const APP_COLORS = [
  { from: '#4F46E5', to: '#7C3AED' }, // indigo to purple
  { from: '#7C3AED', to: '#C026D3' }, // purple to fuchsia
  { from: '#EC4899', to: '#F97316' }, // pink to orange
  { from: '#14B8A6', to: '#10B981' }, // teal to emerald
  { from: '#6366F1', to: '#8B5CF6' }, // indigo to violet
  { from: '#F59E0B', to: '#F97316' }, // amber to orange
]

/**
 * User color palette matching terminal.tsx RUN_ID_COLORS
 * These colors are used consistently across cursors, avatars, and terminal run IDs
 */
export const USER_COLORS = [
  '#4ADE80', // Green
  '#F472B6', // Pink
  '#60C5FF', // Blue
  '#FF8533', // Orange
  '#C084FC', // Purple
  '#FCD34D', // Yellow
] as const

interface PresenceColorPalette {
  gradient: string
  accentColor: string
  baseColor: string
}

const HEX_COLOR_REGEX = /^#(?:[0-9a-fA-F]{3}){1,2}$/

function hashIdentifier(identifier: string | number): number {
  if (typeof identifier === 'number' && Number.isFinite(identifier)) {
    return Math.abs(Math.trunc(identifier))
  }

  if (typeof identifier === 'string') {
    return Math.abs(Array.from(identifier).reduce((acc, char) => acc + char.charCodeAt(0), 0))
  }

  return 0
}

function withAlpha(hexColor: string, alpha: number): string {
  if (!HEX_COLOR_REGEX.test(hexColor)) {
    return hexColor
  }

  const normalized = hexColor.slice(1)
  const expanded =
    normalized.length === 3
      ? normalized
          .split('')
          .map((char) => `${char}${char}`)
          .join('')
      : normalized

  const r = Number.parseInt(expanded.slice(0, 2), 16)
  const g = Number.parseInt(expanded.slice(2, 4), 16)
  const b = Number.parseInt(expanded.slice(4, 6), 16)

  return `rgba(${r}, ${g}, ${b}, ${Math.min(Math.max(alpha, 0), 1)})`
}

function buildGradient(fromColor: string, toColor: string, rotationSeed: number): string {
  const rotation = (rotationSeed * 25) % 360
  return `linear-gradient(${rotation}deg, ${fromColor}, ${toColor})`
}

export function getPresenceColors(
  identifier: string | number,
  explicitColor?: string
): PresenceColorPalette {
  const paletteIndex = hashIdentifier(identifier)

  if (explicitColor) {
    const normalizedColor = explicitColor.trim()
    const lighterShade = HEX_COLOR_REGEX.test(normalizedColor)
      ? withAlpha(normalizedColor, 0.85)
      : normalizedColor

    return {
      gradient: buildGradient(lighterShade, normalizedColor, paletteIndex),
      accentColor: normalizedColor,
      baseColor: lighterShade,
    }
  }

  const colorPair = APP_COLORS[paletteIndex % APP_COLORS.length]

  return {
    gradient: buildGradient(colorPair.from, colorPair.to, paletteIndex),
    accentColor: colorPair.to,
    baseColor: colorPair.from,
  }
}

/**
 * Gets a consistent color for a user based on their ID.
 * The same user will always get the same color across cursors, avatars, and terminal.
 *
 * @param userId - The unique user identifier
 * @returns A hex color string
 */
export function getUserColor(userId: string): string {
  const hash = hashIdentifier(userId)
  return USER_COLORS[hash % USER_COLORS.length]
}

/**
 * Creates a stable mapping of user IDs to color indices for a list of users.
 * Useful when you need to maintain consistent color assignments across renders.
 *
 * @param userIds - Array of user IDs to map
 * @returns Map of user ID to color index
 */
export function createUserColorMap(userIds: string[]): Map<string, number> {
  const colorMap = new Map<string, number>()
  let colorIndex = 0

  for (const userId of userIds) {
    if (!colorMap.has(userId)) {
      colorMap.set(userId, colorIndex++)
    }
  }

  return colorMap
}
