package api

import (
	"bytes"
	"encoding/json"
	"fmt"
	"net/http"
	"net/http/httptest"
	"path/filepath"
	"strings"
	"testing"

	"tefter/server/store"
)

// client is a minimal reimplementation of the frontend sync loop (pull-then-push,
// last-write-wins with conflict copies) used to prove two devices converge.
type client struct {
	t      *testing.T
	base   string
	token  string
	cursor int64
	notes  map[string]*clientNote
}

type clientNote struct {
	store.Note
	BaseVersion int64
	Dirty       bool
}

func newClient(t *testing.T, base, token string) *client {
	return &client{t: t, base: base, token: token, notes: map[string]*clientNote{}}
}

func (c *client) req(method, path string, body any, out any) int {
	var rdr *bytes.Reader
	if body != nil {
		b, _ := json.Marshal(body)
		rdr = bytes.NewReader(b)
	} else {
		rdr = bytes.NewReader(nil)
	}
	req, _ := http.NewRequest(method, c.base+path, rdr)
	req.Header.Set("Authorization", "Bearer "+c.token)
	req.Header.Set("Content-Type", "application/json")
	res, err := http.DefaultClient.Do(req)
	if err != nil {
		c.t.Fatal(err)
	}
	defer res.Body.Close()
	if out != nil {
		if err := json.NewDecoder(res.Body).Decode(out); err != nil {
			c.t.Fatal(err)
		}
	}
	return res.StatusCode
}

func (c *client) edit(id, content string) {
	n, ok := c.notes[id]
	if !ok {
		n = &clientNote{}
		n.ID = id
		c.notes[id] = n
	}
	n.Content = content
	n.Dirty = true
}

func (c *client) pull() {
	for {
		var body struct {
			Notes  []store.Note `json:"notes"`
			Cursor int64        `json:"cursor"`
			More   bool         `json:"more"`
		}
		if code := c.req("GET", fmt.Sprintf("/api/v1/changes?since=%d&limit=2", c.cursor), nil, &body); code != 200 {
			c.t.Fatalf("pull HTTP %d", code)
		}
		for _, sn := range body.Notes {
			if local, ok := c.notes[sn.ID]; ok && local.Dirty {
				continue // dirty local copy wins until pushed
			}
			c.notes[sn.ID] = &clientNote{Note: sn, BaseVersion: sn.Version}
		}
		c.cursor = body.Cursor
		if !body.More {
			return
		}
	}
}

func (c *client) push() {
	var dirty []map[string]any
	for _, n := range c.notes {
		if n.Dirty {
			dirty = append(dirty, map[string]any{
				"id": n.ID, "content": n.Content, "tags": n.Tags,
				"created_at": n.CreatedAt, "modified_at": n.ModifiedAt,
				"deleted": n.Deleted, "baseVersion": n.BaseVersion,
			})
		}
	}
	if dirty == nil {
		return
	}
	var body struct {
		Results []store.PushResult `json:"results"`
	}
	if code := c.req("POST", "/api/v1/notes/batch", map[string]any{"notes": dirty}, &body); code != 200 {
		c.t.Fatalf("push HTTP %d", code)
	}
	for _, r := range body.Results {
		n := c.notes[r.ID]
		switch r.Status {
		case "accepted":
			n.Dirty = false
			n.BaseVersion = r.Version
			n.Version = r.Version
		case "conflict":
			if r.ServerNote != nil {
				c.notes[r.ID] = &clientNote{Note: *r.ServerNote, BaseVersion: r.ServerNote.Version}
			}
		}
	}
}

func (c *client) sync() { c.pull(); c.push(); c.pull() }

func (c *client) visible() map[string]string {
	out := map[string]string{}
	for id, n := range c.notes {
		if !n.Deleted {
			out[id] = n.Content
		}
	}
	return out
}

