//! What the `.ftl` catalogues have to hold true, checked against the files
//! themselves rather than against what a reviewer remembers of them.
//!
//! Key parity and duplicates are the ordinary half. The other half guards the
//! one place where catalogue text is trusted as markup:
//!
//! A handful of templates render a translation with Askama's `|safe`, because
//! the message carries its own `<strong>` or `<code>`. That makes those
//! messages the only strings in the catalogue that reach a page as HTML rather
//! than as text — and the `sk` and `cs` catalogues were machine-translated, so
//! "the translator would not write a `<script>`" is not something anyone
//! checked. These tests check it, for every locale, every time they run.
//!
//! Two properties, together:
//!
//! 1. A message rendered `|safe` may contain only the tags below, balanced.
//! 2. Every *other* message contains no markup at all, so moving a message to a
//!    `|safe` site later cannot quietly bring markup along with it.

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

/// The tags a translator may use: inline emphasis, plus links to elsewhere in
/// this app. Nothing that can carry script, load a remote resource, or open an
/// interactive control.
const ALLOWED_TAGS: [&str; 4] = ["strong", "code", "em", "a"];

const LOCALES: [&str; 3] = ["en", "sk", "cs"];

fn crate_dir() -> PathBuf {
    PathBuf::from(env!("CARGO_MANIFEST_DIR"))
}

/// Every message key some template renders with `|safe`.
///
/// Read out of the templates rather than listed here, so the test cannot drift
/// from the markup it is guarding.
fn keys_rendered_as_html() -> BTreeSet<String> {
    let mut keys = BTreeSet::new();
    let mut files = Vec::new();
    collect_html(&crate_dir().join("templates"), &mut files);
    assert!(!files.is_empty(), "found no templates to scan");

    for file in files {
        let markup = fs::read_to_string(&file).expect("template is readable");
        for expression in markup.split("{{").skip(1) {
            let Some(expression) = expression.split("}}").next() else {
                continue;
            };
            if !expression.contains("|safe") {
                continue;
            }
            // `nav.tr("k")`, `nav.tr_args("k", …)`, `locale.lookup("k")`: the
            // key is the first quoted string of the call either way.
            if let Some(key) = first_quoted(expression) {
                keys.insert(key);
            }
        }
    }
    keys
}

fn collect_html(directory: &Path, found: &mut Vec<PathBuf>) {
    for entry in fs::read_dir(directory).expect("template directory is readable") {
        let path = entry.expect("directory entry is readable").path();
        if path.is_dir() {
            collect_html(&path, found);
        } else if path.extension().is_some_and(|extension| extension == "html") {
            found.push(path);
        }
    }
}

fn first_quoted(expression: &str) -> Option<String> {
    let rest = expression.split_once('"')?.1;
    Some(rest.split_once('"')?.0.to_string())
}

/// Every `key = value` in one catalogue, with continuation lines joined.
///
/// Deliberately a small hand parser rather than a Fluent one: the point is to
/// look at the *source text* a translator wrote, before any placeable is
/// resolved.
fn messages(locale: &str) -> Vec<(String, String)> {
    let path = crate_dir().join("locales").join(locale).join("main.ftl");
    let catalogue = fs::read_to_string(&path)
        .unwrap_or_else(|_| panic!("catalogue {} is readable", path.display()));

    let mut messages: Vec<(String, String)> = Vec::new();
    for line in catalogue.lines() {
        let trimmed = line.trim_start();
        if trimmed.is_empty() || trimmed.starts_with('#') {
            continue;
        }
        let is_continuation = line.starts_with(' ') || line.starts_with('\t');
        if is_continuation {
            if let Some(last) = messages.last_mut() {
                last.1.push(' ');
                last.1.push_str(trimmed);
            }
            continue;
        }
        if let Some((key, value)) = line.split_once(" = ") {
            messages.push((key.trim().to_string(), value.trim().to_string()));
        }
    }
    assert!(!messages.is_empty(), "catalogue {locale} parsed as empty");
    messages
}

/// Splits a message's `<…>` spans out, returning them in order.
///
/// A `<` that no name follows is a literal less-than sign — `ecb-less-than-1s`
/// is the string `<1s` — and is not markup.
fn tags(value: &str) -> Vec<String> {
    let mut tags = Vec::new();
    let mut rest = value;
    while let Some((_, after)) = rest.split_once('<') {
        if !after.starts_with(|character: char| character.is_ascii_alphabetic() || character == '/')
        {
            rest = after;
            continue;
        }
        match after.split_once('>') {
            Some((tag, remainder)) => {
                tags.push(tag.trim().to_string());
                rest = remainder;
            }
            None => break,
        }
    }
    tags
}

