//! Export and import (part 9c). `:export md` and `:export txt` write the
//! document (or, typed in visual mode, the selection) as Markdown headings
//! or an indented outline (the user's picks), next to the document unless a
//! file is named. As vim's `:w` does with another file, a file that's there
//! already stays unless it's `:export!` (the user's pick). `:import` reads
//! Markdown, a list or indented lines from a file, and the nodes go under
//! the cursor's node, as `p` pastes them.

use std::collections::BTreeSet;
use std::path::{Path, PathBuf};

use super::App;
use super::action::{self, CursorAfter, DocAction, Message, PasteAt};
use super::commands;
use crate::command::parse::ExportFormat;
use crate::model::{Clip, NodeId};
use crate::storage::names::{self, file_name};
use crate::storage::{markdown, plain_text, write_atomically};

impl App {
    /// `:export`: `on` is the selection it was typed on (none: the whole
    /// document), `typed` the file named.
    pub(super) fn export(
        &mut self,
        format: ExportFormat,
        typed: Option<String>,
        force: bool,
        on: &[NodeId],
    ) -> Option<Message> {
        let (word, extension) = match format {
            ExportFormat::Markdown => ("md", "md"),
            ExportFormat::Text => ("txt", "txt"),
        };
        let open = self.shared.docs.get(self.buffer());
        let doc = open.buffer.doc();
        let ids: BTreeSet<NodeId> =
            if on.is_empty() { doc.outline().into_iter().collect() } else { on.iter().copied().collect() };
        let clip = Clip::take(doc, &ids);
        let path = match &typed {
            Some(typed) => {
                let path = self.typed_path(typed);
                if path.extension().is_none() { path.with_extension(extension) } else { path }
            }
            // Named after the document, or after the first branch selected.
            None => {
                let stem = match clip.roots.first() {
                    Some(top) if !on.is_empty() => file_name(top.node.title().as_str()),
                    _ => open.file_name(),
                };
                let stem = stem.strip_suffix(&format!(".{}", names::EXTENSION)).unwrap_or(&stem).to_string();
                self.folder().join(format!("{stem}.{extension}"))
            }
        };
        let name = file_label(&path);
        if path.extension().is_some_and(|found| found == names::EXTENSION) {
            return Some(Message::problem("an export is Markdown or text: name a .md or .txt file"));
        }
        let there = path.exists();
        if there && !force {
            let again =
                typed.map_or_else(|| format!(":export! {word}"), |typed| format!(":export! {word} {typed}"));
            return Some(Message::problem(format!("{name} is there already: {again} writes over it")));
        }
        let text = match format {
            ExportFormat::Markdown => markdown::export(&clip),
            ExportFormat::Text => plain_text::write(&clip),
        };
        if let Err(error) = write_atomically(&path, &text) {
            return Some(Message::problem(format!("couldn't write {name}: {error}")));
        }
        let over = if there { " (over the one there)" } else { "" };
        Some(Message::done(format!("wrote {} to {name}{over}", action::nodes(clip.count()))))
    }

    /// `:import`: the nodes in a Markdown or text file, under the cursor's
    /// node as its last children, laid out as a mind map: one undo step.
    pub(super) fn import(&mut self, typed: &str) -> Option<Message> {
        if let Some(refused) = self.refuse_read_only() {
            return Some(refused);
        }
        let path = self.typed_path(typed);
        let name = file_label(&path);
        if path.extension().is_some_and(|found| found == names::EXTENSION) {
            return Some(Message::info(format!(
                "{name} is a cumulus document: :e opens it, :portal leads to it"
            )));
        }
        let text = match std::fs::read_to_string(&path) {
            Ok(text) => text,
            Err(error) if error.kind() == std::io::ErrorKind::NotFound => {
                return Some(Message::problem(format!("there's no {name} there")));
            }
            Err(error) => return Some(Message::problem(format!("couldn't read {name}: {error}"))),
        };
        let Some(mut clip) = markdown::read(&text) else {
            return Some(Message::info(format!("nothing to import in {name}: it has no text")));
        };
        let ctx = self.shared.ctx(self.buffer());
        clip.lay_out(|node| ctx.box_size(node));
        let count = clip.count();
        let op = commands::paste(&ctx, clip, PasteAt::Child, 1)?;
        let edit = DocAction::Edit { op: Box::new(op), cursor: CursorAfter::Added, group: None };
        if let Some(problem) = self.doc_action(edit) {
            return Some(problem);
        }
        Some(Message::done(format!("imported {} from {name} · u undoes it", action::nodes(count))))
    }

    /// A file named on the command line: `~` is the home folder, and a
    /// relative path starts at the document's folder.
    fn typed_path(&self, typed: &str) -> PathBuf {
        let path = self.paths.expand(typed.trim());
        if path.is_relative() { self.folder().join(path) } else { path }
    }
}

/// A file's name, for messages.
fn file_label(path: &Path) -> String {
    path.file_name().map_or_else(|| path.display().to_string(), |name| name.to_string_lossy().into_owned())
}