//! Domain Services
//!
//! Services contain the business logic of the application.

use std::collections::HashSet;
use std::sync::Arc;

use chrono::{DateTime, Duration, TimeZone, Utc};
use chrono_tz::Tz;
use rand::seq::SliceRandom;
use uuid::Uuid;

use crate::entities::{
    BlockContent, CurrentBroadcast, GeneratedSchedule, MediaItem, PlaybackRecord,
    ProgrammingBlock, ScheduledSlot,
};
use crate::errors::{DomainError, DomainResult};
use crate::ports::IMediaProvider;
use crate::repositories::{ChannelRepository, ScheduleRepository, UserRepository};
use crate::value_objects::{
    BlockId, ChannelId, Email, FillStrategy, MediaFilter, MediaItemId, RecyclePolicy,
};

// ============================================================================
// UserService
// ============================================================================

/// Service for managing users.
pub struct UserService {
    user_repository: Arc<dyn UserRepository>,
}

impl UserService {
    pub fn new(user_repository: Arc<dyn UserRepository>) -> Self {
        Self { user_repository }
    }

    pub async fn find_or_create(&self, subject: &str, email: &str) -> DomainResult<crate::entities::User> {
        if let Some(user) = self.user_repository.find_by_subject(subject).await? {
            return Ok(user);
        }

        if let Some(mut user) = self.user_repository.find_by_email(email).await? {
            if user.subject != subject {
                user.subject = subject.to_string();
                self.user_repository.save(&user).await?;
            }
            return Ok(user);
        }

        let email = Email::try_from(email)?;
        let user = crate::entities::User::new(subject, email);
        self.user_repository.save(&user).await?;
        Ok(user)
    }

    pub async fn find_by_id(&self, id: Uuid) -> DomainResult<crate::entities::User> {
        self.user_repository
            .find_by_id(id)
            .await?
            .ok_or(DomainError::UserNotFound(id))
    }

    pub async fn find_by_email(&self, email: &str) -> DomainResult<Option<crate::entities::User>> {
        self.user_repository.find_by_email(email).await
    }

    pub async fn create_local(
        &self,
        email: &str,
        password_hash: &str,
    ) -> DomainResult<crate::entities::User> {
        let email = Email::try_from(email)?;
        let user = crate::entities::User::new_local(email, password_hash);
        self.user_repository.save(&user).await?;
        Ok(user)
    }
}

// ============================================================================
// ChannelService
// ============================================================================

/// Service for managing channels (CRUD + ownership enforcement).
pub struct ChannelService {
    channel_repo: Arc<dyn ChannelRepository>,
}

impl ChannelService {
    pub fn new(channel_repo: Arc<dyn ChannelRepository>) -> Self {
        Self { channel_repo }
    }

    pub async fn create(
        &self,
        owner_id: crate::value_objects::UserId,
        name: &str,
        timezone: &str,
    ) -> DomainResult<crate::entities::Channel> {
        let channel = crate::entities::Channel::new(owner_id, name, timezone);
        self.channel_repo.save(&channel).await?;
        Ok(channel)
    }

    pub async fn find_by_id(
        &self,
        id: ChannelId,
    ) -> DomainResult<crate::entities::Channel> {
        self.channel_repo
            .find_by_id(id)
            .await?
            .ok_or(DomainError::ChannelNotFound(id))
    }

    pub async fn find_all(&self) -> DomainResult<Vec<crate::entities::Channel>> {
        self.channel_repo.find_all().await
    }

    pub async fn find_by_owner(
        &self,
        owner_id: crate::value_objects::UserId,
    ) -> DomainResult<Vec<crate::entities::Channel>> {
        self.channel_repo.find_by_owner(owner_id).await
    }

    pub async fn update(
        &self,
        channel: crate::entities::Channel,
    ) -> DomainResult<crate::entities::Channel> {
        self.channel_repo.save(&channel).await?;
        Ok(channel)
    }

    /// Delete a channel, enforcing that `requester_id` is the owner.
    pub async fn delete(
        &self,
        id: ChannelId,
        requester_id: crate::value_objects::UserId,
    ) -> DomainResult<()> {
        let channel = self.find_by_id(id).await?;
        if channel.owner_id != requester_id {
            return Err(DomainError::forbidden("You don't own this channel"));
        }
        self.channel_repo.delete(id).await
    }
}

