local mt = {}

local function _new_block(v)
    local block = {
        value = v,
        next = false,
        prev = false,
    }
    return block
end

local endian_fmt = {
    ["little"] = "<",
    ["big"] = ">",
}
local function pack_data(data, header_len, endian)
    local len = #data
    local fmt = endian_fmt[endian] .. "I" .. header_len .. "c" .. (len)
    return string.pack(fmt, len, data)
end

local function insert_free_list(self, block)
    block.prev = false
    block.next = false
    local count = self.v_free_list_count
    count = count + 1
    self.v_free_list_count = count
    self.v_free_list[count] = block
end

local function get_block(self)
    local count = self.v_free_list_count
    if count > 0 then
        local block = self.v_free_list[count]
        self.v_free_list[count] = nil
        self.v_free_list_count = count - 1
        return block
    else
        return _new_block()
    end
end

local function free_block(self, block)
    local next = block.next
    local prev = block.prev

    if next then
        next.prev = prev
    end

    if prev then
        prev.next = next
    end
    insert_free_list(self, block)
end

local function init_buffer(self)
    local DEF_FREE_BLOCK = 3

    for _ = 1, DEF_FREE_BLOCK do
        insert_free_list(self, _new_block())
    end
end

local function create()
    local raw = {
        v_free_list = {},
        v_free_list_count = 0,

        v_block_head = false,
        v_block_tail = false,
        v_size = 0,
    }

    init_buffer(raw)
    setmetatable(raw, {
        __index = mt,
    })
    return raw
end

function mt:push(data)
    local block = get_block(self)
    block.value = data
    local size = self.v_size
    self.v_size = size + #data

    if not self.v_block_head then
        assert(self.v_block_tail == false)
        self.v_block_head = block
    end

    local tail = self.v_block_tail
    if tail then
        tail.next = block
        block.prev = tail
        block.next = false
    end

    self.v_block_tail = block
end

local buff = {}
function mt:look(nbytes)
    local head = self.v_block_head
    local size = self.v_size
    if head and nbytes > 0 and size >= nbytes then
        local count = 0
        local index = 0
        while head and count ~= nbytes do
            local value = head.value
            local len = #(value)
            if count + len > nbytes then
                local sub = nbytes - count
                value = string.sub(value, 1, sub)
                count = count + sub
            else
                count = count + len
            end
            index = index + 1
            buff[index] = value
            head = head.next
        end
        return table.concat(buff, "", 1, index)
    end
    return false
end

function mt:pop(nbytes)
    local head = self.v_block_head
    nbytes = nbytes or (head and #(head.value))
    if head and nbytes > 0 and self.v_size >= nbytes then
        local count = 0
        local index = 0
        while head and count ~= nbytes do
            local len = #(head.value)
            index = index + 1
            if count + len > nbytes then
                local sub = nbytes - count
                local value = head.value
                local sub_value = string.sub(value, 1, sub)
                buff[index] = sub_value
                count = count + sub
                head.value = string.sub(value, sub + 1)
            else
                count = count + len
                buff[index] = head.value
                local next = head.next
                free_block(self, head)
                head = next
            end
        end

        self.v_block_head = head
        self.v_size = self.v_size - count
        if not head then
            self.v_block_tail = false
        end
        local ret = table.concat(buff, "", 1, index)
        assert(#ret == nbytes)
        return ret
    end
    return false
end

function mt:pop_all(out)
    local v = self:pop()
    local count = 0

    while v do
        count = count + 1
        out[count] = v
        v = self:pop()
    end
    return count
end

function mt:push_block(data, header_len, endian)
    data = pack_data(data, header_len, endian)
    self:push(data)
end

function mt:pop_block(header_len, endian)
    if self.v_size > header_len then
        local header = self:look(header_len)
        local fmt = endian_fmt[endian] .. "I" .. header_len
        -- local fmt = endian_fmt[endian].."H"
        local len = string.unpack(fmt, header)
        if self.v_size >= len + header_len then
            self:pop(header_len)
            return self:pop(len)
        end
    end
    return false
end

function mt:pop_all_block(out, header_len, endian)
    local v = self:pop_block(header_len, endian)
    local count = 0

    while v do
        count = count + 1
        out[count] = v
        v = self:pop_block(header_len, endian)
    end
    return count
end

function mt:clear()
    local head = self.v_block_head
    while head do
        insert_free_list(self, head)
        head = head.next
    end
    self.v_block_head = false
    self.v_block_tail = false
    self.v_size = 0
end

function mt:get_head_data()
    local head = self.v_block_head
    return head and head.value or false
end

---- for test
local function _dump_list(list)
    while list do
        print(" node = ", list)
        for k, v in pairs(list) do
            print(" ", k, v)
        end
        print("----------")
        list = list.next
    end
end

function mt:dump()
    print("==== meta info ====")
    for k, v in pairs(self) do
        print(k, v)
    end

    print("===== free list ====", self.v_free_list_count)
    local free_list = self.v_free_list
    for k, v in pairs(free_list) do
        print(k, v)
    end

    print("===== head list ====")
    _dump_list(self.v_block_head)
end

return {
    create = create,
    pack_data = pack_data,
}