// internal/ai/ambient.go
package ai

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
)

// AmbientDriftJudge judges whether current activity serves the user's standing
// frame when NO task is declared. Like Nudge it takes primitives, not domain
// types, so ai stays a leaf. The returned string is a one-sentence advisory, or
// "" when the activity is plausibly on-track.
type AmbientDriftJudge interface {
	AmbientDrift(ctx context.Context, frame string, recentTitles []string) (string, error)
}

// ErrInvalidAmbientDrift marks a parseable-but-unusable ambient response.
var ErrInvalidAmbientDrift = errors.New("ai: invalid ambient drift")

// AmbientDrift makes Service satisfy AmbientDriftJudge over the same backend.
func (s *Service) AmbientDrift(ctx context.Context, frame string, recentTitles []string) (string, error) {
	out, err := s.backend.Run(ctx, buildAmbientPrompt(frame, recentTitles))
	if err != nil {
		return "", err
	}
	return parseAmbientDrift(out)
}

func buildAmbientPrompt(frame string, recentTitles []string) string {
	return `You are an ambient coach. The user has NOT declared a task. Below is their standing frame — goals, values, and life-domains — and today's tasks, then the recent sequence of window titles. Decide whether the recent activity plausibly serves ANY of what matters to them, or whether it is a slide into drift.

Be forgiving: legitimate breaks, rest, admin, and unplanned-but-useful work are ON-TRACK. Only call drift when the activity clearly serves none of what matters.

Respond with ONLY a JSON object, no prose and no code fences, exactly this shape:
{"drifting": <true or false>, "message": "<short explanation, one sentence>"}

Rules:
- drifting: true only if the recent activity serves none of the frame; false otherwise.
- message: one short sentence naming the drift. REQUIRED when drifting is true.

## Frame
` + frame + `

## Recent window titles (oldest to newest)
` + strings.Join(recentTitles, "\n")
}

type rawAmbientDrift struct {
	Drifting bool   `json:"drifting"`
	Message  string `json:"message"`
}

// parseAmbientDrift extracts the advisory from raw CLI output. On-track yields
// "". A drift with no message degrades to "" (silence) rather than an error:
// the ambient signal is advisory, so the safe degenerate is to say nothing —
// exactly like parseNudge.
func parseAmbientDrift(s string) (string, error) {
	if strings.TrimSpace(s) == "" {
		return "", ErrEmptyResponse
	}
	if strings.IndexByte(s, '{') < 0 {
		return "", ErrNoJSON
	}
	jsonStr, err := extractJSON(s)
	if err != nil {
		return "", fmt.Errorf("%w: %v", ErrInvalidAmbientDrift, err)
	}
	var raw rawAmbientDrift
	if err := json.Unmarshal([]byte(jsonStr), &raw); err != nil {
		return "", fmt.Errorf("%w: %v", ErrInvalidAmbientDrift, err)
	}
	if !raw.Drifting {
		return "", nil
	}
	return strings.TrimSpace(raw.Message), nil
}