#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdint.h>

#include "gifenc.h"

/* helper to write a little-endian 16-bit number portably */
#define write_num(fd, n) write((fd), (uint8_t []) {(n) & 0xFF, (n) >> 8}, 2)

struct Node {
    uint16_t key;
    struct Node *children[];
};
typedef struct Node Node;

static Node *
new_node(uint16_t key, int degree)
{
    Node *node = calloc(1, sizeof(*node) + sizeof(Node *[degree]));
    if (node)
        node->key = key;
    return node;
}

static void
del_trie(Node *root, int degree)
{
    if (!root)
        return;
    for (int i = 0; i < degree; i++)
        del_trie(root->children[i], degree);
    free(root);
}

static void put_loop(GIF *gif, uint16_t loop);

GIF *
new_gif(
    const char *fname, uint16_t width, uint16_t height,
    uint8_t *palette, int depth, int loop
)
{
    GIF *gif = calloc(1, sizeof(*gif) + 2*width*height);
    if (!gif)
        goto no_gif;
    gif->w = width; gif->h = height;
    gif->depth = depth > 1 ? depth : 2;
    gif->frame = (uint8_t *) &gif[1];
    gif->back = &gif->frame[width*height];
    gif->fd = creat(fname, 0666);
    if (gif->fd == -1)
        goto no_fd;
    write(gif->fd, "GIF89a", 6);
    write_num(gif->fd, width);
    write_num(gif->fd, height);
    write(gif->fd, (uint8_t []) {0xF0 | (depth-1), 0x00, 0x00}, 3);
    write(gif->fd, palette, 3 << depth);
    if (loop >= 0 && loop <= 0xFFFF)
        put_loop(gif, (uint16_t) loop);
    return gif;
no_fd:
    free(gif);
no_gif:
    return NULL;
}

static void
put_loop(GIF *gif, uint16_t loop)
{
    write(gif->fd, (uint8_t []) {'!', 0xFF, 0x0B}, 3);
    write(gif->fd, "NETSCAPE2.0", 11);
    write(gif->fd, (uint8_t []) {0x03, 0x01}, 2);
    write_num(gif->fd, loop);
    write(gif->fd, "\0", 1);
}

/* Add packed key to buffer, updating offset and partial.
 *   gif->offset holds position to put next *bit*
 *   gif->partial holds bits to include in next byte */
static void
put_key(GIF *gif, uint16_t key, int key_size)
{
    int byte_offset, bit_offset, bits_to_write;
    byte_offset = gif->offset / 8;
    bit_offset = gif->offset % 8;
    gif->partial |= ((uint32_t) key) << bit_offset;
    bits_to_write = bit_offset + key_size;
    while (bits_to_write >= 8) {
        gif->buffer[byte_offset++] = gif->partial & 0xFF;
        if (byte_offset == 0xFF) {
            write(gif->fd, "\xFF", 1);
            write(gif->fd, gif->buffer, 0xFF);
            byte_offset = 0;
        }
        gif->partial >>= 8;
        bits_to_write -= 8;
    }
    gif->offset = (gif->offset + key_size) % (0xFF * 8);
}

static void
end_key(GIF *gif)
{
    int byte_offset;
    byte_offset = gif->offset / 8;
    gif->buffer[byte_offset++] = gif->partial & 0xFF;
    write(gif->fd, (uint8_t []) {byte_offset}, 1);
    write(gif->fd, gif->buffer, byte_offset);
    write(gif->fd, "\0", 1);
    gif->offset = gif->partial = 0;
}

static void
put_image(GIF *gif, uint16_t w, uint16_t h, uint16_t x, uint16_t y)
{
    int nkeys, key_size, i, j;
    Node *node, *child, *root;
    int degree = 1 << gif->depth;

