package inventory

import (
	"context"
	"sort"
	"strings"

	"github.com/novox/mesh-controller/internal/builder"
	"github.com/novox/mesh-controller/internal/catalogue"
)

// The kinds of edge in the catalogue's one dependency relation (novox/hq ADR 0162).
const (
	// EdgeStandsOn: the module's artifact is built on the other's.
	EdgeStandsOn = "stands-on"
	// EdgePackages: the module's build read the other's repository. **No longer drawn** (novox/hq ADR 0267
	// rule 4): sharing a repository is no dependency, and a changed file moves every module whose build
	// source holds it, directly. Kept so an edge recorded or snapshotted before is read, and then neither
	// widens nor orders a plan.
	EdgePackages = "packages"
	// EdgeBuiltBy: the module is built by the holder of the build-machine seat.
	EdgeBuiltBy = "built-by"
	// EdgeDeclared: the manifest's own `build.on`.
	EdgeDeclared = "declared"
	// EdgeWorkerOf: the module holds the build seat, whose worker the control plane defines
	// (novox/hq issue 206). The one place a *running* order enters the graph: a build machine rolled
	// before the controller that redefines its worker cannot bind it, and nothing can then build the
	// controller that would end that — so the holder of the build seat follows the controller, and
	// the controller is built by whichever build machine is running, as it always was.
	EdgeWorkerOf = "worker-of"
)

// TheControlPlane is the module that defines every seat's worker on the bus.
const TheControlPlane = "mesh-controller"

// Edge is one dependency: From depends on To, in the way Kind says.
type Edge struct {
	From string `json:"from"`
	To   string `json:"to"`
	Kind string `json:"kind"`
}

// Dependencies is the catalogue's dependency relation, whole: every module the mesh holds, with
// an edge to each module it depends on and the kind of dependency on the edge. One answer, so
// nothing else computes an edge (novox/hq ADR 0162) — the merge handler, `build --on` and the
// overview all read this.
//
// Three sources, one relation: a manifest's `build.on`; the artifacts the latest build was made
// against (an `artifact-store://<module>/…` reference is an edge to that module); and the build machine,
// which every source-built module is built by. The repositories a build read are no edge (novox/hq ADR
// 0267 rule 4).
func (i *Inventory) Dependencies(ctx context.Context) ([]Edge, error) {
	entries, err := i.Catalogued(ctx)
	if err != nil {
		return nil, err
	}
	against, err := i.BuiltAgainst(ctx)
	if err != nil {
		return nil, err
	}
	held, err := i.Held(ctx)
	if err != nil {
		return nil, err
	}
	return dependenciesWith(entries, against, held), nil
}

// packagesHeld is, by package name, the module whose artifact the mesh holds as that package: a
// `package` artifact's reference is `<name>@<version>` (the builder's publishPackage), never an
// artifact-store reference, so a build that stood on it recorded the package's name and version.
func packagesHeld(held map[string]string) map[string]string {
	out := map[string]string{}
	for key, reference := range held {
		module, _, ok := strings.Cut(key, "/")
		if !ok {
			continue
		}
		if name := packageName(reference); name != "" {
			out[name] = module
		}
	}
	return out
}

// packageName is the name of a `<name>@<version>` package reference, or "" for anything else: a
// kept or pinned image (`…@sha256:…`), a URL, or a reference with no version.
func packageName(reference string) string {
	if strings.HasPrefix(reference, catalogue.ArtifactStoreScheme) || strings.Contains(reference, "@sha256:") ||
		strings.Contains(reference, "://") {
		return ""
	}
	at := strings.LastIndex(reference, "@")
	if at <= 0 || at == len(reference)-1 {
		return ""
	}
	return reference[:at]
}

// dependenciesOf is Dependencies over what was read, so a test can hand it a catalogue.
//
// `read` draws no edge (novox/hq ADR 0267 rule 4): what a build read moves it through its build source, in
// the planner, never through the relation.
func dependenciesOf(entries []Entry, against map[string][]string, _ map[string][]ReadRepository) []Edge {
	return dependenciesWith(entries, against, nil)
}

