package services

// DashboardLayoutSpec — JSON shape for paliad.user_dashboard_layouts.layout_json.
//
// Design: docs/design-dashboard-configurable-2026-05-20.md §5.2.
//
// Validation surface:
//   - version must be 1 (v0 / unknown versions seed the factory default at
//     read time; the validator only ever sees writes from a current client).
//   - widgets is at most 32 entries (sanity cap; catalog can grow but a
//     single user's layout shouldn't).
//   - each widget.key must be in KnownWidgetKeys on WRITE.
//   - no duplicate keys.
//   - each widget.settings (if present) is validated against its catalog
//     entry's WidgetSettingsSchema.
//
// On READ, unknown keys are dropped silently — see SanitizeForRead.

import (
	"encoding/json"
	"fmt"
	"slices"
)

// LayoutSpecVersion is the only supported version for v1.
const LayoutSpecVersion = 1

// LayoutWidgetCap is the sanity cap on widgets per layout. The v1 catalog
// has 7 entries; 32 leaves room for catalog growth without unbounded JSON
// blobs.
const LayoutWidgetCap = 32

// DashboardGridColumns is the column count of the dashboard layout grid. The CSS
// `.dashboard-grid` template is `repeat(DashboardGridColumns, 1fr)` and the
// validator caps X+W ≤ DashboardGridColumns. Twelve is the industry-standard
// dashboard grain — supports halves, thirds, quarters, sixths.
const DashboardGridColumns = 12

// MaxGridRowSpan caps how tall a single widget can grow. Five vertical
// cells is enough for a fully-expanded calendar without letting a
// runaway resize fill the entire viewport.
const MaxGridRowSpan = 5

// DashboardWidgetRef is a single widget entry in the ordered widgets[] array.
// Visible=false entries are kept in the array so the picker can show them as
// "hidden" and re-adding restores their position.
//
// Position fields (X/Y/W/H) carry the widget's slot in the 12-column grid.
// X is 0-indexed column-start (0..DashboardGridColumns-1); Y is 0-indexed row-start.
// W is column span (1..DashboardGridColumns); H is row span (1..MaxGridRowSpan).
// When W=0 the widget is treated as full-width (W=DashboardGridColumns); H=0
// means H=1. This keeps pre-overhaul layouts (no positions on the wire)
// rendering sensibly under the new grid — they get auto-placed full-
// width in array order.
type DashboardWidgetRef struct {
	Key      WidgetKey       `json:"key"`
	Visible  bool            `json:"visible"`
	X        int             `json:"x,omitempty"`
	Y        int             `json:"y,omitempty"`
	W        int             `json:"w,omitempty"`
	H        int             `json:"h,omitempty"`
	Settings json.RawMessage `json:"settings,omitempty"`
}

// DashboardLayoutSpec is the persisted layout shape.
type DashboardLayoutSpec struct {
	Version int                  `json:"v"`
	Widgets []DashboardWidgetRef `json:"widgets"`
}

// FactoryDefaultLayout returns the Slice A1 baseline layout — every
// widget in KnownWidgetKeys, in canonical order, with per-widget default
// settings + grid positions drawn from the catalog. Visible widgets get
// placed row-by-row using a greedy left-to-right packer (next widget
// goes into the leftmost slot wide enough on the current row, else
// wraps to a new row). Hidden widgets carry default sizes but no
// position — they get one when re-added via the picker.
func FactoryDefaultLayout() DashboardLayoutSpec {
	catalog := WidgetCatalog()
	byKey := make(map[WidgetKey]WidgetDef, len(catalog))
	for _, def := range catalog {
		byKey[def.Key] = def
	}

	widgets := make([]DashboardWidgetRef, 0, len(KnownWidgetKeys))
	// Greedy packer: place each visible widget left-to-right on the
	// current row. When the widget doesn't fit, wrap to a new row at y
	// = max-row-height-so-far. rowMaxH tracks the tallest widget in the
	// row currently being filled — wrapping by only the new widget's
	// height would let taller previous neighbours overlap. cursorX is
	// the next free column on the current row.
	cursorX, cursorY, rowMaxH := 0, 0, 0
	for _, k := range KnownWidgetKeys {
		def, ok := byKey[k]
		if !ok {
			continue
		}
		ref := DashboardWidgetRef{Key: k, Visible: def.DefaultVisible}
		if settings := defaultSettingsJSON(def); settings != nil {
			ref.Settings = settings
		}
		w := def.DefaultW
		if w <= 0 || w > DashboardGridColumns {
			w = DashboardGridColumns
		}
		h := def.DefaultH
		if h <= 0 {
			h = 1
		}
		ref.W = w
		ref.H = h
		if def.DefaultVisible {
			if cursorX+w > DashboardGridColumns {
				cursorY += rowMaxH
				cursorX = 0
				rowMaxH = 0
			}
			ref.X = cursorX
			ref.Y = cursorY
			cursorX += w
			if h > rowMaxH {
				rowMaxH = h
			}
		}
		widgets = append(widgets, ref)
	}

