// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.

//! # Storage layer for Notesmachine
//!
//! This library implements the core functionality of Notesmachine and
//! describes that functionality to a storage layer.  There's a bit of
//! intermingling in here which can't be helped, although it may make
//! sense in the future to separate the decomposition of the note
//! content into a higher layer.
//!
//! Notesmachine storage notes consist of two items: Note and Kasten.
//! This distinction is somewhat arbitrary, as structurally these two
//! items are stored in the same table.
//!
//! - Boxes have titles (and date metadata)
//! - Notes have content and a type (and date metadata)
//! - Notes are stored in boxes
//!   - Notes are positioned with respect to other notes.
//!   - There are two positions:
//!     - Siblings, creating lists
//!     - Children, creating trees like this one
//! - Notes may have references (pointers) to other boxes
//! - Notes may be moved around
//! - Notes may be deleted
//! - Boxes may be deleted
//! - When a box is renamed, every reference to that box is auto-edited to
//!   reflect the change. If a box is renamed to match an existing box, the
//!   notes in both boxes are merged.
//!   
//! Note-to-note relationships form trees, and are kept in a SQL database of
//! (`parent_id`, `child_id`, `position`, `relationship_type`). The
//! `position` is a monotonic index on the parent (that is, every pair
//! (`parent_id`, `position`) must be unique).  The `relationship_type` is
//! an enum and can specify that the relationship is *original*,
//! *embedding*, or *referencing*.  An embedded or referenced note may be
//! read/write or read-only with respect to the original, but there is only
//! one original note at any time.
//!
//! Note-to-box relationships form a graph, and are kept in the SQL database
//! as a collection of *edges* from the note to the box (and naturally
//! vice-versa).
//!
//! - Decision: When an original note is deleted, do all references and
//!   embeddings also get deleted, or is the oldest one elevated to be a new
//!   "original"?  Or is that something the user may choose?
//!
//! - Decision: Should the merging issue be handled at this layer, or would
//!   it make sense to move this to a higher layer, and only provide the
//!   hooks for it here?
//!

use crate::errors::NoteStoreError;
use crate::reference_parser::build_references;
use crate::store::private::*;
use crate::structs::*;
use sqlx::sqlite::SqlitePool;
use std::cmp;
// use std::collections::HashMap;
use std::sync::Arc;

/// A handle to our Sqlite database.
#[derive(Clone, Debug)]
pub struct NoteStore(Arc<SqlitePool>);

pub type NoteResult<T> = core::result::Result<T, NoteStoreError>;

// After wrestling for a while with the fact that 'box' is a reserved
// word in Rust, I decided to just go with Note (note) and Kasten
// (box).

impl NoteStore {
	/// Initializes a new instance of the note store.  Note that the
	/// note store holds an Arc internally; this code is (I think)
	/// safe to Send.
	pub async fn new(url: &str) -> NoteResult<Self> {
		let pool = SqlitePool::connect(url).await?;
		Ok(NoteStore(Arc::new(pool)))
	}
	/// Erase all the data in the database and restore it
	/// to its original empty form.  Do not use unless you
	/// really, really want that to happen.
	pub async fn reset_database(&self) -> NoteResult<()> {
		reset_database(&*self.0)
			.await
			.map_err(NoteStoreError::DBError)
	}

	/// Fetch page by slug
	///
	/// Supports the use case of the user navigating to a known place
	/// via a bookmark or other URL.  Since the title isn't clear from
	/// the slug, the slug is insufficient to generate a new page, so
	/// this use case says that in the event of a failure to find the
	/// requested page, return a basic NotFound.
	pub async fn get_kasten_by_slug(&self, slug: &str) -> NoteResult<(Vec<Note>, Vec<Note>)> {
		let kasten = select_kasten_by_slug(&*self.0, &NoteId(slug.to_string())).await?;
		if kasten.is_empty() {
			return Err(NoteStoreError::NotFound);
		}

		let note_id = NoteId(kasten[0].id.clone());
		Ok((
			kasten,
			select_backreferences_for_kasten(&*self.0, &note_id).await?,
		))
	}

