package runtime

import (
	"context"
	"encoding/json"
	"fmt"
	"strings"
	"testing"
	"time"

	"github.com/krow/krow-backend/go-api/internal/authctx"
	"github.com/krow/krow-backend/go-api/internal/gateway"
	"github.com/krow/krow-backend/go-api/internal/tools"
)

// fakeSubagents resolves subagents from a map, and remembers who asked — which
// is how I1 is checked below.
type fakeSubagents struct {
	agents map[string]*Agent
	asked  []string
	ident  authctx.Identity
}

func (f *fakeSubagents) LoadExecutableAgent(_ context.Context, ident authctx.Identity, id string) (*Agent, error) {
	f.asked = append(f.asked, id)
	f.ident = ident
	if a, ok := f.agents[id]; ok {
		return a, nil
	}
	return nil, fmt.Errorf("no agent %q", id)
}

func childAgent() *Agent {
	return &Agent{
		ID: "talent-pool-agent", Name: "Talent Pool Agent", Version: 1,
		Description: "Who is available in the pool.",
		Reasoning:   "balanced",
		Pages:       []string{"talent-pool"},
	}
}

// parentWith returns an agent declaring the given subagents, and a resolver
// that can supply the child.
func parentWith(subs ...string) (*Agent, *fakeSubagents) {
	p := testAgent()
	p.Subagents = subs
	return p, &fakeSubagents{agents: map[string]*Agent{"talent-pool-agent": childAgent()}}
}

func delegationCall(id, tool, question string) gateway.ToolCall {
	return gateway.ToolCall{
		ID: id, Name: tool,
		Input: json.RawMessage(fmt.Sprintf(`{"question":%q}`, question)),
	}
}

// A subagent is offered to the model as a tool. Before this, `subagents:`
// parsed, loaded, and was dropped — the model was never told the agent existed.
func TestDelegationOffersSubagentsAsTools(t *testing.T) {
	parent, res := parentWith("talent-pool-agent")
	gw := &scriptedGateway{}
	exec := NewModelExecutor(gw, &MemorySink{}, tools.NewRegistry()).WithSubagents(res)

	if _, err := exec.ExecuteAgent(context.Background(), parent, testInput("who is free?")); err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(gw.seen) == 0 {
		t.Fatal("the model was never called")
	}
	var names []string
	for _, td := range gw.seen[0].Tools {
		names = append(names, td.Name)
	}
	want := delegationToolName("talent-pool-agent")
	if len(names) != 1 || names[0] != want {
		t.Fatalf("offered tools = %v, want exactly [%s]", names, want)
	}
	if len(res.asked) != 1 {
		t.Errorf("the resolver was asked %d times, want 1 — subagents resolve once per run", len(res.asked))
	}
}

// Without a resolver, delegation is off and the agent runs alone. This is the
// behaviour every deployment had, and it must stay a quiet degrade rather than
// a failure.
func TestDelegationIsOffWithoutAResolver(t *testing.T) {
	parent, _ := parentWith("talent-pool-agent")
	gw := &scriptedGateway{}
	exec := NewModelExecutor(gw, &MemorySink{}, tools.NewRegistry())

	res, err := exec.ExecuteAgent(context.Background(), parent, testInput("who is free?"))
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if res.Termination != TerminationCompleted {
		t.Errorf("Termination = %q, want Completed", res.Termination)
	}
	if len(gw.seen[0].Tools) != 0 {
		t.Errorf("offered %d tools with no resolver, want 0", len(gw.seen[0].Tools))
	}
}

// The subagent runs, its answer reaches the parent's model, and it writes its
// OWN trajectory linked by parent_run_id (§6).
func TestDelegationRunsTheSubagentAndLinksItsTrajectory(t *testing.T) {
	parent, resolver := parentWith("talent-pool-agent")
	tool := delegationToolName("talent-pool-agent")

	gw := &scriptedGateway{steps: []*gateway.Response{
		// parent asks
		{ToolCalls: []gateway.ToolCall{delegationCall("c1", tool, "who is available?")},
			StopReason: "tool_use", Model: "fake-model"},
		// child answers
		{Text: "Five workers are available.", StopReason: "end_turn", Model: "fake-model"},
		// parent answers from it
		{Text: "Five are free this week.", StopReason: "end_turn", Model: "fake-model"},
	}}
	sink := &MemorySink{}
	exec := NewModelExecutor(gw, sink, tools.NewRegistry()).WithSubagents(resolver)

	res, err := exec.ExecuteAgent(context.Background(), parent, testInput("who is free?"))
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if res.Termination != TerminationCompleted || res.Output != "Five are free this week." {
		t.Fatalf("Termination=%q Output=%q", res.Termination, res.Output)
	}

