#pragma once
#include <kernel/arch/generic.h>
#include <kernel/handle.h>
#include <kernel/vfs/mount.h>
#include <shared/syscalls.h>
#include <stdbool.h>

enum process_state {
	PS_RUNNING,
	PS_DEAD,    // return message wasn't collected
	PS_DEADER,  // return message was collected
	PS_WAITS4CHILDDEATH,
	PS_WAITS4FS,
	PS_WAITS4REQUEST,
	PS_WAITS4IRQ, // set by root vfs
	PS_LAST,
};

struct process {
	struct pagedir *pages;
	struct registers regs;
	enum process_state state;

	bool deathbed; // kill instead of switching to PS_RUNNING

	struct process *sibling;
	struct process *child;
	struct process *parent;

	uint32_t id; // only for debugging, don't expose to userland

	// saved value, meaning depends on .state
	union {
		int death_msg; // PS_DEAD
		struct {
			struct vfs_request req;
		} waits4fs; // PS_WAITS4FS
		struct {
			char __user *buf;
			size_t max_len;
			struct fs_wait_response __user *res;
		} awaited_req; // PS_WAITS4REQUEST
		struct {
			struct vfs_request req;
			bool (*ready)();
			void (*callback)(struct process *);
		} waits4irq;
	};
	struct vfs_request *handled_req;

	/* vfs_backend controlled (not exclusively) by this process */
	struct vfs_backend *controlled;

	struct vfs_mount *mount;

	struct handle handles[HANDLE_MAX];
};

extern struct process *process_first;
extern struct process *process_current;

// creates the root process
struct process *process_seed(void);
struct process *process_fork(struct process *parent);
void process_free(struct process *);
_Noreturn void process_switch(struct process *proc);
_Noreturn void process_switch_any(void); // switches to any running process

/** If there are any processes waiting for IRQs, wait with them. Otherwise, shut down */
_Noreturn void process_idle(void);

/** Used for iterating over all processes */
struct process *process_next(struct process *);

struct process *process_find(enum process_state);
size_t process_find_multiple(enum process_state, struct process **buf, size_t max);

handle_t process_find_handle(struct process *proc); // finds the first free handle

void process_transition(struct process *, enum process_state);

void process_kill(struct process *proc, int ret);

/** Tries to transistion from PS_DEAD to PS_DEADER.
 * @return a nonnegative length of the quit message if successful, a negative val otherwise*/
int process_try2collect(struct process *dead);