package api

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

	"github.com/gin-gonic/gin"

	"gitea.stevedudenhoeffer.com/steve/pansy/internal/domain"
)

// writeServiceError maps a service-layer sentinel error to pansy's JSON error
// envelope ({"error":{"code","message"}}). One mapper serves every handler
// (auth and resources) so the status/code for a given sentinel is defined once.
//
// ErrNotFound covers both a genuinely missing row and one the actor may not see
// (existence is masked). ErrVersionConflict here is a fallback that omits the
// current row — handlers that can produce one special-case it with
// writeVersionConflict before falling through here. Login failures never leak
// which of email/password was wrong.
func writeServiceError(c *gin.Context, err error) {
	switch {
	case errors.Is(err, domain.ErrNotFound):
		writeAPIError(c, http.StatusNotFound, "NOT_FOUND", "not found")
	case errors.Is(err, domain.ErrForbidden):
		writeAPIError(c, http.StatusForbidden, "FORBIDDEN", "you don't have access")
	case errors.Is(err, domain.ErrVersionConflict):
		writeAPIError(c, http.StatusConflict, "VERSION_CONFLICT", "the resource was modified; refetch and retry")
	case errors.Is(err, domain.ErrPlantInUse):
		writeAPIError(c, http.StatusConflict, "PLANT_IN_USE", "this plant is used by plantings and can't be deleted")
	case errors.Is(err, domain.ErrShareUserNotFound):
		writeAPIError(c, http.StatusNotFound, "SHARE_USER_NOT_FOUND", "no account with that email")
	case errors.Is(err, domain.ErrCannotShareWithSelf):
		writeAPIError(c, http.StatusBadRequest, "CANNOT_SHARE_WITH_SELF", "you can't share a garden with yourself")
	case errors.Is(err, domain.ErrShareExists):
		writeAPIError(c, http.StatusConflict, "SHARE_EXISTS", "this garden is already shared with that user")
	case errors.Is(err, domain.ErrInvalidCredentials):
		writeAPIError(c, http.StatusUnauthorized, "INVALID_CREDENTIALS", "invalid email or password")
	case errors.Is(err, domain.ErrEmailTaken):
		writeAPIError(c, http.StatusConflict, "EMAIL_TAKEN", "an account with that email already exists")
	case errors.Is(err, domain.ErrRegistrationClosed):
		writeAPIError(c, http.StatusForbidden, "REGISTRATION_CLOSED", "registration is closed")
	case errors.Is(err, domain.ErrLocalAuthDisabled):
		writeAPIError(c, http.StatusForbidden, "LOCAL_AUTH_DISABLED", "local authentication is disabled")
	case errors.Is(err, domain.ErrOIDCNoEmail):
		writeAPIError(c, http.StatusBadRequest, "OIDC_NO_EMAIL", "the identity provider returned no email")
	case errors.Is(err, domain.ErrOIDCEmailUnverified):
		writeAPIError(c, http.StatusForbidden, "OIDC_EMAIL_UNVERIFIED", "the identity provider's email is not verified")
	case errors.Is(err, domain.ErrOIDCIdentityConflict):
		writeAPIError(c, http.StatusConflict, "OIDC_IDENTITY_CONFLICT", "this identity conflicts with an existing account")
	case errors.Is(err, domain.ErrInvalidInput):
		writeAPIError(c, http.StatusBadRequest, "INVALID_INPUT", "invalid input")
	default:
		slog.Error("api: unhandled service error", "error", err)
		writeAPIError(c, http.StatusInternalServerError, "INTERNAL", "internal error")
	}
}

// writeVersionConflict writes the 409 envelope for an optimistic-concurrency
// failure: the standard error object plus the current server row under
// "current", so the client can rebase its edit onto the fresh version and retry.
// This shape is the contract for every version-guarded (mutable) resource.
func writeVersionConflict(c *gin.Context, current any) {
	c.JSON(http.StatusConflict, gin.H{
		"error":   gin.H{"code": "VERSION_CONFLICT", "message": "the resource was modified; refetch and retry"},
		"current": current,
	})
}

// parseNullable decodes any JSON value into (value, present) for a nullable
// column: absent → (nil, false); explicit null → (nil, true); anything else →
// the decoded value. That three-way distinction is what lets a PATCH tell "clear
// this to NULL" apart from "leave it alone", and every nullable field in the API
// needs it, so it lives here rather than in whichever file happened to want it
// first.
func parseNullable[T any](raw json.RawMessage) (*T, bool, error) {
	if len(raw) == 0 {
		return nil, false, nil
	}
	if string(raw) == "null" {
		return nil, true, nil
	}
	var v T
	if err := json.Unmarshal(raw, &v); err != nil {
		return nil, false, err
	}
	return &v, true, nil
}

// intQuery reads a non-negative integer query parameter, falling back to def on
// an absent or malformed value.
func intQuery(c *gin.Context, name string, def int) int {
	raw := c.Query(name)
	if raw == "" {
		return def
	}
	v, err := strconv.Atoi(raw)
	if err != nil || v < 0 {
		return def
	}
	return v
}

// parseIDParam reads a positive int64 path parameter, writing a 400 and
// returning ok=false on a malformed value.
func parseIDParam(c *gin.Context, name string) (int64, bool) {
	id, err := strconv.ParseInt(c.Param(name), 10, 64)
	if err != nil || id < 1 {
		writeAPIError(c, http.StatusBadRequest, "INVALID_INPUT", "invalid id")
		return 0, false
	}
	return id, true
}