use sqlx::SqlitePool;
use kon_core::error::{KonError, Result};

/// Each migration is a (version, description, sql) tuple.
/// Migrations MUST be append-only — never modify an existing migration.
/// Column defaults and NOT NULL constraints must exactly match the existing schema.
const MIGRATIONS: &[(i64, &str, &str)] = &[
    (1, "initial schema", r#"
        CREATE TABLE IF NOT EXISTS transcripts (
            id TEXT PRIMARY KEY,
            text TEXT NOT NULL DEFAULT '',
            source TEXT NOT NULL DEFAULT 'microphone',
            title TEXT,
            audio_path TEXT,
            duration REAL NOT NULL DEFAULT 0.0,
            engine TEXT,
            model_id TEXT,
            inference_ms INTEGER,
            sample_rate INTEGER,
            audio_channels INTEGER,
            format_mode TEXT,
            remove_fillers INTEGER NOT NULL DEFAULT 0,
            british_english INTEGER NOT NULL DEFAULT 0,
            anti_hallucination INTEGER NOT NULL DEFAULT 0,
            created_at TEXT NOT NULL DEFAULT (datetime('now'))
        );

        CREATE TABLE IF NOT EXISTS segments (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            transcript_id TEXT NOT NULL REFERENCES transcripts(id) ON DELETE CASCADE,
            start_time REAL NOT NULL,
            end_time REAL NOT NULL,
            text TEXT NOT NULL DEFAULT ''
        );

        CREATE TABLE IF NOT EXISTS tasks (
            id TEXT PRIMARY KEY,
            text TEXT NOT NULL,
            bucket TEXT NOT NULL DEFAULT 'inbox',
            list_id TEXT,
            effort TEXT,
            done INTEGER NOT NULL DEFAULT 0,
            done_at TEXT,
            created_at TEXT NOT NULL DEFAULT (datetime('now')),
            source_transcript_id TEXT
        );

        CREATE TABLE IF NOT EXISTS task_lists (
            id TEXT PRIMARY KEY,
            name TEXT NOT NULL,
            built_in INTEGER NOT NULL DEFAULT 0,
            profile_id TEXT,
            created_at TEXT NOT NULL DEFAULT (datetime('now'))
        );

        CREATE TABLE IF NOT EXISTS settings (
            key TEXT PRIMARY KEY,
            value TEXT NOT NULL
        );

        CREATE TABLE IF NOT EXISTS error_log (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            timestamp TEXT NOT NULL DEFAULT (datetime('now')),
            context TEXT NOT NULL,
            error_code TEXT,
            message TEXT NOT NULL,
            metadata TEXT
        );

        CREATE INDEX IF NOT EXISTS idx_transcripts_created ON transcripts(created_at);
        CREATE INDEX IF NOT EXISTS idx_segments_transcript ON segments(transcript_id);
        CREATE INDEX IF NOT EXISTS idx_tasks_bucket ON tasks(bucket);
        CREATE INDEX IF NOT EXISTS idx_tasks_transcript ON tasks(source_transcript_id);
        CREATE INDEX IF NOT EXISTS idx_error_log_context ON error_log(context)
    "#),
    (2, "transcripts FTS5 + dictionary table", r#"
        CREATE VIRTUAL TABLE IF NOT EXISTS transcripts_fts USING fts5(
            text,
            title,
            content='transcripts',
            content_rowid='rowid',
            tokenize='porter unicode61 remove_diacritics 2'
        );

        CREATE TRIGGER IF NOT EXISTS transcripts_ai AFTER INSERT ON transcripts BEGIN
            INSERT INTO transcripts_fts(rowid, text, title)
            VALUES (new.rowid, new.text, COALESCE(new.title, ''));
        END;

        CREATE TRIGGER IF NOT EXISTS transcripts_ad AFTER DELETE ON transcripts BEGIN
            INSERT INTO transcripts_fts(transcripts_fts, rowid, text, title)
            VALUES ('delete', old.rowid, old.text, COALESCE(old.title, ''));
        END;

        CREATE TRIGGER IF NOT EXISTS transcripts_au AFTER UPDATE ON transcripts BEGIN
            INSERT INTO transcripts_fts(transcripts_fts, rowid, text, title)
            VALUES ('delete', old.rowid, old.text, COALESCE(old.title, ''));
            INSERT INTO transcripts_fts(rowid, text, title)
            VALUES (new.rowid, new.text, COALESCE(new.title, ''));
        END;

