package llm

import (
	"errors"
	"fmt"
	"io"
	"reflect"
	"strings"
	"testing"
	"unicode/utf8"
)

type guardedReader struct {
	reader    io.Reader
	remaining int64
	bytes     int64
	violated  bool
}

func (r *guardedReader) Read(buffer []byte) (int, error) {
	if int64(len(buffer)) > r.remaining {
		r.violated = true
		return 0, errors.New("reader was read past its allowed boundary")
	}
	n, err := r.reader.Read(buffer)
	r.bytes += int64(n)
	r.remaining -= int64(n)
	return n, err
}

type failingReader struct {
	err error
}

func (r failingReader) Read([]byte) (int, error) {
	return 0, r.err
}

func TestProviderHTTPErrorEnvelopeParsing(t *testing.T) {
	tests := []struct {
		name string
		body string
		want providerErrorDetails
	}{
		{
			name: "all supported string fields",
			body: `{"error":{"message":"diagnostic","type":"invalid_request_error","code":"unsupported_parameter"}}`,
			want: providerErrorDetails{providerMessage: "diagnostic", providerType: "invalid_request_error", providerCode: "unsupported_parameter"},
		},
		{
			name: "integer code",
			body: `{"error":{"code":17}}`,
			want: providerErrorDetails{providerCode: "17"},
		},
		{
			name: "fractional code",
			body: `{"error":{"code":1.25}}`,
			want: providerErrorDetails{providerCode: "1.25"},
		},
		{
			name: "exponent code",
			body: `{"error":{"code":6.02e+23}}`,
			want: providerErrorDetails{providerCode: "6.02e+23"},
		},
		{
			name: "invalid fields do not discard valid fields",
			body: `{"error":{"message":null,"type":"invalid_request_error","code":false}}`,
			want: providerErrorDetails{providerType: "invalid_request_error"},
		},
		{
			name: "unknown fields are ignored",
			body: `{"trace":"do not retain","error":{"param":"temperature","metadata":{"secret":"x"}}}`,
			want: providerErrorDetails{},
		},
		{name: "missing error", body: `{}`, want: providerErrorDetails{}},
		{name: "null error", body: `{"error":null}`, want: providerErrorDetails{}},
		{name: "scalar error", body: `{"error":"nope"}`, want: providerErrorDetails{}},
		{name: "empty error", body: `{"error":{}}`, want: providerErrorDetails{}},
		{name: "malformed", body: `{"error":`, want: providerErrorDetails{}},
		{name: "truncated", body: `{"error":{"message":"x"`, want: providerErrorDetails{}},
		{name: "trailing garbage", body: `{"error":{"message":"x"}} garbage`, want: providerErrorDetails{}},
		{name: "second document", body: `{"error":{"message":"x"}} {}`, want: providerErrorDetails{}},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			if got := parseProviderErrorEnvelope([]byte(tc.body)); !reflect.DeepEqual(got, tc.want) {
				t.Fatalf("parseProviderErrorEnvelope() = %#v, want %#v", got, tc.want)
			}
		})
	}
}

func TestProviderErrorTextNormalizationAndLimits(t *testing.T) {
	validIdentifier := strings.Repeat("界", maxProviderErrorIdentifierRunes)
	validMessage := strings.Repeat("界", maxProviderErrorMessageRunes)
	tests := []struct {
		name string
		got  string
		want string
	}{
		{name: "multibyte text", got: "Grüße 世界", want: "Grüße 世界"},
		{name: "invalid UTF-8", got: string([]byte{'a', 0xff, 'b'}), want: "a�b"},
		{name: "whitespace control and format runs", got: " \n\talpha\x00\u200b\u200bbeta \r ", want: "alpha beta"},
		{name: "blank normalization", got: "\t\u200b\n", want: ""},
	}
	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			if got := normalizeProviderErrorText(tc.got); got != tc.want {
				t.Fatalf("normalizeProviderErrorText() = %q, want %q", got, tc.want)
			}
		})
	}

	if got := normalizeProviderErrorIdentifier(validIdentifier); got != validIdentifier {
		t.Fatalf("exact identifier boundary = %q, want retained value", got)
	}
	if got := normalizeProviderErrorIdentifier(validIdentifier + "界"); got != "" {
		t.Fatalf("overlong identifier = %q, want empty", got)
	}
	if got := normalizeProviderErrorMessage(validMessage); got != validMessage {
		t.Fatalf("exact message boundary = %q, want retained value", got)
	}
	wantTruncatedMessage := strings.Repeat("界", maxProviderErrorMessageRunes-1) + "…"
	if got := normalizeProviderErrorMessage(validMessage + "界"); got != wantTruncatedMessage {
		t.Fatalf("overlong message length = %d, want %d", utf8.RuneCountInString(got), maxProviderErrorMessageRunes)
	}
}

