oxframe 0.4.0

use std::fmt;
use std::path::PathBuf;
use std::rc::Rc;

use oxframe_2d::{SceneGraph, View};
use oxframe_core::Executor;
use oxframe_protocol::{MarkerInfo, Meta, MetaError, SceneInfo};
use oxframe_render::{Image, RenderOptions, Renderer};

use crate::{Project, SceneDef};

/// Why a project could not be loaded.
#[derive(Debug)]
pub enum EngineError {
    /// A `meta.json` file is invalid.
    Meta {
        /// The file.
        path: PathBuf,
        /// What is wrong with it.
        error: MetaError,
    },
    /// A file could not be read or written.
    Io {
        /// The file.
        path: PathBuf,
        /// The I/O error.
        error: std::io::Error,
    },
    /// `Project::scene` was never called.
    NoScenes,
}

impl fmt::Display for EngineError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Meta { path, error } => write!(f, "{}: {error}", path.display()),
            Self::Io { path, error } => write!(f, "{}: {error}", path.display()),
            Self::NoScenes => write!(f, "the project has no scenes"),
        }
    }
}

impl std::error::Error for EngineError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            Self::Meta { error, .. } => Some(error),
            Self::Io { error, .. } => Some(error),
            Self::NoScenes => None,
        }
    }
}

/// A section of `meta.json`, for [`Engine::edit_meta`].
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum MetaSection {
    /// `markers`.
    Markers,
    /// `eases`.
    Eases,
    /// `tunables`.
    Tunables,
}

impl MetaSection {
    fn singular(self) -> &'static str {
        match self {
            Self::Markers => "marker",
            Self::Eases => "ease",
            Self::Tunables => "tunable",
        }
    }
}

/// One execution of a scene: its graph and executor.
struct SceneRun {
    graph: Rc<SceneGraph>,
    exec: Executor,
    theme: oxframe_2d::Theme,
}

impl SceneRun {
    fn new(def: &SceneDef, project: &Project, meta: Meta) -> Self {
        let graph = SceneGraph::new(project.size.0, project.size.1);
        let fut = (def.factory)(View::current());
        Self {
            graph,
            exec: Executor::new(
                f64::from(project.fps),
                meta,
                scene_seed(project.seed, def.name),
                fut,
            ),
            theme: project.theme.clone(),
        }
    }

    fn step(&mut self) -> bool {
        let theme = self.theme.clone();
        oxframe_2d::enter_theme(&theme, || {
            let Self { graph, exec, .. } = self;
            graph.enter(|| exec.step())
        })
    }

    /// Index of the last computed frame, if any.
    fn last_frame(&self) -> Option<u32> {
        self.exec.frames_done().checked_sub(1)
    }
}

struct SceneState {
    def: SceneDef,
    meta: Meta,
    meta_path: PathBuf,
    start: u32,
    frames: u32,
    run: Option<SceneRun>,
}

/// Runs a [`Project`]: knows the length of every scene and produces the
/// state of any global frame.
///
/// Seeking backwards re-simulates the scene from frame 0 without rendering;
/// seeking forwards continues from the current state.
pub struct Engine {
    project: Project,
    scenes: Vec<SceneState>,
}

impl Engine {
    /// Loads the metas and runs every scene once to find its length.
    ///
    /// # Errors
    ///
    /// If a `meta.json` cannot be read or is invalid, or there are no scenes.
    pub fn new(project: Project) -> Result<Self, EngineError> {
        if project.scenes.is_empty() {
            return Err(EngineError::NoScenes);
        }
        let mut scenes = Vec::with_capacity(project.scenes.len());
        for def in &project.scenes {
            let meta_path = match &project.meta_dir {
                Some(dir) => dir.join(format!("{}.meta.json", def.name)),
                None => def.meta_path(),
            };
            let meta = match &project.inline_meta {
                Some(m) => m.get(def.name).cloned().unwrap_or_default(),
                None => load_meta(&meta_path)?,
            };
            scenes.push(SceneState {
                def: *def,
                meta,
                meta_path,
                start: 0,
                frames: 0,
                run: None,
            });
        }
        // The soundtrack is project-wide; its offset lives in the first
        // scene's meta.
        if let Some(file) = &project.audio
            && let Some(first) = scenes.first_mut()
            && first.meta.audio.as_ref().is_none_or(|a| &a.file != file)
        {
            let offset = first.meta.audio.as_ref().map_or(0.0, |a| a.offset);
            first.meta.audio = Some(oxframe_protocol::AudioMeta {
                file: file.clone(),
                offset,
                extra: Default::default(),
            });
            if project.write_meta && project.inline_meta.is_none() {
                save_meta(&first.meta_path, &first.meta)?;
            }
        }
        let mut engine = Self { project, scenes };
        for i in 0..engine.scenes.len() {
            engine.measure(i)?;
        }
        engine.layout();
        Ok(engine)
    }

