/* spl_syscall.c — built-in syscall implementations + registration
 *
 * All syscalls validate nargs, cast spl_val_t args to the expected C types,
 * execute, and return the result as spl_val_t.
 *
 * Simple syscalls use the SYSCALL_N macros; complex ones are written
 * manually but follow the same template.
 */

#include "spl_syscall.h"
#include "include/core_map.h"
#include "include/core_vec.h"
#include "spl_ir.h"
#include "spl_vm.h"

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

/* =================================================================
 * Macro templates
 *
 * Each SYSCALL_N macro:
 *  1. Validates nargs (prints error and returns -1 on mismatch)
 *  2. Casts args[n] from spl_val_t to the specified C type via
 *     (type)(uintptr_t) — this handles both integer and pointer types
 *  3. Evaluates the expression and returns the result as spl_val_t
 * ================================================================= */

#define CHECK_NARGS(fname, expected)                                                               \
    do {                                                                                           \
        if (nargs != (expected)) {                                                                 \
            fprintf(stderr, fname ": expected " #expected " args, got %d\n", nargs);               \
            return -1;                                                                             \
        }                                                                                          \
    } while (0)

#define SYSCALL_0(name, ret_expr)                                                                  \
    static spl_val_t name(int nargs, spl_val_t *args) {                                            \
        CHECK_NARGS(#name, 0);                                                                     \
        (void)args;                                                                                \
        return (spl_val_t)(uintptr_t)(ret_expr);                                                   \
    }

#define SYSCALL_1(name, t1, ret_expr)                                                              \
    static spl_val_t name(int nargs, spl_val_t *args) {                                            \
        CHECK_NARGS(#name, 1);                                                                     \
        t1 a1 = (t1)(uintptr_t)args[0];                                                            \
        return (spl_val_t)(uintptr_t)(ret_expr);                                                   \
    }

#define SYSCALL_2(name, t1, t2, ret_expr)                                                          \
    static spl_val_t name(int nargs, spl_val_t *args) {                                            \
        CHECK_NARGS(#name, 2);                                                                     \
        t1 a1 = (t1)(uintptr_t)args[0];                                                            \
        t2 a2 = (t2)(uintptr_t)args[1];                                                            \
        return (spl_val_t)(uintptr_t)(ret_expr);                                                   \
    }

#define SYSCALL_3(name, t1, t2, t3, ret_expr)                                                      \
    static spl_val_t name(int nargs, spl_val_t *args) {                                            \
        CHECK_NARGS(#name, 3);                                                                     \
        t1 a1 = (t1)(uintptr_t)args[0];                                                            \
        t2 a2 = (t2)(uintptr_t)args[1];                                                            \
        t3 a3 = (t3)(uintptr_t)args[2];                                                            \
        return (spl_val_t)(uintptr_t)(ret_expr);                                                   \
    }

#define SYSCALL_4(name, t1, t2, t3, t4, ret_expr)                                                  \
    static spl_val_t name(int nargs, spl_val_t *args) {                                            \
        CHECK_NARGS(#name, 4);                                                                     \
        t1 a1 = (t1)(uintptr_t)args[0];                                                            \
        t2 a2 = (t2)(uintptr_t)args[1];                                                            \
        t3 a3 = (t3)(uintptr_t)args[2];                                                            \
        t4 a4 = (t4)(uintptr_t)args[3];                                                            \
        return (spl_val_t)(uintptr_t)(ret_expr);                                                   \
    }

/* =================================================================
 * OS syscalls
 * ================================================================= */

/* vm_exit — terminate process with the given exit code */
SYSCALL_1(vm_exit, int, (exit(a1), (spl_val_t)0))

/* vm_putchar — write a single character to stdout */
SYSCALL_1(vm_putchar, int, putchar(a1))

/* vm_getchar — read a single character from stdin */
SYSCALL_0(vm_getchar, getchar())

