use std::collections;
use std::error::Error;
use std::ops::Add;
use std::sync::{Arc, Mutex};

use mysql::{Binary, Pool, ResultSet, Value};
use mysql::prelude::Queryable;

use crate::data::config::DatabaseConfig;
use crate::data::error::{ExecError, ResultBoxError};

/// Database access helper
///
/// @author Pierre Hubert

pub type ProcessRowResult<E> = Result<E, Box<dyn Error>>;

// Pool shared across threads
static mut POOL: Option<Arc<Mutex<mysql::Pool>>> = None;

/// Connect to the database
pub fn connect(conf: &DatabaseConfig) -> Result<(), Box<dyn Error>> {
    let url = format!(
        "mysql://{}:{}@{}:3306/{}",
        conf.username, conf.password, conf.host, conf.name
    );

    let pool = Pool::new(url)?;
    let pool = Some(Arc::new(Mutex::new(pool)));

    unsafe {
        POOL = pool;
    }

    Ok(())
}

/// Get a connection to the database
pub fn get_connection() -> Result<mysql::PooledConn, Box<dyn Error>> {
    let pool: Pool;

    unsafe {
        let guard = POOL.as_ref().unwrap().lock();
        pool = guard.unwrap().clone()
    }

    Ok(pool.get_conn()?)
}


pub struct QueryInfo {
    /// Fetched table
    pub table: String,

    /// Query limits
    pub conditions: collections::HashMap<String, String>,

    /// Limit of the query (0 = no limit)
    pub limit: u64,

    /// Queried arguments
    pub fields: Vec<String>,
}

impl QueryInfo {
    /// Initialize a new query on the database
    pub fn new(table: &str) -> QueryInfo {
        QueryInfo {
            table: table.to_string(),
            conditions: collections::HashMap::new(),
            limit: 0,
            fields: Vec::new(),
        }
    }

    pub fn cond(mut self, key: &str, val: &str) -> QueryInfo {
        self.conditions.insert(key.to_string(), val.to_string());
        self
    }
}

/// Struct used to read the result of a request
pub struct RowResult<'a> {
    row: &'a mysql::Row
}

impl<'a> RowResult<'a> {
    pub fn new(row: &mysql::Row) -> RowResult {
        RowResult {
            row
        }
    }

    /// Find a column in result set
    fn find_col(&self, name: &str) -> Result<usize, ExecError> {
        let name_bytes = name.as_bytes();
        let mut index = 0;
        for c in self.row.columns_ref() {
            if c.name_ref().eq(name_bytes) {
                return Ok(index);
            }

            index += 1;
        }

        Err(ExecError(format!("Column {} not found in database result set!", name)))
    }

    /// Find an integer included in the request
    pub fn get_int64(&self, name: &str) -> Result<i64, Box<dyn Error>> {
        let value = self.row.get_opt(self.find_col(name)?);

        match value {
            None => Err(ExecError::boxed_string(
                format!("Could not extract integer field {} !", name))),
            Some(s) => Ok(s?)
        }
    }

    /// Find a string included in the request
    pub fn get_str(&self, name: &str) -> Result<String, Box<dyn Error>> {
        let value = self.row.get_opt(self.find_col(name)?);

        match value {
            None => Err(ExecError::boxed_string(
                format!("Could not extract string field {} !", name))),
            Some(s) => Ok(s?)
        }
    }

    /// Check out whether a given value is null or not
    pub fn is_null(&self, name: &str) -> ResultBoxError<bool> {
        let value = self.row.get_opt(self.find_col(name)?);

        match value {
            None => Ok(true),
            Some(Ok(Value::NULL)) => Ok(true),
            _ => Ok(false)
        }
    }

    /// Get an optional string => Set to None if string is null
    pub fn get_optional_str(&self, name: &str) -> ResultBoxError<Option<String>> {
        match self.is_null(name)? {
            true => Ok(None),
            false => Ok(Some(self.get_str(name)?))
        }
    }
}


/// Query a single row of the database
pub fn query_row<E, F: Fn(&RowResult) -> ProcessRowResult<E>>(mut info: QueryInfo,
                                                              process_function: F) -> Result<E, Box<dyn Error>> {
    info.limit = 1;
    let mut list = query(info, process_function)?;

    match list.len() {
        0 => Err(ExecError::boxed_new("Request did not return a result!")),
        _ => Ok(list.remove(0))
    }
}

/// Make a simple query
pub fn query<E, F: Fn(&RowResult) -> ProcessRowResult<E>>(info: QueryInfo, process_function: F)
                                                          -> Result<Vec<E>, Box<dyn Error>> {
    let mut params = vec![];

    let select_elements = match info.fields.len() {
        0 => "*".to_string(),
        _ => info.fields.join(", ")
    };

    // Build query
    let mut query = format!("SELECT {} FROM {} ", select_elements, info.table);


    // WHERE clause
    if !info.conditions.is_empty() {
        let mut where_args = vec![];

        for (k, v) in info.conditions {
            where_args.push(format!("{} = ?", k));
            params.push(v)
        }

        let where_args = format!(" WHERE {} ", where_args.join(" AND "));
        query = query.add(&where_args);
    }

    // LIMIT clause
    if info.limit > 0 {
        query = query.add(&format!(" LIMIT {}", info.limit));
    }

    // Execute query
    let mut con = get_connection()?;
    let stmt = con.prep(&query)?;

    let mut res = con.exec_iter(stmt, params)?;

    // This system is made to support only one dataset
    let result_set = res.next_set();
    if let None = result_set {
        return Err(Box::new(ExecError::new("No result set in a query!")));
    }
    let result_set: ResultSet<Binary> = result_set.unwrap()?;


    // Parse each result of the dataset
    let mut res: Vec<E> = vec![];
    for row in result_set {
        let row = row?;
        let result = RowResult::new(&row);

        let parsed = process_function(&result)?;
        res.push(parsed);
    }


    Ok(res)
}