package gateway

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"net/http"
	"net/http/httptest"
	"strings"
	"testing"
)

// sse stands up an endpoint that replays the given event lines.
func sse(t *testing.T, events ...string) *OpenAIGateway {
	t.Helper()
	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Content-Type", "text/event-stream")
		for _, e := range events {
			_, _ = io.WriteString(w, e+"\n")
		}
	}))
	t.Cleanup(srv.Close)
	return NewOpenAI(Config{
		APIKey:   "test-key",
		BaseURL:  srv.URL,
		Balanced: Routing{Model: "m-balanced", Effort: EffortHigh},
	})
}

func TestStreamDeliversTextAsItArrives(t *testing.T) {
	gw := sse(t,
		`data: {"model":"m-1","choices":[{"delta":{"content":"Three "}}]}`,
		`data: {"choices":[{"delta":{"content":"are "}}]}`,
		`data: {"choices":[{"delta":{"content":"free."},"finish_reason":"stop"}]}`,
		`data: {"choices":[],"usage":{"prompt_tokens":40,"completion_tokens":4}}`,
		`data: [DONE]`,
	)

	var deltas []string
	resp, err := gw.Stream(context.Background(), ask("who is free?"), func(d string) {
		deltas = append(deltas, d)
	})
	if err != nil {
		t.Fatalf("Stream: %v", err)
	}

	if strings.Join(deltas, "") != "Three are free." {
		t.Errorf("deltas joined to %q", strings.Join(deltas, ""))
	}
	if len(deltas) != 3 {
		t.Errorf("got %d deltas, want 3 — text must arrive in fragments, not in one lump", len(deltas))
	}
	if resp.Text != "Three are free." {
		t.Errorf("Text = %q", resp.Text)
	}
	// Usage arrives in a trailing chunk with no choices. Missing it would mean
	// a streamed run cost nothing on the ledger, and I3 cannot enforce a budget
	// it cannot measure.
	if resp.Usage.Total() != 44 {
		t.Errorf("Usage.Total() = %d, want 44 — the trailing usage chunk was dropped", resp.Usage.Total())
	}
	if resp.StopReason != "end_turn" {
		t.Errorf("StopReason = %q", resp.StopReason)
	}
}

// THE ONE THAT IS EASY TO GET WRONG.
//
// Providers interleave the fragments of parallel tool calls, so arrival order
// is not call order. Appending fragments as they land splices one call's
// arguments onto another's — producing two calls that are each valid JSON and
// both wrong, which is the worst possible failure: the tools run, with the
// wrong inputs, and nothing errors.
func TestStreamAccumulatesInterleavedToolCallsByIndex(t *testing.T) {
	gw := sse(t,
		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_a","function":{"name":"find_workers","arguments":"{\"day\""}}]}}]}`,
		`data: {"choices":[{"delta":{"tool_calls":[{"index":1,"id":"call_b","function":{"name":"open_shifts","arguments":"{\"week\""}}]}}]}`,
		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"arguments":":\"friday\"}"}}]}}]}`,
		`data: {"choices":[{"delta":{"tool_calls":[{"index":1,"function":{"arguments":":\"next\"}"}}]}}]}`,
		`data: {"choices":[{"delta":{},"finish_reason":"tool_calls"}]}`,
		`data: [DONE]`,
	)

	resp, err := gw.Stream(context.Background(), ask("cover friday"), nil)
	if err != nil {
		t.Fatalf("Stream: %v", err)
	}
	if len(resp.ToolCalls) != 2 {
		t.Fatalf("got %d tool calls, want 2: %+v", len(resp.ToolCalls), resp.ToolCalls)
	}

	want := []struct{ id, name, day string }{
		{"call_a", "find_workers", "friday"},
		{"call_b", "open_shifts", "next"},
	}
	for i, w := range want {
		got := resp.ToolCalls[i]
		if got.ID != w.id || got.Name != w.name {
			t.Errorf("call %d = {%s %s}, want {%s %s}", i, got.ID, got.Name, w.id, w.name)
		}
		// Each must be valid JSON on its own. A spliced pair usually is too,
		// which is exactly why the value is asserted and not just the parse.
		var args map[string]string
		if err := json.Unmarshal(got.Input, &args); err != nil {
			t.Fatalf("call %d input %q is not valid JSON: %v", i, got.Input, err)
		}
		if len(args) != 1 {
			t.Errorf("call %d carried %d args, want 1 — fragments from another call were spliced in: %v",
				i, len(args), args)
		}
		for _, v := range args {
			if v != w.day {
				t.Errorf("call %d arg = %q, want %q", i, v, w.day)
			}
		}
	}
	if resp.StopReason != "tool_use" {
		t.Errorf("StopReason = %q, want tool_use", resp.StopReason)
	}
}

