//! Augmented-manifest construction (ADR-0011, outline shape per ADR-0029).
//!
//! The template (`exports/<target>.typ`) reads the manifest via
//! `toml(sys.inputs.manifest)`, then for each **element** outline entry
//! `include`s its content fields by a **computed** path and reads scalar
//! fields from `<path>/element.toml`. For *optional* content fields the
//! template must know whether the file exists on disk — typst has no
//! file-exists primitive and a missing `include` is a hard error (see the OPEN
//! contract point in `render/templates/student.typ`).
//!
//! The ENGINE has filesystem access, so it closes that gap: it builds an
//! **augmented manifest** = the lesson's `[info]` + the ordered `[[outline]]`
//! (ADR-0029's depth-first rendering order — elements interleaved with section
//! headings at their DFS-open position). Each `[[outline]]` entry carries a
//! `type` discriminator (`"element"` | `"section"`):
//!
//! - `type = "element"`: `kind`, `path`, and a per-part **`fields` array**
//!   listing the content fields whose `<field>.typ` actually exists under the
//!   lesson root (same contract as before ADR-0029).
//! - `type = "section"`: `kind`, `title`, `depth`, `path` — a section heading;
//!   the template renders it without touching any content file.
//!
//! The augmented manifest is served as an in-memory virtual file in the
//! [`crate::world::LessonWorld`] (it is **never** written to the user's tree),
//! and injected via `sys.inputs.manifest`.
//!
//! ## `fields` is computed from `cph-schema`
//!
//! `cph-schema` already encodes each kind's content fields
//! ([`cph_schema::KindSchema::content_field_names`]) — the same knowledge the
//! render package exposes as `part-fields`. We reuse it here rather than
//! re-deriving a kind→fields map, so the engine and the template agree on what a
//! kind's content fields are. For each element, a content field is listed in
//! `fields` iff `<root>/<part.path>/<field>.typ` is a real file.

use std::path::Path;

use cph_model::{Bundle, BundleLesson, Lesson, OutlineEntry};

/// Build the augmented-manifest TOML source for `lesson`.
///
/// The result is a self-contained TOML document the template's
/// `toml(sys.inputs.manifest)` reads. It carries `[info]` (title + optional
/// author) and the ordered `[[outline]]` (ADR-0029's depth-first rendering
/// order), each entry typed `"element"` or `"section"` per the module docs. It
/// does **not** reproduce `[project]` or `[targets.*]` — the template only
/// consumes `info` and `outline`.
pub fn build_augmented_manifest(lesson: &Lesson) -> String {
    let mut doc = toml::Table::new();

    doc.insert("info".to_string(), toml::Value::Table(info_table(lesson)));

    // [[outline]] — ADR-0029's depth-first rendering order: elements
    // interleaved with section headings at their DFS-open position.
    let outline: Vec<toml::Value> = lesson
        .outline
        .iter()
        .map(|entry| toml::Value::Table(outline_entry_table(lesson, entry, None)))
        .collect();
    doc.insert("outline".to_string(), toml::Value::Array(outline));

    toml::to_string(&doc).expect("augmented manifest serializes")
}

/// Build the augmented **bundle** manifest TOML source for `bundle` (ADR-0030).
///
/// The bundle template (`exports/<target>.typ` under the `bundle.toml` root)
/// reads it via `toml(sys.inputs.manifest)`. It carries `[info]` (the bundle's
/// own title/author) and the ordered `[[lessons]]`, each a
/// `(info, target, outline)` table — the same shape a single-lesson template
/// would assemble, except every outline entry's `path` is **prefixed with that
/// lesson's own bundle-root-relative directory** (`BundleLesson::path`), since
/// the bundle template's computed include paths resolve against the *bundle*
/// root, not each lesson's own root (ADR-0030: combination reads
/// already-authored lessons at export time; each lesson's `path` bookkeeping
/// stays correct because the prefix is applied only here, in the manifest the
/// template consumes — never inside a lesson's own authored content).
pub fn build_augmented_bundle_manifest(bundle: &Bundle) -> String {
    let mut doc = toml::Table::new();

    let mut info = toml::Table::new();
    info.insert(
        "title".to_string(),
        toml::Value::String(bundle.info.title.clone()),
    );
    if !bundle.info.authors.is_empty() {
        let authors = bundle
            .info
            .authors
            .iter()
            .cloned()
            .map(toml::Value::String)
            .collect();
        info.insert("author".to_string(), toml::Value::Array(authors));
    }
    doc.insert("info".to_string(), toml::Value::Table(info));

    let lessons: Vec<toml::Value> = bundle
        .lessons
        .iter()
        .map(|bl| toml::Value::Table(bundle_lesson_table(bl)))
        .collect();
    doc.insert("lessons".to_string(), toml::Value::Array(lessons));

    toml::to_string(&doc).expect("augmented bundle manifest serializes")
}

/// Build one `[[lessons]]` entry's table: that member lesson's own `info`,
/// its selected `target`, and its outline with every entry's `path` prefixed
/// by the lesson's bundle-relative directory.
fn bundle_lesson_table(bl: &BundleLesson) -> toml::Table {
    let mut t = toml::Table::new();
    t.insert(
        "info".to_string(),
        toml::Value::Table(info_table(&bl.lesson)),
    );
    t.insert("target".to_string(), toml::Value::String(bl.target.clone()));
    let outline: Vec<toml::Value> = bl
        .lesson
        .outline
        .iter()
        .map(|entry| toml::Value::Table(outline_entry_table(&bl.lesson, entry, Some(&bl.path))))
        .collect();
    t.insert("outline".to_string(), toml::Value::Array(outline));
    t
}