/* vm_putint — print an integer to stdout */
SYSCALL_1(vm_putint, int, (fprintf(stdout, "%d", a1), (spl_val_t)0))

/* vm_putstr — print a string to stdout (no trailing newline) */
SYSCALL_1(vm_putstr, const char *, (fputs(a1, stdout), (spl_val_t)0))

/* vm_fopen — open a file, returns FILE* as spl_val_t */
SYSCALL_2(vm_fopen, const char *, const char *, (uintptr_t)fopen(a1, a2))

/* vm_fclose — close a file, returns 0 on success */
SYSCALL_1(vm_fclose, FILE *, fclose(a1))

/* vm_fread — read from file, returns number of items read */
SYSCALL_4(vm_fread, void *, size_t, size_t, FILE *, fread(a1, a2, a3, a4))

/* vm_fwrite — write to file, returns number of items written */
SYSCALL_4(vm_fwrite, const void *, size_t, size_t, FILE *, fwrite(a1, a2, a3, a4))

/* vm_fsize — get file size in bytes */
static spl_val_t vm_fsize(int nargs, spl_val_t *args) {
    CHECK_NARGS("vm_fsize", 1);
    FILE *f = (FILE *)(uintptr_t)args[0];
    long cur = ftell(f);
    fseek(f, 0, SEEK_END);
    long sz = ftell(f);
    fseek(f, cur, SEEK_SET);
    return (spl_val_t)(uintptr_t)sz;
}

SYSCALL_0(vm_stdin, stdin)
SYSCALL_0(vm_stdout, stdout)
SYSCALL_0(vm_stderr, stderr)

/* vm_read_file — read entire file into a malloc'd, null-terminated buffer */
static spl_val_t vm_read_file(int nargs, spl_val_t *args) {
    CHECK_NARGS("vm_read_file", 1);
    const char *path = (const char *)(uintptr_t)args[0];
    if (path == nullptr) {
        fprintf(stderr, "filepath can't be null");
        return 1;
    }
    FILE *f = fopen(path, "rb");
    if (!f) {
        fprintf(stderr, "filepath %s can't be open", path);
        return 1;
    }
    fseek(f, 0, SEEK_END);
    long sz = ftell(f);
    fseek(f, 0, SEEK_SET);
    char *buf = (char *)malloc((size_t)sz + 1);
    if (!buf) {
        fclose(f);
        return 0;
    }
    size_t nread = fread(buf, 1, (size_t)sz, f);
    fclose(f);
    buf[nread] = '\0';
    return (spl_val_t)(uintptr_t)buf;
}

/* vm_alloc — allocate memory (malloc) */
SYSCALL_1(vm_alloc, size_t, (uintptr_t)malloc(a1))

/* vm_free — free memory */
SYSCALL_1(vm_free, void *, (free(a1), (spl_val_t)0))

/* vm_realloc — reallocate memory (realloc) */
SYSCALL_2(vm_realloc, void *, size_t, (uintptr_t)realloc(a1, a2))

/* vm_strlen — get string length */
SYSCALL_1(vm_strlen, const char *, strlen(a1))

/* vm_strcmp — compare two strings */
SYSCALL_2(vm_strcmp, const char *, const char *, strcmp(a1, a2))

/* vm_memcpy — copy memory, returns dst */
SYSCALL_3(vm_memcpy, void *, const void *, size_t, (memcpy(a1, a2, a3), (uintptr_t)a1))

