/**
 * @file foreach.c
 * @author Ambroz Bizjak <ambrop7@gmail.com>
 * 
 * @section LICENSE
 * 
 * This file is part of BadVPN.
 * 
 * BadVPN is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2
 * as published by the Free Software Foundation.
 * 
 * BadVPN is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 * 
 * @section DESCRIPTION
 * 
 * Synopsis:
 *   foreach(list list, string template, list args)
 * 
 * Description:
 *   Initializes a template process for each element of list, sequentially,
 *   obeying to the usual execution model of NCD.
 *   It's equivalent to (except for special variables):
 * 
 *   call(template, args);
 *   ...
 *   call(template, args); # one call() for every element of list
 * 
 * Template process specials:
 * 
 *   _index - index of the list element corresponding to the template process,
 *            as a decimal string, starting from zero
 *   _elem - element of list corresponding to the template process
 *   _caller.X - X as seen from the foreach() statement
 */

#include <stdlib.h>

#include <misc/balloc.h>
#include <misc/string_begins_with.h>
#include <system/BReactor.h>
#include <ncd/NCDModule.h>

#include <generated/blog_channel_ncd_foreach.h>

#define ModuleLog(i, ...) NCDModuleInst_Backend_Log((i), BLOG_CURRENT_CHANNEL, __VA_ARGS__)

#define RETRY_TIME 5000

#define ISTATE_WORKING 1
#define ISTATE_UP 2
#define ISTATE_WAITING 3
#define ISTATE_TERMINATING 4

#define ESTATE_FORGOTTEN 1
#define ESTATE_DOWN 2
#define ESTATE_UP 3
#define ESTATE_WAITING 4
#define ESTATE_TERMINATING 5

struct element;

struct instance {
    NCDModuleInst *i;
    char *template_name;
    NCDValue *args;
    BTimer timer;
    size_t num_elems;
    struct element *elems;
    size_t gp; // good pointer
    size_t ip; // initialized pointer
    int state;
};

struct element {
    struct instance *inst;
    size_t i;
    NCDValue *value;
    NCDModuleProcess process;
    int state;
};

static void assert_state (struct instance *o);
static void work (struct instance *o);
static void advance (struct instance *o);
static void timer_handler (struct instance *o);
static void element_process_handler_event (struct element *e, int event);
static int element_process_func_getspecialvar (struct element *e, const char *name, NCDValue *out);
static NCDModuleInst * element_process_func_getspecialobj (struct element *e, const char *name);
static void instance_free (struct instance *o);

static void assert_state (struct instance *o)
{
    ASSERT(o->gp <= o->num_elems)
    ASSERT(o->ip <= o->num_elems)
    ASSERT(o->gp <= o->ip)
    
#ifndef NDEBUG
    // check GP
    for (size_t i = 0; i < o->gp; i++) {
        if (o->gp > 0 && i == o->gp - 1) {
            ASSERT(o->elems[i].state == ESTATE_UP || o->elems[i].state == ESTATE_DOWN ||
                   o->elems[i].state == ESTATE_WAITING)
        } else {
            ASSERT(o->elems[i].state == ESTATE_UP)
        }
    }
    
    // check IP
    size_t ip = o->num_elems;
    while (ip > 0 && o->elems[ip - 1].state == ESTATE_FORGOTTEN) {
        ip--;
    }
    ASSERT(o->ip == ip)
    
    // check gap
    for (size_t i = o->gp; i < o->ip; i++) {
        if (o->ip > 0 && i == o->ip - 1) {
            ASSERT(o->elems[i].state == ESTATE_UP || o->elems[i].state == ESTATE_DOWN ||
                   o->elems[i].state == ESTATE_WAITING || o->elems[i].state == ESTATE_TERMINATING)
        } else {
            ASSERT(o->elems[i].state == ESTATE_UP || o->elems[i].state == ESTATE_DOWN ||
                   o->elems[i].state == ESTATE_WAITING)
        }
    }
#endif
}

static void work (struct instance *o)
{
    assert_state(o);
    
    // stop timer
    BReactor_RemoveTimer(o->i->reactor, &o->timer);
    
    if (o->state == ISTATE_WAITING) {
        return;
    }
    
    if (o->state == ISTATE_UP && !(o->gp == o->ip && o->gp == o->num_elems && (o->gp == 0 || o->elems[o->gp - 1].state == ESTATE_UP))) {
        // signal down
        NCDModuleInst_Backend_Down(o->i);
        
        // set state waiting
        o->state = ISTATE_WAITING;
        return;
    }
    
    if (o->gp < o->ip) {
        // get last element
        struct element *le = &o->elems[o->ip - 1];
        ASSERT(le->state != ESTATE_FORGOTTEN)
        
        // start terminating if not already
        if (le->state != ESTATE_TERMINATING) {
            // request termination
            NCDModuleProcess_Terminate(&le->process);
            
