#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "Operation.h"
#include "Script.h"

static const char* MISSING_INT_CONSTANT = "cannot read an int from the bytecode";
static const char* NOT_AN_INT = "object is not an int";
static const char* NOT_PRINTABLE = "cannot print given object";
static const char* STACK_OVERFLOW = "stack overflow";
static const char* STACK_UNDERFLOW = "stack underflow";

static bool sRead(Script* sc, void* buffer, int length) {
    if(sc->readIndex + length > sc->byteCodeLength) {
        return true;
    }
    memcpy(buffer, sc->byteCode + sc->readIndex, length);
    sc->readIndex += length;
    return false;
}

static Operation sReadOperation(Script* sc) {
    unsigned char c;
    if(sRead(sc, &c, 1)) {
        return OP_NOTHING;
    }
    return c;
}

static void sPush(Script* sc, Object* o) {
    if(sc->stackIndex >= SCRIPT_STACK_SIZE) {
        sc->error = STACK_OVERFLOW;
        return;
    }
    sc->stack[sc->stackIndex++] = *o;
}

static bool sPop(Script* sc, Object* o) {
    if(sc->stackIndex <= 0) {
        sc->error = STACK_UNDERFLOW;
        return true;
    }
    *o = sc->stack[--sc->stackIndex];
    return false;
}

static void sPushInt(Script* sc) {
    int value = 0;
    if(sRead(sc, &value, sizeof(int))) {
        sc->error = MISSING_INT_CONSTANT;
        return;
    }
    Object o = {.type = OT_INT, .data.intValue = value};
    sPush(sc, &o);
}

void sAdd(Script* sc) {
    Object a;
    if(sPop(sc, &a)) {
        return;
    }
    Object b;
    if(sPop(sc, &b)) {
        return;
    }
    if(a.type != OT_INT || b.type != OT_INT) {
        sc->error = NOT_AN_INT;
        return;
    }
    Object o = {.type = OT_INT, .data.intValue = a.data.intValue + b.data.intValue};
    sPush(sc, &o);
}

void sPrint(Script* sc) {
    Object o;
    if(sPop(sc, &o)) {
        return;
    }
    if(o.type == OT_INT) {
        printf("%d\n", o.data.intValue);
    } else {
        sc->error = NOT_PRINTABLE;
    }
}

static void sConsumeInstruction(Script* sc) {
    switch(sReadOperation(sc)) {
        case OP_NOTHING: break;
        case OP_PUSH_INT: sPushInt(sc); break;
        case OP_ADD: sAdd(sc); break;
        case OP_PRINT: sPrint(sc); break;
    }
}

static bool sHasData(Script* sc) {
    return sc->readIndex < sc->byteCodeLength;
}

Script* sInit(unsigned char* byteCode, int codeLength) {
    Script* sc = malloc(sizeof(Script));
    sc->error = NULL;
    sc->byteCode = byteCode;
    sc->byteCodeLength = codeLength;
    sc->readIndex = 0;
    sc->stackIndex = 0;
    return sc;
}

void sDelete(Script* sc) {
    free(sc->byteCode);
}

void sRun(Script* sc) {
    while(sHasData(sc)) {
        sConsumeInstruction(sc);
        if(sc->error != NULL) {
            puts(sc->error);
            return;
        }
    }
}