// Package handler — history.go: orchestrates writes of "record" YAML
// files (mdl rows, rsk rows, ssr.yaml) with three guarantees the
// generic file API cannot make on its own:
//
//  1. Audit fields are server-managed. created_at / created_by /
//     updated_at / updated_by / revision / previous_sha are stripped
//     from incoming bodies and stamped from the request context,
//     making client-side forgery impossible.
//
//  2. Prior bytes are preserved. Before the live file is overwritten
//     the previous content is copied (byte-for-byte) into
//     <dir>/.history/<base>/<RFC3339Nano-UTC>-<sha8>.<ext>. The
//     filename embeds the timestamp + the SHA-256 prefix of the prior
//     bytes — the same value that's stamped into the new record's
//     previous_sha field — so the chain is auditable.
//
//  3. Filename composition is enforced. When the matched RecordRule
//     declares a filename_format, the server composes the expected
//     basename from body fields and rejects writes whose URL doesn't
//     agree. This binds the on-disk identity to the body's
//     tracking-number components, eliminating drift.
//
// Records are identified by the cascade: a .zddc records: entry
// matched against the basename selects the rule. Files that don't
// match any rule fall through to a plain write — non-record YAML
// (table.yaml, form.yaml, plain documents) is unaffected.

package handler

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"time"

	"codeberg.org/VARASYS/ZDDC/zddc/internal/config"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/jsonschema"
	"codeberg.org/VARASYS/ZDDC/zddc/internal/zddc"
	"gopkg.in/yaml.v3"
)

// Audit-field key names. Snake-case to match the existing .zddc
// `created_by:` precedent rather than the camelCase used in form
// schemas (those describe domain data; these describe provenance).
const (
	auditFieldCreatedAt   = "created_at"
	auditFieldCreatedBy   = "created_by"
	auditFieldUpdatedAt   = "updated_at"
	auditFieldUpdatedBy   = "updated_by"
	auditFieldRevision    = "revision"
	auditFieldPreviousSha = "previous_sha"
)

// historyDirName is the dot-prefixed bookkeeping folder under each
// record-containing directory. resolveTargetPath's dot-segment
// rejection means no client URL can reach into .history/ — only the
// server's own history-write code path touches it.
const historyDirName = ".history"

// WriteRecordResult carries what serveFilePut needs to surface a
// response after a successful record write.
type WriteRecordResult struct {
	FinalBody []byte // bytes actually written to disk (after stamping)
	Created   bool   // true if no prior file existed (response 201 vs 200)
}

// WriteWithHistory orchestrates a record write at abs (which must be
// the canonical on-disk path — virtual-view rewriting already
// applied). cleanURL is the URL the caller surfaces (for audit
// logging). body is the raw request bytes.
//
// Returns:
//   - res, nil, nil:    success; caller writes 200/201 + ETag.
//   - _, errs, nil:     422 with the validation errors (locked
//                       mismatch, field_code violation, filename
//                       composition mismatch).
//   - _, _, err:        internal error; caller writes 500.
//
// The function does NOT do ACL, ETag-precondition, or canonical-
// ancestor seeding — those are still serveFilePut's job and run
// before this call. The function DOES handle prior-bytes capture,
// audit stamping, history write, and live write.
func WriteWithHistory(cfg config.Config, abs, cleanURL string, body []byte, principalEmail string) (WriteRecordResult, []jsonschema.Error, error) {
	dir := filepath.Dir(abs)
	base := filepath.Base(abs)

	// Resolve cascade at the record's parent dir.
	chain, err := zddc.EffectivePolicy(cfg.Root, dir)
	if err != nil {
		return WriteRecordResult{}, nil, fmt.Errorf("effective policy: %w", err)
	}
	_, rule, hasRule := chain.EffectiveRecordRule(base)

	// Read prior bytes (nil if create).
	var priorBody []byte
	priorExisted := false
	if data, err := os.ReadFile(abs); err == nil {
		priorBody = data
		priorExisted = true
	} else if !errors.Is(err, os.ErrNotExist) {
		return WriteRecordResult{}, nil, fmt.Errorf("read prior: %w", err)
	}