// ============================================================================
// ScheduleEngineService
// ============================================================================

/// Core scheduling engine.
///
/// Generates 48-hour broadcast schedules by walking through a channel's
/// `ScheduleConfig` day by day, resolving each `ProgrammingBlock` into concrete
/// `ScheduledSlot`s via the `IMediaProvider`, and applying the `RecyclePolicy`
/// to avoid replaying recently aired items.
pub struct ScheduleEngineService {
    media_provider: Arc<dyn IMediaProvider>,
    channel_repo: Arc<dyn ChannelRepository>,
    schedule_repo: Arc<dyn ScheduleRepository>,
}

impl ScheduleEngineService {
    pub fn new(
        media_provider: Arc<dyn IMediaProvider>,
        channel_repo: Arc<dyn ChannelRepository>,
        schedule_repo: Arc<dyn ScheduleRepository>,
    ) -> Self {
        Self {
            media_provider,
            channel_repo,
            schedule_repo,
        }
    }

    // -------------------------------------------------------------------------
    // Public API
    // -------------------------------------------------------------------------

    /// Generate and persist a 48-hour schedule for `channel_id` starting at `from`.
    ///
    /// The algorithm:
    /// 1. Walk each calendar day in the 48-hour window.
    /// 2. For each `ProgrammingBlock`, compute its UTC wall-clock interval for that day.
    /// 3. Clip the interval to `[from, from + 48h)`.
    /// 4. Resolve the block content via the media provider, applying the recycle policy.
    /// 5. Record every played item in the playback history.
    ///
    /// Gaps between blocks are left empty — clients render them as a no-signal state.
    pub async fn generate_schedule(
        &self,
        channel_id: ChannelId,
        from: DateTime<Utc>,
    ) -> DomainResult<GeneratedSchedule> {
        let channel = self
            .channel_repo
            .find_by_id(channel_id)
            .await?
            .ok_or(DomainError::ChannelNotFound(channel_id))?;

        let tz: Tz = channel
            .timezone
            .parse()
            .map_err(|_| DomainError::TimezoneError(channel.timezone.clone()))?;

        let history = self
            .schedule_repo
            .find_playback_history(channel_id)
            .await?;

        let generation = self
            .schedule_repo
            .find_latest(channel_id)
            .await?
            .map(|s| s.generation + 1)
            .unwrap_or(1);

        let valid_from = from;
        let valid_until = from + Duration::hours(48);

        let start_date = from.with_timezone(&tz).date_naive();
        let end_date = valid_until.with_timezone(&tz).date_naive();

        let mut slots: Vec<ScheduledSlot> = Vec::new();
        let mut current_date = start_date;

        while current_date <= end_date {
            for block in &channel.schedule_config.blocks {
                let naive_start = current_date.and_time(block.start_time);

                // `earliest()` handles DST gaps — if the local time doesn't exist
                // (e.g. clocks spring forward) we skip this block occurrence.
                let block_start_utc = match tz.from_local_datetime(&naive_start).earliest() {
                    Some(dt) => dt.with_timezone(&Utc),
                    None => continue,
                };

                let block_end_utc =
                    block_start_utc + Duration::minutes(block.duration_mins as i64);

                // Clip to the 48-hour window.
                let slot_start = block_start_utc.max(valid_from);
                let slot_end = block_end_utc.min(valid_until);

                if slot_end <= slot_start {
                    continue;
                }

                let mut block_slots = self
                    .resolve_block(
                        block,
                        slot_start,
                        slot_end,
                        &history,
                        &channel.recycle_policy,
                        generation,
                    )
                    .await?;

                slots.append(&mut block_slots);
            }

            current_date = current_date.succ_opt().ok_or_else(|| {
                DomainError::validation("Date overflow during schedule generation")
            })?;
        }

        // Blocks in ScheduleConfig are not required to be sorted; sort resolved slots.
        slots.sort_by_key(|s| s.start_at);

        let schedule = GeneratedSchedule {
            id: Uuid::new_v4(),
            channel_id,
            valid_from,
            valid_until,
            generation,
            slots,
        };

        self.schedule_repo.save(&schedule).await?;

