package ai

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

// OffscreenProposal is the brain's suggestion for one worthwhile thing to do
// away from the screen. It is deliberately distinct from Proposal (the focus
// coach's commitment shape) to avoid a name collision.
type OffscreenProposal struct {
	NextAction string `json:"next_action"`
	Rationale  string `json:"rationale"`
}

// Proposer turns an off-screen brief (goals, life-domain notes, today's tasks)
// into a single grounded off-screen action.
type Proposer interface {
	Propose(ctx context.Context, brief string) (OffscreenProposal, error)
}

// Propose makes Service satisfy Proposer over the same backend as Coach.
func (s *Service) Propose(ctx context.Context, brief string) (OffscreenProposal, error) {
	out, err := s.backend.Run(ctx, buildProposePrompt(brief))
	if err != nil {
		return OffscreenProposal{}, err
	}
	return parseOffscreenProposal(out)
}

func buildProposePrompt(brief string) string {
	return `You are an off-screen advisor. Read the brief below — the user's goals, life-domain notes, and today's tasks — and pick ONE worthwhile thing for them to do now, away from the screen.

Respond with ONLY a JSON object, no prose and no code fences, exactly this shape:
{"next_action": "<one worthwhile off-screen action to do now>", "rationale": "<one short sentence: which goal or value it serves>"}

Rules:
- next_action: a single concrete off-screen action, doable now.
- rationale: one short sentence naming the goal or value it serves.

## Brief
` + brief
}

// parseOffscreenProposal extracts and validates an OffscreenProposal from raw
// CLI output, mirroring parseProposal's error discipline.
func parseOffscreenProposal(s string) (OffscreenProposal, error) {
	if strings.TrimSpace(s) == "" {
		return OffscreenProposal{}, ErrEmptyResponse
	}
	if strings.IndexByte(s, '{') < 0 {
		return OffscreenProposal{}, ErrNoJSON
	}
	jsonStr, err := extractJSON(s)
	if err != nil {
		return OffscreenProposal{}, fmt.Errorf("%w: %v", ErrInvalidProposal, err)
	}
	var raw OffscreenProposal
	if err := json.Unmarshal([]byte(jsonStr), &raw); err != nil {
		return OffscreenProposal{}, fmt.Errorf("%w: %v", ErrInvalidProposal, err)
	}
	na := strings.TrimSpace(raw.NextAction)
	if na == "" {
		return OffscreenProposal{}, ErrInvalidProposal
	}
	return OffscreenProposal{
		NextAction: na,
		Rationale:  strings.TrimSpace(raw.Rationale),
	}, nil
}