            // set element state terminating
            le->state = ESTATE_TERMINATING;
        }
        
        return;
    }
    
    if (o->state == ISTATE_TERMINATING) {
        // finally die
        instance_free(o);
        return;
    }
    
    if (o->gp == o->num_elems && (o->gp == 0 || o->elems[o->gp - 1].state == ESTATE_UP)) {
        if (o->state == ISTATE_WORKING) {
            // signal up
            NCDModuleInst_Backend_Up(o->i);
            
            // set state up
            o->state = ISTATE_UP;
        }
        
        return;
    }
    
    if (o->gp > 0 && o->elems[o->gp - 1].state == ESTATE_WAITING) {
        // get last element
        struct element *le = &o->elems[o->gp - 1];
        
        // continue process
        NCDModuleProcess_Continue(&le->process);
        
        // set state down
        le->state = ESTATE_DOWN;
        return;
    }
    
    if (o->gp > 0 && o->elems[o->gp - 1].state == ESTATE_DOWN) {
        return;
    }
    
    ASSERT(o->gp == 0 || o->elems[o->gp - 1].state == ESTATE_UP)
    
    advance(o);
    return;
}

static void advance (struct instance *o)
{
    assert_state(o);
    ASSERT(o->gp == o->ip)
    ASSERT(o->gp < o->num_elems)
    ASSERT(o->gp == 0 || o->elems[o->gp - 1].state == ESTATE_UP)
    ASSERT(o->elems[o->gp].state == ESTATE_FORGOTTEN)
    
    // get next element
    struct element *e = &o->elems[o->gp];
    
    // copy arguments
    NCDValue args;
    if (!NCDValue_InitCopy(&args, o->args)) {
        ModuleLog(o->i, BLOG_ERROR, "NCDValue_InitCopy failed");
        goto fail;
    }
    
    // init process
    if (!NCDModuleProcess_Init(&e->process, o->i, o->template_name, args, e, (NCDModuleProcess_handler_event)element_process_handler_event)) {
        ModuleLog(o->i, BLOG_ERROR, "NCDModuleProcess_Init failed");
        NCDValue_Free(&args);
        goto fail;
    }
    
    // set special functions
    NCDModuleProcess_SetSpecialFuncs(&e->process,
                                     (NCDModuleProcess_func_getspecialvar)element_process_func_getspecialvar,
                                     (NCDModuleProcess_func_getspecialobj)element_process_func_getspecialobj);
    
    // set element state down
    e->state = ESTATE_DOWN;
    
    // increment GP and IP
    o->gp++;
    o->ip++;
    return;
    
fail:
    // set timer
    BReactor_SetTimer(o->i->reactor, &o->timer);
}

static void timer_handler (struct instance *o)
{
    assert_state(o);
    ASSERT(o->gp == o->ip)
    ASSERT(o->gp < o->num_elems)
    ASSERT(o->gp == 0 || o->elems[o->gp - 1].state == ESTATE_UP)
    ASSERT(o->elems[o->gp].state == ESTATE_FORGOTTEN)
    
    advance(o);
    return;
}

static void element_process_handler_event (struct element *e, int event)
{
    struct instance *o = e->inst;
    assert_state(o);
    ASSERT(e->i < o->ip)
    ASSERT(e->state != ESTATE_FORGOTTEN)
    
    switch (event) {
        case NCDMODULEPROCESS_EVENT_UP: {
            ASSERT(e->state == ESTATE_DOWN)
            ASSERT(o->gp == o->ip)
            ASSERT(o->gp == e->i + 1)
            
            // set element state up
            e->state = ESTATE_UP;
        } break;
        
        case NCDMODULEPROCESS_EVENT_DOWN: {
            ASSERT(e->state == ESTATE_UP)
            
            // set element state waiting
            e->state = ESTATE_WAITING;
            
            // bump down GP
            if (o->gp > e->i + 1) {
                o->gp = e->i + 1;
            }
        } break;
        
        case NCDMODULEPROCESS_EVENT_TERMINATED: {
            ASSERT(e->state == ESTATE_TERMINATING)
            ASSERT(o->gp < o->ip)
            ASSERT(o->ip == e->i + 1)
            
            // free process
            NCDModuleProcess_Free(&e->process);
            
            // set element state forgotten
            e->state = ESTATE_FORGOTTEN;
            