	return DashboardLayoutSpec{
		Version: LayoutSpecVersion,
		Widgets: widgets,
	}
}

// defaultSettingsJSON encodes the per-widget defaults declared on the
// catalog entry. Returns nil when the widget has no settings.
func defaultSettingsJSON(def WidgetDef) json.RawMessage {
	if def.DefaultCount == nil && def.DefaultHorizon == nil {
		return nil
	}
	out := map[string]int{}
	if def.DefaultCount != nil {
		out["count"] = *def.DefaultCount
	}
	if def.DefaultHorizon != nil {
		out["horizon_days"] = *def.DefaultHorizon
	}
	b, err := json.Marshal(out)
	if err != nil {
		return nil
	}
	return b
}

// Validate enforces the structural invariants on write. Returns
// ErrInvalidInput wrapped with a precise message on the first violation.
func (s DashboardLayoutSpec) Validate() error {
	if s.Version != LayoutSpecVersion {
		return fmt.Errorf("%w: layout version %d not supported (want %d)",
			ErrInvalidInput, s.Version, LayoutSpecVersion)
	}
	if len(s.Widgets) > LayoutWidgetCap {
		return fmt.Errorf("%w: layout has %d widgets (cap %d)",
			ErrInvalidInput, len(s.Widgets), LayoutWidgetCap)
	}

	seen := make(map[WidgetKey]bool, len(s.Widgets))
	for i, w := range s.Widgets {
		if !slices.Contains(KnownWidgetKeys, w.Key) {
			return fmt.Errorf("%w: widgets[%d].key %q is not a known widget",
				ErrInvalidInput, i, w.Key)
		}
		if seen[w.Key] {
			return fmt.Errorf("%w: widgets has duplicate key %q",
				ErrInvalidInput, w.Key)
		}
		seen[w.Key] = true

		def, ok := LookupWidgetDef(w.Key)
		if !ok {
			// Defense in depth — KnownWidgetKeys was checked above.
			return fmt.Errorf("%w: widgets[%d].key %q has no catalog entry",
				ErrInvalidInput, i, w.Key)
		}
		if err := def.Settings.Validate(w.Settings); err != nil {
			return fmt.Errorf("widgets[%d]: %w", i, err)
		}
		if err := validatePosition(i, w, def); err != nil {
			return err
		}
	}
	return nil
}

// validatePosition checks grid X/Y/W/H against schema clamps. Zero
// values are accepted (auto-flow + default size); non-zero values must
// fit the 12-column grid and the widget's MinW/MaxW/MinH/MaxH clamps.
func validatePosition(i int, w DashboardWidgetRef, def WidgetDef) error {
	if w.X < 0 || w.X >= DashboardGridColumns {
		return fmt.Errorf("%w: widgets[%d].x %d outside [0,%d)", ErrInvalidInput, i, w.X, DashboardGridColumns)
	}
	if w.Y < 0 {
		return fmt.Errorf("%w: widgets[%d].y %d must be >= 0", ErrInvalidInput, i, w.Y)
	}
	if w.W < 0 || w.W > DashboardGridColumns {
		return fmt.Errorf("%w: widgets[%d].w %d outside [0,%d]", ErrInvalidInput, i, w.W, DashboardGridColumns)
	}
	if w.W > 0 && w.X+w.W > DashboardGridColumns {
		return fmt.Errorf("%w: widgets[%d] x+w (%d) overflows grid (%d)", ErrInvalidInput, i, w.X+w.W, DashboardGridColumns)
	}
	if w.H < 0 || w.H > MaxGridRowSpan {
		return fmt.Errorf("%w: widgets[%d].h %d outside [0,%d]", ErrInvalidInput, i, w.H, MaxGridRowSpan)
	}
	if def.MinW > 0 && w.W > 0 && w.W < def.MinW {
		return fmt.Errorf("%w: widgets[%d].w %d below MinW=%d", ErrInvalidInput, i, w.W, def.MinW)
	}
	if def.MaxW > 0 && w.W > def.MaxW {
		return fmt.Errorf("%w: widgets[%d].w %d above MaxW=%d", ErrInvalidInput, i, w.W, def.MaxW)
	}
	if def.MinH > 0 && w.H > 0 && w.H < def.MinH {
		return fmt.Errorf("%w: widgets[%d].h %d below MinH=%d", ErrInvalidInput, i, w.H, def.MinH)
	}
	if def.MaxH > 0 && w.H > def.MaxH {
		return fmt.Errorf("%w: widgets[%d].h %d above MaxH=%d", ErrInvalidInput, i, w.H, def.MaxH)
	}
	return nil
}

