// `make check` used to run `prettier --check .` twice: once inside the lint
// container (`script/lint` builds `Dockerfile.lint`, which runs eslint and
// prettier as build steps) and once again on the host, because `script/check`
// also called `script/fmt-check`. Two passes, one verdict, and the host one is
// the weaker of the two — its prettier is whatever the working tree happens to
// have installed, while the container's is digest-pinned and installed under
// `--frozen-lockfile`.
//
// The fix was to delete the host call from `script/check` and `script/precommit`.
// Nothing about that fix is self-enforcing: anyone can wire `script/fmt-check`
// back in, or add a prettier step to a Dockerfile, and every build stays green
// while quietly doing the work twice again. So the count is asserted here
// rather than promised in a comment.
//
// The assertion is a static walk of the invocation graph, not a string match
// against one file. Starting from an entrypoint, it follows every edge the repo
// actually uses to reach another command — `run:` steps in the CI workflow,
// `"$SCRIPT_DIR/<name>"` and `script/<name>` into other scripts, `make <target>`
// and `$(MAKE) <target>` through the Makefile shims, the prerequisites of a
// Makefile target, `yarn run <name>` through the `package.json` scripts, and
// `docker build` into the `RUN` steps of the Dockerfile it names, heredoc
// bodies included — and counts the prettier invocations it finds.
//
// What that covers is worth stating exactly rather than as "anywhere", because
// a comment claiming more than the code delivers is the same defect as an
// assertion that cannot fail — and an earlier draft of this header did claim
// it, while `check: fmt-check` and `@$(MAKE) fmt-check` both walked straight
// past it. Command names are read as `[a-z][a-z0-9_-]*` for Makefile targets
// and `script/` files, and `[A-Za-z][A-Za-z0-9_:-]*` for `package.json`
// scripts. A command reached by some other means — `sh -c`, a shell alias, an
// `include`d makefile, a name outside those charsets, a generated file — is
// not followed. Recipe lines reached through a make conditional are followed,
// without evaluating the condition, and so is a recipe written on the target
// line after a `;`; a recipe built by an `include`d makefile, a pattern rule,
// or a target name outside that charset is not. A variable given a literal
// value on one line — `VAR := ...`, `VAR = ...`, `VAR ?= ...` — is substituted
// wherever the Makefile spells it `$(VAR)` or `${VAR}`, because this Makefile
// writes its recipes that way (`@$(YARN) tsc --watch`); the substitution is
// one pass over literals, so a value that itself names another variable, a
// value built by a make function (`$(shell ...)`, `$(addprefix ...)`), and the
// body of a `define`/`endef` block are not expanded and not followed. A
// `docker build` resolves to the file named by `-f`, `-f=`, `-f<file>` with
// the value attached to the flag, `--file` or `--file=`, wherever in the
// invocation that flag sits, and to `Dockerfile` when it names none; a
// Dockerfile chosen some other way — a bundled short flag cluster
// (`-qf <file>`), a value this walk cannot expand to a literal — resolves to
// the default rather than to the real file. Within those edges, a
// prettier call is caught wherever it is added.
//
// Two entrypoints are walked, because they cover different graphs: `make check`
// is what a developer runs, and `.gitea/workflows/check.yml` is what CI runs.
// The CI walk starts at the workflow file rather than at a hand-picked script,
// so "the path CI executes" is read out of the repo instead of assumed; it
// reaches `script/cibuild`, and through it the `Dockerfile` image that `make
// check` never touches. Walking only `make check` is how a duplicate prettier
// pass in `Dockerfile` stayed invisible.
//
// Undercounting is the failure mode that would make this test worthless. Three
// things guard against it: the walk is asserted to have reached the nodes that
// matter, an unresolvable or empty node is a thrown error rather than a quiet
// zero, and prettier is counted per occurrence rather than per line, so two
// invocations chained with `&&` cannot read as one.
import { describe, expect, it } from "vitest";
import { readFileSync } from "node:fs";
import { fileURLToPath } from "node:url";
import { join } from "node:path";

const repoRoot = fileURLToPath(new URL("../../", import.meta.url));

const read = (name: string): string =>
    readFileSync(join(repoRoot, name), "utf-8");

// A backslash at end of line continues the command; the resolver has to see the
// whole invocation, since the interesting flags (`-f Dockerfile.lint`) can sit
// on the continuation.
const joinContinuations = (text: string): string[] => {
    const joined: string[] = [];
    for (const raw of text.split("\n")) {
        const line = raw.trim();
        const previous = joined[joined.length - 1];
        if (previous !== undefined && previous.endsWith("\\")) {
            joined[joined.length - 1] =
                `${previous.slice(0, -1).trim()} ${line}`;
        } else {
            joined.push(line);
        }
    }
    return joined;
};

// Comments are stripped everywhere. The headers of these scripts explain the
// duplication this test exists to prevent, and therefore name `prettier` and
// `script/fmt-check` repeatedly; counting them would make the test assert the
// prose instead of the behaviour.
const executable = (text: string): string[] =>
    joinContinuations(text).filter(
        (line) => line !== "" && !line.startsWith("#"),
    );

// Every occurrence, not "does this line mention prettier": a line that reads
// `yarn run prettier --check . && yarn run prettier --check src` is two passes
// over the same tree, which is exactly the bug this file exists to catch, and
// counting it as one would hide it. `.prettierrc` and `.prettierignore` are not
// invocations and do not match, because `\b` requires a non-word character
// after the name.
const countPrettier = (line: string): number =>
    (line.match(/\bprettier\b/g) ?? []).length;

