use rusqlite::Connection;

use std::collections::HashSet;

use crate::core::error::{LoreError, Result};
use crate::core::timeline::{
    EntityRef, ExpandedEntityRef, MatchedDiscussion, THREAD_MAX_NOTES, THREAD_NOTE_MAX_CHARS,
    ThreadNote, TimelineEvent, TimelineEventType, truncate_to_chars,
};

/// Collect all events for seed and expanded entities, interleave chronologically.
///
/// Steps 4-5 of the timeline pipeline:
/// 1. For each entity, collect Created, StateChanged, Label, Milestone, Merged events
/// 2. Collect discussion threads from matched discussions
/// 3. Merge in evidence notes from the seed phase
/// 4. Sort chronologically with stable tiebreak
/// 5. Apply --since filter and --limit
pub fn collect_events(
    conn: &Connection,
    seed_entities: &[EntityRef],
    expanded_entities: &[ExpandedEntityRef],
    evidence_notes: &[TimelineEvent],
    matched_discussions: &[MatchedDiscussion],
    since_ms: Option<i64>,
    limit: usize,
) -> Result<(Vec<TimelineEvent>, usize)> {
    let mut all_events: Vec<TimelineEvent> = Vec::new();

    // Collect events for seed entities
    for entity in seed_entities {
        collect_entity_events(conn, entity, true, &mut all_events)?;
    }

    // Collect events for expanded entities
    for expanded in expanded_entities {
        collect_entity_events(conn, &expanded.entity_ref, false, &mut all_events)?;
    }

    // Collect discussion threads
    let entity_lookup = build_entity_lookup(seed_entities, expanded_entities);
    collect_discussion_threads(conn, matched_discussions, &entity_lookup, &mut all_events)?;

    // Add evidence notes from seed phase
    all_events.extend(evidence_notes.iter().cloned());

    // Sort chronologically (uses Ord impl from timeline.rs)
    all_events.sort();

    // Apply --since filter
    if let Some(since) = since_ms {
        all_events.retain(|e| e.timestamp >= since);
    }

    // Capture total before applying limit (for meta.total_events vs meta.showing)
    let total_before_limit = all_events.len();

    // Apply limit
    all_events.truncate(limit);

    Ok((all_events, total_before_limit))
}

/// Collect all events for a single entity.
fn collect_entity_events(
    conn: &Connection,
    entity: &EntityRef,
    is_seed: bool,
    events: &mut Vec<TimelineEvent>,
) -> Result<()> {
    collect_creation_event(conn, entity, is_seed, events)?;
    collect_state_events(conn, entity, is_seed, events)?;
    collect_label_events(conn, entity, is_seed, events)?;
    collect_milestone_events(conn, entity, is_seed, events)?;
    collect_merged_event(conn, entity, is_seed, events)?;
    Ok(())
}

/// Collect the Created event from the entity's own table.
fn collect_creation_event(
    conn: &Connection,
    entity: &EntityRef,
    is_seed: bool,
    events: &mut Vec<TimelineEvent>,
) -> Result<()> {
    let table = match entity.entity_type.as_str() {
        "issue" => "issues",
        "merge_request" => "merge_requests",
        _ => return Ok(()),
    };

    let sql =
        format!("SELECT created_at, author_username, title, web_url FROM {table} WHERE id = ?1");

    let result = conn.query_row(&sql, rusqlite::params![entity.entity_id], |row| {
        Ok((
            row.get::<_, Option<i64>>(0)?,
            row.get::<_, Option<String>>(1)?,
            row.get::<_, Option<String>>(2)?,
            row.get::<_, Option<String>>(3)?,
        ))
    });

    if let Ok((Some(created_at), author, title, url)) = result {
        let type_label = if entity.entity_type == "issue" {
            "Issue"
        } else {
            "MR"
        };
        let title_str = title.as_deref().unwrap_or("(untitled)");
        events.push(TimelineEvent {
            timestamp: created_at,
            entity_type: entity.entity_type.clone(),
            entity_id: entity.entity_id,
            entity_iid: entity.entity_iid,
            project_path: entity.project_path.clone(),
            event_type: TimelineEventType::Created,
            summary: format!("{type_label} #{} created: {title_str}", entity.entity_iid),
            actor: author,
            url,
            is_seed,
        });
    }