static spl_val_t vm_printf(int nargs, spl_val_t *args) {
    (void)args;
    if (nargs <= 0) {
        return 0;
    }
    const char *fmt = (const char *)args[0];
    usize fmt_len = strlen(fmt);
    typedef VEC(char) string_builder_t;
    string_builder_t buffer;
    vec_init(buffer);
    if (nargs <= 1) {
        printf("%s", fmt);
        return nargs;
    }
    int arg_idx = 0;
    char tmp_buf[32];
    memset(tmp_buf, 0, sizeof(tmp_buf));
    for (usize i = 0; i < fmt_len; ++i) {
        if (fmt[i] != '%') {
            vec_push(buffer, fmt[i]);
            continue;
        }
        arg_idx += 1;
        if (++i >= fmt_len) {
            continue;
        }
        switch (fmt[i]) {
        case 'd':
            snprintf(tmp_buf, sizeof(tmp_buf), "%zd", args[arg_idx]);
            for (usize j = 0; j < strlen(tmp_buf); ++j) {
                vec_push(buffer, tmp_buf[j]);
            }
            break;
        case 'c':
            vec_push(buffer, (char)args[arg_idx]);
            break;
        case 's':
            for (usize j = 0; j < strlen((const char *)args[arg_idx]); ++j) {
                vec_push(buffer, ((const char *)args[arg_idx])[j]);
            }
            break;
        default:
            continue;
        }
    }
    vec_push(buffer, '\0');
    printf("%s", buffer.data);
    vec_free(buffer);
    return nargs;
}

/* =================================================================
 * VM syscalls (for comptime — compile-time code execution)
 *
 * These let SPL code create isolated sub-VMs, load compiled .sir
 * programs into them, push arguments, call functions, and run.
 * ================================================================= */

/* vm_new — create a new sub-VM instance, returns spl_vm_t* */
static spl_val_t vm_new(int nargs, spl_val_t *args) {
    CHECK_NARGS("vm_new", 0);
    (void)args;
    spl_vm_t *vm = (spl_vm_t *)malloc(sizeof(spl_vm_t));
    if (!vm)
        return 0;
    spl_vm_init(vm);
    return (spl_val_t)(uintptr_t)vm;
}

/* vm_drop — destroy a sub-VM and its loaded program */
static spl_val_t vm_drop(int nargs, spl_val_t *args) {
    CHECK_NARGS("vm_drop", 1);
    spl_vm_t *vm = (spl_vm_t *)(uintptr_t)args[0];
    if (!vm)
        return 0;
    if (vm->prog) {
        spl_prog_drop(vm->prog);
        free(vm->prog);
        vm->prog = NULL;
    }
    spl_vm_drop(vm);
    free(vm);
    return 0;
}

/* vm_load — load a .sir file, register syscalls, return spl_prog_t* */
static spl_val_t vm_load(int nargs, spl_val_t *args) {
    CHECK_NARGS("vm_load", 2);
    spl_vm_t *vm = (spl_vm_t *)(uintptr_t)args[0];
    const char *path = (const char *)(uintptr_t)args[1];
    if (!vm || !path)
        return -1;

    spl_prog_t *prog = (spl_prog_t *)malloc(sizeof(spl_prog_t));
    if (!prog)
        return -1;
    if (spl_prog_load_from_file(path, prog) != 0) {
        free(prog);
        return -1;
    }
    spl_syscall_register(prog);
    if (spl_vm_load_prog(vm, prog) != 0) {
        spl_prog_drop(prog);
        free(prog);
        return -1;
    }
    return (spl_val_t)(uintptr_t)prog;
}

/* vm_push — push a value onto the sub-VM's stack (for passing arguments) */
static spl_val_t vm_push(int nargs, spl_val_t *args) {
    CHECK_NARGS("vm_push", 2);
    spl_vm_t *vm = (spl_vm_t *)(uintptr_t)args[0];
    spl_val_t val = args[1];
    if (!vm)
        return -1;
    if (vm->sp >= vm->config.max_stack_depth) {
        fprintf(stderr, "vm_push: stack overflow\n");
        return -1;
    }
    vm->stacks.data[vm->sp++] = val;
    return 0;
}

