package theme

import (
	"math"

	renderer "github.com/bnema/vev-vt"
	"github.com/bnema/vev/internal/domain"
)

const accentContrastMin = 3.0

// RelativeLuminance returns a color's WCAG 2.x relative luminance.
func RelativeLuminance(color renderer.RGB) float64 {
	linearize := func(channel uint8) float64 {
		srgb := float64(channel) / 255
		if srgb <= 0.04045 {
			return srgb / 12.92
		}
		return math.Pow((srgb+0.055)/1.055, 2.4)
	}

	return 0.2126*linearize(color.R) +
		0.7152*linearize(color.G) +
		0.0722*linearize(color.B)
}

// ContrastRatio returns the WCAG 2.x contrast ratio between two colors.
func ContrastRatio(a, b renderer.RGB) float64 {
	aLuminance := RelativeLuminance(a)
	bLuminance := RelativeLuminance(b)
	lighter := math.Max(aLuminance, bLuminance)
	darker := math.Min(aLuminance, bLuminance)
	return (lighter + 0.05) / (darker + 0.05)
}

// PulseColor derives the attention pulse color at intensity while preserving
// the base style's remaining attributes.
func PulseColor(base renderer.Style, intensity float64) renderer.Style {
	style := base
	style.Bold = true
	if base.HasForegroundRGB && base.HasBackgroundRGB {
		style.ForegroundRGB = Blend(base.BackgroundRGB, base.ForegroundRGB, intensity)
	} else {
		style.HasForegroundRGB = false
		style.Foreground = 244 + int(intensity*11)
	}
	return style
}

// PulseAttribute is PulseColor for reduced-color attachments: the glyph's
// on/off beat already pulses, so the visible beat is just bold. Grey indexes
// would quantize to arbitrary slots or vanish.
func PulseAttribute(base renderer.Style) renderer.Style {
	base.Bold = true
	return base
}

// MRUFade fades an MRU style by position, reaching 60 percent of the terminal
// background color at the oldest entry.
func MRUFade(base renderer.Style, t Theme, i, count int) renderer.Style {
	if count <= 1 || !base.HasForegroundRGB || !base.HasBackgroundRGB || !t.HasBG {
		return base
	}
	amount := (float64(i) / float64(count-1)) * 0.6
	base.ForegroundRGB = Blend(base.ForegroundRGB, t.Background, amount)
	base.BackgroundRGB = Blend(base.BackgroundRGB, t.Background, amount)
	return base
}

// Styles is the complete semantic set of terminal chrome styles. The legacy
// aliases remain until daemon renderers consume the semantic fields directly.
type Styles struct {
	// Reduced marks the ANSI16/monochrome policy: no RGB anywhere, and the
	// attention pulse uses bold instead of a grey ramp (see ResolveForColor).
	Reduced bool

	// mruStyles are all position/count combinations that status composition
	// can display. They keep OKLab interpolation out of render paths.
	mruStyles [9][9]renderer.Style

	SurfaceBar      renderer.Style
	SurfaceInactive renderer.Style
	SurfaceRecent   renderer.Style
	SurfaceActive   renderer.Style
	BorderMuted     renderer.Style
	BorderActive    renderer.Style
	// BorderWarn is the amber-hued warn-severity border. Unlike every other
	// role in this camaïeu palette it does not blend toward the resolved
	// accent color: it keeps the accent's lightness/chroma band but shifts
	// hue to a fixed amber target (see warnHueDegrees), so Warn reads as
	// amber and stays distinct from Error regardless of the accent hue.
	BorderWarn renderer.Style
	// NeutralBorder is the non-accent structural border for pane dividers and
	// unfocused pane title bars. It is resolved with the rest of the immutable
	// chrome snapshot so composition never derives theme colors.
	NeutralBorder renderer.Style

	TabInactive      renderer.Style
	TabInactiveTitle renderer.Style
	TabActive        renderer.Style
	TabActiveTitle   renderer.Style
	MRURecent        renderer.Style

	PickerBase      renderer.Style
	PickerSelection renderer.Style
	// HintKey is the keycap badge style for key hints: an accent background
	// over " key " padding, distinct from PickerSelection's full-line emphasis.
	HintKey           renderer.Style
	PickerDescription renderer.Style
	PickerSeparator   renderer.Style
	PromptBase        renderer.Style
	CopyStatus        renderer.Style
	SearchSelection   renderer.Style

	// Compatibility aliases for pre-cache render paths.
	StatusBar            renderer.Style
	Accent               renderer.Style
	Border               renderer.Style
	Selection            renderer.Style
	PaletteDesc          renderer.Style
	TabName              renderer.Style
	TabNameActive        renderer.Style
	TabTitle             renderer.Style
	TabTitleActive       renderer.Style
	PickerName           renderer.Style
	PickerSelectionName  renderer.Style
	PickerSelectionMuted renderer.Style
}

// NewStyles applies the default automatic policy. New callers that own a
// policy should use Resolve and retain its complete immutable result.
func NewStyles(t Theme) Styles {
	return Resolve(t, domain.ThemeAccent{Mode: domain.ThemeAccentAuto}).Styles
}

// MRUStyle returns the position-dependent recent-session surface. Color
// interpolation stays owned by theme; renderers consume only this cached
// semantic style snapshot.
func (s Styles) MRUStyle(index, count int) renderer.Style {
	if count <= 0 || count > len(s.mruStyles) {
		return s.MRURecent
	}
	if index < 0 {
		index = 0
	}
	if index >= count {
		index = count - 1
	}
	return s.mruStyles[count-1][index]
}