//! Forward fence, the frontend-globals ratchet.
//!
//! The legacy `static/*.js` files register behavior as `window.<name> = fn`
//! globals (the pre-module `data-action` dispatcher pattern). The frontend
//! restructure (`_private/docs/mnw/frontend/`) migrates these into typed ES
//! modules under `frontend/src`. This seal keeps the count monotonically
//! non-increasing: adding a new global fails the build, and every migrated file
//! must lower `HIGH_WATER`. Same idea as the migration HIGH_WATER seal.
//!
//! When you remove globals, lower `HIGH_WATER` to the new count (the failure
//! message reports it). Never raise it.
//!
//! # What counts as a global
//!
//! Both trees are read, `static/*.js` and `frontend/src`, and an alias bound to
//! `window` in a file is followed within that file: a typed module assigning
//! through `const w = window as unknown as Record<string, unknown>` is counted
//! like a direct `window.x =`. Without that, moving a file out of `static/`
//! while keeping its global lowers the seal without lowering the global
//! surface, and a conversion batch reports progress it did not make.
//!
//! A bare top-level `function foo() {}` in a classic script is a global too,
//! with no assignment to match. Every `static/*.js` file is loaded by a plain
//! `<script src>` with no `type="module"`, so those declarations count.
//!
//! **The rule is per tree, and that is the point.** A top-level function in an
//! ES module under `frontend/src` is scoped to the module and is not a global,
//! so [`count_script_globals`] runs only over `static/*.js` while
//! [`count_globals`] runs over both. Applying it everywhere would count the
//! typed tree's own functions as the surface the typed tree exists to remove.
//!
//! `HIGH_WATER` moves down when globals are removed, and is restated only when
//! a correction changes what this test can see. It must not move for any other
//! reason.

use std::fs;
use std::path::{Path, PathBuf};

/// Ratchets down only, never up. Lower it to the count the failure message
/// reports whenever globals are removed.
///
/// A ratchet that only refuses to grow lets removals go unrecorded, so this
/// number is a ceiling rather than a progress figure: measure before trusting
/// it as one.
const HIGH_WATER: usize = 161;

/// Every file whose global assignments count: the legacy scripts and the typed
/// modules that replaced them.
///
/// `frontend/src` is walked rather than listed, because the whole point of the
/// restructure is that files move there, and a seal that has to be told about
/// each new one is a seal that silently stops covering the tree.
fn sources() -> Vec<PathBuf> {
    let root = Path::new(env!("CARGO_MANIFEST_DIR"));
    let mut files = Vec::new();

    for entry in fs::read_dir(root.join("static")).expect("read static/ dir") {
        let path = entry.expect("dir entry").path();
        let Some(name) = path.file_name().and_then(|n| n.to_str()) else {
            continue;
        };
        // Vendored libraries are not our global surface, and a minified one
        // aliases `window` internally dozens of times, so the alias rule below
        // would read htmx's own bookkeeping as names this server put on the
        // page. `htmx.min.js` did contribute one direct `window.htmx =` to the
        // old count; that was noise the narrower regex happened to admit.
        let is_js = path.extension().and_then(|e| e.to_str()) == Some("js");
        if name.ends_with(".min.js") || !is_js {
            continue;
        }
        files.push(path);
    }
    collect_ts(&root.join("frontend/src"), &mut files);

    files
}

/// The typed tree, recursively. Type declarations and tests are skipped: a
/// `.d.ts` describes globals rather than creating them, and a test asserting on
/// one is not a page that ships one.
fn collect_ts(dir: &Path, out: &mut Vec<PathBuf>) {
    let Ok(entries) = fs::read_dir(dir) else {
        return;
    };
    for entry in entries {
        let path = entry.expect("dir entry").path();
        if path.is_dir() {
            collect_ts(&path, out);
            continue;
        }
        let Some(name) = path.file_name().and_then(|n| n.to_str()) else {
            continue;
        };
        if name.ends_with(".d.ts") || name.contains(".test.") {
            continue;
        }
        if matches!(path.extension().and_then(|e| e.to_str()), Some("ts" | "js")) {
            out.push(path);
        }
    }
}

/// Count bare top-level function declarations, in one CLASSIC-script file.
///
/// `82315c45`. A `<script src>` with no `type="module"` shares the global
/// scope, so `function foo() {}` at the top level of one lands `foo` on the
/// global object without ever writing an assignment. Neither rule in
/// [`count_globals`] can see that, and 55 of this server's globals are that
/// shape.
///
/// **Only for `static/*.js`.** The same declaration in an ES module under
/// `frontend/src` is scoped to the module and is not a global, so counting it
/// there would charge the typed tree for the surface it exists to remove.
fn count_script_globals(src: &str) -> usize {
    // Column zero is the whole test for "top level", and it is enough because
    // every one of the 55 is written that way. A declaration indented inside an
    // IIFE is correctly not counted: that is a function scope, not the global
    // object. A regex cannot know the difference and does not have to.
    regex::Regex::new(r"(?m)^(?:async )?function [A-Za-z_][A-Za-z0-9_]*\s*\(")
        .unwrap()
        .find_iter(src)
        .count()
}

