package stacks

import (
	"bytes"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"

	"gopkg.in/yaml.v3"
)

// ── The update ladder on the box (`09` §3 decision 14, §6.4 part 5; controller v0.268.0) ─────────
//
// WHAT IT REPLACES. Until v0.267.0 one press moved an app straight to the catalog's CURRENT
// definition, however many tested steps lay between. Measured 2026-09-23: vikunja installed at 2.3.0,
// the drill catalog then took 2.4.0 and 2.5.0, one press → 2.5.0 in 9.5 s and 2.4.0 never ran; and on
// demo-hp's 9201 romm took its app step AND its engine step in one press — each tested alone, never
// together. Decision 14: a box behind climbs ONE TESTED STEP at a time, in order, and never jumps.
//
// WHERE A STEP'S DEFINITION LIVES. Not in git history — the box's catalog clone is `--depth 1`
// (`sync.go`), and the commit that moved an image is not always the definition that works (romm's
// 15f9ebf OOM-looped; the working step is its images under the later f4eb94f template). So the catalog
// keeps, for every step but the newest, the step's OWN complete compose file at
// `templates/<app>/steps/<StepKey(to)>.yml`, written by `upgrade-test.py --write-ladder` and refused
// absent by `check-test-record.py`. The newest step's definition is the template's docker-compose.yml.
// The box reads both straight from its clone; the syncer copies nothing new into the stack dir.
//
// ONE PRESS = ONE STEP. The guarded update (§6.1) runs unchanged around it: same precondition, same
// safety dump, same undo copy, same health wait, same undo. Only the definition it pins differs.
//
// AN APP OLDER THAN THE LADDER. An installed version that matches no entry's `from` has no record to
// climb — today's behaviour (the catalog's current definition) applies, logged by name. Pinned by
// TestLadder_UnknownInstalledJumpsAndSaysSo.

// LadderEntry is one line of `.felhom.yml`'s `update_ladder:` — the fields the box reads. The catalog's
// `scripts/ladder.py` documents the whole record.
type LadderEntry struct {
	From    map[string]string `yaml:"from" json:"from"`
	To      map[string]string `yaml:"to" json:"to"`
	Digest  map[string]string `yaml:"digest" json:"digest"`
	Verdict string            `yaml:"verdict" json:"verdict"`
	// TestedAt is when the step was proven (RFC3339) — the badge compares it with the install (v0.269.0).
	TestedAt string `yaml:"tested_at" json:"tested_at"`
	// Marks are decision 13's two exceptions the test sets on a step (v0.271.0 reads them): the
	// automatic leg never takes a step that needs a person, and takes a files-may-change step only when
	// a fresh WHOLE copy exists. A person's press ignores both — the marks bind the leg only.
	Marks LadderMarks `yaml:"marks" json:"marks"`
}

// LadderMarks is the `marks` object of a ladder entry. NeedsPerson is JSON null (nil) or the tester's
// reason; an entry with no `marks` key reads as no marks.
type LadderMarks struct {
	FilesMayChange bool    `yaml:"files_may_change" json:"files_may_change"`
	NeedsPerson    *string `yaml:"needs_person" json:"needs_person"`
	MemoryTight    bool    `yaml:"memory_tight" json:"memory_tight"`
}

// LadderPrint is a short fingerprint of an app's whole ladder as the box parsed it — what R-680's
// failed-step record is tied to: when the catalog changes the ladder (a new step, a re-test, a mark),
// the print changes and the automatic leg may try again. "" = no ladder.
func LadderPrint(ladder []LadderEntry) string {
	if len(ladder) == 0 {
		return ""
	}
	b, _ := json.Marshal(ladder)
	sum := sha256.Sum256(b)
	return hex.EncodeToString(sum[:])[:16]
}

type ladderDoc struct {
	UpdateLadder []LadderEntry `yaml:"update_ladder"`
}

// LoadLadder reads the ladder from a `.felhom.yml`. No key → (nil, nil). The entries are JSON flow
// mappings, which YAML reads as ordinary maps.
func LoadLadder(felhomPath string) ([]LadderEntry, error) {
	data, err := os.ReadFile(felhomPath)
	if err != nil {
		return nil, err
	}
	var d ladderDoc
	if err := yaml.Unmarshal(data, &d); err != nil {
		return nil, fmt.Errorf("parsing update_ladder in %s: %w", felhomPath, err)
	}
	return d.UpdateLadder, nil
}

// StepKey names a step's definition file: the first 16 hex of the sha256 of `to` as canonical JSON —
// keys sorted, no spaces, no HTML escaping. The catalog computes the SAME string in Python
// (`json.dumps(to, sort_keys=True, separators=(",", ":"))`); TestLadder_StepKeyMatchesTheCatalog pins
// one real value both sides print.
func StepKey(to map[string]string) string {
	var buf bytes.Buffer
	enc := json.NewEncoder(&buf)
	enc.SetEscapeHTML(false)
	_ = enc.Encode(to) // a map[string]string always encodes; Go sorts map keys
	sum := sha256.Sum256(bytes.TrimRight(buf.Bytes(), "\n"))
	return hex.EncodeToString(sum[:])[:16]
}

// StepFile is the step's definition path inside a template directory.
func StepFile(templateDir string, to map[string]string) string {
	return filepath.Join(templateDir, "steps", StepKey(to)+".yml")
}