    /// The project definition.
    pub fn project(&self) -> &Project {
        &self.project
    }

    /// Runs scene `i` to completion to learn its length and to record
    /// defaults (markers, eases, tunables) into its meta.
    fn measure(&mut self, i: usize) -> Result<(), EngineError> {
        let max = (self.project.max_scene_seconds * f64::from(self.project.fps)).ceil() as u32;
        let scene = &mut self.scenes[i];
        let mut run = SceneRun::new(&scene.def, &self.project, scene.meta.clone());
        while !run.step() && run.exec.frames_done() < max.max(1) {}
        scene.frames = run.exec.frames_done();
        if run.exec.take_meta_changed() {
            scene.meta = run.exec.meta();
            if self.project.write_meta && self.project.inline_meta.is_none() {
                save_meta(&scene.meta_path, &scene.meta)?;
            }
        }
        // Reuse the run: it is positioned at the last frame.
        scene.run = Some(run);
        Ok(())
    }

    fn layout(&mut self) {
        let mut start = 0;
        for s in &mut self.scenes {
            s.start = start;
            start += s.frames;
        }
    }

    /// Frames per second.
    pub fn fps(&self) -> u32 {
        self.project.fps
    }

    /// Project size in pixels.
    pub fn size(&self) -> (u32, u32) {
        self.project.size
    }

    /// Length of all scenes together, in frames.
    pub fn total_frames(&self) -> u32 {
        self.scenes.last().map_or(0, |s| s.start + s.frames)
    }

    /// Scenes with their first frame and length.
    pub fn scenes(&self) -> Vec<SceneInfo> {
        self.scenes
            .iter()
            .map(|s| SceneInfo {
                name: s.def.name.to_owned(),
                start: s.start,
                frames: s.frames,
            })
            .collect()
    }

    /// Markers of all scenes.
    pub fn markers(&self) -> Vec<MarkerInfo> {
        self.scenes
            .iter()
            .flat_map(|s| {
                s.meta.markers.iter().map(|(name, &time)| MarkerInfo {
                    scene: s.def.name.to_owned(),
                    name: name.clone(),
                    time,
                })
            })
            .collect()
    }

    /// Soundtrack file and offset (seconds), if the project has one.
    pub fn audio(&self) -> Option<(String, f64)> {
        let a = self.scenes.first()?.meta.audio.as_ref()?;
        Some((a.file.clone(), a.offset))
    }

    /// Meta of every scene, as `(scene, meta)`.
    pub fn metas(&self) -> Vec<(String, Meta)> {
        self.scenes
            .iter()
            .map(|s| (s.def.name.to_owned(), s.meta.clone()))
            .collect()
    }

    /// Meta of one scene.
    pub fn meta(&self, scene: &str) -> Option<&Meta> {
        self.scenes
            .iter()
            .find(|s| s.def.name == scene)
            .map(|s| &s.meta)
    }

    /// Scene index and local frame of a global frame (clamped to the end).
    pub fn locate(&self, frame: u32) -> (usize, u32) {
        let total = self.total_frames();
        let frame = frame.min(total.saturating_sub(1));
        let i = self
            .scenes
            .iter()
            .rposition(|s| s.start <= frame)
            .unwrap_or(0);
        (i, frame - self.scenes[i].start)
    }

