damus/damus-c/damus.c

//
//  damus.c
//  damus
//
//  Created by William Casarin on 2022-10-17.
//

#include "damus.h"
#include <stdlib.h>
#include <string.h>

typedef unsigned char u8;

struct cursor {
    const u8 *p;
    const u8 *start;
    const u8 *end;
};

static inline int is_whitespace(char c) {
    return c == ' ' || c == '\t' || c == '\n' || c == '\v' || c == '\f' || c == '\r';
}

static void make_cursor(struct cursor *c, const u8 *content, size_t len)
{
    c->start = content;
    c->end = content + len;
    c->p = content;
}

static int consume_until_whitespace(struct cursor *cur, int or_end) {
    char c;
    
    while (cur->p < cur->end) {
        c = *cur->p;
        
        if (is_whitespace(c))
            return 1;
        
        cur->p++;
    }
    
    return or_end;
}

static int parse_char(struct cursor *cur, char c) {
    if (cur->p >= cur->end)
        return 0;
        
    if (*cur->p == c) {
        cur->p++;
        return 1;
    }
    
    return 0;
}

static inline int peek_char(struct cursor *cur, int ind) {
    if ((cur->p + ind < cur->start) || (cur->p + ind >= cur->end))
        return -1;
    
    return *(cur->p + ind);
}

static int parse_digit(struct cursor *cur, int *digit) {
    int c;
    if ((c = peek_char(cur, 0)) == -1)
        return 0;
    
    c -= '0';
    
    if (c >= 0 && c <= 9) {
        *digit = c;
        cur->p++;
        return 1;
    }
    return 0;
}

static int parse_str(struct cursor *cur, const char *str) {
    unsigned long len = strlen(str);
    
    if (cur->p + len >= cur->end)
        return 0;
    
    if (!memcmp(cur->p, str, len)) {
        cur->p += len;
        return 1;
    }
    
    return 0;
}

static int parse_mention(struct cursor *cur, struct block *block) {
    int d1, d2, d3, ind;
    const u8 *start = cur->p;
    
    if (!parse_str(cur, "#["))
        return 0;
    
    if (!parse_digit(cur, &d1)) {
        cur->p = start;
        return 0;
    }
    
    ind = d1;
    
    if (parse_digit(cur, &d2))
        ind = (d1 * 10) + d2;
    
    if (parse_digit(cur, &d3))
        ind = (d1 * 100) + (d2 * 10) + d3;
    
    if (!parse_char(cur, ']')) {
        cur->p = start;
        return 0;
    }
    
    block->type = BLOCK_MENTION;
    block->block.mention = ind;
    
    return 1;
}

static int parse_hashtag(struct cursor *cur, struct block *block) {
    int c;
    const u8 *start = cur->p;
    
    if (!parse_char(cur, '#'))
        return 0;
    
    c = peek_char(cur, 0);
    if (c == -1 || is_whitespace(c) || c == '#') {
        cur->p = start;
        return 0;
    }
    
    consume_until_whitespace(cur, 1);
    
    block->type = BLOCK_HASHTAG;
    block->block.str.start = (const char*)(start + 1);
    block->block.str.end = (const char*)cur->p;
    
    return 1;
}

static int add_block(struct blocks *blocks, struct block block)
{
    if (blocks->num_blocks + 1 >= MAX_BLOCKS)
        return 0;
    
    blocks->blocks[blocks->num_blocks++] = block;
    return 1;
}

static int add_text_block(struct blocks *blocks, const u8 *start, const u8 *end)
{
    struct block b;
    
    b.type = BLOCK_TEXT;
    b.block.str.start = (const char*)start;
    b.block.str.end = (const char*)end;
    
    return add_block(blocks, b);
}

static int parse_url(struct cursor *cur, struct block *block) {
    const u8 *start = cur->p;
    
    if (!parse_str(cur, "http"))
        return 0;
    
    if (parse_char(cur, 's')) {
        if (!parse_str(cur, "://")) {
            cur->p = start;
            return 0;
        }
    } else {
        if (!parse_str(cur, "://")) {
            cur->p = start;
            return 0;
        }
    }
    
    if (!consume_until_whitespace(cur, 1)) {
        cur->p = start;
        return 0;
    }
    
    block->type = BLOCK_URL;
    block->block.str.start = (const char *)start;
    block->block.str.end = (const char *)cur->p;
    
    return 1;
}

int damus_parse_content(struct blocks *blocks, const char *content) {
    int cp, c;
    struct cursor cur;
    struct block block;
    const u8 *start, *pre_mention;
    
    blocks->num_blocks = 0;
    make_cursor(&cur, (const u8*)content, strlen(content));
    
    start = cur.p;
    while (cur.p < cur.end && blocks->num_blocks < MAX_BLOCKS) {
        cp = peek_char(&cur, -1);
        c  = peek_char(&cur, 0);
        
        pre_mention = cur.p;
        if (cp == -1 || is_whitespace(cp)) {
            if (c == '#' && (parse_mention(&cur, &block) || parse_hashtag(&cur, &block))) {
                if (!add_text_block(blocks, start, pre_mention))
                    return 0;
                
                start = cur.p;
                
                if (!add_block(blocks, block))
                    return 0;
                
                continue;
            } else if (c == 'h' && parse_url(&cur, &block)) {
                if (!add_text_block(blocks, start, pre_mention))
                    return 0;
                
                start = cur.p;
                
                if (!add_block(blocks, block))
                    return 0;
                
                continue;
            }
        }
        
        cur.p++;
    }
    
    if (cur.p - start > 0) {
        if (!add_text_block(blocks, start, cur.p))
            return 0;
    }
    
    return 1;
}

void blocks_init(struct blocks *blocks) {
    blocks->blocks = malloc(sizeof(struct block) * MAX_BLOCKS);
    blocks->num_blocks = 0;
}

void blocks_free(struct blocks *blocks) {
    if (blocks->blocks) {
        free(blocks->blocks);
        blocks->num_blocks = 0;
    }
}