package delivery

import (
	"encoding/json"
	"fmt"
	"maps"
	"slices"
	"strings"
	"time"
)

// How far a repository reached (novox/hq ADR 0556, issue 1280). The indexer says, per repository, the last merge it took in
// (TakenBucket); the delivery view keeps, per repository, how far each of its modules reached on the nodes that want it, and
// derives from it the repository's reached head (ReachBucket): the newest head of the repository at which every wanted
// module runs, on every node, a build at or after its last change. A merge at or before the reached head is on the
// machines. Nothing records a merge as delivered (ADR 0429 §1): the gate and the tracker derive it from this state.

// TakenBucket is the indexer's state `taken`: one key per repository (RepositoryKey), the last merge it took in.
const TakenBucket = IndexerModule + "_taken"

// ReachBucket is the delivery view's state `reach`: one key per repository (RepositoryKey), how far its modules reached.
const ReachBucket = ViewModule + "_reach"

// RepositoryKey is a repository's key in TakenBucket and ReachBucket: its forge name `owner/name` (RepositoryName), in
// lower case as the forge compares it, escaped as a key part (EscapeName). An empty spelling, or one with no owner, is
// refused.
func RepositoryKey(repository string) (string, error) {
	name := strings.ToLower(RepositoryName(repository))
	if owner, repo, ok := strings.Cut(name, "/"); !ok || owner == "" || repo == "" {
		return "", fmt.Errorf("delivery: %q names no repository as owner/name", repository)
	}
	return EscapeName(name), nil
}

// Taken is the value of a taken key: the repository, the merge commit the indexer last took in (applied its message
// whole), and when.
type Taken struct {
	V          int       `json:"v"`
	Repository string    `json:"repository"`
	Merge      string    `json:"merge"`
	At         time.Time `json:"at"`
}

// EncodeTaken is t as JSON at Version; a value with no repository or merge is refused.
func EncodeTaken(t Taken) ([]byte, error) {
	if t.Repository == "" || t.Merge == "" {
		return nil, fmt.Errorf("delivery: a taken value names its repository and merge")
	}
	t.V = Version
	return json.Marshal(t)
}

// DecodeTaken reads a taken value; it refuses an unknown version (ErrUnknownVersion) and one with no merge.
func DecodeTaken(data []byte) (Taken, error) {
	var t Taken
	if err := decode(data, &t); err != nil {
		return t, err
	}
	if t.Repository == "" || t.Merge == "" {
		return t, fmt.Errorf("delivery: a taken value names no repository or merge")
	}
	return t, nil
}

// Reach is the value of a reach key: how far the modules of one repository reached on the nodes. Indexed is the last
// merge the indexer took in for it (Taken.Merge), empty while it took in none. A repository the indexer holds no module
// of (a library) has no Modules. Reached is the reached head: the newest head of the repository in the source's history,
// not past Indexed, at which every module with a node that wants it has its floor at or after its last change at or before
// that head; ReachedSrc is the source revision that named it. Holds says, in words, what keeps the next head of the
// repository from being reached (a module on a node, the indexer's lag); empty when the repository's newest head is reached.
type Reach struct {
	V          int                    `json:"v"`
	Repository string                 `json:"repository"`
	Indexed    string                 `json:"indexed,omitempty"`
	Modules    map[string]ModuleReach `json:"modules,omitempty"`
	Reached    string                 `json:"reached,omitempty"`
	ReachedSrc uint64                 `json:"reached_src,omitempty"`
	Holds      []string               `json:"holds,omitempty"`
}

// ModuleReach is how far one module reached. FP is its fingerprint at the indexer now; Nodes how many nodes want it
// (a want not removed); Changes its fingerprints the view knows of, each with the merge commit it first appeared at,
// newest first. Floor is the oldest first-appearance commit among the fingerprints its nodes' haves run, a running have
// counting whether its health check passes or not; it is empty when a node that wants the module has no running have, or
// runs a fingerprint not among Changes. Waiting names, in words, every node where the module is not settled (its have
// different from its want, not running, or not healthy), with or without a floor: health is said here and never moves the
// floor (ADR 0556 clause 2). A module whose floor is empty while a node wants it holds no head of the repository back: a
// reader takes a merge among its Changes as not yet on the machines, with these words. A module no node wants has neither.
type ModuleReach struct {
	FP      string   `json:"fp,omitempty"`
	Nodes   int      `json:"nodes"`
	Changes []Change `json:"changes,omitempty"`
	Floor   string   `json:"floor,omitempty"`
	Waiting string   `json:"waiting,omitempty"`
}

// Change is one fingerprint of a module, the merge commit it first appeared at (Module.Commit), and the source revision
// that named that commit as the repository's head (Module.Src, or the source's history), 0 when not known.
type Change struct {
	Commit string `json:"commit"`
	FP     string `json:"fp"`
	Src    uint64 `json:"src,omitempty"`
}

// MostChanges is how many changes of a module a reach value keeps: as many revisions as the indexer's modules bucket keeps.
const MostChanges = ModulesHistory

func (r Reach) check() error {
	if r.Repository == "" {
		return fmt.Errorf("delivery: a reach value names no repository")
	}
	if (r.Reached == "") != (r.ReachedSrc == 0) {
		return fmt.Errorf("delivery: the reach of %s names its reached head and its source revision together", r.Repository)
	}
	for name, m := range r.Modules {
		if name == "" {
			return fmt.Errorf("delivery: a reach value names a module with no name")
		}
		if m.Nodes < 0 {
			return fmt.Errorf("delivery: the reach of %s counts %d nodes", name, m.Nodes)
		}
		if len(m.Changes) > MostChanges {
			return fmt.Errorf("delivery: the reach of %s keeps %d changes, more than %d", name, len(m.Changes), MostChanges)
		}
		for _, c := range m.Changes {
			if c.Commit == "" || c.FP == "" {
				return fmt.Errorf("delivery: a change of %s names no commit or fingerprint", name)
			}
		}
	}
	return nil
}

// EncodeReach is r as JSON at Version; a value that does not check is refused.
func EncodeReach(r Reach) ([]byte, error) {
	if err := r.check(); err != nil {
		return nil, err
	}
	r.V = Version
	return json.Marshal(r)
}

// DecodeReach reads a reach value; it refuses an unknown version (ErrUnknownVersion) and one that does not check.
func DecodeReach(data []byte) (Reach, error) {
	var r Reach
	if err := decode(data, &r); err != nil {
		return r, err
	}
	return r, r.check()
}

// SameReach says whether two reach values are the same, so the view writes only when they differ.
func SameReach(a, b Reach) bool {
	if a.Repository != b.Repository || a.Indexed != b.Indexed || len(a.Modules) != len(b.Modules) ||
		a.Reached != b.Reached || a.ReachedSrc != b.ReachedSrc || !slices.Equal(a.Holds, b.Holds) {
		return false
	}
	for _, name := range slices.Sorted(maps.Keys(a.Modules)) {
		x, ok := b.Modules[name]
		y := a.Modules[name]
		if !ok || x.FP != y.FP || x.Nodes != y.Nodes || x.Floor != y.Floor || x.Waiting != y.Waiting ||
			!slices.Equal(x.Changes, y.Changes) {
			return false
		}
	}
	return true
}