size_t i = 0; i < inbufcnt; ++i) {

        self->state.bufs.entries[i] = inbufs[i];

    }

    self->state.bufs.size = inbufcnt;

    self->state.stream_state = state;

    real_send(self);

}

static void on_stop(h2o_ostream_t *_self, h2o_req_t *req)

{

    throttle_resp_t *self = (void *)_self;

    if (h2o_timer_is_linked(&self->timeout_entry))

        h2o_timer_unlink(&self->timeout_entry);

}

static void on_setup_ostream(h2o_filter_t *self, h2o_req_t *req, h2o_ostream_t **slot)

{

    throttle_resp_t *throttle;

    size_t bytes_per_sec;

    /* only handle 200 OK with content */

    if (req->res.status != 200)

        goto Next;

    if (h2o_memis(req->input.method.base, req->input.method.len, H2O_STRLIT("HEAD")))

        goto Next;

    { /* obtain the rate from X-Traffic header field and delete the header field, or skip */

        ssize_t xt_index;

        if ((xt_index = h2o_find_header(&req->res.headers, H2O_TOKEN_X_TRAFFIC, -1)) == -1)

            goto Next;

        char *buf = req->res.headers.entries[xt_index].value.base;

        if (H2O_UNLIKELY((bytes_per_sec = h2o_strtosizefwd(&buf, req->res.headers.entries[xt_index].value.len)) == SIZE_MAX))

            goto Next;

        h2o_delete_header(&req->res.headers, xt_index);

    }

    /* instantiate the ostream filter */

    throttle = (void *)h2o_add_ostream(req, H2O_ALIGNOF(*throttle), sizeof(*throttle), slot);

    throttle->super.do_send = on_send;

    throttle->super.stop = on_stop;

    h2o_timer_init(&throttle->timeout_entry, on_timer);

    throttle->window.at = h2o_now(req->conn->ctx->loop);

    throttle->window.bytes_left = 0;

    throttle->req = req;

    throttle->bytes_per_sec = bytes_per_sec;

    memset(&throttle->state.bufs, 0, sizeof(throttle->state.bufs));

    throttle->state.stream_state = H2O_SEND_STATE_IN_PROGRESS;

    { /* reduce `preferred_chunk_size` so that we'd be sending one chunk every 100ms */

        size_t chunk_size = bytes_per_sec / 10;

        if (chunk_size < 4096)

            chunk_size = 4096;

        if (req->preferred_chunk_size > chunk_size)

            req->preferred_chunk_size = chunk_size;

    }

    slot = &throttle->super.next;

Next:

    h2o_setup_next_ostream(req, slot);

}

void h2o_throttle_resp_register(h2o_pathconf_t *pathconf)

{

    h2o_filter_t *self = h2o_create_filter(pathconf, sizeof(*self));

    self->on_setup_ostream = on_setup_ostream;

}