#include "cache.h"
#include "commit.h"
#include "notes.h"
#include "refs.h"
#include "utf8.h"
#include "strbuf.h"
#include "tree-walk.h"

/*
 * Use a non-balancing simple 16-tree structure with struct int_node as
 * internal nodes, and struct leaf_node as leaf nodes. Each int_node has a
 * 16-array of pointers to its children.
 * The bottom 2 bits of each pointer is used to identify the pointer type
 * - ptr & 3 == 0 - NULL pointer, assert(ptr == NULL)
 * - ptr & 3 == 1 - pointer to next internal node - cast to struct int_node *
 * - ptr & 3 == 2 - pointer to note entry - cast to struct leaf_node *
 * - ptr & 3 == 3 - pointer to subtree entry - cast to struct leaf_node *
 *
 * The root node is a statically allocated struct int_node.
 */
struct int_node {
	void *a[16];
};

/*
 * Leaf nodes come in two variants, note entries and subtree entries,
 * distinguished by the LSb of the leaf node pointer (see above).
 * As a note entry, the key is the SHA1 of the referenced commit, and the
 * value is the SHA1 of the note object.
 * As a subtree entry, the key is the prefix SHA1 (w/trailing NULs) of the
 * referenced commit, using the last byte of the key to store the length of
 * the prefix. The value is the SHA1 of the tree object containing the notes
 * subtree.
 */
struct leaf_node {
	unsigned char key_sha1[20];
	unsigned char val_sha1[20];
};

#define PTR_TYPE_NULL     0
#define PTR_TYPE_INTERNAL 1
#define PTR_TYPE_NOTE     2
#define PTR_TYPE_SUBTREE  3

#define GET_PTR_TYPE(ptr)       ((uintptr_t) (ptr) & 3)
#define CLR_PTR_TYPE(ptr)       ((void *) ((uintptr_t) (ptr) & ~3))
#define SET_PTR_TYPE(ptr, type) ((void *) ((uintptr_t) (ptr) | (type)))

#define GET_NIBBLE(n, sha1) (((sha1[n >> 1]) >> ((~n & 0x01) << 2)) & 0x0f)

#define SUBTREE_SHA1_PREFIXCMP(key_sha1, subtree_sha1) \
	(memcmp(key_sha1, subtree_sha1, subtree_sha1[19]))

static struct int_node root_node;

static int initialized;

static void load_subtree(struct leaf_node *subtree, struct int_node *node,
		unsigned int n);

/*
 * To find a leaf_node:
 * 1. Start at the root node, with n = 0
 * 2. Use the nth nibble of the key as an index into a:
 *    - If a[n] is an int_node, recurse into that node and increment n
 *    - If a leaf_node with matching key, return leaf_node (assert note entry)
 *    - If a matching subtree entry, unpack that subtree entry (and remove it);
 *      restart search at the current level.
 *    - Otherwise, we end up at a NULL pointer, or a non-matching leaf_node.
 *      Backtrack out of the recursion, one level at a time and check a[0]:
 *      - If a[0] at the current level is a matching subtree entry, unpack that
 *        subtree entry (and remove it); restart search at the current level.
 */
static struct leaf_node *note_tree_find(struct int_node *tree, unsigned char n,
		const unsigned char *key_sha1)
{
	struct leaf_node *l;
	unsigned char i = GET_NIBBLE(n, key_sha1);
	void *p = tree->a[i];

	switch(GET_PTR_TYPE(p)) {
	case PTR_TYPE_INTERNAL:
		l = note_tree_find(CLR_PTR_TYPE(p), n + 1, key_sha1);
		if (l)
			return l;
		break;
	case PTR_TYPE_NOTE:
		l = (struct leaf_node *) CLR_PTR_TYPE(p);
		if (!hashcmp(key_sha1, l->key_sha1))
			return l; /* return note object matching given key */
		break;
	case PTR_TYPE_SUBTREE:
		l = (struct leaf_node *) CLR_PTR_TYPE(p);
		if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_sha1)) {
			/* unpack tree and resume search */
			tree->a[i] = NULL;
			load_subtree(l, tree, n);
			free(l);
			return note_tree_find(tree, n, key_sha1);
		}
		break;
	case PTR_TYPE_NULL:
	default:
		assert(!p);
		break;
	}