func newTestServer(t *testing.T) (*httptest.Server, string) {
	st, err := store.Open(filepath.Join(t.TempDir(), "api.db"))
	if err != nil {
		t.Fatal(err)
	}
	t.Cleanup(func() { st.Close() })
	tok, err := st.EnsureToken()
	if err != nil {
		t.Fatal(err)
	}
	srv := httptest.NewServer((&Server{Store: st, Version: "test"}).Handler())
	t.Cleanup(srv.Close)
	return srv, tok
}

func TestAuthRequired(t *testing.T) {
	srv, _ := newTestServer(t)
	res, err := http.Get(srv.URL + "/api/v1/changes?since=0")
	if err != nil {
		t.Fatal(err)
	}
	res.Body.Close()
	if res.StatusCode != http.StatusUnauthorized {
		t.Fatalf("want 401, got %d", res.StatusCode)
	}
	res, err = http.Get(srv.URL + "/api/v1/health")
	if err != nil {
		t.Fatal(err)
	}
	res.Body.Close()
	if res.StatusCode != http.StatusOK {
		t.Fatalf("health must be open, got %d", res.StatusCode)
	}
}

func TestTwoClientsConverge(t *testing.T) {
	srv, tok := newTestServer(t)
	a := newClient(t, srv.URL, tok)
	b := newClient(t, srv.URL, tok)

	// A creates three notes, B pulls them.
	a.edit("n1", "groceries\nmilk")
	a.edit("n2", "ideas")
	a.edit("n3", "scratch")
	a.sync()
	b.sync()
	if len(b.visible()) != 3 {
		t.Fatalf("B should see 3 notes, sees %d", len(b.visible()))
	}

	// Independent edits on different notes converge cleanly.
	a.edit("n1", "groceries\nmilk, bread")
	b.edit("n2", "ideas\nbuild tefter")
	a.sync()
	b.sync()
	a.sync()
	if fmt.Sprint(a.visible()) != fmt.Sprint(b.visible()) {
		t.Fatalf("divergence:\nA=%v\nB=%v", a.visible(), b.visible())
	}

	// Concurrent edit of the SAME note → conflict copy, never silent overwrite.
	a.edit("n3", "scratch from A")
	b.edit("n3", "scratch from B")
	a.sync()
	b.sync() // B's push conflicts; server truth restored + copy created
	a.sync()
	b.sync()

	av, bv := a.visible(), b.visible()
	if fmt.Sprint(av) != fmt.Sprint(bv) {
		t.Fatalf("divergence after conflict:\nA=%v\nB=%v", av, bv)
	}
	if len(av) != 4 {
		t.Fatalf("want 4 notes (3 + conflict copy), got %d: %v", len(av), av)
	}
	foundCopy := false
	for _, content := range av {
		if strings.Contains(content, "conflicted copy") && strings.Contains(content, "scratch from B") {
			foundCopy = true
		}
	}
	if !foundCopy {
		t.Fatalf("conflict copy missing: %v", av)
	}
	// Both edits survived somewhere — no data loss.
	joined := fmt.Sprint(av)
	if !strings.Contains(joined, "scratch from A") || !strings.Contains(joined, "scratch from B") {
		t.Fatalf("an edit was silently lost: %v", av)
	}
}

func TestDeleteEditConflictAcrossClients(t *testing.T) {
	srv, tok := newTestServer(t)
	a := newClient(t, srv.URL, tok)
	b := newClient(t, srv.URL, tok)

	a.edit("n1", "keep me")
	a.sync()
	b.sync()

	// A deletes while B edits concurrently; edit must win.
	an := a.notes["n1"]
	an.Deleted = true
	an.Dirty = true
	b.edit("n1", "keep me — edited")
	b.sync() // B's edit lands first
	a.sync() // A's stale delete is dropped, server truth restored
	b.sync()

	if fmt.Sprint(a.visible()) != fmt.Sprint(b.visible()) {
		t.Fatalf("divergence:\nA=%v\nB=%v", a.visible(), b.visible())
	}
	if a.visible()["n1"] != "keep me — edited" {
		t.Fatalf("edit did not win: %v", a.visible())
	}
}