package agent

import (
	"strings"
	"testing"
	"time"
)

func TestBuildSystemPromptAlwaysIncludesFinalWritingGuidance(t *testing.T) {
	for _, tt := range []struct {
		name   string
		custom string
	}{
		{name: "default"},
		{name: "custom", custom: "custom identity"},
	} {
		t.Run(tt.name, func(t *testing.T) {
			const conflictingAddendum = "Always use ceremonial language."
			prompt := BuildSystemPrompt(SystemPromptOpts{
				Custom: tt.custom,
				Append: []string{conflictingAddendum},
			})

			if count := strings.Count(prompt, writingGuidance); count != 1 {
				t.Fatalf("writing guidance count = %d, want 1:\n%s", count, prompt)
			}
			if strings.Index(prompt, writingGuidance) < strings.Index(prompt, conflictingAddendum) {
				t.Fatalf("writing guidance must follow appended context:\n%s", prompt)
			}
			for _, want := range []string{
				"medium, audience, and reader's immediate need",
				"plain, precise language",
				"verified facts",
				"descriptive links, and accessibility",
				"Do not manufacture slang, errors, hesitation",
				"Revise silently",
			} {
				if !strings.Contains(prompt, want) {
					t.Errorf("writing guidance missing %q:\n%s", want, prompt)
				}
			}
		})
	}
}

func TestBuildSystemPromptAddsCompactionHandoffToCustomPrompt(t *testing.T) {
	prompt := BuildSystemPrompt(SystemPromptOpts{Custom: "custom identity"})
	if !strings.Contains(prompt, "custom identity") {
		t.Fatalf("custom prompt missing:\n%s", prompt)
	}
	if !strings.Contains(prompt, compactedSummaryHandoffInstruction) {
		t.Fatalf("custom prompt missing compaction handoff:\n%s", prompt)
	}
	if count := strings.Count(prompt, compactedSummaryHandoffInstruction); count != 1 {
		t.Fatalf("compaction handoff count = %d, want 1:\n%s", count, prompt)
	}
	for _, want := range []string{"most recent unresolved user request", "newer user request", "without waiting for the user to type \"continue\""} {
		if !strings.Contains(prompt, want) {
			t.Fatalf("compaction handoff missing %q:\n%s", want, prompt)
		}
	}
}

func TestBuildSystemPromptCustomOmitsBuiltInDocs(t *testing.T) {
	got := BuildSystemPrompt(SystemPromptOpts{
		CWD:        "/workspace",
		Custom:     "Custom instructions",
		Append:     []string{"Additional context"},
		Now:        time.Date(2026, time.August, 6, 0, 0, 0, 0, time.UTC),
		ZutDocsDir: "/zut/docs",
	})

	if strings.Contains(got, "Zut's own docs") || strings.Contains(got, "/zut/docs") {
		t.Fatalf("custom prompt includes built-in docs guidance:\n%s", got)
	}
	for _, want := range []string{
		"Custom instructions",
		"Additional context",
		"Current date: 2026-08-06",
		"Current working directory: /workspace",
	} {
		if !strings.Contains(got, want) {
			t.Errorf("custom prompt missing %q:\n%s", want, got)
		}
	}
}

func TestBuildSystemPromptDefaultIncludesBuiltInDocs(t *testing.T) {
	got := BuildSystemPrompt(SystemPromptOpts{
		CWD:        "/workspace",
		Now:        time.Date(2026, time.August, 6, 0, 0, 0, 0, time.UTC),
		ZutDocsDir: "/zut/docs",
	})

	if !strings.Contains(got, "Zut's own docs are installed under /zut/docs") {
		t.Fatalf("default prompt missing built-in docs guidance:\n%s", got)
	}
}