package config

import (
	"errors"
	"io"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
	"testing"
)

// discardLogger returns a logger that swallows all output, for tests
// that exercise code paths which log.
func discardLogger() *slog.Logger {
	return slog.New(slog.NewTextHandler(io.Discard, nil))
}

// TestCacheMaxBytesExplicitValueUsedWithoutFloor verifies that an
// explicitly configured cache_max_bytes value is used exactly as
// given: the 500 MiB floor applies only to the computed default, never
// to explicit values.
func TestCacheMaxBytesExplicitValueUsedWithoutFloor(t *testing.T) {
	yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 1024\n"

	c, err := configFromYAML(t, yamlContent)
	if err != nil {
		t.Fatalf("explicit cache_max_bytes must be accepted, got error: %v", err)
	}

	if c.CacheMaxBytes != 1024 {
		t.Errorf("CacheMaxBytes = %d, want 1024 (no floor for explicit values)",
			c.CacheMaxBytes)
	}
}

// TestCacheMaxBytesZeroIsValidAndDisablesCache verifies that an
// explicit zero is a valid value (it disables the disk cache), not an
// error.
func TestCacheMaxBytesZeroIsValidAndDisablesCache(t *testing.T) {
	yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 0\n"

	c, err := configFromYAML(t, yamlContent)
	if err != nil {
		t.Fatalf("cache_max_bytes: 0 must be accepted, got error: %v", err)
	}

	if c.CacheMaxBytes != 0 {
		t.Errorf("CacheMaxBytes = %d, want 0", c.CacheMaxBytes)
	}
}

// TestCacheMaxBytesLargeExplicitValueParses verifies that values above
// 32-bit range parse correctly (the field is an int64 byte count).
func TestCacheMaxBytesLargeExplicitValueParses(t *testing.T) {
	yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 10737418240\n"

	c, err := configFromYAML(t, yamlContent)
	if err != nil {
		t.Fatalf("large cache_max_bytes must be accepted, got error: %v", err)
	}

	if c.CacheMaxBytes != 10737418240 {
		t.Errorf("CacheMaxBytes = %d, want 10737418240", c.CacheMaxBytes)
	}
}

// TestCacheMaxBytesInvalidValuesAbortStartup verifies that a SET but
// invalid cache_max_bytes value aborts startup naming the key and the
// offending value, per the no-silent-fallback rule: defaults apply
// only to omitted keys.
func TestCacheMaxBytesInvalidValuesAbortStartup(t *testing.T) {
	signingKeyLine := "signing_key: " + validTestSigningKey + "\n"

	cases := []struct {
		name string
		yaml string
		// wantErrSubstrings must all appear in the error message.
		wantErrSubstrings []string
	}{
		{
			name:              "negative",
			yaml:              signingKeyLine + "cache_max_bytes: -1024\n",
			wantErrSubstrings: []string{"cache_max_bytes", "-1024"},
		},
		{
			name:              "float",
			yaml:              signingKeyLine + "cache_max_bytes: 3.5\n",
			wantErrSubstrings: []string{"cache_max_bytes", "3.5"},
		},
		{
			name:              "non-numeric string",
			yaml:              signingKeyLine + "cache_max_bytes: banana\n",
			wantErrSubstrings: []string{"cache_max_bytes", "banana"},
		},
		{
			name:              "explicit null",
			yaml:              signingKeyLine + "cache_max_bytes: null\n",
			wantErrSubstrings: []string{"cache_max_bytes", "null"},
		},
		{
			name:              "bare key no value",
			yaml:              signingKeyLine + "cache_max_bytes:\n",
			wantErrSubstrings: []string{"cache_max_bytes", "null"},
		},
		{
			name:              "boolean",
			yaml:              signingKeyLine + "cache_max_bytes: true\n",
			wantErrSubstrings: []string{"cache_max_bytes", "true"},
		},
		{
			name:              "list",
			yaml:              signingKeyLine + "cache_max_bytes:\n  - 1\n",
			wantErrSubstrings: []string{"cache_max_bytes"},
		},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			c, err := configFromYAML(t, tc.yaml)
			if err == nil {
				t.Fatalf("config with %s cache_max_bytes must abort startup, got config: %+v",
					tc.name, c)
			}

			t.Logf("got expected error: %v", err)

			for _, want := range tc.wantErrSubstrings {
				if !strings.Contains(err.Error(), want) {
					t.Errorf("error %q does not mention %q", err.Error(), want)
				}
			}
		})
	}
}