// Makefile targets are thin shims (`check:` / tab / `@script/check`), so a
// `make <target>` edge has to resolve through them to keep "per `make check`"
// meaning what it says. Recipe lines are the tab-indented ones.
//
// The prerequisite list is read as well, and it is not decoration: make runs a
// target's prerequisites before its recipe, so `check: fmt-check` invokes
// fmt-check every bit as much as a `@script/fmt-check` line in the recipe
// would. An earlier version of this parser captured the target name and threw
// the rest of the line away, which made `check: fmt-check` — a one-token edit,
// and the most natural way for someone to wire the host formatting check back
// into `make check` — a second prettier pass that this file scored as one. The
// shipped Makefile already relies on prerequisites (`install: build-bin`), so
// this is the file's own house style rather than a contrived evasion.
interface MakeTarget {
    prerequisites: string[];
    recipe: string[];
}

// Names are lowercase-with-dashes here, plus digits and underscores. The
// leading character is deliberately not uppercase: `YARN := yarn run` is a
// variable assignment, not a rule, and `(?!=)` alone would not say so on a
// line spelled `YARN: yarn run`.
const MAKE_TARGET_NAME = "[a-z][a-z0-9_-]*";

// Conditional directives are not target lines, and they are not recipe lines
// either — they are parse-time structure wrapped around the recipe that
// encloses them. Treating one as an ordinary non-tab line ends the current
// recipe, and every tab-indented line after it is discarded, so
//
//     check:
//     \t@script/check
//     ifeq (1,1)
//     \t@script/fmt-check
//     endif
//
// reads as a recipe of one command while `make -n check` prints two. The
// condition is deliberately not evaluated: that would mean evaluating make
// variables, and the conservative reading — every branch is reachable, so
// every branch's lines are recipe lines — is the one that cannot lose an
// invocation. Counting a command from a branch make would skip is a false
// alarm someone fixes; missing one is the failure this file exists to prevent.
const MAKE_CONDITIONAL = /^\s*(?:ifeq|ifneq|ifdef|ifndef|else|endif)\b/;

// `@$(FMT)` is one token away from being a second prettier pass, and until the
// variable is resolved it reads as a line that invokes nothing: `make -n check`
// printed both `script/check` and `script/fmt-check` while this file scored
// one. `$(MAKE)` was already special-cased below, which is this same rule
// half-applied to a single name; this is the general form of it.
//
// Deliberately only the simple case: a name assigned a literal on one line,
// optionally through an `export`/`override` prefix. `:=` and `=` differ in
// when make expands them, which does not change the single value a literal can
// take, so those two are read the same way and the last one wins. `?=` differs
// in whether it assigns at all — it is skipped when the name already has a
// value — so among assignments to one name the first `?=` wins, and reading it
// as last-wins would resolve a reference to the string make discards. What is
// not read is anything needing evaluation — a value containing another
// `$(...)`, a make function, or a `define` body —
// because expanding those means implementing make, and a half-implementation
// that resolves a variable to the wrong string would count invocations that do
// not happen. An unresolved reference is left standing verbatim instead, which
// is the same dead end as any other unfollowed edge rather than a wrong answer.
const MAKE_ASSIGNMENT = new RegExp(
    `^(?:(?:export|override)\\s+)*([A-Za-z_][A-Za-z0-9_]*)\\s*(:=|\\?=|=)\\s*(.*)$`,
);
const MAKE_VARIABLE_REFERENCE = /\$[({]([A-Za-z_][A-Za-z0-9_]*)[)}]/g;

// `define`/`endef` bodies are skipped rather than parsed: the body is a
// multi-line value, so reading its lines as assignments would take whatever
// `=` they happen to contain and call it a variable.
const makeVariables = (text: string): Map<string, string> => {
    const variables = new Map<string, string>();
    let inDefine = false;
    for (const raw of text.split("\n")) {
        if (/^\s*endef\b/.test(raw)) {
            inDefine = false;
            continue;
        }
        if (/^\s*define\b/.test(raw)) {
            inDefine = true;
            continue;
        }
        if (inDefine || raw.startsWith("\t")) continue;
        const assignment = MAKE_ASSIGNMENT.exec(raw.replace(/#.*$/, "").trim());
        if (assignment === null) continue;
        const [, name, operator, value] = assignment;
        if (name === undefined || operator === undefined || value === undefined)
            continue;
        // `?=` assigns only when the name has no value yet, so the first one
        // wins where `:=` and `=` let the last one win. Overwriting here would
        // resolve the reference to a string make never uses.
        if (operator === "?=" && variables.has(name)) continue;
        // A value that is itself a reference is the recursive case, and is not
        // resolved. Recording it would hand the substitution below a string it
        // cannot finish expanding.
        if (/\$[({]/.test(value)) continue;
        variables.set(name, value.trim());
    }
    return variables;
};

