import { pairs, deepEqual } from '../util.js';

/* agent structure:
 * {
 *   id: string
 *   net: network
 *   state: network_state
 *   x, y: number
 *   flags: object
 * }
 */


/* cell structure:
 * {
 *   type: string
 *   flags: object
 * }
 */

/* action structure:
 * {
 *   name: string,
 *   propose: (agent) => proposal[]
 * }
 */


/* proposal structure
 * all proposed world and agent changes must be included for the proposed action to be valid
 * similarly, if any world or agent change creates merge conflicts, the proposal cannot be merged
 * and must be removed
 * {
 *   world_changes: proposal_world_change[]?
 *   agent_changes: proposal_agent_change[]?
 * }
 */

/* proposal_world_change
 * { 
 *   x, y: number
 *   from: string
 *   to:   string
 *   flags: object?
 * }
 */

/* proposal_agent_change
 * {
 *   agent_id: string
 *   x, y: number?
 *   flags: object?
 * }
 */


// check that two flags objects are compatible
// flags are considered compatible if they do not have any common keys with different values
function flags_compatible(a, b) {
  const keys = [...new Set(Object.keys(a).concat(Object.keys(b)))];
  return keys.reduce(
    (acc, key) => {
      const eq = (a[key] === undefined || b[key] === undefined) ? true : deepEqual(a[key], b[key]);
      return acc && eq;
    },
    true
  );
}


// return a tuple [conflict, merge]
// conflict is true if the two world_changes are incompatible
// merge is true if the two world changes are identical
// otherwise they are false
function world_change_conflict(a, b) {
  if (deepEqual(a, b)) {
    // merge
    return [false, true];
  } 
  if (
    a.x === b.x && 
    a.y === b.y &&
    (a.to != b.to || !flags_compatible(a.flags || {}, b.flags || {}))
  ) {
    // conflict!
    return [true, false];
  } else {
    // no conflict c:
    return [false, false];
  }
}


// returns true as long as x & y are both defined
function pos_exists(a) {
  if (a.x !== undefined && a.y !== undefined) {
    return true;
  } else {
    return false;
  }
}


// check the equality of two objects with (x,y) keys
function pos_equal(a, b) {
  if (a.x !== b.x) { return false; }
  if (a.y !== b.y) { return false; }
  return true;
}


// agent changes merge if they are identical
// they conflict if two agents are trying to move to the same tile, or
// if the same agent is trying to move to two different tiles, or if an agent
// is being updated to incompatible flags
//
//
function agent_change_conflict(a, b) {
  if (deepEqual(a, b)) {
    // identical: merge
    return [false, true];
  } else if (a.agent_id === b.agent_id) {
    if (
      pos_exists(a) && pos_exists(b) && !pos_equal(a, b)
    ) {
      // same agent, different positions: conflict
      return [true, false];
    } else if (!flags_compatible(a.flags, b.flags)) {
      // same agent, incompatible flags: conflict
      return [true, false];
    } else {
      // no conflict c:
      return [false, false];
    }
  } else {
    // different agents
    if (pos_exists(a) && pos_exists(b) && pos_equal(a, b)) {
      // different agents, same position: conflict
      return [true, false];
    } else {
      // no conflict c:
      return [false, false];
    }
  }
}


// combine world_change and agent_change conflict/merge tuples for a pair of proposals
function proposal_conflict_merge(a, b) {
  const [world_conflict, world_merge] = pairs(a.world_changes || [], b.world_changes || []).reduce(
    (acc, [a, b]) => {
      const [conflict, merge] = world_change_conflict(a, b);
      return [acc[0] || conflict, acc[1] || merge];
    }, 
    [false, false]
  );
  const [agent_conflict, agent_merge] = pairs(a.agent_changes || [], b.agent_changes || []).reduce(
    (acc, [a, b]) => {
      const [conflict, merge] = agent_change_conflict(a, b);
      return [acc[0] || conflict, acc[1] || merge];
    },
    [false, false]
  );
  return [world_conflict || agent_conflict, world_merge || agent_merge];
}


// merge proposals
// if two sub-updates conflict, they are both omitted from the final merged proposal
export function proposal_merge(arr, proposal) {
  const conflict_merge = arr.map(x => proposal_conflict_merge(x, proposal));

  // if any conflicts are detected then don't merge
  if (conflict_merge.reduce((acc, [c, m]) => acc || c, false)) {
    const conflict_free = arr.filter((x, i) => !conflict_merge[i][0]);
    return conflict_free;
  } else {
    // no conflicts, but need to merge identical actions
    const no_merge = arr.filter((x, i) => !conflict_merge[i][1]);
    return [...no_merge, proposal];
  }
}