feat(wpcarro/slx): Simple Select impl'd in JS r/5680

Proof-of-concept implementation of "simple select" to write browser
apps that can filter lists with labels like:

```
author:Hemingway title:For\sWhom.+
```

Change-Id: I6c4cc65fe6319c9230fdc1e983462864acdc6aef
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7812
Reviewed-by: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI

1 files changed, 273 insertions, 0 deletions

diff --git a/users/wpcarro/scratch/simple-select/index.js b/users/wpcarro/scratch/simple-select/index.js
new file mode 100644
index 000000000000..85d057e117bc
--- /dev/null
+++ b/users/wpcarro/scratch/simple-select/index.js
@@ -0,0 +1,273 @@
+// const input = '-director:"Von \\"Fluke\\" Neumann" foo:/this is a test/ (director:"Tarantino" OR director:"Scorsese")';
+const input = 'director:"Tarantino" OR director:"Scorsese"';
+
+const state = {
+    // Match values case sensitively when filtering.
+    caseSensitive: false,
+    // Coerce values into regular expressions (instead of strings) when they're defined as atoms.
+    preferRegex: false,
+};
+
+// TODO(wpcarro): Support global queries like "Tarantino" that try to match against all columns in a row.
+// TODO(wpcarro): Support filtering by date (before, after).
+
+function select(query, xs) {
+    const predicate = compile(parse(query));
+    return xs.filter(predicate);
+}
+
+function compile(ast) {
+    if (ast.type === 'CONJUNCTION') {
+        const lhs = compile(ast.lhs);
+        const rhs = compile(ast.rhs);
+
+        if (ast.joint === 'AND') {
+            return function(x) {
+                return lhs(x) && rhs(x);
+            };
+        }
+        if (ast.joint === 'OR') {
+            return function(x) {
+                return lhs(x) || rhs(x);
+            };
+        }
+    }
+    if (ast.type === 'SELECTION') {
+        const f = compile(ast.val);
+        return function(row) {
+            return ast.negate ? f(row[ast.key]) : f(row[ast.key]);
+        };
+    }
+    if (ast.type === 'STRING') {
+        return function(x) {
+            if (state.caseSensitive) {
+                return x === ast.val;
+            } else {
+                return x.toLowerCase() === ast.val.toLowerCase();
+            }
+        };
+    }
+    if (ast.type === 'REGEX') {
+        return function(x) {
+            return ast.val.test(x);
+        };
+    }
+}
+
+// A "selection" without a "$column:" prefix should fuzzy-search all columns.
+//
+// conjunction -> selection ( ( "AND" | "OR" )? selection )* ;
+// selection   -> "-"? COLUMN ":" ( regex | string ) | regex ;
+// regex       -> [_-a-zA-Z0-9] | "/" [ _-a-zA-Z0-9] "/" | string ;
+// string      -> "\"" [ _-a-zA-Z0-9] "\"" ;
+
+// Whatever characters are valid for a JS regex.
+const ATOM_REGEX = /[-_.\[\]a-zA-Z0-9*+^$]/;
+
+function tokenize(x) {
+    const result = [];
+    let i = 0;
+    while (i < x.length) {
+        if (x[i] === ' ') {
+            i += 1;
+            while (i < x.length && x[i] === ' ') {
+                i += 1;
+            }
+            result.push(['WHITESPACE', null]);
+            continue;
+        }
+        if (x[i] === '-') {
+            result.push(['NEGATE', null]);
+            i += 1;
+            continue;
+        }
+        if (ATOM_REGEX.test(x[i])) {
+            let curr = x[i];
+            i += 1;
+            while (i < x.length && ATOM_REGEX.test(x[i])) {
+                curr += x[i];
+                i += 1;
+            }
+            result.push(['ATOM', curr]);
+            continue;
+        }
+        if (x[i] === ':') {
+            result.push(['COLON', null]);
+            i += 1;
+            continue;
+        }
+        if (x[i] === '(') {
+            result.push(['LPAREN', null]);
+            i += 1;
+            continue;
+        }
+        if (x[i] === ')') {
+            result.push(['RPAREN', null]);
+            i += 1;
+            continue;
+        }
+        if (x[i] === '/') {
+            let start = i;
+            let curr = '';
+            i += 1;
+            while (i < x.length && x[i] !== '/') {
+                curr += x[i];
+                i += 1;
+            }
+            // error