// One pass, and only over names that were assigned a literal: the result is
// never re-scanned for further references, so this cannot recurse or diverge.
const expandMakeVariables = (
    line: string,
    variables: Map<string, string>,
): string =>
    line.replace(
        MAKE_VARIABLE_REFERENCE,
        (reference, name: string) => variables.get(name) ?? reference,
    );

const parseMakefile = (text: string): Map<string, MakeTarget> => {
    const recipes = new Map<string, MakeTarget>();
    // Collected in a pass of their own because make reads the whole file
    // before it runs anything: a recipe may spell a variable that the Makefile
    // assigns further down, and a single pass would leave that one unexpanded
    // purely because of where its author put it.
    const variables = makeVariables(text);
    let current: string | null = null;
    for (const line of text.split("\n")) {
        // Expanded before parsing rather than only on recipe lines, so a
        // prerequisite written `check: $(FMT)` resolves the same way a recipe
        // line does. Assignment lines are expanded too and are unaffected: a
        // literal value has nothing to substitute.
        const raw = expandMakeVariables(line, variables);
        if (raw.startsWith("\t")) {
            if (current !== null) {
                recipes
                    .get(current)
                    ?.recipe.push(raw.trim().replace(/^[@-]+/, ""));
            }
            continue;
        }
        if (MAKE_CONDITIONAL.test(raw)) continue;
        const target = new RegExp(`^(${MAKE_TARGET_NAME})\\s*:(?!=)(.*)$`).exec(
            raw,
        );
        current = target === null ? null : (target[1] ?? null);
        if (target === null || current === null) continue;
        // `target: prereqs ; command` puts the first recipe line on the target
        // line itself. Read as prerequisites the whole of it, `;` and the
        // command split into tokens that name no target and are filtered out,
        // and the invocation disappears — `check: ; @script/fmt-check` was a
        // second prettier pass this parser scored as none.
        const rest = target[2] ?? "";
        const semicolon = rest.indexOf(";");
        const inlineRecipe =
            semicolon === -1 ? "" : rest.slice(semicolon + 1).trim();
        // Trailing `# comment` is not a prerequisite; neither is the empty
        // string a split leaves behind.
        const prerequisites = (
            semicolon === -1 ? rest : rest.slice(0, semicolon)
        )
            .replace(/#.*$/, "")
            .trim()
            .split(/\s+/)
            .filter((name) => name !== "");
        const existing = recipes.get(current);
        if (existing === undefined) {
            recipes.set(current, { prerequisites, recipe: [] });
        } else {
            existing.prerequisites.push(...prerequisites);
        }
        if (inlineRecipe !== "") {
            recipes
                .get(current)
                ?.recipe.push(inlineRecipe.replace(/^[@-]+/, ""));
        }
    }
    return recipes;
};

const recipes = parseMakefile(read("Makefile"));

// Only prerequisites that name a target of this Makefile are followed: the
// rest are filenames, or expansions of variables this parser does not
// evaluate, and neither is an invocation of anything it could read.
const prerequisitesOf = (node: string): string[] => {
    if (!node.startsWith("make:")) return [];
    const target = recipes.get(node.slice("make:".length));
    if (target === undefined) return [];
    return target.prerequisites
        .filter((name) => recipes.has(name))
        .map((name) => `make:${name}`);
};

const packageScripts = (): Record<string, string> => {
    const pkg = JSON.parse(read("package.json")) as {
        scripts?: Record<string, string>;
    };
    return pkg.scripts ?? {};
};

const scripts = packageScripts();

// A `RUN <<EOF` body is a command the image executes, and BuildKit runs it on
// the default frontend with no `# syntax=` directive, so keeping only the
// lines that begin `RUN ` would let a whole shell script hide one line below
// one. The body is returned alongside the `RUN` line that opened it. An
// unterminated heredoc is a thrown error rather than a silent truncation of
// the rest of the file, for the same reason every other dead end here is.
const HEREDOC_OPEN = /<<-?\s*(['"]?)([A-Za-z_][A-Za-z0-9_]*)\1/;

const dockerRunCommands = (text: string): string[] => {
    const commands: string[] = [];
    let terminator: string | null = null;
    for (const line of executable(text)) {
        if (terminator !== null) {
            if (line === terminator) terminator = null;
            else commands.push(line);
            continue;
        }
        if (!line.startsWith("RUN ")) continue;
        const command = line.slice("RUN ".length);
        terminator = HEREDOC_OPEN.exec(command)?.[2] ?? null;
        commands.push(command);
    }
    if (terminator !== null) {
        throw new Error(`unterminated heredoc: ${terminator}`);
    }
    return commands;
};

// Node keys: `script/<name>`, `docker:<Dockerfile>`, `make:<target>`,
// `yarn:<package.json script>`, `workflow:<CI workflow file>`.
const resolve = (node: string): string[] => {
    if (node.startsWith("script/")) return executable(read(node));
    if (node.startsWith("docker:")) {
        return dockerRunCommands(read(node.slice("docker:".length)));
    }
    // The `run:` steps of a workflow, in file order. `uses:` steps are actions,
    // not commands, and have no edges into this repo's graph. A `run: |` block
    // would resolve to the bare `|`, which reaches nothing and therefore fails
    // the count rather than passing quietly.
    if (node.startsWith("workflow:")) {
        return executable(read(node.slice("workflow:".length)))
            .filter((line) => /^-?\s*run:\s*\S/.test(line))
            .map((line) => line.replace(/^-?\s*run:\s*/, ""));
    }
    if (node.startsWith("make:")) {
        const target = node.slice("make:".length);
        const recipe = recipes.get(target);
        // A renamed or deleted target must be a loud failure: silently walking
        // an empty recipe would report zero prettier invocations, which reads
        // like the tidiest possible result.
        if (recipe === undefined) {
            throw new Error(`no such Makefile target: ${target}`);
        }
        return recipe.recipe;
    }
    if (node.startsWith("yarn:")) {
        const name = node.slice("yarn:".length);
        const script = scripts[name];
        if (script === undefined) {
            throw new Error(`no such package.json script: ${name}`);
        }
        return [script];
    }
    throw new Error(`unresolvable node: ${node}`);
};