	/// Fetch page by title

	/// The most common use case: the user is navigating by requesting
	/// a page.  The page either exists or it doesn't.  If it
	/// doesn't, we go out and make it.  Since we know it doesn't exist,
	/// we also know no backreferences to it exist, so in that case you
	/// get back two empty vecs.
	pub async fn get_kasten_by_title(&self, title: &str) -> NoteResult<(Vec<Note>, Vec<Note>)> {
		if title.len() == 0 {
			return Err(NoteStoreError::NotFound);
		}

		let kasten = select_kasten_by_title(&*self.0, title).await?;
		if kasten.len() > 0 {
			let note_id = NoteId(kasten[0].id.clone());
			return Ok((
				kasten,
				select_backreferences_for_kasten(&*self.0, &note_id).await?,
			));
		}

		// Sanity check!
		let references = build_references(&title);
		if references.len() > 0 {
			return Err(NoteStoreError::InvalidNoteStructure(
				"Titles may not contain nested references.".to_string(),
			));
		}

		let mut tx = self.0.begin().await?;
		let slug = generate_slug(&mut tx, title).await?;
		let zettlekasten = create_zettlekasten(&title, &slug);
		let _ = insert_note(&mut tx, &zettlekasten).await?;
		tx.commit().await?;

		Ok((vec![Note::from(zettlekasten)], vec![]))
	}

	pub async fn add_note(
		&self,
		note: &NewNote,
		parent_id: &str,
		location: Option<i64>,
	) -> NoteResult<String> {
		let new_id = self
			.insert_note(
				note,
				&ParentId(parent_id.to_string()),
				location,
				RelationshipKind::Direct,
			)
			.await?;
		Ok(new_id)
	}

	/// Move a note from one location to another.
	pub async fn move_note(
		&self,
		note_id: &str,
		old_parent_id: &str,
		new_parent_id: &str,
		new_location: i64,
	) -> NoteResult<()> {
		let mut tx = self.0.begin().await?;

		let old_parent_id = ParentId(old_parent_id.to_string());
		let new_parent_id = ParentId(new_parent_id.to_string());
		let note_id = NoteId(note_id.to_string());

		let old_note = select_note_to_note_relationship(&mut tx, &old_parent_id, &note_id).await?;
		let old_note_location = old_note.location;
		let old_note_kind = old_note.kind;

		let _ = delete_note_to_note_relationship(&mut tx, &old_parent_id, &note_id).await?;
		let _ = close_hole_for_deleted_note(&mut tx, &old_parent_id, old_note_location).await?;
		let parent_max_location =
			assert_max_child_location_for_note(&mut tx, &new_parent_id).await?;
		let new_location = cmp::min(parent_max_location + 1, new_location);
		let _ = make_room_for_new_note(&mut tx, &new_parent_id, new_location).await?;
		let _ = insert_note_to_note_relationship(
			&mut tx,
			&new_parent_id,
			&note_id,
			new_location,
			&old_note_kind,
		)
		.await?;
		tx.commit().await?;
		Ok(())
	}

	/// Updates a note's content.  Completely rebuilds the note's
	/// outgoing edge reference list every time.
	pub async fn update_note_content(&self, note_id: &str, content: &str) -> NoteResult<()> {
		let references = build_references(&content);
		let note_id = NoteId(note_id.to_string());

		let mut tx = self.0.begin().await?;
		let _ = update_note_content(&mut tx, &note_id, &content).await?;
		let _ = delete_bulk_note_to_kasten_relationships(&mut tx, &note_id).await?;
		let found_references =
			find_all_kasten_from_list_of_references(&mut tx, &references).await?;
		let new_references = diff_references(&references, &found_references);
		let mut known_reference_ids: Vec<NoteId> = Vec::new();
		for one_reference in new_references.iter() {
			let slug = generate_slug(&mut tx, one_reference).await?;
			let zettlekasten = create_zettlekasten(&one_reference, &slug);
			let _ = insert_note(&mut tx, &zettlekasten).await?;
			known_reference_ids.push(NoteId(slug));
		}

		known_reference_ids.append(
			&mut found_references
				.iter()
				.map(|r| NoteId(r.id.clone()))
				.collect(),
		);
		let _ = insert_bulk_note_to_kasten_relationships(&mut tx, &note_id, &known_reference_ids)
			.await?;
		tx.commit().await?;
		Ok(())
	}

