//! Calendar event domain model.
//!
//! This module provides the core `Event` and `EventBuilder` types for representing
//! calendar events with recurrence support, metadata tracking, and validation.
//!
//! # Overview
//!
//! The `Event` struct represents a single calendar entry
//! with start and end times, optional recurrence rules, and metadata.
//! Use the `EventBuilder` to construct events with validation of required fields
//! and sensible defaults for optional ones.
//!
//! # Examples
//!
//! ```
//! # use uuid::Uuid;
//! # use chrono::Utc;
//! # let cal_id = Uuid::new_v4();
//! let event = EventBuilder::new(
//!     cal_id,
//!     "Team Meeting".to_string(),
//!     Utc::now(),
//!     Utc::now() + chrono::Duration::hours(1)
//! )?
//!     .color(5)
//!     .description(Some("Quarterly sync".to_string()))
//!     .build();
//! # Ok::<(), String>(())
//! ```

use chrono::{DateTime, TimeDelta, Utc};
use getset::Getters;
use uuid::Uuid;
use crate::domain::recurrence::RecurrenceRule;

/// A calendar event with optional recurrence, metadata, and state tracking.
///
/// `Event` represents a single calendar entry with start and end times,
/// optional recurrence rules, and metadata like color and cancellation status.
/// All mutation operations update the `updated_at` timestamp.
///
/// # Fields
///
/// * `id` - Unique identifier for the event
/// * `calendar_id` - The calendar this event belongs to
/// * `title` - Display title of the event
/// * `description` - Optional detailed description
/// * `start` - Event start time in UTC
/// * `end` - Event end time in UTC
/// * `recurring` - Optional recurrence rule for repeating events
/// * `created_at` - When the event was created
/// * `updated_at` - When the event was last modified
/// * `color` - Color identifier (0-255)
/// * `is_all_day` - Whether this is an all-day event
/// * `is_cancelled` - Whether this event is cancelled
#[derive(Clone, Debug, Getters)]
#[getset(get = "pub")]
pub struct Event {
    id: Uuid,
    calendar_id: Uuid,
    title: String,
    description: Option<String>,
    start: DateTime<Utc>,
    end: DateTime<Utc>,
    recurring: Option<RecurrenceRule>,
    created_at: DateTime<Utc>,
    updated_at: DateTime<Utc>,
    color: u8,
    is_all_day: bool,
    is_cancelled: bool
}

/// Builder for constructing `Event` instances with validation.
///
/// Provides an ergonomic way to create events with required field validation.
/// Required fields are `calendar_id`, `title`, `start`, and `end`.
/// Optional fields have sensible defaults.
///
/// # Examples
///
/// ```
/// # use uuid::Uuid;
/// # use chrono::Utc;
/// # let cal_id = Uuid::new_v4();
/// let event = EventBuilder::new(
///     cal_id,
///     "Team Meeting".to_string(),
///     Utc::now(),
///     Utc::now() + chrono::Duration::hours(1)
/// )?
///     .color(5)
///     .description(Some("Quarterly sync".to_string()))
///     .build();
/// ```
pub struct EventBuilder {
    calendar_id: Uuid,
    title: String,
    start: DateTime<Utc>,
    end: DateTime<Utc>,
    description: Option<String>,
    recurring: Option<RecurrenceRule>,
    color: u8,
    is_all_day: bool,
    is_cancelled: bool,
}

impl EventBuilder {
    /// Creates a new `EventBuilder` with required fields.
    ///
    /// # Arguments
    ///
    /// * `calendar_id` - The calendar to which this event belongs
    /// * `title` - The display title of the event (cannot be empty)
    /// * `start` - The event start time in UTC
    /// * `end` - The event end time in UTC (must be after `start`)
    ///
    /// # Errors
    ///
    /// Returns an error if:
    /// - `title` is empty
    /// - `start` is not strictly before `end`
    pub fn new(
        calendar_id: Uuid,
        title: String,
        start: DateTime<Utc>,
        end: DateTime<Utc>
    ) -> Result<Self, String> {
        if title.is_empty() {
            Err("Title cannot be empty".to_string())
        } else if start >= end {
            Err("Start time must be strictly before end time".to_string())
        } else {
            Ok(Self {
                calendar_id,
                title,
                start,
                end,
                description: None,
                recurring: None,
                color: 0,
                is_all_day: false,
                is_cancelled: false
            })
        }
    }

