use futures::StreamExt;
use rusqlite::{Connection, params};
use tracing::{debug, info, warn};

use crate::Config;
use crate::core::error::Result;
use crate::core::payloads::{StorePayloadOptions, store_payload};
use crate::core::time::now_ms;
use crate::documents::SourceType;
use crate::gitlab::GitLabClient;
use crate::gitlab::transformers::{
    NormalizedDiscussion, NormalizedNote, transform_mr_discussion,
    transform_notes_with_diff_position,
};
use crate::gitlab::types::GitLabDiscussion;
use crate::ingestion::dirty_tracker;

use super::merge_requests::MrForDiscussionSync;

#[derive(Debug, Default)]
pub struct IngestMrDiscussionsResult {
    pub discussions_fetched: usize,
    pub discussions_upserted: usize,
    pub notes_upserted: usize,
    pub notes_skipped_bad_timestamp: usize,
    pub diffnotes_count: usize,
    pub pagination_succeeded: bool,
}

#[derive(Debug)]
pub struct PrefetchedMrDiscussions {
    pub mr: MrForDiscussionSync,
    pub discussions: Vec<PrefetchedDiscussion>,
    pub fetch_error: Option<String>,
    pub had_transform_errors: bool,
    pub notes_skipped_count: usize,
}

#[derive(Debug)]
pub struct PrefetchedDiscussion {
    pub raw: GitLabDiscussion,
    pub normalized: NormalizedDiscussion,
    pub notes: Vec<NormalizedNote>,
}

pub async fn prefetch_mr_discussions(
    client: &GitLabClient,
    gitlab_project_id: i64,
    local_project_id: i64,
    mr: MrForDiscussionSync,
) -> PrefetchedMrDiscussions {
    debug!(mr_iid = mr.iid, "Prefetching discussions for MR");

    let raw_discussions = match client
        .fetch_all_mr_discussions(gitlab_project_id, mr.iid)
        .await
    {
        Ok(d) => d,
        Err(e) => {
            return PrefetchedMrDiscussions {
                mr,
                discussions: Vec::new(),
                fetch_error: Some(e.to_string()),
                had_transform_errors: false,
                notes_skipped_count: 0,
            };
        }
    };

    let mut discussions = Vec::with_capacity(raw_discussions.len());
    let mut had_transform_errors = false;
    let mut notes_skipped_count = 0;

    for raw in raw_discussions {
        let notes = match transform_notes_with_diff_position(&raw, local_project_id) {
            Ok(n) => n,
            Err(e) => {
                warn!(
                    mr_iid = mr.iid,
                    discussion_id = %raw.id,
                    error = %e,
                    "Note transform failed during prefetch"
                );
                had_transform_errors = true;
                notes_skipped_count += raw.notes.len();
                continue;
            }
        };

        let normalized = transform_mr_discussion(&raw, local_project_id, mr.local_mr_id);

        discussions.push(PrefetchedDiscussion {
            raw,
            normalized,
            notes,
        });
    }

    PrefetchedMrDiscussions {
        mr,
        discussions,
        fetch_error: None,
        had_transform_errors,
        notes_skipped_count,
    }
}

pub fn write_prefetched_mr_discussions(
    conn: &Connection,
    config: &Config,
    local_project_id: i64,
    prefetched: PrefetchedMrDiscussions,
) -> Result<IngestMrDiscussionsResult> {
    let sync_succeeded = prefetched.fetch_error.is_none() && !prefetched.had_transform_errors;

    let mut result = IngestMrDiscussionsResult {
        pagination_succeeded: sync_succeeded,
        notes_skipped_bad_timestamp: prefetched.notes_skipped_count,
        ..Default::default()
    };

    let mr = &prefetched.mr;

    if let Some(error) = &prefetched.fetch_error {
        warn!(mr_iid = mr.iid, error = %error, "Prefetch failed for MR");
        record_sync_health_error(conn, mr.local_mr_id, error)?;
        return Ok(result);
    }

    let run_seen_at = now_ms();

