use core::fmt::{self, Write};

use crate::{
    path::Path,
    update::{set_remove::SetRemove, Set},
    value::{Value, ValueOrRef},
};

/// Represents an update expression to [set an attribute if it doesn't exist][1].
///
/// See also: [`Path::if_not_exists`]
///
/// [1]: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.UpdateExpressions.html#Expressions.UpdateExpressions.SET.PreventingAttributeOverwrites
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct IfNotExists {
    pub(crate) dst: Path,
    pub(crate) src: Option<Path>,
    pub(crate) value: ValueOrRef,
}

impl IfNotExists {
    pub fn builder<T>(dst: T) -> Builder
    where
        T: Into<Path>,
    {
        Builder {
            dst: dst.into(),
            src: None,
        }
    }

    /// Add an additional [`Set`] or [`Remove`] statement to this expression.
    ///
    /// ```
    /// # fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
    /// use dynamodb_expression::{Num, Path, update::Set};
    /// # use pretty_assertions::assert_eq;
    ///
    /// let set = "foo"
    ///     .parse::<Path>()?
    ///     .if_not_exists()
    ///     .set(Num::new(7))
    ///     .and("bar".parse::<Path>()?.set("a value"));
    /// assert_eq!(r#"SET foo = if_not_exists(foo, 7), bar = "a value""#, set.to_string());
    /// #
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// [`Remove`]: crate::update::Remove
    pub fn and<T>(self, action: T) -> SetRemove
    where
        T: Into<SetRemove>,
    {
        Set::from(self).and(action)
    }
}

impl fmt::Display for IfNotExists {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.dst.fmt(f)?;
        f.write_str(" = if_not_exists(")?;
        // If no source field is specified, default to using the destination.
        self.src.as_ref().unwrap_or(&self.dst).fmt(f)?;
        f.write_str(", ")?;
        self.value.fmt(f)?;
        f.write_char(')')
    }
}

/// Builds an [`IfNotExists`] instance. Create an instance of this by using [`IfNotExists::builder`].
///
/// See also: [`Path::if_not_exists`]
#[must_use = "Consume this `Builder` by using its `.value()` method"]
#[derive(Debug, Clone)]
pub struct Builder {
    dst: Path,
    src: Option<Path>,
}

impl Builder {
    /// Sets the source [`Path`] to check for existence.
    ///
    /// Defaults to the destination [`Path`].
    ///
    /// ```
    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # use dynamodb_expression::{Num, Path};
    /// # use pretty_assertions::assert_eq;
    /// #
    /// let if_not_exists = "foo"
    ///     .parse::<Path>()?
    ///     .if_not_exists()
    ///     .src("bar".parse::<Path>()?)
    ///     .set(Num::new(42));
    /// assert_eq!("foo = if_not_exists(bar, 42)", if_not_exists.to_string());
    /// #
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Compare with the default, where the destination [`Path`] is used:
    ///
    /// ```
    /// # fn main() -> Result<(), Box<dyn std::error::Error>> {
    /// # use dynamodb_expression::{Num, Path};
    /// # use pretty_assertions::assert_eq;
    /// #
    /// let if_not_exists = "foo"
    ///     .parse::<Path>()?
    ///     .if_not_exists()
    ///     .set(Num::new(42));
    /// assert_eq!("foo = if_not_exists(foo, 42)", if_not_exists.to_string());
    /// #
    /// # Ok(())
    /// # }
    /// ```
    pub fn src<T>(mut self, src: T) -> Self
    where
        T: Into<Path>,
    {
        self.src = Some(src.into());

        self
    }

    /// The value to conditionally set.
    ///
    /// Consumes this [`Builder`] and creates an [`IfNotExists`] instance.
    ///
    /// See also: [`Path::if_not_exists`]
    #[deprecated(since = "0.2.0-beta.6", note = "Use `.set(value)` instead")]
    pub fn assign<T>(self, value: T) -> IfNotExists
    where
        T: Into<Value>,
    {
        self.set(value)
    }

    /// The value to conditionally set.
    ///
    /// Consumes this [`Builder`] and creates an [`IfNotExists`] instance.
    ///
    /// See also: [`Path::if_not_exists`]
    pub fn set<T>(self, value: T) -> IfNotExists
    where
        T: Into<Value>,
    {
        let Self { dst, src } = self;

        IfNotExists {
            dst,
            src,
            value: value.into().into(),
        }
    }
}

#[cfg(test)]
mod test {
    use std::error::Error;

    use pretty_assertions::assert_eq;

    use crate::{
        update::{set_remove::SetRemove, Assign, Set, SetAction},
        Num, Path,
    };

    use super::IfNotExists;

    #[test]
    fn and() -> Result<(), Box<dyn Error>> {
        let if_not_exists: IfNotExists = "foo".parse::<Path>()?.if_not_exists().set("a value");
        let assign: Assign = "bar".parse::<Path>()?.set(Num::new(8));

        // Should be able to concatenate anything that can be turned into a SetAction.

        let combined = if_not_exists.clone().and(assign.clone());
        assert_eq!(
            r#"SET foo = if_not_exists(foo, "a value"), bar = 8"#,
            combined.to_string()
        );

        // Should be able to concatenate a SetAction instance.

        let combined = if_not_exists.clone().and(SetAction::from(assign.clone()));
        assert_eq!(
            r#"SET foo = if_not_exists(foo, "a value"), bar = 8"#,
            combined.to_string()
        );

        // Should be able to concatenate a Set instance

        let set: Set = [
            SetAction::from(assign),
            SetAction::from("baz".parse::<Path>()?.math().add(1)),
        ]
        .into_iter()
        .collect();
        let combined = if_not_exists.clone().and(set);
        assert_eq!(
            r#"SET foo = if_not_exists(foo, "a value"), bar = 8, baz = baz + 1"#,
            combined.to_string()
        );

        // Should be able to concatenate a Remove instance

        let combined = if_not_exists.clone().and("quux".parse::<Path>()?.remove());
        assert_eq!(
            r#"SET foo = if_not_exists(foo, "a value") REMOVE quux"#,
            combined.to_string()
        );

        // Should be able to concatenate a SetRemove instance

        let combined = if_not_exists.and(SetRemove::from("quux".parse::<Path>()?.remove()));
        assert_eq!(
            r#"SET foo = if_not_exists(foo, "a value") REMOVE quux"#,
            combined.to_string()
        );

        Ok(())
    }
}