/// Build the `[info]` table shared by a single-lesson manifest and a bundle
/// member's `info` entry.
fn info_table(lesson: &Lesson) -> toml::Table {
    let mut info = toml::Table::new();
    info.insert(
        "title".to_string(),
        toml::Value::String(lesson.info.title.clone()),
    );
    if !lesson.info.authors.is_empty() {
        let authors = lesson
            .info
            .authors
            .iter()
            .cloned()
            .map(toml::Value::String)
            .collect();
        info.insert("author".to_string(), toml::Value::Array(authors));
    }
    info
}

/// Build one `[[outline]]` entry's table for either variant of
/// [`OutlineEntry`]. `bundle_prefix`, when set (ADR-0030's bundle case), is
/// joined onto the emitted `path` so the bundle template's computed include
/// resolves against the bundle root rather than the lesson's own root.
fn outline_entry_table(
    lesson: &Lesson,
    entry: &OutlineEntry,
    bundle_prefix: Option<&Path>,
) -> toml::Table {
    let mut e = toml::Table::new();
    match entry {
        OutlineEntry::Element { part_index, .. } => {
            let part = &lesson.parts[*part_index];
            e.insert("type".to_string(), toml::Value::String("element".into()));
            e.insert("kind".to_string(), toml::Value::String(part.kind.clone()));
            e.insert(
                "path".to_string(),
                toml::Value::String(prefixed_forward_slash(bundle_prefix, &part.path)),
            );
            let fields = present_fields(lesson, part)
                .into_iter()
                .map(toml::Value::String)
                .collect();
            e.insert("fields".to_string(), toml::Value::Array(fields));
        }
        OutlineEntry::Section {
            kind,
            title,
            depth,
            path,
            notes: _,
        } => {
            e.insert("type".to_string(), toml::Value::String("section".into()));
            e.insert("kind".to_string(), toml::Value::String(kind.clone()));
            e.insert("title".to_string(), toml::Value::String(title.clone()));
            e.insert("depth".to_string(), toml::Value::Integer(i64::from(*depth)));
            e.insert(
                "path".to_string(),
                toml::Value::String(prefixed_forward_slash(bundle_prefix, path)),
            );
        }
    }
    e
}

/// [`path_to_forward_slash`], with `prefix` (a bundle member's own
/// bundle-relative directory) joined in front when present.
fn prefixed_forward_slash(prefix: Option<&Path>, path: &Path) -> String {
    match prefix {
        Some(p) => path_to_forward_slash(&p.join(path)),
        None => path_to_forward_slash(path),
    }
}

/// The content fields of `part`'s kind whose `<root>/<part.path>/<field>.typ`
/// file exists on disk, in schema order.
///
/// The kind→content-fields knowledge is reused from `cph-schema`
/// ([`cph_schema::schema_for`]); an unknown kind has no schema and yields an
/// empty list (the render package surfaces an unknown kind on its own). Both
/// required and optional content fields are probed — listing a *required* field
/// here is harmless (the template includes required fields unconditionally), and
/// it keeps `fields` a faithful "what exists on disk" record.
fn present_fields(lesson: &Lesson, part: &cph_model::Part) -> Vec<String> {
    let Some(schema) = cph_schema::schema_for(&part.kind) else {
        return Vec::new();
    };
    let part_dir = lesson.root.join(&part.path);
    schema
        .content_field_names()
        .into_iter()
        .filter(|field| part_dir.join(format!("{field}.typ")).is_file())
        .map(str::to_string)
        .collect()
}

/// Render a relative `PathBuf` as a forward-slash string, dropping any leading
/// `./` or `/` and ignoring `..` (already rejected by the cph-model loader).
/// Element folder names are UTF-8 (e.g. Chinese) and kept verbatim. The template
/// rebuilds an absolute root-relative include path as `"/" + path + "/" + field`,
/// so `path` must be a clean relative slash path.
fn path_to_forward_slash(path: &std::path::Path) -> String {
    use std::path::Component;
    let mut out = String::new();
    for comp in path.components() {
        if let Component::Normal(s) = comp {
            if !out.is_empty() {
                out.push('/');
            }
            out.push_str(&s.to_string_lossy());
        }
    }
    out
}

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

    #[test]
    fn forward_slash_path_keeps_unicode() {
        let p = std::path::Path::new("segments/开场对照导言");
        assert_eq!(path_to_forward_slash(p), "segments/开场对照导言");
    }
}