use std::{cmp::max, collections::HashMap, sync::Mutex};

use crate::{handles, Connection, Error};
use odbc_sys::{AttrOdbcVersion, FetchOrientation};
use widestring::{U16CStr, U16Str, U16String};

/// An ODBC 3.8 environment.
///
/// Associated with an `Environment` is any information that is global in nature, such as:
///
/// * The `Environment`'s state
/// * The current environment-level diagnostics
/// * The handles of connections currently allocated on the environment
/// * The current stetting of each environment attribute
///
/// Creating the environment is the first applications do, then interacting with an ODBC driver
/// manager. There must only be one environment in the entire process.
pub struct Environment {
    environment: handles::Environment,
    /// ODBC environments use interior mutability to maintain iterator state then iterating over
    /// driver and / or data source information. The environment is otherwise protected by interior
    /// synchronization mechanism, yet in order to be able to access to iterate over information
    /// using a shared reference we need to protect the interior iteraton state with a mutex of its
    /// own.
    info_iterator_state: Mutex<()>,
}

impl Environment {
    /// Entry point into this API. Allocates a new ODBC Environment and declares to the driver
    /// manager that the Application wants to use ODBC version 3.8.
    ///
    /// # Safety
    ///
    /// There may only be one ODBC environment in any process at any time. Take care using this
    /// function in unit tests, as these run in parallel by default in Rust. Also no library should
    /// probably wrap the creation of an odbc environment into a safe function call. This is because
    /// using two of these "safe" libraries at the same time in different parts of your program may
    /// lead to race condition thus violating Rust's safety guarantees.
    ///
    /// Creating one environment in your binary is safe however.
    pub unsafe fn new() -> Result<Self, Error> {
        let environment = crate::handles::Environment::new()?;
        environment.declare_version(AttrOdbcVersion::Odbc3_80)?;
        Ok(Self {
            environment,
            info_iterator_state: Mutex::new(()),
        })
    }

    /// Allocates a connection handle and establishes connections to a driver and a data source.
    ///
    /// * See [Connecting with SQLConnect][1]
    /// * See [SQLConnectFunction][2]
    ///
    /// # Arguments
    ///
    /// * `data_source_name` - Data source name. The data might be located on the same computer as
    /// the program, or on another computer somewhere on a network.
    /// * `user` - User identifier.
    /// * `pwd` - Authentication string (typically the password).
    ///
    /// # Example
    ///
    /// ```no_run
    /// use odbc_api::Environment;
    ///
    /// // I herby solemnly swear that this is the only ODBC environment in the entire process, thus
    /// // making this call safe.
    /// let env = unsafe {
    ///     Environment::new()?
    /// };
    ///
    /// let mut conn = env.connect("YourDatabase", "SA", "<YourStrong@Passw0rd>")?;
    /// # Ok::<(), odbc_api::Error>(())
    /// ```
    ///
    /// [1]: https://docs.microsoft.com/sql/odbc/reference/syntax/sqlconnect-function
    /// [2]: https://docs.microsoft.com/sql/odbc/reference/syntax/sqlconnect-function
    pub fn connect(
        &self,
        data_source_name: &str,
        user: &str,
        pwd: &str,
    ) -> Result<Connection<'_>, Error> {
        let data_source_name = U16String::from_str(data_source_name);
        let user = U16String::from_str(user);
        let pwd = U16String::from_str(pwd);
        self.connect_utf16(&data_source_name, &user, &pwd)
    }

    /// Allocates a connection handle and establishes connections to a driver and a data source.
    ///
    /// * See [Connecting with SQLConnect][1]
    /// * See [SQLConnectFunction][2]
    ///
    /// # Arguments
    ///
    /// * `data_source_name` - Data source name. The data might be located on the same computer as
    /// the program, or on another computer somewhere on a network.
    /// * `user` - User identifier.
    /// * `pwd` - Authentication string (typically the password).
    ///
    /// [1]: https://docs.microsoft.com/sql/odbc/reference/syntax/sqlconnect-function
    /// [2]: https://docs.microsoft.com/sql/odbc/reference/syntax/sqlconnect-function
    pub fn connect_utf16(
        &self,
        data_source_name: &U16Str,
        user: &U16Str,
        pwd: &U16Str,
    ) -> Result<Connection<'_>, Error> {
        let mut connection = self.environment.allocate_connection()?;
        connection.connect(data_source_name, user, pwd)?;
        Ok(Connection::new(connection))
    }

