import type { ExecutionHostId } from './execution-host'
import type { GlobalSettings } from './global-settings-types'

/** Per-host overrides for client preferences that genuinely vary by execution
 *  host. NARROW by design: only settings whose value is meaningless to share
 *  across hosts belong here.
 *  - `displayLabel`: a client-side rename for the host shown in sidebar/pickers.
 *  - `defaultWorktreeLocation`: the host's root worktree directory; a remote
 *    SSH/runtime host has a different filesystem layout than the local Mac, so
 *    the client `workspaceDir` default cannot apply unchanged. */
export type HostSettingOverrides = {
  displayLabel?: string
  defaultWorktreeLocation?: string
}

// Why: per-host preferences follow `effective = host override ?? client default`.
// These pure helpers centralize that rule so the UI, registry, and tests share a
// single implementation instead of re-deriving the fallback at each call site.

export type HostSettingOverrideKey = keyof HostSettingOverrides

type HostSettingsSlice = Pick<GlobalSettings, 'hostSettingOverrides'>

function normalize(value: string | undefined): string | undefined {
  const trimmed = value?.trim()
  return trimmed ? trimmed : undefined
}

/** Returns the host's override for `key` if present and non-empty, else `undefined`. */
export function getHostSettingOverride(
  settings: HostSettingsSlice | null | undefined,
  hostId: ExecutionHostId,
  key: HostSettingOverrideKey
): string | undefined {
  return normalize(settings?.hostSettingOverrides?.[hostId]?.[key])
}

/** `host override ?? client default`. Unknown hosts and cleared overrides fall back. */
export function getEffectiveHostSetting(
  settings: HostSettingsSlice | null | undefined,
  hostId: ExecutionHostId,
  key: HostSettingOverrideKey,
  clientDefault: string
): string {
  return getHostSettingOverride(settings, hostId, key) ?? clientDefault
}

/** Pure update: returns the next `hostSettingOverrides` map with the override set.
 *  An empty/whitespace value clears the key instead of persisting blank text. */
export function setHostSettingOverride(
  settings: HostSettingsSlice | null | undefined,
  hostId: ExecutionHostId,
  key: HostSettingOverrideKey,
  value: string
): Partial<Record<ExecutionHostId, HostSettingOverrides>> {
  const normalized = normalize(value)
  if (normalized === undefined) {
    return clearHostSettingOverride(settings, hostId, key)
  }
  const current = settings?.hostSettingOverrides ?? {}
  return {
    ...current,
    [hostId]: { ...current[hostId], [key]: normalized }
  }
}

/** Pure update: returns the next map with the key removed, dropping the host
 *  entry entirely once it has no remaining overrides. */
export function clearHostSettingOverride(
  settings: HostSettingsSlice | null | undefined,
  hostId: ExecutionHostId,
  key: HostSettingOverrideKey
): Partial<Record<ExecutionHostId, HostSettingOverrides>> {
  const current = settings?.hostSettingOverrides
  const hostOverrides = current?.[hostId]
  if (!current || !hostOverrides || !(key in hostOverrides)) {
    return current ?? {}
  }
  const { [key]: _removed, ...remaining } = hostOverrides
  const next = { ...current }
  if (Object.keys(remaining).length === 0) {
    delete next[hostId]
  } else {
    next[hostId] = remaining
  }
  return next
}

/** Builds the `displayLabel` lookup map the host registry consumes. */
export function getHostDisplayLabelOverrides(
  settings: HostSettingsSlice | null | undefined
): ReadonlyMap<ExecutionHostId, string> {
  const result = new Map<ExecutionHostId, string>()
  for (const [hostId, overrides] of Object.entries(settings?.hostSettingOverrides ?? {})) {
    const label = normalize(overrides?.displayLabel)
    if (label) {
      result.set(hostId as ExecutionHostId, label)
    }
  }
  return result
}