use crate::common::config::AppConfig;
use sqlx::{PgPool, postgres::PgPoolOptions};
use std::time::Duration;

/// Database initialization error.
#[derive(Debug, thiserror::Error)]
#[error("{0}")]
pub struct DbError(String);

type Result<T> = std::result::Result<T, DbError>;

/// Segmented database pools.
///
/// `primary` is used for all user-facing request paths (REST, WebDAV, CalDAV,
/// CardDAV).  `maintenance` is a smaller, isolated pool reserved for
/// background / batch operations (verify_integrity, garbage_collect,
/// update_all_users_storage_usage, trash cleanup) so they can never starve
/// interactive requests.
pub struct DbPools {
    /// Pool for user-facing request paths.
    pub primary: PgPool,
    /// Pool for background / batch maintenance tasks.
    pub maintenance: PgPool,
}

/// Create both the primary and maintenance database pools.
///
/// The schema is applied once via the primary pool.  The maintenance pool
/// shares the same connection string but has its own, smaller budget.
pub async fn create_database_pools(config: &AppConfig) -> Result<DbPools> {
    tracing::info!(
        "Initializing PostgreSQL connections with URL: {}",
        config
            .database
            .connection_string
            .replace("postgres://", "postgres://[user]:[pass]@")
    );

    // --- primary pool ---
    let primary = create_pool_with_retries(
        &config.database.connection_string,
        config.database.max_connections,
        config.database.min_connections,
        config.database.connect_timeout_secs,
        config.database.idle_timeout_secs,
        config.database.max_lifetime_secs,
        "primary",
    )
    .await?;

    // Apply schema through the primary pool (idempotent)
    tracing::info!("Applying database schema...");
    if let Err(e) = apply_schema(&primary).await {
        return Err(DbError(format!(
            "Database schema could not be applied: {}. \
             Run manually: psql -f db/schema.sql",
            e
        )));
    }
    tracing::info!("Database schema applied successfully");

    // --- maintenance pool ---
    let maintenance = create_pool_with_retries(
        &config.database.connection_string,
        config.database.maintenance_max_connections,
        config.database.maintenance_min_connections,
        config.database.connect_timeout_secs,
        config.database.idle_timeout_secs,
        config.database.max_lifetime_secs,
        "maintenance",
    )
    .await?;

    tracing::info!(
        "Database pools ready — primary: {} max / {} min, maintenance: {} max / {} min",
        config.database.max_connections,
        config.database.min_connections,
        config.database.maintenance_max_connections,
        config.database.maintenance_min_connections,
    );

    Ok(DbPools {
        primary,
        maintenance,
    })
}

/// Internal helper: create a single pool with retry logic.
async fn create_pool_with_retries(
    connection_string: &str,
    max_connections: u32,
    min_connections: u32,
    connect_timeout_secs: u64,
    idle_timeout_secs: u64,
    max_lifetime_secs: u64,
    label: &str,
) -> Result<PgPool> {
    let mut attempt = 0;
    const MAX_ATTEMPTS: usize = 5;

    while attempt < MAX_ATTEMPTS {
        attempt += 1;
        tracing::info!(
            "PostgreSQL {} pool connection attempt #{}/{}",
            label,
            attempt,
            MAX_ATTEMPTS
        );

        match PgPoolOptions::new()
            .max_connections(max_connections)
            .min_connections(min_connections)
            .acquire_timeout(Duration::from_secs(connect_timeout_secs))
            .idle_timeout(Duration::from_secs(idle_timeout_secs))
            .max_lifetime(Duration::from_secs(max_lifetime_secs))
            .connect(connection_string)
            .await
        {
            Ok(pool) => match sqlx::query("SELECT 1").execute(&pool).await {
                Ok(_) => {
                    tracing::info!("PostgreSQL {} pool established successfully", label);
                    return Ok(pool);
                }
                Err(e) => {
                    tracing::error!("Error verifying {} pool connection: {}", label, e);
                    if attempt >= MAX_ATTEMPTS {
                        return Err(DbError(format!(
                            "Error verifying PostgreSQL {} pool connection: {}",
                            label, e
                        )));
                    }
                }
            },
            Err(e) => {
                tracing::error!(
                    "Error connecting to PostgreSQL {} pool (attempt {}/{}): {}",
                    label,
                    attempt,
                    MAX_ATTEMPTS,
                    e
                );
                if attempt >= MAX_ATTEMPTS {
                    return Err(DbError(format!(
                        "Error in PostgreSQL {} pool connection: {}",
                        label, e
                    )));
                }
                tokio::time::sleep(Duration::from_secs(2)).await;
            }
        }
    }

    Err(DbError(format!(
        "Could not establish PostgreSQL {} pool connection after {} attempts",
        label, MAX_ATTEMPTS
    )))
}

