#include "rss.h"
#include "download.h"
#include "buffer.h"
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

static int is_alpha_lowercase(char c) {
    return c >= 'a' && c <= 'z';
}

static int is_digit(char c) {
    return c >= '0' && c <= '9';
}

static char* get_amp_end(char *str) {
    for(;;) {
        char c = *str;
        if(is_alpha_lowercase(c) || is_digit(c) || c == '#')
            ++str;
        else if(c == ';' || c == '\0')
            break;
    }
    return str;
}

static void xml_unescape(char *str, char *result, int result_length) {
    int index = 0;
    for(;;) {
        char c = *str;
        if(c == '&') {
            char *amp_end = get_amp_end(str + 1);
            char prev_char = *amp_end;
            *amp_end = '\0';

            if(str[1] == '#') {
                result[index++] = atoi(str + 2);
            } else {
                if(strcmp(str + 1, "amp") == 0)
                    result[index++] = '&';
                else if(strcmp(str + 1, "lt") == 0)
                    result[index++] = '<';
                else if(strcmp(str + 1, "gt") == 0)
                    result[index++] = '>';
                else if(strcmp(str + 1, "apos") == 0)
                    result[index++] = '\'';
            }

            *amp_end = prev_char;
            str = amp_end;
            if(prev_char != '\0')
                ++str;
        } else if(c == '\0') {
            result[index] = '\0';
            break;
        } else {
            result[index++] = c;
            ++str;
        }

        if(index == result_length - 1) {
            result[index] = '\0';
            break;
        }
    }
}

static char* string_substr_before_tag_end(char *str, const char *tag) {
    char *tag_p = strstr(str, tag);
    if(tag_p)
        *tag_p = '\0';
    return tag_p;
}

typedef void (*RssParseCallback)(const char *title, const char *link, void *userdata);

static int parse_rss(char *str, char *rss_title_str, int rss_title_str_size, RssParseCallback parse_callback, void *userdata) {
    char *channel_start = strstr(str, "<channel>");
    if(!channel_start)
        return 1;

    char *after_channel = channel_start + 9;

    char *rss_title = strstr(after_channel, "<title>");
    char *first_item = strstr(after_channel, "<item>");
    if(!first_item) {
        rss_title += 7;
        string_substr_before_tag_end(rss_title, "</title>");
        xml_unescape(rss_title, rss_title_str, rss_title_str_size);
        return 0;
    }

    if(rss_title < first_item) {
        rss_title += 7;
        string_substr_before_tag_end(rss_title, "</title>");
        xml_unescape(rss_title, rss_title_str, rss_title_str_size);
    } else {
        rss_title_str[0] = '\0';
    }

    char title_str[256];
    char link_str[2084];

    char *item = first_item;
    for(;;) {
        char *after_first_item = item + 6;
        char *item_end = strstr(after_first_item, "</item>");
        if(!item_end)
            return 1;

        char *item_title = strstr(after_first_item, "<title>");
        if(!item_title)
            return 1;

        if(item_title >= item_end)
            return 1;
        
        item_title += 7;
        char *after_title = string_substr_before_tag_end(item_title, "</title>");
        if(!after_title)
            return 1;

        after_title += 8;
        char *item_link = strstr(after_title, "<link>");
        if(!item_link)
            return 1;

        if(item_link >= item_end)
            return 1;

        item_link += 6;
        string_substr_before_tag_end(item_link, "</link>");

        xml_unescape(item_title, title_str, sizeof(title_str));
        xml_unescape(item_link, link_str, sizeof(link_str));
        parse_callback(title_str, link_str, userdata);

        item = strstr(item_end + 7, "<item>");
        if(!item)
            return 0;
    }
}

static void rss_parse_callback(const char *title, const char *link, void *userdata) {
    (void)userdata;
    fprintf(stderr, "title: |%s|, link: |%s|\n", title, link);
}

int add_rss(const char *name, const char *url, const char *rss_config_dir, const char *start_after) {
    (void)name;
    (void)rss_config_dir;
    (void)start_after;
    int result = 0;

    Buffer buffer;
    buffer_init(&buffer);
    int res = download_to_buffer(url, &buffer);
    if(res != 0) {
        fprintf(stderr, "Failed to download rss: %s\n", url);
        result = res;
        goto cleanup;
    }

    char rss_title[256];
    res = parse_rss(buffer.data, rss_title, sizeof(rss_title), rss_parse_callback, NULL);
    if(res != 0) {
        fprintf(stderr, "Failed to parse rss for url: %s\n", url);
        result = res;
        goto cleanup;
    }
    fprintf(stderr, "rss title: |%s|\n", rss_title);

    cleanup:
    buffer_deinit(&buffer);
    return result;
}