/// Count assignments that land a name on `window`, in one file.
///
/// Two forms, because the code uses two. The direct `window.foo = …` is what
/// the legacy scripts write. The aliased form is what a typed module writes,
/// since assigning to `window.foo` in TypeScript needs the index signature the
/// alias provides, so the bridge binds `window` to a local first.
///
/// The alias is followed only inside the file that binds it, and only when it
/// was bound to `window` itself, so a local named `w` holding anything else
/// contributes nothing.
///
/// Runs over both trees, unlike [`count_script_globals`]: an assignment to
/// `window` is a global wherever it is written.
fn count_globals(src: &str) -> usize {
    // `=[^=]` matches an assignment `=` while excluding the first `=` of a
    // comparison operator. The regex crate has no lookahead, so this is the
    // portable form.
    let direct = regex::Regex::new(r"window\.[A-Za-z_][A-Za-z0-9_]*\s*=[^=]").unwrap();
    let binding =
        regex::Regex::new(r"(?:const|let|var)\s+([A-Za-z_][A-Za-z0-9_]*)\s*=\s*window\b").unwrap();

    let mut total = direct.find_iter(src).count();

    for bound in binding.captures_iter(src) {
        let alias = &bound[1];
        let through =
            regex::Regex::new(&format!(r"\b{alias}\.[A-Za-z_][A-Za-z0-9_]*\s*=[^=]")).unwrap();
        total += through.find_iter(src).count();
    }

    total
}

#[test]
fn frontend_globals_do_not_grow() {
    let count: usize = sources()
        .iter()
        .map(|path| {
            let src = fs::read_to_string(path).unwrap_or_default();
            // A bare top-level function is a global only in a classic script,
            // which is what `static/` holds and `frontend/src` does not. See
            // `count_script_globals`.
            let classic = path.parent().and_then(Path::file_name) == Some("static".as_ref());
            count_globals(&src)
                + if classic {
                    count_script_globals(&src)
                } else {
                    0
                }
        })
        .sum();

    assert!(
        count <= HIGH_WATER,
        "globals across static/*.js and frontend/src rose to {count} \
         (HIGH_WATER {HIGH_WATER}). New frontend code must be a typed ES module in \
         frontend/src registered through the dispatcher, not a global -- and note \
         that a bare top-level `function` in a classic script is one too. If you \
         REMOVED globals, lower HIGH_WATER to {count}."
    );
}

#[test]
fn the_seal_sees_a_bare_top_level_function_in_a_classic_script() {
    // `82315c45`. The shape that was invisible until 2026-08-26: no assignment
    // anywhere, and `exportItemSalesCSV` was still a global the dispatcher
    // called by name.
    assert_eq!(
        count_script_globals("function exportItemSalesCSV() {\n}\n"),
        1
    );
    assert_eq!(count_script_globals("async function loadThing(id) {}"), 1);

    // Two shapes that are NOT the global scope, and must not be counted.
    assert_eq!(
        count_script_globals("(function () {\n    function inner() {}\n})();"),
        0,
        "a declaration inside an IIFE is a function scope"
    );
    assert_eq!(count_script_globals("const f = function named() {};"), 0);
}

#[test]
fn the_two_counters_do_not_double_count_one_name() {
    // A file that both declares and assigns is two globals by two routes, and
    // the seal should say two rather than collapsing them. The point is that
    // neither counter reaches into the other's shape.
    let src = "function draw() {}\nwindow.draw = draw;\n";
    assert_eq!(count_script_globals(src), 1);
    assert_eq!(count_globals(src), 1);
}

#[test]
fn the_seal_sees_a_global_assigned_through_an_alias() {
    // The hole `7df1a7de` names, as a unit. Without this the count is a
    // measure of which directory a file sits in rather than of how many names
    // reach `window`, and a migration that moves a file and keeps its global
    // reads as progress.
    let bridged = "const w = window as unknown as Record<string, unknown>;\n\
                   w.escapeHtml = escapeHtml;\n\
                   w.showToast = showToast;\n";
    assert_eq!(count_globals(bridged), 2);

    // A local that is not `window` contributes nothing, which is what keeps the
    // alias rule from counting every object property assignment in the tree.
    let ordinary = "const w = document.body;\nw.className = 'x';\n";
    assert_eq!(count_globals(ordinary), 0);

    // And a comparison is not an assignment, in either form.
    let compared = "if (window.foo === bar) {}\nconst w = window;\nif (w.foo == bar) {}\n";
    assert_eq!(count_globals(compared), 0);
}