use std::ops::Deref;

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

use crate::Config;
use crate::core::error::{LoreError, 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::merge_request::transform_merge_request;
use crate::gitlab::types::GitLabMergeRequest;
use crate::ingestion::dirty_tracker;

#[derive(Debug, Default)]
pub struct IngestMergeRequestsResult {
    pub fetched: usize,
    pub upserted: usize,
    pub labels_created: usize,
    pub assignees_linked: usize,
    pub reviewers_linked: usize,
}

#[derive(Debug, Clone)]
pub struct MrForDiscussionSync {
    pub local_mr_id: i64,
    pub iid: i64,
    pub updated_at: i64,
}

#[derive(Debug, Default)]
struct SyncCursor {
    updated_at_cursor: Option<i64>,
    tie_breaker_id: Option<i64>,
}

pub async fn ingest_merge_requests(
    conn: &Connection,
    client: &GitLabClient,
    config: &Config,
    project_id: i64,
    gitlab_project_id: i64,
    full_sync: bool,
) -> Result<IngestMergeRequestsResult> {
    let mut result = IngestMergeRequestsResult::default();

    if full_sync {
        reset_sync_cursor(conn, project_id)?;
        reset_discussion_watermarks(conn, project_id)?;
        info!("Full sync: cursor and discussion watermarks reset");
    }

    let cursor = get_sync_cursor(conn, project_id)?;
    debug!(?cursor, "Starting MR ingestion with cursor");

    let mut page = 1u32;
    let per_page = 100u32;

    loop {
        let page_result = client
            .fetch_merge_requests_page(
                gitlab_project_id,
                cursor.updated_at_cursor,
                config.sync.cursor_rewind_seconds,
                page,
                per_page,
            )
            .await?;

        let mut last_updated_at: Option<i64> = None;
        let mut last_gitlab_id: Option<i64> = None;

        for mr in &page_result.items {
            result.fetched += 1;

            let mr_updated_at = match parse_timestamp(&mr.updated_at) {
                Ok(ts) => ts,
                Err(e) => {
                    warn!(
                        gitlab_id = mr.id,
                        error = %e,
                        "Skipping MR with invalid timestamp"
                    );
                    continue;
                }
            };

            if !passes_cursor_filter_with_ts(mr.id, mr_updated_at, &cursor) {
                debug!(gitlab_id = mr.id, "Skipping already-processed MR");
                continue;
            }

            let mr_result = process_single_mr(conn, config, project_id, mr)?;
            result.upserted += 1;
            result.labels_created += mr_result.labels_created;
            result.assignees_linked += mr_result.assignees_linked;
            result.reviewers_linked += mr_result.reviewers_linked;

            last_updated_at = Some(mr_updated_at);
            last_gitlab_id = Some(mr.id);
        }

        if let (Some(ts), Some(id)) = (last_updated_at, last_gitlab_id) {
            update_sync_cursor(conn, project_id, ts, id)?;
            debug!(page, "Page-boundary cursor update");
        }

        if page_result.is_last_page {
            break;
        }
        match page_result.next_page {
            Some(np) => page = np,
            None => break,
        }
    }

    info!(
        fetched = result.fetched,
        upserted = result.upserted,
        labels_created = result.labels_created,
        assignees_linked = result.assignees_linked,
        reviewers_linked = result.reviewers_linked,
        "MR ingestion complete"
    );

    Ok(result)
}

struct ProcessMrResult {
    labels_created: usize,
    assignees_linked: usize,
    reviewers_linked: usize,
}

fn process_single_mr(
    conn: &Connection,
    config: &Config,
    project_id: i64,
    mr: &GitLabMergeRequest,
) -> Result<ProcessMrResult> {
    let payload_bytes = serde_json::to_vec(mr)?;
    let transformed = transform_merge_request(mr, project_id)
        .map_err(|e| LoreError::Other(format!("MR transform failed: {}", e)))?;

    let tx = conn.unchecked_transaction()?;
    let result =
        process_mr_in_transaction(&tx, config, project_id, mr, &payload_bytes, &transformed)?;
    tx.commit()?;

