#include <kernel/iovec.h>
#include <kernel/libc/stdio.h>
#include <kernel/object.h>
#include <kernel/panic.h>
#include <kernel/printk.h>
#include <kernel/util.h>
#include <kernel/vm-object.h>
#include <kernel/vm-region.h>
#include <mango/status.h>

/*** STATIC DATA + MACROS *****************************************************/

#undef ASLR

#define INVALID_OFFSET ((off_t) - 1)

#ifdef ASLR
#define region_find_free_area(region, length)                                  \
	region_find_free_area_random(region, length)
#else
#define region_find_free_area(region, length)                                  \
	region_find_free_area_linear(region, length)
#endif

enum search_direction {
	SEARCH_LEFT,
	SEARCH_RIGHT,
};

#define VM_REGION_CAST(p)                                                      \
	OBJECT_C_CAST(struct vm_region, vr_base, &vm_region_type, p)

static struct object_type vm_region_type = {
	.ob_name = "vm-region",
	.ob_size = sizeof(struct vm_region),
	.ob_header_offset = offsetof(struct vm_region, vr_base),
};

static struct vm_cache mapping_cache = {
	.c_name = "vm-region-mapping",
	.c_obj_size = sizeof(struct vm_region_mapping),
};

/*** INTERNAL UTILITY FUNCTION ************************************************/

static struct vm_region *region_from_entry(struct vm_region_entry *entry)
{
	if (!entry || entry->e_type != VM_REGION_ENTRY_REGION) {
		return NULL;
	}

	return BTREE_CONTAINER(struct vm_region, vr_entry, entry);
}

static struct vm_region_mapping *mapping_from_entry(
	struct vm_region_entry *entry)
{
	if (!entry || entry->e_type != VM_REGION_ENTRY_MAPPING) {
		return NULL;
	}

	return BTREE_CONTAINER(struct vm_region_mapping, m_entry, entry);
}

static virt_addr_t entry_absolute_address(struct vm_region_entry *entry)
{
	virt_addr_t result = 0;
	while (entry) {
		result += entry->e_offset;
		entry = entry->e_parent;
	}

	return result;
}

static void region_put_entry(
	struct vm_region *parent,
	struct vm_region_entry *child)
{
	struct btree_node *cur = parent->vr_entries.b_root;
	if (!cur) {
		parent->vr_entries.b_root = &child->e_node;
		btree_insert_fixup(&parent->vr_entries, &child->e_node);
		return;
	}

	off_t child_base = child->e_offset;
	off_t child_limit = child_base + child->e_size - 1;

	while (cur) {
		struct vm_region_entry *cur_entry
			= BTREE_CONTAINER(struct vm_region_entry, e_node, cur);

		struct btree_node *next = NULL;
		off_t cur_base = cur_entry->e_offset;
		off_t cur_limit = cur_base + cur_entry->e_size - 1;

		if (child_limit < cur_base) {
			next = btree_left(cur);
		} else if (child_base > cur_limit) {
			next = btree_right(cur);
		} else {
			panic("tried to add an overlapping entry to vm-region");
		}

		if (next) {
			cur = next;
			continue;
		}

		if (child_limit < cur_base) {
			btree_put_left(cur, &child->e_node);
		} else {
			btree_put_right(cur, &child->e_node);
		}

		btree_insert_fixup(&parent->vr_entries, &child->e_node);
		break;
	}
}

/* find the child entry that covers the specified offset.
 * DOES NOT search recursively! */
static struct vm_region_entry *region_get_entry(
	struct vm_region *region,
	off_t offset,
	size_t len)
{
	struct btree_node *cur = region->vr_entries.b_root;
	if (!cur) {
		return NULL;
	}

	struct vm_region_entry *result = NULL;

	off_t base = offset, limit = offset + len - 1;

	while (cur) {
		struct vm_region_entry *child
			= BTREE_CONTAINER(struct vm_region_entry, e_node, cur);

		struct btree_node *next = NULL;
		off_t child_base = child->e_offset;
		off_t child_limit = child->e_offset + child->e_size - 1;

		if (limit < child_base) {
			next = btree_left(cur);
		} else if (base > child_limit) {
			next = btree_right(cur);
		} else {
			result = child;
			break;
		}

		cur = next;
	}

	return result;
}

/* find the child region that covers the area [*offp,len]. searches recursively
 * the value in `offp` is updated to the offset of the returned entry relative
 * to its parent */
static struct vm_region *region_get_child_region_recursive(
	struct vm_region *region,
	off_t *offp,
	size_t len)
{
	off_t offset = *offp;
	if (offset >= region->vr_entry.e_size) {
		return NULL;
	}

	while (1) {
		struct vm_region_entry *next
			= region_get_entry(region, offset, len);

		struct vm_region *next_region = region_from_entry(next);
		if (next_region) {
			offset -= next->e_offset;
			region = next_region;
		} else {
			break;
		}
	}

