// Package httpapi contains HTTP handlers, routing and middleware.
package httpapi

import (
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"

	"github.com/jackc/pgx/v5"
)

// Problem is a small RFC 7807-ish error body.
type Problem struct {
	Type   string `json:"type,omitempty"`
	Title  string `json:"title"`
	Status int    `json:"status"`
	Detail string `json:"detail,omitempty"`
}

// renderJSON writes v as JSON with the given status code.
func renderJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	if v == nil {
		return
	}
	if err := json.NewEncoder(w).Encode(v); err != nil {
		slog.Error("write json response failed", "error", err)
	}
}

// renderError writes a Problem response.
func renderError(w http.ResponseWriter, status int, title, detail string) {
	renderJSON(w, status, Problem{
		Title:  title,
		Status: status,
		Detail: detail,
	})
}

// apiError maps well-known errors to HTTP status codes. Returns true if handled.
func apiError(w http.ResponseWriter, err error) bool {
	switch {
	case errors.Is(err, pgx.ErrNoRows):
		renderError(w, http.StatusNotFound, "Not found", "The requested resource does not exist.")
	case errors.Is(err, ErrUnauthorized):
		renderError(w, http.StatusUnauthorized, "Unauthorized", err.Error())
	case errors.Is(err, ErrForbidden):
		renderError(w, http.StatusForbidden, "Forbidden", err.Error())
	case errors.Is(err, ErrConflict):
		renderError(w, http.StatusConflict, "Conflict", err.Error())
	case errors.Is(err, ErrBadRequest):
		renderError(w, http.StatusBadRequest, "Bad request", err.Error())
	default:
		return false
	}
	return true
}

// Sentinel domain errors mapped by apiError.
var (
	ErrBadRequest   = errors.New("bad request")
	ErrUnauthorized = errors.New("unauthorized")
	ErrForbidden    = errors.New("forbidden")
	ErrConflict     = errors.New("conflict")
)

// decodeJSON decodes r.Body into v. Returns false and writes an error on failure.
func decodeJSON(w http.ResponseWriter, r *http.Request, v any) bool {
	dec := json.NewDecoder(r.Body)
	dec.DisallowUnknownFields()
	if err := dec.Decode(v); err != nil {
		renderError(w, http.StatusBadRequest, "Invalid JSON", err.Error())
		return false
	}
	return true
}