    for disc in &prefetched.discussions {
        let diffnotes_in_disc = disc
            .notes
            .iter()
            .filter(|n| n.position_new_path.is_some() || n.position_old_path.is_some())
            .count();
        let notes_in_disc = disc.notes.len();

        let tx = conn.unchecked_transaction()?;

        let payload_bytes = serde_json::to_vec(&disc.raw)?;
        let payload_id = Some(store_payload(
            &tx,
            StorePayloadOptions {
                project_id: Some(local_project_id),
                resource_type: "discussion",
                gitlab_id: &disc.raw.id,
                json_bytes: &payload_bytes,
                compress: config.storage.compress_raw_payloads,
            },
        )?);

        upsert_discussion(&tx, &disc.normalized, run_seen_at, payload_id)?;

        let local_discussion_id: i64 = tx.query_row(
            "SELECT id FROM discussions WHERE project_id = ? AND gitlab_discussion_id = ?",
            params![local_project_id, &disc.normalized.gitlab_discussion_id],
            |row| row.get(0),
        )?;

        dirty_tracker::mark_dirty_tx(&tx, SourceType::Discussion, local_discussion_id)?;

        for note in &disc.notes {
            let should_store_payload = !note.is_system
                || note.position_new_path.is_some()
                || note.position_old_path.is_some();

            let note_payload_id = if should_store_payload {
                let note_data = disc.raw.notes.iter().find(|n| n.id == note.gitlab_id);
                if let Some(note_data) = note_data {
                    let note_payload_bytes = serde_json::to_vec(note_data)?;
                    Some(store_payload(
                        &tx,
                        StorePayloadOptions {
                            project_id: Some(local_project_id),
                            resource_type: "note",
                            gitlab_id: &note.gitlab_id.to_string(),
                            json_bytes: &note_payload_bytes,
                            compress: config.storage.compress_raw_payloads,
                        },
                    )?)
                } else {
                    None
                }
            } else {
                None
            };

            upsert_note(&tx, local_discussion_id, note, run_seen_at, note_payload_id)?;
        }

        tx.commit()?;

        result.discussions_fetched += 1;
        result.discussions_upserted += 1;
        result.notes_upserted += notes_in_disc;
        result.diffnotes_count += diffnotes_in_disc;
    }

    if sync_succeeded {
        sweep_stale_discussions(conn, mr.local_mr_id, run_seen_at)?;
        sweep_stale_notes(conn, local_project_id, mr.local_mr_id, run_seen_at)?;
        mark_discussions_synced(conn, mr.local_mr_id, mr.updated_at)?;
        clear_sync_health_error(conn, mr.local_mr_id)?;

        debug!(
            mr_iid = mr.iid,
            "MR discussion sync complete, watermark advanced"
        );
    } else if prefetched.had_transform_errors {
        warn!(
            mr_iid = mr.iid,
            notes_skipped = prefetched.notes_skipped_count,
            "Transform errors occurred; watermark NOT advanced to preserve data"
        );
    }

    Ok(result)
}

pub async fn ingest_mr_discussions(
    conn: &Connection,
    client: &GitLabClient,
    config: &Config,
    gitlab_project_id: i64,
    local_project_id: i64,
    mrs: &[MrForDiscussionSync],
) -> Result<IngestMrDiscussionsResult> {
    let mut total_result = IngestMrDiscussionsResult {
        pagination_succeeded: true,
        ..Default::default()
    };

    for mr in mrs {
        let result = ingest_discussions_for_mr(
            conn,
            client,
            config,
            gitlab_project_id,
            local_project_id,
            mr,
        )
        .await?;

        total_result.discussions_fetched += result.discussions_fetched;
        total_result.discussions_upserted += result.discussions_upserted;
        total_result.notes_upserted += result.notes_upserted;
        total_result.notes_skipped_bad_timestamp += result.notes_skipped_bad_timestamp;
        total_result.diffnotes_count += result.diffnotes_count;
        if !result.pagination_succeeded {
            total_result.pagination_succeeded = false;
        }
    }

    info!(
        mrs_processed = mrs.len(),
        discussions_fetched = total_result.discussions_fetched,
        discussions_upserted = total_result.discussions_upserted,
        notes_upserted = total_result.notes_upserted,
        notes_skipped = total_result.notes_skipped_bad_timestamp,
        diffnotes = total_result.diffnotes_count,
        pagination_succeeded = total_result.pagination_succeeded,
        "MR discussion ingestion complete"
    );