	*offp = offset;
	return region;
}

static struct vm_region_mapping *region_get_mapping_recursive(
	struct vm_region *region,
	off_t *offp,
	size_t len)
{
	off_t offset = *offp;
	region = region_get_child_region_recursive(region, &offset, len);
	if (!region) {
		return NULL;
	}

	struct vm_region_entry *entry = region_get_entry(region, offset, len);
	*offp = offset;

	return mapping_from_entry(entry);
}

static off_t generate_random_address(
	off_t area_base,
	size_t area_length,
	size_t target_length)
{
	size_t random_range = area_length - target_length;

	off_t offset = 0;
	fill_random(&offset, sizeof offset);

	offset %= random_range;
	return area_base + offset;
}

static struct vm_region_entry *region_get_random_entry(struct vm_region *region)
{
	enum {
		STEP_LEFT = 0,
		STEP_RIGHT = 1,
		STEP_FINISH = 2,
	} step;

	struct btree_node *result = NULL;
	struct btree_node *cur = region->vr_entries.b_root;
	if (!cur) {
		return NULL;
	}

	while (1) {
		unsigned long r;
		fill_random(&r, sizeof r);

		struct btree_node *next = NULL;

		step = r % 3;
		switch (step) {
		case STEP_LEFT:
			next = btree_left(cur);
			break;
		case STEP_RIGHT:
			next = btree_right(cur);
			break;
		case STEP_FINISH:
			result = cur;
			break;
		default:
			return NULL;
		}

		if (!next) {
			result = cur;
			break;
		}

		cur = next;
	}

	if (!result) {
		return NULL;
	}

	return BTREE_CONTAINER(struct vm_region_entry, e_node, result);
}

static virt_addr_t region_find_free_area_ex(
	struct vm_region *region,
	size_t target_length,
	struct btree_node *start,
	enum search_direction direction,
	bool random)
{
	if (region->vr_entry.e_size < target_length) {
		return 0;
	}

	struct btree_node *left_node = NULL, *right_node = NULL;

	switch (direction) {
	case SEARCH_LEFT:
		right_node = start;
		left_node = start ? btree_left(start) : NULL;
		break;
	case SEARCH_RIGHT:
		left_node = start;
		right_node = start ? btree_left(start) : NULL;
		break;
	default:
		return 0;
	}

	if (!left_node && !right_node) {
		return 0;
	}

	while (1) {
		struct vm_region_entry *left = BTREE_CONTAINER(
			struct vm_region_entry,
			e_node,
			left_node);
		struct vm_region_entry *right = BTREE_CONTAINER(
			struct vm_region_entry,
			e_node,
			right_node);

		/* addresses of the first and last free bytes in the area
		 * respectively. */
		off_t area_base, area_limit;
		if (left && right) {
			area_base = left->e_offset + left->e_size;
			area_limit = right->e_offset - 1;
		} else if (right) {
			area_base = region->vr_entry.e_offset;
			area_limit = left->e_offset - 1;
		} else if (left) {
			area_base = left->e_offset + left->e_size;
			area_limit = region->vr_entry.e_offset
			           + region->vr_entry.e_size - 1;
		} else {
			return 0;
		}

		area_base &= ~VM_PAGE_MASK;
		size_t area_size = 0;
		if (area_limit >= area_base) {
			area_size = area_limit - area_base + 1;
		}

		if (area_size >= target_length) {
			if (random) {
				area_base = generate_random_address(
					area_base,
					area_size,
					target_length);
				area_base &= ~VM_PAGE_MASK;
			}

			return area_base;
		}

		if (direction == SEARCH_RIGHT) {
			left_node = right_node;
			right_node = btree_next(right_node);
		} else {
			right_node = left_node;
			left_node = btree_prev(right_node);
		}
	}

	return 0;
}

static off_t region_find_free_area_linear(
	struct vm_region *region,
	size_t target_length)
{
	if (!region->vr_entries.b_root) {
		return region->vr_entry.e_offset;
	}

	return region_find_free_area_ex(
		region,
		target_length,
		btree_first(&region->vr_entries),
		SEARCH_RIGHT,
		false);
}

static off_t region_find_free_area_random(
	struct vm_region *region,
	size_t target_length)
{
	if (!region->vr_entries.b_root) {
		off_t offset = generate_random_address(
			0,
			region->vr_entry.e_size,
			target_length);
		return offset & ~VM_PAGE_MASK;
	}