	/*
	 * Did not find key at this (or any lower) level.
	 * Check if there's a matching subtree entry in tree->a[0].
	 * If so, unpack tree and resume search.
	 */
	p = tree->a[0];
	if (GET_PTR_TYPE(p) != PTR_TYPE_SUBTREE)
		return NULL;
	l = (struct leaf_node *) CLR_PTR_TYPE(p);
	if (!SUBTREE_SHA1_PREFIXCMP(key_sha1, l->key_sha1)) {
		/* unpack tree and resume search */
		tree->a[0] = NULL;
		load_subtree(l, tree, n);
		free(l);
		return note_tree_find(tree, n, key_sha1);
	}
	return NULL;
}

/*
 * To insert a leaf_node:
 * 1. Start at the root node, with n = 0
 * 2. Use the nth nibble of the key as an index into a:
 *    - If a[n] is NULL, store the tweaked pointer directly into a[n]
 *    - If a[n] is an int_node, recurse into that node and increment n
 *    - If a[n] is a leaf_node:
 *      1. Check if they're equal, and handle that (abort? overwrite?)
 *      2. Create a new int_node, and store both leaf_nodes there
 *      3. Store the new int_node into a[n].
 */
static int note_tree_insert(struct int_node *tree, unsigned char n,
		const struct leaf_node *entry, unsigned char type)
{
	struct int_node *new_node;
	const struct leaf_node *l;
	int ret;
	unsigned char i = GET_NIBBLE(n, entry->key_sha1);
	void *p = tree->a[i];
	assert(GET_PTR_TYPE(entry) == PTR_TYPE_NULL);
	switch(GET_PTR_TYPE(p)) {
	case PTR_TYPE_NULL:
		assert(!p);
		tree->a[i] = SET_PTR_TYPE(entry, type);
		return 0;
	case PTR_TYPE_INTERNAL:
		return note_tree_insert(CLR_PTR_TYPE(p), n + 1, entry, type);
	default:
		assert(GET_PTR_TYPE(p) == PTR_TYPE_NOTE ||
			GET_PTR_TYPE(p) == PTR_TYPE_SUBTREE);
		l = (const struct leaf_node *) CLR_PTR_TYPE(p);
		if (!hashcmp(entry->key_sha1, l->key_sha1))
			return -1; /* abort insert on matching key */
		new_node = (struct int_node *)
			xcalloc(sizeof(struct int_node), 1);
		ret = note_tree_insert(new_node, n + 1,
			CLR_PTR_TYPE(p), GET_PTR_TYPE(p));
		if (ret) {
			free(new_node);
			return -1;
		}
		tree->a[i] = SET_PTR_TYPE(new_node, PTR_TYPE_INTERNAL);
		return note_tree_insert(new_node, n + 1, entry, type);
	}
}

/* Free the entire notes data contained in the given tree */
static void note_tree_free(struct int_node *tree)
{
	unsigned int i;
	for (i = 0; i < 16; i++) {
		void *p = tree->a[i];
		switch(GET_PTR_TYPE(p)) {
		case PTR_TYPE_INTERNAL:
			note_tree_free(CLR_PTR_TYPE(p));
			/* fall through */
		case PTR_TYPE_NOTE:
		case PTR_TYPE_SUBTREE:
			free(CLR_PTR_TYPE(p));
		}
	}
}

/*
 * Convert a partial SHA1 hex string to the corresponding partial SHA1 value.
 * - hex      - Partial SHA1 segment in ASCII hex format
 * - hex_len  - Length of above segment. Must be multiple of 2 between 0 and 40
 * - sha1     - Partial SHA1 value is written here
 * - sha1_len - Max #bytes to store in sha1, Must be >= hex_len / 2, and < 20
 * Returns -1 on error (invalid arguments or invalid SHA1 (not in hex format).
 * Otherwise, returns number of bytes written to sha1 (i.e. hex_len / 2).
 * Pads sha1 with NULs up to sha1_len (not included in returned length).
 */
static int get_sha1_hex_segment(const char *hex, unsigned int hex_len,
		unsigned char *sha1, unsigned int sha1_len)
{
	unsigned int i, len = hex_len >> 1;
	if (hex_len % 2 != 0 || len > sha1_len)
		return -1;
	for (i = 0; i < len; i++) {
		unsigned int val = (hexval(hex[0]) << 4) | hexval(hex[1]);
		if (val & ~0xff)
			return -1;
		*sha1++ = val;
		hex += 2;
	}
	for (; i < sha1_len; i++)
		*sha1++ = 0;
	return len;
}

