What this page does

Imports the core Tkinter module that provides all windowing and widget capabilities.

Code (this page)

import tkinter as tk

Explanation

• tkinter is Python's standard GUI library
• Aliased as tk for shorter references throughout the code
• Provides windows, buttons, labels, and layout management
• No application logic runs yet—this only makes GUI tools available

Why this matters

Without this import, Python cannot create windows or any visual interface. This single line unlocks the entire GUI capability of the application.

What this page does

Imports the time module for clock display and accurate countdown timing.

Code (this page)

import time

Explanation

• time.strftime() formats the current time for the clock display
• time.monotonic() provides a clock that never goes backward
• Standard library module with no external dependencies
• Essential for both display and countdown accuracy

Why this matters

Without the time module, we couldn't display the current time or measure elapsed time accurately. The monotonic clock is critical for drift-free countdown timing.

What this page does

Imports the Optional type hint for expressing nullable values.

Code (this page)

from typing import Optional

Explanation

• Optional[float] means "either a float or None"
• Used for timing variables that may be unset
• Improves code clarity and enables IDE support
• No runtime cost—purely for documentation and tooling

Why this matters

Without Optional, return types like "float or None" would be ambiguous. This type hint documents intent directly in variable declarations.

What this page does

Creates a dedicated object to hold all mutable runtime state of the countdown timer.

Code (this page)

class TimerState:
    """Transient runtime state for the countdown timer."""

    def __init__(self, duration_seconds: int):
        self.remaining_seconds: int = duration_seconds
        self.is_running: bool = False
        self.alarm_triggered: bool = False

Explanation

• remaining_seconds tracks how much time is left on the countdown
• is_running indicates whether the timer is actively counting down
• alarm_triggered prevents the alarm from firing more than once
• Takes initial duration as parameter (comes from app constant)
• This object is never saved to disk—it exists only while running

Why this matters

Without a dedicated state object, timer variables would be scattered. This creates a single source of truth for runtime behavior. State transitions (start, pause, reset, alarm) all modify this one object.

What this page does

Defines the main application controller that owns the window, state, and behavior.

Code (this page)

class StudyTimerApp:
    """Main application controller."""

Explanation

• All application behavior will live inside this class
• This object coordinates UI, timing, and state
• External code interacts only through this controller
• No logic is executed yet—this establishes structure

Why this matters

Without a central controller, behavior would be distributed across functions and global variables. This class becomes the single entry point for understanding the application.

What this page does

Declares fixed timing values used throughout the application.

Code (this page)

# Timing constants
    TICK_INTERVAL_MS = 200
    CLOCK_UPDATE_MS = 1000

Explanation

• TICK_INTERVAL_MS controls how often the timer logic runs (200ms = 5 times per second)
• CLOCK_UPDATE_MS controls how often the clock display updates (1000ms = once per second)
• Constants are defined once and reused everywhere
• Class-level constants shared by all instances

Why this matters

Without named constants, 200 and 1000 would appear scattered throughout the code. Changing timing behavior would require hunting through multiple locations. This centralizes timing decisions.

What this page does

Declares the hardcoded countdown duration used by the timer.

Code (this page)

DEFAULT_DURATION = 25 * 60  # 25 minutes in seconds

Explanation

• 25 minutes is the classic Pomodoro technique duration
• Stored in seconds (1500) for internal calculations
• Expression 25 * 60 is clearer than raw 1500
• This is a class constant—hardcoded, not user-configurable

Why this matters

Foundation stage uses hardcoded values. This constant is the single source of truth for the countdown duration. Later stages (Configuration) will replace this with user-adjustable settings.

What this page does

Creates the initialization method that sets up the application.

Code (this page)

def __init__(self, root: tk.Tk):
        self.root = root
        self.root.title("Academic Study Timer")
        self.root.resizable(False, False)

Explanation

• Stores the Tk root window for later use
• Sets a descriptive window title
• Prevents resizing to preserve layout integrity
• Type hint tk.Tk documents the expected argument

Why this matters

Without storing the root window, later methods cannot schedule callbacks or modify the window. Without disabling resize, users could break the layout.

