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v/vlib/flag/flag.v
2019-07-12 15:47:27 +02:00

264 lines
6.7 KiB
Go

// module flag for command-line flag parsing
//
// - parsing flags like '--flag' or '--stuff=things' or '--things stuff'
// - handles bool, int, float and string args
// - is able to pring usage
// - handled unknown arguments as error
//
// Usage example:
//
// ```v
// module main
//
// import os
// import flag
//
// fn main() {
// mut fp := flag.new_flag_parser(os.args)
// fp.application('flag_example_tool')
// fp.version('v0.0.0')
// fp.description('This tool is only designed to show how the flag lib is working')
//
// fp.skip_executable()
//
// an_int := fp.int('an_int', 666, 'some int to define 666 is default')
// a_bool := fp.bool('a_bool', false, 'some \'real\' flag')
// a_float := fp.float('a_float', 1.0, 'also floats')
// a_string := fp.string('a_string', 'no text', 'finally, some text')
//
// additional_args := fp.finalize() or {
// eprintln(err)
// println(fp.usage())
// return
// }
//
// println('
// an_int: $an_int
// a_bool: $a_bool
// a_float: $a_float
// a_string: \'$a_string\'
// ')
// println(additional_args.join_lines())
// }
// ```
module flag
// data object storing informations about a defined flag
struct Flag {
pub:
name string // name as it appears on command line
usage string // help message
val_desc string // something like '<arg>' that appears in usage
}
//
struct FlagParser {
pub mut:
args []string // the arguments to be parsed
flags []Flag // registered flags
application_name string
application_version string
application_description string
}
// create a new flag set for parsing command line arguments
pub fn new_flag_parser(args []string) &FlagParser {
return &FlagParser{args:args}
}
// change the application name to be used in 'usage' output
pub fn (fs mut FlagParser) application(n string) {
fs.application_name = n
}
// change the application version to be used in 'usage' output
pub fn (fs mut FlagParser) version(n string) {
fs.application_version = n
}
// change the application version to be used in 'usage' output
pub fn (fs mut FlagParser) description(n string) {
fs.application_description = n
}
// in most cases you do not need the first argv for flag parsing
pub fn (fs mut FlagParser) skip_executable() {
fs.args.delete(0)
}
// private helper to register a flag
fn (fs mut FlagParser) add_flag(n, u, vd string) {
fs.flags << Flag{
name: n,
usage: u
val_desc: vd
}
}
// private: general parsing a single argument
// - search args for existance
// if true
// extract the defined value as string
// else
// return an (dummy) error -> argument is not defined
//
// - the name, usage are registered
// - found arguments and corresponding values are removed from args list
fn (fs mut FlagParser) parse_value(n string) ?string {
c := '--$n'
for i, a in fs.args {
if a == c {
if fs.args.len > i+1 && fs.args[i+1].left(2) != '--' {
val := fs.args[i+1]
fs.args.delete(i+1)
fs.args.delete(i)
return val
} else {
panic('Missing argument for \'$n\'')
}
} else if a.len > c.len && c == a.left(c.len) && a.substr(c.len, c.len+1) == '=' {
val := a.right(c.len+1)
fs.args.delete(i)
return val
}
}
return error('parameter \'$n\' not found')
}
// special parsing for bool values
// see also: parse_value
//
// special: it is allowed to define bool flags without value
// -> '--flag' is parsed as true
// -> '--flag' is equal to '--flag=true'
fn (fs mut FlagParser) parse_bool_value(n string) ?string {
c := '--$n'
for i, a in fs.args {
if a == c {
if fs.args.len > i+1 && (fs.args[i+1] in ['true', 'false']) {
val := fs.args[i+1]
fs.args.delete(i+1)
fs.args.delete(i)
return val
} else {
val := 'true'
fs.args.delete(i)
return val
}
} else if a.len > c.len && c == a.left(c.len) && a.substr(c.len, c.len+1) == '=' {
val := a.right(c.len+1)
fs.args.delete(i)
return val
}
}
return error('parameter \'$n\' not found')
}
// defining and parsing a bool flag
// if defined
// the value is returned (true/false)
// else
// the default value is returned
//TODO error handling for invalid string to bool conversion
pub fn (fs mut FlagParser) bool(n string, v bool, u string) bool {
fs.add_flag(n, u, '')
parsed := fs.parse_bool_value(n) or {
return v
}
return parsed == 'true'
}
// defining and parsing an int flag
// if defined
// the value is returned (int)
// else
// the default value is returned
//TODO error handling for invalid string to int conversion
pub fn (fs mut FlagParser) int(n string, i int, u string) int {
fs.add_flag(n, u, '<int>')
parsed := fs.parse_value(n) or {
return i
}
return parsed.int()
}
// defining and parsing a flaot flag
// if defined
// the value is returned (float)
// else
// the default value is returned
//TODO error handling for invalid string to float conversion
pub fn (fs mut FlagParser) float(n string, f f32, u string) f32 {
fs.add_flag(n, u, '<float>')
parsed := fs.parse_value(n) or {
return f
}
return parsed.f32()
}
// defining and parsing a string flag
// if defined
// the value is returned (string)
// else
// the default value is returned
pub fn (fs mut FlagParser) string(n, v, u string) string {
fs.add_flag(n, u, '<arg>')
parsed := fs.parse_value(n) or {
return v
}
return parsed
}
const (
// used for formating usage message
SPACE = ' '
)
// collect all given information and
pub fn (fs FlagParser) usage() string {
mut use := '\n'
use += 'usage ${fs.application_name} [options] [ARGS]\n'
use += '\n'
if fs.flags.len > 0 {
use += 'options:\n'
for f in fs.flags {
flag_desc := ' --$f.name $f.val_desc'
space := if flag_desc.len > SPACE.len-2 {
'\n$SPACE'
} else {
SPACE.right(flag_desc.len)
}
use += '$flag_desc$space$f.usage\n'
}
}
use += '\n'
use += '$fs.application_name $fs.application_version\n'
if fs.application_description != '' {
use += '\n'
use += 'description:\n'
use += '$fs.application_description'
}
return use
}
// finalize argument parsing -> call after all arguments are defined
//
// all remaining arguments are returned in the same order they are defined on
// commandline
//
// if additional flag are found (things starting with '--') an error is returned
// error handling is up to the application developer
pub fn (fs FlagParser) finalize() ?[]string {
for a in fs.args {
if a.left(2) == '--' {
return error('Unknown argument \'${a.right(2)}\'')
}
}
return fs.args
}