package imagegen

import "context"

// FaceSwapRequest transfers an identity from Source into Target.
//
// This is a DIFFERENT OPERATION from Edit, not a better-tuned one. Measured
// against the instruction-edit models on 2026-07-31, asking a diffusion model
// to put a specific person's face into a photo does not work by any route —
// by name, by description, or by supplying the portrait as a reference image.
// Face swapping is a dedicated detect/align/blend pipeline; a provider that
// cannot do it should not pretend Edit is a substitute.
type FaceSwapRequest struct {
	// Target is the photo to edit — the pose, expression, lighting and
	// everything outside the face are preserved from it.
	Target Image

	// Source is a photo of the face to put in. Only the identity travels;
	// the source's own pose and expression do not.
	Source Image

	// Index selects WHICH face in Target, in the provider's documented
	// ordering (llamaswap: left to right by box centre, as reported by
	// ListFaces). nil = the largest face, which is right for a portrait and
	// wrong for a group — enumerate first when it matters.
	Index *int

	// All swaps every detected face and ignores Index.
	All bool
}

// FaceSwapOption mutates a FaceSwapRequest before it is sent.
type FaceSwapOption func(*FaceSwapRequest)

// WithFaceIndex selects which face in the target to replace.
func WithFaceIndex(i int) FaceSwapOption { return func(r *FaceSwapRequest) { r.Index = &i } }

// WithAllFaces swaps every detected face.
func WithAllFaces() FaceSwapOption { return func(r *FaceSwapRequest) { r.All = true } }

// Apply returns a copy of the request with all options applied.
func (r FaceSwapRequest) Apply(opts ...FaceSwapOption) FaceSwapRequest {
	for _, opt := range opts {
		opt(&r)
	}
	return r
}

// DetectedFace is one face located in an image, in PIXEL coordinates.
type DetectedFace struct {
	// Index is the face's position in the provider's stable ordering, and
	// the value FaceSwapRequest.Index expects.
	Index int
	// Box is [x0, y0, x1, y1].
	Box [4]int
	// Score is the detector's confidence, 0-1.
	Score float64
	// Width and Height are the box dimensions, carried so a caller can pick
	// "the big face" without recomputing them.
	Width, Height int
}

// FaceSwapper is the optional face-transfer surface. Separate interface so
// existing providers keep compiling; callers type-assert.
type FaceSwapper interface {
	// ListFaces enumerates the faces in an image, in the SAME ordering
	// FaceSwapRequest.Index uses. Exposed because a caller asked to change
	// "the man on the right" needs a way to name one face and to check its
	// own choice against pixel boxes.
	ListFaces(ctx context.Context, img Image) ([]DetectedFace, error)

	// FaceSwap transfers Source's identity into Target.
	FaceSwap(ctx context.Context, req FaceSwapRequest, opts ...FaceSwapOption) (*Result, error)
}