import fs from "fs";
import dayjs from "dayjs";
import { createInterface } from "readline";
import { DynamicTask } from "../model";
import { Task, TaskPriority } from "../types/task";
import { jsMapper } from "../util/code";

/**
 * Returns all tasks from specified directory and filters them with optional query.
 */
export async function loadTasks(directories: string[], query?: string, exclude?: string): Promise<Task[]> {
  const ctx = {
    now: dayjs(),
    LOWEST: TaskPriority.LOWEST,
    LOW: TaskPriority.LOW,
    NORMAL: TaskPriority.NORMAL,
    MEDIUM: TaskPriority.MEDIUM,
    HIGH: TaskPriority.HIGH,
    HIGHEST: TaskPriority.HIGHEST
  };

  const excludeFn = exclude ? jsMapper<string, boolean>(exclude, {}) : () => false;
  const filter = query && jsMapper<Task, boolean>(query, ctx);  
  const tasks = await Promise.all(directories.map(readTasksFromDirectory(excludeFn)));
  
  return tasks.flat().filter(t => filter ? filter(t) : true);
}

/**
 * Read all files in specific directory and returns all tasks from those files.
 */
function readTasksFromDirectory(excludeFn: (path: string) => boolean) {
  return async (directory: string) => walk(directory, readTasksFromFile, excludeFn);
}

/**
 * Walks through a specific directory recursively and invokes visitor on each file.
 * Returns a flat list of items returned by visitors.
 */
async function walk<T>(directory: string, visitor: (path: string) => Promise<T[]>, excludeFn: (path: string) => boolean): Promise<T[]> {  
  const list = [];

  for(const file of fs.readdirSync(directory)) {
    const path = `${directory}/${file}`;  

    if (fs.statSync(path).isDirectory()) {
      const items = await walk(path, visitor, excludeFn);
      list.push(...items);
    } else if (path.endsWith("md") || (path.endsWith("MD"))) {      
      if (!excludeFn(path)) {        
        const items = await visitor(path);
        list.push(...items);        
      }      
    }
  }

  return list;
}

/**
 * Reads all tasks from file path.
 */
async function readTasksFromFile(path: string): Promise<Task[]> {
  const fileStream = fs.createReadStream(path);

  const lines = createInterface({
    input: fileStream,
    crlfDelay: Infinity
  });

  const list: Task[] = [];
  let lineNumber = 1;

  for await (const line of lines) {
    try {
      const task = DynamicTask.parse(line, path, lineNumber);
    
      if(task) {
        list.push(task);
      }
    } catch(e: any) {
      console.warn(`Parsing error in file '${path}', for line:`);
      console.warn(line);
      if(e.location) {
        console.warn(' '.repeat(e.location.start.column + 2) + "^" + '~'.repeat(e.location.end.column - e.location.start.column - 1) + "^")      
      }
      console.warn(e.message);
      console.warn("This line will be ignored. Please check the source and adjust it accordingly.");
    } finally {
      lineNumber++;
    }
  }

  return list;
}