            // decrement IP
            o->ip--;
        } break;
        
        default: ASSERT(0);
    }
    
    work(o);
    return;
}

static int element_process_func_getspecialvar (struct element *e, const char *name, NCDValue *out)
{
    struct instance *o = e->inst;
    ASSERT(e->state != ESTATE_FORGOTTEN)
    
    if (e->i >= o->gp) {
        BLog(BLOG_ERROR, "tried to resolve variable %s but it's dirty", name);
        return 0;
    }
    
    if (!strcmp(name, "_index")) {
        char str[64];
        snprintf(str, sizeof(str), "%zu", e->i);
        
        if (!NCDValue_InitString(out, str)) {
            ModuleLog(o->i, BLOG_ERROR, "NCDValue_InitString failed");
            return 0;
        }
        
        return 1;
    }
    
    if (!strcmp(name, "_elem")) {
        if (!NCDValue_InitCopy(out, e->value)) {
            ModuleLog(o->i, BLOG_ERROR, "NCDValue_InitCopy failed");
            return 0;
        }
        
        return 1;
    }
    
    size_t p;
    if (p = string_begins_with(name, "_caller.")) {
        return NCDModuleInst_Backend_GetVar(o->i, name + p, out);
    }
    
    return 0;
}

static NCDModuleInst * element_process_func_getspecialobj (struct element *e, const char *name)
{
    struct instance *o = e->inst;
    ASSERT(e->state != ESTATE_FORGOTTEN)
    
    if (e->i >= o->gp) {
        BLog(BLOG_ERROR, "tried to resolve object %s but it's dirty", name);
        return NULL;
    }
    
    size_t p;
    if (p = string_begins_with(name, "_caller.")) {
        return NCDModuleInst_Backend_GetObj(o->i, name + p);
    }
    
    return NULL;
}

static void func_new (NCDModuleInst *i)
{
    // allocate instance
    struct instance *o = malloc(sizeof(*o));
    if (!o) {
        ModuleLog(i, BLOG_ERROR, "failed to allocate instance");
        goto fail0;
    }
    NCDModuleInst_Backend_SetUser(i, o);
    
    // init arguments
    o->i = i;
    
    // read arguments
    NCDValue *arg_list;
    NCDValue *arg_template;
    NCDValue *arg_args;
    if (!NCDValue_ListRead(i->args, 3, &arg_list, &arg_template, &arg_args)) {
        ModuleLog(i, BLOG_ERROR, "wrong arity");
        goto fail1;
    }
    if (NCDValue_Type(arg_list) != NCDVALUE_LIST || NCDValue_Type(arg_template) != NCDVALUE_STRING ||
        NCDValue_Type(arg_args) != NCDVALUE_LIST
    ) {
        ModuleLog(i, BLOG_ERROR, "wrong type");
        goto fail1;
    }
    o->template_name = NCDValue_StringValue(arg_template);
    o->args = arg_args;
    
    // init timer
    BTimer_Init(&o->timer, RETRY_TIME, (BTimer_handler)timer_handler, o);
    
    // count elements
    o->num_elems = NCDValue_ListCount(arg_list);
    
    // allocate elements
    if (!(o->elems = BAllocArray(o->num_elems, sizeof(o->elems[0])))) {
        ModuleLog(i, BLOG_ERROR, "BAllocArray failed");
        goto fail1;
    }
    
    NCDValue *ev = NCDValue_ListFirst(arg_list);
    
    for (size_t i = 0; i < o->num_elems; i++) {
        struct element *e = &o->elems[i];
        
        // set instance
        e->inst = o;
        
        // set index
        e->i = i;
        
        // set value
        e->value = ev;
        
        // set state forgotten
        e->state = ESTATE_FORGOTTEN;
        
        ev = NCDValue_ListNext(arg_list, ev);
    }
    
    // set GP and IP zero
    o->gp = 0;
    o->ip = 0;
    
    // set state working
    o->state = ISTATE_WORKING;
    
    work(o);
    return;
    
fail1:
    free(o);
fail0:
    NCDModuleInst_Backend_SetError(i);
    NCDModuleInst_Backend_Dead(i);
}

static void instance_free (struct instance *o)
{
    NCDModuleInst *i = o->i;
    ASSERT(o->gp == 0)
    ASSERT(o->ip == 0)
    
    // free elements
    BFree(o->elems);
    
    // free timer
    BReactor_RemoveTimer(o->i->reactor, &o->timer);
    
    // free instance
    free(o);
    
    NCDModuleInst_Backend_Dead(i);
}

static void func_die (void *vo)
{
    struct instance *o = vo;
    assert_state(o);
    ASSERT(o->state != ISTATE_TERMINATING)
    
    // set GP zero
    o->gp = 0;
    
    // set state terminating
    o->state = ISTATE_TERMINATING;
    
    work(o);
    return;
}

static void func_clean (void *vo)
{
    struct instance *o = vo;
    
    if (o->state != ISTATE_WAITING) {
        return;
    }
    
    // set state working
    o->state = ISTATE_WORKING;
    
    work(o);
    return;
}

static const struct NCDModule modules[] = {
    {
        .type = "foreach",
        .func_new = func_new,
        .func_die = func_die,
        .func_clean = func_clean
    }, {
        .type = NULL
    }
};

const struct NCDModuleGroup ncdmodule_foreach = {
    .modules = modules
};