package httpapi

import (
	"bytes"
	"encoding/json"
	"errors"
	"io"
	"log"
	"net/http"
	"regexp"
	"strings"

	"github.com/descrybe/descrybe-v2/apps/api/internal/i18n"
)

const maxJSONBodyBytes = 2 << 20 // 2 MiB

var errJSONBodyTooLarge = errors.New("request body too large")
var errJSONTrailingContent = errors.New("request body must contain a single JSON object")

// secretLikeRE matches common secret material that must never appear in logs.
var secretLikeRE = regexp.MustCompile(`(?i)(password|passwd|secret|api[_-]?key|token|authorization|bearer|sk_live|sk_test|whsec_)[^\s]{0,64}`)

func redactForLog(msg string) string {
	if msg == "" {
		return msg
	}
	return secretLikeRE.ReplaceAllStringFunc(msg, func(m string) string {
		parts := strings.SplitN(m, "=", 2)
		if len(parts) == 2 {
			return parts[0] + "=[REDACTED]"
		}
		if i := strings.IndexByte(m, ':'); i > 0 && i < 24 {
			return m[:i+1] + "[REDACTED]"
		}
		return "[REDACTED]"
	})
}

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

func Error(w http.ResponseWriter, status int, msg string) {
	JSON(w, status, map[string]string{"error": PublicMessage(w, msg)})
}

// FieldError writes the usual public error string plus an additive field map:
//
//	{ "error": "...", "code": "...?", "fields": { "<field>": "..." } }
//
// `error` stays the localized human message. Optional `code` is a stable
// machine token (never translated). `fields` lets dashboards highlight inputs
// under any Accept-Language without English substring matching.
// Clients that only read `error` keep working (no BREAKING change).
func FieldError(w http.ResponseWriter, status int, msg string, code string, fields map[string]string) {
	localized := PublicMessage(w, msg)
	out := map[string]any{"error": localized}
	if code != "" {
		out["code"] = code
	}
	if len(fields) > 0 {
		lf := make(map[string]string, len(fields))
		for k, v := range fields {
			if k == "" {
				continue
			}
			text := v
			if text == "" {
				text = msg
			}
			lf[k] = PublicMessage(w, text)
		}
		if len(lf) > 0 {
			out["fields"] = lf
		}
	}
	JSON(w, status, out)
}

// CodedError writes the legacy public-API error envelope:
//
//	{ "error": { "code": "...", "message": "..." } }
//
// Used for /api/v1 API-key auth failures so clients migrating from Descrybe
// see the same shape as err(code, message) in the Next.js app.
// Code is never translated; message respects Accept-Language via Locale middleware.
func CodedError(w http.ResponseWriter, status int, code, message string) {
	JSON(w, status, map[string]any{
		"error": map[string]string{"code": code, "message": PublicMessage(w, message)},
	})
}

// PublicMessage localizes a client-facing string for the request locale.
// Stable machine codes (password_not_set, maintenance, …) stay unchanged.
func PublicMessage(w http.ResponseWriter, msg string) string {
	return i18n.T(localeOf(w), msg)
}

// LogAndError logs the real error server-side (secrets redacted) and returns a safe public message.
func LogAndError(w http.ResponseWriter, status int, publicMsg string, err error) {
	if err != nil {
		log.Printf("httpapi: %s: %s", publicMsg, redactForLog(err.Error()))
	}
	Error(w, status, publicMsg)
}

// ClientOrLog writes a known client message, or logs and returns publicFallback.
func ClientOrLog(w http.ResponseWriter, status int, publicFallback string, err error, clientMsg func(error) (string, bool)) {
	if msg, ok := clientMsg(err); ok {
		Error(w, status, msg)
		return
	}
	LogAndError(w, status, publicFallback, err)
}

func DecodeJSON(r *http.Request, dst any) error {
	return decodeJSON(r, dst, true)
}

// DecodeJSONAllowUnknown decodes JSON without DisallowUnknownFields.
// Used for legacy public process payloads that may include extra item keys.
func DecodeJSONAllowUnknown(r *http.Request, dst any) error {
	return decodeJSON(r, dst, false)
}

func decodeJSON(r *http.Request, dst any, disallowUnknown bool) error {
	defer r.Body.Close()
	data, err := io.ReadAll(io.LimitReader(r.Body, maxJSONBodyBytes+1))
	if err != nil {
		return err
	}
	if len(data) > maxJSONBodyBytes {
		return errJSONBodyTooLarge
	}
	dec := json.NewDecoder(bytes.NewReader(data))
	if disallowUnknown {
		dec.DisallowUnknownFields()
	}
	if err := dec.Decode(dst); err != nil {
		return err
	}
	if err := dec.Decode(&struct{}{}); !errors.Is(err, io.EOF) {
		return errJSONTrailingContent
	}
	return nil
}

func DecodeJSONOptional(r *http.Request, dst any) error {
	err := DecodeJSON(r, dst)
	if errors.Is(err, io.EOF) {
		return nil
	}
	return err
}