package inventory

import (
	"context"
	"encoding/json"
)

// 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
	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) {
	query := `select b.module, b.id, b.commit_hash, b.source_fingerprint, b.made, b.manifest,
	                 coalesce(g.verdict = 'failed', false)
	            from build b left join build_gate g on g.build = b.id
	           where b.module is not null and b.module <> '' and b.failed = ''`
	args := []any{}
	if module != "" {
		query += ` and b.module = $1`
		args = append(args, module)
	}
	rows, err := i.store.Pool().Query(ctx, query+` order by b.module, coalesce(b.asked, b.at) desc, b.at desc`, args...)
	if err != nil {
		return nil, nil, err
	}
	defer rows.Close()
	out := map[string][]sourceRow{}
	var order []string
	for rows.Next() {
		var m string
		var r sourceRow
		if err := rows.Scan(&m, &r.id, &r.commit, &r.fingerprint, &r.made, &r.manifest, &r.failedGate); err != nil {
			return nil, nil, err
		}
		if _, seen := out[m]; !seen {
			order = append(order, m)
		}
		out[m] = append(out[m], r)
	}
	return out, order, rows.Err()
}

// 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.
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].fingerprint != fp || builds[j].failedGate {
			break
		}
		at = j
	}
	return at
}

// 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)]
			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) {
	all, _, err := i.sourceRows(ctx, "")
	if err != nil {
		return nil, err
	}
	out := map[string]map[string]string{}
	for m, builds := range all {
		for _, b := range builds {
			if b.fingerprint == "" || b.commit == "" {
				continue
			}
			if out[m] == nil {
				out[m] = map[string]string{}
			}
			if _, seen := out[m][b.commit]; !seen {
				out[m][b.commit] = b.fingerprint
			}
		}
	}
	return out, nil
}

// BuildSourceFingerprints is SourceFingerprints for one module: commit → fingerprint.
func (i *Inventory) BuildSourceFingerprints(ctx context.Context, module string) (map[string]string, error) {
	all, err := i.SourceFingerprints(ctx)
	if err != nil {
		return nil, err
	}
	if all[module] == nil {
		return map[string]string{}, nil
	}
	return all[module], nil
}

// 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) {
	all, _, err := i.sourceRows(ctx, "")
	if err != nil {
		return nil, err
	}
	out := map[string][]Artifact{}
	for m, builds := range all {
		if len(builds) == 0 {
			continue
		}
		var made []Artifact
		if err := json.Unmarshal(builds[standing(builds, 0)].made, &made); err != nil {
			// Skipped rather than fatal, as Held always did: the build that needs it says it is missing.
			continue
		}
		out[m] = made
	}
	return out, nil
}

// 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
}