    /// Allocates a connection handle and establishes connections to a driver and a data source.
    ///
    /// An alternative to `connect`. It supports data sources that require more connection
    /// information than the three arguments in `connect` and data sources that are not defined in
    /// the system information.
    ///
    /// To find out your connection string try: <https://www.connectionstrings.com/>
    ///
    /// # Example
    ///
    /// ```no_run
    /// use odbc_api::Environment;
    ///
    /// // I herby solemnly swear that this is the only ODBC environment in the entire process, thus
    /// // making this call safe.
    /// let env = unsafe {
    ///     Environment::new()?
    /// };
    ///
    /// let connection_string = "
    ///     Driver={ODBC Driver 17 for SQL Server};\
    ///     Server=localhost;\
    ///     UID=SA;\
    ///     PWD=<YourStrong@Passw0rd>;\
    /// ";
    ///
    /// let mut conn = env.connect_with_connection_string(connection_string)?;
    /// # Ok::<(), odbc_api::Error>(())
    /// ```
    pub fn connect_with_connection_string(
        &self,
        connection_string: &str,
    ) -> Result<Connection<'_>, Error> {
        let connection_string = U16String::from_str(connection_string);
        self.connect_with_connection_string_utf16(&connection_string)
    }

    /// Allocates a connection handle and establishes connections to a driver and a data source.
    ///
    /// An alternative to `connect`. It supports data sources that require more connection
    /// information than the three arguments in `connect` and data sources that are not defined in
    /// the system information.
    ///
    /// To find out your connection string try: <https://www.connectionstrings.com/>
    pub fn connect_with_connection_string_utf16(
        &self,
        connection_string: &U16Str,
    ) -> Result<Connection<'_>, Error> {
        let mut connection = self.environment.allocate_connection()?;
        connection.connect_with_connection_string(connection_string)?;
        Ok(Connection::new(connection))
    }

    /// Get information about available drivers. Only 32 or 64 Bit drivers will be listed, depending
    /// on wether you are building a 32 Bit or 64 Bit application.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use odbc_api::Environment;
    ///
    /// let env = unsafe { Environment::new () }?;
    /// for driver_info in env.drivers()? {
    ///     println!("{:#?}", driver_info);
    /// }
    ///
    /// # Ok::<_, odbc_api::Error>(())
    /// ```
    pub fn drivers(&self) -> Result<Vec<DriverInfo>, Error> {
        let mut driver_info = Vec::new();

        // Since we have exclusive ownership of the environment handle and we take the lock, we can
        // guarantee that this method is currently the only one changing the state of the internal
        // iterators of the environment.
        let _lock = self.info_iterator_state.lock().unwrap();
        unsafe {
            // Find required buffer size to avoid truncation.
            let (mut desc_len, mut attr_len) = if let Some(v) = self
                .environment
                // Start with first so we are independent of state
                .drivers_buffer_len(FetchOrientation::First)?
            {
                v
            } else {
                // No drivers present
                return Ok(Vec::new());
            };

            // If there are let's loop over the rest
            while let Some((candidate_desc_len, candidate_attr_len)) = self
                .environment
                .drivers_buffer_len(FetchOrientation::Next)?
            {
                desc_len = max(candidate_desc_len, desc_len);
                attr_len = max(candidate_attr_len, attr_len);
            }

            // Allocate +1 character extra for terminating zero
            let mut desc_buf = vec![0; desc_len as usize + 1];
            let mut attr_buf = vec![0; attr_len as usize + 1];

            while self.environment.drivers_buffer_fill(
                FetchOrientation::Next,
                &mut desc_buf,
                &mut attr_buf,
            )? {
                let description = U16CStr::from_slice_with_nul(&desc_buf).unwrap();
                let attributes = U16CStr::from_slice_with_nul(&attr_buf).unwrap();

                let description = description.to_string().unwrap();
                let attributes = attributes.to_string().unwrap();
                let attributes = attributes_iter(&attributes).collect();

                driver_info.push(DriverInfo {
                    description,
                    attributes,
                });
            }
        }

        Ok(driver_info)
    }

    /// User and system data sources
    ///
    /// # Example
    ///
    /// ```no_run
    /// use odbc_api::Environment;
    ///
    /// let env = unsafe { Environment::new () }?;
    /// for data_source in env.data_sources()? {
    ///     println!("{:#?}", data_source);
    /// }
    ///
    /// # Ok::<_, odbc_api::Error>(())
    /// ```
    pub fn data_sources(&self) -> Result<Vec<DataSourceInfo>, Error> {
        self.data_sources_impl(FetchOrientation::First)
    }