What this page does

Creates the initial runtime timer state using the hardcoded default duration.

Code (this page)

# Timer state
        self.timer_state = TimerState(self.DEFAULT_DURATION)

Explanation

• Instantiates TimerState with the hardcoded duration constant
• Sets remaining_seconds to 1500 (25 minutes)
• Initializes timer in a non-running, non-alarmed state
• Creates the single source of truth for runtime behavior

Why this matters

Without creating TimerState, there would be no countdown to manage. Using the class constant ensures consistency between initialization and reset.

What this page does

Sets up internal variables used for accurate time tracking.

Code (this page)

# Timing bookkeeping
        self._last_tick_time: Optional[float] = None
        self._accumulated_time: float = 0.0

Explanation

• _last_tick_time stores the previous tick timestamp (None when not running)
• _accumulated_time stores fractional seconds between ticks
• Both prefixed with _ to indicate internal use
• These prevent timing drift and handle tick jitter

Why this matters

Without tracking elapsed time between ticks, the countdown would drift based on UI responsiveness. Without accumulating fractional seconds, the timer would lose precision.

What this page does

Delegates all UI creation to a dedicated method.

Code (this page)

# Build UI
        self._build_ui()

Explanation

• Calls a separate method to construct all widgets
• Keeps __init__ readable and linear
• Ensures UI is built after all state is initialized
• Method will be defined later in the code

Why this matters

Without delegation, `__init__` would grow to hundreds of lines. Separating "prepare data" from "build visuals" keeps code organized and maintainable.

What this page does

Starts the recurring clock update and timer tick loops.

Code (this page)

# Start background updates
        self._update_clock()
        self._tick()

Explanation

• _update_clock() updates the live time display every second
• _tick() drives the countdown logic at regular intervals
• Both methods reschedule themselves using root.after()
• No threads are created—all execution stays in Tkinter's event loop

Why this matters

Without background updates, the clock would freeze and the timer would never count down. Using `root.after()` keeps the UI responsive without threading complexity.

What this page does

Creates the top-level layout frame that holds all widgets.

Code (this page)

def _build_ui(self):
        """Construct all UI elements."""
        # Main container
        main_frame = tk.Frame(self.root, padx=20, pady=20)
        main_frame.pack(fill=tk.BOTH, expand=True)

Explanation

• main_frame serves as the root container for all UI elements
• Padding (padx, pady) creates visual spacing from window edges
• fill and expand allow the frame to occupy all available space
• All subsequent UI elements will attach to this frame

Why this matters

Without a container frame, widgets would attach directly to the root window, making layout changes difficult. This establishes a single containment hierarchy.

What this page does

Creates a horizontal container for the live clock display.

Code (this page)

# Clock header
        clock_frame = tk.Frame(main_frame)
        clock_frame.pack(fill=tk.X, pady=(0, 15))

Explanation

• clock_frame contains the clock label and value
• fill=tk.X stretches horizontally to match parent width
• pady=(0, 15) adds 15 pixels of space below (asymmetric padding)
• Separates clock from the timer display below

Why this matters

Without a dedicated frame, clock elements would mix with timer elements. The bottom padding creates clear visual separation between header and body.

What this page does

Adds the "Current Time:" text label that never changes.

Code (this page)

tk.Label(
            clock_frame,
            text="Current Time:",
            font=("TkDefaultFont", 10)
        ).pack(side=tk.LEFT)

Explanation

• Creates a Label widget with static text
• Uses system default font at size 10
• Packs to the left side of clock_frame
• Not stored in a variable—never needs updating

Why this matters

Without a label, users would see a time value with no explanation. Left-packing ensures the label aligns with the dynamic value that follows.

What this page does

Creates the label that displays the actual current time, updated every second.

Code (this page)

self.clock_label = tk.Label(
            clock_frame,
            text="",
            font=("TkDefaultFont", 10, "bold")
        )
        self.clock_label.pack(side=tk.LEFT, padx=(5, 0))

Explanation

• Stored as self.clock_label for later updates by _update_clock()
• Bold font differentiates dynamic content from static label
• Left padding separates it from "Current Time:"
• Initial text is empty—populated by the update method

Why this matters

Without storing as instance variable, `_update_clock` couldn't modify the text. This creates the target for the clock update loop.

