#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);
}