#include <utility>

#include "../routes.h"
#include "../../servehelper.h"
#include "../../pixivclient.h"
#include "common.h"

static inline uint64_t to_ull(const std::string& str);
static Element generate_pager(size_t page, size_t items, size_t items_per_page);
static inline Element generate_content(const std::vector<uint64_t>& illust_ids, size_t page, size_t items_per_page);

static inline size_t page_count(size_t items, size_t items_per_page);
static inline std::pair<size_t, size_t> page_to_offsets(size_t page, size_t items, size_t items_per_page);

void user_illustrations_route(const httplib::Request& req, httplib::Response& res, const Config& config, PixivClient& pixiv_client) {
    uint64_t user_id = to_ull(req.matches[1].str());
    uint64_t page = req.has_param("p") ? to_ull(req.get_param_value("p")) - 1 : 0;
    User user;
    std::vector<uint64_t> illust_ids;

    try {
        user = pixiv_client.get_user(user_id);
        illust_ids = pixiv_client.get_illusts(user_id);
    } catch (const PixivException& e) {
        if (e.status == 404) {
            res.status = 404;
            serve_error(req, res, config, "404: User not found", e.what());
        } else {
            res.status = 500;
            serve_error(req, res, config, "500: Internal server error", "Failed to fetch user information", e.what());
        }
        return;
    } catch (const std::exception& e) {
        res.status = 500;
        serve_error(req, res, config, "500: Internal server error", "Failed to fetch user information", e.what());
        return;
    }

    const constexpr size_t items_per_page = 18; // on pixiv touch
    Element body("body", {
        generate_user_header(std::move(user), config),
        generate_pager(page, illust_ids.size(), items_per_page),
        Element("br"),
        generate_content(std::move(illust_ids), page, items_per_page),
        generate_pager(page, illust_ids.size(), items_per_page)
    });
    (void)page_to_offsets;
    serve(req, res, config, user.display_name + " illustrations", std::move(body));
}

static inline uint64_t to_ull(const std::string& str) {
    char* endptr;

    errno = 0;
    uint64_t res = strtoull(str.c_str(), &endptr, 10);
    if (res == ULLONG_MAX && errno == ERANGE) {
        throw std::overflow_error(str + " is too big");
    } else if (endptr[0] != '\0') {
        throw std::invalid_argument(str + " contains trailing text or is not an integer");
    }
    return res;
}

static Element generate_pager(size_t page, size_t items, size_t items_per_page) {
    using namespace std::string_literals;

    size_t total_pages = page_count(items, items_per_page);
    auto link = [](std::string href, const char* text, bool add_link) {
        Element b("b");
        if (add_link) {
            b.nodes.push_back(Element("a", {{"href", std::move(href)}}, {text}));
        } else {
            b.nodes.push_back(text);
        }
        return b;
    };
    return Element("div", {{"class", "center"}}, {
        link("?p=1", "First", page != 0), " ",
        link("?p="s + std::to_string(page), "Prev", page != 0), " ",
        std::to_string(page + 1), "/", std::to_string(total_pages), " ",
        link("?p="s + std::to_string(page + 2), "Next", page + 1 < total_pages), " ",
        link("?p="s + std::to_string(total_pages), "Last", page + 1 < total_pages)
    });
}

static inline Element generate_content(const std::vector<uint64_t>& illust_ids, size_t page, size_t items_per_page) {
    // TODO be real
    Element ul("ul");
    std::pair<size_t, size_t> illust_ids_offsets = page_to_offsets(page, illust_ids.size(), items_per_page);

    ul.nodes.reserve(items_per_page);
    for (size_t i = illust_ids_offsets.first; i < illust_ids_offsets.second; i++) {
        ul.nodes.push_back(Element("li", {
            std::to_string(illust_ids[i])
        }));
    }

    return ul;
}

static inline size_t page_count(size_t items, size_t items_per_page) {
    size_t ret = items / items_per_page;
    if (items % items_per_page != 0) {
        ret++;
    }
    return ret;
}

static inline std::pair<size_t, size_t> page_to_offsets(size_t page, size_t items, size_t items_per_page) {
    size_t start_offset = page * items_per_page;
    size_t end_offset = start_offset + items_per_page;
    return {items > start_offset ? start_offset : items, items > end_offset ? end_offset : items};
}