/// Apply the embedded schema.sql to the database.
/// First tries `raw_sql` (simple query protocol). If that fails, falls back
/// to splitting the SQL into individual statements and executing them one by one.
async fn apply_schema(pool: &PgPool) -> Result<()> {
    let schema_sql = include_str!("../../db/schema.sql");

    // Attempt 1: raw_sql sends the entire script via the simple query protocol
    match sqlx::raw_sql(schema_sql).execute(pool).await {
        Ok(_) => return Ok(()),
        Err(e) => {
            tracing::warn!(
                "raw_sql failed ({}), falling back to statement-by-statement execution",
                e
            );
        }
    }

    // Attempt 2: split into individual statements respecting dollar-quoting
    let statements = split_sql_statements(schema_sql);
    for (i, stmt) in statements.iter().enumerate() {
        let trimmed = stmt.trim();
        if trimmed.is_empty() || trimmed == ";" {
            continue;
        }
        if let Err(e) = sqlx::raw_sql(trimmed).execute(pool).await {
            let preview = if trimmed.len() > 200 {
                &trimmed[..200]
            } else {
                trimmed
            };
            tracing::error!(
                "Schema statement {} failed: {}\n--- SQL ---\n{}\n-----------",
                i + 1,
                e,
                preview
            );
            return Err(DbError(format!("Schema statement {} failed: {}", i + 1, e)));
        }
    }

    Ok(())
}

/// Split a SQL script into individual statements, correctly handling:
/// - Dollar-quoted blocks (`$BODY$...$BODY$`, `$$...$$`)
/// - Single-quoted strings (`'...'`)
/// - Line comments (`-- ...`)
/// - Block comments (`/* ... */`)
///
/// Uses byte-level iteration over the `&str` directly — no intermediate
/// `Vec<char>` allocation (saves ~4× the input size in heap memory).
/// SQL is ASCII-safe, so byte comparison is sufficient for all delimiters.
fn split_sql_statements(sql: &str) -> Vec<String> {
    let mut statements = Vec::new();
    let mut current = String::new();
    let bytes = sql.as_bytes();
    let len = bytes.len();
    let mut i = 0;

    while i < len {
        let b = bytes[i];

        // Line comment
        if b == b'-' && i + 1 < len && bytes[i + 1] == b'-' {
            while i < len && bytes[i] != b'\n' {
                current.push(bytes[i] as char);
                i += 1;
            }
            continue;
        }

        // Block comment
        if b == b'/' && i + 1 < len && bytes[i + 1] == b'*' {
            current.push('/');
            current.push('*');
            i += 2;
            while i + 1 < len && !(bytes[i] == b'*' && bytes[i + 1] == b'/') {
                current.push(bytes[i] as char);
                i += 1;
            }
            if i + 1 < len {
                current.push('*');
                current.push('/');
                i += 2;
            }
            continue;
        }

        // Single-quoted string
        if b == b'\'' {
            current.push('\'');
            i += 1;
            while i < len {
                current.push(bytes[i] as char);
                if bytes[i] == b'\'' {
                    if i + 1 < len && bytes[i + 1] == b'\'' {
                        current.push('\'');
                        i += 2;
                    } else {
                        i += 1;
                        break;
                    }
                } else {
                    i += 1;
                }
            }
            continue;
        }

        // Dollar-quoted string ($tag$...$tag$ or $$...$$)
        if b == b'$' {
            i += 1;
            let mut tag = String::from("$");
            while i < len && (bytes[i].is_ascii_alphanumeric() || bytes[i] == b'_') {
                tag.push(bytes[i] as char);
                i += 1;
            }
            if i < len && bytes[i] == b'$' {
                tag.push('$');
                i += 1;
                // We have a dollar-quote tag, find the closing tag
                current.push_str(&tag);
                let tag_bytes = tag.as_bytes();
                loop {
                    if i >= len {
                        break;
                    }
                    if bytes[i] == b'$' && i + tag_bytes.len() <= len
                        && &bytes[i..i + tag_bytes.len()] == tag_bytes
                    {
                        current.push_str(&tag);
                        i += tag_bytes.len();
                        break;
                    }
                    current.push(bytes[i] as char);
                    i += 1;
                }
            } else {
                // Not a valid dollar-quote, push what we consumed
                current.push_str(&tag);
            }
            continue;
        }

        // Statement separator
        if b == b';' {
            current.push(';');
            let trimmed = current.trim().to_string();
            if !trimmed.is_empty() && trimmed != ";" {
                statements.push(trimmed);
            }
            current.clear();
            i += 1;
            continue;
        }

        current.push(b as char);
        i += 1;
    }

    // Trailing statement without semicolon
    let trimmed = current.trim().to_string();
    if !trimmed.is_empty() && trimmed != ";" {
        statements.push(trimmed);
    }

    statements
}