	int tmp = 0;
	struct vm_region_entry *basis = region_get_random_entry(region);

	fill_random(&tmp, sizeof tmp);
	enum search_direction direction = tmp % 2;

	return region_find_free_area_ex(
		region,
		target_length,
		&basis->e_node,
		direction,
		true);
}

static bool region_is_area_free(
	const struct vm_region *region,
	off_t base,
	size_t len)
{
	if (len >= region->vr_entry.e_size) {
		return false;
	}

	if (base + len > region->vr_entry.e_size) {
		return false;
	}

	off_t limit = base + len - 1;

	struct btree_node *cur = region->vr_entries.b_root;
	if (!cur) {
		return true;
	}

	while (cur) {
		struct vm_region_entry *entry
			= BTREE_CONTAINER(struct vm_region_entry, e_node, cur);

		struct btree_node *next = NULL;
		off_t entry_limit = entry->e_offset + entry->e_size - 1;

		if (base > entry_limit) {
			next = btree_right(cur);
		} else if (limit < entry->e_offset) {
			next = btree_left(cur);
		} else {
			return false;
		}

		cur = next;
	}

	return true;
}

static kern_status_t region_validate_allocation(
	struct vm_region *parent,
	enum vm_prot prot,
	off_t *offp,
	size_t len)
{
	off_t offset = *offp;

	if ((prot & parent->vr_prot) != prot) {
		/* child region protection must match or be a
		 * subset of parent region protection */
		return KERN_INVALID_ARGUMENT;
	}

	if (offset == VM_REGION_ANY_OFFSET) {
		offset = region_find_free_area(parent, len);
		if (offset == 0) {
			return KERN_NO_MEMORY;
		}
	} else if (!region_is_area_free(parent, offset, len)) {
		return KERN_INVALID_ARGUMENT;
	}

	*offp = offset;
	return KERN_OK;
}

/*** PUBLIC API ***************************************************************/

kern_status_t vm_region_type_init(void)
{
	vm_cache_init(&mapping_cache);
	return object_type_register(&vm_region_type);
}

kern_status_t vm_region_create(
	struct vm_region *parent,
	const char *name,
	off_t offset,
	size_t len,
	enum vm_prot prot,
	struct vm_region **out)
{
	if (!offset || !len) {
		return KERN_INVALID_ARGUMENT;
	}

	if (len & VM_PAGE_MASK) {
		len &= ~VM_PAGE_MASK;
		len += VM_PAGE_SIZE;
	}

	kern_status_t status = KERN_OK;
	if (parent) {
		status = region_validate_allocation(parent, prot, &offset, len);
	}

	if (status != KERN_OK) {
		return status;
	}

	struct object *region_object = object_create(&vm_region_type);
	if (!region_object) {
		return KERN_NO_MEMORY;
	}

	struct vm_region *region = VM_REGION_CAST(region_object);

	region->vr_prot = prot;
	region->vr_entry.e_type = VM_REGION_ENTRY_REGION;
	region->vr_entry.e_offset = offset;
	region->vr_entry.e_size = len;

	if (parent) {
		region->vr_entry.e_parent = &parent->vr_entry;
		region->vr_pmap = parent->vr_pmap;
		region_put_entry(parent, &region->vr_entry);
	}

	if (name) {
		strncpy(region->vr_name, name, sizeof region->vr_name);
		region->vr_name[sizeof region->vr_name - 1] = '\0';
	}

	*out = region;
	return KERN_OK;
}

kern_status_t vm_region_map_object(
	struct vm_region *region,
	off_t region_offset,
	struct vm_object *object,
	off_t object_offset,
	size_t length,
	enum vm_prot prot,
	virt_addr_t *out)
{
	object_offset &= ~VM_PAGE_MASK;

	if (length & VM_PAGE_MASK) {
		length &= ~VM_PAGE_MASK;
		length += VM_PAGE_SIZE;
	}

	if (!region || !object || !out) {
		return KERN_INVALID_ARGUMENT;
	}

	if ((prot & region->vr_prot) != prot) {
		return KERN_INVALID_ARGUMENT;
	}

	if ((prot & object->vo_prot) != prot) {
		return KERN_INVALID_ARGUMENT;
	}

	if (!length || object_offset + length > object->vo_size) {
		return KERN_INVALID_ARGUMENT;
	}

	if (region_offset != VM_REGION_ANY_OFFSET) {
		region = region_get_child_region_recursive(
			region,
			&region_offset,
			length);
	}

