/* OpenCOBOL with embedded spidermonkey javascript */
/*   cobc -c -I/usr/include/smjs ocjs.c   
 *   cobc -x -lsmjs jscaller.cob    
 *   some people found mozjs before smjs
 */
#include <stdio.h>
#include <string.h>

/* javascript api requires an environment type */
#define XP_UNIX

#if (defined(XP_WIN) || defined(XP_UNIX) || defined(XP_BEOS) || defined(XP_OS2))
#include "jsapi.h"
#else
#error "Must define one of XP_BEOS, XP_OS2, XP_WIN or XP_UNIX"
#endif

/* Error codes */
#define OCJS_ERROR_RUNTIME  -1
#define OCJS_ERROR_CONTEXT  -2
#define OCJS_ERROR_GLOBAL   -3
#define OCJS_ERROR_STANDARD -4
#define OCJS_ERROR_EVALUATE -5

/* OpenCOBOL main CALL interface */
/* javascript layer requires   
 *   a runtime per process,    
 *   a context per thread,     
 *   a global object per context   
 * and will initialize   
 *   standard classes.
 */
static JSRuntime *rt;
static JSContext *cx;
static JSObject *global;
static JSClass global_class = {
    "global",0,
    JS_PropertyStub,JS_PropertyStub,JS_PropertyStub,JS_PropertyStub,
    JS_EnumerateStub,JS_ResolveStub,JS_ConvertStub,JS_FinalizeStub
};

/* Initialize the engine resources */
int ocjsInitialize(int rtsize, int cxsize) {
    JSBool ok;

    /* on zero sizes, pick reasonable values */
    if (rtsize == 0) { rtsize = 0x100000; }
    if (cxsize == 0) { cxsize = 0x1000; }
    
    /* Initialize a runtime space */
    rt = JS_NewRuntime(rtsize);
    if (rt == NULL) { return OCJS_ERROR_RUNTIME; }
    /* Attach a context */
    cx = JS_NewContext(rt, cxsize);
    if (cx == NULL) { return OCJS_ERROR_CONTEXT; }
    /* And a default global */
    global = JS_NewObject(cx, &global_class, NULL, NULL);
    if (global == NULL) { return OCJS_ERROR_GLOBAL; }
    /* Load standard classes */
    ok = JS_InitStandardClasses(cx, global);

    /* Return success or standard class load error */
    return (ok == JS_TRUE) ? 0 : OCJS_ERROR_STANDARD;
}

/* Evaluate script */
int ocjsEvaluate(char *script, char *result, int length) {
    jsval rval;
    JSString *str;
    int reslen = OCJS_ERROR_EVALUATE;

    JSBool ok;

    /* filename and line number, not reported */
    char *filename = NULL;
    int lineno = 0;

    /* clear the result field */
    memset(result, ' ', length);

    /* Evaluate javascript */
    ok = JS_EvaluateScript(cx, global, script, strlen(script), filename, lineno, &rval);

    /* Convert js result to JSString form */
    if (ok == JS_TRUE) {
        str = JS_ValueToString(cx, rval);
        reslen = strlen(JS_GetStringBytes(str));
        if (length < reslen) { reslen = length; }
        /* convert down to char and move to OpenCOBOl result field */
        memcpy(result, JS_GetStringBytes(str), reslen);
    }
    return reslen;
}

/* Evaluate script from file */
int ocjsFromFile(char *filename, char *result, int length) {
    FILE *fin;
    int bufsize = 10240;
    char inbuf[bufsize];
    int reslen;

    fin = fopen(filename, "r");
    if (fin == NULL) { return OCJS_ERROR_EVALUATE; }
    //while (fread(inbuf, sizeof(char), bufsize, fin) > 0) {
    if (fread(inbuf, 1, bufsize, fin) > 0) {
        reslen = ocjsEvaluate(inbuf, result, length);
    }
    return reslen;
}

/* release js engine */
int ocjsRunDown() {
    if (cx != NULL) { JS_DestroyContext(cx); }
    if (rt != NULL) { JS_DestroyRuntime(rt); }
    JS_ShutDown();
    return 0;
}    

/* Quick call; start engine, evaluate, release engine */
int ocjsString(char *script, char *result, int length) {
    int reslen;

    reslen = ocjsInitialize(0, 0);
    if (reslen < 0) { return reslen; }
    reslen = ocjsEvaluate(script, result, length);
    ocjsRunDown();
    return reslen;
}