/*! \file
 *  \brief Structs and methods related to the \ref ACPI "Advanced Configuration
 * and Power Interface (ACPI)""
 */

#pragma once
#include "../types.h"

/*! \brief Abstracts the ACPI standard that provides interfaces for hardware
 * detection, device configuration, and energy management.
 *  \ingroup io
 *
 *  ACPI is the successor to APM (Advanced Power Management), aiming to give the
 * operating system more control over the hardware. This extended control, for
 * instance, enables the operating system to assign a particular amount of
 * energy to every device (e.g., by disabling a device or changing to standby
 * mode). For this purpose, BIOS and chipset provide a set of tables that
 * describe the system and its components and provide routines the OS can call.
 *  These tables contain details about the system, such as the number of CPU
 * cores and the LAPIC/IOAPIC, which are determined during system boot.
 */

namespace ACPI {

/*! \brief Root System Description Pointer (RSDP)
 *
 * The first step to using ACPI is finding the RSDP that is used to find the
 * RSDT / XSDT, which themselves contain pointers to even more tables.
 *
 * On UEFI systems, the RSDP can be found in the EFI_SYSTEM_TABLE; for non-UEFI
 * systems we have to search for the signature 'RSD PTR ' in the EBDA (Extended
 * Bios Data Area) or in the memory area up to `FFFFFh`.
 *
 * \see [ACPI-Specification 5.2.5.3; Root System Description Pointer (RSDP)
 * Structure](acpi.pdf#page=161)
 */

struct RSDP {
  char signature[8]; /* must exactly be equal to 'RSD PTR ' */
  uint8_t checksum;
  char oemid[6];
  uint8_t revision;     /* specifies the ACPI version */
  uint32_t rsdtaddress; /* physical address of the RSDT */
  uint32_t length;
  uint64_t xsdtaddress; /* physical address of the XSDT */
  uint8_t extended_checksum;
  uint8_t reserved[3];
} __attribute__((packed));

/*! \brief System Description Table Header (SDTH)
 *
 * All System Description Tables (e.g., the RSDT) contain the same entries at
 * the very beginning of the structure, which are abstracted in the SDTH.
 *
 * \see [ACPI-Specification 5.2.6; System Description Table
 * Header](acpi.pdf#page=162)
 */
struct SDTH {
  uint32_t signature; /* table id */
  uint32_t length;
  uint8_t revision;
  uint8_t checksum;
  char oemid[6];
  char oem_table_id[8];
  uint32_t oem_revision;
  uint32_t creator_id;
  uint32_t creator_revision;

  /* \brief Helper method
   * \return Pointer to the end of the table
   */
  void *end() { return reinterpret_cast<uint8_t *>(this) + length; }
} __attribute__((packed));

/*! \brief Root System Description Table (RSDT)
 *
 * The RSDT can be found in the RSDP. The RSDT contains physical addresses of
 * all other System Description Tables, for example the MADT.
 *
 * \see [ACPI-Specification 5.2.7; Root System Description Table
 * (RSDT)](acpi.pdf#page=167)
 */

struct RSDT : SDTH {
  uint32_t entries[];
} __attribute__((packed));

/*! \brief Extended System Description Table (XSDT)
 *
 * Like RSDT, but contains 64-bit instead of 32-bit addresses.
 *
 * \see [ACPI-Specification 5.2.8; Extended System Description Table
 * (XSDT)](acpi.pdf#page=168)
 */

struct XSDT : SDTH {
  uint64_t entries[];
} __attribute__((packed));

/*! \brief Helper structure
 *
 * Is used for accessing the substructures present in SRAT / MADT.
 *
 */
struct SubHeader {
  uint8_t type;
  uint8_t length;

  /* Method to traverse multiple substructures  */
  SubHeader *next() {
    return reinterpret_cast<SubHeader *>(reinterpret_cast<uint8_t *>(this) +
                                         length);
  }
} __attribute__((packed));

/*! \brief Multiple APIC Description Table (MADT)
 *
 * Describes all interrupt controllers present within the system. Is used to
 * obtain the IDs of the APICs, along with the number of available processor
 * cores.
 *
 * \see [ACPI-Specification 5.2.12; Multiple APIC Description Table
 * (MADT)](acpi.pdf#page=193)
 */
struct MADT : SDTH {
  uint32_t local_apic_address;
  uint32_t flags_pcat_compat : 1, flags_reserved : 31;