    Ok(())
}

/// Collect state change events. State='merged' produces Merged, not StateChanged.
fn collect_state_events(
    conn: &Connection,
    entity: &EntityRef,
    is_seed: bool,
    events: &mut Vec<TimelineEvent>,
) -> Result<()> {
    let (id_col, id_val) = entity_id_column(entity)?;

    let sql = format!(
        "SELECT state, actor_username, created_at FROM resource_state_events
         WHERE {id_col} = ?1
         ORDER BY created_at ASC"
    );

    let mut stmt = conn.prepare(&sql)?;
    let rows = stmt.query_map(rusqlite::params![id_val], |row| {
        Ok((
            row.get::<_, String>(0)?,
            row.get::<_, Option<String>>(1)?,
            row.get::<_, i64>(2)?,
        ))
    })?;

    for row_result in rows {
        let (state, actor, created_at) = row_result?;

        // state='merged' is handled by collect_merged_event — skip here
        if state == "merged" {
            continue;
        }

        let summary = format!("State changed to {state}");
        events.push(TimelineEvent {
            timestamp: created_at,
            entity_type: entity.entity_type.clone(),
            entity_id: entity.entity_id,
            entity_iid: entity.entity_iid,
            project_path: entity.project_path.clone(),
            event_type: TimelineEventType::StateChanged { state },
            summary,
            actor,
            url: None,
            is_seed,
        });
    }

    Ok(())
}

/// Collect label add/remove events.
fn collect_label_events(
    conn: &Connection,
    entity: &EntityRef,
    is_seed: bool,
    events: &mut Vec<TimelineEvent>,
) -> Result<()> {
    let (id_col, id_val) = entity_id_column(entity)?;

    let sql = format!(
        "SELECT action, label_name, actor_username, created_at FROM resource_label_events
         WHERE {id_col} = ?1
         ORDER BY created_at ASC"
    );

    let mut stmt = conn.prepare(&sql)?;
    let rows = stmt.query_map(rusqlite::params![id_val], |row| {
        Ok((
            row.get::<_, String>(0)?,
            row.get::<_, Option<String>>(1)?,
            row.get::<_, Option<String>>(2)?,
            row.get::<_, i64>(3)?,
        ))
    })?;

    for row_result in rows {
        let (action, label_name, actor, created_at) = row_result?;
        let label = label_name.unwrap_or_else(|| "[deleted label]".to_owned());

        let (event_type, summary) = match action.as_str() {
            "add" => {
                let summary = format!("Label added: {label}");
                (TimelineEventType::LabelAdded { label }, summary)
            }
            "remove" => {
                let summary = format!("Label removed: {label}");
                (TimelineEventType::LabelRemoved { label }, summary)
            }
            _ => continue,
        };

        events.push(TimelineEvent {
            timestamp: created_at,
            entity_type: entity.entity_type.clone(),
            entity_id: entity.entity_id,
            entity_iid: entity.entity_iid,
            project_path: entity.project_path.clone(),
            event_type,
            summary,
            actor,
            url: None,
            is_seed,
        });
    }

