package inventory

import (
	"context"
	"encoding/json"
	"strings"

	"github.com/novox/mesh-controller/internal/chain"
)

// A build whose source is unchanged is never a move (novox/hq issue 280).
//
// The builder says what each build was made from, hashed (its source fingerprint). Two successful
// builds of a module with one fingerprint are one build, whatever digests they made — an image is not
// byte-reproducible, and reading a rebuild's new image digest as a new build made a merge that never
// touched the bus demand a planned bus upgrade before anything could be sent to the machine running
// it. So:
//
//   - a module's builds, newest request first, fall into runs of one fingerprint; **the oldest build of
//     the newest run stands for the run**: its artifacts are the ones the mesh registers and hands
//     every module that stands on it (Held), so a rebuild of an unchanged source changes nothing any
//     machine is sent, and nothing standing on it moves either;
//   - a build that failed its gate ends a run: what was put back is never what a later build stands for;
//   - an empty fingerprint — a builder that predates it, a source that does not pin its build — is a
//     run of its own, as every build was before.

// sourceRow is one successful build of a module, as the runs are read.
type sourceRow struct {
	id, commit, fingerprint string
	made                    []byte
	manifest                []byte
	manifestDigest          string
	failedGate              bool
}

// sourceRows is every successful build of each module (of one module, when named), newest request
// first.
func (i *Inventory) sourceRows(ctx context.Context, module string) (map[string][]sourceRow, []string, error) {
	c, err := i.theChain(ctx)
	if err != nil {
		return nil, nil, err
	}
	return i.chainSourceRows(ctx, c, module)
}

// standing is, of a module's builds newest first, the index of the build that stands for the build at
// `from`: the oldest of the unbroken run of builds behind it with its source fingerprint.
//
// **Across the switch to the new form** (novox/hq ADR 0453 §6, ADR 0499; R4e A9): a build of the new form (`src2:`, taken
// from the builder's key) continues the run of the build before it of the old form (`src1:` or none, build-agent's)
// when every artifact of the two has the same digest: the fingerprints cannot be compared, the programs can, and equal
// digests are no move. Past it the run goes on by the old fingerprint.
func standing(builds []sourceRow, from int) int {
	at := from
	fp := builds[from].fingerprint
	if fp == "" || builds[from].failedGate {
		return at
	}
	for j := from + 1; j < len(builds); j++ {
		if builds[j].failedGate {
			break
		}
		if builds[j].fingerprint != fp {
			if !newForm(fp) || newForm(builds[j].fingerprint) || !sameDigests(builds[at].made, builds[j].made) {
				break
			}
			fp = builds[j].fingerprint
		}
		at = j
	}
	return at
}

// newForm says a source fingerprint is of the new form (ADR 0453 §6).
func newForm(fp string) bool { return strings.HasPrefix(fp, "src2:") }

// sameDigests says two builds' artifacts, as recorded (JSON of []Artifact), are the same programs: the same names, each
// with the same digest, wherever each was pushed. A build naming an artifact with no digest is never the same.
func sameDigests(a, b []byte) bool {
	digests := func(raw []byte) map[string]string {
		var made []Artifact
		if json.Unmarshal(raw, &made) != nil || len(made) == 0 {
			return nil
		}
		out := map[string]string{}
		for _, m := range made {
			d := digestIn(m.Reference)
			if d == "" {
				return nil
			}
			out[m.Name] = d
		}
		return out
	}
	da, db := digests(a), digests(b)
	if da == nil || db == nil || len(da) != len(db) {
		return false
	}
	for name, d := range da {
		if db[name] != d {
			return false
		}
	}
	return true
}

// StandingBuild is the build that stands for a module's build (novox/hq issue 280): the oldest build of
// the unbroken run of builds with its source fingerprint, at or before it — itself when its fingerprint
// is empty or it starts the run. Answers its id and the manifest it was recorded with; empty when the
// build is not a successful build of the module on record.
func (i *Inventory) StandingBuild(ctx context.Context, module, build string) (string, []byte, error) {
	all, _, err := i.sourceRows(ctx, module)
	if err != nil {
		return "", nil, err
	}
	builds := all[module]
	for k, b := range builds {
		if b.id == build {
			s := builds[standing(builds, k)]
			if len(s.manifest) == 0 && s.manifestDigest != "" {
				// The manifest is kept apart from the record (issue 1121): one Get.
				c, err := i.theChain(ctx)
				if err != nil {
					return "", nil, err
				}
				raw, err := manifestOfRecord(ctx, c, chain.Build{ID: s.id, ManifestDigest: s.manifestDigest})
				return s.id, raw, err
			}
			return s.id, s.manifest, nil
		}
	}
	return "", nil, nil
}

// SourceFingerprints is, per module, per commit, the source fingerprint of the newest successful build
// from it that has one: module → commit → fingerprint. A commit whose builds carry none is absent.
func (i *Inventory) SourceFingerprints(ctx context.Context) (map[string]map[string]string, error) {
	c, err := i.theChain(ctx)
	if err != nil {
		return nil, err
	}
	// Read from the commit pointers, which carry each commit's source fingerprint: no record is read (issue 1121).
	return i.chainSourceFingerprints(ctx, c)
}

// BuildSourceFingerprints is SourceFingerprints for one module: commit → fingerprint.
func (i *Inventory) BuildSourceFingerprints(ctx context.Context, module string) (map[string]string, error) {
	c, err := i.theChain(ctx)
	if err != nil {
		return nil, err
	}
	// This module's commit pointers only (issue 1121).
	return i.chainBuildSourceFingerprints(ctx, c, module)
}

// heldMade is, per module, what the build standing for its newest successful build made — what Held
// answers (novox/hq issue 280).
func (i *Inventory) heldMade(ctx context.Context) (map[string][]Artifact, error) {
	c, err := i.theChain(ctx)
	if err != nil {
		return nil, err
	}
	return i.chainHeldMade(ctx, c)
}

// SameSourceCommits is the commits of the builds in a build's run (novox/hq issue 280): the build and
// every build behind it back to the one standing for it, all made from one source. Empty when the
// build stands for itself — no earlier build was made from its source — so a commit alone never says
// two builds are one: a dependent rebuilt because its base moved keeps its commit and is a move.
func (i *Inventory) SameSourceCommits(ctx context.Context, module, build string) (map[string]bool, error) {
	all, _, err := i.sourceRows(ctx, module)
	if err != nil {
		return nil, err
	}
	builds := all[module]
	for k, b := range builds {
		if b.id != build {
			continue
		}
		s := standing(builds, k)
		if s == k {
			return nil, nil
		}
		out := map[string]bool{}
		for j := k; j <= s; j++ {
			if builds[j].commit != "" {
				out[builds[j].commit] = true
			}
		}
		return out, nil
	}
	return nil, nil
}