// Same reasoning as the missing-target error, applied to every node kind: a
// node that resolves to no commands contributes zero prettier invocations and
// zero edges, which is indistinguishable from a clean result. Fail instead.
//
// A Makefile target with prerequisites and an empty recipe is the one case
// that is genuinely not vacuous — it runs its prerequisites — so it is not
// caught here.
const commandsOf = (node: string): string[] => {
    const commands = resolve(node);
    if (commands.length === 0 && prerequisitesOf(node).length === 0) {
        throw new Error(`node resolved to no commands: ${node}`);
    }
    return commands;
};

const edgesOf = (line: string): string[] => {
    const edges: string[] = [];

    // `"$SCRIPT_DIR/lint"`, `"$ROOT/script/lint"` and a bare `script/lint` are
    // all the same edge.
    for (const match of line.matchAll(
        new RegExp(
            `(?:\\$SCRIPT_DIR|\\$\\{SCRIPT_DIR\\}|script)/(${MAKE_TARGET_NAME})`,
            "g",
        ),
    )) {
        edges.push(`script/${match[1]}`);
    }

    // Only real targets: `pkg_install gnumake make make make` in
    // script/bootstrap is a package name, not an invocation of this Makefile.
    //
    // `$(MAKE)` and `${MAKE}` count as `make`. Recursive make is spelled that
    // way by convention rather than as a literal `make`, and this Makefile
    // already expands variables into recipes (`@$(YARN) tsc --watch`), so a
    // case-sensitive literal-only match left `@$(MAKE) fmt-check` — the other
    // one-token way to put the host prettier pass back into `make check` —
    // unfollowed. Valueless flags between the command and the target (`make
    // -n check`, `make -j4 check`) are skipped. A flag that takes a separate
    // argument is not: `make -C sub build` runs `sub/Makefile`'s target, not
    // this one's, and resolving it against these recipes would be wrong
    // rather than merely incomplete.
    for (const match of line.matchAll(
        new RegExp(
            `(?:\\$\\(MAKE\\)|\\$\\{MAKE\\}|\\bmake)(?:\\s+-\\S+)*\\s+(${MAKE_TARGET_NAME})`,
            "g",
        ),
    )) {
        if (recipes.has(match[1] ?? "")) edges.push(`make:${match[1]}`);
    }

    // Same rule for yarn: `yarn run prettier` is the linter itself (counted,
    // not followed), `yarn run fmt-check` would be a package.json script that
    // runs it indirectly.
    //
    // The name charset is wider than the Makefile's because `package.json`
    // script names conventionally carry colons, digits and underscores
    // (`lint:fmt`, `test:e2e`). Under the narrower charset `yarn run lint:fmt`
    // read as `yarn run lint`, which is not a script, so it produced no edge
    // and no count.
    for (const match of line.matchAll(
        /\byarn(?:\s+run)?\s+([A-Za-z][A-Za-z0-9_:-]*)/g,
    )) {
        if ((match[1] ?? "") in scripts) edges.push(`yarn:${match[1]}`);
    }

    // The container lint pass lives behind a `docker build`; without following
    // it the count would miss the one invocation that is supposed to survive.
    //
    // Every spelling of the file flag is read, not just `-f <file>`. Docker
    // accepts `--file <file>`, `--file=<file>`, `-f=<file>` and the value
    // attached to the short flag as one token (`-f<file>`) for the same thing,
    // and matching `-f ` alone resolved all of them to the default
    // `Dockerfile` edge — so `docker build --file=Dockerfile.lint .` in a
    // recipe was followed into the wrong file, counted nothing, and reported
    // green. The flag is searched for anywhere in the invocation, as `-f`
    // already was, because a real build line wraps it in `--build-arg` and
    // other flags. A leading `\s` is required so that a longer flag ending in
    // the same letters cannot supply the match, and the attached form is
    // allowed only for the short flag, so that `--force-rm` — a long flag that
    // merely starts with the same letters — still does not read as one.
    if (/\bdocker\s+build\b/.test(line)) {
        const file = /\s(?:--file[=\s]+|-f=?\s*)(\S+)/.exec(line);
        edges.push(`docker:${file === null ? "Dockerfile" : file[1]}`);
    }

    return edges;
};

interface Walk {
    prettier: number;
    reached: Set<string>;
}

// Repeated invocations must count repeatedly — running the same script twice is
// exactly the bug — so nodes are not deduplicated. The path stack is only there
// to turn a cycle into a loud failure instead of a hang.
//
// Counting and edge-following both happen for every line: a line that invokes
// prettier can also invoke something else, and skipping the edges of counted
// lines silently truncated the graph.
const walk = (node: string, path: string[] = [], into?: Walk): Walk => {
    const result = into ?? { prettier: 0, reached: new Set<string>() };
    if (path.includes(node)) {
        throw new Error(`invocation cycle: ${[...path, node].join(" -> ")}`);
    }
    result.reached.add(node);

    // Before the recipe, exactly as make does.
    for (const edge of prerequisitesOf(node)) {
        walk(edge, [...path, node], result);
    }

    for (const line of commandsOf(node)) {
        result.prettier += countPrettier(line);
        for (const edge of edgesOf(line)) {
            walk(edge, [...path, node], result);
        }
    }
    return result;
};

describe("prettier runs exactly once per make check", () => {
    const check = walk("make:check");

    // The headline assertion, and the one the issue is about.
    it("invokes prettier once for the whole of make check", () => {
        expect(check.prettier).toBe(1);
    });