	// Parse incoming body as a YAML map. Empty body is allowed
	// (the schema validator catches required-field omissions, or
	// the caller-side spec is permissive); we use an empty map.
	bodyMap := map[string]any{}
	if len(body) > 0 {
		if err := yaml.Unmarshal(body, &bodyMap); err != nil {
			return WriteRecordResult{}, []jsonschema.Error{{Path: "/", Message: "body is not valid YAML: " + err.Error()}}, nil
		}
		if bodyMap == nil {
			bodyMap = map[string]any{}
		}
	}

	// Strip client-supplied audit fields. The server is the sole
	// authority for these; any value we'd accept here is forgeable.
	stripAuditFields(bodyMap)

	// Honor records: rule. If no rule matched the basename, fall
	// through to a plain write (no stamping, no history) — this
	// covers non-record YAML files like table.yaml that may share
	// a directory with records.
	if !hasRule {
		if err := zddc.WriteAtomic(abs, body); err != nil {
			return WriteRecordResult{}, nil, fmt.Errorf("write: %w", err)
		}
		return WriteRecordResult{FinalBody: body, Created: !priorExisted}, nil, nil
	}

	codes := chain.EffectiveFieldCodes()

	// Inject field_defaults for keys the body omitted (so the
	// stamped result is self-describing) and check locked: against
	// any conflicting client values.
	var verrs []jsonschema.Error
	for k, want := range rule.FieldDefaults {
		got, present := bodyMap[k]
		if !present {
			bodyMap[k] = want
			continue
		}
		if locked := containsString(rule.Locked, k); locked {
			gotStr := asString(got)
			if gotStr != want {
				verrs = append(verrs, jsonschema.Error{
					Path:    "/" + k,
					Message: fmt.Sprintf("field is locked to %q in this folder; got %q", want, gotStr),
				})
			}
		}
	}

	// Validate body values against field_codes (best-effort: only
	// fields actually present in the body are checked; absent
	// fields are someone else's concern — typically the form
	// schema's required: list).
	for k, code := range codes {
		raw, ok := bodyMap[k]
		if !ok {
			continue
		}
		s := asString(raw)
		if s == "" {
			continue // empty/optional — schema enforces presence
		}
		if err := code.Validate(s); err != nil {
			verrs = append(verrs, jsonschema.Error{
				Path:    "/" + k,
				Message: err.Error(),
			})
		}
	}

	if len(verrs) > 0 {
		return WriteRecordResult{}, verrs, nil
	}

	// Compose filename from body when filename_format is set, and
	// verify the URL basename matches. Skipped when the rule has
	// no format (SSR: identity is the parent folder name).
	if rule.FilenameFormat != "" {
		composed, cerr := composeFilename(rule.FilenameFormat, bodyMap)
		if cerr != nil {
			return WriteRecordResult{}, []jsonschema.Error{{Path: "/", Message: cerr.Error()}}, nil
		}
		ext := filepath.Ext(base)
		composedWithExt := composed + ext
		if composedWithExt != base {
			return WriteRecordResult{}, []jsonschema.Error{{
				Path:    "/",
				Message: fmt.Sprintf("filename mismatch: URL is %q, body composes to %q", base, composedWithExt),
			}}, nil
		}
	}

