// Package workphase holds the sealed output of a cognitive phase.
//
// A phase artifact is what survives a phase boundary. The conversation that
// produced it does not: the next phase starts from the sealed artifact, which
// is the whole point of separating research from planning from implementation.
//
// Implementation state is deliberately absent here. It already has a format,
// continuity.Handoff, and a third one would be a third thing to keep in sync.
package workphase

import (
	"encoding/json"
	"fmt"
	"regexp"
	"sort"
	"strings"
)

// Confidence separates what research observed from what it concluded. A plan
// that cites an assumption as if it were a fact is the failure this exists to
// make visible.
type Confidence string

const (
	// Fact is directly observed in the repository or from a live probe.
	Fact Confidence = "fact"
	// Inference is supported by evidence but was not verified directly.
	Inference Confidence = "inference"
	// Assumption is required because the evidence is missing.
	Assumption Confidence = "assumption"
)

func (c Confidence) Valid() bool {
	switch c {
	case Fact, Inference, Assumption:
		return true
	}
	return false
}

// Finding is one thing research established, with the evidence for it.
//
// ID is what makes a finding citable. A plan phase references "research:r12",
// and the seal resolves that against the accepted research, so a plan cannot
// rest on a finding nobody recorded. The advertised schema at agentctx.go
// promised id and confidence for months while the struct dropped both.
type Finding struct {
	ID         string     `json:"id"`
	Claim      string     `json:"claim"`
	Evidence   string     `json:"evidence"`
	Confidence Confidence `json:"confidence"`
}

// findingID is deliberately narrow. An id appears in plan prose as
// "research:<id>", so anything with spaces or punctuation would make the
// citation ambiguous to both a parser and a reader.
var findingID = regexp.MustCompile(`^[a-z0-9][a-z0-9_-]{0,63}$`)

// CodePath is a location the next phase will need, and why.
type CodePath struct {
	Path string `json:"path"`
	Why  string `json:"why"`
}

type DeadEnd struct {
	Tried     string `json:"tried"`
	WhyFailed string `json:"why_failed"`
}

// Research is the sealed result of a research phase. It is bounded on
// purpose: an unbounded research artifact is a transcript with extra steps.
type Research struct {
	Findings   []Finding  `json:"findings"`
	Code       []CodePath `json:"relevant_code,omitempty"`
	Invariants []string   `json:"invariants,omitempty"`
	DeadEnds   []DeadEnd  `json:"dead_ends,omitempty"`
	Unknowns   []string   `json:"unknowns,omitempty"`
}

// Change is one intended modification. Target names what changes, Intent says
// what it should do afterwards. Neither is a diff: a plan that carries the
// patch is an implementation, and reviewing it costs what reviewing code costs.
type Change struct {
	Target string `json:"target"`
	Intent string `json:"intent"`
}

// Plan is the sealed result of a planning phase.
type Plan struct {
	Changes         []Change `json:"changes"`
	Verification    []string `json:"verification,omitempty"`
	Risks           []string `json:"risks,omitempty"`
	DecisionsNeeded []string `json:"human_decisions_needed,omitempty"`
}

const maxItems = 64
const maxLine = 500

func (r Research) Validate() error {
	if len(r.Findings) == 0 {
		return fmt.Errorf("research: at least one finding is required")
	}
	if err := bound("findings", len(r.Findings)); err != nil {
		return err
	}
	seen := map[string]bool{}
	for i, f := range r.Findings {
		if !findingID.MatchString(f.ID) {
			return fmt.Errorf("research: findings[%d].id %q must be lowercase letters, digits, dash or underscore, at most 64 characters", i, f.ID)
		}
		if seen[f.ID] {
			return fmt.Errorf("research: duplicate finding id %q", f.ID)
		}
		seen[f.ID] = true
		if !f.Confidence.Valid() {
			return fmt.Errorf("research: findings[%d].confidence %q is not fact, inference, or assumption", i, f.Confidence)
		}
		if err := line(fmt.Sprintf("findings[%d].claim", i), f.Claim, true); err != nil {
			return err
		}
		if err := line(fmt.Sprintf("findings[%d].evidence", i), f.Evidence, true); err != nil {
			return err
		}
	}
	for i, c := range r.Code {
		if err := line(fmt.Sprintf("relevant_code[%d].path", i), c.Path, true); err != nil {
			return err
		}
		if strings.HasPrefix(c.Path, "/") {
			return fmt.Errorf("research: relevant_code[%d].path must be repository-relative", i)
		}
		if err := line(fmt.Sprintf("relevant_code[%d].why", i), c.Why, false); err != nil {
			return err
		}
	}
	for i, d := range r.DeadEnds {
		if err := line(fmt.Sprintf("dead_ends[%d].tried", i), d.Tried, true); err != nil {
			return err
		}
		if err := line(fmt.Sprintf("dead_ends[%d].why_failed", i), d.WhyFailed, true); err != nil {
			return err
		}
	}
	if err := bound("relevant_code", len(r.Code)); err != nil {
		return err
	}
	if err := bound("dead_ends", len(r.DeadEnds)); err != nil {
		return err
	}
	return lists(map[string][]string{"invariants": r.Invariants, "unknowns": r.Unknowns})
}

