//! Tools to interpret dust source code.
//!
//! This module has three tools to run Dust code.
//!
//! - [interpret] is the simplest way to run Dust code inside of an application or library
//! - [interpret_with_context] allows you to set variables on the execution context
//! - [Interpreter] is an advanced tool that can parse, validate, run and format Dust code
//!
//! # Examples
//!
//! Run some Dust and get the result.
//!
//! ```rust
//! # use dust_lang::*;
//! assert_eq!(
//!     interpret("1 + 2 + 3"),
//!     Ok(Value::Integer(6))
//! );
//! ```
//!
//! Create a custom context with variables you can use in your code.
//!
//! ```rust
//! # use dust_lang::*;
//! let context = Context::new();
//!
//! context.set_value("one".into(), 1.into()).unwrap();
//! context.set_value("two".into(), 2.into()).unwrap();
//! context.set_value("three".into(), 3.into()).unwrap();
//!
//! let dust_code = "four = 4; one + two + three + four";
//!
//! assert_eq!(
//!     interpret_with_context(dust_code, context),
//!     Ok(Value::Integer(10))
//! );
//! ```
use tree_sitter::{Parser, Tree as SyntaxTree};

use crate::{language, AbstractTree, Context, ContextMode, Error, Format, Root, Value};

/// Interpret the given source code. Returns the value of last statement or the
/// first error encountered.
///
/// See the [module-level docs][self] for more info.
pub fn interpret(source: &str) -> Result<Value, Error> {
    interpret_with_context(source, Context::new(ContextMode::RemoveGarbage))
}

/// Interpret the given source code with the given context.
///
/// See the [module-level docs][self] for more info.
pub fn interpret_with_context(source: &str, context: Context) -> Result<Value, Error> {
    let mut interpreter = Interpreter::new(context);
    let value = interpreter.run(source)?;

    Ok(value)
}

/// A source code interpreter for the Dust language.
///
/// The interpreter's most important functions are used to parse dust source
/// code, verify it is safe and run it. They are written in a way that forces
/// them to be used safely: each step in this process contains the prior
/// steps, meaning that the same code is always used to create the syntax tree,
/// abstract tree and final evaluation. This avoids a critical logic error.
///
/// ```
/// # use dust_lang::*;
/// let context = Context::new();
/// let mut interpreter = Interpreter::new(context);
/// let result = interpreter.run("2 + 2");
///
/// assert_eq!(result, Ok(Value::Integer(4)));
/// ```
pub struct Interpreter {
    parser: Parser,
    context: Context,
}

impl Interpreter {
    /// Create a new interpreter with the given context.
    pub fn new(context: Context) -> Self {
        let mut parser = Parser::new();

        parser
            .set_language(language())
            .expect("Language version is incompatible with tree sitter version.");

        parser.set_logger(Some(Box::new(|_log_type, message| {
            log::trace!("{}", message)
        })));

        Interpreter { parser, context }
    }

    /// Generate a syntax tree from the source. Returns an error if the the
    /// parser is cancelled for taking too long. The syntax tree may contain
    /// error nodes, which represent syntax errors.
    ///
    /// Tree sitter is designed to be run on every keystroke, so this is
    /// generally a lightweight function to call.
    pub fn parse(&mut self, source: &str) -> Result<SyntaxTree, Error> {
        if let Some(tree) = self.parser.parse(source, None) {
            Ok(tree)
        } else {
            Err(Error::ParserCancelled)
        }
    }

    /// Check the source for errors and generate an abstract tree.
    ///
    /// The order in which this function works is:
    ///
    /// - parse the source into a syntax tree
    /// - generate an abstract tree from the source and syntax tree
    /// - check the abstract tree for errors
    pub fn validate(&mut self, source: &str) -> Result<Root, Error> {
        let syntax_tree = self.parse(source)?;
        let abstract_tree = Root::from_syntax(syntax_tree.root_node(), source, &self.context)?;

        abstract_tree.validate(source, &self.context)?;

        Ok(abstract_tree)
    }

    /// Run the source, returning the final statement's value or first error.
    ///
    /// This function [parses][Self::parse], [validates][Self::validate] and
    /// [runs][Root::run] using the same source code.
    pub fn run(&mut self, source: &str) -> Result<Value, Error> {
        let final_value = self.validate(source)?.run(source, &self.context)?;

        Ok(final_value)
    }

    /// Return an s-expression displaying a syntax tree of the source or an
    /// error.
    pub fn syntax_tree(&mut self, source: &str) -> Result<String, Error> {
        Ok(self.parse(source)?.root_node().to_sexp())
    }

    /// Return a formatted version of the source.
    pub fn format(&mut self, source: &str) -> Result<String, Error> {
        let mut formatted_output = String::new();

        self.validate(source)?.format(&mut formatted_output, 0);

        Ok(formatted_output)
    }
}

impl Default for Interpreter {
    fn default() -> Self {
        Interpreter::new(Context::default())
    }
}