#include <stddef.h>
#include <stdint.h>
#include <stdbool.h>
#include <lib/acpi.h>
#include <lib/blib.h>
#include <lib/libc.h>
#include <lib/print.h>

// Following function based on https://github.com/qword-os/lai/blob/master/helpers/pc-bios.c's function lai_bios_calc_checksum()
uint8_t acpi_checksum(void *ptr, size_t size) {
    uint8_t sum = 0, *_ptr = ptr;
    for (size_t i = 0; i < size; i++)
        sum += _ptr[i];
    return sum;
}

void *acpi_get_rsdp(void) {
    size_t ebda = EBDA;

    for (size_t i = ebda; i < 0x100000; i += 16) {
        if (i == ebda + 1024) {
            // We probed the 1st KiB of the EBDA as per spec, move onto 0xe0000
            i = 0xe0000;
        }
        if (!memcmp((char *)i, "RSD PTR ", 8)
         && !acpi_checksum((void *)i, sizeof(struct rsdp))) {
            print("acpi: Found RSDP at %x\n", i);
            return (void *)i;
        }
    }

    return NULL;
}

void *acpi_get_table(const char *signature, int index) {
    int cnt = 0;

    struct rsdp_rev2 *rsdp = acpi_get_rsdp();
    if (rsdp == NULL)
        return NULL;

    bool use_xsdt = false;
    if (rsdp->rev >= 2 && rsdp->xsdt_addr)
        use_xsdt = true;

    struct rsdt *rsdt;
    if (use_xsdt)
        rsdt = (struct rsdt *)(uintptr_t)rsdp->xsdt_addr;
    else
        rsdt = (struct rsdt *)(uintptr_t)rsdp->rsdt_addr;

    for (size_t i = 0; i < rsdt->length - sizeof(struct sdt); i++) {
        struct sdt *ptr;
        if (use_xsdt)
            ptr = (struct sdt *)(uintptr_t)((uint64_t *)rsdt->ptrs_start)[i];
        else
            ptr = (struct sdt *)(uintptr_t)((uint32_t *)rsdt->ptrs_start)[i];

        if (!memcmp(ptr->signature, signature, 4)
         && !acpi_checksum(ptr, ptr->length)
         && cnt++ == index) {
            print("acpi: Found \"%s\" at %x\n", signature, ptr);
            return ptr;
        }
    }

    print("acpi: \"%s\" not found\n", signature);
    return NULL;
}