package gateway

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

// serve stands up a fake OpenAI-compatible endpoint and returns a gateway
// pointed at it, plus a pointer to the last request body it received.
func serve(t *testing.T, handler func(w http.ResponseWriter, body *oaiRequest)) (*OpenAIGateway, *oaiRequest) {
	t.Helper()
	var captured oaiRequest

	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		raw, _ := io.ReadAll(r.Body)
		if err := json.Unmarshal(raw, &captured); err != nil {
			t.Errorf("request body was not valid JSON: %v", err)
		}
		handler(w, &captured)
	}))
	t.Cleanup(srv.Close)

	gw := NewOpenAI(Config{
		Provider:        ProviderOpenAI,
		APIKey:          "test-key",
		BaseURL:         srv.URL,
		Fast:            Routing{Model: "m-fast", Effort: EffortLow},
		Balanced:        Routing{Model: "m-balanced", Effort: EffortHigh},
		Deep:            Routing{Model: "m-deep", Effort: EffortXhigh},
		MaxOutputTokens: 4096,
	})
	return gw, &captured
}

func ask(text string) Request {
	return Request{Tier: TierBalanced, Messages: []Message{{Role: RoleUser, Text: text}}}
}

// THE REGRESSION THIS FILE EXISTS FOR.
//
// OpenAI reports prompt_tokens INCLUSIVE of the cached prefix; Anthropic
// reports input tokens EXCLUSIVE of it. Usage.Total() adds all four fields, so
// copying both numbers across verbatim bills the cached prefix twice — and it
// does it worst on long conversations, which is exactly where I3's budget
// matters most. A wrong total here is invisible: the run still answers, it just
// terminates BudgetExceeded earlier than it should.
func TestUsageDoesNotDoubleCountCachedTokens(t *testing.T) {
	usage := oaiUsage{PromptTokens: 1000, CompletionTokens: 200}
	usage.PromptTokensDetails.CachedTokens = 800

	got := usage.normalise()

	if got.InputTokens != 200 {
		t.Errorf("InputTokens = %d, want 200 (1000 prompt less 800 cached)", got.InputTokens)
	}
	if got.CacheReadTokens != 800 {
		t.Errorf("CacheReadTokens = %d, want 800", got.CacheReadTokens)
	}
	if got.Total() != 1200 {
		t.Errorf("Total() = %d, want 1200 — the wire billed 1000 prompt + 200 output, "+
			"and anything higher is the cached prefix counted twice", got.Total())
	}
}

// A provider reporting more cached tokens than prompt tokens is wrong, but the
// failure must not hand the run free budget: a negative charge would reduce the
// total, which is the one direction a bug must never go.
func TestUsageClampsImpossibleCacheReport(t *testing.T) {
	usage := oaiUsage{PromptTokens: 100, CompletionTokens: 10}
	usage.PromptTokensDetails.CachedTokens = 500

	got := usage.normalise()
	if got.InputTokens < 0 {
		t.Fatalf("InputTokens = %d, want no negative charge", got.InputTokens)
	}
	if got.Total() < got.OutputTokens {
		t.Errorf("Total() = %d is below OutputTokens = %d", got.Total(), got.OutputTokens)
	}
}

// Tool results are blocks inside one user turn on the Anthropic wire and
// standalone role:"tool" messages here. Getting the split wrong detaches a
// result from the call it answers, which most providers reject outright and
// some silently mis-attribute.
func TestEncodeMessagesSplitsToolResults(t *testing.T) {
	msgs := []Message{
		{Role: RoleUser, Text: "who is free friday?"},
		{Role: RoleAssistant, ToolCalls: []ToolCall{
			{ID: "call_1", Name: "find_workers", Input: json.RawMessage(`{"day":"friday"}`)},
			{ID: "call_2", Name: "open_shifts", Input: json.RawMessage(`{}`)},
		}},
		{Role: RoleUser, ToolResults: []ToolResult{
			{CallID: "call_1", Content: `{"workers":3}`},
			{CallID: "call_2", Content: `{"shifts":1}`},
		}},
	}

	got := encodeOpenAIMessages("you are a scheduler", msgs)

	wantRoles := []string{"system", "user", "assistant", "tool", "tool"}
	if len(got) != len(wantRoles) {
		t.Fatalf("got %d messages, want %d: %+v", len(got), len(wantRoles), got)
	}
	for i, want := range wantRoles {
		if got[i].Role != want {
			t.Errorf("messages[%d].Role = %q, want %q", i, got[i].Role, want)
		}
	}
	if got[0].Content != "you are a scheduler" {
		t.Errorf("system message = %q", got[0].Content)
	}
	if len(got[2].ToolCalls) != 2 {
		t.Fatalf("assistant turn carried %d tool calls, want 2", len(got[2].ToolCalls))
	}
	// The call id is the model's own handle. A result carrying a different one
	// is a result attached to the wrong question.
	if got[3].ToolCallID != "call_1" || got[4].ToolCallID != "call_2" {
		t.Errorf("tool results correlated to %q and %q, want call_1 and call_2",
			got[3].ToolCallID, got[4].ToolCallID)
	}
}