    Ok(total_result)
}

async fn ingest_discussions_for_mr(
    conn: &Connection,
    client: &GitLabClient,
    config: &Config,
    gitlab_project_id: i64,
    local_project_id: i64,
    mr: &MrForDiscussionSync,
) -> Result<IngestMrDiscussionsResult> {
    let mut result = IngestMrDiscussionsResult {
        pagination_succeeded: true,
        ..Default::default()
    };

    debug!(
        mr_iid = mr.iid,
        local_mr_id = mr.local_mr_id,
        "Fetching discussions for MR"
    );

    let run_seen_at = now_ms();

    let mut discussions_stream = client.paginate_mr_discussions(gitlab_project_id, mr.iid);

    let mut received_first_response = false;

    while let Some(disc_result) = discussions_stream.next().await {
        if !received_first_response {
            received_first_response = true;
        }

        let gitlab_discussion = match disc_result {
            Ok(d) => d,
            Err(e) => {
                warn!(
                    mr_iid = mr.iid,
                    error = %e,
                    "Error during MR discussion pagination"
                );
                result.pagination_succeeded = false;
                record_sync_health_error(conn, mr.local_mr_id, &e.to_string())?;
                break;
            }
        };
        let notes = match transform_notes_with_diff_position(&gitlab_discussion, local_project_id) {
            Ok(notes) => notes,
            Err(e) => {
                warn!(
                    mr_iid = mr.iid,
                    discussion_id = %gitlab_discussion.id,
                    error = %e,
                    "Note transform failed; preserving existing notes"
                );
                result.notes_skipped_bad_timestamp += gitlab_discussion.notes.len();
                result.pagination_succeeded = false;
                continue;
            }
        };

        let diffnotes_in_disc = notes
            .iter()
            .filter(|n| n.position_new_path.is_some() || n.position_old_path.is_some())
            .count();
        let notes_count = notes.len();

        let normalized_discussion =
            transform_mr_discussion(&gitlab_discussion, local_project_id, mr.local_mr_id);

        let tx = conn.unchecked_transaction()?;

        let payload_bytes = serde_json::to_vec(&gitlab_discussion)?;
        let payload_id = Some(store_payload(
            &tx,
            StorePayloadOptions {
                project_id: Some(local_project_id),
                resource_type: "discussion",
                gitlab_id: &gitlab_discussion.id,
                json_bytes: &payload_bytes,
                compress: config.storage.compress_raw_payloads,
            },
        )?);

        upsert_discussion(&tx, &normalized_discussion, run_seen_at, payload_id)?;

        let local_discussion_id: i64 = tx.query_row(
            "SELECT id FROM discussions WHERE project_id = ? AND gitlab_discussion_id = ?",
            params![
                local_project_id,
                &normalized_discussion.gitlab_discussion_id
            ],
            |row| row.get(0),
        )?;

        dirty_tracker::mark_dirty_tx(&tx, SourceType::Discussion, local_discussion_id)?;

        for note in &notes {
            let should_store_payload = !note.is_system
                || note.position_new_path.is_some()
                || note.position_old_path.is_some();

            let note_payload_id = if should_store_payload {
                let note_data = gitlab_discussion
                    .notes
                    .iter()
                    .find(|n| n.id == note.gitlab_id);
                if let Some(note_data) = note_data {
                    let note_payload_bytes = serde_json::to_vec(note_data)?;
                    Some(store_payload(
                        &tx,
                        StorePayloadOptions {
                            project_id: Some(local_project_id),
                            resource_type: "note",
                            gitlab_id: &note.gitlab_id.to_string(),
                            json_bytes: &note_payload_bytes,
                            compress: config.storage.compress_raw_payloads,
                        },
                    )?)
                } else {
                    None
                }
            } else {
                None
            };

