// Package fakegitea is a stateful in-memory Gitea API fake used by the
// test suite and the smoke run. The real forge is NEVER contacted. It
// implements exactly the endpoints the gitea client uses, enforces
// "Authorization: token <key>" auth on every one of them, and records
// every request so tests can assert round-trips. Error responses
// deliberately echo the presented token back in the body: any test that
// survives that proves the client never surfaces response bodies
// (token-redaction guarantee).
package fakegitea

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/http/httptest"
	"sort"
	"strconv"
	"strings"
	"sync"
)

// Request is one recorded exchange (auth checked, body captured).
type Request struct {
	Method string
	Path   string // path without query
	Query  string // raw query
	Body   string
}

// User is the account shape.
type User struct {
	ID       int64  `json:"id"`
	Login    string `json:"login"`
	FullName string `json:"full_name"`
}

// Repo is the stored repository (server side).
type Repo struct {
	ID            int64  `json:"id"`
	Owner         User   `json:"owner"`
	Name          string `json:"name"`
	FullName      string `json:"full_name"`
	Description   string `json:"description"`
	Private       bool   `json:"private"`
	DefaultBranch string `json:"default_branch"`
	HTMLURL       string `json:"html_url"`
	CloneURL      string `json:"clone_url"`
}

// Branch is the branch shape (Commit carries the tip sha).
type Branch struct {
	Name      string     `json:"name"`
	Commit    CommitInfo `json:"commit"`
	Protected bool       `json:"protected"`
}

// CommitInfo is the commit projection branches carry.
type CommitInfo struct {
	ID      string `json:"id"`
	Message string `json:"message"`
}

// StatusRecord is one stored commit status (append-only per sha).
type StatusRecord struct {
	ID          int64  `json:"id"`
	State       string `json:"state"`
	Context     string `json:"context"`
	Description string `json:"description"`
	TargetURL   string `json:"target_url"`
	CreatedAt   string `json:"created_at"`
	UpdatedAt   string `json:"updated_at"`
}

// PullRequest is the stored PR.
type PullRequest struct {
	Number    int64    `json:"number"`
	Title     string   `json:"title"`
	Body      string   `json:"body"`
	State     string   `json:"state"` // open|closed
	User      User     `json:"user"`
	Base      PRBranch `json:"base"`
	Head      PRBranch `json:"head"`
	Mergeable bool     `json:"mergeable"`
	Merged    bool     `json:"merged"`
	MergedAt  string   `json:"merged_at"`
	HTMLURL   string   `json:"html_url"`
	CreatedAt string   `json:"created_at"`
	UpdatedAt string   `json:"updated_at"`
}

// PRBranch is one end of a pull request.
type PRBranch struct {
	Ref  string `json:"ref"`
	SHA  string `json:"sha"`
	Repo Repo   `json:"repo"`
}

type repoState struct {
	repo     Repo
	branches map[string]string // name -> tip sha
	order    []string          // insertion order of branch names
	statuses map[string][]StatusRecord
	prs      map[int64]*PullRequest
	nextPR   int64
}

// Server is the fake Gitea.
type Server struct {
	URL   string
	Login string // the account the token authenticates as
	Token string

	mu       sync.Mutex
	srv      *httptest.Server
	requests []Request
	repos    map[string]*repoState // "owner/name" -> state
	nextRepo int64
	nextStat int64
	// Fail, when non-nil, is returned instead of normal handling; it is
	// consumed by the first request that sees it.
	Fail *FailSpec
}

// FailSpec pins the next response (error-mapping tests).
type FailSpec struct {
	Status int
	Body   string // may contain one %s: the presented token
}

// New starts a fake on a random port authenticating as login.
func New(token, login string) *Server {
	s := newServer(token, login)
	mux := http.NewServeMux()
	mux.HandleFunc("/", s.handler)
	s.srv = httptest.NewServer(mux)
	s.URL = s.srv.URL
	return s
}

