// Package pipeline is the C-core runner: deterministic prompt rendering,
// request hashing, chunk checkpoints and the stage loop. Phase 0 is the
// mini-runner C1 (draft→edit, one chunk); the per-chapter/per-chunk loops,
// gates and escalation grow here in Phase 1 (Р2: this is runner code, not config).
package pipeline

import (
	"crypto/sha256"
	"encoding/binary"
	"encoding/hex"
	"fmt"
	"os"
	"strconv"
	"strings"
	"unicode"

	"textmachine/backend/internal/config"
	"textmachine/backend/internal/llm"
)

// render.go enforces the determinism invariant (03-implementation-notes §3.1):
// the rendered prompt is a PURE function of (snapshot, committed prior
// outputs, chunk). Timestamps/UUIDs are forbidden; no map iteration — only a
// fixed list of placeholders. Verified by a "two renders are byte-for-byte
// identical" test. Break determinism → break the request-hash → resume
// re-translates and re-pays for the chapter, and the DeepSeek cache (byte prefix
// match) misses.

// chunkerVersion versions the segmentation/ingestion rules (including the source
// normalization text.NormalizeSource, the txt/epub ingest layer and the target chunk
// size targetChunkTokens); it is part of the snapshot, so re-chunking a book is an
// explicit re-translation, not a silent cache miss (§3.4 — [DECISION NEEDED] item
// 2в). Step 3a replaced the Milestone-2 char-budget paragraph packer with the real
// source segmenter (sentence-aware, ~1–2k-token packing over ingest-split
// chapters — chunker.go/ingest.go), so the version bumps: any earlier project DB
// re-pins loudly via the --resnapshot gate (a re-chunk is a deliberate
// re-translation), never a silent divergent re-pay. NOTE: the chunk target is a
// const covered by THIS string; if it ever becomes config-tunable it must ALSO be
// folded into the top-level snapshot (like coverageSnap), never left to the
// version alone (§7d). Bumped v3→v4 closing external-review 3a: invalid-UTF-8 is
// now normalized once in text.NormalizeSource (#3), the ASCII sentence boundary honors
// quote-depth (#4), and <br> inside <ruby> no longer leaks a newline into the body
// (#5) — all segmentation/ingest behaviour changes → a loud --resnapshot.
// Bumped v4→v5 (WS2): the packing budget moved from input-token heuristic (const 1500) to OUTPUT
// (ru) tokens via fertility (est_out), draft chunks decoupled from coarse EDIT units (grouped whole
// chunks to EditCeilingOut), oversized-sentence flag added. The budget itself is ALSO folded via
// segmentationSnap (snapshot.go), so this version covers only the algorithm shape.
// Ш-2 EXTENSION (see text/norm.go; beyond the owner-named normalizer/classifier/style set — justified: same
// silent-drift class): chunk.TokenClassCounts (chunker.go) classifies source runes via unicode.Han/Hiragana/
// Katakana/Hangul to compute est_out, which SETS chunk boundaries → the wire. A toolchain Unicode bump that
// reclassifies a rune would silently re-chunk the book; weaving unicode.Version makes it a loud --resnapshot.
const chunkerVersion = "chunker-v5-output-budget-editunit+u" + unicode.Version

// estimatorVersion versions EstimateTokens: its output feeds into max_tokens and
// through it into the request-hash, so re-calibrating the weights is likewise an
// explicit invalidation via the snapshot, not a silent miss of every checkpoint
// (review finding: a code-only edit to the estimator would re-pay for half the book).
// Ш-2 EXTENSION (see text/norm.go): EstimateTokens classifies runes via the same unicode ranges to size
// max_tokens (∈ request_hash), so a toolchain Unicode reclassification shifts the wire — folded loudly.
const estimatorVersion = "estimator-v0+u" + unicode.Version

