// placement-seed writes the catalogue's first placement files (novox/hq ADR 0549 §4, ADR 0555 §6, issue 1126) from the
// answer of the controller's one read-only verb `placement-export`: one `placement/<node>.json` per node, each the
// node's placement as the controller's own code read it from its own store, checked as the catalogue's check checks it
// (delivery.CheckPlacements) before anything is written. The pull request it makes merges only when its composition check
// composes every node equal to what it runs.
//
//	placement-seed -catalogue <checkout of mesh-catalog> < export.json
//	placement-seed -catalogue <dir> -export export.json
//
// export.json is the verb's answer as it prints it ({"<node>": <placement>, ...}, or the verb's wrapping with it under
// "answer"). It opens no network connection, bus or store; it writes only <dir>/placement/<node>.json, and refuses to
// write over a placement file already there. Exit codes: 0 written; 1 the export cannot be read, is refused by the
// check, or a file is there; 2 the flags are wrong.
package main

import (
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"

	"git.novox.be/novox/mesh-sdk/go/delivery"
)

func main() {
	catalogue := flag.String("catalogue", "", "the checkout of the catalogue to write placement/<node>.json into")
	export := flag.String("export", "", "the verb's answer; standard input when absent")
	flag.Parse()
	if *catalogue == "" || flag.NArg() > 0 {
		fmt.Fprintln(os.Stderr, "usage: placement-seed -catalogue <dir> [-export <file>]")
		os.Exit(2)
	}
	in := io.Reader(os.Stdin)
	if *export != "" {
		f, err := os.Open(*export)
		if err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		defer f.Close()
		in = f
	}
	written, err := Seed(in, *catalogue)
	for _, path := range written {
		fmt.Println(path)
	}
	if err != nil {
		fmt.Fprintln(os.Stderr, "placement-seed:", err)
		os.Exit(1)
	}
}

// Seed reads the export and writes each node's placement file under root, answering the paths written. Nothing is
// written when the export does not read, the check refuses it, or a placement file is already there.
func Seed(export io.Reader, root string) ([]string, error) {
	raw, err := io.ReadAll(export)
	if err != nil {
		return nil, err
	}
	placements, err := read(raw)
	if err != nil {
		return nil, err
	}
	all := func(string) bool { return true }
	if refused := delivery.CheckPlacements(placements, all, all); len(refused) > 0 {
		return nil, fmt.Errorf("the export is refused by the catalogue's check: %v", refused)
	}
	nodes := make([]string, 0, len(placements))
	for node := range placements {
		nodes = append(nodes, node)
	}
	sort.Strings(nodes)
	files := map[string][]byte{}
	for _, node := range nodes {
		p := placements[node]
		p.Revision = "" // only the indexer writes a revision, into the key
		if _, err := delivery.EncodePlacement(p); err != nil {
			return nil, fmt.Errorf("%s: %w", node, err)
		}
		p.V = delivery.Version
		body, err := json.MarshalIndent(p, "", "  ")
		if err != nil {
			return nil, err
		}
		path := filepath.Join(root, filepath.FromSlash(delivery.PlacementFile(node)))
		if _, err := os.Stat(path); err == nil {
			return nil, fmt.Errorf("%s is already there; the seed is written once (ADR 0549 §4)", path)
		} else if !errors.Is(err, os.ErrNotExist) {
			return nil, err
		}
		files[path] = append(body, '\n')
	}
	var written []string
	for _, node := range nodes {
		path := filepath.Join(root, filepath.FromSlash(delivery.PlacementFile(node)))
		if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
			return written, err
		}
		if err := os.WriteFile(path, files[path], 0o644); err != nil {
			return written, err
		}
		written = append(written, path)
	}
	return written, nil
}

// read is the export as the verb prints it, or wrapped as a verb's answer (the controller's verbAnswer: its JSON under
// "answer").
func read(raw []byte) (map[string]delivery.Placement, error) {
	var wrapped struct {
		Answer json.RawMessage `json:"answer"`
	}
	if json.Unmarshal(raw, &wrapped) == nil && len(wrapped.Answer) > 0 {
		raw = wrapped.Answer
	}
	var byNode map[string]json.RawMessage
	if err := json.Unmarshal(raw, &byNode); err != nil {
		return nil, fmt.Errorf("the export is not {<node>: <placement>}: %w", err)
	}
	if len(byNode) == 0 {
		return nil, errors.New("the export names no node")
	}
	out := map[string]delivery.Placement{}
	for node, body := range byNode {
		p, err := delivery.DecodePlacement(body)
		if err != nil {
			return nil, fmt.Errorf("%s: %w", node, err)
		}
		if p.Node != node {
			return nil, fmt.Errorf("the export's placement of %s names the node %q", node, p.Node)
		}
		out[node] = p
	}
	return out, nil
}