//! Files of a course. For now only the lecture notes: markdown written in the app,
//! rendered to pdf with the course template, and tagged `notes`.
//!
//! Both files of a note live in the folder of the course, named after the note:
//! `Cours/CS-477 Advanced OS/Notes/Lecture 1 Notes - Intro.md` and `.pdf`. They are
//! moved when the note is renamed. The `.md` holds the front matter expected by the
//! template, so it can also be rendered by hand with `mdpdf`. The editor only sees what
//! comes after it.

use thiserror::Error;
use tracing::error;

use crate::core::{
    controller::{ControllerError, courses::file_name},
    models::{
        course::{Course, CourseId},
        course_file::{CourseFile, CourseFileId, FileKind, LectureNoteContent, SavedLectureNote},
        tag::NOTES_TAG,
    },
    repositories::{RepositoryError, pdf_renderer::RenderError},
};

/// Values of the front matter that do not depend on the note
#[derive(Debug, Clone, Default)]
pub struct NotesSettings {
    pub student_name: Option<String>,
    pub student_id: Option<String>,
    /// Absolute path of the logo
    pub logo: Option<String>,
}

/// Sub folder of the course holding the notes
const NOTES_FOLDER: &str = "Notes";

fn markdown_path(course: &Course, path: &str) -> String {
    format!("{}/{path}.md", course.folder)
}

fn pdf_path(course: &Course, path: &str) -> String {
    format!("{}/{path}.pdf", course.folder)
}

/// Path of a note in the folder of its course, without extension
fn note_path(title: &str) -> String {
    format!("{NOTES_FOLDER}/{}", file_name(title))
}

impl super::AppController {
    pub async fn get_course_files(
        &self,
        course_id: CourseId,
    ) -> Result<Vec<CourseFile>, ControllerError> {
        // 404 rather than an empty list for a course that does not exist
        self.db.get_course(course_id).await?;
        self.db
            .get_course_files(course_id)
            .await
            .map_err(Into::into)
    }

    /// `NotFound` if the file does not exist or is not a note
    async fn get_note(&self, id: CourseFileId) -> Result<CourseFile, ControllerError> {
        let file = self.db.get_course_file(id).await?;
        if file.kind != FileKind::Note {
            return Err(RepositoryError::NotFound(format!("lecture note {id}")).into());
        }
        Ok(file)
    }

    pub async fn get_lecture_note(
        &self,
        id: CourseFileId,
    ) -> Result<LectureNoteContent, ControllerError> {
        let note = self.get_note(id).await?;
        let course = self.db.get_course(note.course_id).await?;
        let content = match self
            .storage
            .read_file(&markdown_path(&course, &note.path))
            .await
        {
            Ok(bytes) => String::from_utf8_lossy(&bytes).into_owned(),
            // Lost file: the note can still be rewritten
            Err(RepositoryError::NotFound(_)) => String::new(),
            Err(err) => return Err(err.into()),
        };
        Ok(LectureNoteContent {
            file: note,
            content: strip_front_matter(&content).to_owned(),
        })
    }

    /// `NotFound` if the note does not exist or its last rendering failed
    pub async fn get_lecture_note_pdf(&self, id: CourseFileId) -> Result<Vec<u8>, ControllerError> {
        let note = self.get_note(id).await?;
        let course = self.db.get_course(note.course_id).await?;
        self.storage
            .read_file(&pdf_path(&course, &note.path))
            .await
            .map_err(Into::into)
    }

    pub async fn create_lecture_note(
        &self,
        course_id: CourseId,
        title: String,
        content: String,
    ) -> Result<SavedLectureNote, ControllerError> {
        let title = validate_title(title)?;
        let course = self.db.get_course(course_id).await?;
        let path = note_path(&title);
        self.check_path_free(course_id, &path, None).await?;
        let notes_tag = self.db.get_tag_id(NOTES_TAG).await?;
        let note = self
            .db
            .create_lecture_note(course_id, title.clone(), path, &[notes_tag])
            .await?;
        self.save_lecture_note(&course, note, title, content).await
    }

    pub async fn update_lecture_note(
        &self,
        id: CourseFileId,
        title: String,
        content: String,
    ) -> Result<SavedLectureNote, ControllerError> {
        let title = validate_title(title)?;
        let note = self.get_note(id).await?;
        let course = self.db.get_course(note.course_id).await?;