    /// Only system data sources
    ///
    /// # Example
    ///
    /// ```no_run
    /// use odbc_api::Environment;
    ///
    /// let env = unsafe { Environment::new () }?;
    /// for data_source in env.system_data_sources()? {
    ///     println!("{:#?}", data_source);
    /// }
    ///
    /// # Ok::<_, odbc_api::Error>(())
    /// ```
    pub fn system_data_sources(&self) -> Result<Vec<DataSourceInfo>, Error> {
        self.data_sources_impl(FetchOrientation::FirstSystem)
    }

    /// Only user data sources
    ///
    /// # Example
    ///
    /// ```no_run
    /// use odbc_api::Environment;
    ///
    /// let mut env = unsafe { Environment::new () }?;
    /// for data_source in env.user_data_sources()? {
    ///     println!("{:#?}", data_source);
    /// }
    ///
    /// # Ok::<_, odbc_api::Error>(())
    /// ```
    pub fn user_data_sources(&self) -> Result<Vec<DataSourceInfo>, Error> {
        self.data_sources_impl(FetchOrientation::FirstUser)
    }

    fn data_sources_impl(&self, direction: FetchOrientation) -> Result<Vec<DataSourceInfo>, Error> {
        let mut data_source_info = Vec::new();

        // Since we have exclusive ownership of the environment handle and we take the lock, we can
        // guarantee that this method is currently the only one changing the state of the internal
        // iterators of the environment.
        let _lock = self.info_iterator_state.lock().unwrap();
        unsafe {
            // Find required buffer size to avoid truncation.
            let (mut server_name_len, mut driver_len) =
                if let Some(v) = self.environment.data_source_buffer_len(direction)? {
                    v
                } else {
                    // No drivers present
                    return Ok(Vec::new());
                };

            // If there are let's loop over the rest
            while let Some((candidate_name_len, candidate_decs_len)) = self
                .environment
                .drivers_buffer_len(FetchOrientation::Next)?
            {
                server_name_len = max(candidate_name_len, server_name_len);
                driver_len = max(candidate_decs_len, driver_len);
            }

            // Allocate +1 character extra for terminating zero
            let mut server_name_buf = vec![0; server_name_len as usize + 1];
            let mut driver_buf = vec![0; driver_len as usize + 1];

            let mut not_empty = self.environment.data_source_buffer_fill(
                direction,
                &mut server_name_buf,
                &mut driver_buf,
            )?;
            while not_empty {
                let server_name = U16CStr::from_slice_with_nul(&server_name_buf).unwrap();
                let driver = U16CStr::from_slice_with_nul(&driver_buf).unwrap();

                let server_name = server_name.to_string().unwrap();
                let driver = driver.to_string().unwrap();

                data_source_info.push(DataSourceInfo {
                    server_name,
                    driver,
                });
                not_empty = self.environment.data_source_buffer_fill(
                    FetchOrientation::Next,
                    &mut server_name_buf,
                    &mut driver_buf,
                )?;
            }
        }

        Ok(data_source_info)
    }
}

/// Struct holding information available on a driver. Can be obtained via [`Environment::drivers`].
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct DriverInfo {
    /// Name of the ODBC driver
    pub description: String,
    /// Attributes values of the driver by key
    pub attributes: HashMap<String, String>,
}

/// Holds name and description of a datasource
///
/// Can be obtained via [`Environment::data_sources`]
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct DataSourceInfo {
    /// Name of the data source
    pub server_name: String,
    /// Description of the data source
    pub driver: String,
}

/// Called by drivers to pares list of attributes
///
/// Key value pairs are separated by `\0`. Key and value are separated by `=`
fn attributes_iter(attributes: &str) -> impl Iterator<Item = (String, String)> + '_ {
    attributes
        .split('\0')
        .take_while(|kv_str| *kv_str != String::new())
        .map(|kv_str| {
            let mut iter = kv_str.split('=');
            let key = iter.next().unwrap();
            let value = iter.next().unwrap();
            (key.to_string(), value.to_string())
        })
}

#[cfg(test)]
mod test {

    use super::*;

    #[test]
    fn parse_attributes() {
        let buffer = "APILevel=2\0ConnectFunctions=YYY\0CPTimeout=60\0DriverODBCVer=03.\
                      50\0FileUsage=0\0SQLLevel=1\0UsageCount=1\0\0";
        let attributes: HashMap<_, _> = attributes_iter(buffer).collect();
        assert_eq!(attributes["APILevel"], "2");
        assert_eq!(attributes["ConnectFunctions"], "YYY");
        assert_eq!(attributes["CPTimeout"], "60");
        assert_eq!(attributes["DriverODBCVer"], "03.50");
        assert_eq!(attributes["FileUsage"], "0");
        assert_eq!(attributes["SQLLevel"], "1");
        assert_eq!(attributes["UsageCount"], "1");
    }
}