// A turn that is only tool results carries no text, and dropping it would strip
// every answer the tools produced.
func TestEncodeMessagesKeepsResultOnlyTurn(t *testing.T) {
	got := encodeOpenAIMessages("", []Message{
		{Role: RoleUser, Text: "hi"},
		{Role: RoleUser, ToolResults: []ToolResult{{CallID: "c1", Content: "{}"}}},
	})
	if len(got) != 2 || got[1].Role != "tool" {
		t.Fatalf("result-only turn was not encoded: %+v", got)
	}
}

func TestCompleteDecodesTextAndUsage(t *testing.T) {
	gw, captured := serve(t, func(w http.ResponseWriter, _ *oaiRequest) {
		_, _ = io.WriteString(w, `{
			"model":"m-balanced-0625",
			"choices":[{"message":{"role":"assistant","content":"Three are free."},
			            "finish_reason":"stop"}],
			"usage":{"prompt_tokens":120,"completion_tokens":8}
		}`)
	})

	resp, err := gw.Complete(context.Background(), ask("who is free?"))
	if err != nil {
		t.Fatalf("Complete: %v", err)
	}
	if resp.Text != "Three are free." {
		t.Errorf("Text = %q", resp.Text)
	}
	// The id ACTUALLY used, not the tier that was asked for — a change of
	// routing has to be visible in the trajectory rather than inferred.
	if resp.Model != "m-balanced-0625" {
		t.Errorf("Model = %q, want the id the provider reported", resp.Model)
	}
	if resp.StopReason != "end_turn" {
		t.Errorf("StopReason = %q, want end_turn", resp.StopReason)
	}
	if resp.Usage.Total() != 128 {
		t.Errorf("Usage.Total() = %d, want 128", resp.Usage.Total())
	}
	if captured.Model != "m-balanced" {
		t.Errorf("requested model = %q, want the balanced tier's", captured.Model)
	}
}

func TestCompleteDecodesToolCalls(t *testing.T) {
	gw, _ := serve(t, func(w http.ResponseWriter, _ *oaiRequest) {
		_, _ = io.WriteString(w, `{
			"choices":[{"message":{"role":"assistant","tool_calls":[
				{"id":"call_x","type":"function",
				 "function":{"name":"find_workers","arguments":"{\"day\":\"friday\"}"}}]},
			 "finish_reason":"tool_calls"}],
			"usage":{"prompt_tokens":10,"completion_tokens":5}
		}`)
	})

	resp, err := gw.Complete(context.Background(), ask("who is free?"))
	if err != nil {
		t.Fatalf("Complete: %v", err)
	}
	if len(resp.ToolCalls) != 1 {
		t.Fatalf("got %d tool calls, want 1", len(resp.ToolCalls))
	}
	call := resp.ToolCalls[0]
	if call.ID != "call_x" || call.Name != "find_workers" {
		t.Errorf("call = %+v", call)
	}
	// The loop branches on len(ToolCalls), but the trajectory records the stop
	// reason, and it has to read the same as the Anthropic path's.
	if resp.StopReason != "tool_use" {
		t.Errorf("StopReason = %q, want tool_use", resp.StopReason)
	}
	var args map[string]string
	if err := json.Unmarshal(call.Input, &args); err != nil {
		t.Fatalf("tool input was not valid JSON: %v", err)
	}
	if args["day"] != "friday" {
		t.Errorf("args = %v", args)
	}
}

// An argumentless call arrives as "" on this wire, which is not valid JSON. The
// handler's decoder would reject it for a reason that has nothing to do with
// the request.
func TestEmptyToolArgumentsBecomeEmptyObject(t *testing.T) {
	gw, _ := serve(t, func(w http.ResponseWriter, _ *oaiRequest) {
		_, _ = io.WriteString(w, `{"choices":[{"message":{"tool_calls":[
			{"id":"c1","function":{"name":"workspace_summary","arguments":""}}]},
			"finish_reason":"tool_calls"}]}`)
	})

	resp, err := gw.Complete(context.Background(), ask("summarise"))
	if err != nil {
		t.Fatalf("Complete: %v", err)
	}
	if string(resp.ToolCalls[0].Input) != "{}" {
		t.Errorf("Input = %q, want {}", resp.ToolCalls[0].Input)
	}
}