	// Stamp audit fields. On create: created_* and updated_* are
	// both the current principal/timestamp; revision = 1. On
	// update: preserve created_* (parse from priorBody), refresh
	// updated_*, increment revision, set previous_sha = sha-prefix
	// of priorBody.
	now := time.Now().UTC().Format(time.RFC3339Nano)
	if principalEmail == "" {
		principalEmail = "anonymous"
	}
	priorAudit := parsePriorAudit(priorBody)
	if !priorExisted {
		bodyMap[auditFieldCreatedAt] = now
		bodyMap[auditFieldCreatedBy] = principalEmail
		bodyMap[auditFieldRevision] = 1
	} else {
		if priorAudit.createdAt != "" {
			bodyMap[auditFieldCreatedAt] = priorAudit.createdAt
		} else {
			// Lazy migration: the prior file had no created_*
			// stamp. Treat this write as the establishment of
			// audit history — created and updated are the same
			// principal/timestamp (we don't know who originally
			// authored it).
			bodyMap[auditFieldCreatedAt] = now
		}
		if priorAudit.createdBy != "" {
			bodyMap[auditFieldCreatedBy] = priorAudit.createdBy
		} else {
			bodyMap[auditFieldCreatedBy] = principalEmail
		}
		bodyMap[auditFieldRevision] = priorAudit.revision + 1
		bodyMap[auditFieldPreviousSha] = sha8(priorBody)
	}
	bodyMap[auditFieldUpdatedAt] = now
	bodyMap[auditFieldUpdatedBy] = principalEmail

	finalBody, err := yaml.Marshal(bodyMap)
	if err != nil {
		return WriteRecordResult{}, nil, fmt.Errorf("marshal: %w", err)
	}

	// Write history BEFORE live. If we crash after history but
	// before live, the prior version is safe (still on disk under
	// its history filename). The reverse order would lose the
	// prior bytes if the live write succeeded but history failed.
	// On a clean retry, the history filename is deterministic
	// (timestamp+sha8 of priorBody) — rewriting it idempotently
	// is harmless when the live write later succeeds.
	if priorExisted {
		histDir := filepath.Join(dir, historyDirName, stripExt(base))
		if err := os.MkdirAll(histDir, 0o755); err != nil {
			return WriteRecordResult{}, nil, fmt.Errorf("mkdir history: %w", err)
		}
		histName := now + "-" + sha8(priorBody) + filepath.Ext(base)
		histPath := filepath.Join(histDir, histName)
		if err := zddc.WriteAtomic(histPath, priorBody); err != nil {
			return WriteRecordResult{}, nil, fmt.Errorf("write history: %w", err)
		}
	}

	if err := zddc.WriteAtomic(abs, finalBody); err != nil {
		return WriteRecordResult{}, nil, fmt.Errorf("write live: %w", err)
	}

	return WriteRecordResult{FinalBody: finalBody, Created: !priorExisted}, nil, nil
}

// priorAuditSnapshot is the minimum we need from a prior version's
// body to stamp the next revision: who created it (preserved
// forever) and what revision number it carried (so we can ++).
type priorAuditSnapshot struct {
	createdAt string
	createdBy string
	revision  int
}

func parsePriorAudit(body []byte) priorAuditSnapshot {
	if len(body) == 0 {
		return priorAuditSnapshot{}
	}
	m := map[string]any{}
	if err := yaml.Unmarshal(body, &m); err != nil {
		return priorAuditSnapshot{}
	}
	out := priorAuditSnapshot{}
	if v, ok := m[auditFieldCreatedAt].(string); ok {
		out.createdAt = v
	}
	if v, ok := m[auditFieldCreatedBy].(string); ok {
		out.createdBy = v
	}
	switch v := m[auditFieldRevision].(type) {
	case int:
		out.revision = v
	case int64:
		out.revision = int(v)
	case float64:
		out.revision = int(v)
	}
	return out
}

func stripAuditFields(m map[string]any) {
	delete(m, auditFieldCreatedAt)
	delete(m, auditFieldCreatedBy)
	delete(m, auditFieldUpdatedAt)
	delete(m, auditFieldUpdatedBy)
	delete(m, auditFieldRevision)
	delete(m, auditFieldPreviousSha)
}