    Ok(result)
}

fn process_mr_in_transaction(
    tx: &Transaction<'_>,
    config: &Config,
    project_id: i64,
    mr: &GitLabMergeRequest,
    payload_bytes: &[u8],
    transformed: &crate::gitlab::transformers::merge_request::MergeRequestWithMetadata,
) -> Result<ProcessMrResult> {
    let mut labels_created = 0;
    let mr_row = &transformed.merge_request;
    let now = now_ms();

    let payload_id = store_payload(
        tx.deref(),
        StorePayloadOptions {
            project_id: Some(project_id),
            resource_type: "merge_request",
            gitlab_id: &mr.id.to_string(),
            json_bytes: payload_bytes,
            compress: config.storage.compress_raw_payloads,
        },
    )?;

    tx.execute(
        "INSERT INTO merge_requests (
            gitlab_id, project_id, iid, title, description, state, draft,
            author_username, source_branch, target_branch, head_sha,
            references_short, references_full, detailed_merge_status,
            merge_user_username, created_at, updated_at, merged_at, closed_at,
            last_seen_at, web_url, 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)
        ON CONFLICT(gitlab_id) DO UPDATE SET
            title = excluded.title,
            description = excluded.description,
            state = excluded.state,
            draft = excluded.draft,
            author_username = excluded.author_username,
            source_branch = excluded.source_branch,
            target_branch = excluded.target_branch,
            head_sha = excluded.head_sha,
            references_short = excluded.references_short,
            references_full = excluded.references_full,
            detailed_merge_status = excluded.detailed_merge_status,
            merge_user_username = excluded.merge_user_username,
            updated_at = excluded.updated_at,
            merged_at = excluded.merged_at,
            closed_at = excluded.closed_at,
            last_seen_at = excluded.last_seen_at,
            web_url = excluded.web_url,
            raw_payload_id = excluded.raw_payload_id",
        params![
            mr_row.gitlab_id,
            project_id,
            mr_row.iid,
            &mr_row.title,
            &mr_row.description,
            &mr_row.state,
            mr_row.draft,
            &mr_row.author_username,
            &mr_row.source_branch,
            &mr_row.target_branch,
            &mr_row.head_sha,
            &mr_row.references_short,
            &mr_row.references_full,
            &mr_row.detailed_merge_status,
            &mr_row.merge_user_username,
            mr_row.created_at,
            mr_row.updated_at,
            mr_row.merged_at,
            mr_row.closed_at,
            now,
            &mr_row.web_url,
            payload_id,
        ],
    )?;

    let local_mr_id: i64 = tx.query_row(
        "SELECT id FROM merge_requests WHERE project_id = ? AND iid = ?",
        (project_id, mr_row.iid),
        |row| row.get(0),
    )?;

    dirty_tracker::mark_dirty_tx(tx, SourceType::MergeRequest, local_mr_id)?;

    tx.execute(
        "DELETE FROM mr_labels WHERE merge_request_id = ?",
        [local_mr_id],
    )?;
    for label_name in &transformed.label_names {
        let label_id = upsert_label_tx(tx, project_id, label_name, &mut labels_created)?;
        tx.execute(
            "INSERT OR IGNORE INTO mr_labels (merge_request_id, label_id) VALUES (?, ?)",
            (local_mr_id, label_id),
        )?;
    }

    tx.execute(
        "DELETE FROM mr_assignees WHERE merge_request_id = ?",
        [local_mr_id],
    )?;
    let assignees_linked = transformed.assignee_usernames.len();
    for username in &transformed.assignee_usernames {
        tx.execute(
            "INSERT OR IGNORE INTO mr_assignees (merge_request_id, username) VALUES (?, ?)",
            (local_mr_id, username),
        )?;
    }

    tx.execute(
        "DELETE FROM mr_reviewers WHERE merge_request_id = ?",
        [local_mr_id],
    )?;
    let reviewers_linked = transformed.reviewer_usernames.len();
    for username in &transformed.reviewer_usernames {
        tx.execute(
            "INSERT OR IGNORE INTO mr_reviewers (merge_request_id, username) VALUES (?, ?)",
            (local_mr_id, username),
        )?;
    }

    Ok(ProcessMrResult {
        labels_created,
        assignees_linked,
        reviewers_linked,
    })
}

fn upsert_label_tx(
    tx: &Transaction<'_>,
    project_id: i64,
    name: &str,
    created_count: &mut usize,
) -> Result<i64> {
    let id: i64 = tx.query_row(
        "INSERT INTO labels (project_id, name) VALUES (?1, ?2)
         ON CONFLICT(project_id, name) DO UPDATE SET name = excluded.name
         RETURNING id",
        (project_id, name),
        |row| row.get(0),
    )?;

    if tx.last_insert_rowid() == id {
        *created_count += 1;
    }

    Ok(id)
}

fn passes_cursor_filter_with_ts(gitlab_id: i64, mr_ts: i64, cursor: &SyncCursor) -> bool {
    let Some(cursor_ts) = cursor.updated_at_cursor else {
        return true;
    };

    if mr_ts < cursor_ts {
        return false;
    }

    if mr_ts == cursor_ts
        && let Some(cursor_id) = cursor.tie_breaker_id
        && gitlab_id <= cursor_id
    {
        return false;
    }

    true
}

fn get_sync_cursor(conn: &Connection, project_id: i64) -> Result<SyncCursor> {
    let row: Option<(Option<i64>, Option<i64>)> = conn
        .query_row(
            "SELECT updated_at_cursor, tie_breaker_id FROM sync_cursors
             WHERE project_id = ? AND resource_type = 'merge_requests'",
            [project_id],
            |row| Ok((row.get(0)?, row.get(1)?)),
        )
        .ok();

