use rusqlite::Connection;
use sqlite_vec::sqlite3_vec_init;
use std::fs;
use std::path::Path;
use tracing::{debug, info};

use super::error::{LoreError, Result};

pub const LATEST_SCHEMA_VERSION: i32 = MIGRATIONS.len() as i32;

const MIGRATIONS: &[(&str, &str)] = &[
    ("001", include_str!("../../migrations/001_initial.sql")),
    ("002", include_str!("../../migrations/002_issues.sql")),
    ("003", include_str!("../../migrations/003_indexes.sql")),
    (
        "004",
        include_str!("../../migrations/004_discussions_payload.sql"),
    ),
    (
        "005",
        include_str!("../../migrations/005_assignees_milestone_duedate.sql"),
    ),
    (
        "006",
        include_str!("../../migrations/006_merge_requests.sql"),
    ),
    ("007", include_str!("../../migrations/007_documents.sql")),
    ("008", include_str!("../../migrations/008_fts5.sql")),
    ("009", include_str!("../../migrations/009_embeddings.sql")),
    ("010", include_str!("../../migrations/010_chunk_config.sql")),
    (
        "011",
        include_str!("../../migrations/011_resource_events.sql"),
    ),
    (
        "012",
        include_str!("../../migrations/012_nullable_label_milestone.sql"),
    ),
    (
        "013",
        include_str!("../../migrations/013_resource_event_watermarks.sql"),
    ),
    (
        "014",
        include_str!("../../migrations/014_sync_runs_enrichment.sql"),
    ),
    (
        "015",
        include_str!("../../migrations/015_commit_shas_and_closes_watermark.sql"),
    ),
    (
        "016",
        include_str!("../../migrations/016_mr_file_changes.sql"),
    ),
    ("017", include_str!("../../migrations/017_who_indexes.sql")),
    (
        "018",
        include_str!("../../migrations/018_fix_assignees_composite_index.sql"),
    ),
    (
        "019",
        include_str!("../../migrations/019_list_performance.sql"),
    ),
    (
        "020",
        include_str!("../../migrations/020_mr_diffs_watermark.sql"),
    ),
    (
        "021",
        include_str!("../../migrations/021_work_item_status.sql"),
    ),
    (
        "023",
        include_str!("../../migrations/023_issue_detail_fields.sql"),
    ),
];

pub fn create_connection(db_path: &Path) -> Result<Connection> {
    // SAFETY: `sqlite3_vec_init` is an extern "C" function provided by the sqlite-vec
    // crate with the exact signature expected by `sqlite3_auto_extension`. The transmute
    // converts the concrete function pointer to the `Option<unsafe extern "C" fn()>` type
    // that the FFI expects. This is safe because:
    // 1. The function is a C-ABI init callback with a stable signature.
    // 2. SQLite calls it once per new connection, matching sqlite-vec's contract.
    // 3. `sqlite3_auto_extension` is idempotent for the same function pointer.
    #[allow(clippy::missing_transmute_annotations)]
    unsafe {
        rusqlite::ffi::sqlite3_auto_extension(Some(std::mem::transmute(
            sqlite3_vec_init as *const (),
        )));
    }

    if let Some(parent) = db_path.parent() {
        fs::create_dir_all(parent)?;
    }

    let conn = Connection::open(db_path)?;

    conn.pragma_update(None, "journal_mode", "WAL")?;
    conn.pragma_update(None, "synchronous", "NORMAL")?;
    conn.pragma_update(None, "foreign_keys", "ON")?;
    conn.pragma_update(None, "busy_timeout", 5000)?;
    conn.pragma_update(None, "temp_store", "MEMORY")?;
    conn.pragma_update(None, "cache_size", -64000)?;
    conn.pragma_update(None, "mmap_size", 268_435_456)?;

    debug!(db_path = %db_path.display(), "Database connection created");

    Ok(conn)
}

pub fn run_migrations(conn: &Connection) -> Result<()> {
    let has_version_table: bool = conn
        .query_row(
            "SELECT COUNT(*) > 0 FROM sqlite_master WHERE type='table' AND name='schema_version'",
            [],
            |row| row.get(0),
        )
        .unwrap_or(false);

    let current_version: i32 = if has_version_table {
        conn.query_row(
            "SELECT COALESCE(MAX(version), 0) FROM schema_version",
            [],
            |row| row.get(0),
        )
        .unwrap_or(0)
    } else {
        0
    };

    for (version_str, sql) in MIGRATIONS {
        let version: i32 = version_str.parse().expect("Invalid migration version");

        if version <= current_version {
            debug!(version, "Migration already applied");
            continue;
        }

        let savepoint_name = format!("migration_{}", version);
        conn.execute_batch(&format!("SAVEPOINT {}", savepoint_name))
            .map_err(|e| LoreError::MigrationFailed {
                version,
                message: format!("Failed to create savepoint: {}", e),
                source: Some(e),
            })?;