// composeFilename interpolates a filename_format template against
// the supplied body fields. Placeholders are {fieldname} for
// required segments and {fieldname?} for optional ones; an optional
// placeholder with an empty/missing body field is dropped along
// with one adjacent separator if both neighbors are static text.
//
// Example, format = "{originator}-{phase?}-{project}-{type}-{sequence}{suffix?}"
// with body = {originator: ACM, project: PRJ, type: SPC, sequence: 0001}
// (phase + suffix absent) yields "ACM-PRJ-SPC-0001".
//
// Adjacent-separator handling: the function recognises a "-" or "_"
// literal immediately preceding an optional placeholder and drops
// it together with the placeholder when the field is empty. Static
// text not adjacent to a placeholder is preserved as-is. A literal
// "{" or "}" must be escaped as "{{" / "}}" (currently unused —
// the embedded defaults don't need it).
func composeFilename(format string, body map[string]any) (string, error) {
	var out strings.Builder
	out.Grow(len(format))
	i := 0
	for i < len(format) {
		c := format[i]
		// Literal { or } escapes: {{ → {, }} → }.
		if c == '{' && i+1 < len(format) && format[i+1] == '{' {
			out.WriteByte('{')
			i += 2
			continue
		}
		if c == '}' && i+1 < len(format) && format[i+1] == '}' {
			out.WriteByte('}')
			i += 2
			continue
		}
		if c != '{' {
			out.WriteByte(c)
			i++
			continue
		}
		// Placeholder: scan to '}'.
		end := strings.IndexByte(format[i+1:], '}')
		if end == -1 {
			return "", fmt.Errorf("filename_format: unterminated placeholder at offset %d", i)
		}
		name := format[i+1 : i+1+end]
		i += end + 2 // past the '}'
		optional := false
		if strings.HasSuffix(name, "?") {
			optional = true
			name = name[:len(name)-1]
		}
		val := asString(body[name])
		if val == "" {
			if !optional {
				return "", fmt.Errorf("filename_format: required field %q is missing or empty", name)
			}
			// Drop the trailing separator we just wrote, if any.
			// For "A-{b?}-C" with b empty we want "A-C": dropping
			// the preceding '-' here, then letting the next
			// iteration emit the trailing '-' from the format, is
			// exactly one connector between A and C. (Earlier
			// versions of this code also skipped the leading
			// separator, which double-elided.)
			s := out.String()
			if n := len(s); n > 0 && (s[n-1] == '-' || s[n-1] == '_') {
				out.Reset()
				out.WriteString(s[:n-1])
			}
			continue
		}
		out.WriteString(val)
	}
	return out.String(), nil
}

// AssignNextRow finds the next free row sequence within the
// row-scope group identified by scopeFields. Used by POST-create
// handlers (rsk row creation) before invoking WriteWithHistory.
// Returns the zero-padded string value to inject into bodyMap[rowField].
//
// Width is fixed at 3 (covers up to 999 rows per table). Operators
// who need more declare a per-deployment field_codes:row pattern;
// the width here is for the auto-assign output, not for parsing
// (which uses the matched pattern from the cascade).
func AssignNextRow(dir, rowField string, scopeFields []string, body map[string]any) (string, error) {
	if rowField == "" {
		return "", fmt.Errorf("row_field is empty")
	}
	entries, err := os.ReadDir(dir)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return "001", nil
		}
		return "", err
	}
	max := 0
	rowRe := regexp.MustCompile(`^[0-9]+$`)
	for _, ent := range entries {
		if ent.IsDir() {
			continue
		}
		name := ent.Name()
		if !strings.HasSuffix(name, filepath.Ext(name)) {
			continue
		}
		path := filepath.Join(dir, name)
		data, err := os.ReadFile(path)
		if err != nil {
			continue
		}
		other := map[string]any{}
		if err := yaml.Unmarshal(data, &other); err != nil {
			continue
		}
		// Same scope group?
		sameGroup := true
		for _, f := range scopeFields {
			if asString(other[f]) != asString(body[f]) {
				sameGroup = false
				break
			}
		}
		if !sameGroup {
			continue
		}
		v := asString(other[rowField])
		if !rowRe.MatchString(v) {
			continue
		}
		n := atoiSafe(v)
		if n > max {
			max = n
		}
	}
	return fmt.Sprintf("%03d", max+1), nil
}

