// mesh.go implements meshgen.Provider against a Hunyuan3D-2.1-style
// api_server reached through llama-swap's /upstream passthrough (ADR-0020):
//
//	POST /upstream/<id>/generate   JSON {image: <b64>, type: "glb"|"stl"|...}
//
// The response body IS the encoded mesh (binary, Content-Type
// application/octet-stream), so one request yields exactly one asset.
package llamaswap

import (
	"bytes"
	"context"
	"encoding/base64"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"

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

// maxMeshResponseBytes caps the /generate body — a high-resolution textured
// mesh legitimately passes the 64MB JSON cap, but stays far under video
// scale.
const maxMeshResponseBytes = 256 << 20

// MeshModel implements meshgen.Provider. The id selects which upstream
// llama-swap loads.
func (p *Provider) MeshModel(id string, opts ...meshgen.ModelOption) (meshgen.Model, error) {
	if err := p.requireBaseURL(); err != nil {
		return nil, err
	}
	_ = meshgen.ApplyModelOptions(opts)
	return &meshModel{p: p, id: id}, nil
}

type meshModel struct {
	p  *Provider
	id string
}

// hunyuanGenerateRequest is the Hunyuan3D api_server /generate shape.
// Optional fields are pointers/omitempty so unset values fall back to the
// server's defaults (mirrors the sd-server wire structs).
type hunyuanGenerateRequest struct {
	Image             string   `json:"image"`
	Type              string   `json:"type,omitempty"`
	Texture           bool     `json:"texture"`
	RemoveBackground  *bool    `json:"remove_background,omitempty"`
	OctreeResolution  int      `json:"octree_resolution,omitempty"`
	NumInferenceSteps *int     `json:"num_inference_steps,omitempty"`
	GuidanceScale     *float64 `json:"guidance_scale,omitempty"`
	Seed              *int64   `json:"seed,omitempty"`
	FaceCount         int      `json:"face_count,omitempty"`
}

// meshFormats maps the supported output containers to MIME types.
var meshFormats = map[string]string{
	"glb": "model/gltf-binary",
	"stl": "model/stl",
	"obj": "model/obj",
}

// Generate implements meshgen.Model.
func (m *meshModel) Generate(ctx context.Context, req meshgen.Request, opts ...meshgen.Option) (*meshgen.Result, error) {
	req = req.Apply(opts...)
	if len(req.Image.Data) == 0 {
		return nil, fmt.Errorf("%w: mesh generation requires an image", llm.ErrUnsupported)
	}
	format := strings.ToLower(strings.TrimSpace(req.Format))
	if format == "" {
		format = "glb"
	}
	mimeType, ok := meshFormats[format]
	if !ok {
		return nil, fmt.Errorf("%w: unsupported mesh format %q (want glb, stl, or obj)", llm.ErrUnsupported, req.Format)
	}
	if req.OctreeResolution < 0 || req.FaceCount < 0 {
		return nil, fmt.Errorf("%w: octree resolution and face count must be >= 0", llm.ErrUnsupported)
	}

	path, err := upstreamPath(m.id, "/generate")
	if err != nil {
		return nil, err
	}
	wire := hunyuanGenerateRequest{
		Image:             base64.StdEncoding.EncodeToString(req.Image.Data),
		Type:              format,
		Texture:           req.Texture,
		RemoveBackground:  req.RemoveBackground,
		OctreeResolution:  req.OctreeResolution,
		NumInferenceSteps: req.Steps,
		GuidanceScale:     req.GuidanceScale,
		Seed:              req.Seed,
		FaceCount:         req.FaceCount,
	}

	// doRaw + manual JSON encode (not doJSON): the SUCCESS body is binary
	// mesh bytes, not JSON.
	encoded, err := json.Marshal(wire)
	if err != nil {
		return nil, fmt.Errorf("llama-swap: encode mesh request: %w", err)
	}
	raw, _, err := m.p.doRaw(ctx, http.MethodPost, path, m.id, "application/json", bytes.NewReader(encoded), maxMeshResponseBytes)
	if err != nil {
		return nil, err
	}
	if len(raw) == 0 {
		return nil, &llm.APIError{Provider: m.p.name, Model: m.id, Message: "mesh response contained no data"}
	}
	// A JSON body on the success path is the server reporting a soft error
	// (or an API drift) — never hand it back as "the mesh".
	if first := strings.TrimLeft(string(raw[:min(len(raw), 64)]), " \t\r\n"); strings.HasPrefix(first, "{") || strings.HasPrefix(first, "[") {
		return nil, &llm.APIError{Provider: m.p.name, Model: m.id,
			Message: "mesh response is JSON, not mesh bytes: " + truncateForError(raw)}
	}
	return &meshgen.Result{Mesh: meshgen.Mesh{Data: raw, Format: format, MIME: mimeType}}, nil
}

// truncateForError bounds a payload quoted into an error message.
func truncateForError(b []byte) string {
	const cap = 500
	if len(b) > cap {
		return string(b[:cap]) + "..."
	}
	return string(b)
}