// A tool call is buffered until the stream closes: a half-built argument object
// is not a smaller version of the finished one, and dispatching on it would run
// a tool with arguments the model had not finished choosing.
func TestStreamNeverEmitsPartialToolArguments(t *testing.T) {
	gw := sse(t,
		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"c","function":{"name":"t","arguments":"{\"a\":"}}]}}]}`,
		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"arguments":"1}"}}]}}]}`,
		`data: {"choices":[{"delta":{},"finish_reason":"tool_calls"}]}`,
		`data: [DONE]`,
	)

	var streamed strings.Builder
	resp, err := gw.Stream(context.Background(), ask("go"), func(d string) { streamed.WriteString(d) })
	if err != nil {
		t.Fatalf("Stream: %v", err)
	}
	if streamed.String() != "" {
		t.Errorf("tool-call JSON reached the reader as text: %q", streamed.String())
	}
	if string(resp.ToolCalls[0].Input) != `{"a":1}` {
		t.Errorf("Input = %q, want the assembled object", resp.ToolCalls[0].Input)
	}
}

// Keep-alives, comment lines and provider-specific events are not failures. A
// stream that died on one would fail against providers that are working fine.
func TestStreamIgnoresNoiseEvents(t *testing.T) {
	gw := sse(t,
		`: keep-alive`,
		``,
		`event: ping`,
		`data: {"not":"a chunk"`,
		`data:{"choices":[{"delta":{"content":"ok"},"finish_reason":"stop"}]}`,
		`data: [DONE]`,
	)

	resp, err := gw.Stream(context.Background(), ask("hi"), nil)
	if err != nil {
		t.Fatalf("Stream: %v", err)
	}
	if resp.Text != "ok" {
		t.Errorf("Text = %q, want ok", resp.Text)
	}
}

// A streamed refusal must come back as the same structured outcome the
// non-streaming path produces, and must not be shown to the reader as though
// it were the answer.
func TestStreamRefusalIsNotShownToTheReader(t *testing.T) {
	gw := sse(t,
		`data: {"choices":[{"delta":{"refusal":"I cannot help with that."},"finish_reason":"stop"}]}`,
		`data: [DONE]`,
	)

	var streamed strings.Builder
	_, err := gw.Stream(context.Background(), ask("do something disallowed"),
		func(d string) { streamed.WriteString(d) })

	var gwErr *Error
	if !errors.As(err, &gwErr) || gwErr.Code != CodeRefused {
		t.Fatalf("err = %v, want a %s", err, CodeRefused)
	}
	if streamed.String() != "" {
		t.Errorf("a refusal was streamed to the reader as an answer: %q", streamed.String())
	}
}

// StreamComplete has to reach the streaming path for a gateway that has one.
// The fallback exists for gateways that do not, and silently taking it here
// would turn every streamed answer into one lump with no error to trace it to.
func TestStreamCompleteUsesTheStreamingPath(t *testing.T) {
	gw := sse(t,
		`data: {"choices":[{"delta":{"content":"a"}}]}`,
		`data: {"choices":[{"delta":{"content":"b"},"finish_reason":"stop"}]}`,
		`data: [DONE]`,
	)

	var deltas int
	resp, err := StreamComplete(context.Background(), gw, ask("hi"), func(string) { deltas++ })
	if err != nil {
		t.Fatalf("StreamComplete: %v", err)
	}
	if deltas != 2 {
		t.Errorf("got %d deltas, want 2 — the non-streaming fallback was taken", deltas)
	}
	if resp.Text != "ab" {
		t.Errorf("Text = %q", resp.Text)
	}
}

// The streamed shape of TestToolCallProviderMetadataIsRoundTripped: the
// metadata arrives on one fragment, and later fragments that carry only
// argument text must not erase it.
func TestStreamKeepsToolCallProviderMetadata(t *testing.T) {
	const sig = `{"google":{"thought_signature":"El4KXAFpFH0T4CM3"}}`
	acc, err := accumulateSSE(strings.NewReader(strings.Join([]string{
		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"id":"call_a","function":{"name":"open_positions","arguments":""},"extra_content":` + sig + `}]}}]}`,
		`data: {"choices":[{"delta":{"tool_calls":[{"index":0,"function":{"arguments":"{}"}}]}}]}`,
		`data: {"choices":[{"delta":{},"finish_reason":"tool_calls"}]}`,
		`data: [DONE]`,
	}, "\n\n")), func(string) {})
	if err != nil {
		t.Fatalf("accumulateSSE: %v", err)
	}
	msg := acc.message()
	if len(msg.ToolCalls) != 1 {
		t.Fatalf("got %d tool calls, want 1", len(msg.ToolCalls))
	}
	if string(msg.ToolCalls[0].ExtraContent) != sig {
		t.Errorf("extra_content after streaming = %s, want %s", msg.ToolCalls[0].ExtraContent, sig)
	}
	if msg.ToolCalls[0].Function.Arguments != "{}" {
		t.Errorf("arguments = %q, want {}", msg.ToolCalls[0].Function.Arguments)
	}
}