// segment.go implements imagegen.SegmentationProvider against a
// GroundingDINO+SAM shim (segment-langsam) reached through llama-swap's
// /upstream passthrough (ADR-0023):
//
//	POST /upstream/<id>/v1/segment   multipart file,prompt[,threshold],output=mask
//
// The response is a single grayscale mask PNG where WHITE marks the prompted
// region — directly usable as imagegen.EditRequest.Mask (white = repaint).
// The shim also offers output=cutout|boxes; this client always requests the
// mask, because a cutout is derivable client-side from mask+original with no
// second GPU call.
package llamaswap

import (
	"context"
	"fmt"
	"math"
	"net/http"
	"strconv"

	"gitea.stevedudenhoeffer.com/steve/majordomo/imagegen"
	"gitea.stevedudenhoeffer.com/steve/majordomo/llm"
)

// SegmentationModel implements imagegen.SegmentationProvider. The id selects
// which upstream llama-swap loads.
func (p *Provider) SegmentationModel(id string, opts ...imagegen.SegmentationModelOption) (imagegen.Segmenter, error) {
	if err := p.requireBaseURL(); err != nil {
		return nil, err
	}
	_ = imagegen.ApplySegmentationModelOptions(opts)
	return &segmentationModel{p: p, id: id}, nil
}

type segmentationModel struct {
	p  *Provider
	id string
}

// Segment implements imagegen.Segmenter.
func (m *segmentationModel) Segment(ctx context.Context, req imagegen.SegmentationRequest, opts ...imagegen.SegmentationOption) (*imagegen.Result, error) {
	req = req.Apply(opts...)
	if len(req.Image.Data) == 0 {
		return nil, fmt.Errorf("%w: segmentation requires an image", llm.ErrUnsupported)
	}
	if req.Prompt == "" {
		return nil, fmt.Errorf("%w: segmentation requires a prompt", llm.ErrUnsupported)
	}
	// NaN fails every comparison, so it would sail through a bare range
	// check and reach the upstream as the literal string "NaN".
	if math.IsNaN(req.Threshold) || req.Threshold < 0 || req.Threshold > 1 {
		return nil, fmt.Errorf("%w: segmentation threshold must be in [0,1], got %g", llm.ErrUnsupported, req.Threshold)
	}
	path, err := upstreamPath(m.id, "/v1/segment")
	if err != nil {
		return nil, err
	}
	threshold := ""
	if req.Threshold != 0 {
		threshold = strconv.FormatFloat(req.Threshold, 'g', -1, 64)
	}
	body, contentType, err := buildMultipart("build segment form",
		filePart{field: "file", filename: "image.png", data: req.Image.Data},
		[]formField{
			{"prompt", req.Prompt, true},
			{"threshold", threshold, false},
			// Always the mask: white = prompted region, EditRequest.Mask
			// polarity. Cutouts are derived client-side.
			{"output", "mask", true},
		})
	if err != nil {
		return nil, err
	}
	raw, respType, err := m.p.doRaw(ctx, http.MethodPost, path, m.id, contentType, body, maxImageResponseBytes)
	if err != nil {
		return nil, err
	}
	return singleImageResult(m.p.name, m.id, "segmentation", raw, respType)
}