local path = require 'pandoc.path'

function format_date(date)
    if not date 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 not year then return nil end

    local time = os.time({ year = tonumber(year), month = tonumber(month), day = tonumber(day) })
    return {
        yyyy_mm_dd = os.date("%F", time),
        yyyy = os.date("%Y", time),
        mm = os.date("%m", time),
        dd = os.date("%d", time),
        rfc3339 = os.date("%FT%T+00:00", time),
        long = os.date("%B %d, %Y", time),
        short = os.date("%b %d, %y", time),
    }
end

function table_to_list(t, kv, cmp)
    local l = pandoc.List()

    if kv then
        for key, value in pairs(t) do l:insert({ key = key, value = value }) end
    else
        for _, value in pairs(t) do l:insert(value) end
    end

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

    return l
end

function group_by(l, field, insert)
    insert = insert or function(group, _, item)
        if not group then
            group = l:new({ item })
            return group
        end
        group:insert(item)
    end

    local groups = {}

    for i = 1, #l do
        local item = l[i]
        local f = field(item)

        if f then
            local out = insert(groups[f], f, item)
            if out then groups[f] = out end
        end
    end

    return groups
end

function make_absolute(rel, base)
    return path.is_absolute(rel) and rel or path.join({ path.directory(base), rel })
end

function resolve_url(site_url, ref_file, target_file)
    target_file = target_file:gsub("/index%.html$", "/")

    local ref_base_dir = path.directory(ref_file)
    local abs = target_file
    local rel = path.make_relative(abs, ref_base_dir, true)

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

function resolve_layout(layout)
    if layout then
        layout = pandoc.utils.stringify(layout)
        return { id = layout, ["is_" .. layout] = true }
    end
end

function resolve_namespace(namespace)
    namespace = pandoc.utils.stringify(namespace)

    local root = "index"
    if namespace ~= "" then root = namespace:gsub("^/([^/]*).*$", "%1") end

    return { root = { id = root, ["is_" .. root] = true }, full = namespace }
end

function prep_menu(active_id, main_menu)
    local active_item = nil

    for i = 1, #main_menu do
        local item = main_menu[i]
        local active = pandoc.utils.stringify(item.id) == active_id
        item.active = active
        if active then active_item = item end
    end

    return {
        items = main_menu:filter(function(item) return not item.hidden or item.active end),
        active = active_item,
    }
end

function process_pages(global, pages_by_id)
    if not pages_by_id then return nil end

    local pages_all = pandoc.List()
    local pages_asc_title = pandoc.List()
    local pages_desc_date = pandoc.List()

    for _, page in pairs(pages_by_id) do
        local p = process(global, page)
        pages_all:insert(p)
        pages_asc_title:insert(p)
        if p.date then pages_desc_date:insert(p) end
    end

    pages_all:sort(function(p1, p2)
        if p1.position then
            if p2.position then
                return tonumber(p1.position) < tonumber(p2.position)
            else
                return true
            end
        elseif p2.position then
            return false
        elseif p1.date then
            if p2.date then
                return p1.date.yyyy_mm_dd > p2.date.yyyy_mm_dd
            else
                return true
            end
        elseif p2.date then
            return false
        else
            return p1.title < p2.title
        end
    end)

    pages_desc_date:sort(function(p1, p2)
        if p1.position then
            if p2.position then
                return tonumber(p1.position) < tonumber(p2.position)
            else
                return true
            end
        else
            return p1.date.yyyy_mm_dd > p2.date.yyyy_mm_dd
        end
    end)

    pages_asc_title:sort(function(p1, p2)
        if p1.position then
            if p2.position then
                return tonumber(p1.position) < tonumber(p2.position)
            else
                return true
            end
        elseif p2.position then
            return false
        else
            return p1.title < p2.title
        end
    end)

    local pages_data = {
        all = pages_all,
        desc_date = pages_desc_date,
        asc_title = pages_asc_title,
        by_id = pages_by_id,
    }

    return pages_data
end

local titlecase_exceptions = pandoc.List({
    "a", "an", "and", "as", "at", "but", "by", "en", "for", "if", "in", "nor", "of", "on", "or",
    "per", "the", "to", "v%.?", "vs%.?", "via",
})

function titlecase(str)
    return str:gsub("(%S)(%S*)(%s*)", function(a, b, space)
        local word = a .. b
        local is_exception = word:match("%u") or
                                 titlecase_exceptions:find_if(
                function(exception) return word:match("^" .. exception .. "$") end)
        if is_exception then return word .. space end
        return string.upper(a) .. b .. space
    end)
end

function process(global, meta)
    meta.namespace = resolve_namespace(meta.namespace)
    meta.file_out = pandoc.utils.stringify(meta.file_out):gsub("^out", "")
    meta.layout = resolve_layout(meta.layout)
    meta.url = resolve_url(global.site.url, global.file_out, meta.file_out)
    meta.title = (meta.title and titlecase(pandoc.utils.stringify(meta.title))) or ""

    if meta.position then meta.position = pandoc.utils.stringify(meta.position) end

    if meta.create_feed then
        if meta.file_out:match(".html$") then
            meta.feed = {
                url = resolve_url(global.site.url, global.file_out,
                    meta.file_out:gsub(".html$", ".xml")),
            }
        else
            meta.page = {
                url = resolve_url(global.site.url, global.file_out,
                    meta.file_out:gsub(".xml$", ".html")),
            }
        end
    end

    if meta.preview then
        meta.preview = make_absolute(pandoc.utils.stringify(meta.preview), meta.file_out)
        meta.preview = resolve_url(global.site.url, global.file_out, meta.preview)
    end

    if meta.menus and meta.menus.main then
        meta.menus.main = prep_menu(meta.namespace.root.id, meta.menus.main)
    end

    meta.pages = process_pages(global, meta.pages)

    if meta.date then
        meta.date = format_date(meta.date)
    elseif meta.pages and #meta.pages.desc_date ~= 0 then
        meta.date = meta.pages.desc_date[1].date
    end

    if meta.last_update then
        meta.last_update = format_date(meta.last_update)
    elseif meta.pages and #meta.pages.desc_date ~= 0 then
        meta.last_update = meta.pages.desc_date[1].last_update
    elseif meta.date then
        meta.last_update = meta.date
    end

    return meta
end

function Meta(meta)
    meta.site.url = pandoc.utils.stringify(meta.site.url):gsub("/$", "")

    return process(meta, meta)
end