--- Generally useful routines.
-- See  @{01-introduction.md.Generally_useful_functions|the Guide}.
-- @module pl.utils
local format,gsub,byte = string.format,string.gsub,string.byte
local clock = os.clock
local stdout = io.stdout
local append = table.insert

local collisions = {}

local utils = {}

utils._VERSION = "1.0.3"

local lua51 = rawget(_G,'setfenv')

utils.lua51 = lua51
if not lua51 then -- Lua 5.2 compatibility
    unpack = table.unpack
    loadstring = load
end

utils.dir_separator = _G.package.config:sub(1,1)

--- end this program gracefully.
-- @param code The exit code or a message to be printed
-- @param ... extra arguments for message's format'
-- @see utils.fprintf
function utils.quit(code,...)
    if type(code) == 'string' then
        utils.fprintf(io.stderr,code,...)
        code = -1
    else
        utils.fprintf(io.stderr,...)
    end
    io.stderr:write('\n')
    os.exit(code)
end

--- print an arbitrary number of arguments using a format.
-- @param fmt The format (see string.format)
-- @param ... Extra arguments for format
function utils.printf(fmt,...)
    utils.assert_string(1,fmt)
    utils.fprintf(stdout,fmt,...)
end

--- write an arbitrary number of arguments to a file using a format.
-- @param f File handle to write to.
-- @param fmt The format (see string.format).
-- @param ... Extra arguments for format
function utils.fprintf(f,fmt,...)
    utils.assert_string(2,fmt)
    f:write(format(fmt,...))
end

local function import_symbol(T,k,v,libname)
    local key = rawget(T,k)
    -- warn about collisions!
    if key and k ~= '_M' and k ~= '_NAME' and k ~= '_PACKAGE' and k ~= '_VERSION' then
        utils.printf("warning: '%s.%s' overrides existing symbol\n",libname,k)
    end
    rawset(T,k,v)
end

local function lookup_lib(T,t)
    for k,v in pairs(T) do
        if v == t then return k end
    end
    return '?'
end

local already_imported = {}

--- take a table and 'inject' it into the local namespace.
-- @param t The Table
-- @param T An optional destination table (defaults to callers environment)
function utils.import(t,T)
    T = T or _G
    t = t or utils
    if type(t) == 'string' then
        t = require (t)
    end
    local libname = lookup_lib(T,t)
    if already_imported[t] then return end
    already_imported[t] = libname
    for k,v in pairs(t) do
        import_symbol(T,k,v,libname)
    end
end

utils.patterns = {
    FLOAT = '[%+%-%d]%d*%.?%d*[eE]?[%+%-]?%d*',
    INTEGER = '[+%-%d]%d*',
    IDEN = '[%a_][%w_]*',
    FILE = '[%a%.\\][:%][%w%._%-\\]*'
}

--- escape any 'magic' characters in a string
-- @param s The input string
function utils.escape(s)
    utils.assert_string(1,s)
    return (s:gsub('[%-%.%+%[%]%(%)%$%^%%%?%*]','%%%1'))
end

--- return either of two values, depending on a condition.
-- @param cond A condition
-- @param value1 Value returned if cond is true
-- @param value2 Value returned if cond is false (can be optional)
function utils.choose(cond,value1,value2)
    if cond then return value1
    else return value2
    end
end

local raise

--- return the contents of a file as a string
-- @param filename The file path
-- @param is_bin open in binary mode
-- @return file contents
function utils.readfile(filename,is_bin)
    local mode = is_bin and 'b' or ''
    utils.assert_string(1,filename)
    local f,err = io.open(filename,'r'..mode)
    if not f then return utils.raise (err) end
    local res,err = f:read('*a')
    f:close()
    if not res then return raise (err) end
    return res
end

--- write a string to a file
-- @param filename The file path
-- @param str The string
-- @return true or nil
-- @return error message
-- @raise error if filename or str aren't strings
function utils.writefile(filename,str)
    utils.assert_string(1,filename)
    utils.assert_string(2,str)
    local f,err = io.open(filename,'w')
    if not f then return raise(err) end
    f:write(str)
    f:close()
    return true
end

