/* Turning a failure into something a reader can act on.
 *
 * `BROWSER-UX-SPEC.md` §71 asks for five kinds of failure to be told apart, and
 * forbids collapsing them into "Something went wrong". They are told apart
 * because each one has a different thing to *do* about it: start Ollama, pull a
 * model, retry the turn, correct the state, look at the server log. A single
 * message leaves the reader guessing which of those they are looking at.
 *
 * The classification reads the message the server actually sent. That is a
 * coupling to backend strings, so it is deliberately a *fallback ladder* rather
 * than a lookup: an unrecognised message still gets a kind ("generation"), still
 * shows its own text, and still offers Retry. Nothing is hidden when the match
 * misses — the reader sees the server's own words either way, and the only thing
 * lost is the tailored hint.
 *
 * The signatures below are the ones `backend/app/providers/openai_compatible.py`
 * raises; each is quoted in the comment beside it so a change over there is
 * findable from here.
 */

/** The five kinds, in the vocabulary §71 uses. */
export const KIND = {
  MODEL: 'model',
  GENERATION: 'generation',
  STATE: 'state',
  KNOWLEDGE: 'knowledge',
  SERVER: 'server',
}

const TITLES = {
  [KIND.MODEL]: 'Model unavailable',
  [KIND.GENERATION]: 'Generation failed',
  [KIND.STATE]: 'Story state could not be updated',
  [KIND.KNOWLEDGE]: 'Imported knowledge problem',
  [KIND.SERVER]: 'The storyteller had a problem',
}

/**
 * Classifies a failure message.
 *
 * Returns `{ kind, title, detail, hint, retryable }`. `detail` is always the
 * server's own text — this never replaces what the server said, only frames it.
 */
export function classifyError(message) {
  const detail = String(message || '').trim() || 'No detail was reported.'
  const low = detail.toLowerCase()

  // ---- Model / endpoint: the story cannot be told at all ----

  // "No model configured — set one in Settings."
  if (low.includes('no model configured')) {
    return {
      kind: KIND.MODEL,
      title: 'No narrator model chosen',
      detail,
      hint: 'Choose an installed Ollama model in Settings, then try again.',
      retryable: false,
      action: { label: 'Open Settings', to: '/settings' },
    }
  }
  // "No embedding model configured — set one in Settings."
  if (low.includes('no embedding model configured')) {
    return {
      kind: KIND.KNOWLEDGE,
      title: 'No embedding model chosen',
      detail,
      hint:
        'Imported knowledge is still searched by keyword. Choose an embedding '
        + 'model in Settings to add meaning-based search.',
      retryable: false,
      action: { label: 'Open Settings', to: '/settings' },
    }
  }
  // "Could not connect to <url> — is the AI server running?"
  // "Request to AI endpoint failed: ..."
  if (low.includes('could not connect') || low.includes('request to ai endpoint failed')) {
    return {
      kind: KIND.MODEL,
      title: 'Ollama is not reachable',
      detail,
      hint:
        'Start Ollama on the machine at the configured endpoint (`ollama serve`), '
        + 'then retry. Nothing you wrote has been lost.',
      retryable: true,
    }
  }
  // "The AI endpoint timed out."
  if (low.includes('timed out') || low.includes('timeout')) {
    return {
      kind: KIND.MODEL,
      title: 'The model took too long',
      detail,
      hint:
        'Loading a model for the first time can take minutes without a GPU. '
        + 'Retry, or raise the model timeout in Settings.',
      retryable: true,
    }
  }
  // "This endpoint can't be used — ..." (the ADR 011 address policy)
  if (low.includes("endpoint can't be used") || low.includes('endpoint cannot be used')) {
    return {
      kind: KIND.MODEL,
      title: 'That endpoint is not allowed',
      detail,
      hint:
        'The storyteller only talks to Ollama on this machine or on your own '
        + 'network. Correct the endpoint in Settings.',
      retryable: false,
      action: { label: 'Open Settings', to: '/settings' },
    }
  }
  // "Endpoint or model not found (HTTP 404). Check ... model '<name>' exists."
  if (low.includes('not found') && low.includes('404')) {
    return {
      kind: KIND.MODEL,
      title: 'Endpoint or model not found',
      detail,
      hint: 'Pull the model on that machine (`ollama pull <model>`), or pick another in Settings.',
      retryable: true,
      action: { label: 'Open Settings', to: '/settings' },
    }
  }
  // TLS is its own case: the fix is installing a CA, not starting a server.
  if (low.includes('certificate') || low.includes('tls') || low.includes('ssl')) {
    return {
      kind: KIND.MODEL,
      title: 'The endpoint’s certificate could not be verified',
      detail,
      hint:
        'If it uses a private or self-signed CA, install that CA on this machine. '
        + 'Certificate checking is not optional.',
      retryable: true,
    }
  }

  // ---- State: the turn happened but could not be recorded ----
  if (
    low.includes('state validation')
    || low.includes('invalid state event')
    || low.includes('narrative state')
    || low.includes('unknown event type')
  ) {
    return {
      kind: KIND.STATE,
      title: TITLES[KIND.STATE],
      detail,
      hint:
        'The story itself is unaffected. Open State to see what the storyteller '
        + 'currently believes, and correct it if it is wrong.',
      retryable: true,
    }
  }

  // ---- Knowledge / derived work ----
  if (low.includes('knowledge') || low.includes('embedding') || low.includes('index')) {
    return {
      kind: KIND.KNOWLEDGE,
      title: TITLES[KIND.KNOWLEDGE],
      detail,
      hint: 'Your story is unaffected. Imported material may not be searched until this is fixed.',
      retryable: true,
    }
  }

  // ---- Server / database ----
  if (
    low.includes('database')
    || low.includes('sqlite')
    || low.includes('integrity')
    || low.includes('internal server error')
    || low.includes('http 500')
  ) {
    return {
      kind: KIND.SERVER,
      title: TITLES[KIND.SERVER],
      detail,
      hint: 'Nothing already written has been changed. The server log has the details.',
      retryable: true,
    }
  }

  // ---- Anything else is a failed generation ----
  //
  // Deliberately the fallback rather than a separate "unknown": the reader is
  // in the middle of a turn, the turn did not happen, and Retry is the useful
  // offer. The server's own words are shown, so nothing is lost by not
  // recognising it.
  return {
    kind: KIND.GENERATION,
    title: TITLES[KIND.GENERATION],
    detail,
    hint: 'Nothing was added to your story. You can try that turn again.',
    retryable: true,
  }
}