static void load_subtree(struct leaf_node *subtree, struct int_node *node,
		unsigned int n)
{
	unsigned char commit_sha1[20];
	unsigned int prefix_len;
	int status;
	void *buf;
	struct tree_desc desc;
	struct name_entry entry;

	buf = fill_tree_descriptor(&desc, subtree->val_sha1);
	if (!buf)
		die("Could not read %s for notes-index",
		     sha1_to_hex(subtree->val_sha1));

	prefix_len = subtree->key_sha1[19];
	assert(prefix_len * 2 >= n);
	memcpy(commit_sha1, subtree->key_sha1, prefix_len);
	while (tree_entry(&desc, &entry)) {
		int len = get_sha1_hex_segment(entry.path, strlen(entry.path),
				commit_sha1 + prefix_len, 20 - prefix_len);
		if (len < 0)
			continue; /* entry.path is not a SHA1 sum. Skip */
		len += prefix_len;

		/*
		 * If commit SHA1 is complete (len == 20), assume note object
		 * If commit SHA1 is incomplete (len < 20), assume note subtree
		 */
		if (len <= 20) {
			unsigned char type = PTR_TYPE_NOTE;
			struct leaf_node *l = (struct leaf_node *)
				xcalloc(sizeof(struct leaf_node), 1);
			hashcpy(l->key_sha1, commit_sha1);
			hashcpy(l->val_sha1, entry.sha1);
			if (len < 20) {
				l->key_sha1[19] = (unsigned char) len;
				type = PTR_TYPE_SUBTREE;
			}
			status = note_tree_insert(node, n, l, type);
			assert(!status);
		}
	}
	free(buf);
}

static void initialize_notes(const char *notes_ref_name)
{
	unsigned char sha1[20], commit_sha1[20];
	unsigned mode;
	struct leaf_node root_tree;

	if (!notes_ref_name || read_ref(notes_ref_name, commit_sha1) ||
	    get_tree_entry(commit_sha1, "", sha1, &mode))
		return;

	hashclr(root_tree.key_sha1);
	hashcpy(root_tree.val_sha1, sha1);
	load_subtree(&root_tree, &root_node, 0);
}

static unsigned char *lookup_notes(const unsigned char *commit_sha1)
{
	struct leaf_node *found = note_tree_find(&root_node, 0, commit_sha1);
	if (found)
		return found->val_sha1;
	return NULL;
}

void free_notes(void)
{
	note_tree_free(&root_node);
	memset(&root_node, 0, sizeof(struct int_node));
	initialized = 0;
}

void get_commit_notes(const struct commit *commit, struct strbuf *sb,
		const char *output_encoding, int flags)
{
	static const char utf8[] = "utf-8";
	unsigned char *sha1;
	char *msg, *msg_p;
	unsigned long linelen, msglen;
	enum object_type type;

	if (!initialized) {
		const char *env = getenv(GIT_NOTES_REF_ENVIRONMENT);
		if (env)
			notes_ref_name = getenv(GIT_NOTES_REF_ENVIRONMENT);
		else if (!notes_ref_name)
			notes_ref_name = GIT_NOTES_DEFAULT_REF;
		initialize_notes(notes_ref_name);
		initialized = 1;
	}

	sha1 = lookup_notes(commit->object.sha1);
	if (!sha1)
		return;

	if (!(msg = read_sha1_file(sha1, &type, &msglen)) || !msglen ||
			type != OBJ_BLOB) {
		free(msg);
		return;
	}

	if (output_encoding && *output_encoding &&
			strcmp(utf8, output_encoding)) {
		char *reencoded = reencode_string(msg, output_encoding, utf8);
		if (reencoded) {
			free(msg);
			msg = reencoded;
			msglen = strlen(msg);
		}
	}

	/* we will end the annotation by a newline anyway */
	if (msglen && msg[msglen - 1] == '\n')
		msglen--;

	if (flags & NOTES_SHOW_HEADER)
		strbuf_addstr(sb, "\nNotes:\n");

	for (msg_p = msg; msg_p < msg + msglen; msg_p += linelen + 1) {
		linelen = strchrnul(msg_p, '\n') - msg_p;

		if (flags & NOTES_INDENT)
			strbuf_addstr(sb, "    ");
		strbuf_add(sb, msg_p, linelen);
		strbuf_addch(sb, '\n');
	}

	free(msg);
}