/// Whether a tag's attributes are ones a translation may carry.
///
/// Only `<a href="…">`, and only to a path inside this app: a `javascript:` or
/// off-site `href` in a machine-translated catalogue would be a redirect —
/// or a script — that no reviewer of the `.ftl` diff is likely to notice.
fn attributes_are_allowed(name: &str, attributes: &str) -> bool {
    if attributes.is_empty() {
        return true;
    }
    if name != "a" {
        return false;
    }
    attributes
        .strip_prefix("href=\"/")
        .and_then(|target| target.strip_suffix('"'))
        .is_some_and(|target| !target.starts_with('/'))
}

#[test]
fn messages_rendered_as_html_use_only_balanced_inline_tags() {
    let safe_keys = keys_rendered_as_html();
    assert!(
        !safe_keys.is_empty(),
        "no `|safe` translations found — has the scan stopped matching?"
    );

    for locale in LOCALES {
        for (key, value) in messages(locale) {
            if !safe_keys.contains(&key) {
                continue;
            }
            let mut open: Vec<String> = Vec::new();
            for tag in tags(&value) {
                let (tag, is_closing) = match tag.strip_prefix('/') {
                    Some(name) => (name.to_string(), true),
                    None => (tag.clone(), false),
                };
                let (name, attributes) = match tag.split_once(char::is_whitespace) {
                    Some((name, attributes)) => (name.to_string(), attributes.trim().to_string()),
                    None => (tag.clone(), String::new()),
                };
                assert!(
                    ALLOWED_TAGS.contains(&name.as_str()),
                    "{locale}/{key} renders as HTML and uses <{name}>, \
                     which is not one of {ALLOWED_TAGS:?}"
                );
                assert!(
                    attributes_are_allowed(&name, &attributes),
                    "{locale}/{key} renders as HTML and its <{name}> carries \
                     `{attributes}`; only a same-app `href=\"/…\"` is allowed"
                );
                if is_closing {
                    assert_eq!(
                        open.pop().as_deref(),
                        Some(name.as_str()),
                        "{locale}/{key} closes </{name}> that is not open"
                    );
                } else {
                    open.push(name);
                }
            }
            assert!(
                open.is_empty(),
                "{locale}/{key} leaves {open:?} unclosed"
            );
        }
    }
}

#[test]
fn messages_not_rendered_as_html_contain_no_markup() {
    let safe_keys = keys_rendered_as_html();

    for locale in LOCALES {
        for (key, value) in messages(locale) {
            if safe_keys.contains(&key) {
                continue;
            }
            let found = tags(&value);
            assert!(
                found.is_empty(),
                "{locale}/{key} contains {found:?} but is rendered as text, so \
                 the tags would show as escaped source; drop them, or move the \
                 message to a `|safe` site deliberately"
            );
        }
    }
}

/// English is the source language and the fallback, so a key it lacks is a key
/// nothing can render, and a key only *it* has is a page that silently falls
/// back to English for a Slovak or Czech reader.
#[test]
fn every_catalogue_defines_the_same_keys() {
    let english: BTreeSet<String> = messages("en").into_iter().map(|(key, _)| key).collect();

    for locale in LOCALES {
        if locale == "en" {
            continue;
        }
        let translated: BTreeSet<String> =
            messages(locale).into_iter().map(|(key, _)| key).collect();

        let untranslated: Vec<&String> = english.difference(&translated).collect();
        assert!(
            untranslated.is_empty(),
            "{locale} is missing {untranslated:?}"
        );
        let orphaned: Vec<&String> = translated.difference(&english).collect();
        assert!(
            orphaned.is_empty(),
            "{locale} defines {orphaned:?}, which English does not"
        );
    }
}

/// A key defined twice silently keeps one of the two. Fluent does not complain.
#[test]
fn no_catalogue_defines_a_key_twice() {
    for locale in LOCALES {
        let mut seen = BTreeSet::new();
        for (key, _) in messages(locale) {
            assert!(seen.insert(key.clone()), "{locale} defines `{key}` twice");
        }
    }
}

/// The `|safe` keys have to exist in every catalogue, or a missing one falls
/// back to the sentinel — which is fine as text and misleading as markup.
#[test]
fn every_key_rendered_as_html_exists_in_every_catalogue() {
    let safe_keys = keys_rendered_as_html();

    for locale in LOCALES {
        let defined: BTreeSet<String> =
            messages(locale).into_iter().map(|(key, _)| key).collect();
        for key in &safe_keys {
            assert!(
                defined.contains(key),
                "{locale} has no `{key}`, which a template renders as HTML"
            );
        }
    }
}