        // Persist playback history so the recycle policy has data for next generation.
        for slot in &schedule.slots {
            let record =
                PlaybackRecord::new(channel_id, slot.item.id.clone(), generation);
            self.schedule_repo.save_playback_record(&record).await?;
        }

        Ok(schedule)
    }

    /// Determine what is currently broadcasting on a schedule.
    ///
    /// Returns `None` when `now` falls in a gap between blocks — the client
    /// should display a no-signal / static screen in that case.
    pub fn get_current_broadcast(
        schedule: &GeneratedSchedule,
        now: DateTime<Utc>,
    ) -> Option<CurrentBroadcast> {
        schedule
            .slots
            .iter()
            .find(|s| s.start_at <= now && now < s.end_at)
            .map(|slot| CurrentBroadcast {
                slot: slot.clone(),
                offset_secs: (now - slot.start_at).num_seconds() as u32,
            })
    }

    /// Look up the schedule currently active at `at` without generating a new one.
    pub async fn get_active_schedule(
        &self,
        channel_id: ChannelId,
        at: DateTime<Utc>,
    ) -> DomainResult<Option<GeneratedSchedule>> {
        self.schedule_repo.find_active(channel_id, at).await
    }

    /// Delegate stream URL resolution to the configured media provider.
    pub async fn get_stream_url(&self, item_id: &MediaItemId) -> DomainResult<String> {
        self.media_provider.get_stream_url(item_id).await
    }

    /// Return all slots that overlap the given time window — the EPG data.
    pub fn get_epg<'a>(
        schedule: &'a GeneratedSchedule,
        from: DateTime<Utc>,
        until: DateTime<Utc>,
    ) -> Vec<&'a ScheduledSlot> {
        schedule
            .slots
            .iter()
            .filter(|s| s.start_at < until && s.end_at > from)
            .collect()
    }

    // -------------------------------------------------------------------------
    // Block resolution
    // -------------------------------------------------------------------------

    async fn resolve_block(
        &self,
        block: &ProgrammingBlock,
        start: DateTime<Utc>,
        end: DateTime<Utc>,
        history: &[PlaybackRecord],
        policy: &RecyclePolicy,
        generation: u32,
    ) -> DomainResult<Vec<ScheduledSlot>> {
        match &block.content {
            BlockContent::Manual { items } => {
                self.resolve_manual(items, start, end, block.id).await
            }
            BlockContent::Algorithmic { filter, strategy } => {
                self.resolve_algorithmic(
                    filter, strategy, start, end, history, policy, generation, block.id,
                )
                .await
            }
        }
    }

    /// Resolve a manual block by fetching each hand-picked item in order.
    /// Stops when the block's time budget (`end`) is exhausted.
    async fn resolve_manual(
        &self,
        item_ids: &[MediaItemId],
        start: DateTime<Utc>,
        end: DateTime<Utc>,
        block_id: BlockId,
    ) -> DomainResult<Vec<ScheduledSlot>> {
        let mut slots = Vec::new();
        let mut cursor = start;

        for item_id in item_ids {
            if cursor >= end {
                break;
            }
            if let Some(item) = self.media_provider.fetch_by_id(item_id).await? {
                let item_end =
                    (cursor + Duration::seconds(item.duration_secs as i64)).min(end);
                slots.push(ScheduledSlot {
                    id: Uuid::new_v4(),
                    start_at: cursor,
                    end_at: item_end,
                    item,
                    source_block_id: block_id,
                });
                cursor = item_end;
            }
            // If item is not found (deleted/unavailable), silently skip it.
        }

        Ok(slots)
    }

    /// Resolve an algorithmic block: fetch candidates, apply recycle policy,
    /// run the fill strategy, and build slots.
    async fn resolve_algorithmic(
        &self,
        filter: &MediaFilter,
        strategy: &FillStrategy,
        start: DateTime<Utc>,
        end: DateTime<Utc>,
        history: &[PlaybackRecord],
        policy: &RecyclePolicy,
        generation: u32,
        block_id: BlockId,
    ) -> DomainResult<Vec<ScheduledSlot>> {
        let candidates = self.media_provider.fetch_items(filter).await?;

        if candidates.is_empty() {
            return Ok(vec![]);
        }

        let pool = Self::apply_recycle_policy(candidates, history, policy, generation);
        let target_secs = (end - start).num_seconds() as u32;
        let selected = Self::fill_block(&pool, target_secs, strategy);

        let mut slots = Vec::new();
        let mut cursor = start;

        for item in selected {
            if cursor >= end {
                break;
            }
            let item_end =
                (cursor + Duration::seconds(item.duration_secs as i64)).min(end);
            slots.push(ScheduledSlot {
                id: Uuid::new_v4(),
                start_at: cursor,
                end_at: item_end,
                item: item.clone(),
                source_block_id: block_id,
            });
            cursor = item_end;
        }