+            if (i >= x.length) {
+                throw `Tokenize Error: EOL while attempting to tokenize the regex beginning at column: ${start}`;
+            }
+            if (x[i] === '/') {
+                result.push(['REGEX', curr]);
+                i += 1;
+            }
+            continue;
+        }
+        if (x[i] === '"') {
+            let start = i;
+            let curr = '';
+            i += 1;
+            while (i < x.length && x[i] !== '"') {
+                // continue on \"
+                if (x[i] === '\\' && x[i + 1] === '"') {
+                    curr += '\"';
+                    i += 2;
+                } else {
+                    curr += x[i];
+                    i += 1;
+                }
+            }
+            if (i >= x.length) {
+                throw `Tokenize Error: EOL while attempting to tokenize the string starting at column: ${start}`;
+            }
+            if (x[i] === '"') {
+                result.push(['STRING', curr]);
+                i += 1;
+            }
+            continue;
+        }
+        else {
+            i += 1;
+        }
+    }
+    return result;
+}
+
+function expect(f, expectation, p) {
+    const [type, val] = p.tokens[p.i];
+    if (f(type, val)) {
+        p.i += 1;
+    } else {
+        throw `Parse Error: expected ${expectation}, but got ${p.tokens[p.i]}; ${JSON.stringify(p)}`
+    }
+}
+
+function matches(f, p) {
+    const [type, val] = p.tokens[p.i];
+    if (f(type, val)) {
+        return true;
+    }
+    return false;
+}
+
+function match(f, expectation, p) {
+    const [type, val] = p.tokens[p.i];
+    if (f(type, val)) {
+        p.i += 1;
+        return val;
+    }
+    throw `Parse Error: expected ${expectation}, but got: ${p.tokens[p.i]}; ${JSON.stringify(p)}`;
+}
+
+function skipWhitespace(p) {
+    while (p.i < p.tokens.length && matches((type, _) => type === 'WHITESPACE', p)) {
+        p.i += 1;
+    }
+}
+
+function parser(tokens) {
+    return { i: 0, tokens };
+}
+
+function parse(x) {
+    const tokens = tokenize(x);
+    const p = parser(tokens);
+    return conjunction(p);
+}
+
+function conjunction(p) {
+    skipWhitespace(p);
+
+    const lhs = selection(p);
+    skipWhitespace(p);
+
+    if (p.i >= p.tokens.length) {
+        return lhs;
+    }
+
+    let joint = 'AND';
+    if (matches((type, val) => type === 'ATOM' && val === 'AND', p)) {
+        joint = 'AND';
+        p.i += 1;
+    } else if (matches((type, val) => type === 'ATOM' && val === 'OR', p)) {
+        joint = 'OR';
+        p.i += 1;
+    }
+    skipWhitespace(p);
+    let rhs = conjunction(p);
+
+    return {
+        type: 'CONJUNCTION',
+        joint,
+        lhs,
+        rhs,
+    };
+}
+
+function selection(p) {
+    // column:value OR -column:value
+    if (matches((type, _) => type === 'ATOM' || type === 'NEGATE', p)) {
+        let negate = false;
+        if (p.tokens[p.i][0] === 'NEGATE') {
+            negate = true;
+            p.i += 1;
+        }
+        const key = match((type, _) => type === 'ATOM', 'a column label', p);
+        expect((type, val) => type === 'COLON', 'a colon', p);
+        const val = value(p);
+        return {
+            type: 'SELECTION',
+            negate,
+            key,
+            val,
+        };
+    } else {
+        return value(p);
+    }
+}
+
+function value(p) {
+    const [type, val] = p.tokens[p.i];
+
+    // Cast atoms into strings or regexes depending on the current state.
+    if (type === 'ATOM') {
+        p.i += 1;
+        if (state.preferRegex) {
+            const regex = state.caseSensitive ? new RegExp(val) : new RegExp(val, "i");
+            return { type: 'REGEX', val: regex };
+        } else {
+            return { type: 'STRING', val }
+        }
+    }
+    if (type === 'STRING') {
+        p.i += 1;
+        return { type, val };
+    }
+    if (type === 'REGEX') {
+        p.i += 1;
+        const regex = state.caseSensitive ? new RegExp(val) : new RegExp(val, "i");
+        return { type, val: regex };
+    }
+    throw `Parse Error: Expected a regular expression or a string, but got: ${p.tokens[p.i]}; ${JSON.stringify(p)}`;
+}