	if len(sink.Runs) != 2 {
		t.Fatalf("%d trajectories saved, want 2 — the subagent gets its own", len(sink.Runs))
	}
	var child, root *Trajectory
	for _, tr := range sink.Runs {
		if tr.AgentID == "talent-pool-agent" {
			child = tr
		} else {
			root = tr
		}
	}
	if child == nil || root == nil {
		t.Fatal("expected one trajectory per agent")
	}
	// ORDER MATTERS, and a MemorySink will not tell you so on its own.
	// agent_runs.parent_run_id is a foreign key, and a subagent finishes
	// before the run that delegated to it — so saving in completion order
	// makes every child insert name a parent row that does not exist yet. The
	// database refuses it, finish does not fail a run over a sink error, and
	// every delegated trajectory disappears without trace. Parent first.
	if sink.Runs[0].AgentID != root.AgentID {
		t.Errorf("saved %q first, want the parent %q — a child written before its "+
			"parent violates the parent_run_id foreign key and is silently dropped",
			sink.Runs[0].AgentID, root.AgentID)
	}
	if child.ParentRunID != root.RunID {
		t.Errorf("child.ParentRunID = %q, want the parent's run id %q", child.ParentRunID, root.RunID)
	}
	if root.ParentRunID != "" {
		t.Errorf("the root run has ParentRunID %q, want empty", root.ParentRunID)
	}

	// The parent's model must actually have received the child's answer.
	last := gw.seen[len(gw.seen)-1]
	var sawAnswer bool
	for _, msg := range last.Messages {
		for _, tr := range msg.ToolResults {
			if strings.Contains(tr.Content, "Five workers are available.") {
				sawAnswer = true
			}
		}
	}
	if !sawAnswer {
		t.Error("the subagent's answer never reached the parent's model")
	}
}

// §6, and the reason delegation cannot be a way to buy more budget.
//
// MaxSteps is 1. The parent spends it, then delegates. If the subagent got a
// FRESH budget it would have a step of its own and answer; sharing the
// parent's means it has nothing left and terminates BudgetExceeded. The
// assertion is on the child's termination, which differs between the two
// designs and cannot be produced by accident.
func TestDelegationSharesTheParentsBudget(t *testing.T) {
	parent, resolver := parentWith("talent-pool-agent")
	tool := delegationToolName("talent-pool-agent")

	gw := &scriptedGateway{steps: []*gateway.Response{
		{ToolCalls: []gateway.ToolCall{delegationCall("c1", tool, "who is available?")},
			StopReason: "tool_use", Model: "fake-model"},
		{Text: "the child should never get this far", StopReason: "end_turn", Model: "fake-model"},
	}}
	sink := &MemorySink{}
	exec := NewModelExecutor(gw, sink, tools.NewRegistry()).WithSubagents(resolver)

	// The parent exhausts the budget too and finish returns an error with its
	// result; that is expected here and not what this test is about.
	_, _ = exec.executeRun(context.Background(), parent, testInput("who is free?"),
		Limits{MaxSteps: 1, MaxToolCalls: 5, MaxTokens: 100_000, Deadline: 30 * time.Second},
		delegation{})

	var child *Trajectory
	for _, tr := range sink.Runs {
		if tr.AgentID == "talent-pool-agent" {
			child = tr
		}
	}
	if child == nil {
		t.Fatal("the subagent never ran")
	}
	if child.Termination != TerminationBudgetExceeded {
		t.Errorf("child Termination = %q, want BudgetExceeded — it was given a fresh budget "+
			"instead of sharing its parent's, which §6 forbids", child.Termination)
	}
}

// I1: a subagent executes as the ORIGINAL caller and never a widened one.
func TestDelegationRunsAsTheOriginalCaller(t *testing.T) {
	parent, resolver := parentWith("talent-pool-agent")
	gw := &scriptedGateway{}
	exec := NewModelExecutor(gw, &MemorySink{}, tools.NewRegistry()).WithSubagents(resolver)

	in := testInput("who is free?")
	if _, err := exec.ExecuteAgent(context.Background(), parent, in); err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if resolver.ident.UserID != in.Identity.UserID || resolver.ident.OrgID != in.Identity.OrgID {
		t.Errorf("subagent resolved as %+v, want the caller %+v", resolver.ident, in.Identity)
	}
}

// §3's depth cap. At the cap, no subagent is offered at all, so a cycle in the
// spec graph is bounded rather than unbounded.
func TestDelegationCapsDepth(t *testing.T) {
	parent, resolver := parentWith("talent-pool-agent")
	gw := &scriptedGateway{}
	sink := &MemorySink{}
	exec := NewModelExecutor(gw, sink, tools.NewRegistry()).WithSubagents(resolver)

	_, err := exec.executeRun(context.Background(), parent, testInput("who is free?"),
		LimitsForTier("balanced"), delegation{depth: MaxDelegationDepth})
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(gw.seen[0].Tools) != 0 {
		t.Errorf("offered %d tools at depth %d, want 0", len(gw.seen[0].Tools), MaxDelegationDepth)
	}
	if len(resolver.asked) != 0 {
		t.Errorf("resolved %d subagents at the cap, want 0 — the cap should short-circuit "+
			"before loading anything", len(resolver.asked))
	}
	// And it must be visible, not silent.
	if !hasError(sink.Last(), "runtime.delegation_depth") {
		t.Error("hitting the depth cap was not recorded in the trajectory")
	}
}

