//! Rust API for the [OpenGL API and Extension Registry].
//!
//! # Usage
//! ```
//! use opengl_registry::Registry;
//!
//! let registry = Registry::retrieve().unwrap();
//!
//! for command in registry.commands() {
//!     println!("Command {}", command.prototype().name());
//!     println!("  Return type: {}", command.prototype().return_type());
//!     println!("  Parameters:");
//!
//!     for param in command.parameters() {
//!         println!("  {} {}", param.get_type(), param.name());
//!     }
//! }
//! ```
//!
//! [OpenGL API and Extension Registry]: https://github.com/KhronosGroup/OpenGL-Registry
#![cfg_attr(doc_cfg, feature(doc_cfg))]
#![deny(clippy::all, clippy::pedantic, missing_docs)]

use std::fs::File;
use std::io::Read;

use crate::command::{Command, Error as CommandError};
use crate::xml::element::{Element, Elements, FromElements};
use crate::xml::parser::{Error as ParserError, Parser};

pub mod command;

mod xml;

#[cfg(feature = "include-xml")]
const GL_REGISTRY_XML: &[u8] = include_bytes!("../OpenGL-Registry/xml/gl.xml");

const REGISTRY_TAG_NAME: &str = "registry";

/// Representation of the OpenGL registry.
pub struct Registry
{
    commands: Vec<Command>,
}

impl Registry
{
    /// Retrieves the OpenGL registry from a included XML file.
    ///
    /// # Errors
    /// Returns `Err` if parsing fails in any way.
    #[cfg(feature = "include-xml")]
    #[cfg_attr(doc_cfg, doc(cfg(feature = "include-xml")))]
    pub fn retrieve() -> Result<Registry, RegistryError>
    {
        Self::retrieve_from_bytes(GL_REGISTRY_XML)
    }

    /// Retrieves the OpenGL registry from XML bytes.
    ///
    /// # Errors
    /// Returns `Err` if parsing fails in any way.
    pub fn retrieve_from_bytes(xml_bytes: &[u8]) -> Result<Registry, RegistryError>
    {
        let mut parser = Parser::new(xml_bytes);

        let elements = parser.parse().map_err(ParsingError)?;

        let registry_element = elements
            .get_first_tagged_element(REGISTRY_TAG_NAME)
            .ok_or(RegistryError::MissingRegistryElement)?;

        let registry = Registry::from_elements(registry_element.child_elements())?;

        Ok(registry)
    }

    /// Retrieves the OpenGL registry from a XML file.
    ///
    /// # Errors
    /// Returns `Err` if:
    /// - Parsing fails in any way.
    /// - An I/O error occurs.
    pub fn retrieve_from_file(xml_file: &mut File) -> Result<Registry, RegistryError>
    {
        let mut buf = Vec::new();

        xml_file.read_to_end(&mut buf)?;

        Self::retrieve_from_bytes(&buf)
    }

    /// Creates a new `Registry`.
    ///
    /// # Note
    /// This will **NOT** use anything from the actual OpenGL registry. Use the
    /// [`Registry::retrieve`] method for that.
    pub fn new(commands: impl IntoIterator<Item = Command>) -> Self
    {
        Self {
            commands: commands.into_iter().collect(),
        }
    }

    /// Returns the available commands.
    #[must_use]
    pub fn commands(&self) -> &[Command]
    {
        &self.commands
    }
}

impl FromElements for Registry
{
    type Error = RegistryError;

    fn from_elements(elements: &Elements) -> Result<Self, Self::Error>
    {
        let commands_element = elements
            .get_first_tagged_element("commands")
            .ok_or(Self::Error::MissingCommandsElement)?;

        let command_elements =
            commands_element
                .child_elements()
                .into_iter()
                .filter_map(|element| match element {
                    Element::Tagged(tagged_element)
                        if tagged_element.name() == "command" =>
                    {
                        Some(tagged_element)
                    }
                    _ => None,
                });

        let commands = command_elements
            .into_iter()
            .map(|command_element| {
                Command::from_elements(command_element.child_elements())
            })
            .collect::<Result<Vec<_>, _>>()?;

        Ok(Self { commands })
    }
}

/// [`Registry`] error.
#[derive(Debug, thiserror::Error)]
pub enum RegistryError
{
    /// No 'registry' element was found.
    #[error("No 'registry' element was found")]
    MissingRegistryElement,

    /// No 'commands' element was found.
    #[error("No 'commands' element was found")]
    MissingCommandsElement,

    /// A command is invalid.
    #[error("Invalid command")]
    InvalidCommand(#[from] CommandError),

    /// Parsing failed.
    #[error("Parsing failed")]
    ParsingFailed(#[from] ParsingError),

    /// I/O failed.
    #[error("I/O failed")]
    IOFailed(#[from] std::io::Error),
}

/// Parsing error.
#[derive(Debug, thiserror::Error)]
#[error(transparent)]
pub struct ParsingError(#[from] ParserError);