Genarrative/src/data/encounterTransition.ts

import { GameState } from '../types';
import { getFacingTowardPlayer, getMonsterGroupAnchorX, PLAYER_BASE_X_METERS } from './hostileNpcs';

function roundMeters(value: number) {
  return Number(value.toFixed(2));
}

function lerp(start: number, end: number, progress: number) {
  return roundMeters(start + ((end - start) * progress));
}

export function hasEncounterEntity(state: Pick<GameState, 'sceneHostileNpcs' | 'currentEncounter'>) {
  return state.sceneHostileNpcs.length > 0 || Boolean(state.currentEncounter);
}

export function buildEncounterEntryState(
  finalState: GameState,
  entryX: number,
): GameState {
  if (finalState.sceneHostileNpcs.length > 0) {
    const anchorX = getMonsterGroupAnchorX(finalState.sceneHostileNpcs);
    return {
      ...finalState,
      sceneHostileNpcs: finalState.sceneHostileNpcs.map(monster => {
        const offset = monster.xMeters - anchorX;
        const xMeters = roundMeters(entryX + offset);
        return {
          ...monster,
          xMeters,
          animation: 'move' as const,
          facing: getFacingTowardPlayer(xMeters, PLAYER_BASE_X_METERS),
        };
      }),
      currentEncounter: null,
    };
  }

  if (finalState.currentEncounter) {
    return {
      ...finalState,
      currentEncounter: {
        ...finalState.currentEncounter,
        xMeters: entryX,
      },
      sceneHostileNpcs: [],
    };
  }

  return finalState;
}

export function buildEncounterTransitionState(
  finalState: GameState,
  sourceState: Pick<GameState, 'sceneHostileNpcs' | 'currentEncounter'>,
): GameState {
  if (finalState.sceneHostileNpcs.length > 0) {
    const sourceById = new Map(sourceState.sceneHostileNpcs.map(monster => [monster.id, monster]));
    return {
      ...finalState,
      sceneHostileNpcs: finalState.sceneHostileNpcs.map(monster => {
        const sourceMonster = sourceById.get(monster.id);
        const xMeters = sourceMonster?.xMeters ?? monster.xMeters;
        return {
          ...monster,
          xMeters,
          animation: 'move' as const,
          facing: getFacingTowardPlayer(xMeters, PLAYER_BASE_X_METERS),
        };
      }),
      currentEncounter: null,
    };
  }

  if (finalState.currentEncounter) {
    return {
      ...finalState,
      currentEncounter: {
        ...finalState.currentEncounter,
        xMeters: sourceState.currentEncounter?.xMeters ?? finalState.currentEncounter.xMeters,
      },
      sceneHostileNpcs: [],
    };
  }

  return finalState;
}

export function interpolateEncounterTransitionState(
  startState: Pick<GameState, 'sceneHostileNpcs' | 'currentEncounter'>,
  finalState: GameState,
  progress: number,
): GameState {
  if (finalState.sceneHostileNpcs.length > 0) {
    const startById = new Map(startState.sceneHostileNpcs.map(monster => [monster.id, monster]));
    return {
      ...finalState,
      sceneHostileNpcs: finalState.sceneHostileNpcs.map(monster => {
        const startMonster = startById.get(monster.id);
        const xMeters = lerp(startMonster?.xMeters ?? monster.xMeters, monster.xMeters, progress);
        return {
          ...monster,
          xMeters,
          animation: progress < 1 ? ('move' as const) : monster.animation,
          facing: getFacingTowardPlayer(xMeters, PLAYER_BASE_X_METERS),
        };
      }),
      currentEncounter: null,
    };
  }

  if (finalState.currentEncounter) {
    const startX = startState.currentEncounter?.xMeters ?? finalState.currentEncounter.xMeters ?? 0;
    const endX = finalState.currentEncounter.xMeters ?? startX;
    return {
      ...finalState,
      currentEncounter: {
        ...finalState.currentEncounter,
        xMeters: lerp(startX, endX, progress),
      },
      sceneHostileNpcs: [],
    };
  }

  return finalState;
}