        CREATE TABLE IF NOT EXISTS dictionary (
            id INTEGER PRIMARY KEY AUTOINCREMENT,
            term TEXT NOT NULL UNIQUE,
            note TEXT,
            created_at TEXT NOT NULL DEFAULT (datetime('now'))
        );

        CREATE INDEX IF NOT EXISTS idx_dictionary_term ON dictionary(term)
    "#),
];

/// Split SQL into individual statements, respecting BEGIN...END trigger blocks.
fn split_statements(sql: &str) -> Vec<String> {
    let mut result = Vec::new();
    let mut current = String::new();
    let mut depth: i32 = 0;
    let upper = sql.to_ascii_uppercase();
    let ub = upper.as_bytes();
    let ob = sql.as_bytes();
    let n = ob.len();
    let mut i = 0;
    while i < n {
        let prev_alpha = i > 0 && ob[i - 1].is_ascii_alphanumeric();
        if !prev_alpha && ub[i..].starts_with(b"BEGIN") {
            let next_alpha = i + 5 < n && ob[i + 5].is_ascii_alphanumeric();
            if !next_alpha { depth += 1; }
        }
        if !prev_alpha && ub[i..].starts_with(b"END") {
            let next_alpha = i + 3 < n && ob[i + 3].is_ascii_alphanumeric();
            if !next_alpha && depth > 0 { depth -= 1; }
        }
        if ob[i] == b';' && depth == 0 {
            let stmt = current.trim().to_string();
            if !stmt.is_empty() { result.push(stmt); }
            current = String::new();
        } else {
            current.push(ob[i] as char);
        }
        i += 1;
    }
    let stmt = current.trim().to_string();
    if !stmt.is_empty() { result.push(stmt); }
    result
}

/// Ensure the schema_version table exists and run any pending migrations.
pub async fn run_migrations(pool: &SqlitePool) -> Result<()> {
    sqlx::query(
        "CREATE TABLE IF NOT EXISTS schema_version (
            version INTEGER PRIMARY KEY,
            description TEXT NOT NULL,
            applied_at TEXT NOT NULL DEFAULT (datetime('now'))
        )"
    )
    .execute(pool)
    .await
    .map_err(|e| KonError::StorageError(format!("Schema version table creation failed: {e}")))?;

    let current: i64 = sqlx::query_scalar("SELECT COALESCE(MAX(version), 0) FROM schema_version")
        .fetch_one(pool)
        .await
        .map_err(|e| KonError::StorageError(format!("Schema version query failed: {e}")))?;

    for (version, description, sql) in MIGRATIONS {
        if *version > current {
            log::info!("Running migration {}: {}", version, description);

            let statements = split_statements(sql);

            for statement in &statements {
                sqlx::query(statement)
                    .execute(pool)
                    .await
                    .map_err(|e| KonError::StorageError(format!("Migration {} failed: {e}", version)))?;
            }

            sqlx::query("INSERT INTO schema_version (version, description) VALUES (?, ?)")
                .bind(version)
                .bind(description)
                .execute(pool)
                .await
                .map_err(|e| KonError::StorageError(format!("Migration version record failed: {e}")))?;

            log::info!("Migration {} complete", version);
        }
    }

    Ok(())
}

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

    #[tokio::test]
    async fn test_migrations_run_on_empty_db() {
        let pool = SqlitePoolOptions::new()
            .connect("sqlite::memory:")
            .await
            .unwrap();

        run_migrations(&pool).await.unwrap();

        let count: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM schema_version")
            .fetch_one(&pool)
            .await
            .unwrap();
        assert_eq!(count, 1);

        sqlx::query("INSERT INTO settings (key, value) VALUES ('test', 'value')")
            .execute(&pool)
            .await
            .unwrap();
    }

    #[tokio::test]
    async fn test_migrations_idempotent() {
        let pool = SqlitePoolOptions::new()
            .connect("sqlite::memory:")
            .await
            .unwrap();

        run_migrations(&pool).await.unwrap();
        run_migrations(&pool).await.unwrap();

        let count: i64 = sqlx::query_scalar("SELECT COUNT(*) FROM schema_version")
            .fetch_one(&pool)
            .await
            .unwrap();
        assert_eq!(count, 1);
    }
}