/*
 * Wiki - A wiki with editor
 * Copyright (c) 2021 Peter Stuifzand
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"os"
	"path/filepath"
	"sync"
)

const BlocksDirectory = "_blocks"

type FileBlockRepository struct {
	dirname string

	rwLock sync.RWMutex
}

type Block struct {
	Text     string
	Children []string
	Parent   string
}

func NewBlockRepo(dirname string) (*FileBlockRepository, error) {
	err := os.MkdirAll(filepath.Join(dirname, BlocksDirectory), 0777)
	if err != nil {
		return nil, err
	}
	return &FileBlockRepository{
		dirname: dirname,
	}, nil
}

func (blockRepo *FileBlockRepository) GetBlock(blockID string) (Block, error) {
	blockRepo.rwLock.RLock()
	defer blockRepo.rwLock.RUnlock()

	return loadBlock(blockRepo.dirname, blockID)
}

func (blockRepo *FileBlockRepository) SaveBlock(blockID string, block Block) error {
	blockRepo.rwLock.Lock()
	defer blockRepo.rwLock.Unlock()
	return saveBlock(blockRepo.dirname, blockID, block)
}

func (blockRepo *FileBlockRepository) GetBlocks(rootBlockID string) (BlockResponse, error) {
	resp := BlockResponse{
		rootBlockID,
		"",
		nil,
		nil,
		nil,
	}

	resp.Texts = make(map[string]string)
	resp.Children = make(map[string][]string)

	queue := []string{rootBlockID}

	block, err := blockRepo.GetBlock(rootBlockID)
	if err != nil {
		return BlockResponse{}, err
	}
	// NOTE: what does this do?
	if rootBlockID[0] != '_' && block.Children == nil {
		return BlockResponse{}, fmt.Errorf("not a block and has no children: %w", BlockNotFound)
	}

	prevID := rootBlockID
	parentID := block.Parent

	for parentID != "root" {
		parent, err := blockRepo.GetBlock(parentID)
		if err != nil {
			return BlockResponse{}, fmt.Errorf("while loading current parent block (%s->%s): %w", prevID, parentID, err)
		}

		resp.Texts[parentID] = parent.Text
		resp.Children[parentID] = parent.Children
		resp.ParentID = parentID

		resp.Parents = append(resp.Parents, parentID)

		prevID = parentID
		parentID = parent.Parent
	}
	if parentID == "root" {
		resp.ParentID = "root"
	}

	for {
		if len(queue) == 0 {
			break
		}
		current := queue[0]
		queue = queue[1:]
		block, err := blockRepo.GetBlock(current)
		if err != nil {
			return BlockResponse{}, err
		}
		resp.Texts[current] = block.Text
		resp.Children[current] = block.Children
		queue = append(queue, block.Children...)
	}

	return resp, nil
}

func loadBlock(dirname, blockID string) (Block, error) {
	f, err := os.Open(filepath.Join(dirname, BlocksDirectory, blockID))
	if err != nil {
		return Block{}, fmt.Errorf("%q: %w", blockID, BlockNotFound)
	}
	defer f.Close()
	var block Block
	err = json.NewDecoder(f).Decode(&block)
	if err != nil {
		return Block{}, fmt.Errorf("%q: %v", blockID, err)
	}
	return block, nil
}

func saveBlock(dirname, blockID string, block Block) error {
	log.Printf("Writing to %q\n", blockID)
	f, err := os.OpenFile(filepath.Join(dirname, BlocksDirectory, blockID), os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return fmt.Errorf("while saving block %s: %w", blockID, err)
	}
	defer f.Close()
	enc := json.NewEncoder(f)
	enc.SetIndent("", "  ")
	err = enc.Encode(&block)
	if err != nil {
		return fmt.Errorf("while encoding block %s: %w", blockID, err)
	}
	return nil
}