	if (!region) {
		return KERN_INVALID_ARGUMENT;
	}

	if (region_offset == VM_REGION_ANY_OFFSET) {
		region_offset = region_find_free_area(region, length);

		if (region_offset == INVALID_OFFSET) {
			return KERN_NO_MEMORY;
		}
	} else if (!region_is_area_free(region, region_offset, length)) {
		return KERN_INVALID_ARGUMENT;
	}

	struct vm_region_mapping *mapping
		= vm_cache_alloc(&mapping_cache, VM_NORMAL);
	if (!mapping) {
		return KERN_NO_MEMORY;
	}

	mapping->m_object = object;
	mapping->m_prot = prot;
	mapping->m_object_offset = object_offset;
	mapping->m_entry.e_type = VM_REGION_ENTRY_MAPPING;
	mapping->m_entry.e_parent = &region->vr_entry;
	mapping->m_entry.e_offset = region_offset;
	mapping->m_entry.e_size = length;

	region_put_entry(region, &mapping->m_entry);
	queue_push_back(&object->vo_mappings, &mapping->m_object_entry);

#ifdef TRACE
	virt_addr_t abs_base = entry_absolute_address(&mapping->m_entry);
	tracek("mapping %s at [%llx-%llx]",
	       object->vo_name,
	       abs_base,
	       abs_base + length);
#endif

	*out = entry_absolute_address(&mapping->m_entry);
	return KERN_OK;
}

kern_status_t vm_region_demand_map(
	struct vm_region *region,
	virt_addr_t addr,
	enum pmap_fault_flags flags)
{
	addr &= ~VM_PAGE_MASK;
	if (addr < region->vr_entry.e_offset
	    || addr > region->vr_entry.e_offset + region->vr_entry.e_size) {
		return KERN_NO_ENTRY;
	}

	off_t region_offset = addr - region->vr_entry.e_offset;

	struct vm_region_mapping *mapping
		= region_get_mapping_recursive(region, &region_offset, 1);
	if (!mapping) {
		return KERN_NO_ENTRY;
	}

	off_t object_offset = region_offset - mapping->m_entry.e_offset
	                    + mapping->m_object_offset;

	tracek("vm: tried to access vm-object %s at offset=%05llx",
	       mapping->m_object->vo_name,
	       object_offset);

	struct vm_page *pg = vm_object_alloc_page(
		mapping->m_object,
		object_offset,
		VM_PAGE_4K);
	tracek("vm: mapping %07llx -> %10llx", vm_page_get_paddr(pg), addr);
	return pmap_add(
		region->vr_pmap,
		addr,
		vm_page_get_pfn(pg),
		mapping->m_prot,
		PMAP_NORMAL);
}

#ifdef TRACE
void vm_region_dump(struct vm_region *region, int depth)
{
	char line[128] = {0};
	size_t p = 0;

	for (int i = 0; i < depth; i++) {
		p += snprintf(line + p, sizeof line - p, "   ");
	}
	p += snprintf(
		line + p,
		sizeof line - p,
		"region: %s [%llx-%llx]",
		region->vr_name,
		region->vr_entry.e_offset,
		region->vr_entry.e_offset + region->vr_entry.e_size);

	printk("%s", line);

	struct btree_node *cur = btree_first(&region->vr_entries);
	while (cur) {
		memset(line, 0x0, sizeof line);
		p = 0;

		for (int i = 0; i < depth + 1; i++) {
			p += snprintf(line + p, sizeof line - p, "   ");
		}

		struct vm_region_entry *entry
			= BTREE_CONTAINER(struct vm_region_entry, e_node, cur);
		struct vm_region *child_region = region_from_entry(entry);
		struct vm_region_mapping *child_mapping
			= mapping_from_entry(entry);

		switch (entry->e_type) {
		case VM_REGION_ENTRY_REGION:
			break;
		case VM_REGION_ENTRY_MAPPING:
			p += snprintf(
				line + p,
				sizeof line - p,
				"mapping: %s p:[%llx-%llx] -> v:[%llx-%llx]",
				child_mapping->m_object->vo_name,
				child_mapping->m_object_offset,
				child_mapping->m_object_offset
					+ child_mapping->m_entry.e_size,
				child_mapping->m_entry.e_offset,
				child_mapping->m_entry.e_offset
					+ child_mapping->m_entry.e_size);
			printk("%s", line);
			break;
		default:
			p += snprintf(line + p, sizeof line - p, "invalid");
			printk("%s", line);
			break;
		}

		if (child_region) {
			vm_region_dump(child_region, depth + 1);
		}

		cur = btree_next(cur);
	}
}
#endif