    Ok(())
}

/// Collect milestone add/remove events.
fn collect_milestone_events(
    conn: &Connection,
    entity: &EntityRef,
    is_seed: bool,
    events: &mut Vec<TimelineEvent>,
) -> Result<()> {
    let (id_col, id_val) = entity_id_column(entity)?;

    let sql = format!(
        "SELECT action, milestone_title, actor_username, created_at FROM resource_milestone_events
         WHERE {id_col} = ?1
         ORDER BY created_at ASC"
    );

    let mut stmt = conn.prepare(&sql)?;
    let rows = stmt.query_map(rusqlite::params![id_val], |row| {
        Ok((
            row.get::<_, String>(0)?,
            row.get::<_, Option<String>>(1)?,
            row.get::<_, Option<String>>(2)?,
            row.get::<_, i64>(3)?,
        ))
    })?;

    for row_result in rows {
        let (action, milestone_title, actor, created_at) = row_result?;
        let milestone = milestone_title.unwrap_or_else(|| "[deleted milestone]".to_owned());

        let (event_type, summary) = match action.as_str() {
            "add" => {
                let summary = format!("Milestone set: {milestone}");
                (TimelineEventType::MilestoneSet { milestone }, summary)
            }
            "remove" => {
                let summary = format!("Milestone removed: {milestone}");
                (TimelineEventType::MilestoneRemoved { milestone }, summary)
            }
            _ => continue,
        };

        events.push(TimelineEvent {
            timestamp: created_at,
            entity_type: entity.entity_type.clone(),
            entity_id: entity.entity_id,
            entity_iid: entity.entity_iid,
            project_path: entity.project_path.clone(),
            event_type,
            summary,
            actor,
            url: None,
            is_seed,
        });
    }

    Ok(())
}

/// Collect Merged event for MRs. Prefers merged_at from the MR table.
/// Falls back to resource_state_events WHERE state='merged' if merged_at is NULL.
fn collect_merged_event(
    conn: &Connection,
    entity: &EntityRef,
    is_seed: bool,
    events: &mut Vec<TimelineEvent>,
) -> Result<()> {
    if entity.entity_type != "merge_request" {
        return Ok(());
    }

    // Try merged_at from merge_requests table first
    let mr_result = conn.query_row(
        "SELECT merged_at, merge_user_username, web_url FROM merge_requests WHERE id = ?1",
        rusqlite::params![entity.entity_id],
        |row| {
            Ok((
                row.get::<_, Option<i64>>(0)?,
                row.get::<_, Option<String>>(1)?,
                row.get::<_, Option<String>>(2)?,
            ))
        },
    );

    match mr_result {
        Ok((Some(merged_at), merge_user, url)) => {
            events.push(TimelineEvent {
                timestamp: merged_at,
                entity_type: entity.entity_type.clone(),
                entity_id: entity.entity_id,
                entity_iid: entity.entity_iid,
                project_path: entity.project_path.clone(),
                event_type: TimelineEventType::Merged,
                summary: format!("MR !{} merged", entity.entity_iid),
                actor: merge_user,
                url,
                is_seed,
            });
            return Ok(());
        }
        Ok((None, _, _)) => {} // merged_at is NULL, try fallback
        Err(rusqlite::Error::QueryReturnedNoRows) => {} // entity not found, try fallback
        Err(e) => return Err(e.into()),
    }

    // Fallback: check resource_state_events for state='merged'
    let fallback_result = conn.query_row(
        "SELECT actor_username, created_at FROM resource_state_events
         WHERE merge_request_id = ?1 AND state = 'merged'
         ORDER BY created_at DESC LIMIT 1",
        rusqlite::params![entity.entity_id],
        |row| Ok((row.get::<_, Option<String>>(0)?, row.get::<_, i64>(1)?)),
    );

    match fallback_result {
        Ok((actor, created_at)) => {
            events.push(TimelineEvent {
                timestamp: created_at,
                entity_type: entity.entity_type.clone(),
                entity_id: entity.entity_id,
                entity_iid: entity.entity_iid,
                project_path: entity.project_path.clone(),
                event_type: TimelineEventType::Merged,
                summary: format!("MR !{} merged", entity.entity_iid),
                actor,
                url: None,
                is_seed,
            });
        }
        Err(rusqlite::Error::QueryReturnedNoRows) => {} // no merged state event, MR wasn't merged
        Err(e) => return Err(e.into()),
    }