// SanitizeForRead applies the forgiving read-path rules: drop entries whose
// keys are not in the catalog (catalog has shrunk), bump the version to
// the current one if missing, and clamp w/h/x against the catalog's
// MinW/MaxW/MinH/MaxH/grid bounds so a stale row with out-of-range sizes
// can't strand the user with unrenderable widgets (m/paliad#73). Settings
// on surviving entries pass through unchanged — invalid settings on read
// are not worth aborting over and the next write will reject them anyway.
//
// Returns true if anything was changed; callers can use that to decide
// whether to PUT the cleaned spec back.
func (s *DashboardLayoutSpec) SanitizeForRead() bool {
	changed := false
	if s.Version != LayoutSpecVersion {
		s.Version = LayoutSpecVersion
		changed = true
	}
	if len(s.Widgets) == 0 {
		return changed
	}
	out := make([]DashboardWidgetRef, 0, len(s.Widgets))
	for _, w := range s.Widgets {
		def, ok := LookupWidgetDef(w.Key)
		if !ok {
			changed = true
			continue
		}
		if normalizePosition(&w, def) {
			changed = true
		}
		out = append(out, w)
	}
	s.Widgets = out
	return changed
}

// normalizePosition clamps a widget's W/H/X to the catalog bounds and the
// grid extent. Returns true if any field was modified. Zero W/H stay zero
// (auto-flow / default sentinel — the placer fills them in). Negative X
// snaps to 0; X+W overflowing the grid snaps X down.
func normalizePosition(w *DashboardWidgetRef, def WidgetDef) bool {
	changed := false

	if w.W < 0 {
		w.W = 0
		changed = true
	}
	if w.W > DashboardGridColumns {
		w.W = DashboardGridColumns
		changed = true
	}
	// W == 0 is the "auto / default" sentinel — leave it untouched so
	// downstream renderers can substitute DefaultW. Only clamp non-zero
	// values against the per-widget Min/Max.
	if w.W > 0 {
		if def.MinW > 0 && w.W < def.MinW {
			w.W = def.MinW
			changed = true
		}
		if def.MaxW > 0 && w.W > def.MaxW {
			w.W = def.MaxW
			changed = true
		}
	}

	if w.H < 0 {
		w.H = 0
		changed = true
	}
	if w.H > MaxGridRowSpan {
		w.H = MaxGridRowSpan
		changed = true
	}
	if w.H > 0 {
		if def.MinH > 0 && w.H < def.MinH {
			w.H = def.MinH
			changed = true
		}
		if def.MaxH > 0 && w.H > def.MaxH {
			w.H = def.MaxH
			changed = true
		}
	}

	if w.X < 0 {
		w.X = 0
		changed = true
	}
	if w.X >= DashboardGridColumns {
		w.X = DashboardGridColumns - 1
		changed = true
	}
	if w.W > 0 && w.X+w.W > DashboardGridColumns {
		w.X = DashboardGridColumns - w.W
		changed = true
	}
	if w.Y < 0 {
		w.Y = 0
		changed = true
	}

	return changed
}

// ParseDashboardLayoutSpec decodes JSON bytes and validates. Used by the
// HTTP handler on incoming request bodies.
func ParseDashboardLayoutSpec(b []byte) (DashboardLayoutSpec, error) {
	var s DashboardLayoutSpec
	if err := json.Unmarshal(b, &s); err != nil {
		return DashboardLayoutSpec{}, fmt.Errorf("%w: layout JSON decode: %v", ErrInvalidInput, err)
	}
	if err := s.Validate(); err != nil {
		return DashboardLayoutSpec{}, err
	}
	return s, nil
}