package main

import (
	"context"
	"fmt"
	"io"
	"path"
	"reflect"
	"slices"
	"time"

	"github.com/nats-io/nats.go"

	"github.com/novox/mesh-controller/internal/broker"
	"github.com/novox/mesh-controller/internal/inventory"
	"github.com/novox/mesh-controller/internal/link"
)

// What the controller tells mesh-config of an open pull request, and asks it back (novox/hq ADR 0502 clauses 2 and 4,
// issue 1826): a config key a pull request introduces is not declared on the trunk, so a value for it can be judged
// only against the pull request's own declaration, which the core reads from the forge and mesh-config never does
// (ADR 0495 §1). The call is mesh-config's `config` verb in the controller's own name, actions `pull-declares` and
// `held`; the shapes are those of the interface the two sides agreed.

// meshConfigWait is how long the controller waits for mesh-config before it goes on without: a check is never held up
// by a module that does not answer.
const meshConfigWait = 10 * time.Second

// meshConfigAsk is one call of mesh-config's `config` verb in the controller's own name, answering its result. A
// variable so a test needs no bus.
var meshConfigAsk = func(ctx context.Context, args map[string]any) ([]byte, error) {
	var result []byte
	err := onTheBus(func(conn *nats.Conn) error {
		answer, err := link.AskMeshSeatToolAs(ctx, conn, broker.ControllerName, "mesh-config", "config", args, meshConfigWait)
		if err != nil {
			return err
		}
		if answer.Error != "" {
			return fmt.Errorf("%s", answer.Error)
		}
		result = answer.Result
		return nil
	})
	return result, err
}

// pullAt is an open pull request at a head: the change to read, and its number.
type pullAt struct {
	changeSource
	Number int
}

// pullAtOf is a pull request announced, as the change it makes over what it merges into.
func pullAtOf(p link.PullUpdated) pullAt {
	old := p.BaseSHA
	if old == "" {
		old = p.Base
	}
	return pullAt{Number: p.Number, changeSource: changeSource{Owner: p.Owner, Repo: p.Repo, New: p.Commit, Old: old,
		Paths: p.Paths, Truncated: p.PathsTruncated, Removed: p.Removed}}
}

func pullKey(owner, repo string, number int) string {
	return fmt.Sprintf("%s/%s#%d", owner, repo, number)
}

func (p pullAt) key() string { return pullKey(p.Owner, p.Repo, p.Number) }

// pullDeclarations are the config declarations a pull request's head adds or changes over what it merges into, by
// module, in the shape of the declared-config mirror. The bool says the head could be read: false for a pull request whose
// paths are cut (the caller cuts them to the manifests of the modules it moves) or whose base is unknown, which is then
// told nothing, never an empty set.
func pullDeclarations(ctx context.Context, p pullAt) ([]inventory.DeclaredConfigMirrored, bool, error) {
	var out []inventory.DeclaredConfigMirrored
	if p.Truncated || p.Old == "" {
		return nil, false, nil
	}
	for _, file := range p.Paths {
		if path.Base(file) != moduleManifestFile || slices.Contains(p.Removed, file) {
			continue
		}
		now, exists, err := manifestCached(ctx, p.Owner, p.Repo, file, p.New)
		if err != nil {
			return nil, false, err
		}
		if !exists || now.Module == "" {
			continue
		}
		was, _, err := manifestCached(ctx, p.Owner, p.Repo, file, p.Old)
		if err != nil {
			return nil, false, err
		}
		have, err := inventory.DeclaredOf(now.Settings)
		if err != nil {
			return nil, false, fmt.Errorf("%s at %.8s: %w", file, p.New, err)
		}
		had, err := inventory.DeclaredOf(was.Settings)
		if err != nil {
			return nil, false, fmt.Errorf("%s at %.8s: %w", file, p.Old, err)
		}
		changed := map[string]inventory.DeclaredMirrored{}
		for key, d := range have {
			if before, there := had[key]; !there || !reflect.DeepEqual(before, d) {
				changed[key] = d
			}
		}
		if len(changed) > 0 {
			out = append(out, inventory.DeclaredConfigMirrored{Module: now.Module, Settings: changed})
		}
	}
	return out, true, nil
}

// tellPullDeclares tells mesh-config, for each pull request at every announced head, what the head declares, an empty set
// when it declares nothing new: mesh-config re-judges the values held at every head, so a head that reverts the change
// drops them (ADR 0502 clause 6). A
// failure is said to w and the check goes on: the held values are then none (ADR 0502 clause 2).
func tellPullDeclares(ctx context.Context, w io.Writer, pulls []pullAt) {
	for _, p := range pulls {
		mods, readable, err := pullDeclarations(ctx, p)
		if err != nil {
			fmt.Fprintf(w, "%s: what its head declares cannot be read, so mesh-config is told nothing: %v\n", p.key(), err)
			continue
		}
		if !readable {
			continue
		}
		declares := map[string]map[string]inventory.DeclaredMirrored{}
		for _, m := range mods {
			declares[m.Module] = m.Settings
		}
		if _, err := meshConfigAsk(ctx, map[string]any{"action": "pull-declares", "pull": p.key(), "head": p.New,
			"declares": declares}); err != nil {
			fmt.Fprintf(w, "%s: mesh-config cannot be told what its head declares (%v); the check goes on without held values\n",
				p.key(), err)
		}
	}
}

// holdsModules is whether a module of the mesh is built from this repository.
func holdsModules(entries []inventory.Entry, owner, repo string) bool {
	return slices.ContainsFunc(entries, func(e inventory.Entry) bool {
		return sameRepository(e.Source.Repository, link.SourceMoved{Owner: owner, Repo: repo})
	})
}