    // Guards against the count being 1 (or 0) because the walk never got
    // anywhere. `make check` has to reach the suite, the lint script, and the
    // Dockerfile whose build IS the lint verdict.
    it.each(["script/check", "script/test", "script/lint", "Dockerfile.lint"])(
        "reaches %s while counting",
        (node) => {
            const key = node.startsWith("script/") ? node : `docker:${node}`;
            expect([...check.reached]).toContain(key);
        },
    );

    // The one that survives is the container's, not the host's: that is the
    // authoritative verdict, since a successful Dockerfile.lint build is what
    // CI treats as proof of a clean tree.
    it("keeps the surviving invocation inside the lint container", () => {
        expect(walk("docker:Dockerfile.lint").prettier).toBe(1);
    });

    it("does not reach the host formatting check from make check", () => {
        expect([...check.reached]).not.toContain("script/fmt-check");
    });
});

describe("prettier runs exactly once per CI build", () => {
    // Rooted at the workflow file, so this is the graph CI executes rather than
    // the graph someone believed CI executes. `make check` cannot stand in for
    // it: CI runs script/cibuild, which builds Dockerfile as well as
    // Dockerfile.lint, and nothing under `make check` ever reads Dockerfile.
    const ci = walk("workflow:.gitea/workflows/check.yml");

    it("invokes prettier once for the whole CI build", () => {
        expect(ci.prettier).toBe(1);
    });

    // script/cibuild is here because the workflow is asserted to run it;
    // Dockerfile is here because it is the half of the CI graph that the
    // `make check` walk cannot see.
    it.each([
        "script/cibuild",
        "script/lint",
        "docker:Dockerfile.lint",
        "docker:Dockerfile",
    ])("reaches %s while counting", (node) => {
        expect([...ci.reached]).toContain(node);
    });

    // The test and build image must not lint: linting is Dockerfile.lint's job,
    // and a prettier step added here would be a second pass over the same tree
    // for the same verdict — on the one path where it matters most.
    it("keeps prettier out of the test and build image", () => {
        expect(walk("docker:Dockerfile").prettier).toBe(0);
    });
});

describe("the standalone entrypoints still do what their names say", () => {
    // REPO_POLICIES.md requires both `make lint` and `make fmt-check` to exist
    // and mean something. Dropping fmt-check from script/check must not turn it
    // into a target nobody can use, and must not leave `make check` passing
    // because both halves became no-ops.
    it("still checks formatting under make fmt-check", () => {
        expect(walk("make:fmt-check").prettier).toBe(1);
    });

    it("still checks formatting under make lint", () => {
        expect(walk("make:lint").prettier).toBe(1);
    });
});

describe("script/precommit", () => {
    // Same duplication as script/check, same fix. The hook still catches a
    // badly formatted tree before the commit lands, because script/lint is the
    // container prettier run — that is the whole reason the host call could go.
    it("checks formatting exactly once", () => {
        expect(walk("script/precommit").prettier).toBe(1);
    });

    it("gets that check from the lint container", () => {
        expect([...walk("script/precommit").reached]).toContain(
            "docker:Dockerfile.lint",
        );
    });
});

// script/bootstrap installs the dependencies, and it has two install sites: one
// for the case where yarn has to be reached through nvm, and one for the case
// where yarn is already on PATH. A substring check against the whole file
// cannot tell them apart, so it reports the first and says nothing about the
// second — which is the one the containers take, because the pinned node image
// ships yarn. Both are resolved separately here.
const installBranches = (): { withoutYarn: string[]; withYarn: string[] } => {
    const lines = executable(read("script/bootstrap"));
    const open = lines.findIndex((line) =>
        /^install_js_deps\s*\(\)/.test(line),
    );
    if (open === -1) {
        throw new Error("script/bootstrap: no install_js_deps function");
    }
    const close = lines.indexOf("}", open);
    const body = lines.slice(open + 1, close === -1 ? undefined : close);
    // The guard has to be a plain positive `missing yarn` test at the front of
    // the condition. `if ! missing yarn ...` is the same shape to a looser
    // regex but swaps which branch is which, and since the two branches are
    // asserted separately below, that would silently relabel them — a failing
    // test would then name the wrong branch. Anything else throws the named
    // error below, which is the loud failure this file prefers.
    const guard = body.findIndex((line) => /^if\s+missing yarn\b/.test(line));
    const otherwise = body.indexOf("else", guard);
    const end = body.indexOf("fi", otherwise);
    if (guard === -1 || otherwise === -1 || end === -1) {
        throw new Error(
            "script/bootstrap: install_js_deps is not the expected " +
                "if missing yarn / else / fi shape",
        );
    }
    return {
        withoutYarn: body.slice(guard + 1, otherwise),
        withYarn: body.slice(otherwise + 1, end),
    };
};

// Every `yarn install` in the given lines, with its flags, so an unpinned
// install cannot hide next to a pinned one.
const yarnInstalls = (lines: string[]): string[] =>
    lines.flatMap((line) =>
        [...line.matchAll(/\byarn install\b[^"'&|;]*/g)].map((match) =>
            match[0].trim(),
        ),
    );

describe("host and container prettier cannot disagree", () => {
    // With the host pass gone from `make check`, `make fmt-check` is the only
    // host-side formatting check left, and the container is the gate. The two
    // must keep producing the same verdict on the same tree, or a developer
    // running `make fmt-check` gets a green that CI then rejects.
    //
    // Three things make them agree, and all three are load-bearing:
    it("pins the same prettier for both", () => {
        const pkg = JSON.parse(read("package.json")) as {
            devDependencies: Record<string, string>;
        };
        // An exact version, not a range: `^3.8.1` would let the container and
        // the host resolve different builds with different formatting.
        expect(pkg.devDependencies.prettier).toMatch(/^\d+\.\d+\.\d+$/);
    });

