package httputil

import (
	"context"
	"encoding/json"
	"net/http"

	"code.nochebuena.dev/go/valid"
	"code.nochebuena.dev/go/xerrors"
)

// HandlerFunc is an http.Handler that can return an error.
// On non-nil error the error is mapped to the appropriate HTTP response via Error.
// Useful for manual handlers that don't need the typed adapter.
type HandlerFunc func(w http.ResponseWriter, r *http.Request) error

func (h HandlerFunc) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if err := h(w, r); err != nil {
		Error(w, err)
	}
}

// Handle adapts a typed business function to http.HandlerFunc.
// - Decodes JSON request body into Req.
// - Validates Req using the provided Validator.
// - Calls fn with the request context and decoded Req.
// - Encodes Res as JSON with HTTP 200.
// - Maps any returned error to the appropriate HTTP status via xerrors code.
func Handle[Req, Res any](v valid.Validator, fn func(ctx context.Context, req Req) (Res, error)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var req Req
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			Error(w, badRequest("invalid JSON: "+err.Error()))
			return
		}
		if err := v.Struct(req); err != nil {
			Error(w, err)
			return
		}
		res, err := fn(r.Context(), req)
		if err != nil {
			Error(w, err)
			return
		}
		JSON(w, http.StatusOK, res)
	}
}

// HandleNoBody adapts a typed function with no request body (GET, DELETE).
// Calls fn with request context; encodes result as JSON with HTTP 200.
func HandleNoBody[Res any](fn func(ctx context.Context) (Res, error)) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		res, err := fn(r.Context())
		if err != nil {
			Error(w, err)
			return
		}
		JSON(w, http.StatusOK, res)
	}
}

// HandleEmpty adapts a typed function with a body but no response body (returns 204).
// Decodes JSON body into Req, validates, calls fn. Returns 204 on success.
func HandleEmpty[Req any](v valid.Validator, fn func(ctx context.Context, req Req) error) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		var req Req
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			Error(w, badRequest("invalid JSON: "+err.Error()))
			return
		}
		if err := v.Struct(req); err != nil {
			Error(w, err)
			return
		}
		if err := fn(r.Context(), req); err != nil {
			Error(w, err)
			return
		}
		NoContent(w)
	}
}

// badRequest wraps a message in an ErrInvalidInput error.
func badRequest(msg string) error {
	return xerrors.New(xerrors.ErrInvalidInput, msg)
}