// maxTokensPolicyVersion versions the attempt→max_tokens scaling
// (maxTokensForAttempt, disposition.go). attempt-0 budget is already covered by
// estimatorVersion + defaults, but a change to the RETRY scaling would silently
// shift the request_hash of every attempt≥1 (a missed checkpoint → re-pay on
// retried chunks). Folding this version into the snapshot makes such a change a
// loud --resnapshot instead — the same discipline as estimatorVersion, applied
// to the regeneration axis (Milestone 2).
const maxTokensPolicyVersion = "maxtok-v1-double-per-attempt"

// userSeparator splits a prompt template file into the system part and the
// user part. Both parts are versioned templates in prompts/ (the editorial team
// later edits the files, not the code).
const userSeparator = "\n---USER---\n"

// fewShotSeparator optionally splits the SYSTEM part into a core prefix and a
// trailing few-shot example block (D38.4). A stage may drop the block (few_shot:false)
// for a model whose own CoT is disrupted by hand examples (deepseek-thinking, exp14 §2а).
// Absent → the whole system part is core; the toggle is a no-op.
const fewShotSeparator = "\n---FEWSHOT---\n"

// PromptTemplate is one loaded stage template. System is the core system prefix;
// FewShot is the optional example block (empty when the file has no ---FEWSHOT---).
type PromptTemplate struct {
	System  string
	FewShot string
	User    string
	SHA256  string // hash of the raw file — part of the snapshot
}

// LoadPromptTemplate reads and splits a template file into core-system / few-shot / user.
func LoadPromptTemplate(path string) (*PromptTemplate, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("pipeline: read prompt %s: %w", path, err)
	}
	sum := sha256.Sum256(raw)
	parts := strings.SplitN(string(raw), userSeparator, 2)
	if len(parts) != 2 {
		return nil, fmt.Errorf("pipeline: prompt %s lacks the %q separator between system and user parts", path, strings.TrimSpace(userSeparator))
	}
	t := &PromptTemplate{User: strings.TrimSpace(parts[1]), SHA256: hex.EncodeToString(sum[:])}
	// The few-shot block, if present, is the tail of the SYSTEM part (before ---USER---).
	head := strings.SplitN(parts[0], fewShotSeparator, 2)
	t.System = strings.TrimSpace(head[0])
	if len(head) == 2 {
		t.FewShot = strings.TrimSpace(head[1])
	}
	return t, nil
}

// SystemFor returns the effective system prompt for a stage: the core prefix, plus the
// few-shot block when the stage keeps it on (the default). The whole raw file is still
// snapshot-pinned via SHA256, and the few_shot on/off state is folded separately, so
// dropping the block is a loud --resnapshot, not a silent divergence.
func (t *PromptTemplate) SystemFor(fewShotOn bool) string {
	if fewShotOn && t.FewShot != "" {
		return t.System + "\n\n" + t.FewShot
	}
	return t.System
}

// fewShotEnabled resolves a stage's few_shot toggle: absent (nil) defaults to ON, so
// every existing config keeps the few-shot examples without touching its yaml.
func fewShotEnabled(st config.Stage) bool {
	return st.FewShot == nil || *st.FewShot
}

// RenderVars are the ONLY placeholders a template may use. A fixed struct, not
// a map: map iteration order would randomize the render.
type RenderVars struct {
	Book  *config.Book
	Text  string // the source chunk
	Draft string // prior stage output ("" on the first stage)
}