    it("installs from the lockfile on the branch the container takes", () => {
        // Both images are FROM a node image, which ships yarn, so `missing
        // yarn` is false and this is the branch that runs in the container.
        const installs = yarnInstalls(installBranches().withYarn);
        expect(installs).not.toHaveLength(0);
        for (const install of installs) {
            expect(install).toContain("--frozen-lockfile");
        }
    });

    it("installs from the lockfile on the nvm branch too", () => {
        // Not the container's branch, but it is the one a developer without
        // yarn on PATH gets, and their prettier has to match the container's.
        const installs = yarnInstalls(installBranches().withoutYarn);
        expect(installs).not.toHaveLength(0);
        for (const install of installs) {
            expect(install).toContain("--frozen-lockfile");
        }
    });

    it("runs script/bootstrap inside the lint container", () => {
        // Without this the lockfile assertions above would be about a script
        // the container never executes.
        expect([...walk("docker:Dockerfile.lint").reached]).toContain(
            "script/bootstrap",
        );
    });

    it("keeps .gitignore in the build context", () => {
        // Prettier 3 reads .gitignore as a default ignore file, so excluding it
        // from the context would change which files the container checks.
        const dockerignore = read(".dockerignore")
            .split("\n")
            .map((line) => line.trim());
        expect(dockerignore).not.toContain(".gitignore");
    });
});

describe("the walk cannot pass vacuously", () => {
    // An earlier draft of this file computed a Makefile target as
    // `node.slice("make:")` — a string where a number belongs, which coerces to
    // NaN and made every target resolve to nothing. The count went to zero and
    // an assertion of "not twice" would have been satisfied by a walk that had
    // read nothing at all. Every way of reaching nothing is therefore an
    // error here, and the ways are tested rather than assumed.
    it("reports zero for a subgraph that does not run prettier", () => {
        expect(walk("make:clean").prettier).toBe(0);
    });

    it("refuses a Makefile target that does not exist", () => {
        expect(() => walk("make:no-such-target")).toThrow(
            /no such Makefile target/,
        );
    });

    it("refuses a package.json script that does not exist", () => {
        expect(() => walk("yarn:no-such-script")).toThrow(
            /no such package.json script/,
        );
    });

    it("refuses a script that does not exist", () => {
        expect(() => walk("script/no-such-script")).toThrow(/ENOENT/);
    });

    it("refuses a node that resolves to no commands", () => {
        // .dockerignore has no RUN steps, standing in for a Dockerfile whose
        // steps a restructure moved somewhere the resolver cannot see.
        expect(() => walk("docker:.dockerignore")).toThrow(
            /resolved to no commands/,
        );
    });

    it("refuses a node kind it does not understand", () => {
        expect(() => walk("nonsense")).toThrow(/unresolvable node/);
    });

    it("refuses to walk in circles", () => {
        expect(() => walk("make:check", ["script/check"])).toThrow(
            /invocation cycle/,
        );
    });
});

describe("the resolver reads what the shell would run", () => {
    // Counting per line is how `yarn run prettier --check . && yarn run
    // prettier --check src` read as a single invocation.
    it("counts every prettier invocation on a line", () => {
        expect(
            countPrettier(
                "yarn run prettier --check . && yarn run prettier --check src",
            ),
        ).toBe(2);
    });

    it("does not count the config files as invocations", () => {
        expect(countPrettier("COPY .prettierrc .prettierignore ./")).toBe(0);
    });

    // The counting `continue` also dropped every edge that shared a line with a
    // prettier call, so a whole subtree could be hidden behind one `&&`.
    it("still follows the edges of a line that invokes prettier", () => {
        expect(
            edgesOf('yarn run prettier --check . && "$SCRIPT_DIR/lint"'),
        ).toContain("script/lint");
    });

    it("resolves every spelling of a script call to one node", () => {
        expect(
            edgesOf('"$SCRIPT_DIR/lint" "${SCRIPT_DIR}/test" script/fmt'),
        ).toEqual(["script/lint", "script/test", "script/fmt"]);
    });

    // The two edges the previous version of this file could not see, each
    // pinned directly as well as through the graph. Both were reproduced as
    // Makefile mutations that gave `make check` two prettier passes with the
    // whole suite green.
    it("follows a Makefile prerequisite as an invocation", () => {
        // Not hypothetical: this is the shipped Makefile's own `install`.
        expect(prerequisitesOf("make:install")).toEqual(["make:build-bin"]);
        expect(prerequisitesOf("make:check")).toEqual([]);
    });

    it("treats $(MAKE) and ${MAKE} as make", () => {
        expect(edgesOf("$(MAKE) fmt-check")).toContain("make:fmt-check");
        expect(edgesOf("${MAKE} fmt-check")).toContain("make:fmt-check");
        expect(edgesOf("make fmt-check")).toContain("make:fmt-check");
        expect(edgesOf("make -n fmt-check")).toContain("make:fmt-check");
    });