func TestProviderHTTPErrorIdentityAndFormatting(t *testing.T) {
	const marker = "provider-secret-marker"
	err := newProviderHTTPError(429, providerErrorDetails{
		providerCode:    marker + "-code",
		providerType:    marker + "-type",
		providerMessage: marker + "-message",
	})

	if err.StatusCode() != 429 || err.ProviderCode() != marker+"-code" || err.ProviderType() != marker+"-type" || err.ProviderMessage() != marker+"-message" {
		t.Fatalf("accessors returned unexpected values: %#v", err)
	}
	if !errors.Is(err, ErrUnexpectedStatus) {
		t.Fatalf("errors.Is(%v, ErrUnexpectedStatus) = false", err)
	}
	for _, rendered := range []string{fmt.Sprintf("%v", err), fmt.Sprintf("%+v", err), fmt.Sprintf("%#v", err)} {
		if rendered != "llm returned non-success status: status=429" {
			t.Fatalf("formatted error = %q", rendered)
		}
		if strings.Contains(rendered, marker) {
			t.Fatalf("formatted error exposed provider marker: %q", rendered)
		}
	}

	var nilError *ProviderHTTPError
	if nilError.StatusCode() != 0 || nilError.ProviderCode() != "" || nilError.ProviderType() != "" || nilError.ProviderMessage() != "" {
		t.Fatal("nil accessors returned provider values")
	}
	if nilError.Error() != "llm returned non-success status" || nilError.GoString() != "llm returned non-success status" || !errors.Is(nilError, ErrUnexpectedStatus) {
		t.Fatalf("nil error behavior is not safe: %v", nilError)
	}

	zero := &ProviderHTTPError{}
	if zero.Error() != "llm returned non-success status" || zero.GoString() != "llm returned non-success status" || !errors.Is(zero, ErrUnexpectedStatus) {
		t.Fatalf("zero error behavior is not safe: %v", zero)
	}
}

func TestProviderHTTPErrorBodyBounds(t *testing.T) {
	const (
		statusCode = 502
		marker     = "provider-body-marker"
	)

	ordinaryBody := `{"error":{"message":"` + marker + `"}}`
	exactLimitBody := ordinaryBody + strings.Repeat(" ", int(maxProviderErrorResponseBytes)-len(ordinaryBody))
	overLimitBody := ordinaryBody + strings.Repeat(" ", int(maxProviderErrorResponseBytes)+1-len(ordinaryBody))
	tests := []struct {
		name          string
		contentLength int64
		reader        io.Reader
		wantRead      int64
		wantMessage   string
	}{
		{
			name:          "recognized envelope",
			contentLength: int64(len(ordinaryBody)),
			reader:        strings.NewReader(ordinaryBody),
			wantRead:      int64(len(ordinaryBody)),
			wantMessage:   marker,
		},
		{
			name:          "exact limit",
			contentLength: maxProviderErrorResponseBytes,
			reader:        strings.NewReader(exactLimitBody),
			wantRead:      maxProviderErrorResponseBytes,
			wantMessage:   marker,
		},
		{
			name:          "declared oversize does not read",
			contentLength: maxProviderErrorResponseBytes + 1,
			reader:        strings.NewReader(ordinaryBody),
			wantRead:      0,
		},
		{
			name:          "unknown length oversize",
			contentLength: -1,
			reader:        strings.NewReader(overLimitBody),
			wantRead:      maxProviderErrorResponseBytes + 1,
		},
		{
			name:          "underreported oversize",
			contentLength: maxProviderErrorResponseBytes,
			reader:        strings.NewReader(overLimitBody),
			wantRead:      maxProviderErrorResponseBytes + 1,
		},
		{
			name:          "read failure",
			contentLength: -1,
			reader:        failingReader{err: errors.New("read failure")},
			wantRead:      0,
		},
		{
			name:          "empty body",
			contentLength: 0,
			reader:        strings.NewReader(""),
			wantRead:      0,
		},
	}

	for _, tc := range tests {
		t.Run(tc.name, func(t *testing.T) {
			reader := &guardedReader{
				reader:    tc.reader,
				remaining: maxProviderErrorResponseBytes + 1,
			}
			err := providerHTTPErrorFromBody(statusCode, tc.contentLength, reader)
			if err == nil || err.StatusCode() != statusCode {
				t.Fatalf("error status = %v, want %d", err, statusCode)
			}
			if reader.bytes != tc.wantRead {
				t.Fatalf("body bytes read = %d, want %d", reader.bytes, tc.wantRead)
			}
			if reader.violated {
				t.Fatal("body reader was asked to read beyond the overflow probe")
			}
			if got := err.ProviderMessage(); got != tc.wantMessage {
				t.Fatalf("provider message = %q, want %q", got, tc.wantMessage)
			}
			if tc.wantMessage == "" {
				if err.ProviderCode() != "" || err.ProviderType() != "" || strings.Contains(err.Error(), marker) {
					t.Fatalf("discarded details were retained: %#v", err)
				}
			}
		})
	}
}