'use strict';

const debug = require('debug')('egg-core#sequencify');

function sequence(tasks, names, results, missing, recursive, nest, optional, parent) {
  names.forEach(function(name) {
    if (results.requires[name]) return;

    const node = tasks[name];

    if (!node) {
      if (optional === true) return;
      missing.push(name);
    } else if (nest.includes(name)) {
      nest.push(name);
      recursive.push(nest.slice(0));
      nest.pop(name);
    } else if (node.dependencies.length || node.optionalDependencies.length) {
      nest.push(name);
      if (node.dependencies.length) {
        sequence(tasks, node.dependencies, results, missing, recursive, nest, optional, name);
      }
      if (node.optionalDependencies.length) {
        sequence(tasks, node.optionalDependencies, results, missing, recursive, nest, true, name);
      }
      nest.pop(name);
    }
    if (!optional) {
      results.requires[name] = true;
      debug('task: %s is enabled by %s', name, parent);
    }
    if (!results.sequence.includes(name)) {
      results.sequence.push(name);
    }
  });
}

// tasks: object with keys as task names
// names: array of task names
module.exports = function(tasks, names) {
  const results = {
    sequence: [],
    requires: {},
  }; // the final sequence
  const missing = []; // missing tasks
  const recursive = []; // recursive task dependencies

  sequence(tasks, names, results, missing, recursive, [], false, 'app');

  if (missing.length || recursive.length) {
    results.sequence = []; // results are incomplete at best, completely wrong at worst, remove them to avoid confusion
  }

  return {
    sequence: results.sequence.filter(item => results.requires[item]),
    missingTasks: missing,
    recursiveDependencies: recursive,
  };
};