local _G = _G
local require, error, type, print = require, error, type, print
local table, pairs, tostring, tonumber = table, pairs, tostring, tonumber

module('Redis')

local socket = require('socket')       -- requires LuaSocket as a dependency

local redis_commands = {}
local network, request, response, utils = {}, {}, {}, {}, {}

local protocol = { newline = '\r\n', ok = 'OK', err = 'ERR', null = 'nil' }

local function toboolean(value) return value == 1 end

local function load_methods(proto, methods)
    local redis = _G.setmetatable ({}, _G.getmetatable(proto))
    for i, v in pairs(proto) do redis[i] = v end

    for i, v in pairs(methods) do redis[i] = v end
    return redis
end

-- ############################################################################

function network.write(client, buffer)
    local _, err = client.socket:send(buffer)
    if err then error(err) end
end

function network.read(client, len)
    if len == nil then len = '*l' end
    local line, err = client.socket:receive(len)
    if not err then return line else error('Connection error: ' .. err) end
end

-- ############################################################################

function response.read(client)
    local res    = network.read(client)
    local prefix = res:sub(1, -#res)
    local response_handler = protocol.prefixes[prefix]

    if not response_handler then 
        error("Unknown response prefix: " .. prefix)
    else
        return response_handler(client, res)
    end
end

function response.status(client, data)
    local sub = data:sub(2)
    if sub == protocol.ok then return true else return sub end
end

function response.error(client, data)
    local err_line = data:sub(2)

    if err_line:sub(1, 3) == protocol.err then
        error("Redis error: " .. err_line:sub(5))
    else
        error("Redis error: " .. err_line)
    end
end

function response.bulk(client, data)
    local str = data:sub(2)
    local len = tonumber(str)

    if not len then 
        error('Cannot parse ' .. str .. ' as data length.')
    else
        if len == -1 then return nil end
        local next_chunk = network.read(client, len + 2)
        return next_chunk:sub(1, -3);
    end
end

function response.multibulk(client, data)
    local str = data:sub(2)

    -- TODO: add a check if the returned value is indeed a number
    local list_count = tonumber(str)

    if list_count == -1 then 
        return nil
    else
        local list = {}

        if list_count > 0 then 
            for i = 1, list_count do
                table.insert(list, i, response.bulk(client, network.read(client)))
            end
        end

        return list
    end
end

function response.integer(client, data)
    local res = data:sub(2)
    local number = tonumber(res)

    if not number then
        if res == protocol.null then
            return nil
        else
            error('Cannot parse ' .. res .. ' as numeric response.')
        end
    end

    return number
end

protocol.prefixes = {
    ['+'] = response.status, 
    ['-'] = response.error, 
    ['$'] = response.bulk, 
    ['*'] = response.multibulk, 
    [':'] = response.integer, 
}

-- ############################################################################

function request.raw(client, buffer)
    -- TODO: optimize
    local bufferType = type(buffer)

    if bufferType == 'string' then
        network.write(client, buffer)
    elseif bufferType == 'table' then
        network.write(client, table.concat(buffer))
    else
        error('Argument error: ' .. bufferType)
    end

    return response.read(client)
end

function request.inline(client, command, ...)
    if arg.n == 0 then
        network.write(client, command .. protocol.newline)
    else
        local arguments = arg
        arguments.n = nil

        if #arguments > 0 then 
            arguments = table.concat(arguments, ' ')
        else 
            arguments = ''
        end

        network.write(client, command .. ' ' .. arguments .. protocol.newline)
    end

    return response.read(client)
end

function request.bulk(client, command, ...)
    local arguments = arg
    local data      = tostring(table.remove(arguments))
    arguments.n = nil

    -- TODO: optimize
    if #arguments > 0 then 
        arguments = table.concat(arguments, ' ')
    else 
        arguments = ''
    end

    return request.raw(client, { 
        command, ' ', arguments, ' ', #data, protocol.newline, data, protocol.newline 
    })
end

-- ############################################################################

local function custom(command, send, parse)
    return function(self, ...)
        local reply = send(self, command, ...)
        if parse then
            return parse(reply, command, ...)
        else
            return reply
        end
    end
end

local function bulk(command, reader)
    return custom(command, request.bulk, reader)
end

local function inline(command, reader)
    return custom(command, request.inline, reader)
end

