# timer.tcl - Tk countdown timer
# Usage: timer.tcl <seconds>
#   Creates a Tk window displaying the remaining seconds, counts down to zero,
#   then exits with code 0.

if {[catch {package require tk}]} {
    package require Tk
}

if {$::argc < 1} {
    puts stderr "Usage: [file tail [info script]] <seconds>"
    exit 1
}

set seconds [lindex $::argv 0]
if {![string is integer -strict $seconds] || $seconds < 0} {
    puts stderr "timer: seconds must be a non-negative integer (got '$seconds')"
    exit 1
}

# Track the absolute end time so drift in `after` scheduling does not skew the count.
set ::timer_end [expr {[clock milliseconds] + $seconds * 1000}]

proc timer_tick {} {
    set remaining [expr {$::timer_end - [clock milliseconds]}]
    if {$remaining <= 0} {
        .clock configure -text 0
        exit 0
    }
    .clock configure -text [expr {int(($remaining + 999) / 1000)}]
    after 100 timer_tick
}

label .clock -text $seconds -font {TkTextFont 48} -padx 40 -pady 30
pack .clock -expand 1 -anchor center

wm title . "Timer: $seconds s"
after 100 timer_tick