// ServeHistoryList responds to GET <record>.yaml?history=1 with the
// list of prior revisions archived under .history/<base>/. The
// caller has already evaluated ACL against the live record (read
// permission on the parent dir gates history visibility too — if
// you can read the current state you can read its history).
//
// Returns 404 when abs doesn't exist or isn't a record (the caller
// should rely on the live record's GET 404 path instead of leaking
// existence here, but defense in depth costs nothing).
func ServeHistoryList(w http.ResponseWriter, r *http.Request, abs string) {
	if !isRecordPathForHistory(abs) {
		http.NotFound(w, r)
		return
	}
	if _, err := os.Stat(abs); err != nil {
		if errors.Is(err, os.ErrNotExist) {
			// Record file gone; the caller's normal 404 path
			// suppresses existence-leak, so we mirror that.
			http.NotFound(w, r)
			return
		}
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	entries, err := ListHistory(abs)
	if err != nil {
		http.Error(w, "Internal Server Error", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("X-ZDDC-Source", "history-list")
	// json.NewEncoder for streaming; sort already happened in
	// ListHistory.
	enc := json.NewEncoder(w)
	if err := enc.Encode(entries); err != nil {
		// Body already partially flushed at this point; nothing to do.
		return
	}
}

// isRecordPathForHistory mirrors isRecordPath but lives in this file
// so the history-list handler doesn't need to import its caller's
// internal helper. Keep the two in sync — if one accepts a new
// extension the other should too.
func isRecordPathForHistory(abs string) bool {
	base := filepath.Base(abs)
	switch base {
	case "table.yaml", "form.yaml", ".zddc":
		return false
	}
	ext := filepath.Ext(base)
	if ext != ".yaml" && ext != ".yml" {
		return false
	}
	if strings.HasSuffix(base, ".table.yaml") || strings.HasSuffix(base, ".form.yaml") {
		return false
	}
	return true
}

// HistoryEntry describes one prior revision of a record, as listed
// by ServeHistoryList.
type HistoryEntry struct {
	Revision int    `json:"revision"`
	Ts       string `json:"ts"`
	By       string `json:"by"`
	Sha8     string `json:"sha"`
	Path     string `json:"path"`
}

// ListHistory walks the .history/<base>/ directory adjacent to abs
// and returns one HistoryEntry per archived revision, sorted newest
// first. Empty list when the dir doesn't exist (e.g. record never
// updated).
//
// Filename format: <RFC3339Nano>-<sha8>.<ext>. Author/revision are
// read from the YAML body's audit fields — those describe the
// archived bytes' provenance.
func ListHistory(abs string) ([]HistoryEntry, error) {
	dir := filepath.Dir(abs)
	base := filepath.Base(abs)
	histDir := filepath.Join(dir, historyDirName, stripExt(base))
	ents, err := os.ReadDir(histDir)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil, nil
		}
		return nil, err
	}
	out := make([]HistoryEntry, 0, len(ents))
	for _, e := range ents {
		if e.IsDir() {
			continue
		}
		name := e.Name()
		// Expected shape: <ts>-<sha8>.<ext>. Parse from the right
		// to be lenient about timestamps that contain '-'.
		ext := filepath.Ext(name)
		stem := strings.TrimSuffix(name, ext)
		idx := strings.LastIndexByte(stem, '-')
		if idx < 0 {
			continue
		}
		ts := stem[:idx]
		sha := stem[idx+1:]
		entry := HistoryEntry{Ts: ts, Sha8: sha, Path: filepath.Join(historyDirName, stripExt(base), name)}
		// Pull author + revision from the archived body.
		if data, err := os.ReadFile(filepath.Join(histDir, name)); err == nil {
			snap := parsePriorAudit(data)
			entry.Revision = snap.revision
			entry.By = snap.createdBy
			// updated_by is more informative when present.
			m := map[string]any{}
			if err := yaml.Unmarshal(data, &m); err == nil {
				if v, ok := m[auditFieldUpdatedBy].(string); ok && v != "" {
					entry.By = v
				}
			}
		}
		out = append(out, entry)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].Ts > out[j].Ts })
	return out, nil
}

