-----------------------------------------------------------------------------
-- LTN12 - Filters, sources, sinks and pumps.
-- LuaSocket toolkit.
-- Author: Diego Nehab
-- RCS ID: $Id$
-----------------------------------------------------------------------------

-----------------------------------------------------------------------------
-- Declare module
-----------------------------------------------------------------------------
local string = require("string")
local table = require("table")
local base = _G
module("ltn12")

filter = {}
source = {}
sink = {}
pump = {}

-- 2048 seems to be better in windows...
BLOCKSIZE = 2048

-----------------------------------------------------------------------------
-- Filter stuff
-----------------------------------------------------------------------------
-- returns a high level filter that cycles a low-level filter
function filter.cycle(low, ctx, extra)
    base.assert(low)
    return function(chunk)
        local ret
        ret, ctx = low(ctx, chunk, extra)
        return ret
    end
end

-- chains a bunch of filters together
-- (thanks to Wim Couwenberg)
function filter.chain(...) 
    local n = table.getn(arg)
    local top, index = 1, 1
    local retry = ""
    return function(chunk)
        retry = chunk and retry
        while true do 
            if index == top then
                chunk = arg[index](chunk)
                if chunk == "" or top == n then return chunk
                elseif chunk then index = index + 1
                else 
                    top = top+1 
                    index = top
                end
            else
                chunk = arg[index](chunk or "")
                if chunk == "" then
                    index = index - 1
                    chunk = retry
                elseif chunk then
                    if index == n then return chunk
                    else index = index + 1 end
                else base.error("filter returned inappropriate nil") end
            end
        end
    end
end

-----------------------------------------------------------------------------
-- Source stuff
-----------------------------------------------------------------------------
-- create an empty source
local function empty()
    return nil
end

function source.empty()
    return empty
end

-- returns a source that just outputs an error
function source.error(err)
    return function()
        return nil, err
    end
end

-- creates a file source
function source.file(handle, io_err)
    if handle then
        return function()
            local chunk = handle:read(BLOCKSIZE)
            if not chunk then handle:close() end
            return chunk
        end
    else return source.error(io_err or "unable to open file") end
end

-- turns a fancy source into a simple source
function source.simplify(src)
    base.assert(src)
    return function()
        local chunk, err_or_new = src()
        src = err_or_new or src
        if not chunk then return nil, err_or_new
        else return chunk end
    end
end

-- creates string source
function source.string(s)
    if s then
        local i = 1
        return function()
            local chunk = string.sub(s, i, i+BLOCKSIZE-1)
            i = i + BLOCKSIZE
            if chunk ~= "" then return chunk
            else return nil end
        end
    else return source.empty() end
end

-- creates rewindable source
function source.rewind(src)
    base.assert(src)
    local t = {}
    return function(chunk)
        if not chunk then
            chunk = table.remove(t)
            if not chunk then return src()
            else return chunk end
        else
            table.insert(t, chunk)
        end
    end
end

local print = print

-- chains a source with a filter
function source.chain(src, f)
    base.assert(src and f)
    local last_in, last_out = "", ""
    return function()
        if last_out == "" then
            while true do
                local err
                last_in, err = src()
                if err then return nil, err end
                last_out = f(last_in)
                if last_out ~= "" then return last_out end
                if not last_in then 
                    base.error('filter returned inappropriate ""') 
                end
            end
        elseif last_out then
            last_out = f(last_in and "")
            if last_in and not last_out then
                base.error('filter returned inappropriate nil') 
            end
            if last_out == "" and not last_in then
                base.error(base.tostring(f) .. ' returned inappropriate ""') 
            end
            return last_out
        else
            base.error("source is empty", 2)
        end
    end
end

-- creates a source that produces contents of several sources, one after the
-- other, as if they were concatenated
-- (thanks to Wim Couwenberg)
function source.cat(...)
    local src = table.remove(arg, 1)
    return function()
        while src do
            local chunk, err = src()
            if chunk then return chunk end
            if err then return nil, err end
            src = table.remove(arg, 1)
        end
    end
end

-----------------------------------------------------------------------------
-- Sink stuff
-----------------------------------------------------------------------------
-- creates a sink that stores into a table
function sink.table(t)
    t = t or {}
    local f = function(chunk, err)
        if chunk then table.insert(t, chunk) end
        return 1
    end
    return f, t
end

-- turns a fancy sink into a simple sink
function sink.simplify(snk)
    base.assert(snk)
    return function(chunk, err)
        local ret, err_or_new = snk(chunk, err)
        if not ret then return nil, err_or_new end
        snk = err_or_new or snk
        return 1
    end
end

-- creates a file sink
function sink.file(handle, io_err)
    if handle then
        return function(chunk, err)
            if not chunk then 
                handle:close()
                return 1
            else return handle:write(chunk) end
        end
    else return sink.error(io_err or "unable to open file") end
end

-- creates a sink that discards data
local function null()
    return 1
end

function sink.null()
    return null
end

-- creates a sink that just returns an error
function sink.error(err)
    return function()
        return nil, err
    end
end

-- chains a sink with a filter 
function sink.chain(f, snk)
    base.assert(f and snk)
    return function(chunk, err)
        if chunk ~= "" then
            local filtered = f(chunk)
            local done = chunk and ""
            while true do
                local ret, snkerr = snk(filtered, err)
                if not ret then return nil, snkerr end
                if filtered == done then return 1 end
                filtered = f(done)
            end
        else return 1 end
    end
end

-----------------------------------------------------------------------------
-- Pump stuff
-----------------------------------------------------------------------------
-- pumps one chunk from the source to the sink
function pump.step(src, snk)
    local chunk, src_err = src()
    local ret, snk_err = snk(chunk, src_err)
    return chunk and ret and not src_err and not snk_err, src_err or snk_err
end

-- pumps all data from a source to a sink, using a step function
function pump.all(src, snk, step)
    base.assert(src and snk)
    step = step or pump.step
    while true do
        local ret, err = step(src, snk)
        if not ret then return not err, err end
    end
end

--getmetatable(_M).__index = nil