// Copyright (C) 2021-2022 Soni L.
// SPDX-License-Identifier: MIT OR Apache-2.0

#![warn(elided_lifetimes_in_paths)]

//! Datafu is a regex-inspired query language. It was primarily
//! designed for processing object trees parsed from configuration files, but
//! can be used with anything that supports serde.
//!
//! # Languge Reference
//!
//! Datafu expressions have the ability to iterate, index, validate and filter
//! data structures, through the use of the syntax elements below.
//!
//! ## Syntax Elements of Datafu Expressions
//!
//! A datafu pattern starts with an optional value matcher and is otherwise a
//! sequence of iterative elements (see "arrow" below) followed by subvalues.
//!
//! A datafu pattern is composed of the following elements:
//!
//! 1. An arrow, `->` indicates iteration. (Note that datafu operates directly
//!     on serde and deserialization is an iterative process.)
//!
//!     Always followed by a matcher, or a name and an optional matcher.
//! 2. A name is a sequence of alphanumeric characters, not starting with a
//!     digit. A name collects a matched value. The value will be identified by
//!     the name.
//! 3. A matcher is one of the following 5 elements.
//! 4. A literal is a quoted string delimited by `'` with `%` as the escape
//!     character. A literal can contain any Unicode scalar value, and the only
//!     allowed escape codes are `%%` and `%'`, for `%` and `'` respectively,
//!     which must be escaped. A literal matches a string value and can be
//!     optional.
//! 5. A parameter is `$`, optionally followed by `?`, followed by a sequence
//!     of alphanumeric characters, not starting with a digit. This is
//!     currently unimplemented.
//! 6. A regex is a quoted string delimited by `/`, with `%` as the escape
//!     character. A regex can contain any Unicode scalar value, and the only
//!     allowed escape codes are `%%` and `%/`, for `%` and `/` respectively,
//!     which must be escaped. A regex element matches a string value against
//!     the regex it represents, and can be optional.
//! 7. A predicate is `:`, optionally followed by `?`, followed by `$` and a
//!     sequence of alphanumeric characters, not starting with a digit. This is
//!     currently unimplemented.
//! 8. A type is `:`, optionally followed by `?`, followed by one of the
//!     following keywords: TODO
//! 9. A key match is a sequence of iterative elements followed by subvalues,
//!     prefixed by either a matcher or a name and an optional matcher,
//!     and enclosed within `[` and `]`, optionally followed by `?`. A key
//!     match applies to map keys and sequence indices, and aside from the
//!     previously mentioned requirement is otherwise just a datafu pattern.
//! 10. A subvalue is a sequence of iterative elements followed by subvalues,
//!     enclosed within `(` and `)`, optionally followed by `?`. A sequence of
//!     subvalues enables matching distinct patterns on the same value, like
//!     distinct fields of a struct.
//!
//! Some syntax elements can be validating or non-validating. Validating
//! syntax elements will return a [`errors::MatchError::ValidationError`]
//! whenever a value or subpattern fails to match, whereas non-validating
//! ones will skip them. In general, whether an element is validating is
//! determined by the absence of an optional `?` in the documented position,
//! with the exception of key matches, which instead use it to filter entries
//! that didn't match.
//!
//! The empty pattern matches anything, but only does so once. Empty subvalues
//! are ignored.
//!
//! ## Syntax of Datafu Expressions
//!
//! Datafu Expressions follow the given syntax, in (pseudo-)extended BNF:
//!
//! ```text
//! pattern ::= [matcher] tree
//! tree ::= {tag} {subvalue}
//! tag ::= arrow [keymatch] valuematch
//! valuematch ::= matcher | name [matcher]
//! matcher ::= parameter | literal | regex | predicate | type
//!
//! arrow ::= '->'
//! keymatch ::= '[' valuematch tree ']' ['?']
//! subvalue ::= '(' tree ')' ['?']
//! ```
//!
//! For a description of the terminals "parameter", "literal", "regex", "type"
//! and "predicate", see "Syntax Elements of Datafu Expressions" above.
//!
//! # Examples
//!
// FIXME check if this is actually the case :v
//! The Datafu pattern
//!
//! ```datafu
//! :map
//! ->['a'?]:map
//!   ->[b:?str]:?map
//!     (->['x'?]x:?bool)
//!     (->['y'?]y:?bool)?
//! ```
//!
//! When matched against the JSON
//!
//! ```json
//! {"a": {"1": {"y": true}, "2": {"x": true, "y": true}}}
//! ```
//!
//! Produces the same results as if matched against the sub-JSON
//!
//! ```json
//! {"a": {"2": {"x": true, "y": true}}}
//! ```

pub mod errors;
mod graph;
mod parser;
mod pattern;
mod vm;

pub use pattern::Pattern;
pub use pattern::PatternBuilder;

// TODO remove/redesign
/// A predicate.
type Predicate = dyn (Fn(
    &mut dyn erased_serde::Deserializer<'_>
) -> bool) + Send + Sync;

/// Helper to build predicates because closure inference is the worst.
///
/// # Examples
///
/// This doesn't work:
///
/// ```rust compile_fail
/// use serde::Deserialize;
/// use datafu::Predicate;
///
/// let x = Box::new(|v| String::deserialize(v).is_ok()) as Box<Predicate>;
/// ```
///
/// But this does:
///
/// ```rust,ignore
/// use serde::Deserialize;
///
/// let x = datafu::pred(|v| String::deserialize(v).is_ok());
/// ```
fn pred<F>(f: F) -> Box<Predicate>
where
    F: (Fn(
        &mut dyn erased_serde::Deserializer<'_>
    ) -> bool) +  Send + Sync + 'static,
{
    Box::new(f)
}