What this page does

Creates the bordered container that holds the countdown display and status.

Code (this page)

# Timer display frame
        self.timer_frame = tk.Frame(
            main_frame,
            bd=2,
            relief=tk.GROOVE,
            padx=20,
            pady=20
        )
        self.timer_frame.pack(fill=tk.X, pady=(0, 15))

Explanation

• Stored as self.timer_frame for alarm color changes later
• bd=2 creates a 2-pixel border
• relief=tk.GROOVE gives an inset appearance
• Internal padding separates content from borders
• Bottom margin separates from controls below

Why this matters

Without a bordered frame, the countdown would float in empty space. Storing as instance variable enables alarm state to change the background color.

What this page does

Creates the large label that shows the remaining time in MM:SS format.

Code (this page)

# Countdown label
        self.countdown_label = tk.Label(
            self.timer_frame,
            text=self._format_time(self.timer_state.remaining_seconds),
            font=("TkFixedFont", 48, "bold")
        )
        self.countdown_label.pack()

Explanation

• Stored as self.countdown_label for countdown updates
• Large font size (48) makes time highly visible
• Uses _format_time() to display initial value as MM:SS
• Fixed-width font ensures consistent digit spacing
• Centered within timer_frame by default pack behavior

Why this matters

Without a large, prominent display, users couldn't see the countdown at a glance. Storing as instance variable enables the tick loop to update the display.

What this page does

Creates the label that shows the current timer state (Ready, Running, Paused, Time's Up).

Code (this page)

# Status label
        self.status_label = tk.Label(
            self.timer_frame,
            text="Ready",
            font=("TkDefaultFont", 12)
        )
        self.status_label.pack(pady=(10, 0))

Explanation

• Stored as self.status_label for state change updates
• Smaller font than countdown (12 vs 48)—secondary information
• Initial text "Ready" matches initial state
• Top padding separates from countdown display

Why this matters

Without a status label, users would have to infer state from button availability. This explicitly communicates what the timer is doing.

What this page does

Creates a horizontal container for the control buttons.

Code (this page)

# Control buttons
        controls_frame = tk.Frame(main_frame)
        controls_frame.pack(fill=tk.X)

Explanation

• Local variable—buttons are stored individually instead
• fill=tk.X stretches to parent width for button distribution
• No bottom padding needed—this is the last element
• Contains Start, Stop, and Reset buttons

Why this matters

Without a container frame, buttons would need individual positioning. This groups controls and enables even distribution across the width.

What this page does

Creates the button that starts or resumes the countdown.

Code (this page)

self.start_button = tk.Button(
            controls_frame,
            text="Start",
            width=10,
            command=self._on_start
        )
        self.start_button.pack(side=tk.LEFT, expand=True)

Explanation

• Stored as self.start_button for state-based enabling/disabling
• Fixed width of 10 characters for consistent sizing
• command binds to _on_start method
• expand=True with side=tk.LEFT distributes space evenly

Why this matters

Without storing as instance variable, the button couldn't be disabled during countdown. This creates the primary action trigger.

What this page does

Creates the button that pauses the countdown.

Code (this page)

self.stop_button = tk.Button(
            controls_frame,
            text="Stop",
            width=10,
            command=self._on_stop,
            state=tk.DISABLED
        )
        self.stop_button.pack(side=tk.LEFT, expand=True)

Explanation

• Stored as self.stop_button for state management
• Initially disabled (state=tk.DISABLED)—can't stop what isn't running
• Same width as Start for visual consistency
• command binds to _on_stop method

Why this matters

Without initial disabled state, users could click Stop before Start. This implements UI-level guard that matches logical constraints.

What this page does

Creates the button that resets the timer to its initial state.

Code (this page)

self.reset_button = tk.Button(
            controls_frame,
            text="Reset",
            width=10,
            command=self._on_reset
        )
        self.reset_button.pack(side=tk.LEFT, expand=True)

Explanation

• Stored as self.reset_button for potential state management
• Initially enabled—reset is always valid
• Same width as other buttons for consistency
• command binds to _on_reset method

Why this matters

Without a reset button, users would need to restart the application. This returns the timer to its starting condition.