        // Renamed: its files follow
        let path = note_path(&title);
        if path != note.path {
            self.check_path_free(course.id, &path, Some(id)).await?;
            for (from, to) in [
                (
                    markdown_path(&course, &note.path),
                    markdown_path(&course, &path),
                ),
                (pdf_path(&course, &note.path), pdf_path(&course, &path)),
            ] {
                match self.storage.rename(&from, &to).await {
                    Ok(()) | Err(RepositoryError::NotFound(_)) => {}
                    Err(err) => return Err(err.into()),
                }
            }
        }
        let note = CourseFile { path, ..note };
        self.save_lecture_note(&course, note, title, content).await
    }

    pub async fn delete_lecture_note(&self, id: CourseFileId) -> Result<(), ControllerError> {
        let note = self.get_note(id).await?;
        let course = self.db.get_course(note.course_id).await?;
        self.db.delete_course_file(id).await?;
        self.storage
            .delete_file(&markdown_path(&course, &note.path))
            .await?;
        self.storage
            .delete_file(&pdf_path(&course, &note.path))
            .await?;
        Ok(())
    }

    /// `NameTaken` if another file of the course (than `except`) already has this path
    async fn check_path_free(
        &self,
        course_id: CourseId,
        path: &str,
        except: Option<CourseFileId>,
    ) -> Result<(), ControllerError> {
        let files = self.db.get_course_files(course_id).await?;
        if files
            .iter()
            .any(|file| file.path == path && Some(file.id) != except)
        {
            return Err(LectureNotesControllerError::NameTaken.into());
        }
        Ok(())
    }

    /// Writes the markdown, then renders it. The markdown is kept even when the
    /// rendering fails, and the error is returned to be shown in the editor.
    async fn save_lecture_note(
        &self,
        course: &Course,
        note: CourseFile,
        title: String,
        content: String,
    ) -> Result<SavedLectureNote, ControllerError> {
        let markdown = format!("{}{}", self.front_matter(course, &title), content);
        let pdf = pdf_path(course, &note.path);
        self.storage
            .write_file(&markdown_path(course, &note.path), markdown.as_bytes())
            .await?;

        let pdf_error = match self.renderer.render(&markdown).await {
            Ok(content) => {
                self.storage.write_file(&pdf, &content).await?;
                None
            }
            Err(err) => {
                // No stale pdf that would not match the markdown anymore
                self.storage.delete_file(&pdf).await?;
                Some(match err {
                    RenderError::Failed(log) => log,
                    RenderError::Internal(message) => {
                        error!("Unable to render lecture note {}: {message}", note.id);
                        message
                    }
                })
            }
        };

        let note = self
            .db
            .update_lecture_note(note.id, title, note.path, pdf_error.is_none())
            .await?;
        Ok(SavedLectureNote { note, pdf_error })
    }

    /// Front matter read by `template.tex`, e.g. `course: "CS-477 -- Advanced OS"`
    fn front_matter(&self, course: &Course, title: &str) -> String {
        let course_title = match &course.code {
            Some(code) => format!("{code} -- {}", course.name),
            None => course.name.clone(),
        };
        let fields = [
            ("student-name", self.notes.student_name.as_deref()),
            ("student-id", self.notes.student_id.as_deref()),
            ("logo", self.notes.logo.as_deref()),
            ("course", Some(course_title.as_str())),
            ("subtitle", Some(title)),
        ];
        let mut front_matter = String::from("---\n");
        for (key, value) in fields {
            if let Some(value) = value {
                front_matter.push_str(&format!("{key}: {}\n", yaml_string(value)));
            }
        }
        front_matter.push_str("---\n\n");
        front_matter
    }
}

/// A json string is a valid double quoted yaml scalar: quotes and backslashes escaped
fn yaml_string(value: &str) -> String {
    serde_json::to_string(value).unwrap_or_default()
}

/// Content of a markdown file without its front matter
fn strip_front_matter(markdown: &str) -> &str {
    markdown
        .strip_prefix("---\n")
        .and_then(|rest| rest.split_once("\n---\n"))
        .map(|(_, body)| body.trim_start_matches('\n'))
        .unwrap_or(markdown)
}

fn validate_title(title: String) -> Result<String, ControllerError> {
    let title = title.trim().to_owned();
    if title.is_empty() {
        return Err(LectureNotesControllerError::EmptyTitle.into());
    }
    Ok(title)
}

#[derive(Error, Debug)]
pub enum LectureNotesControllerError {
    #[error("The title of the note is empty")]
    EmptyTitle,
    #[error("Another file of the course already has this name")]
    NameTaken,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn strips_front_matter() {
        let markdown = "---\ncourse: \"X\"\nsubtitle: \"Y\"\n---\n\n# Intro\n---\nText";
        assert_eq!(strip_front_matter(markdown), "# Intro\n---\nText");
        assert_eq!(strip_front_matter("# No front matter"), "# No front matter");
    }

    #[test]
    fn escapes_yaml() {
        assert_eq!(yaml_string(r#"Notes: "memory""#), r#""Notes: \"memory\"""#);
    }
}