/**
 * Perform a system migration for the entire World, applying migrations for Actors, Items, and Compendium packs
 * @return {Promise}      A Promise which resolves once the migration is completed
 */
export const migrateWorld = async function() {
  ui.notifications.info(`Applying SW5E System Migration for version ${game.system.data.version}. Please be patient and do not close your game or shut down your server.`, {permanent: true});

  // Migrate World Actors
  for ( let a of game.actors.entities ) {
    try {
      const updateData = migrateActorData(a.data);
      if ( !isObjectEmpty(updateData) ) {
        console.log(`Migrating Actor entity ${a.name}`);
        await a.update(updateData, {enforceTypes: false});
      }
    } catch(err) {
      console.error(err);
    }
  }

  // Migrate World Items
  for ( let i of game.items.entities ) {
    try {
      const updateData = migrateItemData(i.data);
      if ( !isObjectEmpty(updateData) ) {
        console.log(`Migrating Item entity ${i.name}`);
        await i.update(updateData, {enforceTypes: false});
      }
    } catch(err) {
      console.error(err);
    }
  }

  // Migrate Actor Override Tokens
  for ( let s of game.scenes.entities ) {
    try {
      const updateData = migrateSceneData(s.data);
      if ( !isObjectEmpty(updateData) ) {
        console.log(`Migrating Scene entity ${s.name}`);
        await s.update(updateData, {enforceTypes: false});
      }
    } catch(err) {
      console.error(err);
    }
  }

  // Migrate World Compendium Packs
  const packs = game.packs.filter(p => {
    return (p.metadata.package === "world") && ["Actor", "Item", "Scene"].includes(p.metadata.entity)
  });
  for ( let p of packs ) {
    await migrateCompendium(p);
  }

  // Set the migration as complete
  game.settings.set("sw5e", "systemMigrationVersion", game.system.data.version);
  ui.notifications.info(`SW5E System Migration to version ${game.system.data.version} completed!`, {permanent: true});
};

/* -------------------------------------------- */

/**
 * Apply migration rules to all Entities within a single Compendium pack
 * @param pack
 * @return {Promise}
 */
export const migrateCompendium = async function(pack) {
  const entity = pack.metadata.entity;
  if ( !["Actor", "Item", "Scene"].includes(entity) ) return;

  // Begin by requesting server-side data model migration and get the migrated content
  await pack.migrate();
  const content = await pack.getContent();

  // Iterate over compendium entries - applying fine-tuned migration functions
  for ( let ent of content ) {
    try {
      let updateData = null;
      if (entity === "Item") updateData = migrateItemData(ent.data);
      else if (entity === "Actor") updateData = migrateActorData(ent.data);
      else if ( entity === "Scene" ) updateData = migrateSceneData(ent.data);
      if (!isObjectEmpty(updateData)) {
        expandObject(updateData);
        updateData["_id"] = ent._id;
        await pack.updateEntity(updateData);
        console.log(`Migrated ${entity} entity ${ent.name} in Compendium ${pack.collection}`);
      }
    } catch(err) {
      console.error(err);
    }
  }
  console.log(`Migrated all ${entity} entities from Compendium ${pack.collection}`);
};

/* -------------------------------------------- */
/*  Entity Type Migration Helpers               */
/* -------------------------------------------- */

/**
 * Migrate a single Actor entity to incorporate latest data model changes
 * Return an Object of updateData to be applied
 * @param {Actor} actor   The actor to Update
 * @return {Object}       The updateData to apply
 */
export const migrateActorData = function(actor) {
  const updateData = {};

  // Actor Data Updates
  _migrateActorBonuses(actor, updateData);

  // Remove deprecated fields
  _migrateRemoveDeprecated(actor, updateData);

  // Migrate Owned Items
  if ( !actor.items ) return updateData;
  let hasItemUpdates = false;
  const items = actor.items.map(i => {

    // Migrate the Owned Item
    let itemUpdate = migrateItemData(i);

    // Prepared, Equipped, and Proficient for NPC actors
    if ( actor.type === "npc" ) {
      if (getProperty(i.data, "preparation.prepared") === false) itemUpdate["data.preparation.prepared"] = true;
      if (getProperty(i.data, "equipped") === false) itemUpdate["data.equipped"] = true;
      if (getProperty(i.data, "proficient") === false) itemUpdate["data.proficient"] = true;
    }

    // Update the Owned Item
    if ( !isObjectEmpty(itemUpdate) ) {
      hasItemUpdates = true;
      return mergeObject(i, itemUpdate, {enforceTypes: false, inplace: false});
    } else return i;
  });
  if ( hasItemUpdates ) updateData.items = items;
  return updateData;
};

/* -------------------------------------------- */

/**
 * Migrate a single Item entity to incorporate latest data model changes
 * @param item
 */
export const migrateItemData = function(item) {
  const updateData = {};

  // Remove deprecated fields
  _migrateRemoveDeprecated(item, updateData);

  // Return the migrated update data
  return updateData;
};

/* -------------------------------------------- */

/**
 * Migrate a single Scene entity to incorporate changes to the data model of it's actor data overrides
 * Return an Object of updateData to be applied
 * @param {Object} scene  The Scene data to Update
 * @return {Object}       The updateData to apply
 */
export const migrateSceneData = function(scene) {
  const tokens = duplicate(scene.tokens);
  return {
    tokens: tokens.map(t => {
      if (!t.actorId || t.actorLink || !t.actorData.data) {
        t.actorData = {};
        return t;
      }
      const token = new Token(t);
      if ( !token.actor ) {
        t.actorId = null;
        t.actorData = {};
      } else if ( !t.actorLink ) {
        const updateData = migrateActorData(token.data.actorData);
        t.actorData = mergeObject(token.data.actorData, updateData);
      }
      return t;
    })
  };
};

/* -------------------------------------------- */
/*  Low level migration utilities
/* -------------------------------------------- */

/**
 * Migrate the actor bonuses object
 * @private
 */
function _migrateActorBonuses(actor, updateData) {
  const b = game.system.model.Actor.character.bonuses;
  for ( let k of Object.keys(actor.data.bonuses || {}) ) {
    if ( k in b ) updateData[`data.bonuses.${k}`] = b[k];
    else updateData[`data.bonuses.-=${k}`] = null;
  }
}


/* -------------------------------------------- */


/**
 * A general migration to remove all fields from the data model which are flagged with a _deprecated tag
 * @private
 */
const _migrateRemoveDeprecated = function(ent, updateData) {
  const flat = flattenObject(ent.data);

  // Identify objects to deprecate
  const toDeprecate = Object.entries(flat).filter(e => e[0].endsWith("_deprecated") && (e[1] === true)).map(e => {
    let parent = e[0].split(".");
    parent.pop();
    return parent.join(".");
  });

  // Remove them
  for ( let k of toDeprecate ) {
    let parts = k.split(".");
    parts[parts.length-1] = "-=" + parts[parts.length-1];
    updateData[`data.${parts.join(".")}`] = null;
  }
};