    Ok(())
}

/// Return the correct column name and value for querying resource event tables.
fn entity_id_column(entity: &EntityRef) -> Result<(&'static str, i64)> {
    match entity.entity_type.as_str() {
        "issue" => Ok(("issue_id", entity.entity_id)),
        "merge_request" => Ok(("merge_request_id", entity.entity_id)),
        _ => Err(LoreError::Other(format!(
            "Unknown entity type for event collection: {}",
            entity.entity_type
        ))),
    }
}

/// Lookup key: (entity_type, entity_id) -> (iid, project_path)
type EntityLookup = std::collections::HashMap<(String, i64), (i64, String)>;

fn build_entity_lookup(seeds: &[EntityRef], expanded: &[ExpandedEntityRef]) -> EntityLookup {
    let mut lookup = EntityLookup::new();
    for e in seeds {
        lookup.insert(
            (e.entity_type.clone(), e.entity_id),
            (e.entity_iid, e.project_path.clone()),
        );
    }
    for exp in expanded {
        let e = &exp.entity_ref;
        lookup.insert(
            (e.entity_type.clone(), e.entity_id),
            (e.entity_iid, e.project_path.clone()),
        );
    }
    lookup
}

/// Collect full discussion threads for matched discussions.
fn collect_discussion_threads(
    conn: &Connection,
    matched_discussions: &[MatchedDiscussion],
    entity_lookup: &EntityLookup,
    events: &mut Vec<TimelineEvent>,
) -> Result<()> {
    // Deduplicate by discussion_id
    let mut seen = HashSet::new();

    let mut stmt = conn.prepare(
        "SELECT id, author_username, body, created_at FROM notes
         WHERE discussion_id = ?1 AND is_system = 0
         ORDER BY created_at ASC",
    )?;

    for disc in matched_discussions {
        if !seen.insert(disc.discussion_id) {
            continue;
        }

        let (iid, project_path) =
            match entity_lookup.get(&(disc.entity_type.clone(), disc.entity_id)) {
                Some(val) => val.clone(),
                None => continue, // entity not in seed or expanded set
            };

        let rows = stmt.query_map(rusqlite::params![disc.discussion_id], |row| {
            Ok((
                row.get::<_, i64>(0)?,            // id
                row.get::<_, Option<String>>(1)?, // author_username
                row.get::<_, Option<String>>(2)?, // body
                row.get::<_, i64>(3)?,            // created_at
            ))
        })?;

        let mut notes = Vec::new();
        for row_result in rows {
            let (note_id, author, body, created_at) = row_result?;
            let body = truncate_to_chars(body.as_deref().unwrap_or(""), THREAD_NOTE_MAX_CHARS);
            notes.push(ThreadNote {
                note_id,
                author,
                body,
                created_at,
            });
        }

        // Skip empty threads (all notes were system notes)
        if notes.is_empty() {
            continue;
        }

        let first_created_at = notes[0].created_at;

        // Cap notes per thread
        let total_notes = notes.len();
        if total_notes > THREAD_MAX_NOTES {
            notes.truncate(THREAD_MAX_NOTES);
            notes.push(ThreadNote {
                note_id: -1,
                author: None,
                body: format!("[{} more notes not shown]", total_notes - THREAD_MAX_NOTES),
                created_at: notes.last().map_or(first_created_at, |n| n.created_at),
            });
        }

        let note_count = notes.len();
        let actor = notes.first().and_then(|n| n.author.clone());

        events.push(TimelineEvent {
            timestamp: first_created_at,
            entity_type: disc.entity_type.clone(),
            entity_id: disc.entity_id,
            entity_iid: iid,
            project_path,
            event_type: TimelineEventType::DiscussionThread {
                discussion_id: disc.discussion_id,
                notes,
            },
            summary: format!("Discussion ({note_count} notes)"),
            actor,
            url: None,
            is_seed: true,
        });
    }

    Ok(())
}

#[cfg(test)]
#[path = "timeline_collect_tests.rs"]
mod tests;