package httpapi

import (
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"path"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"time"

	"git.librete.ch/public/librenotes/internal/tenant"
)

// NotesHandler exposes per-tenant note CRUD over HTTP. Notes are
// stored as Markdown files in the tenant's sandboxed directory.
//
// The wire format is JSON: { id, title, content, updated_at }.
// Conflict detection uses an If-Unmodified-Since-style flow: the
// client sends ?base=<unix-seconds> on PUT/DELETE, and we 409 if
// the file has been touched since.
type NotesHandler struct {
	// FSFor returns the tenant FS for the given user ID. It must
	// create the directory if missing. Implementations typically
	// memoise per user.
	FSFor func(userID string) (*tenant.FS, error)
}

// noteIDRe constrains note IDs to a safe slug. The tenant FS would
// reject path traversal anyway but rejecting at the parser keeps
// errors clean and prevents weird paths from being created at all.
var noteIDRe = regexp.MustCompile(`^[a-z0-9][a-z0-9_-]{0,127}$`)

const notesPrefix = "/api/notes"

// Mount adds the notes routes onto the given mux. Caller is expected
// to wrap the mux with AuthMiddleware so tenant context is present.
func (h NotesHandler) Mount(mux *http.ServeMux) {
	mux.HandleFunc(notesPrefix, h.handleCollection)
	mux.HandleFunc(notesPrefix+"/", h.handleItem)
}

type noteSummary struct {
	ID        string `json:"id"`
	Title     string `json:"title"`
	UpdatedAt int64  `json:"updated_at"`
}

type note struct {
	ID        string `json:"id"`
	Title     string `json:"title"`
	Content   string `json:"content"`
	UpdatedAt int64  `json:"updated_at"`
}

func (h NotesHandler) handleCollection(w http.ResponseWriter, r *http.Request) {
	t, err := TenantFrom(r.Context())
	if err != nil {
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return
	}
	if r.Method != http.MethodGet {
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
		return
	}
	fs, err := h.FSFor(t.UserID)
	if err != nil {
		http.Error(w, "tenant fs unavailable", http.StatusInternalServerError)
		return
	}
	names, err := fs.List(".")
	if err != nil {
		http.Error(w, "list failed", http.StatusInternalServerError)
		return
	}
	out := make([]noteSummary, 0, len(names))
	for _, name := range names {
		if !strings.HasSuffix(name, ".md") {
			continue
		}
		id := strings.TrimSuffix(name, ".md")
		fi, err := fs.Stat(name)
		if err != nil {
			continue
		}
		title, _ := readTitle(fs, name)
		out = append(out, noteSummary{ID: id, Title: title, UpdatedAt: fi.ModTime().Unix()})
	}
	writeJSON(w, http.StatusOK, out)
}

func (h NotesHandler) handleItem(w http.ResponseWriter, r *http.Request) {
	t, err := TenantFrom(r.Context())
	if err != nil {
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return
	}
	id := strings.TrimPrefix(r.URL.Path, notesPrefix+"/")
	id = strings.TrimSuffix(id, "/")
	if !noteIDRe.MatchString(id) {
		http.Error(w, "invalid note id", http.StatusBadRequest)
		return
	}
	fs, err := h.FSFor(t.UserID)
	if err != nil {
		http.Error(w, "tenant fs unavailable", http.StatusInternalServerError)
		return
	}
	rel := id + ".md"

	switch r.Method {
	case http.MethodGet:
		h.read(w, fs, id, rel)
	case http.MethodPut:
		h.write(w, r, fs, id, rel)
	case http.MethodDelete:
		h.delete(w, r, fs, rel)
	default:
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

func (h NotesHandler) read(w http.ResponseWriter, fs *tenant.FS, id, rel string) {
	data, err := fs.ReadFile(rel)
	if errors.Is(err, tenant.ErrNotFound) {
		http.Error(w, "not found", http.StatusNotFound)
		return
	}
	if err != nil {
		http.Error(w, "read failed", http.StatusInternalServerError)
		return
	}
	fi, err := fs.Stat(rel)
	if err != nil {
		http.Error(w, "stat failed", http.StatusInternalServerError)
		return
	}
	title, body := splitTitle(string(data))
	writeJSON(w, http.StatusOK, note{
		ID: id, Title: title, Content: body, UpdatedAt: fi.ModTime().Unix(),
	})
}

type writeReq struct {
	Title   string `json:"title"`
	Content string `json:"content"`
}

func (h NotesHandler) write(w http.ResponseWriter, r *http.Request, fs *tenant.FS, id, rel string) {
	var req writeReq
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<20)).Decode(&req); err != nil {
		http.Error(w, "invalid body", http.StatusBadRequest)
		return
	}

