/**
 * computeOrgGradient — deterministic gradient pair for an organisation.
 *
 * Maps an org `id` string to one of 8 colour pairs via a simple djb2-style
 * character-code hash. Same id always returns the same pair; no external
 * dependencies.
 *
 * Palette rationale (P7-followup-gradient-brand): the diverse crewli-starter
 * SoT palette. Slot 1 is Crewli's brand teal (`#0D9394` → `#075F60`) so the
 * brand-anchor org renders in true Crewli teal — NOT Tailwind teal-600
 * (`#0d9488`), which had drifted in. Remaining slots span hue families
 * (purple / orange / green / amber / pink / indigo / rose) so multi-org
 * users see clearly distinct avatars rather than a wall of similar teals.
 * Each tuple is `[from, to]` for a 135° linear gradient (darker "to"
 * keeps depth on the logo square).
 */

/** Exported so tests can assert membership without hard-coding values. */
export const GRADIENT_PALETTE: [string, string][] = [
  ['#0D9394', '#075F60'], // Crewli teal (brand anchor)
  ['#7C3AED', '#4C1D95'], // purple
  ['#EA580C', '#9A3412'], // orange
  ['#16A34A', '#14532D'], // green
  ['#F59E0B', '#92400E'], // amber
  ['#EC4899', '#9D174D'], // pink
  ['#4F46E5', '#312E81'], // indigo (added for org-distinguishability)
  ['#E11D48', '#881337'], // rose (added for org-distinguishability)
]

/**
 * Returns a `[fromHex, toHex]` colour pair deterministically derived
 * from `id`.  Handles empty string (hash stays 0; maps to palette[0]).
 */
export function computeOrgGradient(id: string): [string, string] {
  // djb2-style hash: accumulate across char codes
  let hash = 5381
  for (let i = 0; i < id.length; i++) {
    // Equivalent to hash * 33 ^ charCode, kept 32-bit safe via >>> 0
    hash = ((hash << 5) + hash + id.charCodeAt(i)) >>> 0
  }
  const index = hash % GRADIENT_PALETTE.length

  return GRADIENT_PALETTE[index]
}