// Render substitutes placeholders in a SINGLE pass over the template: values
// are inserted verbatim and never re-scanned, so a literal «{{…}}» inside the
// source or the LLM draft is just text, not a marker (review finding: a sequential
// ReplaceAll substituted the draft into a «{{draft}}» from the source and choked on
// «{{TN: примечание}}» in the model output). Unknown {{…}} markers in the TEMPLATE
// are a hard error — a silently empty placeholder is worse than a crash.
func Render(tpl string, v RenderVars) (string, error) {
	// Lookup-only map (no iteration — determinism is not harmed).
	vals := map[string]string{
		"book_id":       v.Book.BookID,
		"title":         v.Book.Title,
		"source_lang":   v.Book.SourceLang,
		"target_lang":   v.Book.TargetLang,
		"genre":         v.Book.Genre,
		"audience":      v.Book.Audience,
		"venuti":        strconv.FormatFloat(v.Book.Venuti, 'f', 2, 64),
		"honorifics":    v.Book.Honorifics,
		"transcription": v.Book.Transcription,
		"footnotes":     v.Book.Footnotes,
		"text":          v.Text,
		"draft":         v.Draft,
	}
	var b strings.Builder
	rest := tpl
	for {
		i := strings.Index(rest, "{{")
		if i < 0 {
			b.WriteString(rest)
			return b.String(), nil
		}
		b.WriteString(rest[:i])
		rest = rest[i:]
		end := strings.Index(rest, "}}")
		if end < 0 {
			return "", fmt.Errorf("pipeline: unterminated placeholder %q in template", snippetStr(rest))
		}
		name := rest[2:end]
		val, ok := vals[name]
		if !ok {
			return "", fmt.Errorf("pipeline: unknown placeholder {{%s}} in template", name)
		}
		b.WriteString(val)
		rest = rest[end+2:]
	}
}

func snippetStr(s string) string {
	if len(s) > 40 {
		return s[:40] + "…"
	}
	return s
}

// Messages builds the wire-neutral message list for a stage with no memory injection
// (the Milestone-0/2 behaviour). Layout per Р5: system (stable prefix, cache
// boundary) → user (volatile tail). Kept as the zero-injection convenience over
// MessagesWithInjection so existing callers/tests are untouched.
func Messages(tpl *PromptTemplate, v RenderVars) ([]llm.Message, error) {
	return MessagesWithInjection(tpl, v, "")
}

// MessagesWithInjection builds the stage messages with the memory bank v2 injection
// surface (step 4 §C, orchestrator variant "а" — a code-assembled message, NOT a new
// RenderVars placeholder, so the fixed template stays stable). Layout per Р5/A6:
//
//	system(stable prefix, CacheBoundary) → [injection: glossary/STM] → user(volatile tail)
//
// The injection is its OWN message placed AFTER the cache boundary (which stays on the
// stable system prefix — the DeepSeek byte-prefix cache still hits; Anthropic's removed,
// no cache_control concern). It is NOT part of ch.Text, so it never leaks into the
// coverage len_ratio or the {{text}} placeholder (the 3a ch.Text contract). Because the
// injection is a message, it is folded into request_hash/content_hash automatically — a
// changed injection is a changed request (a resumed chunk reproduces it deterministically
// from the frozen bank). An empty injection yields the exact 2-message list of Messages.
func MessagesWithInjection(tpl *PromptTemplate, v RenderVars, injection string) ([]llm.Message, error) {
	sys, err := Render(tpl.System, v)
	if err != nil {
		return nil, err
	}
	user, err := Render(tpl.User, v)
	if err != nil {
		return nil, err
	}
	msgs := make([]llm.Message, 0, 3)
	msgs = append(msgs, llm.Message{Role: "system", Content: sys, CacheBoundary: true})
	if strings.TrimSpace(injection) != "" {
		msgs = append(msgs, llm.Message{Role: "system", Content: injection, CacheBoundary: false})
	}
	msgs = append(msgs, llm.Message{Role: "user", Content: user})
	return msgs, nil
}

// Request is everything that determines ONE model call: the addressing (book/chapter/chunk/attempt),
// the stage's wire parameters and the rendered messages. It is the input of RequestHash — a struct
// rather than a positional argument list because the fields are 13 mostly-scalar values whose ORDER is
// the only thing that told them apart at a call site (a swapped chapter/chunkIdx or role/model pair
// compiles and silently addresses a DIFFERENT checkpoint: a re-billed chunk or, worse, a served one).
// Field NAMES are free; the hash is over the values in the fixed order RequestHash writes them.
type Request struct {
	BookID      string
	Chapter     int
	ChunkIdx    int
	Attempt     int // the regeneration dimension (a gate failed → attempt+1 → a new key)
	Stage       string
	Role        string
	Model       string
	Temperature float64
	Reasoning   string
	JSONOnly    bool
	MaxTokens   int
	SnapshotID  string // freezes the volatile context (config/prompts/bank/gates)
	Messages    []llm.Message
}

