# cspell-trie

Trie library for use with cspell

This library allows easily building of a [Trie](https://en.wikipedia.org/wiki/Trie)
from a word list.

The resulting trie can then be compressed into a
[DAFSA|DAWG](https://en.wikipedia.org/wiki/Deterministic_acyclic_finite_state_automaton).

### Installation

```sh
npm install -S cspell-trie-lib
```

## File Format V3

### Header

```
TrieXv3
base=10
# Comments
__DATA__
```

The header has two parts.

- `TrieXv3` -- the format identifier.
- base -- references are stored using the base (10, 16, 32) are common.
  higher the base, the smaller the file. Max is 36

### Data

The data is a stream of characters and operators. Each character represents a node in the Trie. The operators adjust the position in the Trie.

### Conceptual Format

Given a sorted list of words:

```text
joust
jouster
jousting
joy
joyful
joyfuller
joyfullest
```

It is possible to think of the same list stored as a series of operations.

| op    | Meaning             |
| ----- | ------------------- |
| `<`   | remove 1 character  |
| `<<`  | remove 2 characters |
| `<<<` | remove 3 characters |
| `<2`  | remove 2 characters |
| `<3`  | remove 3 characters |
| `$`   | end of word         |
| `_`   | visual place holder |

```text
joust$
_____er$
_____<<
_____ing$
__<<<<<<
__y$
___ful$
______ler$
________<
________st$
```

Becomes:

```text
joust$er$<2ing$<6y$ful$ler$<st$
```

Trie:

```text
j─o┬u─s─t┬$
   │     ├e─r─$
   │     └i─n─g─$
   └y┬$
     └f─u─l┬$
           └l─e┬r─$
               └s─t─$
```

### Data Format

| op    | Meaning                                                                                                   |
| ----- | --------------------------------------------------------------------------------------------------------- |
| `<`   | remove 1 character                                                                                        |
| `<n`  | remove n characters where `n` is `[2-9]` to remove 12 characters use `<9<3`                               |
| `$`   | end of word                                                                                               |
| `\`   | escape next character. All characters can be escaped. <br/> `\\` -> `\` <br/>`\#` -> `#` <br/>`\a` -> `a` |
| `#n;` | reference to an already imported trie node where `n` is the node number                                   |

**Sample Data**

<!--- cspell:disable --->

```text
Big Apple$8races\: \{\}\[\]\(\)$9<5
New York$7umbers \0\1\2\3\4\5\6\7\8\9$9<9
ap#6;<rrow \<$7
big a#5;<4urned$r$2ing$3s$$4
chalk#56;<3u#54;<3
eol \\n$3w \$$4scape \\\$8
fun journey$7wal#27;<7
journalism$tic$2$3s$$2eyer$2man$2e#103;<2$4ste#101;<i#58;<$3vialit#85;<2$4wly$$2yfuller$st$4ness$4$3lessn#120;<$4ou#125;<2ridde#103;<2er$$i#58;<3od#8;<3
stic#27;<4$3
lift#56;<3ong w#86;<6
ref \#$5
t#61;<
wa#62;<2
```

<!--- cspell:enable --->

## File Format V1

### Header

```
TrieXv1
base=10
```

The header has two parts.

- TrieXv1 -- the identifiers
- base -- offsets are stored using the base (10, 16, 32) are common.
  higher the base, the smaller the file. Max is 36

### Data

The first line of data is always a `*`

Each line is a node in the Trie.

The format of each line is:

`star [char index [, char index]*]`

- star - the presence of a star indicates that the node is the ending of a word.
- char - a character that can be appended to the word followed by the node at index.
- index - the offset in the list of nodes to continue appending

In other words, each line has an optional `*` followed by 0 or more (char, index) pairs.
A missing index implies an index of 0, which is the end of word flag.

**Example Line:** `*s1,e` -- The word can stop here, or add an **s** and continue at node _1_, or add an **e**

### Example:

**Word List:**

- walk
- walked
- walker
- walking
- walks
- talk
- talks
- talked
- talker
- talking

becomes

**Output:** (Offsets are added for clarity, but do not exist in output)

```text
Offset  Output
------- --------
        TrieXv1
        base=10
0       *
1       d,r
2       g
3       n2
4       *e1,i3,s
5       k4
6       l5
7       a6
8       t7,w7
```

The root of the trie is the last offset, 8.
It is designed for the entire trie to be in memory, which is why the root is at the end.
This allows for efficiently building the trie as the file loads line by line, because
each line can only refer to previous lines.

How to walk the data to see if "talks" is in it.

1. Start with the root at offset 8.
1. t found goto 7
1. a found goto 6
1. l found goto 5
1. k found goto 4
1. s found stop (goto 0 is stop).

<!---
    cspell:word DAFSA DAWG
-->

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