What this page does

Converts raw seconds into human-readable MM:SS display format.

Code (this page)

def _format_time(self, seconds: int) -> str:
        """Convert seconds to MM:SS format."""
        minutes = seconds // 60
        secs = seconds % 60
        return f"{minutes:02d}:{secs:02d}"

Explanation

• Integer division (//) extracts whole minutes
• Modulo (%) extracts remaining seconds
• f-string with :02d ensures zero-padded two-digit output
• Returns string like "25:00" or "04:37"

Why this matters

Without formatting, users would see raw seconds (1500) instead of readable time (25:00). Zero-padding ensures consistent display width.

What this page does

Creates the method that updates the live clock display every second.

Code (this page)

def _update_clock(self):
        """Update the live clock display."""
        current_time = time.strftime("%H:%M:%S")
        self.clock_label.config(text=current_time)
        self.root.after(self.CLOCK_UPDATE_MS, self._update_clock)

Explanation

• time.strftime("%H:%M:%S") gets current time in 24-hour format
• config(text=...) updates the label
• root.after() schedules next update without blocking
• Method reschedules itself through the event loop

Why this matters

Without `root.after()`, the update would block the UI. Self-rescheduling creates a continuous, non-blocking update cycle.

What this page does

Creates the entry point for the recurring timer tick loop.

Code (this page)

def _tick(self):
        """Process one tick of the countdown timer."""

Explanation

• Method runs continuously via root.after()
• Contains all countdown logic
• Executes regardless of timer state
• Docstring clarifies single-tick responsibility

Why this matters

Without a dedicated tick method, countdown logic would be scattered. This centralizes all timing behavior.

What this page does

Guards countdown logic to only execute when timer is running.

Code (this page)

if self.timer_state.is_running:
            current_time = time.monotonic()

Explanation

• is_running check prevents countdown when paused
• time.monotonic() provides clock immune to adjustments
• Monotonic time never goes backward
• Only captures timestamp when actually running

Why this matters

Without the guard, timer would count down even when paused. Monotonic time prevents system clock changes from corrupting countdown.

What this page does

Computes the real time elapsed since the previous tick.

Code (this page)

if self._last_tick_time is not None:
                elapsed = current_time - self._last_tick_time
                self._accumulated_time += elapsed

Explanation

• Checks previous tick exists (not first tick)
• Calculates actual elapsed time between ticks
• Accumulates fractional seconds for precision
• Handles variable tick intervals gracefully

Why this matters

Without elapsed calculation, countdown would assume perfect 200ms ticks. Accumulation ensures real-time accuracy.

What this page does

Converts accumulated time into countdown decrements.

Code (this page)

while self._accumulated_time >= 1.0 and self.timer_state.remaining_seconds > 0:
                self.timer_state.remaining_seconds -= 1
                self._accumulated_time -= 1.0

Explanation

• while handles multiple seconds if tick delayed
• Only decrements when full second accumulated
• Stops at zero to prevent negative
• Preserves fractional remainder

Why this matters

Without while loop, delayed tick could skip seconds. Zero check prevents negative countdown.

What this page does

Checks if countdown reached zero and alarm hasn't fired.

Code (this page)

if self.timer_state.remaining_seconds == 0 and not self.timer_state.alarm_triggered:
                self._trigger_alarm()

Explanation

• Double condition prevents repeated triggers
• remaining_seconds == 0 detects completion
• not alarm_triggered ensures one-time execution
• Delegates to dedicated alarm method

Why this matters

Without `alarm_triggered` check, alarm would fire every tick at zero. Delegation keeps tick loop clean.

What this page does

Records current timestamp for next tick's calculation.

Code (this page)

self._last_tick_time = current_time

Explanation

• Stores current time for next iteration
• Must happen after all calculations
• Only inside is_running block
• Enables accurate elapsed on next tick

Why this matters

Without updating, elapsed would calculate from original start, causing exponential drift.

What this page does

Triggers visual refresh after processing the tick.

