package imagegen

import "context"

// EditRequest is an image-to-image (edit) request: a prompt applied to an
// initial image. As with Request, zero values mean "backend default"
// (ADR-0018).
type EditRequest struct {
	// Prompt is the text description of the desired edit.
	Prompt string

	// Init is the initial image the edit starts from. Required, EXCEPT when
	// RefImages is set — see there.
	Init Image

	// RefImages carries reference images for INSTRUCTION-EDIT models
	// (FLUX.1 Kontext, Qwen-Image-Edit), which are a different kind of edit
	// from img2img and reach the model by a different path.
	//
	// img2img noises Init and denoises it back under the prompt: the prompt
	// describes the DESIRED IMAGE, and how much of the original survives is a
	// function of Strength. An instruction-edit model instead takes the
	// picture as conditioning and the prompt as an INSTRUCTION about it
	// ("change the sign to read OPEN"), leaving everything it was not asked
	// to touch bit-for-bit intact — no mask, no strength, no compositing.
	//
	// Sending one of these models an Init instead of a RefImage does not
	// degrade gracefully, it silently does the wrong thing: measured against
	// FLUX.1-Kontext on 2026-07-30, "change the blue rectangle to green" via
	// init_images left the rectangle blue and drifted every other region,
	// while the same prompt via a reference image turned it green and left
	// the rest of the frame numerically unchanged.
	//
	// When RefImages is non-empty, Init/Mask/Strength are IGNORED: they
	// describe a pipeline this model does not run.
	RefImages []Image

	// Mask restricts the edit to a region (inpainting): a single-channel or
	// RGB image the same size as Init where WHITE pixels are repainted and
	// BLACK pixels are kept. Empty = whole-image edit. Backends without mask
	// support must reject a masked request rather than silently ignoring it.
	Mask Image

	// Strength is the denoising strength in [0,1] — how far the result may
	// depart from Init (0 = return the input, 1 = ignore it); nil = backend
	// default.
	Strength *float64

	// N is the number of images to generate; 0 = provider default.
	N int

	// Size is the requested resolution, e.g. "1024x1024"; "" = provider
	// default (usually the init image's own resolution).
	Size string

	// Steps is the number of diffusion steps; nil = backend default.
	Steps *int

	// CFGScale is the classifier-free-guidance scale; nil = backend default.
	CFGScale *float64

	// NegativePrompt steers generation away from concepts; "" = none.
	NegativePrompt string

	// Sampler selects the sampling method (e.g. "euler", "euler_a");
	// "" = backend default.
	Sampler string

	// Seed fixes the RNG seed for reproducible output; nil = random.
	Seed *int64
}

// EditOption mutates an EditRequest before it is sent. Options passed to Edit
// are applied to a copy of the request, so an EditRequest value can be reused.
type EditOption func(*EditRequest)

// WithEditMask restricts the edit to a region (white = repaint, black = keep).
func WithEditMask(m Image) EditOption { return func(r *EditRequest) { r.Mask = m } }

// WithEditRefImages supplies reference images for an instruction-edit model
// (Kontext / Qwen-Image-Edit). See EditRequest.RefImages — this selects a
// different edit path, not a variation on img2img.
func WithEditRefImages(imgs ...Image) EditOption {
	return func(r *EditRequest) { r.RefImages = imgs }
}

// WithEditStrength sets the denoising strength in [0,1].
func WithEditStrength(s float64) EditOption { return func(r *EditRequest) { r.Strength = &s } }

// WithEditN sets the number of images to generate.
func WithEditN(n int) EditOption { return func(r *EditRequest) { r.N = n } }

// WithEditSize sets the requested resolution (e.g. "1024x1024").
func WithEditSize(size string) EditOption { return func(r *EditRequest) { r.Size = size } }

// WithEditSteps overrides the number of diffusion steps.
func WithEditSteps(n int) EditOption { return func(r *EditRequest) { r.Steps = &n } }

// WithEditCFGScale overrides the classifier-free-guidance scale.
func WithEditCFGScale(s float64) EditOption { return func(r *EditRequest) { r.CFGScale = &s } }

// WithEditNegativePrompt sets a negative prompt.
func WithEditNegativePrompt(s string) EditOption {
	return func(r *EditRequest) { r.NegativePrompt = s }
}

// WithEditSampler overrides the sampling method.
func WithEditSampler(s string) EditOption { return func(r *EditRequest) { r.Sampler = s } }

// WithEditSeed fixes the RNG seed for reproducible output.
func WithEditSeed(seed int64) EditOption { return func(r *EditRequest) { r.Seed = &seed } }

// Apply returns a copy of the request with all options applied. Providers
// call this once at the top of Edit.
func (r EditRequest) Apply(opts ...EditOption) EditRequest {
	for _, opt := range opts {
		opt(&r)
	}
	return r
}

// Editor is the image-to-image surface. It is a separate, optional interface
// rather than a method on Model so existing Model implementations keep
// compiling; callers type-assert (`m.(imagegen.Editor)`) or require it
// explicitly.
type Editor interface {
	// Edit produces one or more images derived from the request's init image
	// under the request's prompt.
	Edit(ctx context.Context, req EditRequest, opts ...EditOption) (*Result, error)
}