func (p Plan) Validate() error {
	if len(p.Changes) == 0 {
		return fmt.Errorf("plan: at least one change is required")
	}
	if err := bound("changes", len(p.Changes)); err != nil {
		return err
	}
	for i, c := range p.Changes {
		if err := line(fmt.Sprintf("changes[%d].target", i), c.Target, true); err != nil {
			return err
		}
		if err := line(fmt.Sprintf("changes[%d].intent", i), c.Intent, true); err != nil {
			return err
		}
	}
	return lists(map[string][]string{"verification": p.Verification, "risks": p.Risks, "human_decisions_needed": p.DecisionsNeeded})
}

func Encode(v interface{ Validate() error }) ([]byte, error) {
	if err := v.Validate(); err != nil {
		return nil, err
	}
	return json.Marshal(v)
}

// DecodeResearch validates a newly sealed artifact. It is strict: a finding
// without an id or a confidence is refused, and the refusal reaches the agent
// that wrote it.
func DecodeResearch(b []byte) (Research, error) {
	var r Research
	if err := json.Unmarshal(b, &r); err != nil {
		return Research{}, fmt.Errorf("research artifact: %w", err)
	}
	return r, r.Validate()
}

// DecodeStoredResearch reads an artifact already in the CAS. Artifacts sealed
// before ids existed carry neither field, and refusing them would block every
// task whose research predates this change, including at rotation, where the
// agent that could fix it is already gone.
//
// A backfilled finding is labelled inference: the old schema required
// evidence and made no verification claim, so inference is what it actually
// meant. Calling it fact would upgrade an unverified claim on the way in.
func DecodeStoredResearch(b []byte) (Research, error) {
	var r Research
	if err := json.Unmarshal(b, &r); err != nil {
		return Research{}, fmt.Errorf("research artifact: %w", err)
	}
	for i := range r.Findings {
		if r.Findings[i].ID == "" {
			r.Findings[i].ID = fmt.Sprintf("legacy-%d", i+1)
		}
		if r.Findings[i].Confidence == "" {
			r.Findings[i].Confidence = Inference
		}
	}
	return r, r.Validate()
}

func DecodePlan(b []byte) (Plan, error) {
	var p Plan
	if err := json.Unmarshal(b, &p); err != nil {
		return Plan{}, fmt.Errorf("plan artifact: %w", err)
	}
	return p, p.Validate()
}

func bound(field string, n int) error {
	if n > maxItems {
		return fmt.Errorf("%s: %d entries exceeds the %d item bound", field, n, maxItems)
	}
	return nil
}

// line rejects a value that is empty when required, over-long, or
// multi-line. A phase artifact is a set of short claims, not prose: the bound
// is what keeps a sealed artifact cheaper to read than the session that
// produced it.
func line(field, v string, required bool) error {
	s := strings.TrimSpace(v)
	if s == "" {
		if required {
			return fmt.Errorf("%s is required", field)
		}
		return nil
	}
	if len(s) > maxLine {
		return fmt.Errorf("%s: %d characters exceeds the %d character bound", field, len(s), maxLine)
	}
	if strings.ContainsAny(s, "\n\r") {
		return fmt.Errorf("%s must be a single line", field)
	}
	return nil
}

func lists(fields map[string][]string) error {
	names := make([]string, 0, len(fields))
	for name := range fields {
		names = append(names, name)
	}
	// Deterministic error for the same input.
	sort.Strings(names)
	for _, name := range names {
		if err := bound(name, len(fields[name])); err != nil {
			return err
		}
		for i, v := range fields[name] {
			if err := line(fmt.Sprintf("%s[%d]", name, i), v, true); err != nil {
				return err
			}
		}
	}
	return nil
}