From 534ac4b75d5dd5220d233a767a8858acd01e0ae2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?B=C3=A1n=20D=C3=A9nes?= <mr@zealot.hu>
Date: Sun, 26 Dec 2021 14:06:30 +0100
Subject: [PATCH] Filter implementation started

---
 src/filter.js | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 86 insertions(+)
 create mode 100644 src/filter.js

diff --git a/src/filter.js b/src/filter.js
new file mode 100644
index 0000000..ff7a33e
--- /dev/null
+++ b/src/filter.js
@@ -0,0 +1,86 @@
+const u = require('./utils')
+const a = require('./assert')
+const anchor = require('./anchor').parse
+
+const _true = () => true
+const _and = arr => p => arr.map(e => e(p)).reduce((a, b) => a && b)
+const _or = arr => p => arr.map(e => e(p)).reduce((a, b) => a || b)
+
+const similar = (a, b, name, units) => {
+    let neg = false
+
+    if (b.startsWith('-')) {
+        neg = true
+        b = b.slice(1)
+    }
+
+    if (b.startsWith('/')) {
+        //...
+    }
+}
+
+const comparators = {
+    '~': similar
+    // TODO: extension point for other operators...
+}
+const symbols = Object.keys(comparators)
+
+const simple = (exp, name, units) => {
+
+    let a = ['meta.name', 'meta.tags']
+    let op = '~'
+    let b
+    const parts = exp.split(/\s+/g)
+
+    // full case
+    if (symbols.includes(parts[1])) {
+        a = parts[0].split(',')
+        op = parts[1]
+        b = parts.slice(2).join(' ')
+    
+    // middle case, just an operator spec, default "a"
+    } else if (symbols.includes(parts[0])) {
+        op = parts[0]
+        b = parts.slice(1).join(' ')
+
+    // basic case, only "b"
+    } else {
+        b = exp
+    }
+
+    return comparators[op](a, b, name, units)
+}
+
+const complex = (config, name, units, aggregator=_and) => {
+
+    // default is all points
+    if (config === undefined) {
+        return _true
+    }
+
+    // otherwise we branch by type
+    const type = a.type(config)()
+    switch(type) {
+ 
+        // base case is a string, meaning a simple/single filter
+        case 'string':
+            return simple(config, name, units)
+        
+        // arrays are aggregated with alternating and/or conditions
+        case 'array':
+            const alternate = aggregator == _and ? _or : _and
+            return aggregator(config.map(elem => complex(elem, name, units, alternate)))
+
+        default:
+            throw new Error(`Unexpected type "${type}" found at filter "${name}"!`)
+    }
+}
+
+exports.parse = (config, name, points={}, units={}) => {
+    
+    if (a.type(config)() == 'object') {
+        return [anchor(config, name, points)(units)]
+    }
+
+    return Object.values(points).filter(complex(config, name, units))
+}
\ No newline at end of file