--- return the contents of a file as a list of lines
-- @param filename The file path
-- @return file contents as a table
-- @raise errror if filename is not a string
function utils.readlines(filename)
    utils.assert_string(1,filename)
    local f,err = io.open(filename,'r')
    if not f then return raise(err) end
    local res = {}
    for line in f:lines() do
        append(res,line)
    end
    f:close()
    return res
end

--- split a string into a list of strings separated by a delimiter.
-- @param s The input string
-- @param re A Lua string pattern; defaults to '%s+'
-- @param plain don't use Lua patterns
-- @param n optional maximum number of splits
-- @return a list-like table
-- @raise error if s is not a string
function utils.split(s,re,plain,n)
    utils.assert_string(1,s)
    local find,sub,append = string.find, string.sub, table.insert
    local i1,ls = 1,{}
    if not re then re = '%s+' end
    if re == '' then return {s} end
    while true do
        local i2,i3 = find(s,re,i1,plain)
        if not i2 then
            local last = sub(s,i1)
            if last ~= '' then append(ls,last) end
            if #ls == 1 and ls[1] == '' then
                return {}
            else
                return ls
            end
        end
        append(ls,sub(s,i1,i2-1))
        if n and #ls == n then
            ls[#ls] = sub(s,i1)
            return ls
        end
        i1 = i3+1
    end
end

--- split a string into a number of values.
-- @param s the string
-- @param re the delimiter, default space
-- @return n values
-- @usage first,next = splitv('jane:doe',':')
-- @see split
function utils.splitv (s,re)
    return unpack(utils.split(s,re))
end

local lua51_load = load

if utils.lua51 then -- define Lua 5.2 style load()
    function utils.load(str,src,mode,env)
        local chunk,err
        if type(str) == 'string' then
            chunk,err = loadstring(str,src)
        else
            chunk,err = lua51_load(str,src)
        end
        if chunk and env then setfenv(chunk,env) end
        return chunk,err
    end
else
    utils.load = load
    -- setfenv/getfenv replacements for Lua 5.2
    -- by Sergey Rozhenko
    -- http://lua-users.org/lists/lua-l/2010-06/msg00313.html
    -- Roberto Ierusalimschy notes that it is possible for getfenv to return nil
    -- in the case of a function with no globals:
    -- http://lua-users.org/lists/lua-l/2010-06/msg00315.html
    function setfenv(f, t)
        f = (type(f) == 'function' and f or debug.getinfo(f + 1, 'f').func)
        local name
        local up = 0
        repeat
            up = up + 1
            name = debug.getupvalue(f, up)
        until name == '_ENV' or name == nil
        if name then
            debug.upvaluejoin(f, up, function() return name end, 1) -- use unique upvalue
            debug.setupvalue(f, up, t)
        end
        if f ~= 0 then return f end
    end

    function getfenv(f)
        local f = f or 0
        f = (type(f) == 'function' and f or debug.getinfo(f + 1, 'f').func)
        local name, val
        local up = 0
        repeat
            up = up + 1
            name, val = debug.getupvalue(f, up)
        until name == '_ENV' or name == nil
        return val
    end
end


--- execute a shell command.
-- This is a compatibility function that returns the same for Lua 5.1 and Lua 5.2
-- @param cmd a shell command
-- @return true if successful
-- @return actual return code
function utils.execute (cmd)
    local res1,res2,res2 = os.execute(cmd)
    if lua51 then
        return res1==0,res1
    else
        return res1,res2
    end
end

if lua51 then
    function table.pack (...)
        local n = select('#',...)
        return {n=n; ...}
    end
    local sep = package.config:sub(1,1)
    function package.searchpath (mod,path)
        mod = mod:gsub('%.',sep)
        for m in path:gmatch('[^;]+') do
            local nm = m:gsub('?',mod)
            local f = io.open(nm,'r')
            if f then f:close(); return nm end
        end
    end
end

if not table.pack then table.pack = _G.pack end
if not rawget(_G,"pack") then _G.pack = table.pack end

--- take an arbitrary set of arguments and make into a table.
-- This returns the table and the size; works fine for nil arguments
-- @param ... arguments
-- @return table
-- @return table size
-- @usage local t,n = utils.args(...)