// RequestHash is the checkpoint/resume key (§3.1): a stable hash of everything
// that determines the call. The snapshot id freezes the volatile context, so
// identical re-renders after a restart find their checkpoint and are neither
// repeated nor re-billed. Attempt is the regeneration dimension (Phase 1: a gate
// failed → attempt+1 → a new key; without it a regeneration would land on the
// just-failed checkpoint and instantly escalate to premium).
func RequestHash(req Request) string {
	h := sha256.New()
	// Each field is length-prefixed (8 bytes LE) instead of a NUL separator:
	// content with a \x00 byte can no longer shift field boundaries or forge
	// extra messages (review finding). Version v2 pins the hash-format
	// change.
	var lb [8]byte
	w := func(parts ...string) {
		for _, p := range parts {
			binary.LittleEndian.PutUint64(lb[:], uint64(len(p)))
			h.Write(lb[:])
			h.Write([]byte(p))
		}
	}
	w("tm-request-v2", req.BookID, strconv.Itoa(req.Chapter), strconv.Itoa(req.ChunkIdx), strconv.Itoa(req.Attempt),
		req.Stage, req.Role, req.Model,
		strconv.FormatFloat(req.Temperature, 'f', -1, 64), req.Reasoning, strconv.FormatBool(req.JSONOnly),
		strconv.Itoa(req.MaxTokens), req.SnapshotID)
	// Explicit message count: the list length is also part of the key.
	binary.LittleEndian.PutUint64(lb[:], uint64(len(req.Messages)))
	h.Write(lb[:])
	for _, m := range req.Messages {
		w(m.Role, m.Content, strconv.FormatBool(m.CacheBoundary))
	}
	return hex.EncodeToString(h.Sum(nil))
}

// msgsContentHash is a content signature of the rendered messages, INDEPENDENT
// of attempt/max_tokens. It guards the chunk_status resume fast-path (stagerun.go):
// the source bytes are NOT folded into the snapshot (only the chunker RULES and
// the semantic brief are), so a positional chunk_status row must be re-validated
// against the current rendered content — otherwise an edited source would serve
// a stale, divergent translation with no cache miss (the determinism invariant's
// named failure; self-review Milestone 2). Length-prefixed like RequestHash so
// content with NUL bytes cannot forge field/message boundaries. The template is
// already snapshot-pinned, so this only has to catch source/draft edits.
func msgsContentHash(msgs []llm.Message) string {
	h := sha256.New()
	var lb [8]byte
	w := func(s string) {
		binary.LittleEndian.PutUint64(lb[:], uint64(len(s)))
		h.Write(lb[:])
		h.Write([]byte(s))
	}
	w("tm-content-v1")
	binary.LittleEndian.PutUint64(lb[:], uint64(len(msgs)))
	h.Write(lb[:])
	for _, m := range msgs {
		w(m.Role)
		w(m.Content)
	}
	return hex.EncodeToString(h.Sum(nil))
}

// EstimateTokens is a cheap, deterministic token estimate for reservation
// sizing and max_tokens derivation (NOT for billing — billing uses the API's
// usage). Eval calibration: a CJK glyph ≈0.9 tokens, Russian/Latin ≈3 chars per
// token.
func EstimateTokens(s string) int {
	cjk, other := 0, 0
	for _, r := range s {
		switch {
		case unicode.In(r, unicode.Han, unicode.Hiragana, unicode.Katakana, unicode.Hangul):
			cjk++
		case unicode.IsSpace(r):
			// whitespace mostly folds into neighbouring tokens
		default:
			other++
		}
	}
	est := cjk + other/3
	if est < 16 {
		est = 16
	}
	return est
}