package service

import (
	"context"
	"math"
	"strings"

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

// Garden sizing and field bounds. A new garden with no dimensions defaults to a
// 10 m square; dimensions must be finite and within [1 cm, 100 m] — a generous
// sanity range that also rejects NaN/Inf and absurd values. Name/notes are
// length-capped so untrusted input can't balloon storage.
const (
	defaultGardenCM     = 1000   // 10 m
	minGardenCM         = 1      // 1 cm
	maxGardenCM         = 10_000 // 100 m
	defaultGardenGridCM = 100    // 1 m, matching the editor's previous fixed grid
	maxGardenNameLen    = 200
	maxGardenNotesLen   = 10_000
)

// gardenRole ranks a user's access to a garden. Higher includes lower
// (owner can do anything an editor can, etc.). Until sharing (#16), the only
// role anyone holds is owner, on their own gardens.
type gardenRole int

const (
	roleNone gardenRole = iota
	roleViewer
	roleEditor
	roleOwner
)

// String renders a role for the API's Garden.MyRole ("owner"/"editor"/"viewer").
func (r gardenRole) String() string {
	switch r {
	case roleOwner:
		return domain.RoleOwner
	case roleEditor:
		return domain.RoleEditor
	case roleViewer:
		return domain.RoleViewer
	default:
		return ""
	}
}

// GardenInput is the mutable field set for creating or updating a garden.
type GardenInput struct {
	Name       string
	WidthCM    float64
	HeightCM   float64
	UnitPref   string
	Notes      string
	GridSizeCM float64
	SnapToGrid bool
}

// requireGardenRole loads a garden and enforces that the actor holds at least
// min. It is THE place authorization for a garden is decided — REST handlers and
// future agent tools both funnel through here, so neither can skip a check.
//
// A user with no role at all gets ErrNotFound rather than ErrForbidden: we don't
// reveal that a garden exists to someone with no access. A user who has some
// access but not enough (e.g. a viewer trying to edit, once #16 lands) gets
// ErrForbidden. #16 extends effectiveRole to consult garden_shares.
func (s *Service) requireGardenRole(ctx context.Context, actorID, gardenID int64, min gardenRole) (*domain.Garden, error) {
	g, err := s.store.GetGarden(ctx, gardenID)
	if err != nil {
		return nil, err // ErrNotFound or a real error
	}
	role, err := s.effectiveGardenRole(ctx, actorID, g)
	if err != nil {
		return nil, err
	}
	if role == roleNone {
		return nil, domain.ErrNotFound
	}
	if role < min {
		return nil, domain.ErrForbidden
	}
	g.MyRole = role.String() // so every read-through carries the actor's role
	return g, nil
}

// effectiveGardenRole is the actor's role on a garden: owner (implicit via
// gardens.owner_id), else a viewer/editor grant from garden_shares, else none.
func (s *Service) effectiveGardenRole(ctx context.Context, actorID int64, g *domain.Garden) (gardenRole, error) {
	if g.OwnerID == actorID {
		return roleOwner, nil
	}
	role, found, err := s.store.GetShareRole(ctx, g.ID, actorID)
	if err != nil {
		return roleNone, err
	}
	if !found {
		return roleNone, nil
	}
	switch role {
	case domain.RoleEditor:
		return roleEditor, nil
	case domain.RoleViewer:
		return roleViewer, nil
	default:
		return roleNone, nil
	}
}

// CreateGarden creates a garden owned by the actor. Missing dimensions default
// to a 10 m square; unit defaults to metric.
func (s *Service) CreateGarden(ctx context.Context, actorID int64, in GardenInput) (*domain.Garden, error) {
	g, err := gardenFromInput(in, true)
	if err != nil {
		return nil, err
	}
	g.OwnerID = actorID
	created, err := s.store.CreateGarden(ctx, g)
	if err != nil {
		return nil, err
	}
	created.MyRole = roleOwner.String() // the creator owns it
	return created, nil
}

// GetGarden returns a garden the actor may at least view.
func (s *Service) GetGarden(ctx context.Context, actorID, gardenID int64) (*domain.Garden, error) {
	return s.requireGardenRole(ctx, actorID, gardenID, roleViewer)
}

// ListGardens returns the gardens the actor can see: owned plus shared-with-them,
// each row carrying the actor's my_role.
func (s *Service) ListGardens(ctx context.Context, actorID int64) ([]domain.Garden, error) {
	return s.store.ListGardensForActor(ctx, actorID)
}

// UpdateGarden applies a version-guarded update to a garden's metadata; only the
// OWNER may edit metadata (editors edit contents, not the garden itself). On a
// version mismatch it returns (current garden, ErrVersionConflict) so the handler
// can return the fresh row for the client to rebase.
func (s *Service) UpdateGarden(ctx context.Context, actorID, gardenID int64, in GardenInput, version int64) (*domain.Garden, error) {
	before, err := s.requireGardenRole(ctx, actorID, gardenID, roleOwner)
	if err != nil {
		return nil, err
	}
	g, err := gardenFromInput(in, false) // no defaults: an update states every field
	if err != nil {
		return nil, err
	}
	g.ID = gardenID
	g.Version = version
	updated, err := s.store.UpdateGarden(ctx, g)
	if updated != nil {
		updated.MyRole = roleOwner.String() // only the owner reaches here
	}
	if err != nil {
		return updated, err
	}
	// MyRole is computed, not stored; blank it in the snapshot so a revert can't
	// write a role into a row that has no such column.
	snap := *before
	snap.MyRole = ""
	after := *updated
	after.MyRole = ""
	s.record(ctx, gardenID, actorID, "Edited garden settings",
		changeUpdate(domain.EntityGarden, gardenID, &snap, &after))
	return updated, nil
}