-- ############################################################################

function connect(host, port)
    local client_socket = socket.connect(host, port)
    if not client_socket then
        error('Could not connect to ' .. host .. ':' .. port)
    end

    local redis_client = {
        socket  = client_socket, 
        raw_cmd = function(self, buffer)
            return request.raw(self, buffer .. protocol.newline)
        end, 
    }

    return load_methods(redis_client, redis_commands)
end

-- ############################################################################

redis_commands = {
    -- miscellaneous commands
    ping  = inline('PING', 
        function(response) 
            if response == 'PONG' then return true else return false end
        end
    ), 
    echo  = bulk('ECHO'),  
    -- TODO: the server returns an empty -ERR on authentication failure
    auth  = inline('AUTH'), 

    -- connection handling
    quit  = custom('QUIT', 
        function(client, command) 
            -- let's fire and forget! the connection is closed as soon 
            -- as the QUIT command is received by the server.
            network.write(client, command .. protocol.newline)
        end
    ), 

    -- commands operating on string values
    set           = bulk('SET'), 
    set_preserve  = bulk('SETNX', toboolean), 
    get           = inline('GET'), 
    get_multiple  = inline('MGET'), 
    increment     = inline('INCR'), 
    increment_by  = inline('INCRBY'), 
    decrement     = inline('DECR'), 
    decrement_by  = inline('DECRBY'), 
    exists        = inline('EXISTS', toboolean), 
    delete        = inline('DEL', toboolean), 
    type          = inline('TYPE'), 

    -- commands operating on the key space
    keys          = inline('KEYS', 
        function(response) 
            local keys = {}
            response:gsub('%w+', function(key) 
                table.insert(keys, key)
            end)
            return keys
        end
    ),
    random_key       = inline('RANDOMKEY'), 
    rename           = inline('RENAME'), 
    rename_preserve  = inline('RENAMENX'), 
    expire           = inline('EXPIRE', toboolean), 
    database_size    = inline('DBSIZE'), 

    -- commands operating on lists
    push_tail    = bulk('RPUSH'), 
    push_head    = bulk('LPUSH'), 
    list_length  = inline('LLEN'), 
    list_range   = inline('LRANGE'), 
    list_trim    = inline('LTRIM'), 
    list_index   = inline('LINDEX'), 
    list_set     = bulk('LSET'), 
    list_remove  = bulk('LREM'), 
    pop_first    = inline('LPOP'), 
    pop_last     = inline('RPOP'), 

    -- commands operating on sets
    set_add                 = inline('SADD'), 
    set_remove              = inline('SREM'), 
    set_cardinality         = inline('SCARD'), 
    set_is_member           = inline('SISMEMBER'), 
    set_intersection        = inline('SINTER'), 
    set_intersection_store  = inline('SINTERSTORE'), 
    set_members             = inline('SMEMBERS'), 

    -- multiple databases handling commands
    select_database  = inline('SELECT'), 
    move_key         = inline('MOVE'), 
    flush_database   = inline('FLUSHDB'), 
    flush_databases  = inline('FLUSHALL'), 

    -- sorting
    --[[
        TODO: should we pass sort parameters as a table? e.g: 
                params = { 
                    by    = 'weight_*', 
                    get   = 'object_*', 
                    limit = { 0, 10 },
                    sort  = { 'desc', 'alpha' }
                }
    --]]
    sort  = custom('SORT', 
        function(client, command, params)
            -- TODO: here we will put the logic needed to serialize the params 
            --       table to be sent as the argument of the SORT command.
            return request.inline(client, command, params)
        end
    ), 

    -- persistence control commands
    save             = inline('SAVE'), 
    background_save  = inline('BGSAVE'), 
    last_save        = inline('LASTSAVE'), 
    shutdown         = custom('SHUTDOWN',
        function(client, command) 
            -- let's fire and forget! the connection is closed as soon 
            -- as the SHUTDOWN command is received by the server.
            network.write(command .. protocol.newline)
        end
    ), 

    -- remote server control commands
    info  = inline('INFO', 
        function(response) 
            local info = {}
            response:gsub('([^\r\n]*)\r\n', function(kv) 
                local k,v = kv:match(('([^:]*):([^:]*)'):rep(1))
                info[k] = v
            end)
            return info
        end
    ),
}