/* vm_call — call a function by name with pre-pushed arguments
 *
 * Args (3): vm, function_name, nargs
 * The arguments should already be on the sub-VM's stack via vm_push.
 *
 * Mirrors the CALL instruction's frame setup:
 *   - Pushes a sentinel frame (saved_ip=-1) if cp==0 so RET halts properly
 *   - Pushes the actual call frame
 *   - Sets fp = sp - nargs  (so arg0 = data[fp], arg1 = data[fp+1], ...)
 *   - Sets ip to the function address
 */
static spl_val_t vm_call(int nargs, spl_val_t *args) {
    CHECK_NARGS("vm_call", 3);
    spl_vm_t *vm = (spl_vm_t *)(uintptr_t)args[0];
    const char *name = (const char *)(uintptr_t)args[1];
    spl_val_t call_nargs = args[2];
    if (!vm || !name)
        return -1;

    spl_func_t *func = spl_prog_get_func(vm->prog, name);
    if (!func) {
        fprintf(stderr, "vm_call: function '%s' not found\n", name);
        return -1;
    }
    if (vm->cp >= vm->config.max_call_depth - 1) {
        fprintf(stderr, "vm_call: call stack overflow\n");
        return -1;
    }

    /* Sentinel frame so the entry function's RET halts cleanly */
    if (vm->cp == 0) {
        vm->frames.data[vm->cp].saved_fp = 0;
        vm->frames.data[vm->cp].saved_ip = (uintptr_t)-1;
        vm->frames.data[vm->cp].nargs = 0;
        vm->cp++;
    }

    /* Actual call frame (same logic as the CALL instruction) */
    vm->frames.data[vm->cp].saved_fp = vm->fp;
    vm->frames.data[vm->cp].saved_ip = vm->ip;
    vm->frames.data[vm->cp].nargs = call_nargs;
    vm->cp++;
    vm->fp = vm->sp - call_nargs;
    vm->ip = (uintptr_t)func->address;
    return 0;
}

/* vm_run — run a sub-VM to completion, returns exit_code */
SYSCALL_1(vm_run, spl_vm_t *, spl_vm_run_until(a1, 0))

/* =================================================================
 * Registration
 *
 * Called after loading a .sir file.  Matches native declarations in
 * prog->natives against known syscall names and hooks up impl_fn.
 * ================================================================= */

void spl_syscall_register(spl_prog_t *prog) {
    static spl_native_t table[] = {
        /* OS operations */
        {"vm_exit", 0, vm_exit},
        {"vm_putchar", 0, vm_putchar},
        {"vm_getchar", 0, vm_getchar},
        {"vm_putint", 0, vm_putint},
        {"vm_putstr", 0, vm_putstr},
        {"vm_fopen", 0, vm_fopen},
        {"vm_fclose", 0, vm_fclose},
        {"vm_fread", 0, vm_fread},
        {"vm_fwrite", 0, vm_fwrite},
        {"vm_fsize", 0, vm_fsize},
        {"vm_stdin", 0, vm_stdin},
        {"vm_stdout", 0, vm_stdout},
        {"vm_stderr", 0, vm_stderr},
        {"vm_read_file", 0, vm_read_file},
        {"vm_alloc", 0, vm_alloc},
        {"vm_free", 0, vm_free},
        {"vm_realloc", 0, vm_realloc},
        {"vm_strlen", 0, vm_strlen},
        {"vm_strcmp", 0, vm_strcmp},
        {"vm_memcpy", 0, vm_memcpy},
        {"vm_printf", 0, vm_printf},
        /* VM operations (comptime) */
        {"vm_new", 0, vm_new},
        {"vm_drop", 0, vm_drop},
        {"vm_load", 0, vm_load},
        {"vm_push", 0, vm_push},
        {"vm_call", 0, vm_call},
        {"vm_run", 0, vm_run},
    };
    int n = (int)(sizeof(table) / sizeof(table[0]));
    if (!prog)
        return;
    vec_for(prog->natives, i) {
        spl_native_t *nat = &vec_at(prog->natives, i);
        if (!nat->name || nat->impl_fn)
            continue;
        for (int j = 0; j < n; j++) {
            if (strcmp(nat->name, table[j].name) == 0) {
                nat->impl_fn = table[j].impl_fn;
                break;
            }
        }
    }
}