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//! Translate a canonical table alias into another [AliasFormat]() format.
//!

use crate::alias_format::AliasFormat;
use std::collections::HashMap;

/// The translator keeps track of alias numbering and earlier translations to ensure that no collisions happen.
/// That means all [SQL expressions](crate::sql_expr::SqlExpr) must be translated with the same instance,
/// typically using [Resolver](crate::sql_expr::resolver::Resolver).
pub struct AliasTranslator {
    format: AliasFormat,
    table_index: u16,
    translations: HashMap<String, String>, // canonical alias to translated alias
}

impl AliasTranslator {
    pub fn new(format: AliasFormat) -> Self {
        AliasTranslator {
            format,
            table_index: 0,
            translations: HashMap::new(),
        }
    }

    /// Translates a canonical sql alias into a shorter alias
    pub fn translate(&mut self, canonical_alias: &str) -> String {
        use std::collections::hash_map::Entry;

        let a = match self.translations.entry(canonical_alias.to_owned()) {
            Entry::Occupied(o) => o.into_mut(),
            Entry::Vacant(v) => {
                let alias = match self.format {
                    AliasFormat::TinyIndex => {
                        self.table_index += 1;
                        AliasFormat::tiny_index(self.table_index)
                    }
                    AliasFormat::ShortIndex => {
                        self.table_index += 1;
                        AliasFormat::short_index(&canonical_alias, self.table_index)
                    }
                    AliasFormat::MediumIndex => {
                        self.table_index += 1;
                        AliasFormat::medium_index(&canonical_alias, self.table_index)
                    }
                    _ => canonical_alias.to_owned(),
                };
                v.insert(alias)
            }
        }
        .to_owned();

        a
    }
}