--- 'memoize' a function (cache returned value for next call).
-- This is useful if you have a function which is relatively expensive,
-- but you don't know in advance what values will be required, so
-- building a table upfront is wasteful/impossible.
-- @param func a function of at least one argument
-- @return a function with at least one argument, which is used as the key.
function utils.memoize(func)
    return setmetatable({}, {
        __index = function(self, k, ...)
            local v = func(k,...)
            self[k] = v
            return v
        end,
        __call = function(self, k) return self[k] end
    })
end

--- is the object either a function or a callable object?.
-- @param obj Object to check.
function utils.is_callable (obj)
    return type(obj) == 'function' or getmetatable(obj) and getmetatable(obj).__call
end

--- is the object of the specified type?.
-- If the type is a string, then use type, otherwise compare with metatable
-- @param obj An object to check
-- @param tp String of what type it should be
function utils.is_type (obj,tp)
    if type(tp) == 'string' then return type(obj) == tp end
    local mt = getmetatable(obj)
    return tp == mt
end

local fileMT = getmetatable(io.stdout)

--- a string representation of a type.
-- For tables with metatables, we assume that the metatable has a `_name`
-- field. Knows about Lua file objects.
-- @param obj an object
-- @return a string like 'number', 'table' or 'List'
function utils.type (obj)
    local t = type(obj)
    if t == 'table' or t == 'userdata' then
        local mt = getmetatable(obj)
        if mt == fileMT then
            return 'file'
        else
            return mt._name or "unknown "..t
        end
    else
        return t
    end
end

--- is this number an integer?
-- @param x a number
-- @raise error if x is not a number
function utils.is_integer (x)
    return math.ceil(x)==x
end

utils.stdmt = {
    List = {_name='List'}, Map = {_name='Map'},
    Set = {_name='Set'}, MultiMap = {_name='MultiMap'}
}

local _function_factories = {}

--- associate a function factory with a type.
-- A function factory takes an object of the given type and
-- returns a function for evaluating it
-- @param mt metatable
-- @param fun a callable that returns a function
function utils.add_function_factory (mt,fun)
    _function_factories[mt] = fun
end

local function _string_lambda(f)
    local raise = utils.raise
    if f:find '^|' or f:find '_' then
        local args,body = f:match '|([^|]*)|(.+)'
        if f:find '_' then
            args = '_'
            body = f
        else
            if not args then return raise 'bad string lambda' end
        end
        local fstr = 'return function('..args..') return '..body..' end'
        local fn,err = loadstring(fstr)
        if not fn then return raise(err) end
        fn = fn()
        return fn
    else return raise 'not a string lambda'
    end
end

--- an anonymous function as a string. This string is either of the form
-- '|args| expression' or is a function of one argument, '_'
-- @param lf function as a string
-- @return a function
-- @usage string_lambda '|x|x+1' (2) == 3
-- @usage string_lambda '_+1 (2) == 3
-- @function utils.string_lambda
utils.string_lambda = utils.memoize(_string_lambda)

