function format_date(date)
    if date == nil then
        return date
    end

    date = pandoc.utils.normalize_date(pandoc.utils.stringify(date))
    local year, month, day = date:match("(%d%d%d%d)-(%d%d)-(%d%d)")
    if year == nil then
        return nil
    end

    local time = os.time({
        year = tonumber(year),
        month = tonumber(month),
        day = tonumber(day)
    })
    return pandoc.MetaMap({
        yyyy_mm_dd = pandoc.MetaString(os.date("%F", time)),
        yyyy = pandoc.MetaString(os.date("%Y", time)),
        mm_dd = pandoc.MetaString(os.date("%m-%d", time)),
        rfc3339 = pandoc.MetaString(os.date("%FT%T+00:00", time))
    })
end

function table_to_list(t, cmp)
    local l = pandoc.MetaList({})

    for key, value in pairs(t) do
        l:insert(pandoc.MetaMap({
            key = key,
            value = value
        }))
    end

    l:sort(cmp or function(i1, i2)
        return i1.key < i2.key
    end)

    return l
end

function splitstr(input, sep)
    sep = sep or "%s"
    local t = {}
    for str in input:gmatch("([^" .. sep .. "]+)") do
        table.insert(t, str)
    end
    return t
end

function relative_to(dir, target)
    dir = splitstr(dir, "/")
    target = splitstr(target, "/")

    local prefix = true
    local path = ""

    for i = 1, math.min(#dir, #target) do
        local t = target[i]
        if prefix then
            if dir[i] ~= t then
                prefix = false
                path = "../" .. t
            end
        else
            path = "../" .. path .. "/" .. t
        end
    end

    if #dir < #target then
        for i = #dir + 1, #target do
            path = path .. (path == "" and "" or "/") .. target[i]
        end
    elseif #dir > #target then
        for i = #target + 1, #dir do
            path = "../" .. path
        end
    end

    return path
end

function resolve_url(page_type, site_url, content_dir, base_dir, cur_file)
    if page_type == "page" then
        cur_file = cur_file:gsub("%.md$", ".html")
    elseif page_type == "feed" then
        cur_file = cur_file:gsub("%.md$", ".xml")
    end

    local abs = cur_file:gsub("^" .. content_dir, ""):gsub("/index.html$", "/")
    local rel = relative_to(base_dir, cur_file):gsub("/index.html$", "/")

    return pandoc.MetaMap({
        abs = pandoc.MetaString(abs),
        rel = pandoc.MetaString(rel),
        full = pandoc.MetaString(site_url .. abs)
    })
end

function resolve_section(abs_url)
    local section = abs_url:match("^/(.-)[/.]") or "index"
    return pandoc.MetaMap({
        id = pandoc.MetaString(section),
        ["is_" .. section] = pandoc.MetaBool(true)
    })
end

function organize_subpages(site_url, content_dir, base_dir, pages, categories)
    local categories_data = pandoc.MetaList({})

    pages:sort(function(p1, p2)
        if p1.date and p2.date then
            return pandoc.utils.stringify(p1.date.yyyy_mm_dd) > pandoc.utils.stringify(p2.date.yyyy_mm_dd)
        elseif p2.date then
            return true
        elseif p1.date then
            return false
        else
            return pandoc.utils.stringify(p1.title) < pandoc.utils.stringify(p2.title)
        end
    end)

    local pages_data = pandoc.MetaMap({
        all = pages,
        by_year = pandoc.MetaList({}),
        last_update = nil
    })

    if pages then
        local pages_by_year_map = {}
        local categories_map = {}

        for i = 1, #pages do
            local page = pages[i]

            if page.date then
                local yyyy = pandoc.utils.stringify(page.date.yyyy)
                local pages_by_yyyy = pages_by_year_map[yyyy]

                if not pages_by_yyyy then
                    pages_by_yyyy = pandoc.MetaList(pandoc.List())
                    pages_by_year_map[yyyy] = pages_by_yyyy
                end

                pages_by_yyyy:insert(page)
            end

            if page.category and categories then
                local category = pandoc.utils.stringify(page.category)

                if categories[category] then
                    local current_category = categories_map[category]

                    if not current_category then
                        current_category = pandoc.MetaMap({
                            name = pandoc.MetaString(categories[category]),
                            count = 0
                        })
                        categories_map[category] = current_category
                    end

                    current_category.count = current_category.count + 1
                end
            end
        end

        pages_data.by_year = table_to_list(pages_by_year_map, function(i1, i2)
            return i1.key > i2.key
        end)

        categories_data = table_to_list(categories_map)

        for _, item in ipairs(categories_data) do
            item.value.count = pandoc.MetaString(("%d"):format(item.value.count))
        end

        if #pages_data.by_year ~= 0 then
            pages_data.last_update = pages_data.by_year[1].value[1].last_update
        end
    end

    return pages_data, categories_data
end

function Meta(meta)
    meta.content_dir = meta.content_dir:gsub("/$", "")
    meta.site.url = pandoc.utils.stringify(meta.site.url):gsub("/$", "")
    meta.base_dir = meta.base_file:gsub("^(.*)/.-$", "%1")
    meta.type = meta.type or "page"

    meta.date = format_date(meta.date)
    if meta.last_update ~= nil then
        meta.last_update = format_date(meta.last_update)
    else
        meta.last_update = meta.date
    end

    if meta.type == "feed" then
        meta.page = pandoc.MetaMap({
            url = resolve_url("page", meta.site.url, meta.content_dir, meta.base_dir, meta.file)
        })
    end

    meta.url = resolve_url(meta.type, meta.site.url, meta.content_dir, meta.base_dir, meta.file)
    meta.section = resolve_section(meta.url.abs)
    meta.categories = meta.categories[meta.section.id]

    if meta.menus and meta.menus.main then
        for i = 1, #meta.menus.main do
            local item = meta.menus.main[i]
            item.active = pandoc.MetaBool(pandoc.utils.stringify(item.id) == meta.section.id)
        end
    end

    if meta.pages then
        local pages, categories = organize_subpages(meta.site.url, meta.content_dir, meta.base_dir, meta.pages,
                                      meta.categories)
        meta.pages = pages
        meta.categories = categories
    else
        meta.categories = nil
    end

    return meta
end