package delivery

import (
	"encoding/json"
	"fmt"
	"reflect"
	"strings"
)

// The checker's other buckets (ADR 0484 clauses 2 and 3): owed, the acts it owes the forge, which the forge bridge
// performs once per revision of a key, and previews, what the fetch step answered for a head merged onto a trunk commit.
const (
	// CheckerOwedBucket is the checker's bucket of owed acts, in the gate's owed shape: a status with the context
	// StatusContextCheck for each head it judged. One part writes each key: the checker.
	CheckerOwedBucket = CheckerModule + "_owed"
	// CheckerOwedHistory is the revisions the checker's owed bucket keeps per key.
	CheckerOwedHistory = 5
	// PreviewsBucket is the checker's bucket of merge previews; the indexer reads it for the candidates' fingerprints.
	PreviewsBucket = CheckerModule + "_previews"
	// PreviewsHistory is the revisions the previews bucket keeps per key.
	PreviewsHistory = 5
)

// CheckerOwedKey is the key, in CheckerOwedBucket, of the status the checker owes on a pull request at a head: the
// gate's OwedKey with the act `status=mesh/check`, the only act the checker owes.
func CheckerOwedKey(repository string, number int, head string) (string, error) {
	return OwedKey(repository, number, head, OwedStatus+"="+StatusContextCheck)
}

// ParseCheckerOwedKey is the inverse of CheckerOwedKey; it refuses an owed key of any other act.
func ParseCheckerOwedKey(key string) (repository string, number int, head string, err error) {
	repository, number, head, act, err := ParseOwedKey(key)
	if err != nil {
		return "", 0, "", err
	}
	if act != OwedStatus+"="+StatusContextCheck {
		return "", 0, "", fmt.Errorf("delivery: %q is not a checker owed key: the checker owes only status=%s, not %q", key, StatusContextCheck, act)
	}
	return repository, number, head, nil
}

// EncodeCheckerOwed is o as JSON at Version; it refuses what EncodeOwed refuses and any act but a status with the
// context StatusContextCheck.
func EncodeCheckerOwed(o Owed) ([]byte, error) {
	if err := checkCheckerOwed(o); err != nil {
		return nil, err
	}
	return EncodeOwed(o)
}

func checkCheckerOwed(o Owed) error {
	if o.Act != OwedStatus || o.Context != StatusContextCheck {
		return fmt.Errorf("delivery: the checker owes only a status with the context %s, not the act %q with the context %q", StatusContextCheck, o.Act, o.Context)
	}
	return nil
}

// DecodeCheckerOwed reads an owed act of the checker's bucket.
func DecodeCheckerOwed(data []byte) (Owed, error) {
	o, err := DecodeOwed(data)
	if err != nil {
		return Owed{}, err
	}
	if err := checkCheckerOwed(o); err != nil {
		return Owed{}, err
	}
	return o, nil
}

// PreviewKey is the key, in PreviewsBucket, of a head merged onto a trunk commit: `<repository>.<head>.<trunk>`.
func PreviewKey(repository, head, trunk string) (string, error) {
	repo, err := escapeRepository(repository)
	if err != nil {
		return "", err
	}
	if err := checkName("head", head); err != nil {
		return "", err
	}
	if err := checkName("trunk commit", trunk); err != nil {
		return "", err
	}
	return repo + "." + head + "." + trunk, nil
}

// ParsePreviewKey is the inverse of PreviewKey.
func ParsePreviewKey(key string) (repository, head, trunk string, err error) {
	parts := strings.Split(key, ".")
	if len(parts) != 3 {
		return "", "", "", fmt.Errorf("delivery: %q is not a preview key, <repository>.<head>.<trunk>", key)
	}
	repository, err = unescapeRepository(parts[0])
	if err != nil {
		return "", "", "", fmt.Errorf("delivery: %q is not a preview key: %w", key, err)
	}
	if _, err := PreviewKey(repository, parts[1], parts[2]); err != nil {
		return "", "", "", fmt.Errorf("delivery: %q is not a preview key: %w", key, err)
	}
	return repository, parts[1], parts[2], nil
}

// PreviewModule is what the preview holds of one module directory: the tree sha of the directory (or its named tree), the digest of its
// manifest (the key in the manifests bucket) and the hex sha256 of its lock files by path relative to it.
type PreviewModule struct {
	Tree     string            `json:"tree"`
	Manifest string            `json:"manifest"`
	Locks    map[string]string `json:"locks,omitempty"`
	// Paths are, of a module whose every artifact names its paths, each named path's git object id at the merge; Tree
	// is then their NamedTree (novox/hq ADR 0499 clause 2). Absent otherwise.
	Paths map[string]string `json:"paths,omitempty"`
}

// Preview is the value of a preview key: the repository, the head and the trunk commit it was merged onto, the merge
// commit and, for each module directory of the merge, a PreviewModule. A head that does not merge is a preview too: it
// names the files in Conflicts and has no merge commit and no modules (issue 1445).
type Preview struct {
	V          int                      `json:"v"`
	Repository string                   `json:"repository"`
	Head       string                   `json:"head"`
	Trunk      string                   `json:"trunk"`
	Merge      string                   `json:"merge,omitempty"`
	Conflicts  []string                 `json:"conflicts,omitempty"`
	Modules    map[string]PreviewModule `json:"modules,omitempty"`
}

func (p Preview) check() error {
	if _, err := PreviewKey(p.Repository, p.Head, p.Trunk); err != nil {
		return err
	}
	for _, f := range p.Conflicts {
		if f == "" {
			return fmt.Errorf("delivery: a preview names a conflicting file with an empty path")
		}
	}
	if len(p.Conflicts) > 0 {
		if p.Merge != "" || len(p.Modules) > 0 {
			return fmt.Errorf("delivery: a preview of a head in conflict has no merge commit and no modules")
		}
		return nil
	}
	if p.Merge == "" {
		return fmt.Errorf("delivery: a preview names no merge commit")
	}
	for dir, m := range p.Modules {
		if dir == "" {
			return fmt.Errorf("delivery: a preview names a module with an empty directory")
		}
		if m.Tree == "" {
			return fmt.Errorf("delivery: the preview's module %q has no tree", dir)
		}
		if _, err := ManifestsKey(m.Manifest); err != nil {
			return fmt.Errorf("delivery: the preview's module %q: %w", dir, err)
		}
		for path, hash := range m.Locks {
			if path == "" || hash == "" {
				return fmt.Errorf("delivery: the lock %q of the preview's module %q has an empty path or hash", path, dir)
			}
		}
		if err := checkNamed(m.Tree, m.Manifest, m.Paths, fmt.Sprintf("the preview's module %q", dir)); err != nil {
			return err
		}
	}
	return nil
}

// EncodePreview is p as JSON at Version.
func EncodePreview(p Preview) ([]byte, error) {
	if err := p.check(); err != nil {
		return nil, err
	}
	p.V = Version
	return json.Marshal(p)
}

// DecodePreview reads a preview.
func DecodePreview(data []byte) (Preview, error) {
	var p Preview
	if err := decode(data, &p); err != nil {
		return Preview{}, err
	}
	if err := p.check(); err != nil {
		return Preview{}, err
	}
	return p, nil
}

// SamePreview says whether two previews are the same value.
func SamePreview(a, b Preview) bool { return reflect.DeepEqual(a, b) }