// ListenAndServe runs the fake on a fixed address (the smoke run boots it
// in a container). An empty token disables auth checking.
func ListenAndServe(addr, token string) error {
	s := newServer(token, "ukrrs")
	mux := http.NewServeMux()
	mux.HandleFunc("/", s.handler)
	return http.ListenAndServe(addr, mux)
}

func newServer(token, login string) *Server {
	return &Server{
		Token:    token,
		Login:    login,
		repos:    map[string]*repoState{},
		nextRepo: 1000,
		nextStat: 5000,
	}
}

// Close shuts the fake down.
func (s *Server) Close() { s.srv.Close() }

// Requests returns a copy of the recorded exchanges.
func (s *Server) Requests() []Request {
	s.mu.Lock()
	defer s.mu.Unlock()
	out := make([]Request, len(s.requests))
	copy(out, s.requests)
	return out
}

// AddRepo seeds a repository directly (bypassing REST) with the given
// branches (first is the default when defaultBranch is empty) and returns
// its "owner/name" key.
func (s *Server) AddRepo(owner, name, defaultBranch string, branches ...string) string {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.addRepoLocked(owner, name, defaultBranch, branches)
}

func (s *Server) addRepoLocked(owner, name, defaultBranch string, branches []string) string {
	if defaultBranch == "" && len(branches) > 0 {
		defaultBranch = branches[0]
	}
	s.nextRepo++
	st := &repoState{
		repo: Repo{
			ID:            s.nextRepo,
			Owner:         User{ID: 10, Login: owner, FullName: owner},
			Name:          name,
			FullName:      owner + "/" + name,
			DefaultBranch: defaultBranch,
			HTMLURL:       "https://git.example/" + owner + "/" + name,
			CloneURL:      "https://git.example/" + owner + "/" + name + ".git",
		},
		branches: map[string]string{},
		statuses: map[string][]StatusRecord{},
		prs:      map[int64]*PullRequest{},
	}
	for _, b := range branches {
		st.addBranch(b)
	}
	key := owner + "/" + name
	s.repos[key] = st
	return key
}

func (st *repoState) addBranch(name string) string {
	// Distinct, well-formed 40-hex shas derived from the branch key, so
	// short-sha (>= 7 chars) resolution is unambiguous like real git.
	sum := sha256.Sum256([]byte(st.repo.FullName + "/" + name))
	sha := hex.EncodeToString(sum[:])[:40]
	if _, ok := st.branches[name]; !ok {
		st.order = append(st.order, name)
	}
	st.branches[name] = sha
	return sha
}

// AddBranch seeds a branch directly and returns its (new) tip sha.
func (s *Server) AddBranch(owner, name, branch string) string {
	s.mu.Lock()
	defer s.mu.Unlock()
	st := s.repos[owner+"/"+name]
	return st.addBranch(branch)
}

// Repo returns a copy of a stored repo (for assertions).
func (s *Server) Repo(owner, name string) (Repo, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return Repo{}, false
	}
	return st.repo, true
}

// PullRequest returns a copy of a stored PR (for assertions).
func (s *Server) PullRequest(owner, name string, number int64) (PullRequest, bool) {
	s.mu.Lock()
	defer s.mu.Unlock()
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return PullRequest{}, false
	}
	pr, ok := st.prs[number]
	if !ok {
		return PullRequest{}, false
	}
	return *pr, true
}

// Statuses returns the raw status history of one sha (for assertions).
func (s *Server) Statuses(owner, name, sha string) []StatusRecord {
	s.mu.Lock()
	defer s.mu.Unlock()
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return nil
	}
	out := make([]StatusRecord, len(st.statuses[sha]))
	copy(out, st.statuses[sha])
	return out
}

func (s *Server) handler(w http.ResponseWriter, r *http.Request) {
	token := ""
	if s.Token != "" {
		auth := r.Header.Get("Authorization")
		if strings.HasPrefix(auth, "token ") {
			token = strings.TrimPrefix(auth, "token ")
		}
	}
	body, _ := io.ReadAll(io.LimitReader(r.Body, 1<<20))