    // Two more constructs that gave `make check` a second prettier pass with
    // the whole suite green, each reproduced as a Makefile mutation before
    // being pinned here.
    it("keeps recipe lines inside a make conditional", () => {
        const recipes = parseMakefile(
            [
                "check:",
                "\t@script/check",
                "ifeq (1,1)",
                "\t@script/fmt-check",
                "endif",
            ].join("\n"),
        );
        // What `make -n check` prints, in order.
        expect(recipes.get("check")?.recipe).toEqual([
            "script/check",
            "script/fmt-check",
        ]);
    });

    it("reads a recipe written on the target line after a semicolon", () => {
        const recipes = parseMakefile(
            ["check: ; @script/fmt-check", "\t@script/check"].join("\n"),
        );
        expect(recipes.get("check")?.recipe).toEqual([
            "script/fmt-check",
            "script/check",
        ]);
        // And the `;` and the command are not mistaken for prerequisites.
        expect(recipes.get("check")?.prerequisites).toEqual([]);
        expect(
            parseMakefile("check: lint ; @script/fmt-check").get("check"),
        ).toEqual({
            prerequisites: ["lint"],
            recipe: ["script/fmt-check"],
        });
    });

    // The fifth construct that gave `make check` two prettier passes with the
    // whole suite green: `FMT := script/fmt-check` and a recipe of `@$(FMT)`.
    // The shipped Makefile writes recipe lines this way already
    // (`@$(YARN) tsc --watch`), so an unexpanded variable was a gap in the
    // house style rather than in an exotic corner of make.
    it("expands a variable spelled into a recipe line", () => {
        const recipes = parseMakefile(
            [
                "FMT := script/fmt-check",
                "check:",
                "\t@$(FMT)",
                "\t@${FMT}",
                "\t@script/check",
            ].join("\n"),
        );
        // What `make -n check` prints, in order.
        expect(recipes.get("check")?.recipe).toEqual([
            "script/fmt-check",
            "script/fmt-check",
            "script/check",
        ]);
    });

    it("expands a variable spelled into a prerequisite list", () => {
        expect(
            parseMakefile("FMT = fmt-check\ncheck: $(FMT)").get("check")
                ?.prerequisites,
        ).toEqual(["fmt-check"]);
    });

    // A recipe may name a variable the Makefile assigns further down.
    it("expands a variable assigned after the recipe that uses it", () => {
        const recipes = parseMakefile(
            ["check:", "\t@$(FMT)", "FMT ?= script/fmt-check"].join("\n"),
        );
        expect(recipes.get("check")?.recipe).toEqual(["script/fmt-check"]);
    });

    // `export FMT := script/fmt-check` is an assignment make honours and the
    // pattern anchored at the name, so the whole line read as neither an
    // assignment nor a target and `@$(FMT)` stood unresolved: `make -n check`
    // printed `script/check` and `script/fmt-check` while this file scored
    // one. `override` reaches the same place by the same route.
    it("expands a variable assigned through an export or override prefix", () => {
        expect(
            parseMakefile(
                [
                    "export FMT := script/fmt-check",
                    "check:",
                    "\t@$(FMT)",
                    "\t@script/check",
                ].join("\n"),
            ).get("check")?.recipe,
        ).toEqual(["script/fmt-check", "script/check"]);
        expect(
            parseMakefile(
                ["override FMT = script/fmt-check", "check:", "\t@$(FMT)"].join(
                    "\n",
                ),
            ).get("check")?.recipe,
        ).toEqual(["script/fmt-check"]);
        // `export` on its own line names a variable without assigning one, and
        // is not read as an assignment of the empty string.
        expect(
            parseMakefile(
                [
                    "FMT := script/fmt-check",
                    "export FMT",
                    "check:",
                    "\t@$(FMT)",
                ].join("\n"),
            ).get("check")?.recipe,
        ).toEqual(["script/fmt-check"]);
    });

    // `?=` assigns only when the name has no value yet, so among assignments
    // to one name the first `?=` wins where `:=` and `=` let the last one win.
    // Reading every operator as last-wins resolved `@$(FMT)` to the value make
    // discards: the file counted an invocation that never happens and missed
    // the one that does, with the suite green either way.
    it("keeps the first value when a later assignment is conditional", () => {
        expect(
            parseMakefile(
                [
                    "FMT := script/fmt-check",
                    "FMT ?= script/build",
                    "check:",
                    "\t@$(FMT)",
                ].join("\n"),
            ).get("check")?.recipe,
        ).toEqual(["script/fmt-check"]);
        // A `?=` that is itself the first assignment does assign, and a `?=`
        // after it does not.
        expect(
            parseMakefile(
                [
                    "FMT ?= script/fmt-check",
                    "FMT ?= script/build",
                    "check:",
                    "\t@$(FMT)",
                ].join("\n"),
            ).get("check")?.recipe,
        ).toEqual(["script/fmt-check"]);
        // `:=` and `=` stay last-wins, which is what make does.
        expect(
            parseMakefile(
                [
                    "FMT := script/build",
                    "FMT := script/fmt-check",
                    "check:",
                    "\t@$(FMT)",
                ].join("\n"),
            ).get("check")?.recipe,
        ).toEqual(["script/fmt-check"]);
    });

    // The edges of the expansion, asserted so the header's not-followed list
    // is the code's behaviour rather than a claim about it. Each of these
    // leaves the reference standing verbatim, which reaches nothing — the same
    // dead end as any other unfollowed edge, and not a wrong resolution.
    it("leaves a value it cannot resolve to a literal unexpanded", () => {
        // A make function: resolving it would mean running it.
        expect(
            parseMakefile(
                [
                    "FMT := $(shell echo script/fmt-check)",
                    "check:",
                    "\t@$(FMT)",
                ].join("\n"),
            ).get("check")?.recipe,
        ).toEqual(["$(FMT)"]);
        // A `define` body is a multi-line value, not a single-line assignment.
        expect(
            parseMakefile(
                [
                    "define RUNFMT",
                    "@script/fmt-check",
                    "endef",
                    "check:",
                    "\t$(RUNFMT)",
                ].join("\n"),
            ).get("check")?.recipe,
        ).toEqual(["$(RUNFMT)"]);
        // An undefined name is not silently emptied.
        expect(
            parseMakefile(["check:", "\t@$(NOPE)"].join("\n")).get("check")
                ?.recipe,
        ).toEqual(["$(NOPE)"]);
    });

