#include <kernel/acpi.h>
#include <kernel/strcmp.h>

struct rsdp *acpi_locate_rsdp() {
    char *ptr = (char *)BIOS_START;
    char *str = RSDP_SIG;

    while ((uint32_t)ptr <= (uint32_t)BIOS_END - RSDP_SIG_LEN) {
        int i;
        for (i = 0; i < RSDP_SIG_LEN; i++) {
            if (ptr[i] != str[i])
                break;
        }
        if (i == RSDP_SIG_LEN) {
            return (struct rsdp *)ptr;
        }
        ptr++;
    }

    return 0;
}

int acpi_validate_rsdp_checksum(struct rsdp *s) {
    uint8_t *bytes = (uint8_t *)s;
    uint8_t sum = 0;
    for (int i = 0; i < RSDP_SIZE; i++) {
        sum += bytes[i];
    }

    return (sum & 0x0F) == 0;
}

int acpi_validate_sdt_checksum(struct ACPISDTHeader *s) {
    uint8_t sum = 0;
    for (uint32_t i = 0; i < s->Length; i++) {
        sum += ((char *)s)[i];
    }

    return sum == 0;
}

void *acpi_locate_sdt(struct rsdt *rsdt, const char sig[4]) {
    int entries = (rsdt->h.Length - sizeof(rsdt->h)) / 4;
 
    for (int i = 0; i < entries; i++)
    {
        struct ACPISDTHeader *h = (struct ACPISDTHeader *) rsdt->other_sdt[i];
        if (!strncmp(h->Signature, sig, 4)) {
            if (acpi_validate_sdt_checksum(h))
                return (void *) h;
            else 
                return 0;
        }
    }
 
    return 0;
}