  /* method to access the first subheader */
  SubHeader *first() {
    return reinterpret_cast<SubHeader *>(reinterpret_cast<uint8_t *>(this) +
                                         sizeof(MADT));
  }
} __attribute__((packed));

enum class AddressSpace : uint8_t {
  MEMORY = 0x0,
  IO = 0x1,
};

/*! \brief ACPI address format
 *
 * The ACPI standard defines its own address format that is able to handle
 * addresses both in memory address space, as well as IO-port address space.
 */
struct Address {
  AddressSpace address_space;
  uint8_t register_bit_width;
  uint8_t register_bit_offset;
  uint8_t reserved;
  uint64_t address;
} __attribute__((packed));

// Multiple APIC Definition Structure
namespace MADS {
enum Type {
  Type_LAPIC = 0,
  Type_IOAPIC = 1,
  Type_Interrupt_Source_Override = 2,
  Type_LAPIC_Address_Override = 5,
};

/*! \brief Processor Local APIC (LAPIC) Structure
 *
 * Represents a physical processor along with its local interrupt controller.
 * The MADT contains a LAPIC structure for every processor available in the
 * system.
 *
 * \see [ACPI-Specification 5.2.12.2; Processor Local APIC
 * Structure](acpi.pdf#page=195)
 */
struct LAPIC : SubHeader {
  uint8_t acpi_processor_id;
  uint8_t apic_id;
  uint32_t flags_enabled : 1, flags_reserved : 31; /* must be 0 */
} __attribute__((packed));

/*! \brief I/O APIC Structure
 *
 * Represents an I/O-APIC.
 * The MADT contains an IOAPIC structure for every I/O APIC present in the
 * system.
 *
 * \see [ACPI-Specification 5.2.12.3; I/O APIC Structure](acpi.pdf#page=196)
 */

struct IOAPIC : SubHeader {
  uint8_t ioapic_id;
  uint8_t reserved;
  uint32_t ioapic_address;
  uint32_t global_system_interrupt_base;
} __attribute__((packed));

/*! \brief Interrupt Source Override Structure
 *
 * Is required to describe differences between the IA-PC standard interrupt
 * definition and the actual hardware implementation.
 *
 * \see [ACPI-Specification 5.2.12.5; Interrupt Source Override
 * Structure](acpi.pdf#page=197)
 */
struct Interrupt_Source_Override : SubHeader {
  uint8_t bus;
  uint8_t source;
  uint32_t global_system_interrupt;
  uint16_t flags_polarity : 2, flags_trigger_mode : 2,
      flags_reserved : 12; /* must be 0 */
} __attribute__((packed));

/*! \brief Local APIC Address Override Structure
 *
 * Support for 64-bit systems is achieved by replacing the 32-bit physical LAPIC
 * address stored in the MADT with the corresponding 64-bit address.
 *
 * \see [ACPI-Specification 5.2.12.8; Local APIC Address Override
 * Structure](acpi.pdf#page=199)
 */

struct LAPIC_Address_Override : SubHeader {
  uint16_t reserved;
  union {
    uint64_t lapic_address;
    struct {
      uint32_t lapic_address_low;
      uint32_t lapic_address_high;
    } __attribute__((packed));
  };
} __attribute__((packed));

}  // namespace MADS

/*! \brief Initialize the ACPI description table
 *
 * Searches physical memory ranges o 16-byte boundaries for a valid Root System
 * Description Pointer (RSDP) structure signature and checksum. If present, the
 * superseding Extended System Description Table (XSDT) is used.
 *
 * \see [ACPI-Specification 5.2.5 Root System Description Pointer
 * (RSDP)](acpi.pdf#page=160)
 * \see [ACPI-Specification 5.2.8 Extended System Description Table
 * (XSDT)](acpi.pdf#page=168)
 */
bool init();

/*! \brief Number of entries in the description table
 */
unsigned count();

/*! \brief Get entry of description table by index
 *
 * \param num index in description table
 * \return Pointer to corresponding entry or `nullptr` if not available
 */
SDTH *get(unsigned num);

/*! \brief Get entry of description table by four character identifier
 *
 * \param a first character of identifier
 * \param b second character of identifier
 * \param c third character of identifier
 * \param d forth and last character of identifier
 * \return Pointer to corresponding entry or `nullptr` if not available
 */
SDTH *get(char a, char b, char c, char d);

/*! \brief Retrieve the revision from the Root System Description Pointer (RSDP)
 */
int revision();

}  // namespace ACPI