	s.mu.Lock()
	if s.Fail != nil {
		spec := *s.Fail
		s.Fail = nil
		s.requests = append(s.requests, Request{r.Method, r.URL.Path, r.URL.RawQuery, string(body)})
		s.mu.Unlock()
		// The body deliberately embeds the presented token: surviving
		// this proves the client drops response bodies from errors.
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(spec.Status)
		fmt.Fprintf(w, spec.Body, token)
		return
	}
	if s.Token != "" && token != s.Token {
		s.requests = append(s.requests, Request{r.Method, r.URL.Path, r.URL.RawQuery, ""})
		s.mu.Unlock()
		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusUnauthorized)
		fmt.Fprintf(w, `{"message":"bad credentials: token %s was rejected"}`, token)
		return
	}
	s.requests = append(s.requests, Request{r.Method, r.URL.Path, r.URL.RawQuery, string(body)})

	var (
		respStatus = http.StatusOK
		respBody   string
	)
	path := r.URL.Path
	q := r.URL.Query()
	switch {
	case r.Method == http.MethodGet && path == "/api/v1/user/repos":
		respStatus, respBody = s.listRepos(s.Login)
	case r.Method == http.MethodPost && path == "/api/v1/user/repos":
		respStatus, respBody = s.createRepo(s.Login, body)
	case r.Method == http.MethodGet && strings.HasPrefix(path, "/api/v1/users/") && strings.HasSuffix(path, "/repos"):
		owner := strings.TrimSuffix(strings.TrimPrefix(path, "/api/v1/users/"), "/repos")
		respStatus, respBody = s.listRepos(owner)
	case r.Method == http.MethodPost && strings.HasPrefix(path, "/api/v1/orgs/") && strings.HasSuffix(path, "/repos"):
		owner := strings.TrimSuffix(strings.TrimPrefix(path, "/api/v1/orgs/"), "/repos")
		respStatus, respBody = s.createRepo(owner, body)
	case r.Method == http.MethodGet && strings.HasPrefix(path, "/api/v1/repos/") && strings.Count(path, "/") == 5:
		owner, name := splitRepo(strings.TrimPrefix(path, "/api/v1/repos/"))
		respStatus, respBody = s.getRepo(owner, name)
	case r.Method == http.MethodGet && strings.HasSuffix(path, "/branches") && strings.HasPrefix(path, "/api/v1/repos/"):
		owner, name := splitRepo(strings.TrimSuffix(strings.TrimPrefix(path, "/api/v1/repos/"), "/branches"))
		respStatus, respBody = s.listBranches(owner, name)
	case r.Method == http.MethodPost && strings.Contains(path, "/statuses/") && strings.HasPrefix(path, "/api/v1/repos/"):
		rest := strings.TrimPrefix(path, "/api/v1/repos/")
		parts := strings.SplitN(rest, "/statuses/", 2)
		owner, name := splitRepo(parts[0])
		respStatus, respBody = s.createStatus(owner, name, parts[1], body)
	case r.Method == http.MethodGet && strings.HasSuffix(path, "/statuses") && strings.HasPrefix(path, "/api/v1/repos/"):
		rest := strings.TrimSuffix(strings.TrimPrefix(path, "/api/v1/repos/"), "/statuses")
		parts := strings.SplitN(rest, "/commits/", 2)
		owner, name := splitRepo(parts[0])
		respStatus, respBody = s.listStatuses(owner, name, parts[1])
	case r.Method == http.MethodGet && strings.HasSuffix(path, "/status") && strings.HasPrefix(path, "/api/v1/repos/"):
		rest := strings.TrimSuffix(strings.TrimPrefix(path, "/api/v1/repos/"), "/status")
		parts := strings.SplitN(rest, "/commits/", 2)
		owner, name := splitRepo(parts[0])
		respStatus, respBody = s.combinedStatus(owner, name, parts[1])
	case r.Method == http.MethodGet && strings.HasSuffix(path, "/pulls") && strings.HasPrefix(path, "/api/v1/repos/"):
		owner, name := splitRepo(strings.TrimSuffix(strings.TrimPrefix(path, "/api/v1/repos/"), "/pulls"))
		respStatus, respBody = s.listPulls(owner, name, q.Get("state"))
	case r.Method == http.MethodPost && strings.HasSuffix(path, "/pulls") && strings.HasPrefix(path, "/api/v1/repos/"):
		owner, name := splitRepo(strings.TrimSuffix(strings.TrimPrefix(path, "/api/v1/repos/"), "/pulls"))
		respStatus, respBody = s.createPull(owner, name, body)
	case r.Method == http.MethodPost && strings.Contains(path, "/pulls/") && strings.HasSuffix(path, "/merge") && strings.HasPrefix(path, "/api/v1/repos/"):
		rest := strings.TrimPrefix(path, "/api/v1/repos/")
		parts := strings.SplitN(rest, "/pulls/", 2)
		owner, name := splitRepo(parts[0])
		num, _ := strconv.ParseInt(strings.TrimSuffix(parts[1], "/merge"), 10, 64)
		respStatus, respBody = s.mergePull(owner, name, num, body)
	case r.Method == http.MethodGet && strings.Contains(path, "/pulls/") && strings.HasPrefix(path, "/api/v1/repos/"):
		rest := strings.TrimPrefix(path, "/api/v1/repos/")
		parts := strings.SplitN(rest, "/pulls/", 2)
		owner, name := splitRepo(parts[0])
		num, _ := strconv.ParseInt(parts[1], 10, 64)
		respStatus, respBody = s.getPull(owner, name, num)
	default:
		respStatus, respBody = http.StatusNotFound, `{"message":"Not Found"}`
	}
	s.mu.Unlock()