    write(gif->fd, ",", 1);
    write_num(gif->fd, x);
    write_num(gif->fd, y);
    write_num(gif->fd, w);
    write_num(gif->fd, h);
    write(gif->fd, (uint8_t []) {0x00, gif->depth}, 2);
    root = new_node(0, degree);
    /* Create nodes for single pixels. */
    for (nkeys = 0; nkeys < degree; nkeys++)
        root->children[nkeys] = new_node(nkeys, degree);
    node = root;
    nkeys += 2; /* skip clear code and stop code */
    key_size = gif->depth + 1;
    put_key(gif, degree, key_size); /* clear code */
    for (i = y; i < y+h; i++) {
        for (j = x; j < x+w; j++) {
            uint8_t pixel = gif->frame[i*gif->w+j] & (degree - 1);
            child = node->children[pixel];
            if (child) {
                node = child;
            } else {
                put_key(gif, node->key, key_size);
                if (nkeys < 0x1000) {
                    if (nkeys == (1 << key_size))
                        key_size++;
                    node->children[pixel] = new_node(nkeys++, degree);
                }
                node = root->children[pixel];
            }
        }
    }
    put_key(gif, node->key, key_size);
    put_key(gif, degree + 1, key_size); /* stop code */
    end_key(gif);
    del_trie(root, degree);
}

static int
get_bbox(GIF *gif, uint16_t *w, uint16_t *h, uint16_t *x, uint16_t *y)
{
    int i, j, k;
    int left, right, top, bottom;
    left = gif->w; right = 0;
    top = gif->h; bottom = 0;
    k = 0;
    for (i = 0; i < gif->h; i++) {
        for (j = 0; j < gif->w; j++, k++) {
            if (gif->frame[k] != gif->back[k]) {
                if (j < left)   left    = j;
                if (j > right)  right   = j;
                if (i < top)    top     = i;
                if (i > bottom) bottom  = i;
            }
        }
    }
    if (left != gif->w && top != gif->h) {
        *x = left; *y = top;
        *w = right - left + 1;
        *h = bottom - top + 1;
        return 1;
    } else {
        return 0;
    }
}

static void
set_delay(GIF *gif, uint16_t d)
{
    write(gif->fd, (uint8_t []) {'!', 0xF9, 0x04, 0x04}, 4);
    write_num(gif->fd, d);
    write(gif->fd, "\0\0", 2);
}

void
add_frame(GIF *gif, uint16_t delay)
{
    uint16_t w, h, x, y;
    uint8_t *tmp;

    if (delay)
        set_delay(gif, delay);
    if (gif->nframes == 0) {
        w = gif->w;
        h = gif->h;
        x = y = 0;
    } else if (!get_bbox(gif, &w, &h, &x, &y)) {
        /* image's not changed; save one pixel just to add delay */
        w = h = 1;
        x = y = 0;
    }
    put_image(gif, w, h, x, y);
    gif->nframes++;
    tmp = gif->back;
    gif->back = gif->frame;
    gif->frame = tmp;
}

void
close_gif(GIF* gif)
{
    write(gif->fd, ";", 1);
    close(gif->fd);
    free(gif);
}

#ifdef MAIN
int
main()
{
    int i, j;
    int w = 120, h = 90;

    /* create a GIF */
    GIF *gif = new_gif(
        "example.gif",  /* file name */
        w, h,           /* canvas size */
        (uint8_t []) {  /* palette */
            0x00, 0x00, 0x00, /* 0 -> black */
            0xFF, 0x00, 0x00, /* 1 -> red */
            0x00, 0xFF, 0x00, /* 2 -> green */
            0x00, 0x00, 0xFF, /* 3 -> blue */
        },
        2,              /* palette depth == log2(# of colors) */
        0               /* infinite loop */
    );
    /* draw some frames */
    for (i = 0; i < 4*6/3; i++) {
        for (j = 0; j < w*h; j++)
            gif->frame[j] = (i*3 + j) / 6 % 4;
        add_frame(gif, 10);
    }
    /* remember to close the GIF */
    close_gif(gif);
    return 0;
}
#endif