// Package bnp implements `ninja plugin build` and `ninja plugin verify`: it
// compiles a plugin to reactor-mode wasm, extracts its static manifest by
// instantiating the module once and calling HOOK_DESCRIBE, packs the .bnp
// artifact (tar.zst), and re-runs the CMS reader's layout/name/abi/path/size
// checks standalone.
//
// The verify rules here are a deliberate, documented duplication of the CMS
// reader (cms backend/plugin/bnp/reader.go, WO-WZ-008): core cannot import the
// CMS module, so publishers get the same gate the loader applies. WO-WZ-010's
// integration suite keeps the two in lockstep.
package bnp

import (
	"context"
	"fmt"
	"os"

	abiv1 "git.dev.alexdunmow.com/block/core/abi/v1"
	"github.com/tetratelabs/wazero"
	"github.com/tetratelabs/wazero/api"
	"github.com/tetratelabs/wazero/imports/wasi_snapshot_preview1"
	"google.golang.org/protobuf/proto"
)

// hostAbiVersion is the ABI major version the packer speaks when driving
// DESCRIBE. It must equal core's guest AbiVersion / the reader's supported
// major (1) or the guest's symmetric version gate rejects the call.
const hostAbiVersion uint32 = 1

// ExtractManifest instantiates a reactor-mode plugin.wasm with wazero, drives
// one HOOK_DESCRIBE round trip, and returns the decoded PluginManifest.
//
// The host functions the guest imports (blockninja.host_call) are stubbed to
// FAIL: DESCRIBE is publish-time and must not need a live host. A plugin that
// reaches a host capability while its manifest is being extracted (e.g. a
// db.* call from Register) gets an actionable error naming the offending
// method rather than a mystery hang or nil deref.
func ExtractManifest(ctx context.Context, wasm []byte) (*abiv1.PluginManifest, error) {
	r := wazero.NewRuntime(ctx)
	defer func() { _ = r.Close(ctx) }()

	if _, err := wasi_snapshot_preview1.Instantiate(ctx, r); err != nil {
		return nil, fmt.Errorf("instantiate wasi: %w", err)
	}
	if err := installFailingHost(ctx, r); err != nil {
		return nil, fmt.Errorf("install host stub: %w", err)
	}

	mod, err := r.InstantiateWithConfig(ctx, wasm,
		wazero.NewModuleConfig().WithStartFunctions("_initialize").WithName("plugin"))
	if err != nil {
		return nil, fmt.Errorf("instantiate module (is it a reactor-mode wasip1 c-shared build?): %w", err)
	}
	for _, export := range []string{"bn_alloc", "bn_invoke", "bn_free"} {
		if mod.ExportedFunction(export) == nil {
			return nil, fmt.Errorf("module does not export %s — not a BlockNinja wasm guest (missing wasmguest.Serve boilerplate?)", export)
		}
	}

	resp, err := invokeDescribe(ctx, mod)
	if err != nil {
		return nil, err
	}
	if e := resp.GetError(); e != nil {
		return nil, fmt.Errorf("DESCRIBE failed (%s): %s", e.GetCode(), e.GetMessage())
	}
	dr := &abiv1.DescribeResponse{}
	if err := proto.Unmarshal(resp.GetPayload(), dr); err != nil {
		return nil, fmt.Errorf("decode DescribeResponse: %w", err)
	}
	m := dr.GetManifest()
	if m == nil {
		return nil, fmt.Errorf("DESCRIBE returned an empty manifest")
	}
	return m, nil
}

// invokeDescribe drives one bn_alloc / bn_invoke round trip for HOOK_DESCRIBE
// through guest linear memory, mirroring the calling convention in
// core/docs/wasm-abi.md.
func invokeDescribe(ctx context.Context, mod api.Module) (*abiv1.InvokeResponse, error) {
	payload, err := proto.Marshal(&abiv1.DescribeRequest{HostAbiVersion: hostAbiVersion})
	if err != nil {
		return nil, fmt.Errorf("marshal DescribeRequest: %w", err)
	}
	req, err := proto.Marshal(&abiv1.InvokeRequest{Hook: abiv1.Hook_HOOK_DESCRIBE, Payload: payload})
	if err != nil {
		return nil, fmt.Errorf("marshal InvokeRequest: %w", err)
	}

	res, err := mod.ExportedFunction("bn_alloc").Call(ctx, uint64(len(req)))
	if err != nil {
		return nil, fmt.Errorf("bn_alloc: %w", err)
	}
	ptr := uint32(res[0])
	if ptr == 0 {
		return nil, fmt.Errorf("bn_alloc returned 0")
	}
	if !mod.Memory().Write(ptr, req) {
		return nil, fmt.Errorf("write DESCRIBE request out of range")
	}

	res, err = mod.ExportedFunction("bn_invoke").Call(ctx,
		uint64(abiv1.Hook_HOOK_DESCRIBE), uint64(ptr), uint64(len(req)))
	if err != nil {
		return nil, fmt.Errorf("bn_invoke(DESCRIBE): %w", err)
	}
	packed := res[0]
	if packed == 0 {
		return nil, fmt.Errorf("bn_invoke returned packed 0 (guest could not produce a response envelope)")
	}
	respBytes, ok := mod.Memory().Read(uint32(packed>>32), uint32(packed))
	if !ok {
		return nil, fmt.Errorf("read DESCRIBE response out of range")
	}
	resp := &abiv1.InvokeResponse{}
	if err := proto.Unmarshal(respBytes, resp); err != nil {
		return nil, fmt.Errorf("decode InvokeResponse: %w", err)
	}
	_, _ = mod.ExportedFunction("bn_free").Call(ctx, uint64(ptr))
	return resp, nil
}

// installFailingHost exports blockninja.host_call so the guest module can be
// instantiated, but answers every capability call with a PERMISSION_DENIED
// AbiError naming the method — DESCRIBE must not depend on the host.
func installFailingHost(ctx context.Context, r wazero.Runtime) error {
	_, err := r.NewHostModuleBuilder("blockninja").
		NewFunctionBuilder().
		WithFunc(func(ctx context.Context, mod api.Module, ptr, size uint32) uint64 {
			method := "<unknown>"
			if data, ok := mod.Memory().Read(ptr, size); ok {
				hcr := &abiv1.HostCallRequest{}
				if proto.Unmarshal(data, hcr) == nil && hcr.GetMethod() != "" {
					method = hcr.GetMethod()
				}
			}
			out, err := proto.Marshal(&abiv1.HostCallResponse{
				Error: &abiv1.AbiError{
					Code: abiv1.AbiErrorCode_ABI_ERROR_CODE_PERMISSION_DENIED,
					Message: fmt.Sprintf(
						"capability %q is unavailable during manifest extraction (DESCRIBE): a plugin must not call host capabilities at register/describe time",
						method),
				},
			})
			if err != nil {
				return 0
			}
			res, err := mod.ExportedFunction("bn_alloc").Call(ctx, uint64(len(out)))
			if err != nil || len(res) == 0 || res[0] == 0 {
				return 0
			}
			respPtr := uint32(res[0])
			if !mod.Memory().Write(respPtr, out) {
				return 0
			}
			return uint64(respPtr)<<32 | uint64(uint32(len(out)))
		}).
		Export("host_call").
		Instantiate(ctx)
	return err
}

// readWasm is a tiny helper so callers can pass a path.
func readWasm(path string) ([]byte, error) {
	b, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read wasm %s: %w", path, err)
	}
	return b, nil
}