    Ok(match row {
        Some((updated_at, tie_breaker)) => SyncCursor {
            updated_at_cursor: updated_at,
            tie_breaker_id: tie_breaker,
        },
        None => SyncCursor::default(),
    })
}

fn update_sync_cursor(
    conn: &Connection,
    project_id: i64,
    updated_at: i64,
    gitlab_id: i64,
) -> Result<()> {
    conn.execute(
        "INSERT INTO sync_cursors (project_id, resource_type, updated_at_cursor, tie_breaker_id)
         VALUES (?1, 'merge_requests', ?2, ?3)
         ON CONFLICT(project_id, resource_type) DO UPDATE SET
             updated_at_cursor = excluded.updated_at_cursor,
             tie_breaker_id = excluded.tie_breaker_id",
        (project_id, updated_at, gitlab_id),
    )?;
    Ok(())
}

fn reset_sync_cursor(conn: &Connection, project_id: i64) -> Result<()> {
    conn.execute(
        "DELETE FROM sync_cursors WHERE project_id = ? AND resource_type = 'merge_requests'",
        [project_id],
    )?;
    Ok(())
}

fn reset_discussion_watermarks(conn: &Connection, project_id: i64) -> Result<()> {
    conn.execute(
        "UPDATE merge_requests
         SET discussions_synced_for_updated_at = NULL,
             discussions_sync_attempts = 0,
             discussions_sync_last_error = NULL,
             resource_events_synced_for_updated_at = NULL
         WHERE project_id = ?",
        [project_id],
    )?;
    Ok(())
}

pub fn get_mrs_needing_discussion_sync(
    conn: &Connection,
    project_id: i64,
) -> Result<Vec<MrForDiscussionSync>> {
    let mut stmt = conn.prepare(
        "SELECT id, iid, updated_at FROM merge_requests
         WHERE project_id = ?
           AND updated_at > COALESCE(discussions_synced_for_updated_at, 0)",
    )?;

    let mrs: std::result::Result<Vec<_>, _> = stmt
        .query_map([project_id], |row| {
            Ok(MrForDiscussionSync {
                local_mr_id: row.get(0)?,
                iid: row.get(1)?,
                updated_at: row.get(2)?,
            })
        })?
        .collect();

    Ok(mrs?)
}

fn parse_timestamp(ts: &str) -> Result<i64> {
    chrono::DateTime::parse_from_rfc3339(ts)
        .map(|dt| dt.timestamp_millis())
        .map_err(|e| LoreError::Other(format!("Failed to parse timestamp '{}': {}", ts, e)))
}

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

    #[test]
    fn result_default_has_zero_counts() {
        let result = IngestMergeRequestsResult::default();
        assert_eq!(result.fetched, 0);
        assert_eq!(result.upserted, 0);
        assert_eq!(result.labels_created, 0);
        assert_eq!(result.assignees_linked, 0);
        assert_eq!(result.reviewers_linked, 0);
    }

    #[test]
    fn cursor_filter_allows_newer_mrs() {
        let cursor = SyncCursor {
            updated_at_cursor: Some(1705312800000),
            tie_breaker_id: Some(100),
        };

        let later_ts = 1705399200000;
        assert!(passes_cursor_filter_with_ts(101, later_ts, &cursor));
    }

    #[test]
    fn cursor_filter_blocks_older_mrs() {
        let cursor = SyncCursor {
            updated_at_cursor: Some(1705312800000),
            tie_breaker_id: Some(100),
        };

        let earlier_ts = 1705226400000;
        assert!(!passes_cursor_filter_with_ts(99, earlier_ts, &cursor));
    }

    #[test]
    fn cursor_filter_uses_tie_breaker_for_same_timestamp() {
        let cursor = SyncCursor {
            updated_at_cursor: Some(1705312800000),
            tie_breaker_id: Some(100),
        };

        assert!(passes_cursor_filter_with_ts(101, 1705312800000, &cursor));

        assert!(!passes_cursor_filter_with_ts(100, 1705312800000, &cursor));

        assert!(!passes_cursor_filter_with_ts(99, 1705312800000, &cursor));
    }

    #[test]
    fn cursor_filter_allows_all_when_no_cursor() {
        let cursor = SyncCursor::default();
        let old_ts = 1577836800000;
        assert!(passes_cursor_filter_with_ts(1, old_ts, &cursor));
    }
}