// StepMetaFile is the step's own `.felhom.yml` (R-664, v0.269.0): its probe, memory and applied record.
func StepMetaFile(templateDir string, to map[string]string) string {
	return filepath.Join(templateDir, "steps", StepKey(to)+".felhom.yml")
}

func sameRefs(a, b map[string]string) bool {
	if len(a) != len(b) {
		return false
	}
	for k, v := range a {
		if b[k] != v {
			return false
		}
	}
	return true
}

// LadderStep is the one step the next press applies.
type LadderStep struct {
	// Index of the entry in the ladder, -1 when the installed version matches no entry.
	Index int
	// Left counts the steps from this one to the head, this one included. 0 when unknown.
	Left int
	// Source is the compose file the step pins: a steps/ file, or the template's docker-compose.yml.
	Source string
	// Meta is the `.felhom.yml` that belongs to Source (R-664): steps/<key>.felhom.yml when the catalog
	// carries it, else the template's own — never the stack dir's, which a restore may have rewritten
	// with an older one (R-665).
	Meta string
	// Why is one operator-English sentence for the log.
	Why string
}

// nextLadderStep decides WHICH definition the next press pins, from the catalog template directory
// and the app's current pin. It never guesses: a missing or wrong step file is an error, and the
// update refuses before anything moves (a jump past a tested step is the thing this exists to stop).
func nextLadderStep(templateDir string, pinned map[string]string) (LadderStep, error) {
	current := filepath.Join(templateDir, "docker-compose.yml")
	currentMeta := filepath.Join(templateDir, ".felhom.yml")
	ladder, err := LoadLadder(filepath.Join(templateDir, ".felhom.yml"))
	if err != nil && !os.IsNotExist(err) {
		return LadderStep{}, err
	}
	if len(ladder) == 0 {
		return LadderStep{Index: -1, Source: current, Meta: currentMeta, Why: "the template carries no update_ladder — the catalog's current definition"}, nil
	}
	idx := -1
	for i := len(ladder) - 1; i >= 0; i-- { // the NEWEST entry whose `from` is what runs
		if sameRefs(ladder[i].From, pinned) {
			idx = i
			break
		}
	}
	if idx < 0 {
		// R-674 (v0.270.0): a pin equal to the newest entry's `to` is AT THE HEAD, not "older than the
		// ladder" — the old sentence sent an operator looking for a missing record. Pinned by
		// TestR674_HeadIsNotCalledOlder.
		if sameRefs(ladder[len(ladder)-1].To, pinned) {
			return LadderStep{Index: -1, Source: current, Meta: currentMeta,
				Why: fmt.Sprintf("the installed version %s is AT THE HEAD of the update_ladder (%d entries) — the catalog's current definition", summarisePin(pinned), len(ladder))}, nil
		}
		return LadderStep{Index: -1, Source: current, Meta: currentMeta,
			Why: fmt.Sprintf("the installed version %s matches no update_ladder entry (%d entries) — an app older than the ladder has no record to climb; the catalog's current definition", summarisePin(pinned), len(ladder))}, nil
	}
	left := len(ladder) - idx
	if idx == len(ladder)-1 {
		return LadderStep{Index: idx, Left: left, Source: current, Meta: currentMeta,
			Why: fmt.Sprintf("the last step (%d of %d) — the catalog's current definition", idx+1, len(ladder))}, nil
	}
	src := StepFile(templateDir, ladder[idx].To)
	imgs, perr := ParseComposeImages(src)
	if perr != nil {
		return LadderStep{}, fmt.Errorf("step %d of %d (%s) has no definition at %s: %w", idx+1, len(ladder), summarisePin(ladder[idx].To), src, perr)
	}
	if !sameRefs(imgs, ladder[idx].To) {
		return LadderStep{}, fmt.Errorf("step %d of %d: %s names %s, the ladder says %s", idx+1, len(ladder), src, summarisePin(imgs), summarisePin(ladder[idx].To))
	}
	meta := StepMetaFile(templateDir, ladder[idx].To)
	if _, err := os.Stat(meta); err != nil {
		meta = currentMeta // a step written before R-664: the template's own, said in the log
	}
	return LadderStep{Index: idx, Left: left, Source: src, Meta: meta,
		Why: fmt.Sprintf("step %d of %d: %s → %s, from %s (probe from %s)", idx+1, len(ladder), summarisePin(ladder[idx].From), summarisePin(ladder[idx].To), filepath.Base(src), filepath.Base(meta))}, nil
}

// ladderStepsLeft is the page's count: how many tested steps separate this pin from the catalog's
// head. 0 = unknown or none (no ladder, no match, or already at the head).
func ladderStepsLeft(templateDir string, pinned map[string]string) int {
	if len(pinned) == 0 {
		return 0
	}
	ladder, err := LoadLadder(filepath.Join(templateDir, ".felhom.yml"))
	if err != nil || len(ladder) == 0 {
		return 0
	}
	for i := len(ladder) - 1; i >= 0; i-- {
		if sameRefs(ladder[i].From, pinned) {
			return len(ladder) - i
		}
	}
	return 0
}

// loadMetadataFile reads a `.felhom.yml` that is not named `.felhom.yml` (a step's
// `steps/<key>.felhom.yml`) through LoadMetadata — the ONE validating reader — by giving it a scratch
// directory. Only the health check and the resources are read from the result.
func loadMetadataFile(path string) (Metadata, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return Metadata{}, err
	}
	tmp, err := os.MkdirTemp("", "felhom-step-meta-")
	if err != nil {
		return Metadata{}, err
	}
	defer os.RemoveAll(tmp)
	if err := os.WriteFile(filepath.Join(tmp, ".felhom.yml"), data, 0o600); err != nil {
		return Metadata{}, err
	}
	return LoadMetadata(tmp), nil
}