// augmentSchemaFromCascade mutates schema in place to inject
// cascade-resolved field_codes and records:-rule constraints. For
// every property whose name matches a field-code key, the relevant
// enum/pattern/labels are injected. For every record-rule's locked
// field, the corresponding property is marked readOnly. For every
// field_default, the corresponding property's Default is set if
// absent.
//
// gateDir is the directory the cascade was resolved at — needed
// only to pick the right records: rule when multiple patterns
// could match. The current cascade interface gives us the chain
// already; we pull a single "*.yaml" representative rule (matching
// the create-time behaviour in serveFormCreateRollup).
//
// Mutates the input schema. No-op when schema is nil.
func augmentSchemaFromCascade(schema *jsonschema.Schema, chain zddc.PolicyChain, gateDir string) {
	if schema == nil || schema.Properties == nil {
		return
	}
	codes := chain.EffectiveFieldCodes()
	for name, prop := range schema.Properties {
		if code, ok := codes[name]; ok {
			switch code.Kind {
			case zddc.FieldCodeEnum:
				// Populate Enum with the code keys (sorted for
				// deterministic order). Labels carries the
				// human-readable display strings.
				keys := make([]string, 0, len(code.Codes))
				for k := range code.Codes {
					keys = append(keys, k)
				}
				sort.Strings(keys)
				if len(prop.Enum) == 0 {
					prop.Enum = make([]any, len(keys))
					for i, k := range keys {
						prop.Enum[i] = k
					}
				}
				if prop.Labels == nil && len(code.Codes) > 0 {
					prop.Labels = make(map[string]string, len(code.Codes))
					for k, v := range code.Codes {
						prop.Labels[k] = v
					}
				}
			case zddc.FieldCodePattern:
				if prop.Pattern == "" {
					prop.Pattern = code.Pattern
				}
			case zddc.FieldCodeFree:
				// No constraint to inject; description is the
				// only field and the operator can author it
				// directly in the form spec.
			}
		}
	}

	// Apply the matched records:-rule's readOnly + default to
	// matching properties. We probe with "*.yaml" — the records
	// entries shipped in the embedded defaults all match that
	// glob; operator schemas with literal-keyed rules would still
	// be honoured by serveFormCreateRollup but won't be reflected
	// in the form-render augmentation here.
	if _, rule, ok := chain.EffectiveRecordRule("placeholder.yaml"); ok {
		for _, name := range rule.Locked {
			if prop, present := schema.Properties[name]; present {
				prop.ReadOnly = true
			}
		}
		for name, val := range rule.FieldDefaults {
			if prop, present := schema.Properties[name]; present {
				if prop.Default == nil {
					prop.Default = val
				}
			}
		}
	}
}

// ---- small helpers ----

func sha8(data []byte) string {
	sum := sha256.Sum256(data)
	return hex.EncodeToString(sum[:])[:8]
}

func stripExt(name string) string {
	return strings.TrimSuffix(name, filepath.Ext(name))
}

func containsString(haystack []string, needle string) bool {
	for _, s := range haystack {
		if s == needle {
			return true
		}
	}
	return false
}

func asString(v any) string {
	switch s := v.(type) {
	case string:
		return s
	case nil:
		return ""
	case int:
		return fmt.Sprintf("%d", s)
	case int64:
		return fmt.Sprintf("%d", s)
	case float64:
		// Strip trailing .0 for the common integer-in-JSON case.
		if s == float64(int64(s)) {
			return fmt.Sprintf("%d", int64(s))
		}
		return fmt.Sprintf("%v", s)
	default:
		return fmt.Sprintf("%v", s)
	}
}

func atoiSafe(s string) int {
	n := 0
	for _, c := range s {
		if c < '0' || c > '9' {
			return 0
		}
		n = n*10 + int(c-'0')
	}
	return n
}