	// Conflict detection: if the client supplied ?base=<unix>, and
	// the current file's mtime is newer, the file has changed
	// since the client read it. Return 409 with the current state.
	if base := r.URL.Query().Get("base"); base != "" {
		baseUnix, err := strconv.ParseInt(base, 10, 64)
		if err != nil {
			http.Error(w, "invalid base param", http.StatusBadRequest)
			return
		}
		if fi, err := fs.Stat(rel); err == nil {
			if fi.ModTime().Unix() > baseUnix {
				body, _ := fs.ReadFile(rel)
				title, content := splitTitle(string(body))
				writeJSON(w, http.StatusConflict, note{
					ID: id, Title: title, Content: content, UpdatedAt: fi.ModTime().Unix(),
				})
				return
			}
		} else if !errors.Is(err, tenant.ErrNotFound) {
			http.Error(w, "stat failed", http.StatusInternalServerError)
			return
		} else if baseUnix != 0 {
			// Client thought there was a prior version; server has
			// nothing. Treat as conflict so client can resolve.
			http.Error(w, "deleted on server", http.StatusConflict)
			return
		}
	}

	body := composeNote(req.Title, req.Content)
	if err := fs.WriteFile(rel, []byte(body)); err != nil {
		if errors.Is(err, tenant.ErrInvalidPath) {
			http.Error(w, "invalid path", http.StatusBadRequest)
			return
		}
		http.Error(w, "write failed", http.StatusInternalServerError)
		return
	}
	fi, err := fs.Stat(rel)
	if err != nil {
		http.Error(w, "stat failed", http.StatusInternalServerError)
		return
	}
	writeJSON(w, http.StatusOK, note{
		ID: id, Title: req.Title, Content: req.Content, UpdatedAt: fi.ModTime().Unix(),
	})
}

func (h NotesHandler) delete(w http.ResponseWriter, r *http.Request, fs *tenant.FS, rel string) {
	if base := r.URL.Query().Get("base"); base != "" {
		baseUnix, err := strconv.ParseInt(base, 10, 64)
		if err != nil {
			http.Error(w, "invalid base param", http.StatusBadRequest)
			return
		}
		if fi, err := fs.Stat(rel); err == nil {
			if fi.ModTime().Unix() > baseUnix {
				http.Error(w, "modified on server", http.StatusConflict)
				return
			}
		}
	}
	if err := fs.Remove(rel); err != nil && !errors.Is(err, tenant.ErrNotFound) {
		http.Error(w, "delete failed", http.StatusInternalServerError)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// composeNote serialises title + content. We keep it simple: the
// first line is "# <title>" and the rest is the content as-is. This
// way grep / cat / vim still produce a usable view of the raw file.
func composeNote(title, content string) string {
	var b strings.Builder
	if strings.TrimSpace(title) != "" {
		b.WriteString("# ")
		b.WriteString(strings.ReplaceAll(strings.TrimSpace(title), "\n", " "))
		b.WriteString("\n\n")
	}
	b.WriteString(content)
	if !strings.HasSuffix(content, "\n") {
		b.WriteString("\n")
	}
	return b.String()
}

// splitTitle inverts composeNote: extract a leading "# title" line if
// present, return remaining content. If no H1, title falls back to
// the first non-empty line, and content is the whole input.
func splitTitle(s string) (title, content string) {
	lines := strings.SplitN(s, "\n", 2)
	first := strings.TrimSpace(lines[0])
	if strings.HasPrefix(first, "# ") {
		title = strings.TrimSpace(strings.TrimPrefix(first, "# "))
		if len(lines) > 1 {
			content = strings.TrimLeft(lines[1], "\n")
		}
		return
	}
	return first, s
}

func readTitle(fs *tenant.FS, rel string) (string, error) {
	data, err := fs.ReadFile(rel)
	if err != nil {
		return "", err
	}
	t, _ := splitTitle(string(data))
	if t == "" {
		t = strings.TrimSuffix(filepath.Base(rel), ".md")
	}
	return t, nil
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

// SafeNoteID returns a slug for s suitable as a note ID. It is
// exported so cmd/librenotes can derive default IDs from titles.
func SafeNoteID(s string) string {
	s = strings.ToLower(strings.TrimSpace(s))
	out := make([]byte, 0, len(s))
	for i := 0; i < len(s); i++ {
		c := s[i]
		switch {
		case c >= 'a' && c <= 'z', c >= '0' && c <= '9':
			out = append(out, c)
		case c == ' ' || c == '-' || c == '_':
			if len(out) > 0 && out[len(out)-1] != '-' {
				out = append(out, '-')
			}
		}
	}
	id := strings.Trim(string(out), "-")
	if id == "" {
		return strconv.FormatInt(time.Now().UnixNano(), 36)
	}
	if len(id) > 64 {
		id = id[:64]
	}
	if !noteIDRe.MatchString(id) {
		return strconv.FormatInt(time.Now().UnixNano(), 36)
	}
	return id
}

// pathSafe is a sanity helper used by tests; not exported.
func pathSafe(p string) bool {
	clean := path.Clean(p)
	return !strings.Contains(clean, "..") && !strings.HasPrefix(clean, "/")
}

// ensure usage so go vet doesn't complain when tests are absent.
var _ = pathSafe
var _ = fmt.Sprintf