local ops

--- process a function argument.
-- This is used throughout Penlight and defines what is meant by a function:
-- Something that is callable, or an operator string as defined by <code>pl.operator</code>,
-- such as '>' or '#'. If a function factory has been registered for the type, it will
-- be called to get the function.
-- @param idx argument index
-- @param f a function, operator string, or callable object
-- @param msg optional error message
-- @return a callable
-- @raise if idx is not a number or if f is not callable
-- @see utils.is_callable
function utils.function_arg (idx,f,msg)
    utils.assert_arg(1,idx,'number')
    local tp = type(f)
    if tp == 'function' then return f end  -- no worries!
    -- ok, a string can correspond to an operator (like '==')
    if tp == 'string' then
        if not ops then ops = require 'pl.operator'.optable end
        local fn = ops[f]
        if fn then return fn end
        local fn, err = utils.string_lambda(f)
        if not fn then error(err..': '..f) end
        return fn
    elseif tp == 'table' or tp == 'userdata' then
        local mt = getmetatable(f)
        if not mt then error('not a callable object',2) end
        local ff = _function_factories[mt]
        if not ff then
            if not mt.__call then error('not a callable object',2) end
            return f
        else
            return ff(f) -- we have a function factory for this type!
        end
    end
    if not msg then msg = " must be callable" end
    if idx > 0 then
        error("argument "..idx..": "..msg,2)
    else
        error(msg,2)
    end
end

--- bind the first argument of the function to a value.
-- @param fn a function of at least two values (may be an operator string)
-- @param p a value
-- @return a function such that f(x) is fn(p,x)
-- @raise same as @{function_arg}
-- @see pl.func.curry
function utils.bind1 (fn,p)
    fn = utils.function_arg(1,fn)
    return function(...) return fn(p,...) end
end

--- bind the second argument of the function to a value.
-- @param fn a function of at least two values (may be an operator string)
-- @param p a value
-- @return a function such that f(x) is fn(x,p)
-- @raise same as @{function_arg}
function utils.bind2 (fn,p)
    fn = utils.function_arg(1,fn)
    return function(x,...) return fn(x,p,...) end
end


--- assert that the given argument is in fact of the correct type.
-- @param n argument index
-- @param val the value
-- @param tp the type
-- @param verify an optional verfication function
-- @param msg an optional custom message
-- @param lev optional stack position for trace, default 2
-- @raise if the argument n is not the correct type
-- @usage assert_arg(1,t,'table')
-- @usage assert_arg(n,val,'string',path.isdir,'not a directory')
function utils.assert_arg (n,val,tp,verify,msg,lev)
    if type(val) ~= tp then
        error(("argument %d expected a '%s', got a '%s'"):format(n,tp,type(val)),lev or 2)
    end
    if verify and not verify(val) then
        error(("argument %d: '%s' %s"):format(n,val,msg),lev or 2)
    end
end

--- assert the common case that the argument is a string.
-- @param n argument index
-- @param val a value that must be a string
-- @raise val must be a string
function utils.assert_string (n,val)
    utils.assert_arg(n,val,'string',nil,nil,3)
end

local err_mode = 'default'

--- control the error strategy used by Penlight.
-- Controls how <code>utils.raise</code> works; the default is for it
-- to return nil and the error string, but if the mode is 'error' then
-- it will throw an error. If mode is 'quit' it will immediately terminate
-- the program.
-- @param mode - either 'default', 'quit'  or 'error'
-- @see utils.raise
function utils.on_error (mode)
    err_mode = mode
end

--- used by Penlight functions to return errors.  Its global behaviour is controlled
-- by <code>utils.on_error</code>
-- @param err the error string.
-- @see utils.on_error
function utils.raise (err)
    if err_mode == 'default' then return nil,err
    elseif err_mode == 'quit' then utils.quit(err)
    else error(err,2)
    end
end

raise = utils.raise

--- load a code string or bytecode chunk.
-- @param code Lua code as a string or bytecode
-- @param name for source errors
-- @param mode kind of chunk, 't' for text, 'b' for bytecode, 'bt' for all (default)
-- @param env  the environment for the new chunk (default nil)
-- @return compiled chunk
-- @return error message (chunk is nil)
-- @function utils.load


--- Lua 5.2 Compatible Functions
-- @section lua52

--- pack an argument list into a table.
-- @param ... any arguments
-- @return a table with field n set to the length
-- @return the length
-- @function table.pack

------
-- return the full path where a Lua module name would be matched.
-- @param mod module name, possibly dotted
-- @param path a path in the same form as package.path or package.cpath
-- @see path.package_path
-- @function package.searchpath

return utils