// TestComputeDefaultCacheMaxBytesUses75PercentOfFreeSpace verifies the
// computed default is 75% of the probed free space when that exceeds
// the floor.
func TestComputeDefaultCacheMaxBytesUses75PercentOfFreeSpace(t *testing.T) {
	// 4 GiB free -> 3 GiB default.
	probe := func(string) (uint64, error) { return 4294967296, nil }

	got, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
	if err != nil {
		t.Fatalf("ComputeDefaultCacheMaxBytes returned error: %v", err)
	}

	if got != 3221225472 {
		t.Errorf("ComputeDefaultCacheMaxBytes = %d, want 3221225472 (75%% of 4 GiB)", got)
	}
}

// TestComputeDefaultCacheMaxBytesAppliesFloorToComputedDefault
// verifies that when 75% of free space is below 500 MiB, the computed
// default is floored at DefaultCacheMaxBytesFloor.
func TestComputeDefaultCacheMaxBytesAppliesFloorToComputedDefault(t *testing.T) {
	cases := []struct {
		name      string
		freeBytes uint64
	}{
		{name: "100 MiB free", freeBytes: 104857600},
		{name: "zero free", freeBytes: 0},
		{name: "just below floor threshold", freeBytes: 699050665},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			probe := func(string) (uint64, error) { return tc.freeBytes, nil }

			got, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
			if err != nil {
				t.Fatalf("ComputeDefaultCacheMaxBytes returned error: %v", err)
			}

			if got != DefaultCacheMaxBytesFloor {
				t.Errorf("ComputeDefaultCacheMaxBytes = %d, want floor %d",
					got, DefaultCacheMaxBytesFloor)
			}
		})
	}
}

// TestComputeDefaultCacheMaxBytesPropagatesProbeError verifies that a
// failing free-space probe produces an error naming the config key,
// instead of a silently wrong default.
func TestComputeDefaultCacheMaxBytesPropagatesProbeError(t *testing.T) {
	probe := func(string) (uint64, error) { return 0, errors.New("statfs failed") }

	_, err := ComputeDefaultCacheMaxBytes(t.TempDir(), probe)
	if err == nil {
		t.Fatal("probe failure must produce an error, got nil")
	}

	t.Logf("got expected error: %v", err)

	if !strings.Contains(err.Error(), "cache_max_bytes") {
		t.Errorf("error %q does not name the config key cache_max_bytes", err.Error())
	}
}

// TestResolveCacheMaxBytesComputesDefaultWhenOmitted verifies that an
// omitted cache_max_bytes key resolves to the computed default, that
// the probe is pointed at <state_dir>/cache/ (which must be created
// first so statfs measures the right filesystem), and that the result
// lands on the Config.
func TestResolveCacheMaxBytesComputesDefaultWhenOmitted(t *testing.T) {
	c, err := configFromYAML(t, "signing_key: "+validTestSigningKey+"\n")
	if err != nil {
		t.Fatalf("minimal config should be valid, got error: %v", err)
	}

	c.StateDir = t.TempDir()
	wantCacheDir := filepath.Join(c.StateDir, "cache")

	var probedPath string

	// 4 GiB free -> 3 GiB default.
	probe := func(path string) (uint64, error) {
		probedPath = path

		return 4294967296, nil
	}

	if err := c.resolveCacheMaxBytes(discardLogger(), probe); err != nil {
		t.Fatalf("resolveCacheMaxBytes returned error: %v", err)
	}

	if c.CacheMaxBytes != 3221225472 {
		t.Errorf("CacheMaxBytes = %d, want computed default 3221225472", c.CacheMaxBytes)
	}

	if probedPath != wantCacheDir {
		t.Errorf("free space probed at %q, want cache directory %q", probedPath, wantCacheDir)
	}

	info, err := os.Stat(wantCacheDir)
	if err != nil || !info.IsDir() {
		t.Errorf("cache directory %q was not created before probing: info=%v err=%v",
			wantCacheDir, info, err)
	}
}

// TestResolveCacheMaxBytesDoesNotOverrideExplicitValue verifies that
// an explicitly configured value survives resolution untouched and
// that the free-space probe is never consulted for it.
func TestResolveCacheMaxBytesDoesNotOverrideExplicitValue(t *testing.T) {
	yamlContent := "signing_key: " + validTestSigningKey + "\ncache_max_bytes: 1024\n"

	c, err := configFromYAML(t, yamlContent)
	if err != nil {
		t.Fatalf("explicit cache_max_bytes must be accepted, got error: %v", err)
	}

	c.StateDir = t.TempDir()

	probe := func(string) (uint64, error) {
		t.Error("free-space probe must not be consulted for explicit values")

		return 0, errors.New("probe must not be called")
	}

	if err := c.resolveCacheMaxBytes(discardLogger(), probe); err != nil {
		t.Fatalf("resolveCacheMaxBytes returned error: %v", err)
	}

	if c.CacheMaxBytes != 1024 {
		t.Errorf("CacheMaxBytes = %d, want explicit 1024 (no floor, no recompute)",
			c.CacheMaxBytes)
	}
}