package server

import (
	"encoding/json"
	"errors"
	"net/http"
	"strconv"

	"mgit.msbls.de/m/mcables/internal/db"
)

type handlers struct {
	store *db.Store
}

// ---------------------------------------------------------------- utility

// writeJSON encodes v as JSON at the given status. Errors during encoding
// are logged-silent (the response has already started) — this is the
// last-resort path; callers should validate inputs early.
func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

type errorBody struct {
	Error   string `json:"error"`
	Details any    `json:"details,omitempty"`
}

// writeError maps a Store sentinel to an HTTP status + JSON body.
func writeError(w http.ResponseWriter, err error, details any) {
	switch {
	case errors.Is(err, db.ErrNotFound):
		writeJSON(w, http.StatusNotFound, errorBody{Error: err.Error(), Details: details})
	case errors.Is(err, db.ErrConflict):
		writeJSON(w, http.StatusConflict, errorBody{Error: err.Error(), Details: details})
	case errors.Is(err, db.ErrInUse):
		writeJSON(w, http.StatusConflict, errorBody{Error: err.Error(), Details: details})
	case errors.Is(err, db.ErrConfirmName):
		writeJSON(w, http.StatusBadRequest, errorBody{Error: err.Error(), Details: details})
	case errors.Is(err, db.ErrInvalidInput):
		writeJSON(w, http.StatusBadRequest, errorBody{Error: err.Error(), Details: details})
	case errors.Is(err, db.ErrForbidden):
		writeJSON(w, http.StatusForbidden, errorBody{Error: err.Error(), Details: details})
	default:
		writeJSON(w, http.StatusInternalServerError, errorBody{Error: err.Error(), Details: details})
	}
}

func parseInt64Path(r *http.Request, key string) (int64, bool) {
	raw := r.PathValue(key)
	v, err := strconv.ParseInt(raw, 10, 64)
	if err != nil || v <= 0 {
		return 0, false
	}
	return v, true
}

// ---------------------------------------------------------------- health

func (h *handlers) healthz(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

// ---------------------------------------------------------------- projects

type projectCreate struct {
	Name        string `json:"name"`
	DrawingName string `json:"drawing_name"`
	Description string `json:"description"`
}

type projectPatch struct {
	Name        *string `json:"name,omitempty"`
	DrawingName *string `json:"drawing_name,omitempty"`
	Description *string `json:"description,omitempty"`
}

func (h *handlers) listProjects(w http.ResponseWriter, _ *http.Request) {
	ps, err := h.store.ListProjects()
	if err != nil {
		writeError(w, err, nil)
		return
	}
	if ps == nil {
		ps = []db.Project{}
	}
	writeJSON(w, http.StatusOK, ps)
}

func (h *handlers) createProject(w http.ResponseWriter, r *http.Request) {
	var body projectCreate
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
		return
	}
	p, err := h.store.CreateProject(body.Name, body.DrawingName, body.Description)
	if err != nil {
		writeError(w, err, nil)
		return
	}
	writeJSON(w, http.StatusCreated, p)
}

func (h *handlers) getProject(w http.ResponseWriter, r *http.Request) {
	id, ok := parseInt64Path(r, "pid")
	if !ok {
		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
		return
	}
	snap, err := h.store.Snapshot(id)
	if err != nil {
		writeError(w, err, nil)
		return
	}
	writeJSON(w, http.StatusOK, snap)
}

func (h *handlers) patchProject(w http.ResponseWriter, r *http.Request) {
	id, ok := parseInt64Path(r, "pid")
	if !ok {
		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
		return
	}
	var body projectPatch
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
		return
	}
	p, err := h.store.UpdateProject(id, db.ProjectUpdate{
		Name:        body.Name,
		DrawingName: body.DrawingName,
		Description: body.Description,
	})
	if err != nil {
		writeError(w, err, nil)
		return
	}
	writeJSON(w, http.StatusOK, p)
}

func (h *handlers) deleteProject(w http.ResponseWriter, r *http.Request) {
	id, ok := parseInt64Path(r, "pid")
	if !ok {
		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
		return
	}
	confirm := r.URL.Query().Get("confirm")
	if confirm == "" {
		writeError(w, db.ErrConfirmName,
			"DELETE requires ?confirm=<project name> matching the project's current name")
		return
	}
	if err := h.store.DeleteProject(id, confirm); err != nil {
		writeError(w, err, nil)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}

// ---------------------------------------------------------------- cable_types

type cableTypeCreate struct {
	Name  string `json:"name"`
	Color string `json:"color"`
}

type cableTypePatch struct {
	Name  *string `json:"name,omitempty"`
	Color *string `json:"color,omitempty"`
}

func (h *handlers) listCableTypes(w http.ResponseWriter, _ *http.Request) {
	ts, err := h.store.ListCableTypes()
	if err != nil {
		writeError(w, err, nil)
		return
	}
	writeJSON(w, http.StatusOK, ts)
}

func (h *handlers) createCableType(w http.ResponseWriter, r *http.Request) {
	var body cableTypeCreate
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
		return
	}
	t, err := h.store.CreateCableType(body.Name, body.Color)
	if err != nil {
		writeError(w, err, nil)
		return
	}
	writeJSON(w, http.StatusCreated, t)
}

func (h *handlers) patchCableType(w http.ResponseWriter, r *http.Request) {
	id, ok := parseInt64Path(r, "id")
	if !ok {
		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
		return
	}
	var body cableTypePatch
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
		return
	}
	t, err := h.store.UpdateCableType(id, db.CableTypeUpdate{
		Name:  body.Name,
		Color: body.Color,
	})
	if err != nil {
		writeError(w, err, nil)
		return
	}
	writeJSON(w, http.StatusOK, t)
}

func (h *handlers) deleteCableType(w http.ResponseWriter, r *http.Request) {
	id, ok := parseInt64Path(r, "id")
	if !ok {
		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
		return
	}
	if err := h.store.DeleteCableType(id); err != nil {
		// On ErrInUse, count referencing cables so the client can show
		// "blocked by N cables".
		if errors.Is(err, db.ErrInUse) {
			n, _ := h.store.CountCablesUsingType(id)
			writeError(w, err, map[string]int{"in_use_by_cables": n})
			return
		}
		writeError(w, err, nil)
		return
	}
	w.WriteHeader(http.StatusNoContent)
}