multisql 0.4.3

MultiSQL
Documentation 
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mod from;
mod new;
mod planned;
mod resolve;

use {
	crate::{types::ObjectName, Error, Result, Value},
	serde::Serialize,
	sqlparser::ast::{DataType, Expr},
	std::fmt::Debug,
	thiserror::Error as ThisError,
};
pub use {
	from::TryIntoMethod,
	new::MetaRecipe,
	planned::PlannedRecipe,
	resolve::{Resolve, SimplifyBy},
};

#[derive(ThisError, Serialize, Debug, PartialEq)]
pub enum RecipeError {
	#[error("recipe missing components")]
	MissingComponents,

	#[error("{0} is either invalid or unimplemented")]
	InvalidQuery(String),
	#[error("{0} is invalid or unimplemented")]
	InvalidExpression(Expr),
	#[error("a function is either invalid or unimplemented")]
	InvalidFunction,

	#[error("column '{0:?}' could not be found")]
	MissingColumn(ObjectName),
	#[error("column '{0:?}' could mean various different columns, please be more specific with (table).(column)")]
	AmbiguousColumn(ObjectName),

	#[error("{0} is either invalid or unimplemented")]
	UnimplementedQuery(String),
	#[error("{0} is either invalid or unimplemented")]
	UnimplementedMethod(String),
	#[error("{0} is unimplemented")]
	UnimplementedExpression(Expr),
	#[error("something is unimplemented")]
	Unimplemented,

	#[error("other failure occurred: {0}")]
	Failed(String),

	#[error("this should be impossible, please report")]
	UnreachableAggregatationFailed,
	#[error("this should be impossible, please report")]
	UnreachableAggregateFailed,
	#[error("this should be impossible, please report, failure: {0}")]
	UnreachableNotMethod(String),
	#[error("this should be impossible, please report, failure: {0}")]
	UnreachableNotAggregate(String),
	#[error("this should be impossible, please report")]
	UnreachableNoRow,
	#[error("this should be impossible, please report")]
	Unreachable,
}

#[derive(Debug, Clone, PartialEq)]
pub enum Recipe {
	Ingredient(Ingredient),
	Method(Box<Method>),
}

impl Default for Recipe {
	fn default() -> Self {
		Self::NULL
	}
}

#[derive(Debug, Clone, PartialEq)]
pub enum Ingredient {
	Value(Value),
	Column(usize),
	Aggregate(usize),
}

#[derive(Debug, Clone, PartialEq)]
pub enum Method {
	Value(Value), // Only occurs backwards for eval! Should never be returned outside of a recursive simplification!
	Aggregate(AggregateOperator, Recipe), // Only occurs inside Ingredient::Aggregate. Perhaps this should not be a Method.

	UnaryOperation(UnaryOperator, Recipe),
	BinaryOperation(BinaryOperator, Recipe, Recipe),
	Function(FunctionOperator, Vec<Recipe>),

	Cast(DataType, Recipe),

	Case {
		operand: Option<Recipe>,
		cases: Vec<(Recipe, Recipe)>,
		else_result: Option<Recipe>,
	},
}

// Cannot derive Debug for references. Perhaps these shouldn't consume their operators. TODO.
pub type UnaryOperator = fn(Value) -> Result<Value>;
pub type BinaryOperator = fn(Value, Value) -> Result<Value>;
pub type FunctionOperator = fn(Vec<Value>) -> Result<Value>;
pub type AggregateOperator = fn(Value, Value) -> Result<Value>;

pub trait RecipeUtilities
where
	Self: Sized,
{
	fn as_solution(&self) -> Option<Value>;

	fn confirm_or_err(self, error: Error) -> Result<Value> {
		self.as_solution().ok_or(error)
	}

	fn confirm(self) -> Result<Value> {
		self.confirm_or_err(RecipeError::MissingComponents.into())
	}

	fn simplify_by_basic(self) -> Result<Self>;
}
impl RecipeUtilities for Recipe {
	fn as_solution(&self) -> Option<Value> {
		if let Recipe::Ingredient(Ingredient::Value(value)) = self {
			Some(value.clone())
		} else {
			None
		}
	}
	fn simplify_by_basic(self) -> Result<Self> {
		self.simplify(SimplifyBy::Basic)
	}
}
impl RecipeUtilities for MetaRecipe {
	fn as_solution(&self) -> Option<Value> {
		self.recipe.as_solution()
	}
	fn simplify_by_basic(mut self) -> Result<Self> {
		self.recipe = self.recipe.simplify(SimplifyBy::Basic)?;
		Ok(self)
	}
}
impl RecipeUtilities for PlannedRecipe {
	fn as_solution(&self) -> Option<Value> {
		self.recipe.as_solution()
	}
	fn simplify_by_basic(mut self) -> Result<Self> {
		self.recipe = self.recipe.simplify(SimplifyBy::Basic)?;
		Ok(self)
	}
}

impl Recipe {
	pub const NULL: Recipe = Recipe::Ingredient(Ingredient::Value(Value::Null));
	pub const TRUE: Recipe = Recipe::Ingredient(Ingredient::Value(Value::Bool(true)));
	pub const SINGLE_COLUMN: Recipe = Recipe::Ingredient(Ingredient::Column(0));
}