        match conn.execute_batch(sql) {
            Ok(()) => {
                // Framework-managed version bookkeeping: ensures the version is
                // always recorded even if a migration .sql omits the INSERT.
                // Uses OR REPLACE so legacy migrations that self-register are harmless.
                conn.execute(
                    "INSERT OR REPLACE INTO schema_version (version, applied_at, description) \
                     VALUES (?1, strftime('%s', 'now') * 1000, ?2)",
                    rusqlite::params![version, version_str],
                )
                .map_err(|e| LoreError::MigrationFailed {
                    version,
                    message: format!("Failed to record schema version: {e}"),
                    source: Some(e),
                })?;

                conn.execute_batch(&format!("RELEASE {}", savepoint_name))
                    .map_err(|e| LoreError::MigrationFailed {
                        version,
                        message: format!("Failed to release savepoint: {}", e),
                        source: Some(e),
                    })?;
            }
            Err(e) => {
                let _ = conn.execute_batch(&format!("ROLLBACK TO {}", savepoint_name));
                let _ = conn.execute_batch(&format!("RELEASE {}", savepoint_name));
                return Err(LoreError::MigrationFailed {
                    version,
                    message: e.to_string(),
                    source: Some(e),
                });
            }
        }

        info!(version, "Migration applied");
    }

    Ok(())
}

#[allow(dead_code)]
pub fn run_migrations_from_dir(conn: &Connection, migrations_dir: &Path) -> Result<()> {
    let has_version_table: bool = conn
        .query_row(
            "SELECT COUNT(*) > 0 FROM sqlite_master WHERE type='table' AND name='schema_version'",
            [],
            |row| row.get(0),
        )
        .unwrap_or(false);

    let current_version: i32 = if has_version_table {
        conn.query_row(
            "SELECT COALESCE(MAX(version), 0) FROM schema_version",
            [],
            |row| row.get(0),
        )
        .unwrap_or(0)
    } else {
        0
    };

    let mut migrations: Vec<_> = fs::read_dir(migrations_dir)?
        .filter_map(|entry| entry.ok())
        .filter(|entry| entry.path().extension().is_some_and(|ext| ext == "sql"))
        .collect();

    migrations.sort_by_key(|entry| entry.file_name());

    for entry in migrations {
        let filename = entry.file_name();
        let filename_str = filename.to_string_lossy();

        let version: i32 = match filename_str.split('_').next().and_then(|v| v.parse().ok()) {
            Some(v) => v,
            None => continue,
        };

        if version <= current_version {
            continue;
        }

        let sql = fs::read_to_string(entry.path())?;

        let savepoint_name = format!("migration_{}", version);
        conn.execute_batch(&format!("SAVEPOINT {}", savepoint_name))
            .map_err(|e| LoreError::MigrationFailed {
                version,
                message: format!("Failed to create savepoint: {}", e),
                source: Some(e),
            })?;

        match conn.execute_batch(&sql) {
            Ok(()) => {
                conn.execute_batch(&format!("RELEASE {}", savepoint_name))
                    .map_err(|e| LoreError::MigrationFailed {
                        version,
                        message: format!("Failed to release savepoint: {}", e),
                        source: Some(e),
                    })?;
            }
            Err(e) => {
                let _ = conn.execute_batch(&format!("ROLLBACK TO {}", savepoint_name));
                let _ = conn.execute_batch(&format!("RELEASE {}", savepoint_name));
                return Err(LoreError::MigrationFailed {
                    version,
                    message: e.to_string(),
                    source: Some(e),
                });
            }
        }

        info!(version, file = %filename_str, "Migration applied");
    }

    Ok(())
}

pub fn verify_pragmas(conn: &Connection) -> (bool, Vec<String>) {
    let mut issues = Vec::new();

    let journal_mode: String = conn
        .pragma_query_value(None, "journal_mode", |row| row.get(0))
        .unwrap_or_default();
    if journal_mode != "wal" {
        issues.push(format!("journal_mode is {journal_mode}, expected 'wal'"));
    }

    let foreign_keys: i32 = conn
        .pragma_query_value(None, "foreign_keys", |row| row.get(0))
        .unwrap_or(0);
    if foreign_keys != 1 {
        issues.push(format!("foreign_keys is {foreign_keys}, expected 1"));
    }

    let busy_timeout: i32 = conn
        .pragma_query_value(None, "busy_timeout", |row| row.get(0))
        .unwrap_or(0);
    if busy_timeout != 5000 {
        issues.push(format!("busy_timeout is {busy_timeout}, expected 5000"));
    }

    let synchronous: i32 = conn
        .pragma_query_value(None, "synchronous", |row| row.get(0))
        .unwrap_or(0);
    if synchronous != 1 {
        issues.push(format!("synchronous is {synchronous}, expected 1 (NORMAL)"));
    }

    (issues.is_empty(), issues)
}

pub fn get_schema_version(conn: &Connection) -> i32 {
    let has_version_table: bool = conn
        .query_row(
            "SELECT COUNT(*) > 0 FROM sqlite_master WHERE type='table' AND name='schema_version'",
            [],
            |row| row.get(0),
        )
        .unwrap_or(false);

    if !has_version_table {
        return 0;
    }

    conn.query_row(
        "SELECT COALESCE(MAX(version), 0) FROM schema_version",
        [],
        |row| row.get(0),
    )
    .unwrap_or(0)
}