    /// Simulates up to global `frame` and returns the scene graph in that
    /// state. Does not render.
    pub fn seek(&mut self, frame: u32) -> &SceneGraph {
        let (i, local) = self.locate(frame);
        let project = &self.project;
        let scene = &mut self.scenes[i];
        let reusable = scene
            .run
            .as_ref()
            .is_some_and(|r| r.last_frame().is_some_and(|last| last <= local));
        if !reusable {
            scene.run = Some(SceneRun::new(&scene.def, project, scene.meta.clone()));
        }
        let run = scene.run.as_mut().expect("run was just ensured");
        while run.last_frame().is_none_or(|last| last < local) {
            if run.step() {
                break;
            }
        }
        // Drop runs of other scenes; only one graph is alive at a time.
        for (j, s) in self.scenes.iter_mut().enumerate() {
            if j != i {
                s.run = None;
            }
        }
        &self.scenes[i].run.as_ref().expect("run exists").graph
    }

    /// Applies a meta edit to the scene that owns `name` (markers, eases and
    /// tunables are looked up across scenes), re-measures it and saves the
    /// meta. Returns the scene name and its new meta.
    ///
    /// # Errors
    ///
    /// If the scene or name is unknown, the name is invalid, or the meta
    /// cannot be saved.
    pub fn edit_meta(
        &mut self,
        section: MetaSection,
        name: &str,
        scene: Option<&str>,
        apply: impl FnOnce(&mut Meta),
    ) -> Result<(String, Meta), String> {
        let i = match scene {
            Some(scene) => self
                .scenes
                .iter()
                .position(|s| s.def.name == scene)
                .ok_or_else(|| format!("no scene named `{scene}`"))?,
            None => self
                .scenes
                .iter()
                .position(|s| match section {
                    MetaSection::Markers => s.meta.markers.contains_key(name),
                    MetaSection::Eases => s.meta.eases.contains_key(name),
                    MetaSection::Tunables => s.meta.tunables.contains_key(name),
                })
                .ok_or_else(|| format!("no {} named `{name}` in any scene", section.singular()))?,
        };
        let scene = &mut self.scenes[i];
        let mut meta = scene.meta.clone();
        apply(&mut meta);
        meta.validate().map_err(|e| e.to_string())?;
        scene.meta = meta;
        if self.project.write_meta && self.project.inline_meta.is_none() {
            save_meta(&scene.meta_path, &scene.meta).map_err(|e| e.to_string())?;
        }
        scene.run = None;
        self.measure(i).map_err(|e| e.to_string())?;
        self.layout();
        let s = &self.scenes[i];
        Ok((s.def.name.to_owned(), s.meta.clone()))
    }

    /// Converts frame pixels (top-left origin) to scene coordinates.
    pub fn pixels_to_scene(&self, x: f64, y: f64) -> oxframe_core::Point {
        let (w, h) = self.project.size;
        oxframe_core::Point::new(x - f64::from(w) / 2.0, y - f64::from(h) / 2.0)
    }

    /// Simulates up to `frame` and draws it at `size` pixels.
    pub fn render(&mut self, frame: u32, renderer: &mut dyn Renderer, size: (u32, u32)) -> Image {
        let background = self.project.background;
        let graph = self.seek(frame);
        renderer.render(
            graph,
            &RenderOptions {
                width: size.0,
                height: size.1,
                background,
            },
        )
    }
}

/// Per-scene seed: the project seed mixed with an FNV-1a hash of the name,
/// so scenes get independent but reproducible streams.
fn scene_seed(seed: u64, name: &str) -> u64 {
    let mut h: u64 = 0xcbf2_9ce4_8422_2325;
    for b in name.bytes() {
        h = (h ^ u64::from(b)).wrapping_mul(0x0100_0000_01b3);
    }
    seed ^ h
}

fn load_meta(path: &PathBuf) -> Result<Meta, EngineError> {
    match std::fs::read_to_string(path) {
        Ok(text) => Meta::parse(&text).map_err(|error| EngineError::Meta {
            path: path.clone(),
            error,
        }),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(Meta::default()),
        Err(error) => Err(EngineError::Io {
            path: path.clone(),
            error,
        }),
    }
}

fn save_meta(path: &PathBuf, meta: &Meta) -> Result<(), EngineError> {
    let text = meta.to_pretty_string();
    if std::fs::read_to_string(path).is_ok_and(|old| old == text) {
        return Ok(());
    }
    // Write through a temp file so an interrupted write never leaves a
    // truncated meta.json behind.
    let tmp = path.with_extension("json.tmp");
    std::fs::write(&tmp, &text)
        .and_then(|()| std::fs::rename(&tmp, path))
        .map_err(|error| EngineError::Io {
            path: path.clone(),
            error,
        })
}