	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(respStatus)
	if respBody != "" {
		io.WriteString(w, respBody)
	}
}

func splitRepo(s string) (owner, name string) {
	parts := strings.SplitN(s, "/", 2)
	if len(parts) != 2 {
		return "", ""
	}
	return parts[0], parts[1]
}

func jsonReply(v any) (int, string) {
	b, err := json.Marshal(v)
	if err != nil {
		return http.StatusInternalServerError, `{"message":"marshal"}`
	}
	return http.StatusOK, string(b)
}

// --- repos -----------------------------------------------------------------

func (s *Server) listRepos(owner string) (int, string) {
	var out []Repo
	for _, key := range s.sortedRepoKeys() {
		st := s.repos[key]
		if st.repo.Owner.Login == owner {
			out = append(out, st.repo)
		}
	}
	if out == nil {
		out = []Repo{}
	}
	return jsonReply(out)
}

func (s *Server) sortedRepoKeys() []string {
	keys := make([]string, 0, len(s.repos))
	for k := range s.repos {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	return keys
}

func (s *Server) getRepo(owner, name string) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	return jsonReply(st.repo)
}

func (s *Server) createRepo(owner string, body []byte) (int, string) {
	var p struct {
		Name          string `json:"name"`
		Description   string `json:"description"`
		Private       bool   `json:"private"`
		AutoInit      bool   `json:"auto_init"`
		DefaultBranch string `json:"default_branch"`
	}
	if err := json.Unmarshal(body, &p); err != nil {
		return http.StatusBadRequest, `{"message":"bad json"}`
	}
	if p.Name == "" {
		return http.StatusUnprocessableEntity, `{"message":"name is required"}`
	}
	if _, exists := s.repos[owner+"/"+p.Name]; exists {
		return http.StatusConflict, `{"message":"The repository with the same name already exists."}`
	}
	branches := []string(nil)
	if p.AutoInit {
		branches = []string{"main"}
	}
	key := s.addRepoLocked(owner, p.Name, p.DefaultBranch, branches)
	st := s.repos[key]
	st.repo.Description = p.Description
	st.repo.Private = p.Private
	return http.StatusCreated, mustJSON(st.repo)
}

func mustJSON(v any) string {
	b, err := json.Marshal(v)
	if err != nil {
		panic(err)
	}
	return string(b)
}

