#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "types.h"
#include "parser.h"
#include "interpreter.h"
#include "string_utils.h"

extern Token tokens[];
extern int pc;
extern long memory[];
extern int sp;
extern int bp;
extern Symbol locals[];
extern int loc_cnt;
extern Func funcs[];
extern int func_cnt;
extern NativeFuncDef native_funcs[];
extern int native_func_cnt;
extern long ax;

extern void error(char *msg);
extern void match(int type);
extern int find_local(char *name, int len);
extern int find_func(char *name, int len);
extern int find_native_func(char *name, int len);
extern void statement();

long factor() {
    if (pc >= MAX_TOK) return 0;
    Token *t = &tokens[pc];
    long val = 0;

    if (t->type == Num) {
        pc++;
        return t->val;
    }
    else if (t->type == Dbl) {
        pc++;
        union { double d; long l; } u;
        u.d = t->dval;
        return u.l;
    }
    else if (t->type == Str) {
        pc++;
        return (long)t->text;
    }
    else if (t->type == '(') {
        pc++;
        val = expression();
        match(')');
        return val;
    }
    else if (t->type == Id) {
        if (pc + 1 >= MAX_TOK) return 0;
        if (tokens[pc + 1].type == '(') {
            int nf_idx = find_native_func(t->text, t->val);

            if (nf_idx != -1) {
                if (nf_idx < 0 || nf_idx >= native_func_cnt) return 0;
                pc += 2;
                long args[10];
                int argc = 0;

                if (pc >= MAX_TOK) return 0;
                if (tokens[pc].type != ')') {
                    do {
                        if (argc >= 10) break;
                        args[argc++] = expression();
                        if (pc >= MAX_TOK) return 0;
                    } while (tokens[pc].type == ',' && pc++);
                }
                match(')');

                return native_funcs[nf_idx].func(args, argc);
            }

            int f_idx = find_func(t->text, t->val);
            if (f_idx == -1) error("Unknown function");
            if (f_idx < 0 || f_idx >= func_cnt) return 0;
            pc += 2;

            int old_bp = bp;
            long args[10];
            int argc = 0;

            if (pc >= MAX_TOK) return 0;
            if (tokens[pc].type != ')') {
                do {
                    if (argc >= 10) break;
                    args[argc++] = expression();
                    if (pc >= MAX_TOK) return 0;
                } while (tokens[pc].type == ',' && pc++);
            }
            match(')');

            int ret_pc = pc;
            if (sp >= MEM_SIZE) return 0;
            if (bp < 0 || bp >= MEM_SIZE) return 0;
            memory[sp] = bp; bp = sp++;
            if (sp >= MEM_SIZE) return 0;
            memory[sp++] = ret_pc;
            for(int i=0; i<argc; i++) {
                if (sp >= MEM_SIZE) break;
                memory[sp++] = args[i];
            }

            pc = funcs[f_idx].entry_point;
            statement();

            val = ax;

            if (bp < 0 || bp >= MEM_SIZE) return 0;
            sp = bp;
            if (sp < 0 || sp >= MEM_SIZE) return 0;
            bp = memory[sp];
            pc = ret_pc;
            return val;
        }
        else {
            int idx = find_local(t->text, t->val);
            if (idx == -1) error("Undefined variable");
            if (idx < 0 || idx >= loc_cnt) return 0;
            pc++;

            Symbol *sym = &locals[idx];

            if (pc < MAX_TOK && (tokens[pc].type == Inc || tokens[pc].type == Dec)) {
                long val = memory[sym->addr];
                if (tokens[pc].type == Inc) {
                    memory[sym->addr]++;
                } else {
                    memory[sym->addr]--;
                }
                pc++;
                return val;
            }

            if (pc >= MAX_TOK) return 0;
            if (tokens[pc].type == '[') {
                pc++;
                long start_or_index = expression();

                if (pc >= MAX_TOK) return 0;
                if (tokens[pc].type == ':') {
                    pc++;
                    long end = expression();
                    match(']');

                    if (sym->addr < 0 || sym->addr >= MEM_SIZE) return 0;
                    long val = memory[sym->addr];
                    if (is_string_ptr(val)) {
                        return slice_string(val, start_or_index, end);
                    } else {
                        error("Slicing only works on strings");
                    }
                } else {
                    match(']');
                    long addr = sym->addr + start_or_index;
                    if (addr < 0 || addr >= MEM_SIZE) return 0;
                    return memory[addr];
                }
            }

            if (sym->is_array) {
                return sym->addr;
            }

            if (sym->addr < 0 || sym->addr >= MEM_SIZE) return 0;
            return memory[sym->addr];
        }
    }
    return 0;
}