    it("reads a package.json script name that contains a colon", () => {
        // The lookup against `scripts` is what turns this into an edge, and no
        // script in this repo is colon-named, so the charset is asserted on
        // the extraction itself.
        expect(
            [
                ..."yarn run lint:fmt".matchAll(
                    /\byarn(?:\s+run)?\s+([A-Za-z][A-Za-z0-9_:-]*)/g,
                ),
            ].map((match) => match[1]),
        ).toEqual(["lint:fmt"]);
    });

    it("reads the body of a BuildKit heredoc RUN step", () => {
        expect(
            dockerRunCommands(
                [
                    "FROM scratch",
                    "RUN <<EOF",
                    "yarn run prettier --check .",
                    "EOF",
                    "RUN echo done",
                ].join("\n"),
            ),
        ).toContain("yarn run prettier --check .");
    });

    it("refuses a heredoc that is never terminated", () => {
        expect(() =>
            dockerRunCommands("FROM scratch\nRUN <<EOF\nyarn run prettier .\n"),
        ).toThrow(/unterminated heredoc/);
    });

    it("follows a bare docker build to Dockerfile and -f to its file", () => {
        expect(edgesOf("docker build .")).toContain("docker:Dockerfile");
        expect(edgesOf("docker build -f Dockerfile.lint .")).toContain(
            "docker:Dockerfile.lint",
        );
    });

    // `-f` is not the only spelling of the flag. `--file=Dockerfile.lint` and
    // `--file Dockerfile.lint` mean exactly what `-f Dockerfile.lint` means,
    // and matching only `-f` sent both to the default `Dockerfile` edge
    // instead. That is the false-green shape this whole file exists to
    // prevent: a second prettier pass added as
    // `docker build --file=Dockerfile.lint .` was followed into the wrong
    // Dockerfile, counted nothing, and left every build green. The long form
    // is an ordinary thing for a human to write, so it is followed rather than
    // merely documented as unfollowed.
    //
    // The equality rather than containment matters: resolving to the right
    // file is only half of it, the default edge must not also be emitted.
    it("follows --file in all three spellings as it does -f", () => {
        expect(edgesOf("docker build --file=Dockerfile.lint .")).toEqual([
            "docker:Dockerfile.lint",
        ]);
        expect(edgesOf("docker build --file Dockerfile.lint .")).toEqual([
            "docker:Dockerfile.lint",
        ]);
        expect(edgesOf("docker build -f=Dockerfile.lint .")).toEqual([
            "docker:Dockerfile.lint",
        ]);
    });

    // The value may be attached to the short flag with no separator at all:
    // `-fDockerfile.lint` is a single token, and the flag parser reads it as
    // `-f` naming that file, exactly as `-f Dockerfile.lint` does. Requiring a
    // separator sent it to the default `Dockerfile` edge instead — the same
    // false green as the long spellings above, and one the header promised was
    // followed: a second prettier pass added as `docker build
    // -fDockerfile.lint .` was resolved into the wrong file, counted nothing,
    // and left the build green. `-fFILE` is an ordinary thing for a human to
    // write, so it is followed rather than merely documented as unfollowed.
    it("follows a short file flag with its value attached", () => {
        expect(edgesOf("docker build -fDockerfile.lint .")).toEqual([
            "docker:Dockerfile.lint",
        ]);
    });

    // The flag is found anywhere in the invocation rather than at a fixed
    // position, matching how `-f` was already read, since a real build line
    // carries `--build-arg` and friends around it.
    it("finds the file flag after other flags and build args", () => {
        expect(
            edgesOf(
                'docker build --build-arg LINT_EPOCH="1" --file=Dockerfile.lint --progress=plain .',
            ),
        ).toEqual(["docker:Dockerfile.lint"]);
    });

    // A different flag that merely begins with the same letters is not the
    // file flag: `--force-rm` must not read as one, or its next token would be
    // resolved as a Dockerfile and thrown on as unreadable.
    it("does not mistake --force-rm for the file flag", () => {
        expect(edgesOf("docker build --force-rm .")).toEqual([
            "docker:Dockerfile",
        ]);
    });

    // The header says a bundled short flag cluster resolves to the default
    // rather than to the file it names, which is a limitation and so has to be
    // pinned: an unpinned limitation is how the header starts overclaiming
    // again. If someone teaches the resolver to split clusters, this test is
    // the one that tells them to correct the header too.
    it("resolves a bundled -qf cluster to the default Dockerfile", () => {
        expect(edgesOf("docker build -qf Dockerfile.lint .")).toEqual([
            "docker:Dockerfile",
        ]);
    });

    // This exact-equality assertion is also the block-scalar guard, which is
    // not obvious from its name: a `run: |` step resolves to the bare `|`,
    // which reaches nothing, so the prettier count would stay 1 no matter what
    // the block contains. Pinning the resolved list is what makes such a step
    // red. The cost is that any legitimate second `run:` step — a cache step,
    // an `echo` — fails this test for a reason unrelated to prettier.
    it("reads the run steps of the CI workflow and not its uses steps", () => {
        expect(commandsOf("workflow:.gitea/workflows/check.yml")).toEqual([
            "script/cibuild",
        ]);
    });
});