package ingest

import (
	"bytes"
	"encoding/json"
	"fmt"
)

// bankdecisions.go: the two documents of the engine's bank-correction door, `tmctl bank-apply`
// (D39.158) — the request the platform RENDERS and the report it READS BACK. Both live here because
// this package is where the seam's vocabulary lives; the HTTP shapes of the same facts are the
// contract's and stay in httpapi.

// DecisionsVersion and DecisionsReportVersion are the SHAPES of the two documents, as the engine
// declares them (backend/internal/membank/decisions.go). Two constants because they are two
// documents, free to move at different times.
const (
	DecisionsVersion       = "tm-bank-decisions-v1"
	DecisionsReportVersion = "tm-bank-decisions-report-v2"
)

// DepthEditWave is the engine's word for how far an accepted correction reaches: the edit wave —
// the next run refines the produced text rather than re-forming the draft (membank.DecisionDepth).
// A WAVE name, so it must never be forwarded to the wire as it stands.
const DepthEditWave = "edit_wave"

// BankDecision is one correction, in the engine's own request vocabulary (membank.Decision). The
// wire's strictness — a tuple must carry all four members, `null` windows and an empty `sense`
// meaning "none" — is the HANDLER's validation; by the time a value gets here the two forms mean
// the same thing to the engine, which defaults an omitted member (`omitempty` is therefore safe).
// Wire `null` windows are projected to 0 here, the seam's own null (canon §BankCorrection).
type BankDecision struct {
	Action       string `json:"action"`
	ID           string `json:"id,omitempty"`
	Src          string `json:"src,omitempty"`
	Sense        string `json:"sense,omitempty"`
	SinceChapter int    `json:"since_chapter,omitempty"`
	UntilChapter int    `json:"until_chapter,omitempty"`
	Dst          string `json:"dst,omitempty"`
	Kind         string `json:"kind,omitempty"`
	Note         string `json:"note,omitempty"`
}

// MaxDecisionsDocument mirrors the engine's own byte ceiling on the rendered document
// (pipeline.maxDecisionsBytes) — the figure the platform measures BEFORE spawning the verb, so the
// engine's copy of the cap answers as the canon's 413 instead of its refusal class.
const MaxDecisionsDocument = 1 << 20

// EncodeDecisions renders the request document the verb reads (`--decisions`).
//
// HTML escaping is OFF: the document is read by the engine, never by a browser, and Go's default
// escape turns one `&`/`<`/`>` byte into six — enough for a body inside the wire's 1 MiB cap to
// render past the engine's identical cap and come back as «re-decide» instead of «too large»
// (workflow finding, P9). Unescaped, the rendered form differs from the wire's by the envelope
// alone, and the residual band is those few bytes, gated by the caller against MaxDecisionsDocument.
func EncodeDecisions(bookID string, decisions []BankDecision) ([]byte, error) {
	doc := struct {
		Version   string         `json:"decisions_version"`
		BookID    string         `json:"book_id"`
		Decisions []BankDecision `json:"decisions"`
	}{Version: DecisionsVersion, BookID: bookID, Decisions: decisions}
	var buf bytes.Buffer
	enc := json.NewEncoder(&buf)
	enc.SetEscapeHTML(false)
	if err := enc.Encode(doc); err != nil {
		return nil, fmt.Errorf("ingest: encode decisions: %w", err)
	}
	return bytes.TrimSpace(buf.Bytes()), nil
}

// BankReport is the ALLOWLISTED subset of the verb's report (pipeline.BankDecisionsReport). Absent
// on purpose, like everywhere on this seam: the two file paths and the per-file write truth are
// server topology, the canonical-rewrite warnings address an operator of files, and the TEXTS of
// pre-existing faults are the engine's free vocabulary — the wire carries their COUNT.
type BankReport struct {
	Version string `json:"report_version"`
	BookID  string `json:"book_id"`
	// Mode names the outcome: `apply` · `projection` · `refused` · `stopped` · `write_incomplete`.
	Mode    string `json:"mode"`
	Depth   string `json:"depth"`
	Changed bool   `json:"changed"`
	// PreexistingProblems is decoded for its LENGTH; the texts never cross the next boundary.
	PreexistingProblems []string           `json:"preexisting_problems"`
	Accepted            []AcceptedDecision `json:"accepted"`
	Rejected            []RejectedDecision `json:"rejected"`
	Signature           SignatureState     `json:"signature"`
}

// AcceptedDecision is what one accepted correction did.
type AcceptedDecision struct {
	Index  int    `json:"index"`
	Action string `json:"action"`
	ID     string `json:"id"`
	Src    string `json:"src"`
	Dst    string `json:"dst"`
	// State is `applied` or `already_applied` — the whole of idempotency as a caller sees it.
	State string `json:"state"`
	// Replaced is decoded for its PRESENCE: the wire carries the boolean `displaced`, never the
	// engine's free-text itemization.
	Replaced []string `json:"replaced"`
}

// RejectedDecision is one refusal. Index is the decision's position in the request, or -1 for a
// refusal about the result as a whole.
type RejectedDecision struct {
	Index  int    `json:"index"`
	Reason string `json:"reason"`
}

// SignatureState counts the last signing stop's surfaces against the recorded decisions.
// INFORMATIONAL, never a gate (D39.144). `Map` is a server-side path and is read here only for
// "does a stop exist at all": empty means no run has reached one, which the wire says as `null`.
type SignatureState struct {
	Map        string `json:"map"`
	Surfaces   int    `json:"surfaces"`
	Undecided  int    `json:"undecided"`
	Unreadable bool   `json:"unreadable"`
}

// DecodeBankReport parses the verb's report and refuses a shape this build does not speak.
//
// The version is matched EXACTLY, unlike the manifest's presence-only rule, and the asymmetry is
// deliberate: the manifest feeds a read model that a stale field set degrades, while this report is
// the receipt of a WRITE — a half-read receipt would tell a user their correction did something
// other than what it did. An engine that moved the shape is a deployment skew to refuse loudly.
func DecodeBankReport(b []byte) (BankReport, error) {
	var r BankReport
	if err := json.Unmarshal(b, &r); err != nil {
		return BankReport{}, fmt.Errorf("ingest: decode bank report: %w", err)
	}
	if r.Version != DecisionsReportVersion {
		return BankReport{}, fmt.Errorf("ingest: decode bank report: report_version is %q, this build speaks %q",
			r.Version, DecisionsReportVersion)
	}
	return r, nil
}