Process logseq journals to include navigation links

journal_navigation_links.py

"""
This little script is meant to be run from a graph folder, so that the folder "journals"
is a subfolder of the current folder.

It will iterate over all the files in the "journals" folder whose name matches the pattern
YYYY_MM_DD.md and for each one it will add or update the navigation line in the file.

The navigation line is the first item in the file and it will contain a link to the
previous and next dates in the journal with respect to the date of the journal file.

You can edit the global variables at the beginning of the script to change the format.

The script can be run several times. The fist time it will insert the navigation line
in all journal files. Subsequent runs will update the navigation line only if neccessary
(new dates have been inserted or removed)

The last journal file does not have a "next date", so the navigation line will contain
"No next date" in that case. Once the script has be run for the first time, it is more
convenient to use a template that includes the navigation line, and uses the logseq
variables <% yesterday %> and <% tomorrow %> so that each subsequent journal created
has the navigation line already included.
"""

# Global variables that affect the result

# The format of an internal link to a date
date_format = "%Y-%m-%d %A"  # Example: "2021-01-01 Friday"

# The format of the navigation link (first item in each journal file)
navigation_format = "- **Navigation**: Previous entry: [[{previous_date}]], Next entry: [[{next_date}]]\n"

# String for the case in which there is no previous or next date
no_previous_date = "No previous date"
no_next_date = "No next date"


import pathlib
from datetime import datetime, timedelta


class DateChain:
    """This class stores a set of dates and allows to get the next 
    and previous date in the set for a given date"""

    def __init__(self):
        self.dates = set()
        self.minimum = None
        self.maximum = None

    def add(self, date):
        """Adds a date to the set and updates the minimum and maximum dates"""
        self.dates.add(date)
        if self.minimum is None or date < self.minimum:
            self.minimum = date
        if self.maximum is None or date > self.maximum:
            self.maximum = date

    def get_next(self, date):
        """Returns the next date present in the set for a given date"""
        # The implementation is a bit naive, since it loops through all the dates
        # until finding one in the set or reaching the maximum date
        # but it is fast enough for the purpose of this script
        if date >= self.maximum:
            return None
        else:
            while date < self.maximum:
                date += timedelta(days=1)
                if date in self.dates:
                    return date
            return None

    def get_previous(self, date):
        """Returns the previous date present in the set for a given date"""
        if date <= self.minimum:
            return None
        else:
            while date > self.minimum:
                date -= timedelta(days=1)
                if date in self.dates:
                    return date
            return None


# Global variable to store all the dates found in "journal" folder
date_chain = DateChain()


def process_journals_folder():
    """This method iterates over all the files in the "journals" folder
    whose name matches the pattern YYYY_MM_DD.md
    and for each one it calls the method "process_journal_file()"
    passing the date and the absolute path to the file"""

    folder = pathlib.Path("journals")
    file_list = folder.glob("*.md")

    to_process = []
    for fname in file_list:
        name = fname.name
        date_str = name.split(".")[0]
        date = datetime.strptime(date_str, "%Y_%m_%d").date()
        date_chain.add(date)
        to_process.append((date, fname.absolute()))

    for date, fname in to_process:
        process_journal_file(date, fname)


def process_journal_file(date, fname):
    """This function processes a journal file and adds or updates the navigation links
    as the first item in the file"""

    previous_date = date_chain.get_previous(date)
    next_date = date_chain.get_next(date)

    previous_date = (
        previous_date.strftime(date_format) if previous_date else no_previous_date
    )
    next_date = next_date.strftime(date_format) if next_date else no_next_date

    navigation_line = navigation_format.format(
        previous_date=previous_date, next_date=next_date
    )

    with open(fname, "r", encoding="utf-8") as f:
        lines = f.readlines()

    # Insert the navigation line at the beginning of the file
    for i, line in enumerate(lines):
        # Search for the first line starting with "-"
        if line.startswith("-"):
            if line[:10] != navigation_line[:10]:
                # If this file has no navigatio line, insert it
                lines.insert(i, navigation_line)
            else:
                # Otherwise, update it if neccessary
                if lines[i].rstrip() != navigation_line.rstrip():
                    lines[i] = navigation_line
            break

    # Write the result in the same file
    with open(fname, "w", encoding="utf-8") as f:
        f.writelines(lines)


if __name__ == "__main__":
    process_journals_folder()

Screenshot showing the inserted navigation line. Note that the style of the navigation line was customized via css. By default it would look like a regular item in the journal.