            upsert_note(&tx, local_discussion_id, note, run_seen_at, note_payload_id)?;
        }

        tx.commit()?;

        result.discussions_fetched += 1;
        result.discussions_upserted += 1;
        result.notes_upserted += notes_count;
        result.diffnotes_count += diffnotes_in_disc;
    }

    if result.pagination_succeeded && received_first_response {
        sweep_stale_discussions(conn, mr.local_mr_id, run_seen_at)?;

        sweep_stale_notes(conn, local_project_id, mr.local_mr_id, run_seen_at)?;

        mark_discussions_synced(conn, mr.local_mr_id, mr.updated_at)?;
        clear_sync_health_error(conn, mr.local_mr_id)?;

        debug!(
            mr_iid = mr.iid,
            "MR discussion sync complete, watermark advanced"
        );
    } else if result.pagination_succeeded && !received_first_response {
        sweep_stale_discussions(conn, mr.local_mr_id, run_seen_at)?;
        sweep_stale_notes(conn, local_project_id, mr.local_mr_id, run_seen_at)?;
        mark_discussions_synced(conn, mr.local_mr_id, mr.updated_at)?;
        clear_sync_health_error(conn, mr.local_mr_id)?;
    } else {
        warn!(
            mr_iid = mr.iid,
            discussions_seen = result.discussions_upserted,
            notes_skipped = result.notes_skipped_bad_timestamp,
            "Watermark NOT advanced; will retry on next sync"
        );
    }

    Ok(result)
}

fn upsert_discussion(
    conn: &Connection,
    discussion: &crate::gitlab::transformers::NormalizedDiscussion,
    last_seen_at: i64,
    payload_id: Option<i64>,
) -> Result<()> {
    conn.execute(
        "INSERT INTO discussions (
            gitlab_discussion_id, project_id, issue_id, merge_request_id, noteable_type,
            individual_note, first_note_at, last_note_at, last_seen_at,
            resolvable, resolved, raw_payload_id
        ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, ?12)
        ON CONFLICT(project_id, gitlab_discussion_id) DO UPDATE SET
            first_note_at = excluded.first_note_at,
            last_note_at = excluded.last_note_at,
            last_seen_at = excluded.last_seen_at,
            resolvable = excluded.resolvable,
            resolved = excluded.resolved,
            raw_payload_id = COALESCE(excluded.raw_payload_id, raw_payload_id)",
        params![
            &discussion.gitlab_discussion_id,
            discussion.project_id,
            discussion.issue_id,
            discussion.merge_request_id,
            &discussion.noteable_type,
            discussion.individual_note,
            discussion.first_note_at,
            discussion.last_note_at,
            last_seen_at,
            discussion.resolvable,
            discussion.resolved,
            payload_id,
        ],
    )?;
    Ok(())
}

