package main_test

import (
	"os"
	"path/filepath"
	"regexp"
	"slices"
	"strings"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// This file guards the Makefile that builds this program, which is why
// it lives beside it rather than in a package of its own.
//
// Issue #110: `build` was listed in .PHONY with no `build:` rule
// anywhere in the file. That combination is silently successful — make
// considers a phony target with no prerequisites and no recipe already
// satisfied, so `rm -f vaultik && make build` printed "Nothing to be
// done for 'build'" and exited 0 with no binary produced. Declaring the
// name phony is precisely what converts the "No rule to make target"
// error into a green.
//
// The guard is a parse of the Makefile rather than an invocation of
// make. `make test` is what runs these tests, so shelling back into
// `make build` here would nest a build inside the test run and drop a
// binary into the tree as a side effect of testing. The one property a
// parse cannot establish — that the recipe still fails when the build
// fails — is not testable from inside the build either; it is verified
// by hand against a deliberately broken tree.

// phonyDirective introduces the list of phony target names.
const phonyDirective = ".PHONY:"

// ruleLine matches a rule's target list: a target starts in column
// zero, so recipe lines (tab-indented) and the continuation lines of a
// variable assignment (space-indented) are excluded by construction.
//
// The trailing (?:[^=]|$) rejects `:=` assignments such as
// `VERSION := $(shell script/version)`, which are not rules. Directives
// and function calls (`.PHONY:`, `ifeq`, `$(error ...)`) do not match
// because a target here must begin with a letter, digit or underscore.
var ruleLine = regexp.MustCompile(`^([A-Za-z0-9_][A-Za-z0-9_./ -]*):(?:[^=]|$)`)

// TestPhonyTargetsAllHaveRules fails on any name in .PHONY that has no
// rule in the Makefile. Such a name is not a build target at all: it is
// a command that reports success without doing anything, which is worse
// than one that does not exist, because a caller checking the exit code
// cannot tell the difference.
func TestPhonyTargetsAllHaveRules(t *testing.T) {
	t.Parallel()

	makefile := readMakefile(t)

	phony := phonyTargets(makefile)
	require.NotEmpty(t, phony, "no .PHONY names found; the parser is broken")

	rules := declaredRules(makefile)

	// Sanity check on the rule parser before trusting its verdict: a
	// parser that found nothing would pass this test by accident.
	require.Contains(t, rules, "vaultik",
		"the file rule that builds the binary must be recognized")

	for _, target := range phony {
		assert.Contains(t, rules, target,
			"`.PHONY` lists %q but the Makefile declares no %q rule, so "+
				"`make %s` exits 0 without doing anything", target, target, target)
	}
}

// TestBuildTargetBuildsTheBinary pins the specific shape of issue #110:
// `make build` has to reach the rule that produces the binary. The test
// above would also pass if `build:` were given an empty recipe of its
// own, which would be the same silent success under a different
// spelling.
func TestBuildTargetBuildsTheBinary(t *testing.T) {
	t.Parallel()

	prerequisites := rulePrerequisites(readMakefile(t), "build")
	require.NotNil(t, prerequisites, "the Makefile declares no `build` rule")

	assert.Contains(t, prerequisites, "vaultik",
		"`make build` must depend on the rule that builds the binary")
}

// readMakefile returns the contents of the repository's Makefile.
func readMakefile(t *testing.T) string {
	t.Helper()

	return readRepoFile(t, "Makefile")
}

// readRepoFile reads a file by its path relative to the repository
// root.
func readRepoFile(t *testing.T, name string) string {
	t.Helper()

	//nolint:gosec // G304: the path is a constant relative to this repo
	contents, err := os.ReadFile(filepath.Join(repoRoot(t), name))
	require.NoError(t, err)

	return string(contents)
}

// repoRoot returns the repository root. The test binary runs with its
// package directory as the working directory, so the root is found by
// walking up until the module file appears.
func repoRoot(t *testing.T) string {
	t.Helper()

	dir, err := os.Getwd()
	require.NoError(t, err)

	for {
		_, err = os.Stat(filepath.Join(dir, "go.mod"))
		if err == nil {
			return dir
		}

		parent := filepath.Dir(dir)
		require.NotEqual(t, dir, parent,
			"walked to the filesystem root without finding a go.mod")

		dir = parent
	}
}

// phonyTargets returns every name declared phony, across all .PHONY
// lines.
func phonyTargets(makefile string) []string {
	var targets []string

	for line := range strings.SplitSeq(makefile, "\n") {
		if !strings.HasPrefix(line, phonyDirective) {
			continue
		}

		targets = append(targets,
			strings.Fields(strings.TrimPrefix(line, phonyDirective))...)
	}

	return targets
}

// declaredRules returns the set of target names that have a rule.
func declaredRules(makefile string) map[string]bool {
	rules := make(map[string]bool)

	for line := range strings.SplitSeq(makefile, "\n") {
		match := ruleLine.FindStringSubmatch(line)
		if match == nil {
			continue
		}

		// One rule may name several targets: `a b: prereq`.
		for target := range strings.FieldsSeq(match[1]) {
			rules[target] = true
		}
	}

	return rules
}

// rulePrerequisites returns the prerequisites of the named rule, or nil
// if no such rule exists. A rule with none returns an empty slice, so
// "declared with nothing to do" is distinguishable from "not declared".
func rulePrerequisites(makefile, target string) []string {
	for line := range strings.SplitSeq(makefile, "\n") {
		match := ruleLine.FindStringSubmatch(line)
		if match == nil {
			continue
		}

		if !slices.Contains(strings.Fields(match[1]), target) {
			continue
		}

		_, after, _ := strings.Cut(line, ":")

		return append([]string{}, strings.Fields(after)...)
	}

	return nil
}