// dependenciesWith is the relation with the artifacts the mesh holds, "<module>/<artifact>" to its
// reference (Held), so a package a build stood on is read as its module's.
//
// **A built manifest carries no `build`** (catalogue.Resolve drops it), so what a module declared it
// is built on is read from what is kept of it once it is built (novox/hq issue 614): the bases its
// newest build was handed (`against`) — an artifact-store reference, or a package's `<name>@<version>`
// — and the language of every bundle it compiled (`Bundles`). Read only from records the mesh already
// keeps, so it holds for every module built before it, and a controller rolled back to one without it
// reads the same records as before.
func dependenciesWith(entries []Entry, against map[string][]string, held map[string]string) []Edge {
	packages := packagesHeld(held)
	known := map[string]bool{}
	var builders []string
	for _, e := range entries {
		name := e.Manifest.Module
		known[name] = true
		if e.Manifest.ClaimsSeat("node-build-agent") || e.Manifest.ClaimsSeat("mesh-build-machine") {
			builders = append(builders, name)
		}
	}
	seen := map[Edge]bool{}
	var out []Edge
	add := func(from, to, kind string) {
		if from == to || !known[to] {
			return
		}
		e := Edge{From: from, To: to, Kind: kind}
		if !seen[e] {
			seen[e] = true
			out = append(out, e)
		}
	}
	for _, e := range entries {
		name := e.Manifest.Module
		if e.Manifest.Build != nil {
			for _, on := range e.Manifest.Build.On {
				if on.Module != "" {
					add(name, on.Module, EdgeDeclared)
				}
			}
			// **A bundle stands on the toolchain it is compiled in** (novox/hq 04-ISSUES/211). A
			// manifest names its toolchain by language, not in `build.on`, so the edge was implicit
			// and a merge that moved the toolchain and a bundle together built both in one tier —
			// the bundle against the toolchain as it was, recorded as built from the new commit. Read
			// from the manifest, so it holds before any build has recorded what it stood on; and a
			// toolchain that moves rebuilds every bundle compiled in it, which is what a toolchain
			// carrying a bundle's dependencies requires.
			for _, a := range e.Manifest.Build.Artifacts {
				if a.Kind != catalogue.ArtifactBundle {
					continue
				}
				if chain, err := builder.ToolchainFor(a.Language); err == nil {
					add(name, chain.Base, EdgeStandsOn)
				}
			}
		}
		// **And once it is built**, from the bundles its resolved manifest keeps (novox/hq issue 614): the
		// `build` it was declared with is gone by then, and a toolchain that moved rebuilt none of them.
		for _, b := range e.Manifest.Bundles {
			if chain, err := builder.ToolchainFor(b.Language); err == nil {
				add(name, chain.Base, EdgeStandsOn)
			}
		}
		for _, ref := range against[name] {
			if rest, ok := strings.CutPrefix(ref, catalogue.ArtifactStoreScheme); ok {
				// A copy of an upstream image is no module's artifact (novox/hq ADR 0257): its
				// repository is named for the image, and its first segment names no module.
				if strings.HasPrefix(rest, builder.MirrorPrefix) {
					continue
				}
				if base, _, found := strings.Cut(rest, "/"); found {
					add(name, base, EdgeStandsOn)
				}
				continue
			}
			// A package base (`build.on` naming a module's `package` artifact) is recorded as the
			// package's name and version (novox/hq issue 614): the module that publishes that package
			// is what it stood on, whichever version the mesh holds now.
			if base, ok := packages[packageName(ref)]; ok {
				add(name, base, EdgeStandsOn)
			}
		}
		if e.Source.Repository != "" {
			for _, b := range builders {
				add(name, b, EdgeBuiltBy)
			}
		}
	}
	if known[TheControlPlane] {
		for _, b := range builders {
			if b != TheControlPlane {
				add(b, TheControlPlane, EdgeWorkerOf)
			}
		}
	}
	sort.Slice(out, func(a, b int) bool {
		if out[a].From != out[b].From {
			return out[a].From < out[b].From
		}
		if out[a].To != out[b].To {
			return out[a].To < out[b].To
		}
		return out[a].Kind < out[b].Kind
	})
	return out
}