Code (this page)

self._update_timer_display()

Explanation

• Called every tick regardless of running state
• Updates countdown, status, and colors
• Placed outside is_running block (note indentation)
• Ensures UI always reflects current state

Why this matters

Without calling display update, UI would freeze. Must update every tick for consistent visuals.

What this page does

Schedules the next tick loop execution.

Code (this page)

self.root.after(self.TICK_INTERVAL_MS, self._tick)

Explanation

• root.after() schedules without blocking
• TICK_INTERVAL_MS (200ms) for smooth updates
• Method reschedules itself perpetually
• At method level, outside all conditionals

Why this matters

Without rescheduling, tick runs once and stops. Using `after()` keeps UI responsive.

What this page does

Creates the method that synchronizes UI with timer state.

Code (this page)

def _update_timer_display(self):
        """Refresh countdown display and status."""

Explanation

• Called every tick regardless of state
• Updates countdown, status, colors, buttons
• Centralizes all display logic
• Separates rendering from timing

Why this matters

Without dedicated method, display logic would be duplicated. Centralizing ensures consistency.

What this page does

Renders current remaining time in the countdown label.

Code (this page)

# Update countdown text
        self.countdown_label.config(
            text=self._format_time(self.timer_state.remaining_seconds)
        )

Explanation

• Calls _format_time() to convert to MM:SS
• Updates the large countdown label
• Runs every tick for smooth updates
• No conditional—always shows current state

Why this matters

Without updating, users wouldn't see time passing. This is the primary visual feedback.

What this page does

Applies "Time's Up" styling when alarm is active.

Code (this page)

# Handle alarm state visuals
        if self.timer_state.alarm_triggered:
            self.timer_frame.config(bg="#ffcccc")
            self.countdown_label.config(bg="#ffcccc")
            self.status_label.config(bg="#ffcccc", text="Time's Up!", fg="#cc0000")

Explanation

• Light red background (#ffcccc) signals completion
• Dark red text (#cc0000) emphasizes urgency
• Status switches to "Time's Up!"
• Uses alarm_triggered flag as gate

Why this matters

Without visual feedback, users might miss completion if sound muted. Red provides unmistakable indication.

What this page does

Restores default visuals when not in alarm state.

Code (this page)

else:
            # Normal state visuals
            default_bg = self.root.cget("bg")
            self.timer_frame.config(bg=default_bg)
            self.countdown_label.config(bg=default_bg)
            self.status_label.config(bg=default_bg, fg="black")

Explanation

• Clears alarm styling after reset
• root.cget("bg") gets system default background
• Restores black text for readability
• Ensures visual matches logical state

Why this matters

Without restoring, red would persist forever. Using `cget` respects system theme.

What this page does

Determines and applies the appropriate status message.

Code (this page)

# Determine status text
            if self.timer_state.is_running:
                self.status_label.config(text="Running")
            elif self.timer_state.remaining_seconds < self.DEFAULT_DURATION:
                self.status_label.config(text="Paused")
            else:
                self.status_label.config(text="Ready")

Explanation

• "Running" when actively counting down
• "Paused" when stopped with time elapsed
• "Ready" when at full default duration
• Uses DEFAULT_DURATION constant for comparison

Why this matters

Without status, users must infer state. Using the constant ensures correct detection at the hardcoded duration.

What this page does

Enables or disables buttons based on timer state.

Code (this page)

# Update button states
        if self.timer_state.is_running:
            self.start_button.config(state=tk.DISABLED)
            self.stop_button.config(state=tk.NORMAL)
        else:
            self.start_button.config(state=tk.NORMAL)
            self.stop_button.config(state=tk.DISABLED)

Explanation

• Running: disable Start, enable Stop
• Not running: enable Start, disable Stop
• Visual feedback matches logical constraints
• Reset always enabled (not shown)

Why this matters

Without state management, users could click invalid buttons. Disabled state communicates what's allowed.

What this page does

Creates the method that handles countdown completion.