	/// Deletes a note.  If the note's relationship drops to zero, all
	/// references from that note to pages are also deleted.
	pub async fn delete_note(&self, note_id: &str, note_parent_id: &str) -> NoteResult<()> {
		let mut tx = self.0.begin().await?;
		let note_id = NoteId(note_id.to_string());
		let parent_id = ParentId(note_parent_id.to_string());

		if *parent_id != *note_id {
			let _ = delete_note_to_note_relationship(&mut tx, &parent_id, &note_id);
		}
		// The big one: if zero parents report having an interest in this note, then it,
		// *and any sub-relationships*, go away.
		if count_existing_note_relationships(&mut tx, &note_id).await? == 0 {
			let _ = delete_note_to_kasten_relationships(&mut tx, &note_id).await?;
			let _ = delete_note(&mut tx, &note_id).await?;
		}
		tx.commit().await?;
		Ok(())
	}
}

// The Private stuff

impl NoteStore {
	// Pretty much the most dangerous function in our system. Has to
	// have ALL the error checking.
	async fn insert_note(
		&self,
		note: &NewNote,
		parent_id: &ParentId,
		location: Option<i64>,
		kind: RelationshipKind,
	) -> NoteResult<String> {
		if let Some(location) = location {
			if location < 0 {
				return Err(NoteStoreError::InvalidNoteStructure(
					"Add note: A negative location is not valid.".to_string(),
				));
			}
		}

		if parent_id.is_empty() {
			return Err(NoteStoreError::InvalidNoteStructure(
				"Add note: A parent note ID is required.".to_string(),
			));
		}

		if note.id.is_empty() {
			return Err(NoteStoreError::InvalidNoteStructure(
				"Add note: Your note should have an id already".to_string(),
			));
		}

		if note.content.is_empty() {
			return Err(NoteStoreError::InvalidNoteStructure(
				"Add note: Empty notes are not supported.".to_string(),
			));
		}

		let references = build_references(&note.content);

		let mut tx = self.0.begin().await?;
		let location = {
			let max_child = assert_max_child_location_for_note(&mut tx, parent_id).await? + 1;
			if let Some(location) = location {
				cmp::min(max_child, location)
			} else {
				max_child
			}
		};

		let note_id = NoteId(note.id.clone());
		insert_note(&mut tx, &note).await?;
		make_room_for_new_note(&mut tx, &parent_id, location).await?;
		insert_note_to_note_relationship(&mut tx, &parent_id, &note_id, location, &kind).await?;

		let found_references =
			find_all_kasten_from_list_of_references(&mut tx, &references).await?;
		let new_references = diff_references(&references, &found_references);
		let mut known_reference_ids: Vec<NoteId> = Vec::new();
		for one_reference in new_references.iter() {
			let slug = generate_slug(&mut tx, one_reference).await?;
			let zettlekasten = create_zettlekasten(&one_reference, &slug);
			let _ = insert_note(&mut tx, &zettlekasten).await?;
			known_reference_ids.push(NoteId(slug));
		}

		known_reference_ids.append(
			&mut found_references
				.iter()
				.map(|r| NoteId(r.id.clone()))
				.collect(),
		);
		let _ = insert_bulk_note_to_kasten_relationships(&mut tx, &note_id, &known_reference_ids)
			.await?;
		tx.commit().await?;
		Ok(note_id.to_string())
	}
}