#+TITLE: Internals
If your not interested in implementing your own card types or
contributing to this package, you can skip this section.

* Components
** =org-fc.el=
Main file.
** =org-fc-dashboard.el=
Dashboard displaying card / position / review statistics.
** =org-fc-review.el=
Functions related to reviewing cards, updating the review data drawer
and logging review results.
** =org-fc-sm2.el=
Implementation of the [[https://www.supermemo.com/en/archives1990-2015/english/ol/sm2][SM2]] review spacing algorithm,
modified to behave like the algorithm used by [[https://apps.ankiweb.net/docs/manual.html#what-algorithm][Anki]].

It uses four ratings (again, hard, good, easy) instead of the six used
in the supermemo variant.

The first few reviews are done in fixed intervals
(0.01 days / approx 15 minutes, 1 day, 6 days).

After these intervals, reviews are scheduled by multiplying the cards
current interval with its ease (initially 2.5, bound to be >= 1.3 and
<= 5.0), then multiplying a random factor ~1 to avoid "chunking" of
flashcards due for review.

All of these parameters can be configured using the variables defined
in =org-fc-sm2.el=.
** =org-fc-awk.el=
Functions for interacting with the awk indexer / filter / stats scripts.
** =org-fc-overlay.el=
Functions for hiding / revealing parts of org-mode buffers.
** =org-fc-type-<name>.el=
Implementations of flashcard types, for more details, see the "Card
Types" section of this document.
** TODO Document core api of each file
* Coding Style
Components are split into multiple smaller files,
with each function prefixed by the files base-name.

Public functions are named ~basename-functionname~,
internal helper functions are named ~basename--functionname~.
* Testing
Unit-testing is done using ~org-fc-assert-...~ macros
defined in =org-fc-assert.el=.

These assertions are placed right after the function definition
and run when the file is loaded. If an assertion fails,
an ~'org-fc-assertion-error~ is raised.

** TODO Integration Testing
Integration testing is done by providing an input org file, a set of
operations to be performed on it and an org file with the expected
output.

Tests are run by copying the input file to a temporary file, executing
the operations on it, then comparing it to the expected output.

Files for this live in the =fixtures/= folder.
* =awk=
~find~ is used to generate a list of =.org= files in
~org-fc-directories~, these are then passed to =awk= scripts
to generate lists of cards and card-positions.

Only files starting with ~[a-Z0-9_]~ and a ~.org~ extension are
indexed to exclude temp / hidden files.
This can be customized with the ~org-fc-find-name~ variable.

[[https://www.gnu.org/software/gawk/][gawk]] is a programming language for processing / parsing text.

Assuming the input org files are well formatted, they can be
efficiently parsed using regexeps and a small number of state
variables.

=awk= scripts in this package come in three types:

1. Indexing, for generating lists of cards / positions
3. Filtering, e.g. for selecting only unsuspended cards due now
2. Aggregation, for generating statistics from these lists

- =awk/indexer_cards.awk= :: list all card headings
- =awk/indexer_positions.awk= :: list all card positions
- =awk/filter_due.awk= :: select only unsuspended cards due right now
- =awk/stats_cards.awk= :: stats over cards
- =awk/stats_positions.awk= :: stats over positions
- =awk/stats_reviews.awk= :: stats over the reviews tsv file

These scripts use the =gawk= version of =awk= which should be
available on any modern Linux / UNIX distribution.

Configurable tags and properties can be passed to the indexer scripts as
variables. If a tag or property is not passed to the script,
a default value is used.

* CSV Output Format
Output is generated in *tab separated* form and *does not* include a
header with column names. For the indexing scripts, the first two
columns are the filename and the ID of the heading.

The ~org-fc-tsv-parse~ function can be used to parse a tsv
string into a plist, given a list of headers with optional type
specifications.

=0= (false) and =1= (true) are used for boolean values (e.g. for the
"suspended" column).

Dates are converted to ISO-8601 format, no timezone, minute-precision
(e.g. =2019-10-09T16:49=).

Unlike the format used by org mode, timestamps in ISO-8601 format can
be compared lexicographically.

Processing script output *tab separated* key-value pairs with no header.