Code (this page)

def _trigger_alarm(self):
        """Handle alarm when countdown reaches zero."""
        self.timer_state.alarm_triggered = True
        self.timer_state.is_running = False
        self._last_tick_time = None
        self._accumulated_time = 0.0

Explanation

• alarm_triggered = True makes state sticky
• is_running = False stops countdown
• Clears timing variables for clean restart
• State changes happen regardless of sound

Why this matters

Without sticky alarm, it could fire repeatedly. State must transition regardless of audio.

What this page does

Plays the system bell when countdown completes.

Code (this page)

# Always play alarm sound (Foundation has no toggle)
        self.root.bell()

Explanation

• root.bell() plays the system alert sound
• Foundation always plays the sound—no user control
• Called after state is updated
• Simple, platform-native audio feedback

Why this matters

Without audio feedback, users might miss completion. Foundation provides no way to disable this—that comes in Configuration stage.

What this page does

Creates the method that handles Start button clicks.

Code (this page)

def _on_start(self):
        """Handle Start button click."""
        if self.timer_state.is_running:
            return
        if self.timer_state.alarm_triggered:
            return
        if self.timer_state.remaining_seconds == 0:
            return

Explanation

• is_running guard prevents double-start
• alarm_triggered guard requires reset after completion
• remaining_seconds == 0 guard prevents starting exhausted timer
• Early returns keep code flat and readable

Why this matters

Without guards, users could cause undefined behavior. These enforce valid state transitions.

What this page does

Begins countdown timing after passing all guards.

Code (this page)

self.timer_state.is_running = True
        self._last_tick_time = time.monotonic()
        self._accumulated_time = 0.0

Explanation

• is_running = True activates tick countdown logic
• _last_tick_time establishes timing reference
• _accumulated_time = 0.0 ensures clean start
• Monotonic time prevents clock interference

Why this matters

Without setting `is_running`, tick would ignore countdown. Without timing setup, first second could be wrong.

What this page does

Creates the method that pauses the countdown.

Code (this page)

def _on_stop(self):
        """Handle Stop button click."""
        if not self.timer_state.is_running:
            return

        self.timer_state.is_running = False
        self._last_tick_time = None
        self._accumulated_time = 0.0

Explanation

• Guard: stopping stopped timer does nothing
• is_running = False pauses countdown
• Clears timing variables
• Preserves remaining_seconds (true pause)

Why this matters

Without guard, stop could interfere. Without preserving remaining, pause would become reset.

What this page does

Creates the method that returns timer to ready state.

Code (this page)

def _on_reset(self):
        """Handle Reset button click."""
        self.timer_state.is_running = False
        self.timer_state.alarm_triggered = False
        self.timer_state.remaining_seconds = self.DEFAULT_DURATION
        self._last_tick_time = None
        self._accumulated_time = 0.0

Explanation

• Stops any running countdown
• Clears sticky alarm flag
• Restores hardcoded default duration
• Clears all timing bookkeeping
• Safe to call from any state

Why this matters

Without reset, app restart needed after alarm. Using `DEFAULT_DURATION` returns to the hardcoded starting value.

What this page does

Creates the startup function that launches the application.

Code (this page)

def main():
    root = tk.Tk()
    app = StudyTimerApp(root)
    root.mainloop()

Explanation

• Creates Tk root window
• Instantiates application controller
• Starts event loop (blocks until close)
• Encapsulates complete startup

Why this matters

Without main function, startup would be at module level. This encapsulates the three-step launch.

What this page does

Ensures app runs only when executed directly.

Code (this page)

if __name__ == "__main__":
    main()

Explanation

• Allows importing without auto-launch
• Standard Python script pattern
• Keeps module reusable
• Calls main only on direct execution

Why this matters

Without guard, importing for testing would launch GUI. This is Python best practice.

What this page does

Provides the complete code structure for verification.

Code (this page)

# Complete Foundation code should match this structure:
# - 3 imports (tkinter, time, Optional)
# - TimerState class with 3 attributes
# - StudyTimerApp class with DEFAULT_DURATION constant
# - All methods defined
# - main() function and entry guard

Explanation

Why this matters

This checkpoint ensures all code is correct before proceeding. Every feature should work.

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Confirms the Foundation stage is fully complete.

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