// Package layout provides responsive dimension calculations for the Nebara OS TUI.
// All functions operate on terminal cell dimensions, not pixels.
package layout

// Constraints holds calculated layout values for a given terminal size.
type Constraints struct {
	TermWidth  int
	TermHeight int

	// Outer horizontal margin in cells (applied to both left and right sides).
	MarginH int
	// Outer vertical margin in cells (applied to top and bottom).
	MarginV int

	// ContentWidth is the usable width between the two horizontal margins.
	ContentWidth int

	// AppInfoLines is the number of rows reserved for appliance information
	// (product title + 4 metadata rows).
	AppInfoLines int

	// MessageVisible indicates whether the message row should be shown.
	// On very compact terminals it may be suppressed.
	MessageVisible bool

	// MenuInnerPad is the horizontal padding inside the menu border.
	MenuInnerPad int

	// FooterLines is the number of rows occupied by the footer (description + shortcuts).
	FooterLines int

	// IsMinimum flags terminals smaller than the supported minimum.
	IsMinimum bool
}

// MinWidth is the smallest terminal width the application supports gracefully.
const MinWidth = 60

// MinHeight is the smallest terminal height the application supports gracefully.
const MinHeight = 20

// Calculate derives layout constraints from terminal dimensions.
// Reference: Figma frame 1920×1080 with 80px outer margins (4.17% of width)
// and 60px vertical margins (5.56% of height).
func Calculate(termW, termH int) Constraints {
	if termW < MinWidth || termH < MinHeight {
		return Constraints{
			TermWidth:  termW,
			TermHeight: termH,
			IsMinimum:  true,
		}
	}

	// Horizontal margin: ~4.17% of width, min 4 cells, max 12 cells.
	marginH := clamp(termW*417/10000, 4, 12)

	// Vertical margin: ~5.56% of height, min 1 cell, max 4 cells.
	marginV := clamp(termH*556/10000, 1, 4)

	contentWidth := termW - marginH*2

	// Menu inner horizontal padding (space between border char and text).
	menuInnerPad := 2
	if termW < 100 {
		menuInnerPad = 1
	}

	// Message row visibility: suppress on very compact terminals.
	messageVisible := termH >= 24

	return Constraints{
		TermWidth:      termW,
		TermHeight:     termH,
		MarginH:        marginH,
		MarginV:        marginV,
		ContentWidth:   contentWidth,
		AppInfoLines:   6, // blank + product title + blank + 4 metadata rows
		MessageVisible: messageVisible,
		MenuInnerPad:   menuInnerPad,
		FooterLines:    2,
		IsMinimum:      false,
	}
}

func clamp(v, lo, hi int) int {
	if v < lo {
		return lo
	}
	if v > hi {
		return hi
	}
	return v
}