// --- branches ---------------------------------------------------------------

func (s *Server) listBranches(owner, name string) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	out := make([]Branch, 0, len(st.order))
	for _, b := range st.order {
		sha := st.branches[b]
		out = append(out, Branch{Name: b, Commit: CommitInfo{ID: sha, Message: "fake commit " + sha[:7]}})
	}
	return jsonReply(out)
}

// resolveRef maps a ref (full sha, sha prefix, or branch name) to a commit
// sha; ok=false when nothing matches. Prefix matches scan branches in
// insertion order for determinism.
func (st *repoState) resolveRef(ref string) (string, bool) {
	if sha, ok := st.branches[ref]; ok {
		return sha, true
	}
	if len(ref) >= 7 {
		for _, b := range st.order {
			if strings.HasPrefix(st.branches[b], ref) {
				return st.branches[b], true
			}
		}
	}
	return "", false
}

// --- statuses ---------------------------------------------------------------

var validStates = map[string]bool{"pending": true, "success": true, "error": true, "failure": true}

func (s *Server) createStatus(owner, name, sha string, body []byte) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	full, ok := st.resolveRef(sha)
	if !ok {
		return http.StatusNotFound, fmt.Sprintf(`{"message":"commit %s not found"}`, sha)
	}
	var p StatusRecord
	if err := json.Unmarshal(body, &p); err != nil {
		return http.StatusBadRequest, `{"message":"bad json"}`
	}
	if !validStates[p.State] {
		return http.StatusUnprocessableEntity, `{"message":"invalid state"}`
	}
	if p.Context == "" {
		p.Context = "default"
	}
	s.nextStat++
	p.ID = s.nextStat
	p.CreatedAt = "2026-08-29T16:00:00Z"
	p.UpdatedAt = p.CreatedAt
	st.statuses[full] = append(st.statuses[full], p)
	return http.StatusCreated, mustJSON(p)
}

// latestPerContext folds the append-only history into the newest status
// per context (Gitea's reported shape), in insertion order.
func latestPerContext(history []StatusRecord) []StatusRecord {
	idx := map[string]int{}
	var out []StatusRecord
	for _, sr := range history {
		if i, ok := idx[sr.Context]; ok {
			out[i] = sr
		} else {
			idx[sr.Context] = len(out)
			out = append(out, sr)
		}
	}
	return out
}

func (s *Server) listStatuses(owner, name, ref string) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	full, ok := st.resolveRef(ref)
	if !ok {
		return http.StatusNotFound, `{"message":"commit not found"}`
	}
	out := latestPerContext(st.statuses[full])
	if out == nil {
		out = []StatusRecord{}
	}
	return jsonReply(out)
}

func worstState(statuses []StatusRecord) string {
	rank := map[string]int{"success": 0, "pending": 1, "failure": 2, "error": 3}
	worst, seen := "", false
	for _, sr := range statuses {
		if !seen || rank[sr.State] > rank[worst] {
			worst, seen = sr.State, true
		}
	}
	return worst
}

func (s *Server) combinedStatus(owner, name, ref string) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	full, ok := st.resolveRef(ref)
	if !ok {
		return http.StatusNotFound, `{"message":"commit not found"}`
	}
	latest := latestPerContext(st.statuses[full])
	if len(latest) == 0 {
		return http.StatusNotFound, `{"message":"no statuses for this commit"}`
	}
	out := struct {
		State      string         `json:"state"`
		SHA        string         `json:"sha"`
		TotalCount int            `json:"total_count"`
		Statuses   []StatusRecord `json:"statuses"`
	}{worstState(latest), full, len(latest), latest}
	return jsonReply(out)
}