// CopyGarden duplicates a garden into a new one owned by the actor, carrying
// over its dimensions, grid settings, objects and currently-planted plops. A
// blank name defaults to "<source> (copy)".
//
// Owner-only, deliberately: a copy's plops keep pointing at the SOURCE's
// plant_ids, and a custom plant is owned by one user. Letting a viewer copy
// someone else's garden would hand them a garden referencing plants that aren't
// in their catalog — and would block the original owner from ever deleting those
// plants (plantings.plant_id is ON DELETE RESTRICT). Copying a shared garden
// needs a plant-cloning policy first; until then the owner's own copy is the
// case that's unambiguously correct.
func (s *Service) CopyGarden(ctx context.Context, actorID, gardenID int64, name string) (*domain.Garden, error) {
	src, err := s.requireGardenRole(ctx, actorID, gardenID, roleOwner)
	if err != nil {
		return nil, err
	}
	name = strings.TrimSpace(name)
	if name == "" {
		name = copyName(src.Name)
	}
	if len(name) > maxGardenNameLen {
		return nil, domain.ErrInvalidInput
	}
	created, err := s.store.CopyGarden(ctx, gardenID, actorID, name)
	if err != nil {
		return nil, err
	}
	created.MyRole = roleOwner.String() // the copier owns the copy
	return created, nil
}

// copyName derives the default name for a copy. A name already at the length cap
// is trimmed to make room for the suffix, on a rune boundary so the result stays
// valid UTF-8.
func copyName(src string) string {
	const suffix = " (copy)"
	if room := maxGardenNameLen - len(suffix); len(src) > room {
		src = strings.TrimSpace(strings.ToValidUTF8(src[:room], ""))
	}
	return src + suffix
}

// DeleteGarden removes a garden; only the owner may.
func (s *Service) DeleteGarden(ctx context.Context, actorID, gardenID int64) error {
	if _, err := s.requireGardenRole(ctx, actorID, gardenID, roleOwner); err != nil {
		return err
	}
	return s.store.DeleteGarden(ctx, gardenID)
}

// gardenFromInput validates and normalizes input into a domain.Garden (without
// identity/ownership fields). With applyDefaults, absent dimensions/unit are
// filled in (create); without it, dimensions and unit must be supplied (update).
// The grid size is the exception: 0 always means "unset" and is defaulted on both
// paths, so an older client that omits it can't wipe the column to an invalid 0.
func gardenFromInput(in GardenInput, applyDefaults bool) (*domain.Garden, error) {
	name := strings.TrimSpace(in.Name)
	if name == "" || len(name) > maxGardenNameLen {
		return nil, domain.ErrInvalidInput
	}
	notes := strings.TrimSpace(in.Notes)
	if len(notes) > maxGardenNotesLen {
		return nil, domain.ErrInvalidInput
	}

	// 0 means "unset": defaulted on create, rejected on update. Anything else
	// must be a finite length in range — this also rejects negatives, NaN, Inf,
	// and subnormal-tiny values (which are > 0 but below 1 cm).
	width, height := in.WidthCM, in.HeightCM
	if applyDefaults {
		if width == 0 {
			width = defaultGardenCM
		}
		if height == 0 {
			height = defaultGardenCM
		}
	}
	if !validDimensionCM(width) || !validDimensionCM(height) {
		return nil, domain.ErrInvalidInput
	}

	unit := in.UnitPref
	if unit == "" && applyDefaults {
		unit = domain.UnitMetric
	}
	if unit != domain.UnitMetric && unit != domain.UnitImperial {
		return nil, domain.ErrInvalidInput
	}

	// Grid spacing shares the garden dimension range [1 cm, 100 m]. 0 means
	// "unset" — defaulted (not just on create: an older client that omits it must
	// not wipe the column to an invalid 0), so a saved garden always has a usable
	// grid even if snapping is off.
	grid := in.GridSizeCM
	if grid == 0 {
		grid = defaultGardenGridCM
	}
	if !validDimensionCM(grid) {
		return nil, domain.ErrInvalidInput
	}

	return &domain.Garden{
		Name:       name,
		WidthCM:    width,
		HeightCM:   height,
		UnitPref:   unit,
		Notes:      notes,
		GridSizeCM: grid,
		SnapToGrid: in.SnapToGrid,
	}, nil
}

// validDimensionCM reports whether v is a finite length within the allowed
// garden range. Guards against NaN/Inf (which slip past naive < / > comparisons)
// and subnormal-tiny positives.
func validDimensionCM(v float64) bool {
	return !math.IsNaN(v) && !math.IsInf(v, 0) && v >= minGardenCM && v <= maxGardenCM
}