        Ok(slots)
    }

    // -------------------------------------------------------------------------
    // Recycle policy
    // -------------------------------------------------------------------------

    /// Filter `candidates` according to `policy`, returning the eligible pool.
    ///
    /// An item is on cooldown if *either* the day-based or generation-based
    /// threshold is exceeded. If honouring all cooldowns would leave fewer items
    /// than `policy.min_available_ratio` of the total, all cooldowns are waived
    /// and the full pool is returned (prevents small libraries from stalling).
    fn apply_recycle_policy(
        candidates: Vec<MediaItem>,
        history: &[PlaybackRecord],
        policy: &RecyclePolicy,
        current_generation: u32,
    ) -> Vec<MediaItem> {
        let now = Utc::now();

        let excluded: HashSet<MediaItemId> = history
            .iter()
            .filter(|record| {
                let by_days = policy
                    .cooldown_days
                    .map(|days| (now - record.played_at).num_days() < days as i64)
                    .unwrap_or(false);

                let by_gen = policy
                    .cooldown_generations
                    .map(|gens| {
                        current_generation.saturating_sub(record.generation) < gens
                    })
                    .unwrap_or(false);

                by_days || by_gen
            })
            .map(|r| r.item_id.clone())
            .collect();

        let available: Vec<MediaItem> = candidates
            .iter()
            .filter(|i| !excluded.contains(&i.id))
            .cloned()
            .collect();

        let min_count =
            (candidates.len() as f32 * policy.min_available_ratio).ceil() as usize;

        if available.len() < min_count {
            // Pool too small after applying cooldowns — recycle everything.
            candidates
        } else {
            available
        }
    }

    // -------------------------------------------------------------------------
    // Fill strategies
    // -------------------------------------------------------------------------

    fn fill_block<'a>(
        pool: &'a [MediaItem],
        target_secs: u32,
        strategy: &FillStrategy,
    ) -> Vec<&'a MediaItem> {
        match strategy {
            FillStrategy::BestFit => Self::fill_best_fit(pool, target_secs),
            FillStrategy::Sequential => Self::fill_sequential(pool, target_secs),
            FillStrategy::Random => {
                let mut indices: Vec<usize> = (0..pool.len()).collect();
                indices.shuffle(&mut rand::thread_rng());
                let mut remaining = target_secs;
                let mut result = Vec::new();
                for i in indices {
                    let item = &pool[i];
                    if item.duration_secs <= remaining {
                        remaining -= item.duration_secs;
                        result.push(item);
                    }
                }
                result
            }
        }
    }

    /// Greedy bin-packing: at each step pick the longest item that still fits
    /// in the remaining budget, without repeating items within the same block.
    fn fill_best_fit(pool: &[MediaItem], target_secs: u32) -> Vec<&MediaItem> {
        let mut remaining = target_secs;
        let mut selected: Vec<&MediaItem> = Vec::new();
        let mut used: HashSet<usize> = HashSet::new();

        loop {
            let best = pool
                .iter()
                .enumerate()
                .filter(|(idx, item)| {
                    !used.contains(idx) && item.duration_secs <= remaining
                })
                .max_by_key(|(_, item)| item.duration_secs);

            match best {
                Some((idx, item)) => {
                    remaining -= item.duration_secs;
                    used.insert(idx);
                    selected.push(item);
                }
                None => break,
            }
        }

        selected
    }

    /// Sequential: iterate the pool in order, picking items that fit within
    /// the remaining budget. Good for series where episode order matters.
    fn fill_sequential(pool: &[MediaItem], target_secs: u32) -> Vec<&MediaItem> {
        let mut remaining = target_secs;
        let mut result = Vec::new();
        for item in pool {
            if item.duration_secs <= remaining {
                remaining -= item.duration_secs;
                result.push(item);
            }
        }
        result
    }
}