DAX Calculated Column for PRE/POST Sequence in Power BI

I'm working with a Power BI model that includes a table called "All Depots". This is a large, granular table that includes details by customer and product. However, for this particular problem, I'm focusing only on the "Depot", "PRE/POST", and "Transaction date" fields.

## Objective
I need to create a calculated column that assigns a sequence number to PRE and POST periods for each depot. The sequence should work as follows:

- For PRE periods:
- The last (most recent) PRE date should be assigned -1
- The second-to-last PRE date should be assigned -2
- The third-to-last PRE date should be assigned -3
- And so on...

- For POST periods:
- The first (earliest) POST date should be assigned +1
- The second POST date should be assigned +2
- The third POST date should be assigned +3
- And so on...

- The sequence should reset for each depot

## Current Approach
I've tried several DAX formulas, including variations of RANKX and COUNTROWS, but I haven't been able to achieve the desired result. Here's an example of one approach I've tried:

PRE_POST_Sequence =
VAR CurrentDepot = 'All Depots'[Depot]
VAR CurrentDate = 'All Depots'[Transaction date]
VAR CurrentPREPOST = 'All Depots'[PRE/POST]
VAR PRE_Sequence =
IF(CurrentPREPOST = "PRE",
-RANKX(
FILTER(ALL('All Depots'),
'All Depots'[Depot] = CurrentDepot &&
'All Depots'[PRE/POST] = "PRE"
),
'All Depots'[Transaction date],
,
DESC
),
BLANK()
)
VAR POST_Sequence =
IF(CurrentPREPOST = "POST",
RANKX(
FILTER(ALL('All Depots'),
'All Depots'[Depot] = CurrentDepot &&
'All Depots'[PRE/POST] = "POST"
),
'All Depots'[Transaction date],
,
ASC
),
BLANK()
)
RETURN
IF(ISBLANK(PRE_Sequence), POST_Sequence, PRE_Sequence)

```

## Problem
The current formula isn't producing the expected results. It's either not sequencing correctly or not resetting for each depot as needed.

## Question
Can anyone suggest a DAX formula that would achieve the desired sequencing as described above? I'm open to completely different approaches if they can solve this problem more effectively.

## Additional Information
- The "All Depots" table contains multiple rows per day per depot.
- The "PRE/POST" field contains only "PRE" or "POST" values.
- The "Transaction date" is a date field.

Thank you in advance for any help or suggestions!