export function timelineControlsReducer()

in src/components/Timeline/useTimelineControls.ts [39:135]
52 lines of code
17 McCabe index (conditional complexity)

export function timelineControlsReducer(state: TimelineControlsState, action: TimelineAction): TimelineControlsState {
  switch (action.type) {
    case 'update': {
      const end = state.max > action.end ? state.max : action.end;
      if (state.controlled) {
        return {
          ...state,
          max: end,
          min: action.start,
          timelineStart: action.start > state.timelineStart ? action.start : state.timelineStart,
          timelineEnd: end < state.timelineEnd ? end : state.timelineEnd,
        };
      } else {
        return {
          ...state,
          max: action.mode === 'left' ? action.end : end,
          min: action.start,
          timelineEnd: action.mode === 'left' ? action.end : end,
          timelineStart: action.start,
          controlled: false,
        };
      }
    }
    case 'move':
      // Check if any of the edges of scroll bar are out of bounds
      if (startOrEndOutOfBounds(state, action.value)) {
        return {
          ...state,
          timelineStart: startOutOfBounds(state, action.value)
            ? state.min
            : state.max - (state.timelineEnd - state.timelineStart),
          timelineEnd: endOutOfBounds(state, action.value)
            ? state.max
            : state.min + (state.timelineEnd - state.timelineStart),
        };
      } else {
        // Other wise just change start and end position of scrollbar
        return updateGraph(state, action.value);
      }
    case 'zoomIn': {
      const change = getZoomAmount(state);

      if (state.timelineEnd - change <= state.timelineStart + change) return state;

      return { ...updateGraph(state, change, -change), controlled: true };
    }

    case 'zoomOut': {
      const change = getZoomAmount(state);

      if (zoomOverTotalLength(state, change)) {
        return resetTimeline(state);
      } else if (startOrEndOutOfBounds(state, -change, change)) {
        return {
          ...state,
          timelineStart: startOutOfBounds(state, -change)
            ? state.min
            : state.max - (state.timelineEnd - state.timelineStart + change),
          timelineEnd: endOutOfBounds(state, change)
            ? state.max
            : state.min + (state.timelineEnd - state.timelineStart + change),
        };
      } else {
        return updateGraph(state, -change, change);
      }
    }

    case 'setZoom':
      const newVals = {
        timelineEnd: action.end <= action.start ? action.start : action.end,
        timelineStart: action.start >= action.end ? action.end : action.start,
      };

      return {
        ...state,
        ...newVals,
        controlled: newVals.timelineEnd - newVals.timelineStart >= (state.max - state.min) * 0.97 ? false : true,
      };

    case 'resetZoom':
      return resetTimeline(state);

    case 'setControlled':
      return { ...state, controlled: action.value };

    case 'incrementTimelineLength':
      return {
        ...state,
        max: new Date().getTime(),
        timelineEnd: state.controlled ? state.timelineEnd : new Date().getTime(),
      };

    case 'reset':
      return { ...state, controlled: false, min: 0, max: 0, timelineStart: 0, timelineEnd: 0 };
  }
  return state;
}