fn upsert_note(
    conn: &Connection,
    discussion_id: i64,
    note: &NormalizedNote,
    last_seen_at: i64,
    payload_id: Option<i64>,
) -> Result<()> {
    conn.execute(
        "INSERT INTO notes (
            gitlab_id, discussion_id, project_id, note_type, is_system,
            author_username, body, created_at, updated_at, last_seen_at,
            position, resolvable, resolved, resolved_by, resolved_at,
            position_old_path, position_new_path, position_old_line, position_new_line,
            position_type, position_line_range_start, position_line_range_end,
            position_base_sha, position_start_sha, position_head_sha,
            raw_payload_id
        ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11, ?12, ?13, ?14, ?15, ?16, ?17, ?18, ?19, ?20, ?21, ?22, ?23, ?24, ?25, ?26)
        ON CONFLICT(gitlab_id) DO UPDATE SET
            note_type = excluded.note_type,
            body = excluded.body,
            updated_at = excluded.updated_at,
            last_seen_at = excluded.last_seen_at,
            resolvable = excluded.resolvable,
            resolved = excluded.resolved,
            resolved_by = excluded.resolved_by,
            resolved_at = excluded.resolved_at,
            position_old_path = excluded.position_old_path,
            position_new_path = excluded.position_new_path,
            position_old_line = excluded.position_old_line,
            position_new_line = excluded.position_new_line,
            position_type = excluded.position_type,
            position_line_range_start = excluded.position_line_range_start,
            position_line_range_end = excluded.position_line_range_end,
            position_base_sha = excluded.position_base_sha,
            position_start_sha = excluded.position_start_sha,
            position_head_sha = excluded.position_head_sha,
            raw_payload_id = COALESCE(excluded.raw_payload_id, raw_payload_id)",
        params![
            note.gitlab_id,
            discussion_id,
            note.project_id,
            &note.note_type,
            note.is_system,
            &note.author_username,
            &note.body,
            note.created_at,
            note.updated_at,
            last_seen_at,
            note.position,
            note.resolvable,
            note.resolved,
            &note.resolved_by,
            note.resolved_at,
            &note.position_old_path,
            &note.position_new_path,
            note.position_old_line,
            note.position_new_line,
            &note.position_type,
            note.position_line_range_start,
            note.position_line_range_end,
            &note.position_base_sha,
            &note.position_start_sha,
            &note.position_head_sha,
            payload_id,
        ],
    )?;
    Ok(())
}

fn sweep_stale_discussions(conn: &Connection, local_mr_id: i64, run_seen_at: i64) -> Result<usize> {
    let deleted = conn.execute(
        "DELETE FROM discussions
         WHERE merge_request_id = ? AND last_seen_at < ?",
        params![local_mr_id, run_seen_at],
    )?;
    if deleted > 0 {
        debug!(local_mr_id, deleted, "Swept stale discussions");
    }
    Ok(deleted)
}

fn sweep_stale_notes(
    conn: &Connection,
    local_project_id: i64,
    local_mr_id: i64,
    run_seen_at: i64,
) -> Result<usize> {
    let deleted = conn.execute(
        "DELETE FROM notes
         WHERE project_id = ?
           AND discussion_id IN (
             SELECT id FROM discussions WHERE merge_request_id = ?
           )
           AND last_seen_at < ?",
        params![local_project_id, local_mr_id, run_seen_at],
    )?;
    if deleted > 0 {
        debug!(local_mr_id, deleted, "Swept stale notes");
    }
    Ok(deleted)
}

fn mark_discussions_synced(conn: &Connection, local_mr_id: i64, updated_at: i64) -> Result<()> {
    conn.execute(
        "UPDATE merge_requests SET discussions_synced_for_updated_at = ? WHERE id = ?",
        params![updated_at, local_mr_id],
    )?;
    Ok(())
}

fn record_sync_health_error(conn: &Connection, local_mr_id: i64, error: &str) -> Result<()> {
    conn.execute(
        "UPDATE merge_requests SET
            discussions_sync_last_attempt_at = ?,
            discussions_sync_attempts = discussions_sync_attempts + 1,
            discussions_sync_last_error = ?
         WHERE id = ?",
        params![now_ms(), error, local_mr_id],
    )?;
    Ok(())
}

fn clear_sync_health_error(conn: &Connection, local_mr_id: i64) -> Result<()> {
    conn.execute(
        "UPDATE merge_requests SET
            discussions_sync_last_attempt_at = ?,
            discussions_sync_last_error = NULL
         WHERE id = ?",
        params![now_ms(), local_mr_id],
    )?;
    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn result_default_has_zero_counts() {
        let result = IngestMrDiscussionsResult::default();
        assert_eq!(result.discussions_fetched, 0);
        assert_eq!(result.discussions_upserted, 0);
        assert_eq!(result.notes_upserted, 0);
        assert_eq!(result.notes_skipped_bad_timestamp, 0);
        assert_eq!(result.diffnotes_count, 0);
        assert!(!result.pagination_succeeded);
    }

    #[test]
    fn result_pagination_succeeded_false_by_default() {
        let result = IngestMrDiscussionsResult::default();
        assert!(!result.pagination_succeeded);
    }
}