    /// Sets the event description.
    ///
    /// # Arguments
    ///
    /// * `description` - Optional detailed description of the event
    pub fn description(mut self, description: Option<String>) -> Self {
        self.description = description;
        self
    }

    /// Sets the recurrence rule for repeating events.
    ///
    /// # Arguments
    ///
    /// * `recurring` - Optional recurrence rule defining repetition pattern
    pub fn recurring(mut self, recurring: Option<RecurrenceRule>) -> Self {
        self.recurring = recurring;
        self
    }

    /// Sets the color identifier for the event.
    ///
    /// # Arguments
    ///
    /// * `color` - Color identifier in range 0-255
    pub fn color(mut self, color: u8) -> Self {
        self.color = color;
        self
    }

    /// Sets whether this is an all-day event.
    ///
    /// # Arguments
    ///
    /// * `is_all_day` - `true` if this is an all-day event, `false` otherwise
    pub fn is_all_day(mut self, is_all_day: bool) -> Self {
        self.is_all_day = is_all_day;
        self
    }

    /// Sets whether this event is cancelled.
    ///
    /// # Arguments
    ///
    /// * `is_cancelled` - `true` if this event is cancelled, `false` otherwise
    pub fn is_cancelled(mut self, is_cancelled: bool) -> Self {
        self.is_cancelled = is_cancelled;
        self
    }

    /// Builds and returns the constructed `Event`.
    ///
    /// Sets the `id`, `created_at`, and `updated_at` fields to automatically
    /// generated values. The `id` is a new UUID, and both timestamps are set
    /// to the current UTC time.
    pub fn build(self) -> Event {
        let now = Utc::now();
        Event {
            id: Uuid::new_v4(),
            calendar_id: self.calendar_id,
            title: self.title,
            description: self.description,
            start: self.start,
            end: self.end,
            recurring: self.recurring,
            created_at: now,
            updated_at: now,
            color: self.color,
            is_all_day: self.is_all_day,
            is_cancelled: self.is_cancelled,
        }
    }
}

impl Event { 
    /// Updates the event title.
    ///
    /// # Errors
    /// Returns an error if the title is empty.
    pub fn update_title(&mut self, title: String) -> Result<(), String> {
        if title.is_empty() {
            Err("Title cannot be empty".to_string())
        } else {
            self.title = title;
            self.touch();
            Ok(())
        }
    }

    /// Updates the event description.
    pub fn update_description(&mut self, description: Option<String>) {
        self.description = description;
        self.touch();
    }

    /// Updates the recurrence rule.
    pub fn update_recurring(&mut self, recurring: Option<RecurrenceRule>) {
        self.recurring = recurring;
        self.touch();
    }

    /// Reschedules the event to new start and end times.
    ///
    /// # Errors
    /// Returns an error if `start` is not before `end`.
    pub fn reschedule(
        &mut self,
        start: DateTime<Utc>,
        end: DateTime<Utc>
    ) -> Result<(), String> {
        if start >= end {
            Err("Start time must be strictly before end time".to_string())
        } else {
            self.start = start;
            self.end = end;
            self.touch();
            Ok(())
        }
    }

    /// Updates the color identifier.
    pub fn update_color(&mut self, color: u8) {
        self.color = color;
        self.touch();
    }

    /// Updates whether this is an all-day event.
    pub fn update_all_day(&mut self, is_all_day: bool) {
        self.is_all_day = is_all_day;
        self.touch();
    }

    /// Updates whether this event is cancelled.
    pub fn update_is_cancelled(&mut self, is_cancelled: bool) {
        self.is_cancelled = is_cancelled;
        self.touch();
    }

    /// Returns the duration of the event.
    pub fn get_duration(&self) -> TimeDelta {
        self.end - self.start
    }

    /// Returns true if the event has ended.
    pub fn is_past(&self) -> bool {
        self.end < Utc::now()
    }

    /// Returns true if the event is currently happening.
    pub fn is_ongoing(&self) -> bool {
        let now = Utc::now();
        self.start <= now && now < self.end
    }

    /// Returns true if the event has not yet started.
    pub fn is_future(&self) -> bool {
        self.start > Utc::now()
    }

    /// Updates the `updated_at` timestamp to the current time.
    pub fn touch(&mut self) {
        self.updated_at = Utc::now();
    }
}