long unary() {
    if (pc >= MAX_TOK) return 0;
    if (tokens[pc].type == Inc || tokens[pc].type == Dec) {
        int op = tokens[pc++].type;
        Token *t = &tokens[pc];
        if (t->type != Id) error("Expected identifier after ++/--");
        int idx = find_local(t->text, t->val);
        if (idx == -1) error("Undefined variable");
        pc++;
        long addr = locals[idx].addr;
        if (op == Inc) {
            memory[addr]++;
        } else {
            memory[addr]--;
        }
        return memory[addr];
    }
    if (tokens[pc].type == '*') {
        pc++;
        int addr = unary();
        if (addr > MEM_SIZE * 8 || addr < 0) {
             return *(char*)addr;
        }
        if (addr < 0 || addr >= MEM_SIZE) return 0;
        return memory[addr];
    }
    else if (tokens[pc].type == '&') {
        pc++;
        if (pc >= MAX_TOK) return 0;
        Token *t = &tokens[pc];
        if (t->type != Id) error("Expected identifier after &");
        int idx = find_local(t->text, t->val);
        if (idx == -1) error("Undefined variable");
        if (idx < 0 || idx >= loc_cnt) return 0;
        pc++;
        return locals[idx].addr;
    }
    else if (tokens[pc].type == '-') {
        pc++;
        return -unary();
    }
    return factor();
}

long term() {
    long val = unary();
    while (pc < MAX_TOK && (tokens[pc].type == '*' || tokens[pc].type == '/')) {
        int op = tokens[pc++].type;
        long val2 = unary();
        if (op == '*') val = val * val2;
        else {
            if (val2 != 0) val = val / val2;
            else val = 0;
        }
    }
    return val;
}

long add() {
    long val = term();
    while (pc < MAX_TOK && (tokens[pc].type == '+' || tokens[pc].type == '-')) {
        int op = tokens[pc++].type;
        long val2 = term();
        if (op == '+') {
            if (is_string_ptr(val) && is_string_ptr(val2)) {
                val = concat_strings(val, val2);
            } else {
                val = val + val2;
            }
        } else {
            val = val - val2;
        }
    }
    return val;
}

long relational() {
    long val = add();
    while (pc < MAX_TOK && tokens[pc].type >= Eq && tokens[pc].type <= Ge) {
        int op = tokens[pc++].type;
        long val2 = add();
        if (op == Eq) val = val == val2;
        if (op == Ne) val = val != val2;
        if (op == Lt) val = val < val2;
        if (op == Gt) val = val > val2;
    }
    return val;
}

long logical_and() {
    long val = relational();
    while (pc < MAX_TOK && tokens[pc].type == And) {
        pc++;
        long val2 = relational();
        val = val && val2;
    }
    return val;
}

long logical_or() {
    long val = logical_and();
    while (pc < MAX_TOK && tokens[pc].type == Or) {
        pc++;
        long val2 = logical_and();
        val = val || val2;
    }
    return val;
}

long expression() {
    if (pc >= MAX_TOK) return 0;
    if (tokens[pc].type == '*') {
        int save_pc = pc;
        unary();
        if (pc >= MAX_TOK) return 0;
        if (tokens[pc].type == '=') {
            pc = save_pc;
            pc++;
            long addr = unary();
            match('=');
            long val = expression();
            if (addr >= 0 && addr < MEM_SIZE) memory[addr] = val;
            return val;
        }
        pc = save_pc;
    }

    if (pc >= MAX_TOK) return 0;
    if (tokens[pc].type == Id) {
        if (pc + 1 >= MAX_TOK) return 0;
        if (tokens[pc+1].type == '[') {
            int idx = find_local(tokens[pc].text, tokens[pc].val);
            if (idx == -1) error("Assign to unknown var");
            if (idx < 0 || idx >= loc_cnt) return 0;
            pc += 2;
            long start_or_index = expression();

            if (pc >= MAX_TOK) return 0;
            if (tokens[pc].type == ':') {
                pc++;
                long end = expression();
                match(']');

                if (locals[idx].addr < 0 || locals[idx].addr >= MEM_SIZE) return 0;
                long val = memory[locals[idx].addr];
                if (is_string_ptr(val)) {
                    return slice_string(val, start_or_index, end);
                } else {
                    error("Slicing only works on strings");
                }
            }

            match(']');
            int addr = locals[idx].addr;
            if (pc >= MAX_TOK) return 0;
            if (tokens[pc].type == '=') {
                pc++;
                long val = expression();
                long target_addr = addr + start_or_index;
                if (target_addr >= 0 && target_addr < MEM_SIZE) {
                    memory[target_addr] = val;
                }
                return val;
            }
            long read_addr = addr + start_or_index;
            if (read_addr < 0 || read_addr >= MEM_SIZE) return 0;
            return memory[read_addr];
        } else if (tokens[pc+1].type == '=') {
            int idx = find_local(tokens[pc].text, tokens[pc].val);
            if (idx == -1) error("Assign to unknown var");
            if (idx < 0 || idx >= loc_cnt) return 0;
            pc += 2;
            long val = expression();
            if (locals[idx].addr >= 0 && locals[idx].addr < MEM_SIZE) {
                memory[locals[idx].addr] = val;
            }
            return val;
        }
    }

    return logical_or();
}