// --- pull requests ----------------------------------------------------------

func (s *Server) prBranch(st *repoState, ref string) (PRBranch, bool) {
	branch := ref
	if i := strings.IndexByte(ref, ':'); i >= 0 { // fork syntax owner:branch
		branch = ref[i+1:]
	}
	sha, ok := st.branches[branch]
	if !ok {
		return PRBranch{}, false
	}
	return PRBranch{Ref: branch, SHA: sha, Repo: st.repo}, true
}

func (s *Server) createPull(owner, name string, body []byte) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	var p struct {
		Title string `json:"title"`
		Body  string `json:"body"`
		Base  string `json:"base"`
		Head  string `json:"head"`
	}
	if err := json.Unmarshal(body, &p); err != nil {
		return http.StatusBadRequest, `{"message":"bad json"}`
	}
	if p.Title == "" {
		return http.StatusUnprocessableEntity, `{"message":"title is required"}`
	}
	base, ok := s.prBranch(st, p.Base)
	if !ok {
		return http.StatusUnprocessableEntity, fmt.Sprintf(`{"message":"base branch %s does not exist"}`, p.Base)
	}
	head, ok := s.prBranch(st, p.Head)
	if !ok {
		return http.StatusUnprocessableEntity, fmt.Sprintf(`{"message":"head branch %s does not exist"}`, p.Head)
	}
	if base.Ref == head.Ref {
		return http.StatusUnprocessableEntity, `{"message":"head and base cannot be the same"}`
	}
	for _, pr := range st.prs {
		if pr.State == "open" && pr.Base.Ref == base.Ref && pr.Head.Ref == head.Ref {
			return http.StatusConflict, `{"message":"The pull request has already been created."}`
		}
	}
	st.nextPR++
	now := "2026-08-29T16:00:00Z"
	pr := &PullRequest{
		Number:    st.nextPR,
		Title:     p.Title,
		Body:      p.Body,
		State:     "open",
		User:      User{ID: 10, Login: s.Login},
		Base:      base,
		Head:      head,
		Mergeable: true,
		HTMLURL:   st.repo.HTMLURL + "/pulls/" + strconv.FormatInt(st.nextPR, 10),
		CreatedAt: now,
		UpdatedAt: now,
	}
	st.prs[pr.Number] = pr
	return http.StatusCreated, mustJSON(pr)
}

func (s *Server) listPulls(owner, name, state string) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	if state == "" {
		state = "open" // Gitea default
	}
	var nums []int64
	for n := range st.prs {
		nums = append(nums, n)
	}
	sort.Slice(nums, func(i, j int) bool { return nums[i] < nums[j] })
	out := []PullRequest{}
	for _, n := range nums {
		pr := st.prs[n]
		if state == "all" || pr.State == state {
			out = append(out, *pr)
		}
	}
	return jsonReply(out)
}

func (s *Server) getPull(owner, name string, num int64) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	pr, ok := st.prs[num]
	if !ok {
		return http.StatusNotFound, `{"message":"The pull request couldn't be found."}`
	}
	return jsonReply(pr)
}

var mergeStyles = map[string]bool{"merge": true, "rebase": true, "rebase-merge": true, "squash": true, "fast-forward": true}

func (s *Server) mergePull(owner, name string, num int64, body []byte) (int, string) {
	st, ok := s.repos[owner+"/"+name]
	if !ok {
		return http.StatusNotFound, `{"message":"The target couldn't be found."}`
	}
	pr, ok := st.prs[num]
	if !ok {
		return http.StatusNotFound, `{"message":"The pull request couldn't be found."}`
	}
	var p struct {
		Do      string `json:"Do"`
		Title   string `json:"MergeTitleField"`
		Message string `json:"MergeMessageField"`
	}
	if len(body) > 0 {
		if err := json.Unmarshal(body, &p); err != nil {
			return http.StatusBadRequest, `{"message":"bad json"}`
		}
	}
	if p.Do == "" {
		p.Do = "merge"
	}
	if !mergeStyles[p.Do] {
		return http.StatusUnprocessableEntity, `{"message":"invalid merge style"}`
	}
	if pr.State != "open" || pr.Merged {
		return http.StatusConflict, `{"message":"The pull request has already been merged or closed."}`
	}
	pr.Merged = true
	pr.State = "closed"
	pr.Mergeable = false
	pr.MergedAt = "2026-08-29T16:05:00Z"
	pr.UpdatedAt = pr.MergedAt
	// The head lands on base: base now points at the head sha.
	st.branches[pr.Base.Ref] = pr.Head.SHA
	return http.StatusOK, `{"message":"pull request has been merged"}`
}