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use super::ExprNode;

impl ExprNode {
    pub fn case(self) -> CaseNode {
        CaseNode {
            operand: Some(Box::new(self)),
        }
    }
}

pub fn case() -> CaseNode {
    CaseNode { operand: None }
}

pub struct CaseNode {
    operand: Option<Box<ExprNode>>,
}

impl CaseNode {
    pub fn when_then<W: Into<ExprNode>, T: Into<ExprNode>>(self, when: W, then: T) -> WhenThenNode {
        WhenThenNode {
            prev_node: self,
            when_then: vec![(when.into(), then.into())],
        }
    }
}

pub struct WhenThenNode {
    prev_node: CaseNode,
    when_then: Vec<(ExprNode, ExprNode)>,
}

impl WhenThenNode {
    pub fn when_then<W: Into<ExprNode>, T: Into<ExprNode>>(mut self, when: W, then: T) -> Self {
        self.when_then.push((when.into(), then.into()));
        self
    }

    pub fn or_else<T: Into<ExprNode>>(self, else_result: T) -> ExprNode {
        ExprNode::Case {
            operand: self.prev_node.operand,
            when_then: self.when_then,
            else_result: Some(Box::new(else_result.into())),
        }
    }

    pub fn end(self) -> ExprNode {
        ExprNode::Case {
            operand: self.prev_node.operand,
            when_then: self.when_then,
            else_result: None,
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::ast_builder::{case, col, num, test_expr, text};

    #[test]
    fn case_with_operand() {
        let actual = col("id")
            .case()
            .when_then(num(1), text("a"))
            .when_then(2, text("b"))
            .or_else(text("c"));
        let expected = r#"
            CASE id
              WHEN 1 THEN "a"
              WHEN 2 THEN "b"
              ELSE "c"
            END
            "#;
        test_expr(actual, expected);

        let actual = col("id")
            .gt(10)
            .case()
            .when_then(true, text("a"))
            .when_then(false, text("b"))
            .end();
        let expected = r#"
            CASE id > 10
              WHEN True THEN "a"
              WHEN False THEN "b"
            END
            "#;
        test_expr(actual, expected);
    }

    #[test]
    fn case_without_operand() {
        let actual = case()
            .when_then(
                "City IS NULL",
                case()
                    .when_then("Country IS NULL", text("weird"))
                    .or_else("Country"),
            )
            .or_else("City");
        let expected = r#"
            CASE
              WHEN City IS NULL THEN CASE WHEN Country IS NULL THEN 'weird'
                                          ELSE Country
                                          END
              ELSE City
            END
            "#;
        test_expr(actual, expected);
    }
}