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

extern kernel_ctx_t ctx;

rsdp_t *acpi_find_rsdp() {
    char *ptr = (char *)(KERNEL_VMA + BIOS_START);
    const char sig[RSDP_SIG_LEN] = RSDP_SIG;

    for (; (uint32_t)ptr - KERNEL_VMA <= BIOS_END; ptr += 16)  {
        int i = 0;
        for (; i < RSDP_SIG_LEN; i++)
            if (ptr[i] != sig[i]) break;

        if (i == RSDP_SIG_LEN) return (rsdp_t *)ptr;
    }

    return 0;
}

uint8_t acpi_checksum(void *s, int size) {
    uint32_t sum = 0;
    for (int i = 0; i < size; i++) {
        sum += ((uint8_t *)s)[i];
    }

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

void *acpi_find_sdt(rsdt_t *rsdt, const char *sig) {
    int entries = (rsdt->hdr.Length - sizeof(sdt_hdr_t)) / 4;
    for (int i = 0; i < entries; i++) {
        const char *ptr = (const char *)rsdt->other_tables[i];
        int j = 0;
        for (; j < 4; j++)
            if (ptr[j] != sig[j]) break;

        if (j == 4) return (void *)ptr;
    }
    
    return 0;
}

bool acpi_init() {
    rsdp_t *rsdp = acpi_find_rsdp();
    if (!rsdp) {
        LOG("Invalid RSDP\n");
        return FALSE; 
    }
    if (!acpi_checksum(rsdp, sizeof(rsdp_t))) { 
        LOG("Invalid RSDP checksum\n");
        return FALSE;
    }

    if (rsdp->Revision == 0) LOG("Using ACPI version 1.0\n")
    else if (rsdp->Revision == 2) {
        LOG("ACPI versions higher than 1.0 are not currently supported!\n");
        return FALSE;
    }

    rsdt_t *rsdt = (rsdt_t *)(rsdp->RsdtAddress);
    if (!rsdt) {
        LOG("Invalid RSDT\n");
        return FALSE; 
    }
    if (!acpi_checksum(rsdt, rsdt->hdr.Length)) { 
        LOG("Invalid RSDT checksum\n");
        return FALSE;
    }
    ctx.rsdt = rsdt;
    LOG("RSDT is valid\n");

    void *mcfg = acpi_find_sdt(rsdt, "MCFG");
    if (!mcfg) LOG("PCIe not supported\n");

    return TRUE;
}