package main

import (
	"context"
	"fmt"
	"slices"
	"sort"
	"strings"

	"github.com/novox/mesh-controller/internal/inventory"
	"github.com/novox/mesh-controller/internal/link"
)

// **A module moves only when its program changes** (novox/hq issue 721). A merge check builds every module the
// delivery plan moves and compares each with the build the mesh holds of it; a walk is cut without a module whose
// check found its whole image the same as that build, while the mesh still holds it, and says so among the modules
// it left unchanged. A merge of one sentence in a package a program imports but never reaches moves no build of it.

// sameAsRunning are the modules of a walk its checks found the same as the build the mesh holds, each with what its
// check said. **Only when every pull request the walk answers was checked at the head it merged, and every one of
// those checks built the module and found it the same as the build the mesh still holds**: a merge the walk answers
// without a pull request, a check of another head, a check that built it differently, or a held build that moved
// since, leaves the module in the walk.
func sameAsRunning(plan *inventory.Plan, builds []link.CheckedBuild, held map[string]string) map[string]string {
	if plan.Delivery == nil || len(plan.Delivery.Merges) == 0 {
		return nil
	}
	for _, m := range plan.Delivery.Merges {
		if _, ok := pullOf(m); !ok {
			return nil
		}
	}
	pulls := reuseAskOf(plan).Pulls
	heads := mergedHeadsOf(plan)
	out := map[string]string{}
	for name := range plan.Modules {
		said := ""
		for _, pull := range pulls {
			b, ok := checkedBuildOf(builds, pull, heads[pull], name)
			if !ok || !stillHeld(b.Built, name, held) {
				said = ""
				break
			}
			if said == "" {
				said = b.Built.Same
			}
		}
		if said != "" {
			out[name] = said
		}
	}
	if len(out) == 0 {
		return nil
	}
	return out
}

// checkedBuildOf is the newest build a check of the pull request at head made of the module; false when none did.
func checkedBuildOf(builds []link.CheckedBuild, pull link.PullRef, head, module string) (link.CheckedBuild, bool) {
	if head == "" {
		return link.CheckedBuild{}, false
	}
	for _, b := range builds {
		if b.Pull == pull && b.Built.Module == module && link.SameHead(b.Head, head) {
			return b, true
		}
	}
	return link.CheckedBuild{}, false
}

// stillHeld is whether a check found every artifact of the module the same as a build the mesh still holds.
func stillHeld(b link.CheckBuilt, module string, held map[string]string) bool {
	if b.Same == "" || b.NotBuilt != "" || len(b.Made) == 0 || len(b.SameAs) != len(b.Made) {
		return false
	}
	for _, m := range b.Made {
		was := pinnedDigest(b.SameAs[m.Name])
		if was == "" || was != pinnedDigest(held[module+"/"+m.Name]) {
			return false
		}
	}
	return true
}

// pinnedDigest is a reference's pinned digest, empty when it is not pinned.
func pinnedDigest(ref string) string {
	if i := strings.LastIndex(ref, "@"); i >= 0 {
		return ref[i+1:]
	}
	return ""
}

// leaveSameAsRunning takes from a walk being cut every module its checks found the same as the build the mesh holds
// (sameAsRunning), and every dependent in the walk only for one of those (withDependentsOf): what was taken, with why. **Anything not read leaves the walk as it was**, said.
func leaveSameAsRunning(ctx context.Context, inv *inventory.Inventory, plan *inventory.Plan, moved []string,
	edges []inventory.Edge) map[string]string {
	if plan.Delivery == nil || len(plan.Modules) == 0 {
		return nil
	}
	pulls := reuseAskOf(plan).Pulls
	if len(pulls) == 0 {
		return nil
	}
	builds, err := checkedBuildsOf(ctx, pulls)
	if err != nil {
		fmt.Printf("  the checks' builds could not be read, so every module moves: %v\n", err)
		// empty-on-error: said above; nothing left out of the walk is the safe answer, every module moves as before
		return nil
	}
	held, err := inv.RegisteredHeld(ctx)
	if err != nil {
		fmt.Printf("  what the mesh holds could not be read, so every module moves: %v\n", err)
		// empty-on-error: said above; nothing left out of the walk is the safe answer, every module moves as before
		return nil
	}
	same := withDependentsOf(sameAsRunning(plan, builds, held), plan, moved, edges)
	if len(same) == 0 {
		return nil
	}
	names := make([]string, 0, len(same))
	for n := range same {
		names = append(names, n)
	}
	sort.Strings(names)
	withhold(plan, names, nil)
	for _, n := range names {
		fmt.Printf("  %s left out: %s\n", n, same[n])
	}
	return same
}

// withDependentsOf adds to the modules found the same every module of the walk that is in it only as a dependent of
// one of them (novox/hq ADR 0267 rule 3): **a dependent is left out when its base comes out the same**, since the
// base it stands on stays the build the mesh holds. A module a merge moves itself, or a dependent of a base that
// still moves, stays. moved are the modules the walk's merges move; edges the graph the walk was planned along.
func withDependentsOf(same map[string]string, plan *inventory.Plan, moved []string, edges []inventory.Edge) map[string]string {
	if len(same) == 0 {
		return same
	}
	var still []string
	for _, n := range moved {
		if same[n] == "" {
			still = append(still, n)
		}
	}
	keep := map[string]bool{}
	for _, n := range reachableFrom(still, edges) {
		keep[n] = true
	}
	// Until nothing more is found: a dependent of a dependent left out is left out too.
	for grew := true; grew; {
		grew = false
		for n := range plan.Modules {
			if keep[n] || same[n] != "" {
				continue
			}
			var bases []string
			for _, e := range edges {
				ordering := e.Kind == inventory.EdgeBuiltBy || e.Kind == inventory.EdgeWorkerOf ||
					e.Kind == inventory.EdgePackages || e.Kind == edgeChangeOrder
				if !ordering && e.From == n && same[e.To] != "" && !slices.Contains(bases, e.To) {
					bases = append(bases, e.To)
				}
			}
			sort.Strings(bases)
			if len(bases) == 0 {
				// In the walk for no base found the same: whatever brought it in is not said here, so it moves.
				continue
			}
			same[n] = "unchanged: it is in the walk only for " + strings.Join(bases, ", ") +
				", which came out the same as the build the mesh holds (ADR 0267 rule 3)"
			grew = true
		}
	}
	return same
}