// A refusal is a successful HTTP response and one of the six terminations. It
// is still billed: a refusal that cost nothing on the ledger is one the loop
// would happily repeat.
func TestRefusalIsStructuredAndStillBilled(t *testing.T) {
	gw, _ := serve(t, func(w http.ResponseWriter, _ *oaiRequest) {
		_, _ = io.WriteString(w, `{"choices":[{"message":{"role":"assistant",
			"refusal":"I cannot help with that."},"finish_reason":"stop"}],
			"usage":{"prompt_tokens":50,"completion_tokens":6}}`)
	})

	resp, err := gw.Complete(context.Background(), ask("do something disallowed"))

	var gwErr *Error
	if !errors.As(err, &gwErr) || gwErr.Code != CodeRefused {
		t.Fatalf("err = %v, want a %s", err, CodeRefused)
	}
	if gwErr.Retryable() {
		t.Error("a refusal must not be retryable — re-sending it burns the budget on one turn")
	}
	if resp == nil {
		t.Fatal("a refusal must still carry its usage")
	}
	if resp.Usage.Total() != 56 {
		t.Errorf("Usage.Total() = %d, want 56", resp.Usage.Total())
	}
}

func TestErrorsMapToRetryability(t *testing.T) {
	cases := []struct {
		status    int
		wantCode  string
		retryable bool
	}{
		{400, CodeInvalidRequest, false},
		// A model id that does not exist on this endpoint is a configuration
		// mistake and will fail identically next time.
		{404, CodeInvalidRequest, false},
		{401, CodeUnauthorized, false},
		{429, CodeRateLimited, true},
		{500, CodeUpstream, true},
		{503, CodeUpstream, true},
	}
	for _, c := range cases {
		err := translateOpenAI(c.status, []byte(`{"error":{"message":"upstream detail"}}`))
		var gwErr *Error
		if !errors.As(err, &gwErr) {
			t.Fatalf("http %d: not a gateway error", c.status)
		}
		if gwErr.Code != c.wantCode {
			t.Errorf("http %d: code = %s, want %s", c.status, gwErr.Code, c.wantCode)
		}
		if gwErr.Retryable() != c.retryable {
			t.Errorf("http %d: Retryable() = %v, want %v", c.status, gwErr.Retryable(), c.retryable)
		}
		// The upstream reason has to survive: the trajectory records only the
		// message, and "the model call failed" costs an hour to diagnose.
		if !strings.Contains(gwErr.Message, "upstream detail") {
			t.Errorf("http %d: message %q dropped the upstream detail", c.status, gwErr.Message)
		}
	}
}

// Most non-reasoning models reject the whole request rather than ignoring an
// unknown key, so the field must be absent unless a deployment opted in.
func TestReasoningEffortIsOptIn(t *testing.T) {
	gw, captured := serve(t, func(w http.ResponseWriter, _ *oaiRequest) {
		_, _ = io.WriteString(w, `{"choices":[{"message":{"content":"ok"},"finish_reason":"stop"}]}`)
	})
	if _, err := gw.Complete(context.Background(), ask("hi")); err != nil {
		t.Fatalf("Complete: %v", err)
	}
	if captured.ReasoningEffort != "" {
		t.Errorf("reasoning_effort = %q, want it omitted by default", captured.ReasoningEffort)
	}

	gw.cfg.SendReasoningEffort = true
	if _, err := gw.Complete(context.Background(), Request{
		Tier: TierDeep, Messages: []Message{{Role: RoleUser, Text: "hi"}},
	}); err != nil {
		t.Fatalf("Complete: %v", err)
	}
	// Ordering preserved, not spelling: their scale runs minimal/low/medium/
	// high, so the platform's xhigh is their high.
	if captured.ReasoningEffort != "high" {
		t.Errorf("deep tier sent reasoning_effort = %q, want high", captured.ReasoningEffort)
	}
}

// A local model needs no credential. Requiring one would make the zero-cost
// development path impossible to configure.
func TestLocalEndpointNeedsNoCredential(t *testing.T) {
	local := NewOpenAI(Config{BaseURL: "http://localhost:11434/v1"})
	if local.needsCredential() {
		t.Error("a localhost endpoint must not require a key")
	}
	hosted := NewOpenAI(Config{BaseURL: "https://api.groq.com/openai/v1"})
	if !hosted.needsCredential() {
		t.Error("a hosted endpoint must require a key")
	}
	if _, err := NewOpenAI(Config{BaseURL: "https://api.groq.com/openai/v1"}).
		Complete(context.Background(), ask("hi")); err == nil {
		t.Error("a hosted call without a key must fail as NotConfigured")
	}
}

func TestBaseURLDefaultsAndTrimsSlash(t *testing.T) {
	if got := NewOpenAI(Config{}).endpoint(); got != DefaultOpenAIBaseURL+"/chat/completions" {
		t.Errorf("endpoint = %q", got)
	}
	if got := NewOpenAI(Config{BaseURL: "https://x.test/v1/"}).endpoint(); got != "https://x.test/v1/chat/completions" {
		t.Errorf("endpoint = %q, want the trailing slash collapsed", got)
	}
}