// An agent naming itself is refused before the model is offered the call: the
// database has a no-self-parent constraint, and a run that tried would fail on
// insert rather than on anything legible.
func TestDelegationRefusesSelfReference(t *testing.T) {
	parent := testAgent()
	parent.Subagents = []string{parent.ID}
	resolver := &fakeSubagents{agents: map[string]*Agent{}}

	gw := &scriptedGateway{}
	sink := &MemorySink{}
	exec := NewModelExecutor(gw, sink, tools.NewRegistry()).WithSubagents(resolver)

	if _, err := exec.ExecuteAgent(context.Background(), parent, testInput("hello")); err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if len(gw.seen[0].Tools) != 0 {
		t.Errorf("a self-referencing subagent was offered as a tool")
	}
	if !hasError(sink.Last(), "runtime.subagent_self") {
		t.Error("the self-reference was not recorded")
	}
}

// A subagent that cannot be loaded degrades rather than failing the run — the
// same rule as an unknown tool — but is recorded so somebody can fix the spec.
func TestDelegationRecordsAnUnloadableSubagent(t *testing.T) {
	parent := testAgent()
	parent.Subagents = []string{"no-such-agent"}
	resolver := &fakeSubagents{agents: map[string]*Agent{}}

	gw := &scriptedGateway{}
	sink := &MemorySink{}
	exec := NewModelExecutor(gw, sink, tools.NewRegistry()).WithSubagents(resolver)

	res, err := exec.ExecuteAgent(context.Background(), parent, testInput("hello"))
	if err != nil {
		t.Fatalf("unexpected error: %v", err)
	}
	if res.Termination != TerminationCompleted {
		t.Errorf("Termination = %q, want Completed — an unloadable subagent degrades", res.Termination)
	}
	if !hasError(sink.Last(), "runtime.unknown_subagent") {
		t.Error("the unloadable subagent was not recorded")
	}
}

// I4 survives delegation. A write a SUBAGENT wants approved still stops
// everything and asks a person — it does not get performed because it happened
// one level down.
func TestSubagentConfirmationStopsTheParentRun(t *testing.T) {
	writeTool := tools.Tool{
		Name:        "assign_worker",
		Description: "Assigns a worker to a shift, which is a real change to a real rota.",
		InputSchema: map[string]any{"type": "object"},
		Effect:      tools.EffectWrite,
		Confirm: func(context.Context, tools.Context, json.RawMessage) (*tools.Confirmation, *tools.Result) {
			return &tools.Confirmation{Token: "tok_1", Tool: "assign_worker", Title: "Assign Maya to Bar"}, nil
		},
		Handler: func(context.Context, tools.Context, json.RawMessage) tools.Result {
			t.Error("the write ran without approval")
			return tools.OK(map[string]any{})
		},
	}
	reg := tools.NewRegistry()
	reg.MustRegister(writeTool)

	child := childAgent()
	child.Tools = []string{"assign_worker"}
	parent := testAgent()
	parent.Subagents = []string{child.ID}
	resolver := &fakeSubagents{agents: map[string]*Agent{child.ID: child}}

	tool := delegationToolName(child.ID)
	gw := &scriptedGateway{steps: []*gateway.Response{
		{ToolCalls: []gateway.ToolCall{delegationCall("c1", tool, "assign Maya")},
			StopReason: "tool_use", Model: "fake-model"},
		{ToolCalls: []gateway.ToolCall{{ID: "c2", Name: "assign_worker", Input: json.RawMessage(`{}`)}},
			StopReason: "tool_use", Model: "fake-model"},
	}}
	exec := NewModelExecutor(gw, &MemorySink{}, reg).WithSubagents(resolver)

	// The error beside the result is how the loop reports every termination
	// that is not Completed; ConfirmationPending is not a failure and the
	// existing confirmation tests ignore it the same way.
	res, _ := exec.ExecuteAgent(context.Background(), parent, testInput("assign someone"))
	if res.Termination != TerminationConfirmationPending {
		t.Fatalf("Termination = %q, want ConfirmationPending — a subagent's write must "+
			"still stop and ask", res.Termination)
	}
	if len(res.Confirmations) != 1 || res.Confirmations[0].Tool != "assign_worker" {
		t.Fatalf("Confirmations = %+v, want the subagent's pending write", res.Confirmations)
	}
}

// hasError reports whether a trajectory recorded an entry with the given code.
func hasError(tr *Trajectory, code string) bool {
	if tr == nil {
		return false
	}
	for _, e := range tr.Entries {
		if strings.Contains(fmt.Sprint(e), code) {
			return true
		}
	}
	return false
}